Device and method for determining a cardiac sensing control parameter

A medical device processor is configured to receive a first cardiac electrical signal sensed from a first sensing electrode vector, receive a second cardiac electrical signal sensed from a second sensing electrode vector different than the first sensing electrode vector, and construct a third cardiac electrical signal from the first cardiac electrical signal and the second cardiac electrical signal. In some examples, the system determines sensed cardiac events according to at least one setting of a cardiac event sensing threshold control parameter from at least the third cardiac electrical signal and may determine at least one acceptable setting of a sensing control parameter based on the determined sensed cardiac events. The processor may generate an output representative of the determined sensed cardiac events.

TECHNICAL FIELD

The disclosure relates generally to a medical device and method for determining a sensing control parameter to promote reliable sensing of cardiac event signals.

BACKGROUND

Medical devices may sense electrophysiological signals from the heart, brain, nerve, muscle or other tissue. Such devices may be implantable, wearable or external devices using implantable and/or surface (skin) electrodes for sensing the electrophysiological signals. In some cases, such devices may be configured to deliver a therapy based on the sensed electrophysiological signals. For example, implantable or external cardiac pacemakers, cardioverter defibrillators, cardiac monitors and the like, sense cardiac electrical signals from a patient's heart. A cardiac pacemaker or cardioverter defibrillator may sense cardiac electrical signals from the heart and deliver electrical stimulation therapies to the heart using electrodes carried by a transvenous medical electrical lead, a non-transvenous medical electrical lead and/or leadless electrodes coupled directly to the housing of the medical device.

The electrical stimulation therapies may include signals such as pacing pulses or cardioversion/defibrillation shocks. In some cases, a medical device may sense cardiac event signals attendant to the intrinsic or pacing-evoked depolarizations of the heart and control delivery of stimulation signals to the heart based on sensed cardiac event signals. Upon detection of an abnormal rhythm based on the sensed cardiac event signals (or absence thereof), such as bradycardia, tachycardia or fibrillation, an appropriate electrical stimulation signal or signals may be delivered to restore or maintain a more normal rhythm of the heart. For example, an implantable cardioverter defibrillator (ICD) may deliver pacing pulses to the heart of the patient upon detecting bradycardia or tachycardia or deliver cardioversion/defibrillation (CV/DF) shocks to the heart upon detecting tachycardia or fibrillation. Reliable sensing of the cardiac event signals attendant to myocardial depolarizations from cardiac electrical signals is important in controlling appropriate electrical stimulation therapies for the benefit of the patient.

SUMMARY

In general, the disclosure is directed to a device and method for determining sensed cardiac events from a cardiac electrical signal for use in identifying an acceptable or recommended setting of a sensing control parameter. The sensing control parameter may be, for example, a programmable sensing electrode vector or a cardiac event sensing threshold control parameter used in setting the amplitude of the sensing threshold used to sense cardiac event signals. A medical device system configured to sense cardiac electrical signals may include multiple available sensing electrode vectors, each vector being a different combination of electrodes selected from at least three electrodes, for sensing cardiac electrical signals. A medical device system operating according to the techniques disclosed herein senses two cardiac electrical signals using two different sensing electrode vectors and constructs at least one cardiac electrical signal from the two sensed cardiac electrical signals. The medical device system may determine sensed cardiac event signals from multiple cardiac electrical signals, sensed and constructed, according to one or more settings of a cardiac event sensing threshold control parameter for use in determining an acceptable or recommended setting of a sensing control parameter.

In one example, the disclosure provides a medical device comprising a processor configured to receive at least a first sensed cardiac electrical signal and a second sensed cardiac electrical signal and construct a third cardiac electrical signal from the first sensed cardiac electrical signal and the second sensed cardiac electrical signal. The processor determines sensed cardiac events according to at least one setting of a cardiac event sensing threshold control parameter from at least the third cardiac electrical signal and generates an output representative of the determined sensed cardiac events.

In another example, the disclosure provides a method that includes receiving at least a first sensed cardiac electrical signal and a second sensed cardiac electrical signal and constructing a third cardiac electrical signal from the first sensed cardiac electrical signal and the second sensed cardiac electrical signal. The method further includes determining sensed cardiac events from at least the third cardiac electrical signal according to at least one setting of a cardiac event sensing threshold control parameter and generating an output representative of the determined sensed cardiac events.

In another example, the disclosure provides a non-transitory computer-readable medium storing a set of instructions which, when executed by processing circuitry of a medical device system, cause the processing circuitry to receive at least a first sensed cardiac electrical signal and a second sensed cardiac electrical signal and construct a third cardiac electrical signal from the first sensed cardiac electrical signal and the second sensed cardiac electrical signal. The instructions further cause the processing circuitry to determine sensed cardiac events from at least the third cardiac electrical signal according to at least one setting of a cardiac event sensing threshold control parameter and generate an output representative of the determined sensed cardiac events.

In another example, the disclosure provides a graphical user interface system including a processor configured to receive a cardiac electrical signal, determine sensed cardiac events from the cardiac electrical signal according to at least one setting of a sensing threshold control parameter and generate an output of data representative of the determined sensed cardiac events. The graphical user interface system further includes a display unit coupled to the processor and configured to receive the generated output of data from the processor and display a visual representation of the data representative of the determined sensed cardiac events.

Further disclosed herein is the subject matter of the following clauses:1. A medical device comprising a processor configured to:receive at least a first sensed cardiac electrical signal and a second sensed cardiac electrical signal;construct a third cardiac electrical signal from the first sensed cardiac electrical signal and the second sensed cardiac electrical signal;from at least the third cardiac electrical signal, determine sensed cardiac events according to at least one setting of a cardiac event sensing threshold control parameter; andgenerate an output representative of the determined sensed cardiac events.2. The device of clause 1 wherein:the device includes a display unit;the processor is configured to:determine an acceptable setting of at least one of a sensing electrode vector and a cardiac event sensing threshold control parameter; andgenerate the output representative of the determined sensed cardiac events comprising the acceptable setting;the display unit being configured to display the acceptable setting.3. The device of any of clauses 1-2, wherein the processor is configured to determine the sensed cardiac events according to a plurality of settings of the cardiac event sensing threshold control parameter by adjusting at least one of a sensitivity, a starting amplitude of a cardiac event sensing threshold amplitude, an intermediate amplitude of the cardiac event sensing threshold amplitude, or a time interval used for timing an adjustment to the cardiac event sensing threshold.4. The device of any of clauses 1-3, wherein the processor is configured to determine at least one acceptable sensing control parameter setting based on the determined sensed cardiac events by:determining a rate of the determined sensed cardiac events;determining that the rate meets expected rate criteria; anddetermining that an associated sensing control parameter used to determine the sensed cardiac events is an acceptable sensing control parameter in response to the rate meeting the expected rate criteria.5. The device of any of clauses 1-4, wherein the processor is configured to:detect a tachyarrhythmia based on the determined sensed cardiac events from at least one of the first cardiac electrical signal, the second cardiac electrical signal or the third cardiac electrical signal; anddetermine at least one acceptable setting of a sensing control parameter by identifying a sensing control parameter associated with the detected tachyarrhythmia.6. The device of clause 5, wherein the processor is configured to:determine a time to detect the tachyarrhythmia for each of a plurality of settings of the cardiac event sensing threshold control parameter for a given one of the first cardiac electrical signal, second cardiac electrical signal and third cardiac electrical signal; anddetermine the at least one acceptable setting of the sensing control parameter from among the plurality of settings of the cardiac event sensing threshold control parameter associated with a determined time to detect the tachyarrhythmia that is within a tachyarrhythmia detection time limit.7. The device of clause 6, wherein the processor is further configured to determine the tachyarrhythmia detection time limit by:determining a minimum time to detect the tachyarrhythmia among the times to detect the tachyarrhythmia determined for the plurality of settings of the sensing threshold control parameter; anddetermining the tachyarrhythmia detection time limit as the minimum time plus a predetermined increase in the time to detect the tachyarrhythmia.8. The device of any of clauses 6-7, wherein the processor is further configured to determine the at least one acceptable sensing control parameter setting by:determining a highest value of a sensitivity setting associated with a time to detect the tachyarrhythmia that is less than or equal to the tachyarrhythmia detection time limit;determine an acceptable sensitivity setting that is a factor of the highest value, wherein the factor corresponds to a predetermined safety margin for sensing cardiac event signals.9. The device of any of clauses 1-8, comprising:a telemetry unit configured to receive the first cardiac electrical signal and the second cardiac electrical signal transmitted from another medical device;wherein the processor is configured to:receive the first cardiac electrical signal and the second cardiac electrical signal from the telemetry unit, where the first cardiac electrical signal corresponds to a first sensing electrode vector comprising a first electrode and a second electrode, the second cardiac electrical signal corresponds to a second sensing electrode vector comprising the first electrode and a third electrode, andconstruct the third cardiac electrical signal corresponding to a third sensing electrode vector including the second electrode and the third electrode.10. The device of any of clauses 1-9, comprising:a sensing circuit configured to:sense the first cardiac electrical signal from a first sensing electrode vector comprising a first electrode and a second electrode;sense a second cardiac electrical signal from a second sensing electrode vector comprising the first electrode and a third electrode; andthe processor is configured to receive the first cardiac electrical signal and the second cardiac electrical signal from the sensing circuit and construct the third cardiac electrical signal corresponding to a third sensing electrode vector including the second electrode and the third electrode.11. The device of any of clauses 1-9 further comprising a display unit,wherein the processor is configured to generate the output by generating data corresponding to the determined sensed cardiac events for display by the display unit in a graphical user interface.12. The device of clause 11, wherein the processor is configured to receive a user input indicating the at least one setting of the cardiac event sensing threshold control parameter.13. The device of any of clauses 11-12, wherein the processor is configured to:receive a user input indicating a sensing electrode vector; andconstruct the third cardiac electrical signal corresponding the sensing electrode vector.14. The device of any of clauses 11-13, wherein the processor is configured to:receive a user input indicating a selection of at least one sensing control parameter setting from the displayed graphical user interface; andgenerate the output comprising a programming command corresponding to the user input indicating the selection of the at least one sensing control parameter.15. The device of clause 14, wherein the processor is configured to receive the user input indicating the selection of at least one sensing control parameter setting from the displayed graphical user interface as a combination of a sensing electrode vector and a cardiac event sensing threshold control parameter.16. The device of any of clauses 2-15, further comprising a telemetry unit configured to transmit a programming command including the acceptable sensing control parameter setting.17. A method comprising:receiving at least a first sensed cardiac electrical signal and a second sensed cardiac electrical signal;constructing a third cardiac electrical signal from the first sensed cardiac electrical signal and the second sensed cardiac electrical signal;from at least the third cardiac electrical signal, determining sensed cardiac events according to at least one setting of a cardiac event sensing threshold control parameter; and generating an output representative of the determined sensed cardiac events.18. The method of clause 17, comprising:determining an acceptable setting of at least one of a sensing electrode vector and a cardiac event sensing threshold control parameter;generating the output representative of the determined sensed cardiac events comprising the acceptable setting; anddisplaying the acceptable setting by a display unit.19. The method of any of clauses 17-18, comprising determining the sensed cardiac events according to a plurality of settings of the cardiac event sensing threshold control parameter by adjusting at least one of a sensitivity, a starting amplitude of a cardiac event sensing threshold amplitude, an intermediate amplitude of the cardiac event sensing threshold amplitude, or a time interval used for timing an adjustment to the cardiac event sensing threshold amplitude.20. The method of any of clauses 17-19, further comprising determining at least one acceptable sensing control parameter setting based on the determined sensed cardiac events by:determining a rate of the determined sensed cardiac events;determining that the rate meets expected rate criteria; anddetermining that an associated sensing control parameter used to determine the sensed cardiac events is the acceptable sensing control parameter in response to the rate meeting the expected rate criteria.21. The method of any of clauses 17-20, further comprisingdetecting a tachyarrhythmia based on the determined sensed cardiac events from at least one of the first cardiac electrical signal, the second cardiac electrical signal or the third cardiac electrical signal;determining at least one acceptable setting of a sensing control parameter by identifying a sensing control parameter associated with the detected tachyarrhythmia.22. The method of clause 21, comprising:determining a time to detect the tachyarrhythmia for each of a plurality of settings of the cardiac event sensing threshold control parameter for a given one of the first cardiac electrical signal, second cardiac electrical signal and third cardiac electrical signal; anddetermining the at least one acceptable setting of the sensing control parameter by identifying one of the plurality of settings of the cardiac event sensing threshold control parameter associated with a time to detect the tachyarrhythmia that is within a tachyarrhythmia detection time limit.23. The method of clause 22, wherein determining the tachyarrhythmia detection time limit comprises:determining a minimum time to detect the tachyarrhythmia among the times to detect the tachyarrhythmia determined for the plurality of settings of the sensing threshold control parameter; anddetermining the tachyarrhythmia detection time limit as the minimum time plus a predetermined increase in the time to detect the tachyarrhythmia.24. The method of any of clauses 22-23, wherein determining the at least one acceptable setting of the sensing control parameter comprises:determining a highest value of a sensitivity setting associated with a time to detect the tachyarrhythmia that is less than or equal to the tachyarrhythmia detection time limit;determining the acceptable setting of the sensing control parameter as a sensitivity setting that is a factor of the highest value, wherein the factor corresponds to a predetermined safety margin for sensing cardiac event signals.25. The method of any of clauses 17-24, comprising:receiving the first cardiac electrical signal and the second cardiac electrical signal transmitted from another medical device, where the first cardiac electrical signal corresponds to a first sensing electrode vector comprising a first electrode and a second electrode, the second cardiac electrical signal corresponds to a second sensing electrode vector comprising the first electrode and a third electrode, andconstructing the third cardiac electrical signal corresponding to a third sensing electrode vector including the second electrode and the third electrode.26. The method of any of clauses, 17-25, comprising:sensing the first cardiac electrical signal from a first sensing electrode vector comprising a first electrode and a second electrode;sensing a second cardiac electrical signal from a second sensing electrode vector comprising the first electrode and a third electrode; andconstructing the third cardiac electrical signal corresponding to a third sensing electrode vector including the second electrode and the third electrode.27. The method of any of clauses 17-26, wherein generating the output comprises:generating data corresponding to the determined sensed cardiac events; and displaying the generated data in a graphical user interface.28. The method of clause 27, comprising receiving a user input, the user input indicating the at least one setting of the cardiac event sensing threshold control parameter.29. The method of any of clauses 27-28, comprising:receiving a user input indicating a sensing electrode vector; andconstructing the third cardiac electrical signal corresponding the sensing electrode vector.30. The method of any of clauses 27-29, comprising:receiving a user input indicating a selection of at least one sensing control parameter setting from the displayed graphical user interface;wherein generating the output comprises generating a programming command corresponding to the user input indicating the selection of the at least one sensing control parameter.31. The method of clause 27, comprising receiving the user input indicating the selection of at least one sensing control parameter setting from the display as a combination of a sensing electrode vector and a cardiac event sensing threshold control parameter.32. The method of any of clauses 18-31, comprising transmitting a programming command including the acceptable sensing control parameter setting.33. A non-transitory computer-readable medium storing a set of instructions which, when executed by a processor of a medical device, cause the device to:receive at least a first sensed cardiac electrical signal and a second sensed cardiac electrical signal;construct a third cardiac electrical signal from the first sensed cardiac electrical signal and the second sensed cardiac electrical signal;from at least the third cardiac electrical signal, determine sensed cardiac events according to at least one setting of a cardiac event sensing threshold control parameter; andgenerate an output representative of the determined sensed cardiac events.34. A graphical user interface system comprising:a processor configured to:obtain a plurality of cardiac electrical signals sensed via a plurality of sensing electrode vectors;predict, for each of a plurality of cardiac electrical signals, whether tachyarrhythmia detection is expected to be made from the corresponding cardiac electrical signal at a plurality of sensitivity settings;determine one or more acceptable sensitivity settings of at least one of the plurality of sensing electrode vectors based on at least the predictions; andgenerate an output of data representative of acceptable sensitivity settings for tachyarrhythmia detection for the respective plurality of sensing electrode vectors; anda display unit coupled to the processor and configured to:receive the generated output of data from the processor; anddisplay a visual representation of the acceptable sensitivity settings for tachyarrhythmia detection for the respective plurality of sensing electrode vectors.35. The graphical user interface system of clause 34, wherein the processor is configured to:determine one or more acceptable sensitivity settings of at least one of plurality of sensing electrode vectors by determining a recommended sensitivity setting for one of the plurality of sensing electrode vectors based on at least the predictions; andgenerate the output of data to include the recommended sensitivity setting.

This summary is intended to provide an overview of the subject matter described in this disclosure. It is not intended to provide an exclusive or exhaustive explanation of the apparatus and methods described in detail within the accompanying drawings and description below. Further details of one or more examples are set forth in the accompanying drawings and the description below.

DETAILED DESCRIPTION

In general, this disclosure describes a device and techniques for determining sensed cardiac events according to different sensing control parameters. Cardiac events may be sensed by a medical device according to programmed sensing control parameters for determining a cardiac rate and for detecting an abnormal cardiac rhythm, e.g., bradycardia, tachycardia, asystole, etc., for controlling the delivery of cardiac electrical stimulation therapy as needed. The “cardiac event” being sensed is an event associated with a single cardiac cycle such as an R-wave attendant to ventricular depolarization or a P-wave attendant to atrial depolarization. A cardiac event is determined to be sensed when a cardiac electrical signal crosses a cardiac event sensing threshold. Determining sensed cardiac events is therefore equivalent to determining a cardiac event sensing threshold crossing time by a cardiac electrical signal in some examples. Sensing control parameters used to determine sensed cardiac events from a cardiac electrical signal include the sensing electrode vector used to sense the cardiac electrical signal and cardiac event sensing threshold control parameters used to set the amplitude of the cardiac event sensing threshold at any given time during a cardiac cycle.

Cardiac events may be sensed for detecting cardiac arrhythmias. For example, the rate of sensed cardiac events may be determined by a medical device for detecting atrial or ventricular tachyarrhythmia, such as atrial tachycardia (AT), atrial fibrillation (AF), ventricular tachycardia (VT) or ventricular fibrillation (VF). In other examples, the rate of sensed cardiac events may be determined for controlling cardiac pacing for treating bradycardia, asystole, long ventricular pause or other abnormal rhythms or conduction abnormalities. In some examples, one or more alternative settings of a cardiac event sensing threshold control parameter is used for determining cardiac events that are sensed for a given cardiac electrical signal. The cardiac electrical signal may be sensed using electrodes in a selected sensing electrode vector or may be a constructed cardiac electrical signal that is derived from two sensed cardiac electrical signals. One or more cardiac event sensing threshold control parameter settings may be applied to one or more sensed and/or constructed cardiac electrical signals during real time and/or during post processing signal analysis to determine sensed cardiac events. The determined sensed cardiac events may be used to predict cardiac event intervals and/or a cardiac event rate that would be determined from the cardiac electrical signal based on the applied sensing threshold control parameters.

In some examples, the determination of cardiac event rates or intervals according to different sensing control parameter settings may be used to determine whether an arrhythmia detection would be detected and/or a predicted time of arrhythmia detection and/or therapy delivery. For instance, this determination may be used to determine a time required to detect a tachyarrhythmia episode. Using the predicted tachyarrhythmia detections and or predicted times to detect a tachyarrhythmia episode from a cardiac electrical signal according to multiple cardiac event sensing threshold control parameter settings, a medical device operating according to the techniques disclosed herein may determine acceptable settings of at least one sensing control parameter, such as the sensing electrode vector, sensitivity, or other cardiac event sensing threshold control parameters used to set the cardiac event sensing threshold amplitude during a cardiac cycle. The acceptable settings are likely to promote reliable sensing of cardiac events for detection of tachyarrhythmia and promote appropriate and timely therapy delivery as needed.

The techniques disclosed herein for determining sensed cardiac events and analyzing the rate and/or intervals of sensed cardiac events according to different sensing control parameter settings may be implemented in a device associated with a variety of cardiac device systems, such as a system including a cardiac monitor, pacemaker or ICD configured for sensing cardiac events and determining a cardiac event interval or rate for detecting a cardiac rhythm and, in some cases, controlling a cardiac electrical stimulation therapy. At least a portion of the techniques disclosed herein may be performed by a processor of an implantable medical device, such as a cardiac monitor, pacemaker or ICD, or by a processor of an external device configured to sense cardiac electrical signals or receive sensed cardiac electrical signals from another device.

In the illustrative examples presented herein, a pacemaker or ICD is configured to sense cardiac electrical signals and deliver cardiac electrical stimulation pulses for pacing and/or CV/DF therapy delivery. The pacemaker or ICD may be coupled to a transvenous or non-transvenous lead in various examples for carrying electrodes for sensing cardiac electrical signals and delivering electrical stimulation therapy. For example, the pacemaker or ICD may be coupled to an “extra-cardiovascular” lead, referring to a lead that positions electrodes outside the blood vessels, heart, and pericardium surrounding the heart of a patient. Implantable electrodes carried by extra-cardiovascular leads, for example, may be positioned extra-thoracically (outside the ribcage and sternum) or intra-thoracically (beneath the ribcage or sternum, sometimes referred to as a sub-sternal position) but may not necessarily be in intimate contact with myocardial tissue. An extra-cardiovascular lead may also be referred to as a “non-transvenous” lead.

In other examples, the medical device may be coupled to a transvenous lead that positions electrodes within a blood vessel, which may remain outside the heart in an “extra-cardiac” location or be advanced to position electrodes within a heart chamber. For instance, a transvenous medical lead may be advanced along a venous pathway to position electrodes in an extra-cardiac location within the internal thoracic vein (ITV), an intercostal vein, the superior epigastric vein, or the azygos, hemiazygos, or accessory hemiazygos veins, as examples. In still other examples, a transvenous lead may be advanced to position electrodes within the heart, e.g., within an atrial and/or ventricular heart chamber.

More generally, the disclosed techniques may be used in conjunction with any device that is configured to determine a rate or intervals of sensed cardiac events, which may include implantable or external pacemakers and defibrillators and implantable or external heart rate monitors, which may use skin or surface electrodes for sensing cardiac electrical signals. The techniques disclosed herein are not dependent on the particular type of sensing electrodes used or their position, either internal or external. The medical devices shown inFIGS.1A-3are examples of medical devices that may be implemented in a system performing techniques disclosed herein with no limitation intended.

FIGS.1A and1Bare conceptual diagrams of a medical device system10configured to sense cardiac events from a cardiac electrical signal and deliver cardiac electrical stimulation therapies according to one example. System10includes an ICD14connected to a non-transvenous, extra-cardiovascular electrical stimulation and sensing lead16.FIG.1Ais a front view of ICD14implanted within patient12.FIG.1Bis a side view of ICD14implanted within patient12.FIGS.1A and1Bare described in the context of an ICD system10capable of providing high voltage CV/DF shocks and in some examples cardiac pacing pulses.

ICD14includes a housing15that forms a hermetic seal that protects internal components of ICD14. The housing15of ICD14may be formed of a conductive material, such as titanium or titanium alloy. The housing15may function as an electrode (sometimes referred to as a “can” electrode). Housing15may be used as an active can electrode for use in delivering CV/DF shocks or other high voltage pulses delivered using a high voltage therapy circuit. In other examples, housing15may be available for use in delivering unipolar, low voltage cardiac pacing pulses and/or for sensing cardiac electrical signals in combination with electrodes carried by lead16. In other instances, the housing15of ICD14may include a plurality of electrodes on an outer portion of the housing. The outer portion(s) of the housing15functioning as an electrode(s) may be coated with a material, such as titanium nitride, e.g., for reducing post-stimulation polarization artifact.

ICD14includes a connector assembly17(also referred to as a connector block or header) that includes electrical feedthroughs crossing housing15to provide electrical connections between conductors extending within the lead body18of lead16and electronic components included within the housing15of ICD14. As will be described in further detail herein, housing15may house one or more processors, memories, transceivers, cardiac electrical signal sensing circuitry, therapy delivery circuitry, power sources and other components for sensing cardiac electrical signals, detecting a heart rhythm, and controlling and delivering electrical stimulation pulses to treat an abnormal heart rhythm.

Lead16is shown in this example as an extracardiovascular lead implanted outside the ribcage and sternum. Lead16includes an elongated lead body18having a proximal end27that includes a lead connector (not shown) configured to be connected to ICD connector assembly17and a distal portion25that includes one or more electrodes. In the example illustrated inFIGS.1A and1B, the distal portion25of lead body18includes defibrillation electrodes24and26and pace/sense electrodes28and30. In some cases, defibrillation electrodes24and26may together form a defibrillation electrode in that they may be configured to be activated concurrently. Alternatively, defibrillation electrodes24and26may form separate defibrillation electrodes in which case each of the electrodes24and26may be activated independently.

Electrodes24and26(and in some examples housing15) are referred to herein as defibrillation electrodes because they may be utilized, individually or collectively, for delivering high voltage stimulation therapy (e.g., cardioversion or defibrillation shocks). Electrodes24and26may be elongated coil electrodes and generally have a relatively high surface area for delivering high voltage electrical stimulation pulses compared to pacing and sensing electrodes28and30. However, electrodes24and26and housing15may also be utilized to provide pacing functionality, sensing functionality or both pacing and sensing functionality in addition to or instead of high voltage stimulation therapy. In this sense, the use of the term “defibrillation electrode” herein should not be considered as limiting the electrodes24and26for use in only high voltage cardioversion/defibrillation shock therapy applications. For example, either of electrodes24and26may be used as a sensing electrode in a sensing electrode vector for sensing cardiac electrical signals and determining a need for an electrical stimulation therapy.

Electrodes28and30are relatively smaller surface area electrodes which are available for use in sensing electrode vectors for sensing cardiac electrical signals and may be used for delivering relatively low voltage cardiac pacing pulses in some configurations. Electrodes28and30are referred to herein as “pace/sense electrodes” because they are generally configured for use in low voltage applications, e.g., used as either a cathode or anode for delivery of pacing pulses and/or sensing of cardiac electrical signals, as opposed to delivering high voltage CV/DF shocks. In some instances, electrodes28and30may provide only pacing functionality, only sensing functionality or both.

ICD14may sense cardiac electrical signals corresponding to electrical activity of heart8via one or more sensing electrode vectors that include combinations of electrodes24,26,28and/or30. In some examples, housing15of ICD14is used in combination with one or more of electrodes24,26,28and/or30in a sensing electrode vector. In the example illustrated inFIGS.1A and1B, electrode28is located proximal to defibrillation electrode24, and electrode30is located between defibrillation electrodes24and26. One, two or more pace/sense electrodes may be carried by lead body18. For instance, a third pace/sense electrode may be located distal to defibrillation electrode26in some examples. Electrodes28and30are illustrated as ring electrodes; however, electrodes28and30may comprise any of a number of different types of electrodes, including ring electrodes, short coil electrodes, hemispherical electrodes, directional electrodes, segmented electrodes, or the like. Electrodes28and30may be positioned at other locations along lead body18and are not limited to the positions shown. In other examples, lead16may include fewer or more pace/sense electrodes and/or defibrillation electrodes than the example shown here.

Lead16may extend subcutaneously or submuscularly over the ribcage32medially from the connector assembly27of ICD14toward a center of the torso of patient12, e.g., toward xiphoid process20of patient12. At a location near xiphoid process20, lead16may bend or turn to extend superiorly, subcutaneously or submuscularly, over the ribcage and/or sternum, substantially parallel to sternum22. Although illustrated inFIG.1Aas being offset laterally from and extending substantially parallel to sternum22, the distal portion25of lead16may be implanted at other locations, such as over sternum22, offset to the right or left of sternum22, angled laterally from sternum22toward the left or the right, or the like. Alternatively, lead16may be placed along other subcutaneous or submuscular paths. The path of non-transvenous, extra-cardiovascular lead16may depend on the location of ICD14, the arrangement and position of electrodes carried by the lead body18, and/or other factors. The techniques disclosed herein are not limited to a particular path of lead16or final locations of electrodes24,26,28and30.

Electrical conductors (not illustrated) extend through one or more lumens of the elongated lead body18of lead16from the lead connector at the proximal lead end27to electrodes24,26,28, and30located along the distal portion25of the lead body18. The elongated electrical conductors contained within the lead body18, which may be separate respective insulated conductors within the lead body18, are each electrically coupled with respective defibrillation electrodes24and26and pace/sense electrodes28and30. The respective conductors electrically couple the electrodes24,26,28, and30to circuitry, such as a therapy delivery circuit and/or a cardiac electrical signal sensing circuit, of ICD14via connections in the connector assembly17, including associated electrical feedthroughs crossing housing15. The electrical conductors transmit therapy from a therapy delivery circuit within ICD14to one or more of defibrillation electrodes24and26and/or pace/sense electrodes28and30and transmit cardiac electrical signals sensed from the patient's heart8from one or more of defibrillation electrodes24and26and/or pace/sense electrodes28and30to the sensing circuit within ICD14.

The lead body18of lead16may be formed from a non-conductive material, including silicone, polyurethane, fluoropolymers, mixtures thereof, and/or other appropriate materials, and shaped to form one or more lumens within which the one or more conductors extend. Lead body18may be tubular or cylindrical in shape. In other examples, the distal portion25(or all of) the elongated lead body18may have a flat, ribbon or paddle shape. Lead body18may be formed having a preformed distal portion25that is generally straight, curving, bending, serpentine, undulating or zig-zagging.

In the example shown, lead body18includes a curving distal portion25having two “C” shaped curves, which together may resemble the Greek letter epsilon, “ε.” Defibrillation electrodes24and26are each carried by one of the two respective C-shaped portions of the lead body distal portion25. The two C-shaped curves are seen to extend or curve in the same direction away from a central axis of lead body18, along which pace/sense electrodes28and30are positioned. Pace/sense electrodes28and30may, in some instances, be approximately aligned with the central axis of the straight, proximal portion of lead body18such that mid-points of defibrillation electrodes24and26are laterally offset from pace/sense electrodes28and30.

Other examples of extra-cardiovascular leads including one or more defibrillation electrodes and one or more pacing and sensing electrodes may include a curving, serpentine, undulating or zig-zagging distal portion of the lead body18. The techniques disclosed herein are not limited to any particular lead body design, however. In other examples, lead body18is a flexible elongated lead body without any pre-formed shape, bends or curves.

ICD14analyzes the cardiac electrical signals received from one or more sensing electrode vectors to monitor for abnormal rhythms, such as bradycardia, ventricular tachycardia (VT) or ventricular fibrillation (VF). ICD14may analyze the rate of sensed cardiac events and the morphology of the cardiac electrical signals to monitor for tachyarrhythmia in accordance with any of a number of tachyarrhythmia detection techniques. ICD14generates and delivers electrical stimulation therapy in response to detecting a tachyarrhythmia (e.g., VT or VF) using a therapy delivery electrode vector which may be selected from any of the available electrodes24,26,2830and/or housing15. ICD14may deliver anti-tachycardia pacing (ATP) in response to VT detection and in some cases may deliver ATP prior to a CV/DF shock or during high voltage capacitor charging in an attempt to avert the need for delivering a CV/DF shock. If ATP does not successfully terminate VT or when VF is detected, ICD14may deliver one or more CV/DF shocks via one or both of defibrillation electrodes24and26and/or housing15. ICD14may deliver the CV/DF shocks using electrodes24and26individually or together as a cathode (or anode) and with the housing15as an anode (or cathode). ICD14may generate and deliver other types of electrical stimulation pulses such as post-shock pacing pulses, asystole pacing pulses, or bradycardia pacing pulses using a pacing electrode vector that includes one or more of the electrodes24,26,28, and30and the housing15of ICD14.

ICD14is shown implanted subcutaneously on the left side of patient12along the ribcage32. ICD14may, in some instances, be implanted between the left posterior axillary line and the left anterior axillary line of patient12. ICD14may, however, be implanted at other subcutaneous or submuscular locations in patient12. For example, ICD14may be implanted in a subcutaneous pocket in the pectoral region. In this case, lead16may extend subcutaneously or submuscularly from ICD14toward the manubrium of sternum22and bend or turn and extend inferiorly from the manubrium to the desired location subcutaneously or submuscularly. In yet another example, ICD14may be placed abdominally. Lead16may be implanted in other extra-cardiovascular locations as well. For instance, as described with respect toFIGS.2A-2C, the distal portion25of lead16may be implanted underneath the sternum/ribcage in the substernal space.

An external device40is shown in telemetric communication with ICD14by a communication link42. External device40may include a processor52, memory53, display unit54, user interface56and telemetry unit58. Processor52controls external device operations and processes data and signals received from ICD14.

Display54, which may include a graphical user interface (GUI), displays data and other information to a user for reviewing ICD operation and programmed parameters as well as cardiac electrical signals retrieved from ICD14. As described below, processor52may receive sensed cardiac electrical signals from ICD14for processing and analysis according to the techniques disclosed herein. External device processor52may be configured to determine sensed cardiac events from a cardiac electrical signal corresponding to a specified sensing electrode vector and according to one or more different sensing control parameters used to set the cardiac event sensing threshold amplitude. Processor52may be configured to determine a cardiac event rate or cardiac event intervals based on the determined sensed cardiac events. Based on the determined cardiac event rate or cardiac event intervals, processor52may determine an acceptable setting of a sensing control parameter for reliable cardiac event sensing.

Based on the determined cardiac event intervals, for example, processor52may determine whether a tachyarrhythmia detection is expected to be made from the determined cardiac events and may determine a time interval until a predicted tachyarrhythmia detection by ICD14. Processor52may generate a display of data related to the processing and analysis of cardiac electrical signals on display unit54, as further described below. The generated data display may include an acceptable or recommended setting for one or more sensing control parameters determined by processor52. The generated display may be a GUI that a user may interact with for selecting sensing control parameters to be applied for determining sensed cardiac events and/or for authorizing and initiating programming of recommended settings determined by processor52.

Memory53may include any volatile, non-volatile, magnetic, optical, or electrical media, such as a random access memory (RAM), read-only memory (ROM), non-volatile RAM (NVRAM), electrically-erasable programmable ROM (EEPROM), flash memory, or any other digital or analog media. Memory53may be configured to store sensing control parameters and associated programmable settings. Memory53may store sensed cardiac event data determined by processor52for use in generating an output representative of the determined sensed cardiac events as disclosed herein.

User interface56may include a mouse, touch screen, keypad or the like to enable a user to interact with external device40to initiate a telemetry session with ICD14for retrieving data from and/or transmitting data to ICD14, including programmable parameters for controlling cardiac event sensing and therapy delivery. A clinician may use user interface56to send and receive commands to ICD14via external device40. As described herein, a clinician may use user interface56to specify one or more cardiac event sensing control parameters. Typically, user interface56includes one or more input devices and one or more output devices, including display unit54. The input devices of user interface56may include a communication device such as a network interface, keyboard, pointing device, voice responsive system, video camera, biometric detection/response system, button, sensor, mobile device, control pad, microphone, presence-sensitive screen, touch-sensitive screen (which may be included in display unit54), network, or any other type of device for detecting input from a human or machine.

The one or more output devices of user interface56may include a communication unit such as a network interface, display, sound card, video graphics adapter card, speaker, presence-sensitive screen, one or more USB interfaces, video and/or audio output interfaces, or any other type of device capable of generating tactile, audio, video, or other output. Display unit54may function as an input and/or output device using technologies including liquid crystal displays (LCD), quantum dot display, dot matrix displays, light emitting diode (LED) displays, organic light-emitting diode (OLED) displays, cathode ray tube displays, e-ink, or monochrome, color, or any other type of display capable of generating tactile, audio, and/or visual output. In other examples, user interface56may produce an output to a user in another fashion, such as via a sound card, video graphics adapter card, speaker, presence-sensitive screen, touch-sensitive screen, one or more USB interfaces, video and/or audio output interfaces, or any other type of device capable of generating tactile, audio, video, or other output. In some examples, display unit54is a presence-sensitive display that may serve as a user interface device that operates both as one or more input devices and one or more output devices.

Telemetry unit58includes a transceiver and antenna configured for bidirectional communication with a telemetry circuit included in ICD14and is configured to operate in conjunction with processor52for sending and receiving data relating to ICD functions via communication link42. Communication link42may be established between ICD14and external device40using a radio frequency (RF) link such as BLUETOOTH®, Wi-Fi, or Medical Implant Communication Service (MICS) or other RF or communication frequency bandwidth or communication protocols. Data stored or acquired by ICD14, including cardiac electrical signals or associated data derived therefrom, results of device diagnostics, and histories of detected rhythm episodes and delivered therapies, may be retrieved from ICD14by external device40following an interrogation command. In particular, external device40may retrieve episodes of sensed cardiac electrical signals from ICD14.

For example, as described below, external device40may retrieve an episode of at least two different cardiac electrical signals sensed by ICD14using at least two different sensing electrode vectors for processing and analysis by processor52. Processor52may construct at least one cardiac electrical signal from two or more sensed cardiac electrical signals received from ICD14. Processor52may determine a sensed cardiac event rate and/or sensed cardiac event intervals from each cardiac electrical signal, sensed and constructed, based on one or more different cardiac event sensing threshold control parameter settings for use in determining a recommended sensing control parameter setting. The processing and analysis performed by processor52may be performed in real time as cardiac electrical signals are sensed by ICD14and transmitted to external device40. Alternatively, processor40may perform processing and analysis of previously sensed cardiac electrical signal episodes that are stored by ICD14and transmitted to external device40.

External device40may be used to program sensing control parameters, cardiac rhythm detection parameters and therapy delivery control parameters used by ICD14. External device40may be embodied as a programmer used in a hospital, clinic or physician's office to retrieve data from ICD14and to program operating parameters and algorithms in ICD14for controlling ICD functions. External device40may alternatively be embodied as a home monitor or handheld device, which may be a tablet, cell phone or other personal device. While external device40is shown only inFIG.1A, it is to be understood that portions of the techniques disclosed herein may be performed by an external device, such as device40, configured to communicate with an implantable or another external medical device configured to sense and transmit cardiac electrical signals to external device40. Aspects of external device40may generally correspond to the external programming/monitoring unit disclosed in U.S. Pat. No. 5,507,782 (Kieval, et al.), hereby incorporated herein by reference in its entirety. An example programmer that may be configured to perform the techniques disclosed herein is the CARELINK® Programmer, commercially available from Medtronic, Inc., Minneapolis, Minnesota USA.

In some examples, external device40includes external ports55adapted to an interface of one or more external leads that include electrodes for sensing an electrocardiogram. In some examples, external device40may receive, via the one or more electrodes of the one or more external leads, electrocardiogram data from the patient or from another electrocardiogram input source. The electrocardiogram may be received by processor52for determining a heart rate, which may be used in establishing expected cardiac rate criteria for comparing to determined sensed cardiac event data in identifying acceptable sensing control parameters. In some examples, lead16may be coupled to external device40, e.g., via external ports55and any necessary electrical connectors or adaptors. In this case, external device40is configured to receive cardiac electrical signals sensed via electrodes carried by lead16prior to coupling lead16to ICD14, without requiring wireless transmission of the sensed cardiac electrical signals to external device40. A subcutaneous or cutaneous patch electrode or other electrode may be temporarily positioned at an approximate implant site of ICD14to serve as a substitute electrode for ICD housing15. At least two sensing electrode vectors may be selected from the electrodes carried by lead16. In some examples, the electrode positioned temporarily as a substitute for the ICD housing15may be selected in one or both of the sensing electrode vectors to approximate a sensing electrode vector that includes ICD housing15and an electrode carried by lead16. Processing and analysis of cardiac electrical signals sensed using lead16for selecting sensing control parameters may therefore be performed by external device processor52prior to connecting and implanting ICD14. In this way, a clinician can verify that an acceptable implant position of lead16associated with acceptable settings of the sensing control parameters can be achieved for reliably sensing cardiac event signals and tachyarrhythmias based on output generated by external device processor52, prior to implanting ICD14.

FIG.1Cis a conceptual diagram of medical device system10and an external cardiac monitor60. Cardiac monitor60may be coupled to multiple surface electrodes31for sensing surface electrocardiogram (ECG) signals. In some examples, the surface electrodes31may be positioned over and in approximate alignment with implanted electrodes coupled to ICD14or approximate locations of electrodes that are to be implanted and coupled to an ICD. The locations of surface electrodes31as shown inFIG.1Care illustrative in nature. Surface electrodes31may be positioned at other locations corresponding to approximate subcutaneous, substernal or intravenous locations of implanted electrodes or targeted locations of implantable electrodes that are not yet implanted. Surface ECG signals may be acquired by cardiac monitor60, e.g., during an induced tachyarrhythmia during an office visit or implant procedure or during a spontaneous tachyarrhythmia during ambulatory monitoring of patient12.

A processor included in cardiac monitor60may receive, process and analyze the surface ECG signals to determine acceptable or recommended sensing control parameter settings for use by the ICD14when coupled to implantable electrodes corresponding to locations and associated sensing electrode vectors simulated by the surface electrode locations. In other examples, the surface ECG signals may be transmitted to external device40for processing and analysis by external device processor52. The surface ECG signals may be used by the processor of cardiac monitor60or external device40to construct at least one additional ECG signal corresponding to a different sensing electrode vector than the vectors used to sense the surface ECG signals. The constructed ECG signal may be correlated to a sensing electrode vector between implantable electrodes that are or will be coupled to ICD14. The constructed ECG signal be analyzed according to the techniques disclosed herein for determining recommended or acceptable sensing control parameters that may be programmed into ICD14for use in sensing cardiac signals and detecting tachyarrhythmia. In this manner, acceptable sensitivity control parameter settings could be identified prior to implanting ICD14and/or lead16. This technique may be utilized as part of a pre-screening procedure alone or in conjunction with other screening criteria to ensure a patient is an appropriate candidate for the system.

In addition to or alternatively to sensed surface ECG signals, cardiac monitor60may be capable of wireless communication with ICD14for receiving cardiac electrical signals sensed by ICD14. For example, cardiac monitor60may be coupled to an inductive antenna33that may be positioned over ICD14, which may be implanted beneath the skin, to receive cardiac electrical signals sensed by ICD14. The cardiac electrical signals may be received by cardiac monitor60from ICD14in real time via antenna33. Cardiac monitor60may communicate with ICD14using other communication protocols, such as RF communication, whether that be proprietary or utilizing non-proprietary protocol (e.g., Bluetooth).

As described below in conjunction withFIGS.4and5, ICD14includes cardiac electrical signal sensing circuitry which may be configured to sense multiple cardiac electrical signals simultaneously, each using a different sensing electrode vector selected from different combinations of the available electrodes24,26,28,30and housing15. However, due to processing and memory limitations of an implantable device, ICD14may have limited capacity for storing multiple cardiac electrical signals and/or limited capacity for storing signals sampled at relatively high sampling rates over several seconds or minutes. For example, ICD14may be configured to store up to 10, 20, 30, 40, 60, 100 or 120 seconds of at least two wideband filtered cardiac electrical signals sampled at a frequency of 128 Hz in its internal memory. These stored signals may be analyzed by ICD14or transmitted to external device40for post-processing and analysis for determining recommended or acceptable sensing control parameters according to the techniques disclosed herein. However, ICD14may be capable of sensing and transmitting more than two cardiac electrical signals in real time, e.g., three, four (or more) cardiac electrical signals sensed using three, four (or more) different sensing electrode vectors, and/or sensing and transmitting cardiac electrical signals at a relatively higher sampling rate, e.g., 256 Hz. Cardiac electrical signals sensed from more sensing electrode vectors and/or at relatively higher sampling rates than the storage capacity of ICD internal memory may be transmitted to an external device, e.g., external cardiac monitor60or external device40, to enable analysis of a greater number of sensing electrode vectors.

The sensed cardiac electrical signals may be transmitted from ICD14to external device40in real time, for example during an office visit or a tachyarrhythmia induction procedure, to enable post-processing and analysis of multiple signals by processor52of external device40. This analysis of real-time transmitted signals may be limited to cardiac signal episodes obtained during the office visit, e.g., during a tachyarrhythmia induction. In order to enable processing and analysis of cardiac electrical signals acquired during a spontaneous tachyarrhythmia episode detected by ICD14, without the limitations posed by the storage capacity of ICD internal memory, ICD14may be configured to transmit real-time sensed cardiac electrical signals to external cardiac monitor60, e.g., during ambulatory monitoring. External cardiac monitor60may be configured to receive cardiac electrical signals transmitted from ICD14via antenna33, store the cardiac electrical signal data, e.g., in episodes of several seconds or minutes in duration, and transmit the data to external device40for post-processing and analysis according to the techniques disclosed herein. In this way, an external processor which may be included in cardiac monitor60or external device processor52, is enabled to analyze a greater number of sensed cardiac electrical signals, determine a greater number of constructed cardiac electrical signals from the sensed signals, and/or process and analyze sensed cardiac signals acquired at a relatively higher sampling rate.

For example, instead of storing two cardiac electrical signals at a sampling rate of 128 Hz in ICD14, which enables one additional cardiac electrical signal to be constructed from the two sensed signals, external cardiac monitor60may receive four cardiac electrical signals from ICD14, sensed using four different sensing electrode vectors at a higher sampling rate of 256 Hz. The four sensed signals may be transmitted in real time to external cardiac monitor60, e.g., during an implant procedure, during an office visit, during a tachyarrhythmia induction procedure or when ICD14is detecting a spontaneous ventricular tachyarrhythmia, allowing sensed cardiac signal data to be acquired and stored beyond the limits of ICD14memory capacity.

Processor52of external device40may receive episodes of the four cardiac electrical signals, which may correspond to induced or spontaneous tachyarrhythmia episodes, from external cardiac monitor60via communication link35, which may be a wired or wireless communication link, e.g., using RF telemetry. Processor52of external device40may be configured to construct up to four additional cardiac electrical signals, corresponding to four sensing electrode vectors different from the four sensing electrode vectors used to sense the four sensed cardiac electrical signals such that all eight possible sensing electrode vectors selectable from electrodes24,26,28,30and housing15may be analyzed for determining recommended sensing control parameters according to the techniques disclosed herein. As such, in some examples, external device processor52may receive the sensed cardiac electrical signals from ICD14via cardiac monitoring device60. In other examples, a processor included in cardiac monitoring device60may receive the cardiac electrical signals sensed by ICD14via antenna33for processing and analysis by cardiac monitoring device60. Recommended or acceptable sensing control parameters determined by the cardiac monitoring device60or external device40may be displayed to a user, e.g., in a user interface as described below in conjunction withFIGS.11,12and14-16.

Cardiac monitoring device60may be a wearable or portable monitoring device, such as a Holter monitor or mobile cardiac telemetry unit. Cardiac monitoring device60may optionally be coupled to surface or skin electrodes31for acquiring and storing or transmitting ECG signals to a remote patient monitoring database. It is to be understood, however, that ECG signal sensing by cardiac monitoring device60is optional in some examples. Cardiac monitoring device60may be configured to receive sensed cardiac electrical signals from ICD14without necessarily acquiring ECG signals from surface electrodes31. As such cardiac monitoring device60may function as extended memory capacity of medical device system10for storing cardiac electrical signal data received from ICD14and as a relay device for transmitting the stored data received from ICD14to external device40or another computer for processing the received signals.

Cardiac monitoring device60may be configured to receive episodes of at least two cardiac electrical signals sensed by ICD14during one or more detected tachyarrhythmia episodes. The received cardiac signal episodes may be stored in memory of cardiac monitoring device60for later transmission to external device40via communication link35, transmitted in real time to a remote patient monitoring computer or database for subsequent analysis or processed and analyzed by a processor included in cardiac monitoring device60. Cardiac monitoring device60may be configured to receive cardiac electrical signals from ICD14that are sensed during multiple, different tachyarrhythmia episodes detected by ICD14. In this way, the techniques disclosed herein for determining acceptable or recommended sensing control parameters for tachyarrhythmia detection by ICD14may be applied to a greater number of sensed signals and/or signals acquired at a higher sampling rate during one or more spontaneous tachyarrhythmia episodes.

FIGS.2A-2Care conceptual diagrams of patient12implanted with ICD system10in a different implant configuration than the arrangement shown inFIGS.1A-1B.FIG.2Ais a front view of patient12implanted with ICD system10.FIG.2Bis a side view of patient12implanted with ICD system10.FIG.2Cis a transverse view of patient12implanted with ICD system10. In this arrangement, lead16of system10is implanted at least partially underneath sternum22of patient12. Lead16extends subcutaneously or submuscularly from ICD14toward xiphoid process20and at a location near xiphoid process20bends or turns and extends superiorly within anterior mediastinum36in a substernal position.

Anterior mediastinum36may be viewed as being bounded laterally by pleurae39, posteriorly by pericardium38, and anteriorly by sternum22(seeFIG.2C). The distal portion25of lead16may extend along the posterior side of sternum22substantially within the loose connective tissue and/or substernal musculature of anterior mediastinum36. A lead implanted such that the distal portion25is substantially within anterior mediastinum36, or within a pleural cavity or more generally within the thoracic cavity, may be referred to as a “substernal lead.”

In the example illustrated inFIGS.2A-2C, lead16is located substantially centered under sternum22. In other instances, however, lead16may be implanted such that it is offset laterally from the center of sternum22. In some instances, lead16may extend laterally such that distal portion25of lead16is underneath/below the ribcage32in addition to or instead of sternum22. In other examples, the distal portion25of lead16may be implanted in other extra-cardiovascular, intra-thoracic locations, including the pleural cavity or around the perimeter of and adjacent or within the pericardium38of heart8. In the examples described herein in conjunction withFIGS.1A-2C, electrodes for sensing cardiac electrical signals are carried by a lead that may be advanced to a supra-diaphragmatic position, which may be within the thoracic cavity or outside the thorax in various examples.

FIG.3is a conceptual diagram of a medical device system100that may be configured to perform techniques disclosed herein according to another example. System100includes ICD114coupled to transvenous leads116and118in communication with the right atrium (RA) and right ventricle (RV) of heart8. ICD114includes a housing115enclosing circuitry, such as a processor, telemetry circuitry, sensing circuitry and therapy delivery circuitry as described below in conjunction withFIG.4. ICD114includes connector assembly117having connector bores for receiving proximal connectors of RA lead116and RV lead118and providing electrical connection between electrodes carried by leads116and118and internal ICD circuitry.

RA lead116may carry a distal tip electrode120and ring electrode122for sensing atrial electrical signals and producing an atrial intra-cardiac electrogram (EGM) signal. RA electrodes120and122may be used for delivering RA pacing pulses. RV lead118may carry pacing and sensing electrodes132and134for sensing a ventricular electrical signal and producing an RV EGM signal. RV electrodes132and134may be used to deliver RV pacing pulses. RV lead118may also carry an RV defibrillation electrode124and a superior vena cava (SVC) defibrillation electrode126. Defibrillation electrodes124and126are shown as coil electrodes spaced apart proximally from the distal pacing and sensing electrodes132and134. While RA lead116and RV lead118are both shown advanced within a respective heart chamber, in some examples, a transvenous lead may be advanced to position electrodes within a venous location, outside the heart.

ICD114may be configured to provide dual chamber sensing and pacing therapies as well as high voltage CV/DF shock therapies in response to detecting VT or VF. In other examples, ICD114may be configured to provide multi-chamber sensing and pacing therapies, including cardiac resynchronization therapy (CRT), in which case a coronary sinus lead may be advanced along a cardiac vein to position electrodes for sensing and pacing the left ventricle of heart8. In still other examples, ICD114may be a single chamber device coupled to a single lead, e.g., lead116or lead118, for sensing cardiac electrical signals and delivery electrical stimulation therapies. ICD114may be configured to sense at least two cardiac electrical signals that may be processed and analyzed according to the techniques disclosed herein for determining acceptable sensing control parameters. A processor included in ICD114may perform the processing and analysis, or ICD114may transmit episodes of the two cardiac electrical signals to another device, e.g., external device40shown inFIG.1A, for processing and analysis for determining recommended or acceptable sensing control parameters.

FIG.4is a conceptual diagram of a medical device configured to sense cardiac electrical signals according to one example.FIG.4is described in conjunction with the ICD14ofFIGS.1A-2C, including therapy delivery capabilities. It is to be understood, however, the circuitry and functionality attributed to circuitry described in conjunction withFIG.4may be included, in whole or in part, in any of the example medical devices described or listed herein, such as the ICD114shown inFIG.3. The ICD housing15is shown schematically as an electrode inFIG.4because the housing of the medical device may be used as an electrode in a sensing electrode vector for cardiac signal sensing and/or for therapy delivery in some examples. The electronic circuitry enclosed within housing15includes software, firmware and hardware that cooperatively monitor cardiac signals, determine when an electrical stimulation therapy is necessary, and deliver therapy as needed according to programmed therapy delivery algorithms and control parameters.

ICD14as shown inFIG.4includes a control circuit80, memory82, therapy delivery circuit84, cardiac electrical signal sensing circuit86, and telemetry circuit88. Control circuit80communicates, e.g., via a data bus, with therapy delivery circuit84and sensing circuit86for sensing cardiac event signals, detecting cardiac rhythms, and controlling delivery of cardiac electrical stimulation therapies in response to sensed cardiac event signals. Therapy delivery circuit84and sensing circuit86are electrically coupled to electrodes24,26,28,30and the housing15, which may function as a common or ground electrode or as an active can electrode for delivering CV/DF shock pulses or cardiac pacing pulses. As described above electrodes24,26,28and30shown inFIG.4may be carried by a non-transvenous lead advanced to position electrodes in an extra-cardiac location (as shown inFIGS.1A-2C) or by a transvenous lead for positioning electrodes within a blood vessel or an intracardiac location (e.g., electrodes120,122,124,126,132, and134as shown inFIG.3). Furthermore, electrodes coupled to the medical device may include multiple housing-based electrodes not carried by a lead in some examples.

A power source98provides power to the circuitry of ICD14, including each of the components80,82,84,86, and88as needed. Power source98may include one or more energy storage devices, such as one or more rechargeable or non-rechargeable batteries. The connections between power source98and each of the other components80,82,84,86and88are to be understood from the general block diagram ofFIG.4but are not shown for the sake of clarity. For example, power source98may be coupled to one or more charging circuits included in therapy delivery circuit84for charging holding capacitors or other charge storage devices included in therapy delivery circuit84that are discharged at appropriate times under the control of control circuit80for producing electrical pulses according to a therapy protocol. In other examples, power source98may serve as a voltage or current source to therapy delivery circuit84without requiring a charge storage device. Power source98is also coupled to components of cardiac electrical signal sensing circuit86, such as sense amplifiers, analog-to-digital converters, switching circuitry, etc., telemetry circuit88and memory82as needed.

The circuits shown inFIG.4represent functionality included in ICD14or another medical device operating according to the techniques disclosed herein and may include any discrete and/or integrated electronic circuit components that implement analog and/or digital circuits capable of producing the functions attributed to ICD14herein. Functionality associated with one or more circuits may be performed by separate hardware, firmware or software components, or integrated within common hardware, firmware or software components. For example, cardiac event sensing and determination of sensed cardiac event intervals may be performed cooperatively by sensing circuit86and control circuit80and may include operations implemented in a processor81or other signal processing circuitry included in control circuit80executing instructions stored in memory82. Control signals such as blanking and timing intervals associated with setting the cardiac event sensing threshold amplitude may be sent from control circuit80to sensing circuit86according to programmed sensing control parameter settings.

The various circuits of ICD14may include an application specific integrated circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and memory that execute one or more software or firmware programs, a combinational logic circuit, state machine, or other suitable components or combinations of components that provide the described functionality. The particular form of software, hardware and/or firmware employed to implement the functionality disclosed herein will be determined primarily by the particular system architecture employed in the medical device system and by the particular detection and therapy delivery methodologies employed by the medical device system. Providing software, hardware, and/or firmware to accomplish the described functionality in the context of any modern medical device, given the disclosure herein, is within the abilities of one of skill in the art.

Memory82may include any volatile, non-volatile, magnetic, or electrical non-transitory computer readable storage media, such as random access memory (RAM), read-only memory (ROM), non-volatile RAM (NVRAM), electrically-erasable programmable ROM (EEPROM), flash memory, or any other memory device. Furthermore, memory82may include non-transitory computer readable media storing instructions that, when executed by one or more processing circuits, cause control circuit80and/or other ICD components to perform various functions attributed to ICD14or those ICD components. The non-transitory computer-readable media storing the instructions may include any of the media listed above.

Cardiac electrical signal sensing circuit86(also referred to herein as “sensing circuit”86) may be selectively coupled to electrodes28,30and/or housing15in order to sense electrical activity of the patient's heart. Sensing circuit86may additionally be selectively coupled to defibrillation electrodes24and/or26for use in a sensing electrode vector together or in combination with one or more of electrodes28,30and/or housing15. Sensing circuit86may be enabled to selectively receive cardiac electrical signals from at least two different sensing electrode vectors from the available electrodes24,26,28,30, and housing15in some examples. Sensing circuit86may monitor one or more cardiac electrical signals for sensing cardiac events and/or producing digitized cardiac electrical signals passed to control circuit80for processing and analysis and/or for further transmission to external device40via telemetry circuit88. For example, sensing circuit86may include switching circuitry for selecting which of electrodes24,26,28,30, and housing15are coupled to one or more sensing channels of sensing circuit86.

As described below in conjunction withFIG.5, sensing circuit86may be configured to amplify, filter, rectify and digitize or otherwise process the cardiac electrical signal received from each selected sensing electrode vector to improve the signal quality for sensing cardiac electrical events, such as R-waves or P-waves. Cardiac event detection circuitry included within sensing circuit86may include one or more sense amplifiers, filters, rectifiers, threshold detectors, comparators, analog-to-digital converters (ADCs), timers or other analog or digital components configured to sense cardiac events, e.g., R-waves attendant to ventricular depolarizations and P-waves attendant to atrial depolarizations from a sensed cardiac electrical signal received by sensing circuit86via the selected sensing electrode vector.

Sensing circuit86may control the amplitude of an auto-adjusting cardiac event sensing threshold over each cardiac cycle, e.g., as described below in conjunction withFIG.6. Sensing circuit86may sense a cardiac event in response to a cardiac electrical signal crossing the sensing threshold. Sensing circuit86may produce a cardiac sensed event signal, e.g., an atrial sensed event signal in response to a P-wave sensing threshold crossing or a ventricular sensed event signal in response to an R-wave sensing threshold crossing. The cardiac sensed event signals are passed to control circuit80. As described below, various sensing threshold control parameters may be used by sensing circuit86to set and adjust the cardiac event sensing threshold during each cardiac cycle. These sensing threshold control parameters may be stored in memory82and passed to sensing circuit86from control circuit80for use by hardware, firmware and/or software of control circuit80and/or sensing circuit86in controlling the amplitude of the cardiac event sensing threshold.

Control circuit80receives the cardiac sensed event signals from sensing circuit86for determining sensed cardiac event intervals, e.g., RR intervals (RRIs) and/or PP intervals (PPIs), by timing circuit90. An RRI is the time interval between two consecutively sensed R-waves and may be determined between consecutive ventricular sensed event signals received by control circuit80from sensing circuit86. A PPI is the time interval between two consecutively sensed P-waves and may be determined between consecutive atrial sensed event signals received by control circuit80from sensing circuit86. Depending on programmed therapies, timing circuit90may trigger therapy delivery circuit84to generate and deliver an electrical stimulation pulse in response to a sensed event signal and/or start a pacing escape interval timer in response to a sensed event signal and restart the escape interval timer in response to the next sensed event signal. The value of the escape interval timer at the time of the next sensed event signal may be buffered in memory82as the sensed cardiac event interval for the associated sensed event signal. In this way, memory82may store a series of sensed cardiac event intervals for determining a sensed cardiac event rate.

Timing circuit90may include various timers and/or counters used to control the timing of therapy delivery by therapy delivery circuit84. In response to expiration of an escape interval timer without receiving a cardiac sensed event signal, control circuit80may control therapy delivery circuit84to generate and deliver a pacing pulse. Timing circuit90may additionally set time windows such as morphology template windows, morphology analysis windows or perform other timing related functions of ICD14including synchronizing CV/DF shocks or other therapies delivered by therapy delivery circuit84with sensed cardiac events.

Control circuit80may include a tachyarrhythmia detector92configured to analyze signals received from sensing circuit86for detecting tachyarrhythmia. Tachyarrhythmia detector92may detect tachyarrhythmia based on cardiac events sensed by sensing circuit86meeting tachyarrhythmia detection criteria, such as a threshold number of sensed cardiac events occurring at cardiac event intervals falling in a tachyarrhythmia interval range. Tachyarrhythmia detector92may be implemented in control circuit80as hardware, software and/or firmware that processes and analyzes signals received from sensing circuit86for detecting tachyarrhythmia, e.g., supraventricular tachycardia (SVT), VT and/or VF. Tachyarrhythmia detector92may include comparators and counters for counting cardiac event intervals, e.g., PPIs or RRIs determined by timing circuit90, that fall into various rate detection zones for determining an atrial rate and/or a ventricular rate or performing other rate- or interval-based assessment of cardiac sensed event signals for detecting and discriminating tachyarrhythmias.

For example, tachyarrhythmia detector92may compare the RRIs determined by timing circuit90to one or more tachyarrhythmia detection interval zones, such as a tachycardia detection interval zone and a fibrillation detection interval zone. RRIs falling into a detection interval zone are counted by a respective VT interval counter or VF interval counter and in some cases in a combined VT/VF interval counter included in tachyarrhythmia detector92. The VF detection interval threshold may be set to 300 to 350 milliseconds (ms), as an example. For instance, if the VF detection interval is set to 320 ms, RRIs that are less than 320 ms are counted by the VF interval counter. When VT detection is enabled, the VT detection interval may be programmed to be in the range of 350 to 420 ms, or 400 ms as an example. RRIs that are less than the VT detection interval but greater than the VF detection interval may be counted by a VT interval counter. In order to detect VT or VF, the respective VT or VF interval counter is required to reach a threshold “number of intervals to detect” or “NID.”

As an example, the NID to detect VT may require that the VT interval counter reaches 18 VT intervals, 24 VT intervals, 32 VT intervals or other selected NID. In some examples, the VT intervals may be required to be consecutive intervals, e.g., 18 out of 18, 24 out of 24, or 32 out of the most recent 32 consecutive RRIs. The NID required to detect VF may be programmed to a threshold number of X VF intervals out of Y consecutive RRIs. For instance, the NID required to detect VF may be 18 VF intervals out of the most recent 24 consecutive RRIs or 30 VF intervals out 40 consecutive RRIs, as examples. When a VT or VF interval counter reaches an NID, a ventricular tachyarrhythmia may be detected by tachyarrhythmia detector92. The NID may be programmable and range from as low as 12 to as high as 40, with no limitation intended. VT or VF intervals may be detected consecutively or non-consecutively out of a specified number of most recent RRIs. In some cases, a combined VT/VF interval counter may count both VT and VF intervals and detect a tachyarrhythmia episode based on the fastest intervals detected when a specified NID is reached.

Tachyarrhythmia detector92may be configured to perform other signal analysis for determining if other detection criteria are satisfied before detecting VT or VF, such as R-wave morphology criteria and onset criteria. To support additional cardiac signal analyses, sensing circuit86may pass a digitized cardiac electrical signal to control circuit80, e.g., an ECG signal when sensed using electrodes outside the heart or an EGM signal when sensed using intracardiac electrodes. The digitized cardiac electrical signal may be passed to control circuit80for morphology analysis performed by tachyarrhythmia detector92for detecting and discriminating heart rhythms. A cardiac electrical signal from a selected sensing electrode vector may be passed through a filter and amplifier, provided to a multiplexer and thereafter converted to a multi-bit digital signal by an analog-to-digital converter, all included in sensing circuit86, for storage in memory82and/or for real time transmission via telemetry circuit88. Memory82may include one or more circulating buffers to temporarily store digital cardiac electrical signal segments (also referred to herein as “episodes”) for analysis performed by control circuit80and/or by external device processor52after transmission via telemetry circuit88. Control circuit80may be a microprocessor-based controller that employs digital signal analysis techniques to characterize the digitized signals stored in memory82to recognize and classify the patient's heart rhythm employing any of numerous signal processing methodologies for analyzing cardiac electrical signals and cardiac event waveforms, e.g., R-waves.

Therapy delivery circuit84includes charging circuitry, one or more charge storage devices such as one or more high voltage capacitors and/or low voltage capacitors, and switching circuitry that controls when the capacitor(s) are discharged across a selected pacing electrode vector or CV/DF shock vector. Charging of capacitors to a programmed pulse amplitude and discharging of the capacitors for a programmed pulse width may be performed by therapy delivery circuit84according to control signals received from control circuit80. For example, timing circuit90may include programmable digital counters set by a microprocessor of the control circuit80for controlling the basic pacing time intervals associated with various pacing modes or ATP sequences delivered by ICD14. The microprocessor of control circuit80may also set the amplitude, pulse width, polarity or other characteristics of the cardiac pacing pulses, which may be based on programmed values stored in memory82.

In response to detecting VT or VF, control circuit80may schedule a therapy and control therapy delivery circuit84to generate and deliver the therapy, such as ATP and/or CV/DF therapy. Therapy can be generated by initiating charging of high voltage capacitors via a charging circuit, both included in therapy delivery circuit84. Charging is controlled by control circuit80which monitors the voltage on the high voltage capacitors, which is passed to control circuit80via a charging control line. When the voltage reaches a predetermined value set by control circuit80, a logic signal is generated on a capacitor full line and passed to therapy delivery circuit84, terminating charging. A CV/DF pulse is delivered to the heart under the control of the timing circuit90by an output circuit of therapy delivery circuit84via a control bus. The output circuit may include an output capacitor through which the charged high voltage capacitor is discharged via switching circuitry, e.g., an H-bridge, which determines the electrodes used for delivering the cardioversion or defibrillation pulse and the pulse wave shape.

In some examples, the high voltage therapy circuit configured to deliver CV/DF shock pulses can be controlled by control circuit80to deliver pacing pulses, e.g., for delivering ATP, post shock pacing pulses or ventricular pacing pulses. In other examples, therapy delivery circuit84may include a low voltage therapy circuit for generating and delivering pacing pulses for a variety of pacing needs.

It is recognized that the methods disclosed herein for processing and analyzing cardiac electrical signals may be implemented in a medical device system that is used for monitoring cardiac electrical signals by sensing circuit86and control circuit80without necessarily having therapy delivery capabilities or in a pacemaker that monitors cardiac electrical signals and delivers cardiac pacing therapies by therapy delivery circuit84, without high voltage therapy capabilities such as CV/DF shock capabilities.

Control parameters utilized by control circuit80for sensing cardiac events and controlling therapy delivery may be programmed into memory82via telemetry circuit88. Telemetry circuit88includes a transceiver and antenna for communicating with external device40(shown inFIG.1A) using RF communication or other communication protocols as described above. Under the control of control circuit80, telemetry circuit88may receive downlink telemetry from and send uplink telemetry to external device40. Telemetry circuit88may transmit sensed cardiac electrical signals (and in some cases sensed cardiac event markers and associated cardiac event intervals) to another medical device, e.g., external device40, for processing and analysis according to the techniques disclosed herein. In other examples, control circuit80may be configured to perform some or all of the analysis of cardiac electrical signals as disclosed herein and may transmit the data resulting from the analysis to external device40.

FIG.5is a conceptual diagram of circuitry that may be included in sensing circuit86of a medical device, e.g., ICD14, according to one example. Sensing circuit86may be coupled to all available electrodes that may be used in a sensing electrode vector for sensing cardiac electrical signals. Using the example medical device system10ofFIGS.1A-2C, sensing circuit86is shown coupled to pace/sense electrodes28and30, defibrillation electrodes24and26and housing15, which may be selected in any combination as a sensing electrode vector. Sensing circuit86may include switching circuit61for controlling which electrodes are selected in a pair as a sensing electrode vector that is coupled to prefilter and amplifier62. Two or more sensing electrode vectors may be coupled to prefilter and amplifier62. In one example, the two pace/sense electrodes28and30carried by lead16are selected as one sensing electrode vector, and one pace/sense electrode28or30carried by lead16is selected in combination with housing15as a second sensing electrode vector. A sensing electrode vector may be selected by switching circuit61according to control signals from control circuit80. Switching circuit61may include a switch array, switch matrix, multiplexer, or any other type of switching device(s) suitable to selectively couple selected electrodes to the input prefilter and amplifier62.

Each electrical signal developed across the selected sensing electrode vectors, e.g., electrodes28and30in a first sensing electrode vector and electrode30and housing15in a second sensing electrode vector, is received as a differential input signal by the pre-filter and pre-amplifier62. Non-physiological high frequency and DC signals may be filtered by a low pass or bandpass filter included in pre-filter and pre-amplifiers62, and high voltage signals may be removed by protection diodes included in pre-filter and pre-amplifiers62. Pre-filter and pre-amplifier62may amplify the pre-filtered signal by a gain of between10and100, and in one example a gain of 17.5, and may convert the differential signal to a single-ended output signal passed to analog-to-digital converter (ADC)63. Pre-filter and amplifier62may provide anti-alias filtering and noise reduction prior to digitization.

ADC63converts the cardiac electrical signal from an analog signal to a digital bit stream. In one example, ADC63may be a sigma-delta converter (SDC), but other types of ADCs may be used. In some examples, the output of ADC63may be provided to a decimator (not shown), which functions as digital low-pass filter that increases the resolution and reduces the sampling rate of the cardiac electrical signal. The digital output of ADC63may be passed to a digital bandpass filter64and on to cardiac event detector66for sensing cardiac events. Filter64may have a relatively narrow bandpass of approximately 13 Hz to 39 Hz for passing cardiac event signals, such as R-waves, typically occurring in this (or other bandpass) frequency range. The narrowband filtered signal may be passed from filter64to rectifier65to produce a filtered, rectified signal that is received by a cardiac event detector66for sensing cardiac events in response to the narrowband filtered and rectified signal crossing a cardiac event sensing threshold amplitude, for example an R-wave sensing threshold amplitude. In some examples, cardiac event detector66may include a P-wave detector for producing atrial sensed event signals in response to a P-wave sensing threshold.

Cardiac event detector66may include an auto-adjusting sense amplifier, comparator and/or other detection circuitry that compares the filtered and rectified cardiac electrical signal to a cardiac event sensing threshold amplitude and produces a sensed event signal68, which may be a ventricular sensed event signal or an atrial sensed event signal, when the filtered, rectified signal crosses the cardiac event sensing threshold outside of any blanking periods applied by sensing circuit86. A cardiac event sensing threshold applied by cardiac event detector66may be a multi-level sensing threshold, for example as described below in conjunction withFIG.6. Multiple sensing threshold control parameters may be used to adjust the amplitude of the cardiac event sensing threshold starting from the expiration of a post-sense (or post-pace) blanking period until the next cardiac event sensing threshold crossing (or expiration of a pacing interval). The techniques described herein are not limited to a specific behavior of the sensing threshold amplitude and numerous cardiac event sensing threshold control parameters, as described below in conjunction withFIG.6, may be defined and used to control the cardiac event sensing threshold amplitude over a cardiac cycle, until a cardiac event is sensed or a pacing escape interval expires resulting in a pacing pulse.

In some examples, event detector66includes a peak detector, which may include a sample and hold circuit, for detecting the maximum peak amplitude of the rectified signal following a cardiac sensed event signal produced by cardiac event detector66. The maximum peak amplitude may be used by cardiac event detector66for setting the starting amplitude of the cardiac event sensing threshold based on the detected maximum peak amplitude. The starting cardiac event sensing threshold amplitude may be set by cardiac event detector66upon expiration of any post-sense blanking period applied upon detecting a sensing threshold crossing. The cardiac event sensing threshold amplitude may be set to a starting amplitude that is a percentage of the maximum peak amplitude, e.g., 60%, 70%, 80% or other selected percentage. The starting sensing threshold amplitude may be adjusted according to the sensing threshold control parameters down to a sensing floor, which may be equal to the programmed sensitivity, or until a sensing threshold crossing, whichever occurs first. The sensitivity is the lowest amplitude that the cardiac event sensing threshold may be adjusted to and is therefore the lowest amplitude of the cardiac electrical signal that may be sensed as a cardiac event. The lower the programmed value of the sensitivity, e.g., 0.03 millivolts or less, the more sensitive sensing circuit86is to sensing cardiac events. Sensing circuit86is relatively less sensitive to sensing cardiac events when the programmed value of the sensitivity is relatively higher, e.g., 0.9 millivolts or higher.

Sensing circuit86may include wideband filter74for producing a cardiac EGM (sensed by intracardiac electrodes) or ECG (sensed by extra-cardiac electrodes) signal that is passed to control circuit80, e.g., signal78, for performing morphological analysis of the cardiac signal waveforms. For example, control circuit80may perform morphology analysis of the wideband filtered cardiac electrical signal78to detect and distinguish R-waves arising from non-sinus tachycardia or fibrillation waves from normally conducted R-waves. Wideband filter74may have a bandpass of approximately 2.5 to 100 Hz. In some examples, filter74may include a notch filter to attenuate 60 Hz or 50 Hz line noise. The cardiac electrical signal received by the sensing electrode vector between one of pace/sense electrodes28or30and housing15may be passed from ADC63to wideband filter74for morphological analysis by control circuit80for use in tachyarrhythmia detection. A second cardiac electrical signal received by a different sensing electrode vector, e.g., between pace/sense electrodes28and30, may be passed to narrowband filter64and to wideband filter74. Both the first and the second wideband filtered cardiac electrical signals may be analyzed for determining acceptable or recommended sensing control parameters by control circuit80or by the processor of another medical device, e.g., external device processor52(FIG.1A).

Sensing circuit86may be configured to select one sensing electrode vector out of multiple available sensing electrode vectors for cardiac event sensing by event detector66. The sensing electrode vector may be a programmable sensing control parameter. For the sake of illustration, sensing circuit86may select one sensing electrode vector from among three different sensing electrode vectors for sensing cardiac events. The three different sensing electrode vectors may be between pace/sense electrodes28and30, between pace/sense electrode28and housing15, and between pace/sense electrode30and housing15in one example.

Sensing circuit86may be configured to select two or more sensing electrode vector signals for passing to wideband filter74. In some examples, a single wideband filtered signal is used by control circuit80for morphological analysis, e.g., for tachyarrhythmia detection. However, multiple wideband filtered vector signals may be analyzed according to the techniques disclosed herein for determining acceptable or recommended sensing control parameters. For the sake of illustration, sensing circuit86may be configured to select up to four sensing electrode vectors for producing four different wideband filtered digital cardiac electrical signals70,72,76and78from among ten possible sensing electrode vector signals available from the four electrodes24,26,28,30and housing15. In the example shown, the ten possible sensing electrode vectors are between pace/sense electrodes28and30, between pace/sense electrode28and each of housing15, defibrillation electrode24and defibrillation electrode26, between pace/sense electrode30and each of housing15, defibrillation electrode24and defibrillation electrode26, between defibrillation electrodes24and26, between defibrillation electrode24and housing15, and between defibrillation electrode26and housing15.

All four wideband filtered sensing vectors signals70,72,76and78may be analyzed according to techniques disclosed herein for determining acceptable or recommended sensing control parameters. In one example, the wideband filtered signals70,72,76and78are sampled at 256 Hz and transmitted by telemetry circuit88in real time. The transmitted cardiac electrical signals may be received by another device, e.g., external device40, for processing and analysis. In other examples, the wideband filtered signals70,72,74, and/or76may be stored in memory82for post-processing and analysis by control circuit80or for later transmission via telemetry circuit88. Because memory82may have limited capacity for storing cardiac electrical signals, fewer signals and/or signals sampled at a lower sampling rate may be stored in memory82for later analysis or transmission than the number and/or sampling rate of cardiac electrical signals that may be transmitted to external device40in real time for subsequent analysis and processing. For example, two wideband filtered signals sampled at a frequency of 128 Hz may be stored in memory82for post-processing and analysis, which may include transmission to another device for performing the post-processing and analysis.

A user interacting with external device40may select the sensing electrode vector signals that are passed to wideband filter74for storage in memory82or real time transmission. In illustrative examples presented herein, at least two sensing electrode vector signals are selected for wideband filtering for real time transmission or storage in memory82. The two sensing electrode vectors include one electrode common to both sensing electrode vectors such that a third cardiac electrical signal that would be sensed using a third sensing electrode vector between the two electrodes that are unique to the two selected sensing electrode vectors can be constructed. In this way by sensing two cardiac electrical signals, three cardiac electrical signals corresponding to three different sensing electrode vectors are available for processing and analysis for determining acceptable or recommended sensing control parameters. In the illustrative examples presented herein, the two sensed cardiac electrical signal correspond to a first sensing electrode vector between pace/sense electrodes28and30and second sensing electrode vector between pace/sense electrode30and housing15. During processing and analysis, control circuit80or another processor, e.g., external device processor52(FIG.1A), may construct a third cardiac electrical signal that is expected to be sensed between the two electrodes that are not common to the sensed cardiac electrical signal sensing vectors, which would be between pace/sense electrode28and housing15in the illustrative example given here.

By programming selected sensing electrode vector signals for filtering by wideband filter74, one or more additional sensing electrode vectors signals may be constructed by a processor, thereby enabling analysis of multiple sensed and constructed cardiac electrical signals for determining acceptable or recommended sensing control parameters, which may include an acceptable or recommended the sensing electrode vector. The techniques disclosed herein for determining acceptable or recommended sensing control parameters, therefore, do not require all cardiac electrical signals that undergo analysis to be sensed cardiac electrical signals. The number of sensing electrode vector signals available for analysis can be increased by constructing one or more cardiac electrical signals from the sensed cardiac electrical signals. When four different cardiac electrical signals are sensed, e.g., using all four available electrodes24,26,28and30each paired with housing15in four different sensing electrode vectors all having one common electrode (housing15in this example), the remaining six possible sensing electrode vector signals may be constructed from the four sensed cardiac electrical signals. Furthermore, in some examples, a cardiac electrical signal may be constructed from one sensed and one constructed cardiac electrical signal determined from two other cardiac electrical signals or even constructed from two other constructed cardiac electrical signals.

In some examples, sensing circuit86may include two or more sensing channels including the same or different filters, amplifiers, ADCs and/or other signal processing circuitry such that different cardiac electrical signals sensed from one or different sensing electrode vectors may be passed to control circuit80for processing and analysis. While sensing circuit86is shown having a single prefilter and amplifier62, ADC63and wideband filter74for passing up to four sensed cardiac electrical signals70,72,76and78, other sensing circuit configurations may include multiple channels, each having its own prefilter and amplifier, ADC and wideband filter for passing a cardiac electrical signal to control circuit80for storage in memory82and/or transmission by telemetry circuit88. An example sensing circuit having two sensing channels each with a prefilter and preamplifier and ADC is generally described in U.S. Pat. No. 9,956,423 (Zhang, et al.), incorporated herein by reference in its entirety. Sensing circuit86may include more or fewer components than illustrated inFIG.5and some components may be shared between multiple sensing channels for sensing multiple cardiac electrical signals. The configuration of sensing circuit86as shown inFIG.5is therefore illustrative in nature and should not be considered limiting of the techniques described herein for sensing at least two cardiac electrical signals and constructing at least one more cardiac electrical signal. As described below, each sensed cardiac electrical and/or each cardiac electrical signal constructed from the sensed cardiac electrical signals may be analyzed according to multiple sensing threshold control parameter settings. In the illustrative examples disclosed herein, the sensed cardiac electrical signals sensed by sensing circuit86may be transmitted to external device40for post-processing and analysis for constructing at least one more cardiac electrical signal and/or determining sensed cardiac event intervals according to multiple sensing threshold control parameter settings.

FIG.6is a diagram of a filtered and rectified cardiac electrical signal200illustrating one technique for adjusting the cardiac event sensing threshold210by sensing circuit86under the control of control circuit80. Cardiac electrical signal200includes an R-wave202, a T-wave204, and a P-wave206. The cardiac electrical signal200may be representative of the output of rectifier65received by cardiac event detector66as shown inFIG.5. Alternatively, cardiac electrical signal200may represent a narrowband filtered and rectified signal determined from a sensed or constructed wideband filtered signal by control circuit80or external device processor52during processing and analysis of the sensed and constructed cardiac electrical signals for determining sensed cardiac events according to one or more cardiac event sensing threshold control parameter settings. Analysis performed by a processor as disclosed herein to determine sensed cardiac events according to test sensing control parameter settings mimics the processing that occurs by sensing circuit86for sensing cardiac events from the narrowband filtered, rectified signal by cardiac event detector66. In the description that follows, the operations performed to adjust the cardiac event sensing threshold210are described as being performed by sensing circuit86for the sake of convenience. However, during real time or post-processing of a cardiac electrical signal by control circuit80, by external device processor52or by another processor, it is to be understood that determination of sensed cardiac events from the cardiac electrical signal involves the same cardiac event sensing threshold adjustment operations as would be performed by sensing circuit86for determining when the cardiac electrical signal, sensed or constructed, is estimated to cross the cardiac event sensing threshold.

In this example, the cardiac event sensing threshold210is an R-wave sensing threshold that is adjusted for sensing R-waves from the cardiac electrical signal200and determining RRIs. Sensing circuit86adjusts the R-wave sensing threshold210between a starting threshold amplitude212and the minimum sensing threshold amplitude equal to the programmed sensitivity220. The starting threshold amplitude212may be set based on the maximum peak amplitude203of sensed R-wave202. R-wave202is sensed by sensing circuit86in response to the cardiac electrical signal200crossing the R-wave sensing threshold at201. Sensing circuit86produces a ventricular sensed event signal (VS)230(e.g., corresponding to the sensed event signal68output by cardiac event detector66shown inFIG.5) in response to the sensing threshold crossing201. Sensing circuit86may be configured to detect the maximum peak of R-wave202during a post-sense blanking period240for determining maximum peak amplitude203. The starting R-wave sensing threshold amplitude212may be set to a percentage, e.g., between 55% and 70% or another selected percentage, of the maximum peak amplitude203. For example, the percentage used to set starting R-wave sensing threshold amplitude212can be 62.5% of the maximum peak amplitude203.

The starting threshold212may be held for a sense delay interval242to avoid oversensing T-wave204as an R-wave. In other examples, the starting threshold212may decay at a specified decay rate for a predetermined decay interval. In the example shown, R-wave sensing threshold210is decreased by a step decrement214upon expiration of sense delay interval242. Sense delay interval242may be between 300 and 400 ms, as examples, and is 360 ms in one example. At the expiration of sense delay interval242, sensing circuit86adjusts the R-wave sensing threshold210from the starting amplitude212set to a first percentage of maximum peak amplitude203to an intermediate sensing threshold amplitude216that is a second percentage of R-wave maximum peak amplitude203. The second percentage is less than the first percentage. Intermediate sensing threshold amplitude216may be set to between 25% and 60% of the maximum peak amplitude203or between 30% and 35% of the maximum peak amplitude203as examples. Intermediate sensing threshold amplitude216is less than the starting sensing threshold amplitude212by step decrement214.

R-wave sensing threshold210may be held at the intermediate amplitude216for a drop time interval244as shown inFIG.6. In other examples, R-wave sensing threshold210may decay at a specified decay rate from the expiration of the sense delay interval242until the expiration of drop time interval244or until reaching the sensing floor equal to the programmed sensitivity220. In the example shown, upon expiration of drop time interval244, sensing circuit86adjusts R-wave sensing threshold210from the intermediate sensing threshold amplitude216to the sensitivity220in a step decrement218. The sensitivity220defines the minimum sensing threshold amplitude or sensing floor of R-wave sensing threshold210. The drop time interval244may be between 1 second and 2 seconds and is 1.5 seconds in one example. The sensitivity220may be programmable over a range of 0.075 millivolts (mV) to 1.2 mV, as examples, though lower or higher sensitivity settings may be available.

Each of the first percentage used to set starting sensing threshold amplitude212as a percentage of maximum peak amplitude203, the second percentage used to set intermediate sensing threshold amplitude216as a percentage of maximum peak amplitude203, the sensitivity220, the post-sense blanking period240, the sense delay interval242and the drop time interval244may be programmable or adjustable cardiac event sensing threshold control parameters. Accordingly, processor52of external device40(and/or control circuit80) may be configured to determine cardiac sensed events from one or more cardiac electrical signals, sensed and/or constructed, according to one or more different settings of one cardiac event sensing threshold control parameter or combinations of different settings of two or more different sensing threshold control parameters. In illustrative examples described below, programmer52of external device40is configured to at least determine sensed cardiac events according to different settings of sensitivity220for at least one constructed cardiac electrical signal.

As shown inFIG.6, R-wave sensing threshold210is held at sensitivity220until the cardiac electrical signal200crosses the sensing threshold210, at sensing threshold crossing231, resulting in the next VS event signal234produced by sensing circuit86. It is to be understood that the cardiac electrical signal200may not cross the sensing threshold210before a pacing interval expires during some cardiac cycles. In this case, therapy delivery circuit84may generate and deliver a pacing pulse. At other times, the next R-wave248may occur earlier after R-wave202, before R-wave sensing threshold210reaches sensitivity220(before drop time interval244expires) or even before R-wave sensing threshold210reaches the intermediate sensing threshold amplitude216(before sense delay interval242expires). The cardiac event interval246, which is an RRI in this example, may be determined by control circuit80(or processor52of external device40) as the time interval between VS event signal230corresponding to threshold crossing201and VS event signal234corresponding to threshold crossing234.

The particular behavior of R-wave sensing threshold210shown inFIG.6as it is adjusted between the starting threshold amplitude212, set based on the maximum peak amplitude203, and the sensitivity220is one illustrative example of how sensing circuit86may adjust the sensing threshold210. It is to be understood that a variety of cardiac event sensing threshold control parameters, e.g., R-wave sensing threshold control parameters for ventricular rate determination or P-wave sensing threshold control parameters for atrial rate determination, may include one or more decay rates, each associated with a decay interval, and/or one or more step decrements, each associated with a drop time interval. Various cardiac event sensing threshold control parameters may be used by sensing circuit86for adjusting the R-wave sensing threshold210between the starting threshold212and sensitivity220. For example, the R-wave sensing threshold210may decay, linearly or non-linearly, from starting sensing threshold amplitude212to sensitivity220at a predetermined decay rate until a sensing threshold crossing or a pacing interval expires, whichever occurs first.

The techniques disclosed herein for determining sensed cardiac events from one or more cardiac electrical signals (corresponding to different sensing electrode vectors) according to one or more sensing threshold control parameter settings are not limited to use with any particular sensing threshold control parameters or sensing threshold adjustment schemes. The cardiac event sensing threshold control parameters used by sensing circuit86to adjust sensing threshold210, however, are the same cardiac event sensing threshold control parameters used by control circuit80and/or external device processor52for determining sensed cardiac events during post processing of different cardiac electrical signals for determining a recommended sensing control parameter setting. While the same sensing control parameters are used, such as sense delay interval242, drop time interval244and sensitivity220, different settings of these sensing threshold control parameters may be used during a determination of sensed cardiac events from a sensed or constructed cardiac electrical signal. By simulating the adjustment of the cardiac event sensing threshold that is performed by sensing circuit86during real time cardiac event sensing, control circuit80or external device processor52can determine sensed cardiac events for multiple different combinations of sensing control parameters settings without requiring ICD14to be reprogrammed to the multiple different combinations and perform the real time sensing.

FIG.7is a flow chart300of a method that may be performed by a medical device for determining sensed cardiac events according to multiple sensing control parameters according to one example. At block302, sensed cardiac electrical signals are received by a processor of a device performing the cardiac electrical signal analysis. As indicated above, the process for analyzing cardiac electrical signals as disclosed herein may be performed by a medical device that senses the cardiac electrical signals, e.g., by control circuit80of ICD14or processing circuitry of a pacemaker, cardiac monitor or other device configured to sense the cardiac electrical signals. As such, in one example, control circuit80receives at least two sensed cardiac electrical signals from sensing circuit86at block302.

In other examples, the process for analyzing cardiac electrical signals as disclosed herein may be performed by a processor of a device that receives the sensed cardiac electrical signals from another device. For example, the processor52of external device40may receive the sensed cardiac electrical signals from ICD14via communication link42. In other examples, the processor52of external device40may receive the sensed cardiac electrical signals from an external cardiac monitoring device, e.g., cardiac monitoring device60shown inFIG.1C. In some examples, the external cardiac monitoring device60or the external device40may transmit sensed cardiac electrical signals to a patient monitoring database, such as the CARELINK® Network (Medtronic, Minneapolis, Minnesota USA), for processing and analysis by a networked computer or by a computer in a clinic, hospital or doctor's office. Depending on the processing requirements and power capacity of the device sensing the cardiac electrical signals, e.g., ICD14, the sensed cardiac electrical signals may be transmitted to another device for processing and analysis. In still other examples, the processing and analysis of cardiac electrical signals as disclosed herein may be performed in a distributed manner across more than one device of a medical device system. For the sake of illustration, with no limitations intended, the techniques described in conjunction withFIG.7and other flow charts presented herein refer to ICD14as the device sensing the cardiac electrical signals and external device40as receiving the sensed cardiac electrical signals, which may be via cardiac monitoring device60, and performing subsequent processing and analysis for determining acceptable or recommended sensing control parameters.

The cardiac electrical signals received at block302by processor52of external device40may be sensed by sensing circuit86of ICD14using at least two different sensing electrode vectors. The two sensing electrode vectors include one electrode common to both sensing electrode vectors but not both electrodes. For example, the first sensing electrode vector may include pace/sense electrodes28and30carried by lead16as shown inFIG.1Aand the second electrode vector may include one of pace/sense electrodes28or30paired with housing15or a defibrillation electrode24or26.

The two sensed cardiac electrical signals may be passed to control circuit80from sensing circuit86as raw cardiac electrical signals, e.g., as wideband filtered signals from filter74. The sensed cardiac electrical signals may be transmitted from ICD14to external device40as cardiac signal episodes that are a few seconds or a few minutes in duration for example. The sensed cardiac electrical signals may be received in real time via telemetry circuit88or stored in memory82and then passed to telemetry circuit88for transmission to external device40at a later time. In other examples, the sensed cardiac electrical signals may be transmitted in real time to cardiac monitoring device60and processed by the cardiac monitoring device or subsequently transmitted to external device40. In still other examples, the sensed cardiac electrical signals may be surface ECG signals received by cardiac monitoring device60or external device40as described above.

At block304, processor52of external device40constructs a third cardiac electrical signal that is expected to be sensed from a third sensing electrode vector, different than the first and second sensing electrode vectors but including one electrode from each of the sensed cardiac electrical signal sensing electrode vectors. The third sensing electrode vector signal may be determined by determining the voltage difference between the two sensed cardiac electrical signals at each sample point.

FIG.8is a diagram350of some possible sensing electrode vectors that exist between the electrodes24,26,28and30carried by lead16and housing15. Using the example given above, when the first sensing electrode vector S1is between the pace/sense electrode30and pace/sense electrode28and the second sensing electrode vector S2is between the pace/sense electrode30and the housing15, a third, constructed cardiac electrical signal that is expected to be sensed between a third sensing electrode vector C1(between pace/sense electrode28and the housing15) can be determined by subtracting the S1signal from the S2signal. The third cardiac electrical signal expected to be sensed by the third sensing electrode vector C1is therefore constructed based on two cardiac electrical signals sensed from sensing electrode vectors having one common electrode (pace/sense electrode30in this example).

The constructed cardiac electrical signal corresponds to a sensing electrode vector C1including one electrode28from the first S1sensing electrode vector used to sense the first sensed cardiac electrical signal and one electrode (housing15) from the second S2sensing electrode vector used to sense the second sensed cardiac electrical signal. The constructed cardiac electrical signal corresponding to the sensing electrode vector C1between pace/sense electrode28and housing15is determined by determining the voltage amplitude differences of the two sensed cardiac electrical signals corresponding to vectors S1and S2at each sample point time.

Referring back toFIG.7, in some examples, more than two sensed cardiac electrical signals may be received at block302, so that more than one cardiac electrical signal may be constructed from the sensed cardiac electrical signals. In the example ofFIG.1A, all four electrodes24,26,28and30and housing15may be included in four different sensing electrode vectors used to sense four cardiac electrical signals so that a cardiac electrical signal expected to be sensed from each one of the remaining six possible sensing electrode vectors can be constructed. Using the four sensed cardiac electrical signals, additional cardiac electrical signals may be constructed by external device processor52to enable analysis of cardiac electrical signals corresponding to up to 10 different sensing electrode vectors available between the four electrodes24,26,28,30and housing15. For example, if four cardiac electrical signals are sensed using the four sensing electrode vectors between the housing15and each respective electrode24,26,28and30, the cardiac electrical signals expected from the six sensing electrode vectors (defined by electrodes24and26, electrodes24and28, electrodes28and30, electrodes26and28, electrodes26and30, and electrodes28and30) that are available between the four electrodes may be constructed from the four sensed cardiac electrical signals for a total of ten cardiac electrical signals, sensed or constructed.

In some examples, a constructed cardiac electrical signal determined from two sensed cardiac electrical signals may be used by external device processor52to determine another constructed cardiac electrical signal. Referring again toFIG.8, three cardiac electrical signals may be sensed: one between the pace/sense electrodes28and30(S1), one between pace/sense electrode30and housing15(S2), and one between defibrillation electrode26and housing15(S3). A constructed cardiac electrical signal expected to be sensed between pace/sense electrode28and housing15(C1) may be determined using the first two sensed cardiac electrical signals (from sensing vectors S1and S2). Another constructed cardiac electrical signal expected to be sensed between pace/sense electrode28and defibrillation electrode26(C2) may be determined by determining the voltage amplitude differences between the constructed C1cardiac electrical signal between electrode28and housing15and the sensed cardiac electrical signal between defibrillation electrode26and housing15(S3). Accordingly, multiple constructed cardiac electrical signals may be determined from multiple sensed cardiac electrical signals and combinations of constructed and sensed cardiac electrical signals.

At block306, external device processor52determines sensed cardiac events for at least one of the sensed and/or constructed cardiac electrical signals. For example, processor52may determine sensed cardiac events for the constructed cardiac electrical signal by determining a narrowband filtered and rectified signal from the constructed cardiac electrical signal and applying a cardiac event sensing threshold to the rectified signal. Processor52may adjust the cardiac event sensing threshold according to the same cardiac event sensing threshold control parameters that are used by cardiac event detector66of sensing circuit86. Processor52may repeat the analysis for at least one sensed cardiac electrical signal or both sensed cardiac electrical signals. In this way, programmer52may generate sensed cardiac event data corresponding to a third sensing electrode vector that enables a comparison of cardiac event sensing between the third sensing electrode vector and at least one sensing electrode vector that was used to sense the cardiac electrical signals received at block302. This comparison of sensed events determined from the constructed cardiac electrical signal and a sensed cardiac electrical signal provides data for use in selecting the sensing electrode vector that provides reliable cardiac event sensing.

In some examples, processor52may determine the sensed cardiac events for at least one sensed cardiac electrical signal received at block302in addition to determining the sensed cardiac events for at least one constructed cardiac electrical signal. Processor52may determine a narrowband filtered and rectified signal from each received, sensed cardiac electrical signal and apply the cardiac event sensing threshold to determine sensed cardiac events in the manner that cardiac event detector66(FIG.5) would sense cardiac events from a narrowband filtered and rectified signal. In some examples, processor52adjusts the cardiac event sensing threshold according to control parameters currently programmed in ICD14, e.g., the current post sense blanking period, percentages used to determine the starting and intermediate amplitudes of the sensing threshold, the sense delay interval, the drop time interval and the sensitivity as described above in conjunction withFIG.6. This analysis provides a comparison of cardiac event sensing using different sensing electrode vectors. However, processor52may determine sensed cardiac events for the constructed cardiac electrical signal(s) and sensed cardiac electrical signals for multiple different cardiac event sensing threshold control parameter settings.

For example, processor52may set and adjust the R-wave sensing threshold using multiple settings for at least one of the R-wave sensing threshold control parameters to determine sensed cardiac events from each cardiac electrical signal, sensed and constructed, according to the multiple R-wave sensing threshold control parameter settings. Using sensitivity as an example, processor52may determine sensed cardiac events from each of the constructed and sensed cardiac electrical signals for each available sensitivity setting in ICD14to generate sensed cardiac event data at block306. Processor52may adjust the R-wave sensing threshold according to the sensing threshold control parameters for each cardiac electrical signal, sensed and constructed, to determine sensed cardiac events for each one of multiple sensitivity settings.

In other examples, processor52may determine sensed cardiac event signals for each available percentage setting used to determine the starting and/or the intermediate threshold as a percentage of the maximum peak amplitude determined during the post-sense blanking period. In still other examples, processor52may determine sensed cardiac event signals for each available sense delay interval setting and/or each available drop time interval setting. Processor52may determine sensed cardiac events for a range of a given sensing threshold control parameter or different combinations of sensing threshold control parameters for each of the sensed and constructed cardiac electrical signals so that comparisons between the sensed cardiac event intervals or sensed cardiac event rate may be made between different combinations of sensing control parameters and used for identifying reliable or recommended sensing control parameters.

At block308, processor52may determine a predicted sensed cardiac event rate for each sensed and constructed cardiac electrical signal for each tested sensing threshold control parameter setting. For example, processor52may determine a predicted sensed atrial or ventricular rate based on the determined sensed cardiac events and/or generate a series of predicted sensed cardiac event intervals, e.g., PPIs or RRIs, at block308. It is recognized that for at least one of the sensed cardiac electrical signals and set of sensing threshold control parameters the actual time of cardiac event signals sensed by cardiac event detector66of sensing circuit86may be determined by ICD control circuit80and transmitted to external device40with the sensed cardiac electrical signals. This actual sensed cardiac event interval data, a determined cardiac event rate and/or arrhythmia detection by ICD control circuit80may be transmitted to external device40and may be used as an expected cardiac event rate for comparative analysis of other sensing control parameter settings or may be used to compare to determined sensed cardiac event intervals or rates determined from the analysis of other cardiac electrical signals according to other sensing control parameter settings. A comparison between actual sensed cardiac event data and simulated sensed cardiac event data for the same sensing control parameters may be made to verify accuracy and consistency of the determined sensed cardiac events by processor52for the same set of sensing control parameters. In other examples, the determination of sensed cardiac events corresponding to the programmed sensing control parameters need not be performed by external device processor52because the data may be available from and transmitted by ICD14.

At block310, processor52may generate an output based on the sensed cardiac event data determined at block308. In some examples, the output may be generated for display on display unit54. For example, the output may be a graphical or tabular display of the data relating to cardiac event rate and/or cardiac event intervals determined for each sensing threshold control parameter setting applied to each sensed and constructed cardiac electrical signal. Processor52may generate an output of one or more recommended or acceptable sensing control parameter settings, which may be output for display, e.g., included in a GUI. A recommended or acceptable sensing electrode vector and/or sensitivity setting that results in an expected sensed cardiac event rate at a desired safety margin for sensing cardiac events may be determined and identified in a generated display, as an example. The expected or actual cardiac rate may be verified by a user or may be based on the median, mean or mode of the sensed cardiac event rates determined from all cardiac electrical signals and all sensing threshold control parameter settings used in the analysis, assuming the actual cardiac event rate is the most frequently determined sensed cardiac event rate from among the sensing control parameters analyzed. Techniques that may be performed by processor52for determining a sensing control parameter that provides a desired safety margin for sensing cardiac events at the expected or actual cardiac rate are described below in conjunction withFIGS.8-13. In an example, the recommended sensitivity setting for a given sensing electrode vector may be one half of the minimum sensitivity setting that results in an expected or actual cardiac rate to provide a 2× (two times) safety margin for sensing cardiac events.

Accordingly, processor52may be configured to determine a rate of the determined sensed cardiac events, determine that the rate meets expected cardiac event rate criteria and determine that an associated sensing control parameter used to determine the sensed cardiac events meeting the expected cardiac event rate criteria is a recommended sensing control parameter. The expected cardiac event rate criteria may be an actual rate (which may be defined as an acceptable rate range) determined by a user and received by processor52via user interface56. The expected cardiac event rate criteria may alternatively be a rate (or rate range) determined by processor52based on the most frequently determined rate from among the determined sensed cardiac events for each set of sensing control parameters (combinations of sensing electrode vector and cardiac event sensing threshold control parameter settings). In still other examples, as described below in conjunction withFIG.9, the expected rate criteria may be defined by an arrhythmia detection or the time to detect an arrhythmia, such as VT or VF. When a set of sensing control parameters results in determined cardiac event intervals that meet expected rate criteria as determined at block310, processor52may generate a display indicating the acceptable sensing control parameters.

The output generated by processor52at block310may include a programming command that is transmitted by telemetry unit58to ICD telemetry circuit88in some examples. The programming command may include a sensing electrode vector and/or one or more cardiac event sensing threshold control parameters selected as recommended settings for providing reliable cardiac event signal sensing based on the analysis of the sensed and constructed cardiac electrical signals. Control circuit80responds to the programming command by setting the selected sensing electrode vector and/or sensing threshold control parameter(s). Such programming may occur without requiring user intervention. In other examples, a user may confirm a recommended setting prior to transmission of the programming command, e.g., by interacting with user interface56or a GUI displayed on display unit54or via remote monitoring from a computer or other device in communication with external device40.

FIG.9is a flow chart400of a method performed by a medical device system for determining sensed cardiac events from multiple sensing electrode vector signals according to another example. At block402at least two different cardiac electrical signals are sensed by sensing circuit86using two different sensing electrode vectors. At least one electrode is common to both of the two sensing electrode vectors to enable control circuit80or external device processor52to construct at least one more cardiac electrical signal corresponding to a third sensing electrode vector.

At block404, control circuit80may detect tachyarrhythmia based on at least one of the sensed cardiac electrical signals. The tachyarrhythmia may be an induced tachyarrhythmia or a spontaneously occurring tachyarrhythmia. In response to the tachyarrhythmia, control circuit80stores an episode of each of the two sensed cardiac electrical signals in memory82at block406. As described above, the two sensed cardiac electrical signals may be wideband filtered signals received from sensing circuit86. The stored episode extends from the first tachyarrhythmia interval detected by control circuit80(or earlier) until the tachyarrhythmia detection is made (or later) so that control circuit80or processor52of external device40is able to determine the time from the first tachyarrhythmia interval that contributed to tachyarrhythmia detection (e.g., contributed to the NID being reached) until tachyarrhythmia detection is made, referred to as the “time to detect.” While not explicitly shown inFIG.9, it is understood that therapy delivery circuit84of ICD14may respond to the tachyarrhythmia detection by generating a therapy, e.g., ATP or CV/DF shock therapy.

At block408, processor52constructs at least one alternative sensing electrode vector signal from the two sensed cardiac electrical signals. At block408, control circuit80may transmit the stored sensed cardiac electrical signal episodes corresponding to the detected tachyarrhythmia to external device40for processing and analysis. Control circuit80may perform the processing and analysis for determining sensed cardiac events from multiple cardiac electrical signals in some examples. However, in order to reduce processing burden and conserve power source98of ICD14, processing and analysis of sensed cardiac electrical signals may be performed by an external device, e.g., external device40shown inFIG.1A. As noted above, processing and analysis of cardiac electrical signals described in conjunction with flow charts presented herein, including the flow chart400ofFIG.9, may be performed by control circuit80, external device processor52, or cooperatively by both control circuit80and external device processor52or another processing device such as a remote computer in communication with external device40.

Accordingly, while transmission of the stored sensed cardiac electrical signal episodes is not explicitly shown inFIG.9, it is to be understood that transmission of sensed cardiac electrical signals and related data may occur at or after block406in order to enable an external processor52to obtain sensed cardiac electrical signals and perform subsequent processing and analysis. Furthermore, in some examples such as when the detected tachyarrhythmia is an induced tachyarrhythmia, the sensed cardiac electrical signals may be transmitted in real time to external device40during the tachyarrhythmia induction procedure. When transmitted in real time, ICD telemetry circuit88may be capable of transmitting a greater number of sensed cardiac electrical signals (corresponding to more sensing electrode vectors) than the number of cardiac electrical signal episodes that memory82has the capacity to store (for later transmission). For example, four different sensing electrode vector signals may be transmitted by ICD telemetry circuit88in real time during a tachyarrhythmia induction procedure while two different sensing electrode vector signals may be stored in memory82for later transmission to external device40.

FIG.10is a diagram450of three cardiac electrical signals that may be obtained by a processor and analyzed according to the techniques disclosed herein by a medical device system. In this example, cardiac electrical signal452is a sensed cardiac electrical signal that is sensed by a first sensing electrode vector, e.g., between pace/sense electrodes28and30(shown inFIG.1A). Cardiac electrical signal454is a sensed cardiac electrical signal that is sensed using a second sensing electrode vector, e.g., between pace/sense electrode30and housing15. The third cardiac electrical signal456is a constructed cardiac electrical signal that may be determined by processor52using the two sensed cardiac electrical signals452and454. Constructed cardiac electrical signal456corresponds to a cardiac electrical signal that would be sensed between sensing electrode28and housing15. Constructed cardiac electrical signal456may be determined by processor52by subtracting the first sensed cardiac electrical signal452from the second sensed cardiac electrical signal454(note that the millivolt scales are different for the different signals shown inFIG.10). By constructing a third cardiac electrical signal456from two sensed cardiac electrical signals452and454, processor52is able to determine sensed cardiac events from at least three different available sensing electrode vector signals to generate data relating to the determined sensed cardiac events, e.g., event intervals or rates, according to specified sensing threshold control parameter settings. This generated data enables processor52to make comparisons between sets of sensing control parameters, e.g., different combinations of sensing electrode vector and multiple sensitivities, without having to reprogram ICD14and without recording cardiac electrical signals sensed according to a relatively large number of different sensing control parameters. Selection of an acceptable sensing electrode vector and corresponding sensing threshold control parameter settings may be made based on the sensed cardiac event data determined by a processor configured to simulate the sensing operations of sensing circuit86, such as narrowband filtering and rectifying of the sensed and constructed signals and applying a multi-level cardiac event sensing threshold amplitude to determine sensing threshold crossings.

The two sensed cardiac electrical signals452and454are sensed by sensing circuit86during VF in this example and may be transmitted in real time to external processor52, e.g., during a VF induction procedure. In other examples, the two sensed cardiac electrical signals452and454are stored in memory82in response to control circuit80detecting a spontaneous VF episode and transmitted to external device40, e.g., in response to an interrogation command received by ICD telemetry circuit88from external telemetry unit58. In some examples, processor52may control display unit54to generate a display of sensed cardiac electrical signals452and454and the constructed cardiac electrical signal456, e.g., as part of a GUI that may include additional data relating to determined sensed cardiac events and associated event intervals and/or rates.

The cardiac electrical signals452,454and456may be displayed as the wideband filtered cardiac electrical signals before narrowband filtering and rectification is performed for obtaining a filtered, rectified signal that the cardiac event sensing threshold is applied to according to selected sensing threshold control parameter settings. As shown and described below in conjunction withFIG.11, processor52may determine a filtered and rectified signal from each of the raw cardiac electrical signals452,454and456according to the filtering performed by ICD sensing circuit86prior to cardiac event detector66so that the sensing threshold control parameter settings applied by processor52for determining sensed cardiac events simulate the performance of cardiac event detector66for a given set of sensing control parameters (sensing electrode vector and sensing threshold control parameter settings).

Returning toFIG.9, processor52determines sensed cardiac events from at least one constructed cardiac electrical signal at block410. In examples presented herein, processor52determines sensed cardiac events from multiple cardiac electrical signals, sensed and constructed, for multiple settings of at least one sensing threshold control parameter. Processor52may determine sensed cardiac events by identifying sensing threshold crossing times by the cardiac electrical signal under analysis when the sensing threshold is being adjusted according to a specified set of sensing threshold control parameter settings. In some examples, sensed cardiac events and associated event intervals are known for one of the sensed cardiac electrical signals transmitted to external device40, at least for the programmed sensing threshold control parameters that resulted in tachyarrhythmia detection. Processor52may determine the sensed cardiac events from the constructed cardiac electrical signal at block410using the same sensing threshold control parameters used by sensing circuit86and control circuit80that resulted in the tachyarrhythmia detection by control circuit80.

Additionally, processor52may determine sensed cardiac events from the constructed cardiac electrical signal for multiple settings of one or more sensing threshold control parameters. For the sake of illustration, processor52may determine sensed cardiac events from the constructed cardiac electrical signal according to multiple sensitivity settings. Additionally, processor52may determine sensed cardiac events from one or both sensed cardiac electrical signals according to multiple sensitivity settings or other sensing threshold control parameter settings, which may be different than the programmed sensing threshold control parameter settings used to sense cardiac events by sensing circuit86that led to actual detection of the tachyarrhythmia by control circuit80.

As indicated above, the sensed cardiac events determined as sensing threshold crossing times are determined by applying the same filtering, rectification and any other processing of the constructed cardiac electrical signal as performed by sensing circuit86on a sensed cardiac electrical signal prior to passing the signal to event detector66(FIG.5). Processor52applies selected sensing threshold control parameters in the same manner as event detector66to determine sensed cardiac events, e.g., ventricular sensed events or atrial sensed events, from the cardiac electrical signal under analysis. Using the example shown inFIG.6, processor52may determine a starting threshold amplitude212based on a maximum peak amplitude203determined during a blanking period240, hold the starting threshold212for a sense delay interval242, decrement to an intermediate threshold amplitude216held for a drop time interval244, then decrement to the sensitivity220to determine sensed cardiac events (based on sensing threshold crossings) from the episode of the cardiac electrical signal under analysis. This process may be repeated multiple times using a different sensitivity setting each time to determine sensed cardiac events for multiple different sensitivity settings for a given cardiac electrical signal. The process of determining sensed cardiac events for multiple sensitivity settings may be repeated for each cardiac electrical signal, sensed or constructed.

Using the determined sensed cardiac events for each cardiac electrical signal being analyzed according to each setting of one or more sensing threshold control parameters, processor52determines associated cardiac event intervals at block412, e.g., RRIs or PPIs, that occur between each consecutive pair of determined sensed cardiac events. Using the determined cardiac event intervals at block414, processor52may determine whether the tachyarrhythmia detection is predicted to be made from the corresponding sensing electrode vector signal and sensing threshold control parameter settings. In some examples, at block414, processor52may determine a predicted time to detect the tachyarrhythmia for each combination of sensing control parameter settings analyzed, e.g., for each combination of sensing electrode vector and cardiac event sensing threshold control parameter settings. In other examples, processor52may determine whether the tachyarrhythmia is predicted to be detected within a threshold interval of time, e.g., within 30 seconds, or within the time interval represented by a cardiac electrical signal episode stored in memory82in response to the actual tachyarrhythmia detected at block404.

Processor52may determine whether tachyarrhythmia detection is expected at block414and determine the predicted time to detect the tachyarrhythmia. Processor52uses the tachyarrhythmia detection criteria used by ICD14relating to detecting tachyarrhythmia intervals from the determined sensed event intervals and for determining when the required NID to detect the tachyarrhythmia is reached. The time to detect the tachyarrhythmia may be determined as the time from an earliest tachyarrhythmia interval identified from among the determined sensed cardiac event intervals until a required NID is reached that includes the earliest tachyarrhythmia interval. The earliest tachyarrhythmia interval may be the first tachyarrhythmia interval identified from the cardiac electrical signal under analysis for a given set of sensing threshold control parameter settings. In other examples, the time to detect may be determined from a standardized starting time to the time the NID is reached for a given set of sensing control parameters. The standardized starting time may be the time of the first tachyarrhythmia interval of the actual sensed cardiac electrical signal that led to tachyarrhythmia detection. In other examples, the standardized starting may be the earliest or latest tachyarrhythmia interval identified from among all determined sensed cardiac event intervals for a given sensing electrode vector or all sensing electrode vectors.

In some examples, processor52may require a minimum number of sensed cardiac events in the cardiac signal episodes for use in determining the event intervals at block412and determining a time to detect tachyarrhythmia at block414. Because tachyarrhythmia detection criteria may require a threshold number of tachyarrhythmia intervals out of the most recent predetermined number of cardiac event intervals, the number of sensed cardiac events in the received sensed cardiac signals may be required to be at least the threshold number of tachyarrhythmia intervals required to detect the tachyarrhythmia. To illustrate, if the NID is set to 30 tachyarrhythmia intervals out of the most recent 40 cardiac event intervals, processor52may require that at least one of the sensed cardiac electrical signal episodes include at least 30 sensed cardiac events to continue analysis of the sensed and constructed signals associated with the acquired episode. When a threshold number of sensed cardiac events are included in the sensed cardiac electrical signal(s), each of the sensed and constructed signals may undergo further analysis. In some cases, a given episode of a sensed or constructed signal may be repeated in a looping manner during the analysis at block414to provide a signal episode of sufficient length to predict a time to detect tachyarrhythmia. The predicted tachyarrhythmia detection time for some sensing control parameters may be longer than the original cardiac signal episode. As such, the cardiac signal episodes may be looped to generate an episode that is up to one minute long, for example, for each sensed and constructed cardiac signal undergoing analysis to promote an adequate episode duration for predicting a tachyarrhythmia detection time according to various sensing control parameter settings.

At block416, processor52may generate an output of expected tachyarrhythmia detections, the determined times to detect the tachyarrhythmia and/or related cardiac event interval or rate data for each combination of sensing control parameter settings analyzed. Processor52may generate data in a tabular or graphical format for display on display unit54, which may be part of a GUI. In some examples, processor52may generate an output of a recommended sensing control parameter setting, e.g., a recommended sensing electrode vector, a recommended cardiac event sensing threshold control parameter such as the sensitivity or other sensing threshold control parameter(s) described above in conjunction withFIG.6. As described below in conjunction withFIG.13, a recommended sensing threshold control parameter setting for a given sensing electrode vector may be based on the expected tachyarrhythmia detections and/or determined times to detect tachyarrhythmia for that sensing electrode vector and a desired safety margin for sensing cardiac events. In some examples, the output generated by processor52at block416includes a programming command transmitted to ICD14to program a recommended sensing control parameter or combination of parameters, such as a sensing electrode vector and corresponding sensitivity or other cardiac event sensing threshold control parameter(s).

FIG.11is a diagram of a GUI500that may be generated as output at block416ofFIG.9by external device processor52for display on display unit54according to one example. In some examples, display54of external device40is a touch-sensitive screen that is configured to both display GUI500to a user as well as provide touch-sensitive regions of GUI500that allow the user to provide input to GUI500. In other examples, a user may navigate to different user input portions of GUI500, e.g., selectable windows, pop-up-windows, menus, icons, buttons or the like, using a mouse, keyboard or other user interface input device.

GUI500may include a display of a cardiac electrical signal502, a timing diagram510, and a data table520. In a cardiac electrical signal window505of GUI500, a cardiac electrical signal502is displayed, which may be a sensed or constructed cardiac electrical signal. In this example, cardiac electrical signal502is a sensed signal from a sensing electrode vector between pace/sense electrodes28and30(referred to as ring1and ring2, respectively, or R1and R2in GUI500) of lead16. The cardiac electrical signal displayed in window505may be selectable by a user interacting with GUI500. For example, a drop down or scrollable menu506of available cardiac electrical signals may be included in GUI500to enable a user to select different cardiac electrical signals, sensed or constructed, for display in window505. In addition to a sensed or constructed cardiac electrical signal, GUI500may include a display of an electrocardiogram signal from the patient, which may be received via external ports55(shown inFIG.1A) and stored in memory53, to provide the user with a visual comparison between the electrocardiogram and the sensed or constructed cardiac electrical signal.

Cardiac electrical signal502is the wideband filtered, unrectified signal received from ICD14. In some instances, cardiac electrical signal502is transmitted from ICD14after being stored in memory82by control circuit80in response to a tachyarrhythmia detection, e.g., a VF detection. In other instances, cardiac electrical signal502may be a sensed cardiac electrical signal that is transmitted in real time from ICD14to external device40during a tachyarrhythmia induction procedure. In still other examples, a constructed cardiac electrical signal determined by processor52during post-processing and analysis may be selected from a list in user input menu506for display in window505. In other examples, instead of displaying each sensed or constructed cardiac electrical signal one at a time in window505, multiple (or all sensed and constructed) cardiac electrical signals may be displayed simultaneously in window505. Using menu506, a user may be able to select two or more cardiac electrical signals at a time for display in window505for comparison and review.

Processor52may determine the narrowband filtered and rectified cardiac electrical signal504from wideband filtered cardiac electrical signal502. The narrowband filtered and rectified signal504may be included in the display window505. Filtered and rectified cardiac electrical signal504represents the narrowband filtered and rectified signal that would be passed to cardiac event detector66of sensing circuit86during real time cardiac event sensing by ICD14. Processor52applies the cardiac event sensing threshold, adjusted according to sensing threshold control parameter settings, to the filtered and rectified cardiac electrical signal504for determining sensed cardiac events. When more than one sensed and/or constructed cardiac electrical signal is selected from menu506for display in window505, the corresponding, time-aligned filtered and rectified cardiac electrical signal may be displayed along with the sensed or constructed cardiac electrical signal. In other examples, window505may include a display of only the narrowband filtered and rectified cardiac electrical signal(s)504without displaying the corresponding wideband filtered signal(s)502or vice versa.

Timing diagram510includes sensed cardiac event markers512corresponding to sensed cardiac events determined from the filtered and rectified cardiac electrical signal504by processor52. In timing diagram510, each marker512is generated by processor52to indicate the time of a cardiac event sensing threshold crossing by filtered, rectified signal504determined by processor52as the time that a cardiac event would be expected to be sensed by sensing circuit86from the corresponding filtered and rectified cardiac electrical signal504. Timing diagram510may include multiple rows515of sensed cardiac event markers512, with each individual row displaying event makers512generated by processor52according to a different cardiac event sensing threshold control parameter setting. GUI500may include a drop down or scrollable menu508as a user input portion of GUI500for selecting a cardiac event sensing threshold control parameter. Using menu508, a user may select a control parameter from among the programmable cardiac event sensing threshold control parameters. Sensitivity is shown as the selected sensing control parameter in the menu508such that each individual row of rows515corresponds to a different sensitivity setting as displayed in a parameter setting window516adjacent to the respective row of sensed cardiac event markers512. In the example shown, the sensed cardiac event markers512are shown for each available sensitivity setting between 0.075 mV and 1.2 mV as listed in sensing parameter setting window516.

In some examples, a user may select different sensing threshold control parameters from menu508to cause processor52to generate and display cardiac sensed event markers512for each available setting of the selected sensing threshold control parameter. For instance, a user may select the percentage used to set the starting threshold amplitude, the percentage used to set the intermediate threshold amplitude, the sense delay interval, the drop time interval or the sensitivity to cause processor52to generate a timing diagram510of rows515of cardiac sensed event markers512corresponding to each available (or user selected) setting of the selected parameter (and the cardiac electrical signal displayed in window505).

In some cases, two or more different cardiac event sensing threshold parameters may be selected to generate a timing diagram510that includes a row of cardiac sensed event markers512for each combination of settings or a selected subset thereof with the corresponding parameter settings displayed in window516. In still other examples, window516may be a user input portion of GUI500to enable the user to select which settings of a selected sensing threshold control parameter are included in the data displayed in timing diagram510(and optionally in other portions of GUI500, such as table520described below). A user may select the sensing threshold control parameter(s) from menu508and select individual settings for each selected parameter from window516, e.g., using a mouse, pointer, touch screen or the like. In response to the user input, processor52may determine any data necessary from the selected cardiac electrical signal(s) and generate a timing diagram510of cardiac sensed event markers512, which may be arranged in rows with each row corresponding to a combination of selected sensing threshold control parameter settings. While not shown inFIG.11, it is contemplated that GUI500may include a display of determined cardiac event intervals (e.g., in milliseconds) in timing diagram510and/or a determined cardiac event rate (e.g., in beats per minute).

Timing diagram510may further include a tachyarrhythmia detection marker514in each row of rows515corresponding to a predicted time that tachyarrhythmia is expected to be detected according to the corresponding set of sensing control parameters. The tachyarrhythmia detection marker514may be aligned in time (along timeline517relative to the determined sensed event markers512) to indicate the time that an NID is reached for a given sensitivity setting (or other selected parameter setting) based on the determined sensed cardiac event markers512. Processor52may determine the time to detect tachyarrhythmia, the time to detect VF in this example, by determining and summing the time intervals between consecutive sensed cardiac event markers512that include the first and last VF intervals counted toward reaching the NID. Processor52may generate a tachyarrhythmia detection marker514as part of the GUI500displayed by display unit54to indicate the time that VF is detected from the filtered rectified signal504for each sensitivity setting516.

In addition to or alternatively to tachyarrhythmia detection markers514, GUI500may include a window518indicating tachyarrhythmia is expected to be detected or not detected. Window518may additionally or alternatively indicate when cardiac events are expected to be sensed or not sensed at all for a given set of sensing control parameters. In the example shown, when the sensitivity is 0.45 mV or higher for sensing cardiac events from the selected cardiac electrical signal502, VF is not predicted to be detected. An indication of “No detection” is shown in window518for each sensitivity setting 0.45 mV, 0.60 mV, and 0.9 mV. When the sensitivity is set at the highest setting of 1.2 mV, cardiac events are not sensed, as indicated by no sensed cardiac event markers512in the row corresponding to 1.2 mV sensitivity. Instead of or in addition to indicating “No detection” in window518, an indication of “No sensing” may be shown in window518adjacent to sensitivity setting 1.2 mV.

In other illustrative examples of GUI500, instead of showing all rows515of sensed cardiac event markers determined for each available or selected sensing threshold control parameter in timing diagram510, a user may select the sensing threshold control parameter from menu508and a single setting for the selected sensing threshold control parameter from window516(or an analogous menu of available settings). Processor52may generate the GUI500including a single row of sensed cardiac event markers corresponding to determined sensed cardiac events from the selected cardiac electrical signal. Window516may be configured to enable a user to scroll or toggle through different settings of the sensing threshold control parameter to visualize changes in the locations of the sensed cardiac event markers512and tachyarrhythmia detection markers514along the horizontal timeline517of timing diagram510.

While not explicitly shown in GUI500, other user input portions of GUI500may include zoom in and zoom out buttons for viewing cardiac electrical signal window505and/or timing diagram510at different horizontal time resolutions and, in the case of cardiac electrical signal window505, vertical voltage scale resolution. Other user input portions of GUI500may include a pause, fast forward, reverse, store, download, save, print or other operational buttons that enable a user to view, print and/or save data displayed in GUI500as desired.

Processor52may generate data included in data table520for display on display unit54in GUI500to summarize the sensed event data determined from each sensed and constructed cardiac electrical signal for each sensing threshold control parameter tested. In the example shown, table520includes the sensing electrode vector in the first column522that corresponds to each sensed and constructed cardiac electrical signal analyzed. The sensing electrode vectors listed in column522may correspond to the sensed and constructed cardiac electrical signals selectable from menu506. In some examples, the cells in column522, each listing a sensing electrode vector, may be selectable by a user interacting with GUI500for simultaneously selecting which cardiac electrical signal is displayed in window505and which corresponding data is shown in timing diagram510. The sensing threshold control parameter540analyzed for determining the data displayed in timing diagram510may be listed in the first cell540of table520. The analyzed sensing control parameter settings may be listed in the first row524of table520. The selected sensing threshold control parameter is shown as being sensitivity in cell540, and the sensitivity settings analyzed are listed in the first row524.

The data cells in the body of table520indicate the time (in seconds) to detect VF determined by processor52based on the determined sensed cardiac events for the corresponding sensing electrode vector listed in column522and sensitivity setting listed in row524. For example, the row526labeled Ring1-Ring2in this example corresponds to the cardiac electrical signal502, sensed between pace/sense electrodes28and30. The time to detect VF in seconds listed in each data cell for each sensitivity setting corresponds to the time of the tachyarrhythmia detection marker514for each sensitivity setting516shown in the timing diagram510. No detection (ND) is indicated in the data cells for the sensitivity settings 0.45, 0.6 and 0.9 mV in row526at which VF is not detected. No sensing (NS) is indicated for the sensitivity setting 1.2 mV at which no cardiac events are predicted to be sensed as indicated by no sensed event markers for sensitivity setting 1.2 mV in timing diagram510.

Table520may include the time to detect for each of the sensing electrode vectors listed in the first column522and analyzed by processor52. In this example, a second sensing electrode vector between pace/sense electrode30and housing15, referred to a “Ring1-Can” in row528of table520, and a third sensing electrode vector between the pace/sense electrode28and housing15, referred to as “Ring2-Can” in row530of table520, are shown with corresponding predicted VF detection times for sensitivity settings 0.075 to 0.3 mV. No VF detection (ND) is predicted from the sensed and constructed cardiac electrical signals corresponding to these sensing electrode vectors for sensitivity settings of 0.45 mV and higher. The higher sensitivity settings result in predicted undersensing of the fibrillation waves and a predicted failure to detect VF.

The sensitivity setting and sensing electrode vector that are currently programmed in ICD14may be indicated in table520, as shown by the bolded font for time to detect corresponding to the Ring1-Ring2sensing electrode vector and 0.9 mV sensitivity. At this sensitivity, the VF episode is not detected from the first sensed cardiac electrical signal in this example. The data cells containing a time to detect VF, corresponding to a sensing electrode vector and sensitivity setting (e.g., all sensitivity settings less than 0.3 mV for all sensing electrode vectors in this example), may be indicated as acceptable sensing control parameter settings in table520. Indication of acceptable sensing control parameter settings may be made in GUI500by generating the display of times to detect VF in the corresponding data cells in a stylized font, e.g., green or other colored font, bolded, underlined or other distinguishing characteristic. Additionally or alternatively, times to detect that correspond to unacceptable control parameter settings (all ND and NS cells for sensitivities greater than 0.3 mV in this example) may be indicated as unacceptable, e.g., by red font, strike through or other distinguishing display characteristic. Unacceptable sensitivity settings may alternatively or additionally be indicated in row524by shading or other formatting of the columns that include all “ND” and/or “NS” indicators.

In other examples, instead of displaying the time to detect the tachyarrhythmia in the data cells of table520, the data cells may contain an indication of detection or no detection and/or sensing or no sensing. For example, the data cells containing a time to detect tachyarrhythmia in GUI500may alternatively contain a “VT” or “VF” to indicate detection of VT or VF is expected for the combination of sensing control parameters and “ND” to indicate no detection is expected. The indication of detection or no detection may distinguish combinations of sensing control parameter settings that are acceptable from sensing control parameter settings that are deemed unacceptable due to an expected failure to detect the tachyarrhythmia episode. In some cases, a tachyarrhythmia may be detected from a sensing electrode vector signal according to a sensing threshold control parameter but at a predicted detection time that is longer than an acceptable threshold detection time. Processor52may generate an indication of no detection for display in GUI500for a specified combination of sensing control parameters that results in a predicted detection after a specified time limit, e.g., after more than 30 seconds. Processor52may generate an indication of detection for display in GUI500for a specified combination of sensing control parameters that results in detection predicted within the specified time limit, e.g., within 30 seconds or less.

The GUI500shown inFIG.11illustrates data that may be included in a GUI generated for display by display unit54. In other examples, GUI500may include less data or more data than shown inFIG.11. For example, display of the cardiac electrical signal502and/or the narrowband filtered and rectified signal504may be optional. In some examples, timing diagram510is omitted with summary data presented in table520with an indication of acceptable sensing control parameter settings. In some examples, only table520may be shown in GUI500or only timing diagram510, with or without an indication of acceptable or recommended sensing control parameter settings.

A user interacting with GUI500may select one or more sensing control parameter settings for programming in ICD14. For example, data cells included in table520may be user selectable using a pointer, mouse, touch screen or the like. A user may select a combination of sensing electrode vector and sensitivity setting by selecting a data cell in table520and confirming the programming selection using a user input program button or icon. In an illustrative example, upon selection by a user, a data cell545or its contents may become enlarged or bolded. A program confirmation user input window546may be displayed in response to the user selection of a data cell545, e.g., in a programming pop-up window. The program confirmation user input window546may indicate the selected programmable parameters corresponding to the selected data cell, e.g., sensing electrode vector and sensitivity setting, and include “confirm” and “cancel” user input buttons for confirming or cancelling the programming of the selected settings in ICD14. In other examples, a cell in column522corresponding to a specified sensing electrode vector and a cell in row524corresponding to a sensitivity setting may be selectable by a user for generating a sensing control parameter programming command by external device40for transmission to ICD14. In response to a user input confirmation of a sensing control parameter setting(s), processor52may generate the programming command for transmission to ICD14via telemetry unit58.

In some examples, GUI500may include user selection buttons542and544that allow a user to select or toggle between a table view or a graph view of the data generated by processor52. In the example shown, the table view is selected as indicated by enlarged font of button542and the display of table520in GUI500. By clicking on the graph button544, a user may switch the display from the table520to a graph of the data shown in table520. A user may toggle back and forth between a tabular listing of the data as shown inFIG.11and a graphical view of the data, e.g., as shown inFIG.12and described below. Alternatively, a table of the generated data may appear in a pop-up window when table button542is clicked on or otherwise selected by a user, and a graph of the generated data may appear in a pop-up window when the graph button544is clicked or selected by a user.

GUI500may include other patient-related data such as a patient name, birthdate or other identification. GUI500may further include other informational data such as a display of the date and time that a cardiac electrical signal episode was recorded by ICD14(when transmitted at a later time), therapy delivered, therapy outcome, or the like. GUI500may include more or fewer user input portions and/or more or fewer data windows, tables, etc. than shown inFIG.11.

The techniques set forth herein provide specific improvements to the computer-related field of programming medical devices that have practical applications. For example, the use of the techniques herein may enable external device40to generate visualizations of cardiac electrical signal data, determined cardiac event data, determined cardiac event interval data, determined cardiac event rate data, and/or determined cardiac arrhythmia data corresponding to multiple sensing control parameter settings that define the cardiac event sensing performed by ICD14. Such visualizations may enable an external device, such as external device40, to inform a user as to how the ICD14is expected to perform in sensing cardiac events according to a variety of sensing control parameters without requiring ICD14to be reprogrammed to perform actual cardiac event sensing and arrhythmia detection according to the variety of sensing control parameters, which may include both different sensing electrode vectors and different sensing threshold control parameters.

By providing the GUI500or other user interface for displaying the data relating to determined cardiac events, the likelihood of human error in identifying cardiac events that are expected to be sensed by ICD14and in determining and programming sensing control parameters is reduced. Furthermore, the techniques disclosed herein may reduce the complexity of programming a medical device to sense cardiac events to the degree of accuracy required for such cardiac event data to be used for controlling the delivery and timing of cardiac electrical stimulation therapies, e.g., pacing and/or CV/DF therapies. As such, the techniques disclosed herein may enable a medical device, such as ICD14, to be programmed to sense cardiac events in a manner that is simplified, flexible, and patient-specific such that the ICD may reliably sense cardiac events to control delivery and timing of therapies.

FIG.12is a graph550of time to detect data that may be determined by processor52and may be generated as output for display on display unit54according to one example. Graph550may be included in GUI500ofFIG.11in some examples. As indicated above, a graphical display of data based on determined cardiac events for each sensing electrode vector signal may be generated instead of or in addition to a tabular display.

The data represented by graph550represents another example of time to detect data determined by processor52, different than the data shown in GUI500. However, a similar graph could be generated and displayed in GUI500, e.g., by clicking on the graph button544of GUI500. In this example, the predicted time to VF detection (y-axis552) is determined for each available sensitivity setting (x-axis554) between 0.075 mV and 1.2 mV for each of two sensed cardiac electrical signals, shown by graphed lines560and562, and for one constructed cardiac electrical signal (shown by graphed line564). In this example, the time to detect VF from the first sensed cardiac electrical signal (S1), sensed between the pace/sense electrodes28and30(ring1-ring2) of lead16is plotted as the dotted line562. The time to detect VF from the second sensed cardiac electrical signal (S2), sensed between pace/sense electrode30and housing15, is plotted as the solid line560. The time to detect VF from the third cardiac electrical signal (C3), which is a constructed cardiac electrical signal expected to be sensed between the pace/sense electrode28and housing15, is plotted as the dashed line564.

In this example, the predicted time to detect is approximately 6.5 seconds when the sensitivity is set to 0.075 mV for both the constructed C3signal (graphed line564) and the sensed S1signal (graphed line562). At the highest sensitivity setting of 1.2 mV, the predicted time to detect VF increases to approximately 7.8 seconds for the S1signal (graphed line562) and increases to approximately 6.9 seconds for the constructed C3signal (graphed line564). The predicted time to detect VF is approximately 8.8 seconds for the sensed S2signal (graphed line560) when the sensitivity is 0.75 mV and increases to approximately 10.8 seconds at the highest sensitivity of 1.2 mV.

Graph550may be generated by processor52as output for display in GUI500ofFIG.11, which may include simultaneous or selectable displays of the corresponding cardiac electrical signals, e.g., as shown inFIG.11. The GUI may additionally or alternatively include a timing diagram of determined sensed cardiac event markers, tachyarrhythmia detection markers, and/or tabular listings of corresponding data as shown inFIG.11. As indicated above, the graph550may be displayed as a pop-up window in GUI500in some examples.

The data represented in graph550may be used by processor52to determine recommended or acceptable sensing control parameter settings. For example, a sensing electrode vector that is associated with the shortest time to detect tachyarrhythmia may be selected as a recommended electrode vector. In another example, a sensing electrode vector corresponding to tachyarrhythmia detection at all analyzed sensitivity settings may be identified as an acceptable sensing electrode vector. A recommended sensing electrode vector may be identified as a sensing electrode vector with all times to detect for all analyzed sensitivity settings being within a threshold difference of each other or less than a threshold detection time limit. Conversely, when a sensing electrode vector is associated with a longest time to detect, or even a predicted failure to detect the tachyarrhythmia, the sensing electrode vector may be rejected for use as a sensing electrode vector or indicated as a non-acceptable or non-recommended sensing electrode vector. Other sensing control parameters, e.g., sensing threshold control parameters used for setting and adjusting the cardiac event sensing threshold, may be determined as acceptable or recommended settings based on the data represented inFIGS.11and12.

In the example ofFIG.12, graph550is shown as a plot of time to VF detection (y-axis552) as a function of sensitivity (x-axis554). It is to be understood that the predicted time to detect an arrhythmia may be plotted as a function of a different sensing threshold control parameter when a different control parameter is selected to be analyzed. While only three cardiac electrical signals are represented in the graph550, any number of cardiac electrical signals, sensed and/or constructed, analyzed by processor52may be represented in graph550. A user interacting with the GUI may select which cardiac electrical signals are represented in the graph. In some examples, a user may select a sensing control parameter for programming in ICD14by clicking on a sensitivity setting and/or a sensing electrode vector that is displayed in the GUI that includes graph550.

While graph550is shown as a plot of times to detect VF, it is contemplated that other data determined by processor52may additionally or alternatively be represented in a graph that is generated as part of a GUI. For example, determined cardiac event rates or cardiac event intervals may be plotted as a function of a sensing control parameter. The rate or intervals may be determined as the mean, median, maximum, minimum or other metric of the RRIs or PPIs that are determined from each analyzed cardiac electrical signal for each respective sensing threshold control parameter setting (or combinations of parameter settings).

FIG.13is a flow chart600of a method that may be performed by external device processor52(or control circuit80) for determining a recommended sensing control parameter setting according to one example. At block602ofFIG.13, processor52may determine the expected times to detect a tachyarrhythmia from a cardiac electrical signal, sensed or constructed, corresponding to each sensing electrode vector under analysis and each sensing threshold control parameter setting (or combinations of sensing threshold control parameter settings). Using the illustrative examples of the two different data sets represented inFIGS.11and12, processor52may determine the time to detect VF for each available sensitivity setting from each of at least two sensed cardiac electrical signals, sensed using different sensing electrode vectors, and at least one constructed cardiac electrical signal, constructed from the two sensed cardiac electrical signals.

The times to detect may be determined by determining sensed cardiac events for each combination of sensing electrode vector and sensing threshold control parameter(s), determining the associated expected sensed cardiac event intervals, identifying tachyarrhythmia intervals among the sensed cardiac event intervals, counting the tachyarrhythmia intervals to determine when the NID is reached for detecting the tachyarrhythmia, and summing all determined cardiac event intervals between the first tachyarrhythmia interval and the last tachyarrhythmia interval that contributed to the NID being reached. It is to be understood that, when a given set of sensing control parameters are programmed into ICD14, the actual tachyarrhythmia detection by ICD14may be at the predicted time of the NID being reached or later due to processing delays. For instance, when additional detection criteria such as morphology-based detection criteria, noise rejection criteria or other criteria that require additional cardiac electrical signal analysis and processing are required by control circuit80in order to determine that all detection criteria are met before detecting the tachyarrhythmia, an actual tachyarrhythmia detection time may be later than a predicted time to NID being reached.

At block604, processor52may determine a time to detect limit for each sensing electrode vector. In one example, the time to detect limit may be determined as the longest time to detect that is within a predetermined time interval of the shortest time to detect for a given sensing electrode vector. The predetermined time interval may be between 1 and 7 seconds, as examples, and is 2.5 seconds in one example. Using the data ofFIG.12as an example, the shortest time to detect for the constructed cardiac electrical signal (C3) shown by graphed line564is approximately 6.5 seconds at sensitivity settings from 0.075 mV and less than 0.3 mV. The longest time to detect is approximately 6.9 seconds at sensitivity settings from 0.3 to 1.2 mV. Processor52may determine the time to detect limit as 2.5 seconds greater than the shortest time to detect, in this case 6.5 seconds plus 2.5 seconds or 9 seconds. All times to detect for the C3sensing electrode vector fall within this time to detect limit. The time to detect limit may be determined as the detection time at the most sensitive sensitivity setting, e.g., 0.075 mV plus a predetermined time interval, e.g., 2 to 5 seconds or about 2.5 seconds as examples.

At block606ofFIG.13, processor52may identify the cardiac event sensing threshold control parameters that correspond to the time to detect limit. In the example ofFIG.12, processor52may identify the greatest sensitivity setting that resulted in the time to detect being at or less than the time to detect limit. This greatest (highest value) sensitivity setting corresponds to the lowest sensitivity of sensing circuit86in sensing cardiac events (highest sensing floor) that still results in the tachyarrhythmia detection within the time to detect limit. Continuing with the example given above, the greatest sensitivity setting for the C3sensing electrode vector that results in a time to detect that is within 2.5 seconds of the shortest time to detect is 1.2 mV because the 6.9 seconds time to detect is less than the 9 second time to detect limit.

At block608, processor52determines the cardiac event sensing threshold control parameter setting that provides a safety margin for detecting the tachyarrhythmia relative to the threshold control parameter setting identified at the time to detect limit. Using the same example of the C3graphed line564inFIG.12, the greatest sensitivity setting within the time to detect limit is 1.2 mV. A lower sensitivity setting may be determined at block608that provides a desired safety margin for sensing cardiac events, which may be a factor of the greatest sensitivity setting. For example, if a 2× safety margin for sensing cardiac events is desired, the sensitivity setting that is half of the greatest sensitivity setting associated with a time to detect within the time to detect limit may be determined at block608. In this example, a sensitivity setting of 0.6 mV (half of 1.2 mV) is the recommended sensitivity setting for the sensing electrode vector associated with the constructed C3signal represented by graphed line564to provide a 2× safety margin. When a 3× safety margin is desired, processor52may determine 0.45 mV as the recommended sensitivity setting. When a 4× safety margin is desired, processor52may determine 0.3 mV as the recommended sensitivity setting for the C3sensing electrode vector.

With continued reference toFIG.12, the time to detect limit corresponding to the S1sensing electrode vector (graphed line562) is approximately 9 seconds (using the predetermined time interval of 2.5 seconds plus the shortest time to detect of 6.5 seconds at a sensitivity of 0.75 mV). The longest time to detect for the S1sensing electrode vector is 7.8 seconds, which is within the time to detect limit. The greatest sensitivity setting resulting in a time to detect within the time to detect limit is 1.2 mV. Processor52may determine the recommended cardiac event sensing threshold parameter at block608ofFIG.13for the associated S1sensing electrode vector as the sensitivity setting of 0.6 mV for a 2× safety margin for sensing cardiac events.

The time to detect limit for the S2sensing electrode vector associated with graphed line510inFIG.12is approximately 11.1 seconds, based on an acceptable increase of 2.5 seconds from the shortest time to detect of approximately 8.6 seconds at 0.075 mV. The longest time to detect within this time to detect limit is identified by processor52as approximately 10.8 seconds at the 1.2 mV sensitivity setting, which is within the time to detect limit. Processor52may determine the recommended sensitivity setting as being 0.6 mV for a 2× safety margin for sensing cardiac events.

In these examples, processor52determines the time to detect limit as the time to detect at the lowest sensitivity setting, e.g., 0.075 mV in the example ofFIG.12, plus an acceptable increase in time to tachyarrhythmia detection, e.g., 2.5 seconds greater than the time to detect at the lowest sensitivity setting. Note that the lowest value of the sensitivity setting results in the highest sensitivity for sensing cardiac events because the cardiac event sensing threshold is decreased to the lowest possible amplitude (sensing floor), e.g., after the drop time interval as shown inFIG.6. In other examples, the time to detect limit may be based on the shortest time to detect determined for all sensing electrode vectors plus an acceptable increase in time to detection. For example, the time to detect limit for all sensing control parameters being analyzed may be set to a predetermined interval (e.g., 2 to 7 seconds) greater than the shortest time to detect, approximately 6.5 ms for the constructed C3signal (graphed line564) at a sensitivity of 0.075 mV. In some examples, if the maximum time to detect for a given sensing electrode vector is greater than the time to detect limit, processor52may reject that sensing electrode vector in determining recommended or acceptable settings for sensing control parameters at block610. Processor52may determine the time to detect limit as a percentage increase of the shortest time to detect for a given sensing electrode vector or out of all sensing electrode vectors in other examples. In still other examples, the time to detect limit may be a predetermined time interval, e.g., 12 seconds or less, 15 seconds or less, 24 seconds or less, or 30 seconds or less. The greatest sensitivity setting that results in a time to detect that is within the time to detect limit for a given sensing electrode vector may be used by processor52for determining a recommended sensitivity setting according to a desired safety margin at block608.

In another example with reference to the example data represented in table520ofFIG.11, processor52may determine the shortest time to VF detection as 7.56 seconds for 0.075 mV sensitivity from the cardiac electrical signal sensed using the ring1-ring2sensing electrode vector (row526). The highest acceptable increase in the time to detect may be determined as 7.56 seconds plus an acceptable increase of 2.5 seconds for a time to detect limit of approximately 10 seconds. The greatest sensitivity setting that results in a VF detection time within the time to detect limit is 0.2 mV, with a time to detect of 8.32 seconds (11.34 seconds for sensitivity setting 0.3 mV exceeds the time to detect limit). Processor52may determine the 0.1 mV sensitivity setting as the recommended setting to provide a 2× safety margin (half of 0.2 mV) for sensing cardiac events using the Ring1-Ring2sensing electrode vector.

For the second sensing electrode vector (Ring1-Can, row528), the time to detect limit is 11.37 seconds (2.5 seconds plus the 8.87 seconds time to detect at sensitivity setting 0.075 mV). The greatest sensitivity setting falling within the time to detect limit is 0.3 mV, so the recommended setting for a 2× safety margin is 0.15 mV. For the third sensing electrode vector (Ring2-Can, row530), the time to detect limit is 10.20 seconds (2.5 seconds plus 7.70 seconds at the 0.075 sensitivity setting). The greatest sensitivity setting resulting in a time to detect within this time to detect limit is 0.2 mV, so that the recommended sensitivity setting for a 2× safety margin is 0.1 mV for the third sensing electrode vector530. It is to be understood that a different predetermined time interval greater than or less than 2.5 seconds may be used for determining the time to detect limit and other safety margins may be used to identify a recommended sensitivity setting for a given sensing electrode vector.

Returning toFIG.13, at block610, processor52may generate an output of the recommended sensing control parameter settings determined at block608. As described above, the output may be a programming command transmitted to ICD14, which may include a recommended sensing electrode vector and/or sensitivity setting (and/or one or more other sensing threshold control parameters). Additionally or alternatively, the output at block610may include generating a display of recommended or acceptable sensing control parameter settings in a GUI on display unit54. For example, GUI500ofFIG.11may indicate the recommended sensing threshold control parameter setting(s) for each sensing electrode vector that is analyzed by highlighting the recommended setting by distinct color, size, underlining or other stylized font or shading or color of a data cell in table520or a data point in graph550, as examples.

The process ofFIG.13may be repeated each time a tachyarrhythmia induction is performed and/or each time external device40interrogates ICD14and retrieves sensed cardiac electrical signal episodes corresponding to detected tachyarrhythmia episodes. Alternatively, the process ofFIG.13may be performed upon command by a user interacting with user interface56. For example, a user may select sensing electrode vectors and sensing threshold control parameters to be evaluated via GUI500and initiate a tachyarrhythmia induction. Processor52may receive the sensed cardiac electrical signals from ICD14during the tachyarrhythmia induction and process the sensed and constructed cardiac electrical signals for generating the determined cardiac events and data presented in GUI500.

As indicated above, control circuit80of ICD14may be configured to perform some or all of the techniques disclosed herein. In that case, the process ofFIG.13may be performed by control circuit80after detecting a tachyarrhythmia episode without waiting for communication with an external device. At block610, control circuit80may adjust a sensing control parameter to a recommended setting determined at block608. For example, if the sensitivity setting corresponding to a desired safety margin (which may be programmable) changes according to the determined times to detect for the currently selected sensing electrode vector, control circuit80may adjust the sensitivity setting at block610to the recommended setting determined at block608. If a sensing electrode vector is determined to have a prolonged time to detect compared to other sensing electrode vectors (or is predicted to fail to detect the tachyarrhythmia at one or more sensing threshold control parameter settings) according to the post processing analysis, control circuit80may select a different sensing electrode vector at block610.

FIG.14is a GUI650that may be generated as output by processor52for display on display unit54according to one example. GUI650may be generated by external device40for visualization of the performance of cardiac event sensing by ICD14. GUI650may include a cardiac electrical signal window651that may display the cardiac electrical signal corresponding to a sensing electrode vector, which may be selectable by a user via a drop down or scrollable menu653. GUI650may include a table655listing programmable sensing threshold control parameter settings, shown as sensitivity settings652in this example, and a corresponding time to detect tachyarrhythmia656as determined by processor52, e.g., using the techniques described in conjunction withFIG.9, for each of the sensitivity settings652. The data shown in table655corresponds to the sensing electrode vector signal, sensed or constructed, selected in cardiac electrical signal window651. It is to be understood that processor52may generate a table of data or tables of data that include the predicted time to detect the tachyarrhythmia, e.g., time to reach NID, for each sensitivity setting (or other sensing threshold control parameter setting or combinations of settings) for multiple sensing electrode vectors, sensed and constructed.

In this example, the time to detect limit is determined based on the time to detect at the lowest sensitivity setting of 0.075 mV (corresponding to highest sensitivity for sensing cardiac event signals). Processor52determines the time to detect limit by adding an acceptable increase to the time to detect at 0.075 mV sensitivity, e.g., by adding 2.5 seconds. The time to detect limit is 9.7 seconds in this example (7.2 seconds plus 2.5 seconds). Processor52may determine the greatest sensitivity setting at which the time to detect is equal to or less than the time to detect limit. In this example, the times to detect at sensitivity settings 0.9 mV and 1.2 mV (9.8 seconds and 11 seconds, respectively) are greater than the time to detect limit of 9.7 seconds. Table655may include a safety margin column654indicating the safety margin for each sensitivity setting as determined based on the greatest sensitivity setting that results in a time to detect that is less than or equal to the time to detect limit. When a sensitivity setting results in a time to detect that is greater than the limit, processor52may determine a Ox safety margin662for that sensitivity setting, as shown for sensitivity settings 0.9 and 1.2 mV. The GUI650generated by processor52may also denote these unacceptable sensitivity settings by demarcating these sensitivity settings 0.9 and 1.2 from other sensitivity settings by a dashed line (as shown), distinct color, size, or other stylized font, shading or other distinguishing display characteristics.

In the example shown, processor52identifies 0.6 mV as the greatest sensitivity setting that results in a time to detect of 7.6 seconds that is equal to or less than the time to detect limit of 9.7 seconds. Based on this sensitivity setting of 0.6 mV, the safety margin of each of the other sensitivity settings less than 0.6 mV may be determined by processor52and displayed in safety margin column654. The safety margins displayed in column654are determined by dividing the greatest sensitivity setting 0.6 mV corresponding to a time to detect658within the time to detect limit by the lower sensitivity setting. In this example, 0.6 mV has a 1× safety margin, 0.3 mV has a 2× safety margin, 0.2 mV has a 3× safety margin and so on.

Processor52may determine a recommended sensitivity setting660that is a minimum desired safety margin for sensing cardiac electrical signals, e.g., a 2× safety margin. The safety margin may be rounded up to a whole number as shown. When a minimum 2× safety margin is programmed or desired for sensing cardiac electrical signals, the recommended sensitivity setting660is 0.3 mV in the example shown, half of 0.6 mV. As mentioned above, a table similar to table650may be generated by processor52and displayed on display unit54for each sensing electrode vector under analysis or a combined table displaying the sensitivity settings and corresponding safety margins and times to detect determined for each sensing electrode vector may be generated and displayed. The recommended sensing threshold control parameter, in this case sensitivity, for each sensing electrode vector may be highlighted in the table, e.g., by stylized font, highlighted by colored (e.g., green) or shaded cells in table655, encircled by a border as shown in table650or the like.

In some examples, acceptable sensing threshold control parameter settings, e.g., all settings resulting in at least a 2× (or other specified) safety margin may be highlighted by color, bolding, or other stylized font, colored fill of cells in table655or other formatting options in addition to highlighting the recommended sensing threshold control parameter660. For example, the rows corresponding to less than 0.3 mV sensitivity having a predicted safety margin for sensing cardiac events of at least 2× may be highlighted as acceptable sensitivity settings, e.g., in green or yellow font or cell fill. The recommended setting of 0.3 mV at the 2× safety margin may be highlighted by green font or green cell fill and/or enlarged, bolded or encircled to be distinguished as the recommended setting.

Additionally or alternatively, settings that are not considered acceptable, e.g., any setting with a 1× safety margin or less, may be shaded or grayed out, shown in red or displayed with other formatting of the table cells and/or font of the cell contents to indicate settings that are not recommended or not acceptable. In another example, all rows of table655corresponding to a 2× safety margin or more (0.3 mV sensitivity or less) may be shown in green. The recommended setting660at the 2× safety margin may be enlarged, bolded, encircled or otherwise formatted to stand out among the acceptable settings. The sensitivity settings that result in a 1× safety margin may be indicated as unacceptable settings, e.g., by displaying rows corresponding to 0.45 mV and 0.6 mV sensitivity in yellow. The rows corresponding to a time to detect beyond the time limit (or any rows corresponding to a predicted failure to detect the tachyarrhythmia) may be displayed in red, grayed out, or otherwise formatted to indicate that these settings (0.9 and 1.2 mV sensitivity in this example) are not recommended.

In the various GUIs described and shown herein, sensing control parameter settings, cardiac electrical signals corresponding to a sensing electrode vector, timing markers, tables, graphs, or other representations of determined sensed cardiac events and/or predicted tachyarrhythmia detections included in the display of the GUI may be formatted according to various formatting schemes that distinguish between acceptable, recommended and/or not recommended or not acceptable sensing control parameter settings. Such formatting schemes may include colors (e.g., green, yellow and red), shading, bolding, size or other formatting options to provide a visual representation to a user that readily discerns a recommended setting and/or acceptable settings from other settings of sensing control parameters. When a setting is acceptable or recommended, the displayed setting may be selectable by a user, e.g., by clicking on row660, to initiate programming of the acceptable or recommended setting. When a setting is not acceptable or recommended, the display setting may not be selectable by a user. When the setting is clicked on or touched by a user in interacting with GUI650, a warning or error message may occur indicating that the selection is not acceptable or recommended.

While table655is shown displaying times to detect tachyarrhythmia in column656, other data that is based on the determined sensed cardiac events may be displayed in table655, in addition to or instead of times to detect. For example, a column of table655may indicate whether tachyarrhythmia detection is made or not, which may be required to be within some maximum time limit, e.g., using the annotations VF, VT, or ND as examples. When no cardiac events are sensed according to a sensing control parameter setting, the indication “NS” may be included in table655. In other examples, table655may include a column indicating a cardiac rate and/or cardiac event intervals determined by processor52from the selected cardiac electrical signal, which may be selected and displayed in window651.

FIG.15is a diagram of a GUI700that may be generated as output by processor52for display on display unit54according to another example. GUI700may include a user input portion702to enable a user to start a tachyarrhythmia induction, cancel the tachyarrhythmia induction, retrieve sensed cardiac electrical signals from ICD14, which may be stored by ICD14in response to detecting spontaneous tachyarrhythmia episodes, and select a therapy programming screen for programming tachyarrhythmia therapies.

GUI700may include informational data706displayed as chiclets, icons, windows, or the like for displaying the date and time, providing user selectable patient information, patient heart rate or other informational data. GUI700may include other user input chiclets or icons, such as the user inputs740that enable a user to print data, print a cardiac electrical signal test strip, undo an action, or enable external device40to transmit a programming command, as a few examples.

GUI700may further include a data table710, a cardiac electrical signal window720, and/or data graph window730. Table710may include data and information relating to the determined sensed cardiac events, event intervals, rates and/or predicted tachyarrhythmia detection determined by processor52upon processing selected cardiac electrical signals, constructed and/or sensed, according to selected sensing threshold control parameter settings. The cardiac electrical signal window720may display the cardiac signal episodes for each selected sensing electrode vector. User inputs included in the cardiac electrical signal window720may allow the user to move forward, backward, pause, freeze, increase or decrease the vertical scale or other adjustments to the display of the cardiac electrical signals.

One or more graphs may be displayed in data graph window730. The graphs in window730may represent data determined by processor52for more than one tachyarrhythmia episode, induced or spontaneous. In the example shown, graphs of the predicted time to detect (time to NID met) for two different VF episodes each include all predicted times to detect for all available sensitivity settings for each of three different sensing electrode vectors,

Features of the illustrative GUI700and other example GUIs illustrated or described herein may be combined in any combination or arrangement and are not limited to the combinations and arrangements shown here. Furthermore, a GUI presenting sensing control parameter settings and data may include multiple screens and windows that may be toggled between on display unit54.

FIG.16is another example of GUI750that may be displayed by external device40to present a visualization of sensed cardiac event related data determined by processor52. GUI750may include elements described above in conjunction with GUI700ofFIG.15. Reference numbers inFIG.16correspond to identically numbered elements shown inFIG.15. GUI750may include a table of sensing control parameter settings760with an indication of safety margin and recommended sensing control parameter setting, as generally described above in conjunction withFIG.14. In this example, a user input761may be included to allow a user to select which sensing electrode vector data is displayed in table760. The selected sensing threshold control parameter settings, e.g., sensitivity settings, may be listed with corresponding safety margins for sensing cardiac events as determined by processor52. The safety margins may be determined according to the methods described in conjunction withFIG.13. In the example ofFIG.16, table760includes an indication (yes or no) as to whether tachyarrhythmia is expected to be detected by ICD14using the selected sensing control parameters (instead of listing the time to detect as shown inFIG.14). In the example shown, tachyarrhythmia detection is expected for all sensitivity settings, but the time to detect at sensitivities 0.9 mV and 1.2 mV is longer than the time to detect limit resulting in a 0× safety margin being displayed.

A user may select different sensing electrode vectors (sensed or constructed) from a user input menu761for selecting which safety margin and tachyarrhythmia detection data is displayed. A user may accept the recommended sensitivity setting for the selected sensing electrode vector (as indicated by dashed box in table760) by clicking on the program button in user inputs740.

FIG.17is a flow chart800of a method for determining acceptable or recommended sensing control parameters according to another example. For convenience, the method of flow chart800is described in conjunction with external device processor52performing the processing and analysis though other processors included in a medical device system may perform all or portions of the method ofFIG.17. The process of flow chart800may be performed to generate data for display in a GUI to enable visualization of the performance of ICD in sensing cardiac events according to various sensing control parameters.

At block802, a user interacting with a GUI displayed on display unit54may enter selected test sensing control parameters and may specify which ones of available programmable settings are to be tested for each selected sensing control parameter. External device processor52receives the user input test parameter settings, e.g., via the GUI or another user input interface device. For example, as shown inFIGS.15and16, a user may select test settings in window704for one or more of the sensing electrode vector, post-sense blanking period, starting sensing threshold amplitude percentage of maximum peak, post-sense blanking period, sense delay interval, intermediate sensing threshold amplitude percentage of the maximum peak, drop time interval and/or sensitivity (all described above in conjunction withFIG.6).

Sensitivity has been primarily described in the illustrative examples presented herein as the sensing threshold control parameter that is evaluated at multiple programmable settings for each one of the selected sensing electrode vectors. Sensitivity is a key sensing control parameter that can directly and significantly impact ICD sensitivity to detecting VF and providing necessary CV/DF therapy. However, other sensing threshold control parameters can impact the accuracy of cardiac event sensing and the sensitivity of ICD14in detecting VF or other arrhythmias. For example, different settings of other sensing threshold control parameters described herein may result in different determined sensed cardiac events due to oversensing of P-waves, T-waves, non-cardiac noise (muscle noise, electromagnetic interference, or other noise artifacts), or double counting of the QRS complex or undersensing of R-waves.

While selection and programming of sensitivity (and associated sensing electrode vector) may be a high priority in promoting safe and effective detection and treatment of VT/VF, selecting and programming the settings of other sensing threshold control parameters may address and improve cardiac event sensing performance of ICD14to avoid oversensing and/or undersensing of cardiac events according to patient-specific needs. For example, ICD sensing circuit86may oversense P-waves in some patients, which could lead to false VT/VF detection. In order to avoid P-wave oversensing, the drop time interval and/or the intermediate amplitude of the R-wave sensing threshold may be analyzed at multiple settings. In other patients, ICD sensing circuit86may oversense T-waves, e.g., due to a patient-specific long QT interval, requiring analysis for selecting the sense delay interval and/or the intermediate amplitude settings for controlling the R-wave sensing threshold. Sensitivity and sensing electrode vector settings may both need to be analyzed for identifying acceptable settings when oversensing of non-cardiac noise is occurring or R-waves are relatively low amplitude on a selected sensing electrode vector.

At block804, processor52receives at least two sensed cardiac electrical signals from ICD14. Processor52may construct at least one alternative sensing electrode vector signal using the two sensed cardiac electrical signals at block806. As described above, multiple sensed cardiac electrical signals may be used to construct one or more additional cardiac electrical signals for evaluating performance of different sensing threshold control parameters in sensing cardiac events.

At block808, processor52may determine the sensed cardiac events from each cardiac electrical signal selected for analysis according to a first sensing threshold control parameter. One or more settings of the first sensing threshold control parameter may be applied to each signal to determine the effect of different settings on cardiac event sensing and the resulting sensed cardiac event intervals (determined at block810) and rate. In some examples, all available programmable settings of the first sensing threshold control parameter may be applied or a subset of settings that may be selected by the user. In some examples, the first sensing threshold control parameter tested at block808is any of the sensing control parameters listed above except sensitivity. Accordingly, the percentage used to set the starting threshold, the percentage used to set the intermediate threshold, the sense delay interval or the drop time interval may be the first sensing threshold control parameter evaluated at block808. Because sensitivity significantly affects tachyarrhythmia detection in most patients, sensitivity may be evaluated after evaluating another sensing threshold control parameter that may need to be selected based on cardiac signal analysis for an individual patient due to noise, oversensing or other sensing issues, which may be patient specific.

At block812, processor52determines a setting of the first sensing threshold control parameter that results in the determined cardiac events meeting expected rate criteria. The expected rate criteria may be a heart rate confirmed by a user or determined from an electrocardiogram input. In other examples, the expected rate criteria may be a tachyarrhythmia detection, which may be required to occur within a specified time limit. In some cases, when oversensing is an issue, a setting of the first sensing threshold control parameter may result in a determined sensed cardiac event rate that is faster than an expected rate. In other instances, undersensing may occur resulting in a determined sensed cardiac event rate that is slower than the expected rate.

When the determined cardiac event intervals for a first sensing threshold control parameter setting meet expected rate criteria, indicating that a possible oversensing or undersensing issue has been resolved, the setting identified at block812may be applied to the respective cardiac electrical signal being evaluated to redetermine sensed cardiac events according to each of the available sensitivity settings at block814. When a sensing threshold control parameter other than sensitivity needs to be evaluated for a given patient, sensed cardiac events may be redetermined for all sensitivity settings (block814) by processor52using the new setting of the first sensing threshold control parameter to determine the sensitivity setting that meets a desired safety margin (block816) according to the techniques described above.

At block818, processor52may generate an output, e.g., data for display in a GUI for visualization by a user and/or a programming command. The data representing the determined sensed cardiac events, determined sensed cardiac event intervals or rate, detection of a tachyarrhythmia and/or time to detect for each of the first sensing threshold control parameter settings may be presented in the GUI, similar to the GUIs described above. Additionally or alternatively, the first sensing threshold control parameter setting identified at block812may be indicated as the recommended setting and the data corresponding to testing different sensitivity settings using the recommended first sensing threshold control parameter setting may be presented in the GUI. The GUI enables a user to select and program an acceptable sensitivity, e.g., according to a desired safety margin, for sensing cardiac events when the first sensing threshold control parameter setting is at the recommended value.

In an illustrative example, ICD14may be oversensing P-waves in a patient requiring the drop time interval be increased to avoid P-wave oversensing. As shown inFIG.15, a user may select a test drop time interval of 2.0 seconds when the programmed drop time interval is set at 1.5 seconds. Processor52may determine sensed cardiac events for all sensitivity settings at the new drop time interval of 2.0 seconds and generate a table, graph and/or timing diagram representing the determined sensed cardiac event data as described above. Processor52may determine the recommended sensitivity setting for achieving a desired safety margin for sensing cardiac events when the new drop time interval is applied.

For the sake of convenience, the flow chart800depicts determining sensed cardiac events from each cardiac electrical signal according to selected settings of the first sensing threshold parameter and subsequently determining sensed cardiac events according to each sensitivity setting. It is to be understood, however, that disclosed operations may be performed in a different order than shown in the flow charts presented herein or in parallel operations. For example, processor52may determine sensed cardiac events for all combinations of sensing control parameters (each sensing electrode vector, each setting of the first sensing threshold control parameter, and each setting of sensitivity). A user, interacting with a GUI such as the GUI750ofFIG.16or other examples presented herein, may select the test setting of the first sensing threshold control parameter and the sensing electrode vector. Processor52may then generate the display representative of the determined sensed cardiac event data for all sensitivity settings and the selected sensing electrode vector and first sensing threshold control parameter setting. In this way, a user interacting with GUI750may switch between different combinations of sensing electrode vector and the first sensing threshold parameter setting to determine a combination and associated sensitivity setting that results in a desired safety margin and expected cardiac event rate being detected.

Accordingly, the techniques disclosed herein promote programming of an ICD or other cardiac device to a sensitivity setting that provides an acceptable safety margin for sensing cardiac events, e.g., for reliably detecting tachyarrhythmia, while avoiding oversensing of noise or other signals. When oversensing is an issue for an individual patient, the techniques disclosed herein enable a user to visualize how tachyarrhythmia detection is expected to be affected (e.g., by a change in time to detect) by a potential programming change before the programming change goes into effect. The analysis of multiple sensing electrode vector signals according to multiple sensing threshold control parameter settings may be performed efficiently without requiring each vector signal to be sensed by the ICD (or other medical device) and without having to perform time consuming operations of programming the ICD (or other medical device) to multiple different sensing control parameter settings in order to actually sense cardiac events by sensing circuit86and determine actual sensed cardiac event intervals and any corresponding arrhythmia detection. The expected performance of the ICD (or other medical device) in detecting a tachyarrhythmia may be determined for multiple sensing control parameter combinations based on a single tachyarrhythmia episode, induced or spontaneous, thereby eliminating the need to perform multiple tachyarrhythmia inductions. Furthermore, whileFIG.17is described as identifying a first sensing threshold control parameter setting and then testing sensitivity settings, any combination of two or more sensing threshold control parameters, along with one or more sensing electrode vectors, may be evaluated according to the techniques disclosed herein.

It should be understood that, depending on the example, certain acts or events of any of the methods described herein can be performed in a different sequence, may be added, merged, or left out altogether (e.g., not all described acts or events are necessary for the practice of the method). Moreover, in certain examples, acts or events may be performed concurrently, e.g., through multi-threaded processing, interrupt processing, or multiple processors, rather than sequentially. In addition, while certain aspects of this disclosure are described as being performed by a single circuit or unit for purposes of clarity, it should be understood that the techniques of this disclosure may be performed by a combination of units or circuits associated with, for example, a medical device.

In one or more examples, the functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored as one or more instructions or code on a computer-readable medium and executed by a hardware-based processing unit. Computer-readable media may include computer-readable storage media, which corresponds to a tangible medium such as data storage media (e.g., RAM, ROM, EEPROM, flash memory, or any other medium that can be used to store desired program code in the form of instructions or data structures and that can be accessed by a computer).

Thus, a medical device system has been presented in the foregoing description with reference to specific examples. It is to be understood that various aspects disclosed herein may be combined in different combinations than the specific combinations presented in the accompanying drawings. It is appreciated that various modifications to the referenced examples may be made without departing from the scope of the disclosure and the following claims.