Detecting worsening heart failure

A method comprises monitoring a heart rate, a respiration rate and an activity level of a patient, comparing the monitored heart rate, respiration rate and activity level to a predetermined threshold zone which is a function of heart rate, respiration rate and activity level, determining the patient is experiencing worsening heart failure when the monitored heart rate, respiration rate and activity level are outside the predetermined threshold zone; and after determining the patient is experiencing worsening heart failure when the monitored heart rate, respiration rate and activity level are outside the predetermined threshold zone, issuing an alert to indicate that the patient is experiencing worsening heart failure.

TECHNICAL FIELD

The invention relates to medical devices and, more particularly, devices for the detection of worsening heart failure and treatment of related ailments.

BACKGROUND

A variety of medical devices have been used or proposed for use to deliver a therapy to and/or monitor a physiological condition of patients. As examples, such medical devices may deliver therapy and/or monitor conditions associated with the heart, muscle, nerve, brain, stomach or other organs or tissue. Medical devices that deliver therapy include medical devices that deliver one or both of electrical stimulation or a therapeutic agent to the patient. Some medical devices are implantable medical devices (IMDs) that are implanted within the patient.

Some medical devices have been used or proposed for use to monitor heart failure or to detect heart failure events. Typically, such medical devices have been implantable and, in many cases, have been cardiac pacemakers or defibrillators, such as cardioverters, with added heart failure monitoring functionality. In some cases, such medical devices have monitored heart failure by monitoring intrathoracic impedance, which may provide a good indication of the level of pulmonary edema in patients. In other cases, medical devices have monitored pressure in the right ventricle of a patient using a pressure sensor, which can also provide an indication of the level of pulmonary edema in patients.

While pulmonary edema is a sign of many other conditions it is also a sign of worsening heart failure. Worsening heart failure may result in cardiac chamber dilation, increased pulmonary blood volume, and fluid retention in the lungs—all of which contribute to a decrease in intrathoracic impedance. Other diagnostic parameters, such as heart rate variability, have been proposed for use in such devices to identify worsening heart failure or heart failure events, such as decompensation. Decompensation is a condition in which the heart is unable to provide adequate cellular perfusion to all parts of the body, including the lungs, without assistance. Without treatment, decompensation is expected to result in the death of a patient due to heart/lung failure.

Generally, the first indication that a physician would have of the occurrence of decompensation in a patient is not until it becomes a physical manifestation with swelling or breathing difficulties so overwhelming as to be noticed by the patient who then proceeds to be examined by a physician. This is undesirable since hospitalization at such a time would likely be required for a heart failure patient. Accordingly, medical devices have been used to monitor impedance in patients and provide an alert to the patient to seek medical treatment prior to the onset of worsening heart failure with symptoms, such as pulmonary edema, that require hospitalization.

SUMMARY

In patients with chronic heart failure, early detection of an imminent episode of decompensation to prevent or shorten hospitalization is an ongoing challenge. Current detection of heart failure decompensation is based on intra-thoracic impedance measurement detecting fluid accumulation in the lungs. Detection of heart failure decompensation could also be based on estimation of the pulmonary artery pressure (ePAD) using an absolute pressure sensor positioned on a lead in the right ventricle (RV).

Functional impairment of the lungs due to fluid accumulation affects heart function, whereas functional impairment of the heart often affects lung function. This also leads to an increased heart rate and ventilatory effort for the patient at a given activity level.

In order to anticipate decompensation in a patient, the disclosed techniques include monitoring respiration rate, heart rate and activity level of a patient. If the patient is experiencing worsening heart failure, the respiration rate and heart rate will not be consistent with baseline heart rates and baseline respiration rates previously associated with the patient. The techniques may include using measured baseline heart rates and baseline respiration rates for a plurality of activity levels to define a predetermined threshold zone, and issuing an alert if the respiration rate, heart rate and activity level of a patient is outside the predetermined threshold zone.

An activity level of the patient can be obtained by a commonly used activity sensor (accelerometer), whereas heart rate can be obtained from intrinsic sinus beats detected from the intra-cardiac or subcutaneous (subQ) electrogram. Likewise, the ventilation rate can be obtained by measuring intrathoracic impedance. For example, respiration often appears as low-frequency “noise” on an unfiltered intra-cardiac electrogram.

In one example, a method comprises monitoring a heart rate, a respiration rate and an activity level of a patient, comparing the monitored heart rate, respiration rate and activity level to a predetermined threshold zone which is a function of heart rate, respiration rate and activity level, determining the patient is experiencing worsening heart failure when the monitored heart rate, respiration rate and activity level are outside the predetermined threshold zone; and after determining the patient is experiencing worsening heart failure when the monitored heart rate, respiration rate and activity level are outside the predetermined threshold zone, issuing an alert to indicate that the patient is experiencing worsening heart failure.

In another example, a medical system for monitoring a condition of a patient comprises one or more sensors configured to output one or more signals indicative of a heart rate, a respiration rate and an activity level of the patient, a memory configured to store an indication of a predetermined threshold zone which is a function of heart rate, respiration rate and activity level and a diagnostic unit configured to compare the monitored heart rate, respiration rate and activity level to the predetermined threshold zone, and determine the patient is experiencing worsening heart failure when the monitored heart rate, respiration rate and activity level are outside the predetermined threshold zone. The medical system further comprises an alert module configured to issue an alert to indicate that the patient is experiencing worsening heart failure after the diagnostic unit determines the patient is experiencing worsening heart failure when the monitored heart rate, respiration rate and activity level are outside the predetermined threshold zone.

In another example, a system comprises means for monitoring a heart rate of a patient, means for monitoring a respiration rate of the patient, means for monitoring an activity level of the patient, means for comparing the monitored heart rate, respiration rate and activity level to a predetermined threshold zone which is a function of heart rate, respiration rate and activity level, means for determining the patient is experiencing worsening heart failure when the monitored heart rate, respiration rate and activity level are outside the predetermined threshold zone and means for, after determining the patient is experiencing worsening heart failure when the monitored heart rate, respiration rate and activity level are outside the predetermined threshold zone, issuing an alert to indicate that the patient is experiencing worsening heart failure.

In another example, a computer readable storage medium comprises instructions that cause a processor to monitor a heart rate, a respiration rate and an activity level of a patient, compare the monitored heart rate, respiration rate and activity level to a predetermined threshold zone which is a function of heart rate, respiration rate and activity level, determine the patient is experiencing worsening heart failure when the monitored heart rate, respiration rate and activity level are outside the predetermined threshold zone, and after determining the patient is experiencing worsening heart failure when the monitored heart rate, respiration rate and activity level are outside the predetermined threshold zone, issue an alert to indicate that the patient is experiencing worsening heart failure.

DETAILED DESCRIPTION

FIG. 1is a conceptual diagram illustrating an example system10that may be used to determine worsening heart failure in patient14by measuring multiple diagnostic parameters and comparing them to predetermined levels associated with patient14for a given activity level. Patient14ordinarily, but not necessarily, will be a human. System10is configured to generate an alert in response to detecting worsening heart failure so that patient14can seek appropriate treatment before experiencing a heart failure hospitalization event such as decompensation. In addition or in the alternative, system10may alter patient therapy in response to detecting worsening heart failure. For example, system10may increase the charge level of a high voltage energy storage device used to deliver a defibrillation pulse to patient14in preparation for a heart failure event. As another example, system10may alter drug therapy to patient14, such as delivering diuretics to patient14. System10may also perform other suitable techniques to mitigate worsening heart failure.

System10includes implantable medical device (IMD)16, which is coupled to leads18,20, and22, an electrode34located on the can of IMD16, and a programmer24. In some examples, IMD16may be a purely diagnostic device that monitors multiple diagnostic parameters associated with heart failure as well as the activity level of patient14. In other examples, IMD16may additionally operate as a therapy delivery device to deliver electrical signals to heart12via one or more of leads18,20, and22, such as an implantable pacemaker, a cardioverter, and/or defibrillator. In some examples, IMD16may operate as a drug delivery device that delivers therapeutic substances to patient14via catheters (not shown), or as a combination therapy device that delivers both electrical signals and therapeutic substances. Moreover, IMD16is not limited to devices implanted as shown inFIG. 1. As an example, IMD16may be implanted subcutaneously in patient14, or may be an entirely external device with leads attached to the skin of patient14or implanted percutaneously in patient14. In some examples, IMD16need not include leads, but may include a plurality of electrodes, like electrode34, on the housing of IMD16.

In general, IMD16monitors a one or more parameters that are indicative of respiration rate, one or more parameters that are indicative of heart rate and one or more parameters that are indicative of an activity level of patient14. IMD16detects worsening heart failure in patient14at least in part by comparing these measured parameters to predetermined levels associated with patient14for a given activity level.

IMD16includes at least one sensor that provides an output indicative of an activity level of patient14. For example, as described in further detail with respect toFIG. 3, IMD16may include a 3-axis accelerometer, such as a piezoelectric and/or micro-electro-mechanical accelerometer that generates an output based on activity level. In addition, as described in further detail with respect toFIG. 2, IMD16uses electrode34and/or electrodes on one of leads18,20, and22to monitor heart rate, e.g., as part of an electrocardiogram (ECG).

IMD16also monitors the respiration rate of patient14, e.g., by monitoring intrathoracic impedance, which indicative of respiration rate. As an example, intrathoracic impedance may show up as low-frequency “noise” on an unfiltered ECG signal. In different examples, IMD16may filter the same signals used to measure heart rate to determine respiration rate, or IMD16may take separate measurement to determine intrathoracic impedance. In yet another example, IMD16may include an intrathoracic pressure sensor or other sensor that provides an output indicative of respiration rate. It should be noted that these same techniques used to determine a respiration rate can also be used to determine that amplitude of each breath such that IMD16may also determine the minute ventilation of patient14. In some instances, minute ventilation of patient14may be used instead of respiration rate to determine worsening heart failure in patient14.

In the example illustrated inFIG. 1, IMD16includes leads18,20, and22that extend into the heart12of patient14. Right ventricular (RV) lead18extends through one or more veins (not shown), the superior vena cava (not shown), and right atrium26, and into right ventricle28. Left ventricular (LV) coronary sinus lead20extends through one or more veins, the vena cava, right atrium26, and into the coronary sinus30to a region adjacent to the free wall of left ventricle32of heart12. Right atrial (RA) lead22extends through one or more veins and the vena cava, and into the right atrium26of heart12. Other configurations, i.e., number and position of leads, are possible. For example, other leads or lead configurations may be used to monitor pressure and various diagnostic parameters. As described above, in some examples, IMD16need not be coupled to leads.

Intrathoracic impedance may be measured by creating an electrical path between electrodes (not shown inFIG. 1) located on one or more of leads18,20, and22and can electrode34. In some embodiments, the can of IMD16may be used as an electrode in combination with electrodes located on leads18,20, and22. For example, system10may measure intrathoracic impedance by creating an electrical path between RV lead18and electrode34. In additional embodiments, system10may include an additional lead or lead segment having one or more electrodes positioned at a different location in the cardiovascular system or chest cavity, such as within one of the vena cava, subcutaneously at a location substantially opposite IMD16vis-à-vis the thorax of patient14, or epicardially, for measuring intrathoracic impedance.

IMD16may also monitor additional diagnostic parameters in conjunction with parameters that are indicative of respiration rate, heart rate and activity level of patient14. For example, IMD16may monitor atrial fibrillation burden (AF), heart rate during AF, ventricular fibrillation burden (VF), heart rate during VF, atrial tachyarrhythmia burden (AT), heart rate during AT, ventricular tachyarrhythmia burden (VT), heart rate during VT, heart rate variability, night heart rate, difference between day heart rate and night heart rate, heart rate turbulence, heart rate deceleration capacity, respiration rate, baroreflex sensitivity, percentage of cardiac resynchronization therapy (CRT) pacing, metrics of renal function, weight, blood pressure, symptoms entered by the patient via a programmer, and patient history, such as medication history, or history of heart failure hospitalizations.

IMD16or programmer24may be configured to provide an alert in response to detecting worsening heart failure in patient14. The alert may be audible, visual, or tactile and enables patient14to seek medical attention to treat the condition prior to experiencing a heart failure event, or a clinician to direct patient14to do so. In some examples, the alert may be a silent alert transmitted to another device associated with a clinician or other user, such as a silent alert transmitted to a server, as described below, and relayed to a physician via a computing device.

In embodiments in which IMD16operates as a pacemaker, a cardioverter, and/or defibrillator, IMD16may sense electrical signals attendant to the depolarization and repolarization of heart12via electrodes coupled to at least one of the leads18,20,22. In some examples, IMD16provides pacing pulses to heart12based on the electrical signals sensed within heart12. The configurations of electrodes used by IMD16for sensing and pacing may be unipolar or bipolar. IMD16may also provide defibrillation therapy and/or cardioversion therapy via electrodes located on at least one of the leads18,20,22. IMD16may detect arrhythmia of heart12, such as fibrillation of ventricles28and32, and deliver defibrillation therapy to heart12in the form of electrical pulses. In some examples, IMD16may be programmed to deliver a progression of therapies, e.g., pulses with increasing energy levels, until a fibrillation of heart12is stopped. IMD16detects fibrillation employing one or more fibrillation detection techniques known in the art.

It should be understood that IMD16may also include other types of sensors for monitoring various diagnostic parameters. As an example, IMD16may monitors pressure, and one or more of leads18,20, and22and/or the device can of IMD16may include one or more pressure sensors, such as capacitive pressure sensors. IMD16may also include or be coupled to one or more pressure sensors, the output of which may be considered with heart rate to monitor baroreflex sensitivity (as well as respiration rate). In an additional example, IMD16may also communicate with an external sensor, such as a scale for monitoring the weight of patient14. Moreover, in embodiments in which IMD16is implemented as an external device (not shown), leads for monitoring diagnostic parameters may be implanted percutaneously in patient14or attached to the skin of patient14.

In some examples, programmer24may be a handheld computing device, computer workstation, or networked computing device. Programmer24may include a user interface that receives input from a user. The user interface may include, for example, a keypad and a display, which may for example, be a cathode ray tube (CRT) display, a liquid crystal display (LCD) or light emitting diode (LED) display. The keypad may take the form of an alphanumeric keypad or a reduced set of keys associated with particular functions. Programmer24can additionally or alternatively include a peripheral pointing device, such as a mouse, via which a user may interact with the user interface. In some embodiments, a display of programmer24may include a touch screen display, and a user may interact with programmer24via the display. It should be noted that the user may also interact with programmer24remotely via a networked computing device.

A user, such as a physician, technician, surgeon, electrophysiologist, or other clinician, may interact with programmer24to communicate with IMD16. For example, the user may interact with programmer24to retrieve physiological or diagnostic information from IMD16. A user may also interact with programmer24to program IMD16, e.g., select values for operational parameters of the IMD.

For example, the user may use programmer24to retrieve information from IMD16. The information may relate to diagnostic parameters, i.e., information relating to activity level, heart rate, respiration rate, intrathoracic impedance, pressure, AF burden, heart rate during AF, VF burden, heart rate during VF, AT burden, heart rate during AT, VT burden, heart rate during VT, activity level, heart rate variability, night heart rate, difference between day heart rate and night heart rate, heart rate turbulence, heart rate deceleration capacity, respiration rate, baroreflex sensitivity, percentage of CRT pacing, metrics of renal function, weight, blood pressure, symptoms entered by the patient via a programmer, and patient history, such as medication history, or history of heart failure hospitalizations. The information may also include trends therein over time. In some embodiments, the user may use programmer24to retrieve information from IMD16regarding other sensed physiological parameters of patient14. In addition, the user may use programmer24to retrieve information from IMD16regarding the performance or integrity of IMD16or other components of system10, such as leads18,20, and22, or a power source of IMD16.

In one example, a user may also use programmer24to program other parameters related to detecting worsening heart failure, such as parameters associated with the predetermined threshold zone (e.g., as shown inFIGS. 7A-7D) for a given patient activity level. In this case, the user may specify parameters that define the predetermined threshold zone for a given patient activity level, or parameters that control how the predetermined threshold zone for a given patient activity level changes over time. Furthermore, the user may use programmer24to enter clinical information, such as patient history, medication history, history of heart failure hospitalizations, or other historical or current observations of patient condition.

Programmer24may also be used to program a therapy progression, select electrodes to deliver defibrillation pulses, select waveforms for the defibrillation pulse, or select or configure a fibrillation detection algorithm for IMD16. The user may also use programmer24to program aspects of other therapies provided by IMD16, such as cardioversion or pacing therapies. In some examples, the user may activate certain features of IMD16by entering a single command via programmer24, such as depression of a single key or combination of keys of a keypad or a single point-and-select action with a pointing device.

IMD16and programmer24may communicate via wireless communication using any techniques known in the art. Examples of communication techniques may include, for example, low frequency or radiofrequency (RF) telemetry, but other techniques are also contemplated. In some examples, programmer24may include a programming head that may be placed proximate to the patient's body near the IMD16implant site in order to improve the quality or security of communication between IMD16and programmer24.

FIG. 2is a conceptual diagram illustrating IMD16, leads18,20, and22, and electrode34of system10in greater detail. System10is generally described in this disclosure as a therapy system that detects worsening heart failure in patient14and delivers corrective electrical signals to heart12. In particular, system10is as a therapy system that monitors parameters that are indicative of respiration rate, heart rate and activity level to detect worsening heart failure in patient14.

In the example illustrated inFIG. 2, system10includes leads18,20, and22that include electrodes for monitoring parameters that are indicative of respiration rate and heart rate and. Leads18,20, and22may be electrically coupled to a stimulation generator and a sensing module of IMD16via connector block38. In some examples, proximal ends of leads18,20,22may include electrical contacts that electrically couple to respective electrical contacts within connector block38. In addition, in some examples, leads18,20,22may be mechanically coupled to connector block38with the aid of set screws, connection pins, or another suitable mechanical coupling mechanism.

Each of the leads18,20,22includes an elongated insulative lead body, which may carry a number of concentric coiled conductors separated from one another by tubular insulative sheaths. In some cases, each of the leads18,20,22may include cable conductors. Bipolar electrodes40and42are located adjacent to a distal end of lead18. In addition, bipolar electrodes44and46are located adjacent to a distal end of lead20and bipolar electrodes48and50are located adjacent to a distal end of lead22.

Electrodes40,44and48may take the form of ring electrodes, and electrodes42,46and50may take the form of extendable helix tip electrodes mounted retractably within insulative electrode heads52,54and56, respectively. In other embodiments, one or more of electrodes42,46and50may take the form of small circular electrodes at the tip of a tined lead or other fixation element. Leads18,20,22also include elongated electrodes62,64,66, respectively, which may take the form of a coil. Each of the electrodes40,42,44,46,48,50,62,64and66may be electrically coupled to a respective one of the coiled conductors within the lead body of its associated lead18,20,22, and thereby coupled to respective ones of the electrical contacts on the proximal end of leads18,20and22.

As discussed above, IMD16includes one or more housing electrodes, such as housing electrode34, which may be formed integrally with an outer surface of hermetically-sealed housing60of IMD16or otherwise coupled to housing60. In some examples, housing electrode34is defined by an uninsulated portion of an outward facing portion of housing60of IMD16. Other division between insulated and uninsulated portions of housing60may be employed to define two or more housing electrodes. In some examples, housing electrode34comprises substantially all of housing60. As described in further detail with reference toFIG. 3, housing60may enclose a signal generator that generates therapeutic stimulation, such as cardiac pacing pulses and defibrillation shocks, as well as a sensing module for monitoring the rhythm of heart12.

IMD16may sense electrical signals attendant to the depolarization and repolarization of heart12via electrodes34,40,42,44,46,48,50,62,64and66. The electrical signals are conducted to IMD16from the electrodes via the respective leads18,20,22. IMD16may sense such electrical signals via any bipolar combination of electrodes40,42,44,46,48,50,62,64and66. Furthermore, any of the electrodes40,42,44,46,48,50,62,64and66may be used for unipolar sensing in combination with housing electrode34. Additionally, any of the electrodes40,42,44,46,48,50,62,64and66may be used in combination with housing electrode34to sense intrathoracic impedance of patient14.

In some examples, IMD16delivers pacing pulses via bipolar combinations of electrodes40,42,44,46,48and50to produce depolarization of cardiac tissue of heart12. In some examples, IMD16delivers pacing pulses via any of electrodes40,42,44,46,48and50in combination with housing electrode34in a unipolar configuration. Furthermore, IMD16may deliver cardioversion or defibrillation pulses to heart12via any combination of elongated electrodes62,64,66, and housing electrode34. Electrodes34,62,64,66may also be used to deliver cardioversion pulses, e.g., a responsive therapeutic shock, to heart12. Electrodes62,64,66may be fabricated from any suitable electrically conductive material, such as, but not limited to, platinum, platinum alloy or other materials known to be usable in implantable defibrillation electrodes.

The configuration of therapy system10illustrated inFIGS. 1 and 2is merely one example. In other examples, a therapy system may include epicardial leads and/or patch electrodes instead of or in addition to the transvenous leads18,20,22illustrated inFIG. 1. Moreover, IMD16need not be implanted within patient14as shown inFIG. 1. For example, IMD16may be implanted subcutaneously in patient14or may be located outside the body of patient14. In such examples, IMD16may monitor diagnostic parameters and deliver defibrillation pulses and other therapies to heart12via percutaneous leads that extend through the skin of patient14to a variety of positions within or outside of heart12.

In addition, in other examples, system10may include any suitable number of leads coupled to IMD16, and each of the leads may extend to any location within or proximate to heart12or in the chest of patient14. For example, other example therapy systems may include three transvenous leads and an additional lead located within or proximate to left atrium36. As other examples, a therapy system may include a single lead that extends from IMD16into right atrium26or right ventricle28, or two leads that extend into a respective one of the right ventricle28and right atrium26.

FIG. 3is a functional block diagram of one example of IMD16, which includes a processor80, memory82, signal generator84, electrical sensing module86, telemetry module88, power source90, sensor91and diagnostic unit92. Processor80may comprise one or more processors. Memory82includes computer-readable instructions that, when executed by processor80, cause IMD16and processor80to perform various functions attributed to IMD16and processor80herein. Memory82may 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 media.

IMD16includes sensor91generates an output based on activity level of patient14. In exemplary embodiments, sensor91is a 3-axis accelerometer, such as a piezoelectric and/or micro-electro-mechanical accelerometer. In other embodiments, a single axis accelerometer may be employed, or multiple single axis accelerometers may be used in place of one 3-axis accelerometer.

In some embodiments, processor80processes the analog output of sensor91to determine digital activity information. For example, where sensor91comprises a piezoelectric accelerometer, processor80may process the raw signal provided by sensor91to determine activity counts. In some embodiments, IMD16includes multiple sensors oriented along various axes, or sensor91comprises a single multi-axis, e.g., three-axis, accelerometer. In such embodiments, processor80may process the signals provided by the one or more sensor91to determine velocity of motion information for each axis.

Sensor91may comprise one or more sensors. Sensor91is shown inFIG. 6as being housed within a housing (not shown) of IMD16. However, in some embodiments, at least one sensor91is coupled to IMD16via additional leads (not shown). Such sensors may be located anywhere within patient14. In some embodiments, IMD16may be coupled to multiple accelerometers located at various positions within patient14or on the external surface of patient14, and processor80may receive more detailed information about the posture of and activity undertaken by patient14. For example, accelerometer sensor91may be located within the torso and at a position within a limb, e.g. a leg, of patient14.

In some embodiments, one or more sensor91may communicate wirelessly with IMD16instead of requiring a lead to communicate with the IMD. For example, a sensor located external to patient12may communicate wirelessly with processor80, either directly or via programmer24. In some embodiments, one or more sensor91may be included as part of or coupled to programmer24.

Moreover, the invention is not limited to embodiments where sensor91includes one or more accelerometers. In some embodiments, one or more sensor91may take the form of, for example, a thermistor, a pressure transducer, or electrodes to detect thoracic impedance or an electrogram. Such sensors may be appropriately positioned within patient14, or on an external surface of the patient, to allow processor80to measure a physiological parameter of patient14, such as a skin temperature, an arterial or intracardiac pressure, a respiration rate, a heart rate, or a Q-T interval of patient14.

As illustrated inFIG. 3, sensing module86may include an impedance measurement module87. Processor80may control impedance measurement module87to periodically measure an electrical parameter to determine an impedance, such as an intrathoracic impedance. For an intrathoracic impedance measurement, processor80may control stimulation generator84to deliver an electrical signal between selected electrodes and impedance measurement module87to measure a current or voltage amplitude of the signal. Processor80may select any combination of electrodes34,40,42,44,46,48,50,62,64, and66, e.g., by using switch modules in signal generator84and sensing module86. Impedance measurement module87includes sample and hold circuitry or other suitable circuitry for measuring resulting current and/or voltage amplitudes. Processor80determines an impedance value from the amplitude value(s) received from impedance measurement module87.

In some examples, processor80may perform an impedance measurement by causing signal generator84to deliver a voltage pulse between two electrodes and examining resulting current amplitude value measured by impedance measurement module87. In these examples, signal generator84delivers signals that do not necessarily deliver stimulation therapy to heart12, due to, for example, the amplitudes of such signals and/or the timing of delivery of such signals. For example, these signals may comprise sub-threshold amplitude signals that may not stimulate heart12. In some cases, these signals may be delivered during a refractory period, in which case they also may not stimulate heart12.

In other examples, processor80may perform an impedance measurement by causing signal generator84to deliver a current pulse across two selected electrodes. Impedance measurement module87holds a measured voltage amplitude value. Processor80determines an impedance value based upon the amplitude of the current pulse and the amplitude of the resulting voltage that is measured by impedance measurement module87. IMD16may use defined or predetermined pulse amplitudes, widths, frequencies, or electrode polarities for the pulses delivered for these various impedance measurements. In some examples, the amplitudes and/or widths of the pulses may be sub-threshold, e.g., below a threshold necessary to capture or otherwise activate tissue, such as cardiac tissue.

In certain cases, IMD16may measure intrathoracic impedance values that include both a resistive and a reactive (i.e., phase) component. In such cases, IMD16may measure impedance during delivery of a sinusoidal or other time varying signal by signal generator84, for example. Thus, as used herein, the term “impedance” is used in a broad sense to indicate any collected, measured, and/or calculated value that may include one or both of resistive and reactive components.

Electrical sensing module86monitors signals from at least one of electrodes34,40,42,44,46,48,50,62,64or66in order to monitor electrical activity of heart12. Sensing module86may also include a switch module to select which of the available electrodes are used to sense the heart activity. In some examples, processor80may select the electrodes that function as sense electrodes via the switch module within sensing module86, e.g., by providing signals via a data/address bus. In some examples, sensing module86includes one or more sensing channels, each of which may comprise an amplifier. In response to the signals from processor80, the switch module within sensing module86may couple the outputs from the selected electrodes to one of the sensing channels.

In some examples, one channel of sensing module86may include an R-wave amplifier that receives signals from electrodes40and42, which are used for pacing and sensing in right ventricle28of heart12. Another channel may include another R-wave amplifier that receives signals from electrodes44and46, which are used for pacing and sensing proximate to left ventricle32of heart12. In some examples, the R-wave amplifiers may take the form of an automatic gain controlled amplifier that provides an adjustable sensing threshold as a function of the measured R-wave amplitude of the heart rhythm.

In addition, in some examples, one channel of sensing module86may include a P-wave amplifier that receives signals from electrodes48and50, which are used for pacing and sensing in right atrium26of heart12. In some examples, the P-wave amplifier may take the form of an automatic gain controlled amplifier that provides an adjustable sensing threshold as a function of the measured P-wave amplitude of the heart rhythm. Examples of R-wave and P-wave amplifiers are described in U.S. Pat. No. 5,117,824 to Keimel et al., which issued on Jun. 2, 1992 and is entitled, “APPARATUS FOR MONITORING ELECTRICAL PHYSIOLOGIC SIGNALS,” and is hereby incorporated by reference in its entirety. Other amplifiers may also be used. Furthermore, in some examples, one or more of the sensing channels of sensing module84may be selectively coupled to housing electrode34, or elongated electrodes62,64, or66, with or instead of one or more of electrodes40,42,44,46,48or50, e.g., for unipolar sensing of R-waves or P-waves in any of chambers26,28,36, or32of heart12.

In some examples, sensing module84includes a channel that comprises an amplifier with a relatively wider pass band than the R-wave or P-wave amplifiers. Signals from the selected sensing electrodes that are selected for coupling to this wide-band amplifier may be provided to a multiplexer, and thereafter converted to multi-bit digital signals by an analog-to-digital converter for storage in memory82as an electrogram (EGM). In some examples, the storage of such EGMs in memory82may be under the control of a direct memory access circuit. Processor80may employ digital signal analysis techniques to characterize the digitized signals stored in memory82to detect and classify the patient's heart rhythm from the electrical signals. Processor80may detect and classify the patient's heart rhythm by employing any of the numerous signal processing methodologies known in the art.

In the illustrated example shown inFIG. 3, IMD16includes diagnostic unit92. Diagnostic unit92provides functionality that enables IMD16to detect worsening heart failure in patient14. To avoid confusion, although diagnostic unit92is described as performing the various monitoring and detecting techniques proscribed to IMD16, it should be understood that these techniques may also be performed by processor80, e.g., that diagnostic unit92may be a functional module provided or executed by processor80. Accordingly, although processor80and diagnostic unit92are illustrated as separate modules inFIG. 3, processor80and diagnostic unit92may be incorporated in a single processing unit or equivalent circuitry.

In operation, diagnostic unit92monitors respiration rate, one or more parameters that are indicative of heart rate and one or more parameters that are indicative of an activity level of patient14to detect worsening heart failure in patient14. Diagnostic unit92detects worsening heart failure in patient14by comparing respiration rate and heart rate to predetermined levels associated with patient14for a given activity level.

In the example illustrated inFIG. 3, diagnostic unit92may receive signals or indications from processor80, sensing module86or other sensors91to diagnostic parameters. Thus, IMD16may be configured to monitor any physiological parameters that are capable of being sensed using any combination of electrodes34,40,42,44,46,48,50,62,64and66in addition to those indicative of respiration rate and heart rate. For example, IMD16may be configured to monitor intrathoracic impedance and/or electrical activity of heart12, using any combination of electrodes34,40,42,44,46,48,50,62,64and66.

Based on the electrical activity of heart12as indicated by sensing module86, diagnostic unit92may monitor AF burden, heart rate during AF, VF burden, heart rate during VF, AT burden, heart rate during AT, VT burden, heart rate during VT, heart rate variability, night heart rate difference between day heart rate and night heart rate, heart rate turbulence, heart rate deceleration capacity, or baroreflex sensitivity. As previously described, sensing module86monitors signals from a selected combination of electrodes34,40,42,44,46,48,50,62,64, and66and processor80/diagnostic unit92may detect atrial or ventricular tachyarrhythmia based on signals or indications from sensing module86. An AT burden may be determined based on the number and/or duration (individual, average, or collective) of incidents of AT, as well as the ventricular rate during AT. AF, VT and VF burdens may be similar determined. In some examples, AT and AF burdens are combined as an AT/AF burden. VT and VF burdens may likewise be combined, in some examples.

Processor80controls signal generator84to deliver stimulation therapy to heart12based on a selected one or more of therapy programs, which may be stored in memory82. Specifically, processor80may control signal generator84to deliver electrical pulses with the amplitudes, pulse widths, frequency, or electrode polarities specified by the selected one or more therapy programs.

Signal generator84is electrically coupled to electrodes34,40,42,44,46,48,50,62,64, and66, e.g., via conductors of the respective lead18,20,22, or, in the case of housing electrode34, via an electrical conductor disposed within housing60of IMD16. A switch matrix may also be provided to connect signal generator84to one or more of electrodes34,40,42,44,46,48,50,62,64, and66. Signal generator84is configured to generate and deliver electrical stimulation therapy to heart12.

For example, signal generator84may deliver defibrillation shocks to heart12via at least two of electrodes34,62,64,66. Signal generator84may also deliver pacing pulses via ring electrodes40,44,48coupled to leads18,20, and22, respectively, and/or helical electrodes42,46, and50of leads18,20, and22, respectively. In some examples, signal generator84delivers pacing, cardioversion, or defibrillation stimulation in the form of electrical pulses. In other examples, signal generator84may deliver one or more of these types of stimulation in the form of other signals, such as sine waves, square waves, or other substantially continuous time signals.

Signal generator84may include a switch module, and processor80may use the switch module to select, e.g., via a data/address bus, which of the available electrodes are used to deliver defibrillation pulses or pacing pulses. The switch module may include a switch array, switch matrix, multiplexer, transistor array, microelectromechanical switches, or any other type of switching device suitable to selectively couple stimulation energy to selected electrodes.

If IMD16is configured to generate and deliver pacing pulses to heart12, processor80may include pacer timing and control module, which may be embodied as hardware, firmware, software, or any combination thereof. The pacer timing and control module may comprise a dedicated hardware circuit, such as an ASIC, separate from other processor80components, such as a microprocessor, or a software module executed by a component of processor80, which may be a microprocessor or ASIC. The pacer timing and control module may include programmable counters which control the basic time intervals associated with DDD, VVI, DVI, VDD, AAI, DDI, DDDR, VVIR, DVIR, VDDR, AAIR, DDIR and other modes of single and dual chamber pacing. In the aforementioned pacing modes, “D” indicates dual chamber, “V” may indicate a ventricle, “I” indicates inhibited pacing (e.g., no pacing), and “A” indicates an atrium. The first letter in the pacing mode indicates the chamber that is paced, the second letter indicates the chamber that is sensed, and the third letter indicates the pacemaker response to sensing. In addition, “R” indicatives that the therapy is rate-responsive.

Intervals defined by the pacer timing and control module within processor80may include atrial and ventricular pacing escape intervals, refractory periods during which sensed P-waves and R-waves are ineffective to restart timing of the escape intervals, the pulse widths of the pacing pulses, A-V intervals, and V-V intervals for cardiac resynchronization therapy (CRT). As another example, the pacer timing and control module may define a blanking period, and provide signals sensing module86to blank one or more channels, e.g., amplifiers, for a period during and after delivery of electrical stimulation to heart12. As another example, the pacer timing and control module may control intervals for delivery of refractory period stimulation or cardiac potentiation therapy. The durations of these intervals may be determined by processor80in response to stored data in memory82. The pacer timing and control module of processor80may also determine the amplitude of the cardiac pacing pulses.

During pacing, escape interval counters within the pacer timing/control module of processor80may be reset upon sensing of R-waves and P-waves. Stimulation generator84may include pacer output circuits that are coupled, e.g., selectively by a switching module, to any combination of electrodes34,40,42,44,46,48,50,62, or66appropriate for delivery of a bipolar or unipolar pacing pulse to one of the chambers of heart12. Processor80may reset the escape interval counters upon the generation of pacing pulses by stimulation generator84, and thereby control the basic timing of cardiac pacing functions, including anti-tachyarrhythmia pacing (ATP).

The value of the count present in the escape interval counters when reset by sensed R-waves and P-waves may be used by processor80to measure the durations of R-R intervals, P-P intervals, PR intervals and R-P intervals, which are measurements that may be stored in memory82. Processor80may use the count in the interval counters to detect an arrhythmia event, such as an atrial or ventricular fibrillation or tachycardia.

In some examples, processor80may operate as an interrupt driven device, and is responsive to interrupts from pacer timing and control module, where the interrupts may correspond to the occurrences of sensed P-waves and R-waves and the generation of cardiac pacing pulses. Any necessary mathematical calculations to be performed by processor80and any updating of the values or intervals controlled by the pacer timing and control module of processor80may take place following such interrupts. A portion of memory82may be configured as a plurality of recirculating buffers, capable of holding series of measured intervals, which may be analyzed by processor80in response to the occurrence of a pace or sense interrupt to determine whether the patient's heart12is presently exhibiting atrial or ventricular tachyarrhythmia.

In some examples, an arrhythmia detection method may include any suitable tachyarrhythmia detection algorithms. In one example, processor80may utilize all or a subset of the rule-based detection methods described in U.S. Pat. No. 5,545,186 to Olson et al., entitled, “PRIORITIZED RULE BASED METHOD AND APPARATUS FOR DIAGNOSIS AND TREATMENT OF ARRHYTHMIAS,” which issued on Aug. 13, 1996, or in U.S. Pat. No. 5,755,736 to Gillberg et al., entitled, “PRIORITIZED RULE BASED METHOD AND APPARATUS FOR DIAGNOSIS AND TREATMENT OF ARRHYTHMIAS,” which issued on May 26, 1998. U.S. Pat. No. 5,545,186 to Olson et al. and U.S. Pat. No. 5,755,736 to Gillberg et al. are hereby incorporated by reference in their entireties. However, other arrhythmia detection methodologies may also be employed by processor80in other examples.

In the event that processor80detects an atrial or ventricular tachyarrhythmia based on signals from sensing module86, and an anti-tachyarrhythmia pacing regimen is desired, timing intervals for controlling the generation of anti-tachyarrhythmia pacing therapies by signal generator84may be loaded by processor80into the pacer timing and control module to control the operation of the escape interval counters therein and to define refractory periods during which detection of R-waves and P-waves is ineffective to restart the escape interval counters.

If IMD16is configured to generate and deliver defibrillation pulses to heart12, signal generator84may include a high voltage charge circuit and a high voltage output circuit. If IMD16is configured to generate and deliver pacing pulses to heart12, signal generator84may include a low voltage charge circuit and a low voltage output circuit. In the event that generation of a cardioversion or defibrillation pulse is required, processor80may employ the escape interval counter to control timing of such cardioversion and defibrillation pulses, as well as associated refractory periods. In response to the detection of atrial or ventricular fibrillation or tachyarrhythmia requiring a cardioversion pulse, processor80may activate a cardioversion/defibrillation control module, which may, like pacer timing and control module, be a hardware component of processor80and/or a firmware or software module executed by one or more hardware components of processor80. The cardioversion/defibrillation control module may initiate charging of the high voltage capacitors of the high voltage charge circuit of signal generator84under control of a high voltage charging control line.

Processor80may monitor the voltage on the high voltage capacitor may be monitored, e.g., via a voltage charging and potential (VCAP) line. In response to the voltage on the high voltage capacitor reaching a predetermined value set by processor80, processor80may generate a logic signal that terminates charging. Thereafter, timing of the delivery of the defibrillation or cardioversion pulse by signal generator84is controlled by the cardioversion/defibrillation control module of processor80. Following delivery of the fibrillation or tachycardia therapy, processor80may return signal generator84to a cardiac pacing function and await the next successive interrupt due to pacing or the occurrence of a sensed atrial or ventricular depolarization.

Signal generator84may deliver cardioversion or defibrillation pulses with the aid of an output circuit that determines whether a monophasic or biphasic pulse is delivered, whether housing electrode34serves as cathode or anode, and which electrodes are involved in delivery of the cardioversion or defibrillation pulses. Such functionality may be provided by one or more switches or a switching module of signal generator84.

Telemetry module88includes any suitable hardware, firmware, software or any combination thereof for communicating with another device, such as programmer24(FIG. 1). Under the control of processor80, telemetry module88may receive downlink telemetry from and send uplink telemetry to programmer24with the aid of an antenna, which may be internal and/or external. Processor80may provide the data to be uplinked to programmer24and the control signals for the telemetry circuit within telemetry module88, e.g., via an address/data bus. In some examples, telemetry module88may provide received data to processor80via a multiplexer.

In some examples, processor80may transmit atrial and ventricular heart signals (e.g., electrocardiogram signals) produced by atrial and ventricular sense amp circuits within sensing module86to programmer24. Programmer24may interrogate IMD16to receive the heart signals. Processor80may store heart signals within memory82, and retrieve stored heart signals from memory82. Processor80may also generate and store marker codes indicative of different cardiac events that sensing module86detects, and transmit the marker codes to programmer24. An example pacemaker with marker-channel capability is described in U.S. Pat. No. 4,374,382 to Markowitz, entitled, “MARKER CHANNEL TELEMETRY SYSTEM FOR A MEDICAL DEVICE,” which issued on Feb. 15, 1983 and is hereby incorporated by reference in its entirety.

IMD16may also be configured, in various examples, to monitor other diagnostic parameters. In some examples, diagnostic unit92may receive signals or information from external sources, such as programmer24or an external sensor, such as a scale, and monitor such information or signals. Additionally, diagnostic unit92may receive information from processor80, or may maintain information in memory82, indicating percentage of CRT pacing. Diagnostic unit92or processor80may determine whether or not CRT pacing is delivered based on information from processor80of a pacer timing and control module thereof.

If diagnostic unit92detects worsening heart failure of patient14, diagnostic unit92may provide an alert to patient14. Diagnostic unit92may include or be coupled to an alert module (not shown) that provides, as examples, an audible or tactile alert to patient14of the worsening heart failure. In some examples, diagnostic unit92additionally or alternatively provide an indication of worsening heart failure to programmer24or another device via telemetry module88and/or network, which may provide an alert to a user, such as patient14or a clinician.

The various components of IMD16are coupled to power source90, which may include a rechargeable or non-rechargeable battery. A non-rechargeable battery may be capable of holding a charge for several years, while a rechargeable battery may be inductively charged from an external device, e.g., on a daily or weekly basis.

FIG. 4is block diagram of an example programmer24. As shown inFIG. 4, programmer24includes processor100, memory102, user interface104, telemetry module106, and power source108. In some examples, programmer24, as illustrated inFIG. 4, includes a diagnostic unit110. Programmer24may be a dedicated hardware device with dedicated software for programming of IMD16. Alternatively, programmer24may be an off-the-shelf computing device running an application that enables programmer24to program IMD16.

A user may use programmer24to select predetermined threshold zone for a given patient activity level characteristics, and select rules for detecting worsening heart failure in patient14based on the selected diagnostic parameters and predetermined threshold zone for a given patient activity level. A user may also use programmer24to configure other sensing or any therapy provided by IMD16. The clinician may interact with programmer24via user interface104, which may include display to present graphical user interface to a user, and a keypad or another mechanism for receiving input from a user.

Processor100can take the form one or more microprocessors, DSPs, ASICs, FPGAs, programmable logic circuitry, or the like, and the functions attributed to processor100herein may be embodied as hardware, firmware, software or any combination thereof. Diagnostic unit110, although illustrated as a separate module inFIG. 4, may be incorporated in a single processing unit with processor100or functional module executed or provided by processor100. Memory102may store instructions that cause processor100and/or diagnostic unit110to provide the functionality ascribed to programmer24herein, and information used by processor100and/or diagnostic unit110to provide the functionality ascribed to programmer24herein. Memory102may include any fixed or removable magnetic, optical, or electrical media, such as RAM, ROM, CD-ROM, hard or floppy magnetic disks, EEPROM, or the like. Memory102may also include a removable memory portion that may be used to provide memory updates or increases in memory capacities. A removable memory may also allow patient data to be easily transferred to another computing device, or to be removed before programmer24is used to program therapy for another patient. Memory102may also store information that controls operation of IMD16, such as therapy delivery values.

A user, such as a clinician, technician, or patient14, may interact with programmer24via user interface104. User interface106may include display to present graphical user interface to a user, and a keypad or another mechanism for receiving input from a user. In some examples, user interface106may include a touch screen display.

Programmer24may communicate wirelessly with IMD16, such as using RF communication or proximal inductive interaction. This wireless communication is possible through the use of telemetry module106, which may be coupled to an internal antenna or an external antenna. An external antenna that is coupled to programmer24may correspond to the programming head that may be placed over heart12, as described above with reference toFIG. 1. Telemetry module106may be similar to telemetry module88of IMD16(FIG. 3).

Programmer24may also be configured to communicate with another computing device via wireless communication techniques, or direct communication through a wired, e.g., network, connection. Examples of local wireless communication techniques that may be employed to facilitate communication between programmer24and another computing device include RF communication based on the 802.11 or Bluetooth specification sets, infrared communication, e.g., based on the IrDA standard.

Power source108delivers operating power to the components of programmer24. Power source108may include a battery and a power generation circuit to produce the operating power. In some embodiments, the battery may be rechargeable to allow extended operation. Recharging may be accomplished by electrically coupling power source108to a cradle or plug that is connected to an alternating current (AC) outlet. In addition or alternatively, recharging may be accomplished through proximal inductive interaction between an external charger and an inductive charging coil within programmer24. In other embodiments, traditional batteries (e.g., nickel cadmium or lithium ion batteries) may be used. In addition, programmer24may be directly coupled to an alternating current outlet to power programmer24. Power source108may include circuitry to monitor power remaining within a battery. In this manner, user interface104may provide a current battery level indicator or low battery level indicator when the battery needs to be replaced or recharged. In some cases, power source108may be capable of estimating the remaining time of operation using the current battery.

In some examples, IMD16may detect worsening heart failure using any of the techniques described herein, and provide an indication of worsening heart failure to programmer24. In such examples, programmer24need not include diagnostic module110. Processor100may control user interface106to provide an alert of worsening heart failure of patient14to the patient, a clinician, or other users. In some examples, processor100may provide an alert of worsening heart failure of patient14to one or more computing devices via a network. A user may use programmer24to retrieve and/or view data regarding diagnostic parameters.

In some examples, programmer24includes diagnostic module110that receives diagnostic data from IMD16, or other implanted or external sensors or devices, i.e., data regarding diagnostic parameters, and processes the received data to detect worsening heart failure in patient14. In this manner, diagnostic unit110may perform substantially the same functionality as described with respect to diagnostic unit92inFIG. 3. IMD16may not need to include diagnostic unit92in examples in which programmer24includes diagnostic unit110. Diagnostic unit110may include an alert module that provides an alert to patient14or a clinician via user interface104when worsening heart failure is detected in patient14, and/or provides a notification to one or more computing devices via a network.

Alerts provided via user interface104may include a silent, audible, visual, or tactile alert. For example, user interface104may emit a beeping sound, display a text prompt, cause various buttons or screens to flash, or vibrate to alert patient14or another user that a heart failure decompensation event may be likely to occur. Patient14may then seek medical attention, e.g., check in to a hospital or clinic, to receive appropriate treatment, or the other user may instruct patient14to do so.

Although illustrated and described in the context of examples in which programmer24is able to program the functionality of IMD16, in other examples a device capable of communicating with IMD16and providing functionality attributed to programmer24herein need not be capable of programming the functionality of the IMD. For example, an external home or patient monitor may communicate with IMD16for any of the purposes described herein, but need not independently be capable of programming the functionality of the IMD. Such as a device may be capable of communicating with other computing devices via a network, as discussed in greater detail below.

The components of and functionality provided by a diagnostic unit for detecting worsening heart failure are described in greater detail below with respect to diagnostic unit92of IMD16. However, it is understood that any diagnostic unit provided in any device, such as diagnostic unit110of programmer24, may include the same or similar components and provide the same or similar functionality.

FIG. 5is a block diagram of an example configuration of diagnostic unit92. As shown inFIG. 5, diagnostic unit92includes multiple components including diagnostic module120, electrode analysis unit122, and patient activity level unit124, and alert module128. Because either IMD16or programmer24may be configured to include a diagnostic unit, modules120,122,124, and128(and their sub-modules described below with reference toFIGS. 6-8) may be implemented in one or more processors, such as processor80of IMD16or processor100of programmer24. The modules of diagnostic unit92(and their sub-modules described below with reference toFIGS. 6-8) may be embodied as one or more hardware modules, software modules, firmware modules, or any combination thereof.

Generally, diagnostic module120processes data received from electrode analysis unit122and patient activity level unit124to detect worsening heart failure in patient14. Accordingly, electrode analysis unit122and patient activity level unit124may operate in a coordinated manner with diagnostic module120. In one example embodiment, diagnostic module120may retrieve timing information from memory126. The timing information may provide periodic intervals for monitoring a heart rate, a respiration rate and an activity level of a patient and detecting worsening heart failure based on the parameters. Accordingly, diagnostic module120may invoke electrode analysis unit122and patient activity level unit124based on the timing information. Alternatively, diagnostic module120may load the timing information into electrode analysis unit122and patient activity level unit124, and units122and124may monitor corresponding parameters according to the timing information.

Electrode analysis unit122monitors the intrathoracic impedance of patient14as previously described to monitor heart rate and respiration rate. That is, electrode analysis unit122may receive signals indicative of to monitor heart rate respiration rate, e.g., ECG information and/or intrathoracic impedance values. Although electrode analysis unit122is illustrated inFIG. 5, it should be understood that electrode analysis unit122is one example of a diagnostic parameter analysis units that may be utilized to monitor heart rate and respiration rate. In other example embodiments, diagnostic unit92may be configured to include, a pressure analysis unit that monitors one or more intrathoracic or cardiovascular pressures of patient14.

Patient activity level unit124monitors a patient activity level. As an example, patient activity level unit124may receive an input from one or more sensors, including, e.g., a 3-axis accelerometer, such as a piezoelectric and/or micro-electro-mechanical accelerometer that generates an output based on activity level.

Diagnostic module120processes data received from electrode analysis unit122and patient activity level unit124and compares the received data to a predetermined threshold zone that corresponds to baseline heart rates and respiration rates for a given activity level of a patient. Memory82may store an indication of predetermined threshold zone for a patient.

Diagnostic module120invokes alert module128in response to detecting worsening heart failure in patient14. Alert module128provides an alert to patient14by, for example, providing an audible, visual, or tactile alert. Alert module128may cause IMD16to emit a beeping a sound or vibrate. In some examples, alert module128may provide an alert by communicating with an external device, such as programmer24. In response to the communication from alert module128, programmer24may emit a beeping sound, display a text prompt, vibrate, or cause buttons and/or screens of programmer24to flash. Similarly, if the alert module is implemented in programmer24, alert module128may cause programmer24to send a telemetry signal to IMD16that causes IMD16to generate the alert.

In some examples, electrode analysis unit122may determine a current impedance value, a reference impedance value and fluid index value using any of the techniques described in a commonly-assigned commonly-assigned U.S. application Ser. No. 10/727,008 by Stadler et al., published as U.S. Patent Publication No. 2004/0172080 and entitled “METHOD AND APPARATUS FOR DETECTING CHANGE IN INTRATHORACIC IMPEDANCE,” filed on Dec. 3, 2003, which is hereby incorporated by reference in its entirety.

FIG. 6is a flow diagram illustrating an example method to detect worsening heart failure in a patient using a predetermined threshold zone for the patient. For clarity, the techniques shown inFIG. 6are discussed with respect to system10(FIGS. 1-5) and patient14(FIG. 1).

The techniques shown inFIG. 6necessitate establishing a predetermined threshold zone corresponding to a baseline heart rate (HRB) and baseline respiration rate (RRB) at multiple activity levels (AL) for patient14. In the example shown inFIG. 6, a clinician measures baseline heart rates and baseline respiration rates at a multitude of activity levels of patient14(202). Importantly, patient14should not be experiencing decompensation when the clinician measures the baseline heart rates and baseline respiration rates.

As one example, the clinician may measure a patient's baseline heart rates and baseline respiration rates in a controlled setting for multiple activity levels. Examples of different activity levels include sleeping, resting (e.g., reading or watching television), daily activity (e.g., walking or cooking) and high (consistent with exercise). The patient's activity level may be quantified in the controlled environment. As a further example, IMD16may record a series of data points representing measured heart rates, respiration rates and activity levels for over an initial programming period. For example, a clinician may program IMD16to record the series of data points representing measured heart rates, respiration rates and activity levels in an initial patient visit. In such an example, IMD16may record the measured heart rates, respiration rates and activity levels for a predetermined amount of time (e.g., 24 hours, 1 week, 1 month), until a suitable number of data points are recorded for each activity level or until a subsequent patient visit.

After measuring heart rates, respiration rates and activity levels of patient14, the measured heart rates, respiration rates and activity levels of patient14are used to define a predetermined threshold zone (TZ) which is a function of heart rate, respiration rate and activity level (204). As shown in Equation 1, the predetermined threshold zone can be represented as a function of heart rates, respiration rates and activity level.
TZ=F{HRB,RRB,AL}  Equation 1

As discussed in greater detail with respect toFIGS. 7A-7D, the predetermined threshold zone can be graphically represented as a continuous area within a three-dimensional space including dimensions representing heart rate, respiration rates and activity level of patient14.

Once calculated, the IMD16and/or programmer24store the predetermined threshold zone in memory (206). Once the predetermined threshold zone is stored in memory, system10is ready to begin monitoring patient14for worsening heart failure. As examples, after reviewing or imputing the predetermined threshold zone stored in memory of system10, the clinician may program IMD16to begin monitoring the heart rate, respiration rate and activity level of patient14(208) and comparing the monitored heart rate, respiration rate and activity level to the threshold zone (210). In order to prevent false alerts, IMD16may average a series of measurements of heart rate, respiration rate and activity level and compare the average heart rate, respiration rate and activity levels of the patient to the predetermined threshold zone. As examples, system10may average the heart rate, respiration rate and activity level of patient14measurements taken over a period of between five seconds and five minutes for comparison to the predetermined threshold zone. For example,10may average the heart rate, respiration rate and activity level of patient14measurements taken over a period of fifteen seconds, thirty seconds, one minute or two minutes for comparison to the predetermined threshold zone. System10continues to monitor heart rate, respiration rate and activity level unless and until one or more measurements are outside of the predetermined threshold zone.

In the event that, one or more measurements heart rate, respiration rate and activity level of patient14are outside of the predetermined threshold zone for patient14either IMD16or programmer24issues an alert to patient14(212). The alert may be audible, visual, or tactile and enables patient14to seek medical attention to treat the condition prior to experiencing a heart failure event, or a clinician to direct patient14to do so. In some examples, the alert may be a silent alert transmitted to another device associated with a clinician or other user, such as a silent alert transmitted to a server, as described below, and relayed to a physician via a computing device. In some examples, system10may continue to monitor heart rate, respiration rate and activity level even after issuing an alert.

In addition, in some examples system10may store monitored heart rate, respiration rate and activity level information. For example, system10may store the most recent monitored heart rate, respiration rate and activity level information, e.g., the most recent day, week or month of information depending on the amount of memory allocated to store monitored heart rate, respiration rate and activity level information. As another example, system10may store monitored heart rate, respiration rate and activity level information within a defined time period before and after determining that the heart rate, respiration rate and activity level unless are outside of the predetermined threshold zone.

FIGS. 7A-7Dare graphical representations of exemplary predetermined threshold zone272at different activity levels of a patient. Specifically,FIG. 7Aillustrates predetermined threshold zone272at a sleeping activity level;FIG. 7Billustrates predetermined threshold zone272at a resting (e.g., reading or watching television) activity level;FIG. 7Cillustrates predetermined threshold zone272at a daily activity (e.g., walking or cooking) activity level;FIG. 7Dillustrates predetermined threshold zone272at a and high (consistent with exercise) activity level. WhileFIGS. 7A-7Drepresent predetermined threshold zone272at discrete activity levels, predetermined threshold zone272may be considered to be a continuous zone including any activity level. For example, predetermined threshold zone272could be graphically represented as a continuous area within a three-dimensional space including dimensions representing heart rate, respiration rates and activity level. As represented inFIGS. 7A-7D, according to predetermined threshold zone272, a higher activity level corresponds to higher respiration rates and heart rates for the patient.

FIGS. 7A-7Dalso illustrate a series of data points representing baseline heart rates and respiration rates for a patient for each activity level. A representative data point in the series is indicated by reference numeral275inFIG. 7A. As an example, the series of data points shown inFIGS. 7A-7Dcould be produced as described with respect toFIG. 6and step202. The series of data points shown inFIGS. 7A-7Dcan be used to calculate predetermined threshold zone272.

In different examples, either IMD16, programmer24or an external device can be used to calculate the predetermined threshold zone272. Generally, a predetermined threshold zone includes a majority of the data points in the series of data points. For example, the predetermined threshold zone for a patient may include a substantially all of the data points in the series of data points. In addition, the predetermined threshold zone may extend beyond the majority of the data points in the series of data points. As an example, the series of data points may be used as a data set to define the predetermined threshold zone using statistical analysis. As one example, the predetermined threshold zone may extend to 1, 2 or 3 standard deviations from the data points in the series of data points. As another example, the predetermined threshold zone may include any area in which heart rate and/or respiration rate is actually lower than the majority of the data points in the series of data points for a given activity level of patient14as lower heart rate and/or respiration rate for a given activity level would not generally indicate worsening cardiac condition of patient14. In addition, the predetermined threshold zone may extend only a limited amount beyond the majority of the data points in the series of data points for a given activity level of patient14. For example, because a higher heart rate and/or respiration rate for a given activity level is an indication of worsening cardiac condition of patient14, the upper limits of heart rate and respiration rate dimensions of the predetermined threshold zone may be limited.

It should be noted that any suitable technique may be used to calculate the predetermined threshold zone for a patient. As an example, additional factors, including but not limited to patient medical history, family history, age, height, weight, body mass index, gender and race may also be used as inputs to calculate a predetermined threshold zone specifically for a patient.

FIG. 8is a block diagram illustrating an example system300that includes an external device, such as a server314, and one or more computing devices316A-316N (“computing devices316”) that are coupled to IMD16and programmer24shown inFIG. 1via a network312. In this example, IMD16may use its telemetry module88to communicate with programmer24via a first wireless connection, and to communication with an access point310via a second wireless connection. In the example ofFIG. 8, access point310, programmer24, server314, and computing devices316A-216N are interconnected, and able to communicate with each other, through network312. In some cases, one or more of access point310, programmer24, server314, and computing devices316A-316N may be coupled to network312through one or more wireless connections. IMD16, programmer24, server314, and computing devices316A-216N may each comprise one or more processors, such as one or more microprocessors, DSPs, ASICs, FPGAs, programmable logic circuitry, or the like, that may perform various functions and operations, such as those described herein. For example, as illustrated inFIG. 8, server314may comprise one or more processors315and an input/output device313, which need not be co-located.

Server314may, for example, monitor respiration rate, heart rate and activity level of patient14, e.g., based on signals or information received from IMD16and/or programmer24via network312, and compare the monitored levels to predetermined levels to detect worsening heart failure of patient14using any of the techniques described herein. Server314may provide alerts relating to worsening heart failure of patient16via network312to patient14via access point310, or to one or more clinicians via computing devices316. In examples such as those described above in which IMD16and/or programmer24monitor the respiration rate, heart rate and activity level, server314may receive an alert from the IMD or programmer via network312, and provide alerts to one or more clinicians via computing devices316. Server314may generate web-pages to provide alerts and information regarding diagnostic parameters, and may comprise a memory to store alerts and diagnostic or physiological parameter information for a plurality of patients.

Access point310may comprise a device that connects to network312via any of a variety of connections, such as telephone dial-up, digital subscriber line (DSL), or cable modem connections. In other embodiments, access point310may be coupled to network312through different forms of connections, including wired or wireless connections. Network312may comprise a local area network, wide area network, or global network, such as the Internet. System300may be implemented, in some aspects, with general network technology and functionality similar to that provided by the Medtronic CareLink® Network developed by Medtronic, Inc., of Minneapolis, Minn.

Additionally, using programmers24, access points310or computing devices316, physicians and/or event patients may input clinical information regarding the patients (such as symptoms, lab results, health care utilizations, etc.). Furthermore, the functionality described herein with respect to monitoring worsening heart failure may be provided by any one or more of the programmers24, access points310, server314, or computing devices316.

FIGS. 9A-9Bare graphical representations of a patient's heart rate and ventilation rate exceeding a predetermined threshold zone for the patient.FIG. 9Aillustrates predetermined threshold zone272at a sleeping activity level, andFIG. 9Billustrates predetermined threshold zone272at a resting activity level. While merely exemplary, predetermined threshold zone272is the same as predetermined threshold zone272as shown inFIGS. 7A-7D.

In addition,FIG. 9Aillustrates a series of data points representing heart rates and respiration rates for a patient at a sleeping activity level. A representative data point in the series is indicated by reference numeral475. As shown inFIG. 9A, some of the series of data points are outside of predetermined threshold zone272. This indicates that the patient is experiencing worsening heart failure and that a heart failure event, such as decompensation, may occur. As discussed in greater detail with respect toFIG. 6, an IMD monitoring the heart rate and respiration rate of the patient or a programmer may then issue an alert to the patient or a clinician. The alert may indicate that the patient should receive immediate care to mitigate the worsening heart failure.

Similar toFIG. 9A,FIG. 9Billustrates a series of data points representing heart rates and respiration rates for a patient at a resting activity level. A representative data point in the series is indicated by reference numeral477. Each some of the series of data points inFIG. 9Bare outside of predetermined threshold zone272. This indicates that the patient is experiencing worsening heart failure and that a heart failure event, such as decompensation, may occur. Accordingly, an alert may be issued indicating that the patient should receive immediate care to mitigate the worsening heart failure.

FIGS. 9A-9Bprovide example data points in which a patient's respiration rate and heart rate do not correspond to the patient's activity level in that the data points are outside predetermined threshold zone272. WhileFIGS. 9A-9Brepresent instances in which an alert should be issued, it is not necessary for a plurality of data points to be outside predetermined threshold zone272before an alert is issued. For example, an alert could be issued if only a single data point occurs outside predetermined threshold zone272. Other criteria for issuing an alert or for performing any other techniques to mitigate the worsening heart failure may also be used. As previously mentioned, other techniques to mitigate worsening heart failure include, but are not limited to, preparing to deliver a defibrillation pulse to the patient in preparation for a heart failure event, altering drug therapy to the patient, such as delivering diuretics to patient, and/or performing other techniques to mitigate worsening heart failure.

The techniques described in this disclosure, including those attributed to image IMD16, programmer24, or various constituent components, may be implemented, at least in part, in hardware, software, firmware or any combination thereof. For example, various aspects of the techniques may be implemented within one or more processors, including one or more microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), or any other equivalent integrated or discrete logic circuitry, as well as any combinations of such components, embodied in programmers, such as physician or patient programmers, stimulators, image processing devices or other devices. The term “processor” or “processing circuitry” may generally refer to any of the foregoing logic circuitry, alone or in combination with other logic circuitry, or any other equivalent circuitry.

When implemented in software, the functionality ascribed to the systems, devices and techniques described in this disclosure may be embodied as instructions on a computer-readable medium such as random access memory (RAM), read-only memory (ROM), non-volatile random access memory (NVRAM), electrically erasable programmable read-only memory (EEPROM), FLASH memory, magnetic data storage media, optical data storage media, or the like. The instructions may be executed to support one or more aspects of the functionality described in this disclosure.

Various examples have been described. However, one of ordinary skill in the art will appreciate that various modifications may be made to the described examples without departing from the scope of the claims. For example, although described primarily with reference to examples that provide an alert in response to detecting worsening heart failure, other examples may additionally or alternatively automatically modify a therapy in response to detecting worsening heart failure in the patient. The therapy may be, as examples, a substance delivered by an implantable pump, cardiac resynchronization therapy, refractory period stimulation, or cardiac potentiation therapy. These and other examples are within the scope of the following claims.