Detecting and responding to anti-tachyarrhythmia shocks

In some examples, an implantable medical device determines that another medical device delivered an anti-tachyarrhythmia shock, and delivers post-shock pacing in response to the determination. The implantable medical device may be configured to both detect the delivery of the shock in a sensed electrical signal and, if delivery of the shock is not detected, determine that the shock was delivered based on detection of asystole of the heart. The asystole may be detected based on the sensed electrical signal. In some examples, an implantable medical device is configured to revert from a post-shock pacing mode to a baseline pacing mode by iteratively testing a plurality of decreasing values of pacing pulse magnitude until loss of capture is detected. The implantable medical device may update a baseline value of the pacing pulse magnitude for the baseline mode based on the detection of loss of capture.

TECHNICAL FIELD

The disclosure relates generally to medical devices and, more particularly, medical devices configured to deliver post-shock pacing after delivery of an anti-tachyarrhythmia shock.

BACKGROUND

Implantable medical devices (IMDs), including implantable pacemakers and implantable cardioverter-defibrillators (ICDs), record cardiac electrogram (EGM) signals for sensing cardiac events, e.g., P-waves and R-waves. IMDs detect episodes of bradycardia, tachycardia and/or fibrillation from the sensed cardiac events, and respond to the episodes as needed with pacing therapy or high-voltage anti-tachyarrhythmia shocks, e.g., cardioversion or defibrillation shocks. Types of pacing therapy include bradycardia pacing, cardiac resynchronization therapy (CRT), anti-tachycardia pacing (ATP), which may attempted prior to resorting to an anti-tachyarrhythmia shock to terminate a tachyarrhythmia, and post-shock pacing, which may be delivered to help the heart recover from successful termination of a tachyarrhythmia by an anti-tachyarrhythmia shock.

Some IMDs include a can or housing that is implanted subcutaneously or submuscularly, and coupled to one or more intracardiac leads. Such IMDs may be capable of providing cardiac pacing and/or anti-tachyarrhythmia shock therapies via the one or more leads. However, other IMD configurations that avoid the use of intracardiac leads have been proposed. For example, an intracardiac pacing device (IPD) may be fully implantable within the heart, i.e., may include a housing and electrodes configured to be implanted in the heart. The IPD may be configured to deliver one or more types of pacing.

As another example, an extracardiovascular ICD system may include a can or housing that is implanted at a subcutaneous or submuscular location, and at least one lead implanted extracardiovascularly, e.g., subcutaneously or substernally. Extracardiovascular ICD systems deliver anti-tachyarrhythmia shocks, and may also be configured to deliver pacing pulses, using one or more electrodes on the lead and/or housing. However, the greater distance between the electrodes and the cardiac tissue, e.g., relative to the electrodes of an intracardiac lead or IPD, may necessitate greater pacing pulse magnitudes to capture the heart. Consequently, co-implantation of an extracardiovascular ICD system and IPD to provide shock and pacing therapies, respectively, has been proposed.

SUMMARY

In general, this disclosure is directed to techniques related to delivery of post-shock pacing. In some examples, the techniques enable an IMD, e.g., an IPD, to determine whether another medical device, e.g., an extracardiovascular ICD system, delivered an anti-tachyarrhythmia shock. Determining whether the other device delivered the shock may, for example, facilitate delivery of post-shock pacing in response to successful termination of a tachyarrhythmia by the shock.

The IMD is configured to determine whether the other medical device delivered the shock without communicating with the other medical device. The IMD may be configured to both detect the delivery of the shock in a sensed electrical signal and, if delivery of the shock is not detected, determine that the shock was delivered based on detection of asystole of the heart. The IMD may detect the asystole based on the sensed electrical signal, e.g., based on not detecting a cardiac depolarization within the signal for a threshold period of time. In this manner, the IMD may be able to provide post-shock pacing after an anti-tachyarrhythmia shock delivered by another medical device has terminated a tachyarrhythmia without receiving a communication indicating delivery of the shock from the other device, and in situations where the shock may not be reliably detected.

In some examples, an IMD, e.g., an IPD, is configured to revert from a post-shock pacing mode to a baseline pacing mode by iteratively testing decreasing values of pacing pulse magnitude until loss of capture is detected. The IMD may update a baseline value of the pacing pulse magnitude for the baseline mode based on the detection of loss of capture. The baseline pacing mode may be, for example, a bradycardia pacing mode. If one or more pulses at an initial reversion amplitude fail to capture the heart, the IMD may suspend reversion and continue to deliver post-shock pacing, e.g., for a period of time. In this manner, the IMD may revert to the baseline pacing mode at a time when the heart is ready for revision, and identify a baseline pacing magnitude suitable for the post-shock condition of the heart.

In one example, a method for an implantable medical device to revert from a post-shock pacing mode to a baseline pacing mode, wherein the baseline pacing mode specifies a baseline value of a pacing pulse magnitude, and the post-shock pacing mode specifies a post-shock value of the pacing pulse magnitude that is greater than the baseline value, the method comprises iteratively testing, by the implantable medical device delivering a plurality of pacing pulses to a heart of a patient, a plurality of values of the pacing pulse magnitude that decrease from an initial reversion value that is greater than the baseline value and less than the post-shock value. The method further comprises determining, by the implantable medical device, whether each of the plurality of values of the pacing pulse magnitude captures the heart and in response to determining that one of the plurality of values of the pacing pulse magnitude failed to capture the heart, updating, by the implantable medical device, the baseline value of the pacing pulse magnitude, and delivering, by the implantable medical device, pacing pulses having the updated baseline value of the pacing pulse magnitude according to the baseline pacing mode.

In another example, an implantable medical device comprises therapy delivery circuitry configured to deliver pacing pulses to a heart of a patient via a plurality of electrodes. The implantable medical device further comprises a memory configured to store a baseline value of a pacing pulse magnitude for delivery of pacing pulses according to a baseline pacing mode, a post-shock value of the pacing pulse magnitude for delivery of pacing pulses according to a post-shock pacing mode, wherein the post-shock value of the pacing pulse magnitude is greater than the baseline value, and an initial reversion value of the pacing pulse magnitude that is greater than the baseline value and less than the post-shock value. The implantable medical device further comprises processing circuitry configured to revert the implantable medical device from the post-shock pacing mode to the baseline pacing mode by at least: controlling the therapy delivery circuitry to deliver a plurality of pacing pulses to the heart to iteratively test a plurality of values of the pacing pulse magnitude that decrease from the initial reversion value; determining whether each of the plurality of values of the pacing pulse magnitude captured the heart; and in response to determining that one of the plurality of values of the pacing pulse magnitude failed to capture the heart: updating the baseline value of the pacing pulse magnitude; and controlling the therapy delivery circuitry to deliver pacing pulses having the updated baseline value of the pacing pulse magnitude according to the baseline pacing mode.

In another example, a method comprises sensing, by an implantable medical device, an electrical signal via a plurality of electrodes, determining, by the implantable medical device, that an amplitude of the electrical signal is above an anti-tachyarrhythmia shock threshold, and detecting, by the implantable medical device, delivery of a first anti-tachyarrhythmia shock by another medical device based on the determination. The method further comprises detecting, by the implantable medical device, asystole of the heart based on the electrical signal, and determining, by the implantable medical device, that the other medical device delivered a second anti-tachyarrhythmia shock based on the detection of asystole.

In another example, an implantable medical device comprises sensing circuitry configured to sense an electrical signal via a plurality of electrodes, and processing circuitry. The processing circuitry is configured to determine that an amplitude of the electrical signal is above an anti-tachyarrhythmia shock threshold, and detect delivery of an anti-tachyarrhythmia shock by another medical device based on the determination. The processing circuitry is further configured to detect asystole of the heart based on the electrical signal, and determine, without detecting the delivery of the anti-tachyarrhythmia shock, that the other medical device delivered the anti-tachyarrhythmia shock based on the detection of asystole.

In another example, an implantable medical device comprises therapy delivery circuitry configured to deliver pacing pulses to a heart of a patient via a plurality of electrodes, and sensing circuitry configured to sense an electrical signal via the plurality of electrodes. The implantable medical device further comprises a memory configured to store a baseline value of a pacing pulse magnitude for delivery of pacing pulses according to a baseline pacing mode, a post-shock value of the pacing pulse magnitude for delivery of pacing pulses according to a post-shock pacing mode, wherein the post-shock value of the pacing pulse magnitude is greater than the baseline value, and an initial reversion value of the pacing pulse magnitude that is greater than the baseline value and less than the post-shock value. The implantable medical device further comprises processing circuitry configured to control the therapy delivery circuitry to deliver pacing pulses having the baseline value of the pacing pulse magnitude according to the baseline pacing mode. The processing circuitry is further configured to determine that an amplitude of the electrical signal is above an anti-tachyarrhythmia shock threshold, and detect delivery of an anti-tachyarrhythmia shock by another medical device based on the determination. The processing circuitry is further configured to detect asystole of the heart based on the electrical signal, and determine, without detecting the delivery of the anti-tachyarrhythmia shock, that the other medical device delivered the anti-tachyarrhythmia shock based on the detection of asystole. The processing circuitry is further configured to, in response to either detecting the delivery of the anti-tachyarrhythmia shock by another medical device or determining, without detecting the delivery of the anti-tachyarrhythmia shock, that the other medical device delivered the anti-tachyarrhythmia shock, control the therapy delivery circuitry to switch to delivery of pacing pulses having the post-shock value of the pacing pulse magnitude according to the post-shock pacing mode. The processing circuitry is further configured to revert the implantable medical device from the post-shock pacing mode to the baseline pacing mode by at least controlling the therapy delivery circuitry to deliver a plurality of pacing pulses to the heart to iteratively test a plurality of values of the pacing pulse magnitude that decrease from the initial reversion value; determining whether each of the plurality of values of the pacing pulse magnitude captured the heart; and in response to determining that one of the plurality of values of the pacing pulse magnitude failed to capture the heart: updating the baseline value of the pacing pulse magnitude; and controlling the therapy delivery circuitry to deliver pacing pulses having the updated baseline value of the pacing pulse magnitude according to the baseline pacing mode.

In other examples, non-transitory computer-readable media comprise program instructions that, when executed by one or more programmable processors, cause the one or more programmable processors to perform any of the methods or techniques described herein.

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. The details of one or more aspects of the disclosure are set forth in the accompanying drawings and the description below.

DETAILED DESCRIPTION

In general, this disclosure describes example techniques related to delivery of post-shock pacing, including techniques for determining whether another medical device delivered an anti-tachyarrhythmia shock, and for reverting from a post-shock pacing mode to a baseline, e.g., bradycardia, pacing mode. In the following description, references are made to illustrative examples. It is understood that other examples may be utilized without departing from the scope of the disclosure.

FIG. 1A,FIG. 1B, andFIG. 1Care conceptual diagrams illustrating various views of an example implantable medical device (IMD) system8aimplanted within a patient14. IMD system8aincludes an extracardiovascular ICD system30aimplanted in patient14, and an intracardiac pacing device (IPD)16implanted within heart26of patient14.FIG. 1Ais a front view of IMD system8and patient14.FIG. 1Bis a side view of IMD system8and patient14.FIG. 1Cis a transverse view of IMD system8and patient14.

Referring toFIG. 1A, ICD system30aincludes an implantable cardiac defibrillator (ICD)9connected to at least one implantable cardiac defibrillation lead12a. ICD9is configured to deliver high-energy cardioversion or defibrillation pulses to a patient's heart when atrial or ventricular fibrillation is detected. Cardioversion shocks are typically delivered in synchrony with a detected R-wave when fibrillation detection criteria are met. Defibrillation pulses are typically delivered when fibrillation criteria are met, and the R-wave cannot be discerned from signals sensed by ICD9.

ICD9ofFIG. 1Ais implanted subcutaneously or submuscularly on the left side of patient14above the ribcage. Defibrillation lead12amay be implanted at least partially in a substernal location, e.g., between the ribcage and/or sternum22and heart26. In one such configuration, a proximal portion of lead12aextends subcutaneously from ICD9toward sternum22and a distal portion of lead12aextends superior under or below the sternum22in the anterior mediastinum36. The anterior mediastinum36is bounded laterally by the pleurae39(seeFIG. 1C), posteriorly by the pericardium, and anteriorly by the sternum22. In some instances, the anterior wall of the anterior mediastinum may also be formed by the transversus thoracis and one or more costal cartilages. The anterior mediastinum includes a quantity of loose connective tissue (such as areolar tissue), some lymph vessels, lymph glands, substernal musculature (e.g., transverse thoracic muscle), branches of the internal thoracic artery, and the internal thoracic vein. In one example, the distal portion of lead12aextends along the posterior side of the sternum22substantially within the loose connective tissue and/or substernal musculature of the anterior mediastinum. Lead12amay be at least partially implanted in other intrathoracic locations, e.g., other non-vascular, extra-pericardial locations, including the gap, tissue, or other anatomical features around the perimeter of and adjacent to, but not attached to, the pericardium or other portion of the heart and not above the sternum22or ribcage.

In other examples, lead12amay be implanted at other extracardiovascular locations. For example, defibrillation lead12amay extend subcutaneously above the ribcage from ICD9toward a center of the torso of patient14, bend or turn near the center of the torso, and extend subcutaneously superior above the ribcage and/or sternum22. Defibrillation lead12amay be offset laterally to the left or the right of the sternum22or located over the sternum22. Defibrillation lead12amay extend substantially parallel to the sternum22or be angled lateral from the sternum22at either the proximal or distal end.

Defibrillation lead12aincludes an insulative lead body having a proximal end that includes a connector34configured to be connected to ICD9and a distal portion that includes one or more electrodes. Defibrillation lead12aalso includes one or more conductors that form an electrically conductive path within the lead body and interconnect the electrical connector and respective ones of the electrodes.

Defibrillation lead12aincludes a defibrillation electrode that includes two sections or segments28aand28b, collectively (or alternatively) defibrillation electrode28. The defibrillation electrode28is toward the distal portion of defibrillation lead12a, e.g., toward the portion of defibrillation lead12aextending along the sternum22. Defibrillation lead12ais placed below and/or along sternum22such that a therapy vector between defibrillation electrodes28aor28band a housing electrode formed by or on ICD9(or other second electrode of the therapy vector) is substantially across a ventricle of heart26. The therapy vector may, in one example, be viewed as a line that extends from a point on defibrillation electrode28(e.g., a center of one of the defibrillation electrode sections28aor28b) to a point on the housing electrode of ICD9. Defibrillation electrode28may, in one example, be an elongated coil electrode.

Defibrillation lead12amay also include one or more sensing electrodes, such as sensing electrodes32aand32b(individually or collectively, “sensing electrode(s)32”), located along the distal portion of defibrillation lead12a. In the example illustrated inFIG. 1AandFIG. 1B, sensing electrodes32aand32bare separated from one another by defibrillation electrode28a. In other examples, however, sensing electrodes32aand32bmay be both distal of defibrillation electrode28or both proximal of defibrillation electrode28. In other examples, lead12amay include more or fewer electrodes at various locations proximal and/or distal to defibrillation electrode28. In the same or different examples, ICD9may include one or more electrodes on another lead (not shown).

ICD system30amay sense electrical signals via one or more sensing vectors that include combinations of electrodes32aand32band the housing electrode of ICD9. In some instances, ICD9may sense cardiac electrical signals using a sensing vector that includes one of the defibrillation electrode sections28aand28band one of sensing electrodes32aand32bor the housing electrode of ICD9. The sensed electrical intrinsic signals may include electrical signals generated by cardiac muscle and indicative of depolarizations and repolarizations of heart26at various times during the cardiac cycle. ICD9analyzes the electrical signals sensed by the one or more sensing vectors to detect tachyarrhythmia, such as ventricular tachycardia or ventricular fibrillation. In response to detecting the tachyarrhythmia, ICD9may begin to charge a storage element, such as a bank of one or more capacitors, and, when charged, deliver one or more defibrillation pulses via defibrillation electrode28of defibrillation lead12aif the tachyarrhythmia is still present.

In the example ofFIG. 1A, IPD16is implanted within the right ventricle of heart26to sense electrical activity of heart26and deliver pacing therapy, e.g., anti-tachycardia pacing (ATP) therapy, bradycardia pacing therapy, and/or post-shock pacing, to heart26. IPD16may be attached to an interior wall of the tight ventricle of heart26via one or more fixation elements that penetrate the tissue. These fixation elements may secure IPD16to the cardiac tissue and retain an electrode (e.g., a cathode or an anode) in contact with the cardiac tissue. However, in other examples, system8may include additional pacing devices16within respective chambers of heart26(e.g., right or left atrium and/or left ventricle). In further examples, IPD16may be attached to an external surface of heart26(e.g., in contact with the epicardium) such that IPD16is disposed outside of heart26.

IPD16may be capable sensing electrical signals using the electrodes carried on the housing of IPD16. These electrical signals may be electrical signals generated by cardiac muscle and indicative of depolarizations and repolarizations of heart26at various times during the cardiac cycle. IPD16may analyze the sensed electrical signals to detect bradycardia and tachyarrhythmias, such as ventricular tachycardia or ventricular fibrillation. In response to detecting the bradycardia, IPD16may deliver bradycardia pacing via the electrodes of IPD16. In response to detecting tachyarrhythmia, IPD16may, e.g., depending on the type of tachyarrhythmia, deliver ATP therapy via the electrodes of IPD16. In some examples, as described in greater detail herein, IPD16may additionally or alternatively deliver post-shock pacing in response to determining that another medical device, e.g., ICD system30a, delivered an anti-tachyarrhythmia shock.

IPD16and ICD system30amay be configured to operate completely independently of one another. In such a case, IPD16and ICD system30aare not capable of establishing telemetry communication sessions with one another to exchange information about sensing and/or therapy using one-way or two-way communication. Instead, each of IPD16and ICD system30aanalyze the data sensed via their respective electrodes to make tachyarrhythmia detection and/or therapy decisions. As such, each device does not know if the other will detect the tachyarrhythmia, if or when it will provide therapy, and the like.

During a tachyarrhythmia that could be treated with either ATP or an anti-tachyarrhythmia shock, it may be preferred that anti-tachyarrhythmia therapies do not overlap or that ATP therapy does not take place after the defibrillation pulse. Moreover, it would be desirable for IPD16to deliver post-shock pacing after delivery of a cardioversion/defibrillation pulse. Consequently, IPD16and ICD system30amay be configured to coordinate their arrhythmia detection and treatment activities.

In some examples, IPD16and ICD system30amay engage in communication to facilitate the appropriate detection of arrhythmias and/or delivery of therapy. The communication may include one-way communication in which one device is configured to transmit communication messages and the other device is configured to receive those messages. The communication may instead include two-way communication in which each device is configured to transmit and receive communication messages. Two-way communication and coordination of the delivery of patient therapies between IPD16and ICD system30is described in commonly-assigned U.S. Pat. No. 8,744,572 to Greenhut et al., titled, “SYSTEMS AND METHODS FOR LEADLESS PACING AND SHOCK THERAPY,” and issued Jun. 3, 2014, the entire content of which is incorporated by reference herein.

However, device-to-device communication between ICD system30and IPD16, but this may add complexity to the system and not be highly effective, e.g., not be fast enough in response time to prevent unwanted delivery of ATP after a defibrillation shock, or too slow to initiate post-shock pacing therapies at a preferred time post shock. In some examples described herein, IPD16may be configured to detect anti-tachyarrhythmia shocks delivered by ICD9, which improve the coordination of therapy between subcutaneous ICD9and IPD16without requiring device-to-device communication.

IPD16may be configured to detect an anti-tachyarrhythmia shock delivered by ICD system30or an external defibrillator according to the detection of an electrical signal across two or more electrodes of IPD16. IPD16may be configured to detect an anti-tachyarrhythmia shock based on electrical characteristics of the anti-tachyarrhythmia shock. Even though different defibrillation devices may provide different waveforms, including different pulse durations and amplitudes, defibrillation pulses generally have electrical signal characteristics such that detection of an anti-tachyarrhythmia shock can occur even without prior knowledge as to an anti-tachyarrhythmia shock waveform of an implanted or external defibrillator. In this manner, IPD16may coordinate the delivery of cardiac stimulation therapy, including the termination of ATP and the initiation of the delivery of post-shock pacing, with the application of an anti-tachyarrhythmia shock merely through the detection of defibrillation pulses and without the need to communicate with the defibrillation device applying the anti-tachyarrhythmia shock.

In some examples, IPD16detects the anti-tachyarrhythmia shock by measuring the voltage across the electrode inputs of the implanted device. IPD16may detect one or more signal characteristics of an anti-tachyarrhythmia shock including: detection of the high amplitude level of an anti-tachyarrhythmia shock, detection of a high slew rate of the leading and trailing edges, and detection of a large post-shock polarization change. Detection of more than one signal characteristic may improve sensitivity and/or specificity. For example, IPD16may detect a high level of an anti-tachyarrhythmia shock in combination with one or both of the detection of a high slew rate of the leading and trailing edges, and the detection of a large post-shock polarization change. In general, IPD16may detect an anti-tachyarrhythmia shock by detecting an amplitude of a signal above a shock threshold. An amplitude of the signal may include an amplitude of a derivative of the signal.

In one example, IPD16may be configured to receive an indication of a detected cardiac arrhythmia eligible for anti-tachyarrhythmia shock therapy. IPD16may include a set of electrodes configured to be implanted within or near heart26of patient14. In response to receiving the indication of the tachyarrhythmia, IPD16may enable shock detection circuitry of IPD16configured to detect delivery of anti-tachyarrhythmia shock therapy. The shock detection circuitry of IPD16may then detect delivery of anti-tachyarrhythmia shock therapy by measuring the voltage across the electrode inputs (e.g., detect that the shock has been delivered). The shock detection circuitry may apply one or more of the below-identified general techniques for detection of an anti-tachyarrhythmia shock that generally include detection of an amplitude of the signal above a shock threshold: detection of the high level of an anti-tachyarrhythmia shock, detection of a high slew rate of the leading and trailing edges, and detection of a large post-shock polarization change.

In response to detection of the anti-tachyarrhythmia shock, the IPD16may abort and/or temporarily suspend the delivery of ATP and to activate post-shock pacing, such as VVI (Ventricular sensing, Ventricular pacing, Inhibited pacing when activity sensed) post-shock pacing. ATP may remain suspended temporarily following an anti-tachyarrhythmia shock to ensure that the relatively higher-rate pacing pulses will not induce another arrhythmia. Additionally, post-shock pacing may be used to ensure pacing support if the patient's heart does not begin to beat normally immediately following an anti-tachyarrhythmia shock.

IPD16may deliver post-shock pacing according to a post-shock pacing mode. The post-shock pacing mode may specify a higher than normal pacing pulse magnitude (relative to typical cardiac pacing), e.g., higher than normal pulse amplitude and/or pulse width, to minimize the risk of loss of capture following an anti-tachyarrhythmia shock. A higher capture threshold may occur as a result of tissue stunning due to elevated current in the myocardial tissue from the anti-tachyarrhythmia shock delivery. A higher threshold may also occur as a result of physiological changes in the tissue resulting from lack of blood flow to the myocardium during ventricular fibrillation (VF). Furthermore, after an anti-tachyarrhythmia shock there can be increased polarization at the lead interface resulting in the need for a higher magnitude to overcome the lead polarization. In some examples, the post-shock pacing mode may specify a value for a timer, used by IPD16to control how long post-shock pacing is delivered after delivery of the shock.

In some examples, in addition to being configured to detect the shock in the sensed electrical signal, IPD16may be configured to determine that another medical device, e.g., ICD system30a, delivered a shock based on detecting asystole. IPD16may detect asystole based on the sensed electrical signal, e.g., based on not detecting a depolarization of heart26within an asystole threshold period of time. IPD16may compare the asystole threshold to a period of time beginning upon a most recent depolarization of heart26, detection of a tachyarrhythmia, or termination of delivery of ATP by IPD16, as examples.

In some examples IPD16detects a tachyarrhythmia based on the electrical signal sensed via at least a subset of its electrodes, and begins shock detection and asystole detection in response to detecting the tachyarrhythmia. In some examples, IPD16delivers ATP in response to detection the tachyarrhythmia, and begins shock detection and asystole detection in response to end the delivery of ATP. In some examples, IPD16determines that a shock was delivered by another medical device based on detecting asystole within a threshold period of time following detection of a tachyarrhythmia. Being configured to both detect a shock, and determine that a shock was delivered based on asystole, may allow IPD16to provide post-shock pacing in situations in which16and extracardiovascular ICD system30ado not communicate, and IPD16is unable to reliably detect delivery of a shock by ICD system30a.

IPD16may also re-start post-shock pacing if IPD16determines that additional shocks have been delivered. For example, IPD16may be configured to begin delivery of post-shock pacing after delivery of a first shock. IPD16may subsequently identify delivery of a second shock, and, in response to the detection of the second shock, re-start delivery of the post-shock pacing if needed. IPD16may continue to re-start post-shock pacing as long as additional shocks are delivered.

In some examples, IPD16may terminate post-shock pacing in response to various indicators. For example, IPD16may track a period of time following the start of post-shock pacing. IPD16may then determine that the period of time exceeds a timeout threshold. For example, IPD16may use a timer to track this period of time. In response to the determination, IPD16may terminate delivery of post-shock pacing. In other examples, IPD16may terminate post-shock pacing after delivery of a predetermined number of pacing pulses. Alternatively, IPD16may terminate post-shock pacing in response to detection of a normal sinus rhythm or receiving a communication from system30instructing IPD16to terminate post-shock pacing.

After terminating post-shock pacing according to a post-shock pacing mode, IPD16may revert to a baseline pacing mode, such as bradycardia pacing. To revert to the baseline pacing mode, IPD16may iteratively test a plurality of decreasing values of pacing pulse magnitude until loss of capture is detected. IPD16may update a baseline pacing pulse magnitude for the baseline pacing mode based on the loss of capture, e.g., based on a pacing pulse magnitude immediately prior to the pacing pulse magnitude that failed to capture heart26according to the decreasing progression of pacing pulse magnitudes.

External device21may be configured to communicate with one or both of ICD system30aand IPD16. In examples where external device21only communicates with one of ICD system30aand IPD16, the non-communicative device may receive instructions from or transmit data to the device in communication with device21. In some examples, external device21comprises a handheld computing device, computer workstation, or networked computing device. External device21may include a user interface that receives input from a user. In other examples, the user may also interact with device21remotely via a networked computing device. The user may interact with external device21to communicate with IPD16and/or ICD system30.

For example, the user may interact with external device21to send an interrogation request and retrieve sensed physiological data or therapy delivery data stored by one or both of IPD16and ICD system30a, and program or update therapy parameters that define therapy, or perform any other activities with respect to IPD16and/or ICD system30a. Although the user is a physician, technician, surgeon, electrophysiologist, or other healthcare professional, the user may be patient14in some examples. For example, external device21may allow a user to program any thresholds, e.g., amplitudes or interval, or other data described herein as being used by IPD16to detect tachyarrhythmias, shocks and/or asystole, and may program any parameters described herein that control the delivery of pacing, including baseline (e.g., bradycardia) pacing and post-shock pacing by IPD16.

External device21may communicate with IPD16and/or ICD system30avia wireless communication using any techniques known in the art. Examples of communication techniques may include, for example, proprietary and non-proprietary radiofrequency (RF) telemetry, but other techniques are also contemplated. In some examples, external device21may include a programming head that may be placed proximate to the patient's body near the IPD16and/or ICD system30aimplant site in order to improve the quality or security of communication between IPD16and/or ICD system30aand device21.

AlthoughFIGS. 1A-1Care shown or described in the context of IPD16and extracardiovascular ICD system30athat includes lead12awith a substernally placed distal portion, techniques in accordance with one or more aspects of the present disclosure may be applicable to other coexistent systems. For example, an extracardiovascular ICD system may include a lead having a distal portion that is implanted subcutaneously above the sternum (or other location) instead of being implanted substernally. As another example, instead of an IPD, a pacing system may be implanted having a pacemaker and one or more leads connected to and extending from the pacemaker into one or more chambers of the heart or attached to the outside of the heart to provide pacing therapy to the one or more chambers. As such, the example ofFIGS. 1A-1Cis illustrated for example purposes only and should not be considered limiting of the techniques described herein.

FIG. 2is a front view of another example medical device system8bthat includes an extracardiovascular ICD system30band IPD16implanted within a patient. Medical device system8bmay be configured to perform any of the techniques described herein with respect to medical device system8aofFIGS. 1A-1C. For example, IPD16may be both configured to detect shocks delivered by extracardiovascular ICD system30bin a sensed electrical signal, and determine whether a shock was delivered by extracardiovascular ICD system30bbased on detecting asystole. IPD16may also be configured to revert from a post-shock pacing mode to a baseline pacing mode, as described herein. Components with like numbers inFIGS. 1A-1CandFIG. 2may be similarly configured and provide similar functionality.

In the example ofFIG. 2, extracardiovascular ICD system30bincludes ICD9coupled to a defibrillation lead12b. Unlike defibrillation lead12aofFIGS. 1A-1C, defibrillation lead12bextends subcutaneously above the ribcage from ICD9. In the illustrated example, defibrillation lead12bextends toward a center of the torso of patient14, bends or turns near the center of the torso, and extends subcutaneously superior above the ribcage and/or sternum22. Defibrillation lead12bmay be offset laterally to the left or the right of sternum22or located over sternum22. Defibrillation lead12bmay extend substantially parallel to sternum22or be angled lateral from the sternum at either the proximal or distal end.

Defibrillation lead12bincludes an insulative lead body having a proximal end that includes a connector34configured to be connected to ICD9and a distal portion that includes one or more electrodes. Defibrillation lead12balso includes one or more conductors that form an electrically conductive path within the lead body and interconnect the electrical connector and respective ones of the electrodes. In the illustrated example, defibrillation lead12bincludes a single defibrillation electrode28toward the distal portion of defibrillation lead12b, e.g., toward the portion of defibrillation lead12bextending along sternum22. Defibrillation lead12bis placed along sternum such that a therapy vector between defibrillation electrode28and a housing electrode formed by or on ICD9(or other second electrode of the therapy vector) is substantially across a ventricle of heart26.

Defibrillation lead12bmay also include one or more sensing electrodes, such as sensing electrodes32aand32b, located along the distal portion of defibrillation lead12b. In the example illustrated inFIG. 2, sensing electrodes32aand32bare separated from one another by defibrillation electrode28. In other examples, however, sensing electrodes32aand32bmay be both distal of defibrillation electrode28or both proximal of defibrillation electrode28. In other examples, lead12bmay include more or fewer electrodes at various locations proximal and/or distal to defibrillation electrode28, and lead12bmay include multiple defibrillation electrodes, e.g., defibrillation electrodes28aand28bas illustrated in the example ofFIGS. 1A-1C. IPD16may be configured to detect shocks delivered by ICD9via lead12b, or determine that shocks were delivered based on detect asystole.

FIG. 3is a conceptual drawing illustrating an example configuration of IPD16that may utilize the shock detection and asystole detection techniques of this disclosure, as well as the post-shock pacing mode reversion techniques of this disclosure. As shown inFIG. 3, IPD16includes case50, cap58, electrode60, electrode52, fixation mechanisms62, flange54, and opening56. Together, case50and cap58may be considered the housing of IPD16. In this manner, case50and cap58may enclose and protect the various electrical components within IPD16. Case50may enclose substantially all of the electrical components, and cap58may seal case50and create the hermetically sealed housing of IPD16. Although IPD16is generally described as including one or more electrodes, IPD16may typically include at least two electrodes (e.g., electrodes52and60) to deliver an electrical signal (e.g., therapy such as ATP) and/or provide at least one sensing vector.

Electrodes52and60are carried on the housing created by case50and cap58. In this manner, electrodes52and60may be considered leadless electrodes. In the example ofFIG. 3, electrode60is disposed on the exterior surface of cap58. Electrode60may be a circular electrode positioned to contact cardiac tissue upon implantation. Electrode52may be a ring or cylindrical electrode disposed on the exterior surface of case50. Both case50and cap58may be electrically insulating.

Electrode60may be used as a cathode and electrode52may be used as an anode, or vice versa, for delivering cardiac pacing such as bradycardia pacing, ATP, or post-shock pacing. However, electrodes52and60may be used in any stimulation configuration. In addition, electrodes52and60may be used to detect intrinsic electrical signals from cardiac muscle as well as asystole (i.e., the absence of cardiac depolarizations) and shocks delivered by another medical device, e.g., ICD systems30aand30bofFIGS. 1A-2. Cardiac pacing delivered by IPD16, as compared with alternative devices, may be considered to be “painless” to patient14or even undetectable by patient14since the electrical stimulation occurs very close to or at cardiac muscle and at relatively low energy levels.

Fixation mechanisms62may attach IPD16to cardiac tissue. Fixation mechanisms62may be active fixation tines, screws, clamps, adhesive members, or any other mechanisms for attaching a device to tissue. As shown in the example ofFIG. 3, fixation mechanisms62may be constructed of a memory material, such as a shape memory alloy (e.g., nickel titanium), that retains a preformed shape. During implantation, fixation mechanisms62may be flexed forward to pierce tissue and allowed to flex back towards case50. In this manner, fixation mechanisms62may be embedded within the target tissue.

Flange54may be provided on one end of case50to enable tethering or extraction of IPD16. For example, a suture or other device may be inserted around flange54and/or through opening56and attached to tissue. In this manner, flange54may provide a secondary attachment structure to tether or retain IPD16within heart26if fixation mechanisms62fail. Flange54and/or opening56may also be used to extract IPD16once the IPD needs to be explanted (or removed) from patient14if such action is deemed necessary.

The techniques described herein are generally described with regard to a leadless pacing device or intracardiac pacing device such as IPD16. IPD16may be an example of a pacing device configured to implement the techniques of this disclosure. However, other implantable medical devices may be used to perform the same or similar functions as IPD16, e.g., determining whether another device delivered an anti-tachyarrhythmia shock and reverting from a post-shock pacing mode to a baseline pacing mode.

For example, an IPD may include a small housing that carries an electrode, similar to IPD16, and configured to be implanted within a chamber of heart26. The IPD may also include one or more relatively short leads configured to place one or more respective additional electrodes at another location within the same chamber of the heart or a different chamber of the heart. In this manner, the housing of the IPD may not carry all of the electrodes used to perform functions described herein with respect to IPD16. In other examples, each electrode of the IPD may be carried by one or more leads (e.g., the housing of the IPD may not carry any of the electrodes). In some examples, an IPD or other pacing device may include or be coupled to three or more electrodes, where each electrode may deliver therapy and/or detect intrinsic signals.

In another example, a pacing device may be configured to be implanted external to heart26, e.g., near or attached to the epicardium of heart26. An electrode carried by the housing of the pacing may be placed in contact with the epicardium and/or one or more electrodes of leads coupled to the pacing may be placed in contact with the epicardium at locations sufficient to provide cardiac pacing. In still other examples, a pacing device configured to perform the techniques described herein may be implanted subcutaneously or submuscularly, and connected to one or more intracardiac leads carrying one or more electrodes.

FIG. 4is a functional block diagram illustrating an example configuration of IPD16. In the illustrated example, IPD16includes a processing circuitry80and an associated memory82, therapy delivery circuitry84, sensing circuitry86, shock detection circuitry88, and communication circuitry94. Memory82includes computer-readable instructions that, when executed by processing circuitry80, cause IPD16and processing circuitry80to perform various functions attributed to IPD16and processing circuitry80herein (e.g., delivering baseline pacing, detecting arrhythmias, delivering ATP, determining that another device delivered a shock, delivering post-shock pacing, and reverting from post-shock pacing to baseline pacing). 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 or analog media.

Processing circuitry80controls therapy delivery circuitry84to deliver cardiac pacing pulses to heart26according to therapy parameters, including pacing mode parameters90, which may be stored in memory82. For example, processing circuitry80may control therapy delivery circuitry84to deliver electrical pulses with the magnitudes (e.g., amplitudes and pulse widths), frequency, and polarities of electrodes52and60specified by the therapy parameters. In the illustrated example, therapy delivery circuitry84is electrically coupled to electrodes52and60carried on the housing of IPD16.

Pacing mode parameters90include parameters that define how IPD16delivers cardiac pacing according a plurality of pacing modes, e.g., as controlled by processing circuitry80. The pacing modes may include a baseline pacing mode, which may be bradycardia pacing, an ATP mode, and a post-shock pacing mode. Pacing mode parameters90may also define how IPD16reverts from the post-shock pacing mode to the baseline pacing mode.

ATP pacing mode parameters may include a pulse interval defined based on a fraction of a detected ventricular tachycardia (VT) cycle length. The interval may be between approximately 150 milliseconds and 500 milliseconds (e.g., between approximately 2.0 hertz and 7.0 hertz), and a pulse width may be between approximately 0.5 milliseconds and 2.0 milliseconds. The amplitude of each pacing pulse may be between approximately 2.0 volts and 10.0 volts. In some examples, the pulse amplitude may be approximately 6.0 V and the pulse width may be approximately 1.5 milliseconds; another example may include pulse amplitudes of approximately 5.0 V and pulse widths of approximately 1.0 milliseconds. Each train of pulses during ATP may last for a duration of between approximately 0.5 seconds to approximately 15 seconds or be defined as a specific number of pulses. Each pulse, or burst of pulses, may include a ramp up in amplitude or in pulse rate. In addition, trains of pulses in successive ATP periods may be delivered at increasing pulse rate in an attempt to capture the heart and terminate the tachycardia. Example ATP parameters and other criteria involving the delivery of ATP are described in U.S. Pat. No. 6,892,094 to Ousdigian et al., entitled, “COMBINED ANTI-TACHYCARDIA PACING (ATP) AND HIGH VOLTAGE THERAPY FOR TREATING VENTRICULAR ARRHYTHMIAS,” and issued on May 10, 2005, the entire content of which is incorporated herein by reference.

Pacing mode parameters90may also define parameters for a post-shock pacing mode, such as a post-shock value of pacing pulse magnitude. In one example, monophasic post-shock pacing therapy may have a pulse width of approximately 1 millisecond at each phase and a pulse amplitude of approximately 5 volts. The pacing rate may be set to 30-60 beats per minute (0.5-1 hertz). The duration of each post-shock pacing session may be between 10 seconds and 60 seconds, or even longer in other examples. Pacing mode parameters90for the post-shock pacing mode may include an interval or period that defines the duration of each post-shock pacing session. The post-shock value of pacing pulse magnitude may be set to the greatest pacing pulse magnitude value at which IPD16is configurable to deliver pacing pulses.

Pacing mode parameters90may also define parameters for a baseline pacing mode, such as bradycardia pacing, including a baseline value of the pacing pulse magnitude, e.g., pulse amplitude and/or pulse width. Processing circuitry80may perform capture management to determine the baseline value of pacing pulse magnitude. For example, processing circuitry80may determine whether pacing pulses delivered according to the baseline pacing mode captured heart26and, if loss of capture is detected, increase the pacing pulse magnitude until the heart is captured. Processing circuitry80may periodically control therapy delivery circuitry84to deliver one or more pacing pulses having a magnitude below the baseline value, and determine whether the lower magnitude pacing pulse captured heart26. If the lower magnitude pacing pulse(s) capture heart26, processing circuitry80may accordingly lower the baseline value of pacing pulse magnitude. The pacing mode parameters90for the baseline pacing mode may also include parameters that control the timing of pacing pulse delivery relative to a sensed cardiac depolarization.

Therapy delivery circuitry84may include charging circuitry, one or more charge storage devices, such as one or more capacitors, and switching circuitry that controls when the capacitor(s) are discharged to electrodes52and60and the width of pacing pulses. Charging of capacitors to a programmed pacing pulse amplitude and discharging of the capacitors for a programmed pulse width may be performed by therapy delivery circuitry84according to control signals received from processing circuitry80, which are provided by processing circuitry80according to pacing mode parameters90stored in memory82.

Electrical sensing circuitry86monitors signals from electrodes52and60in order to monitor electrical activity of heart26, impedance, or other electrical phenomenon. Sensing may be done to determine heart rates or heart rate variability, or to detect arrhythmias (e.g., tachyarrhythmias or bradycardia) or other electrical signals. In some examples, sensing circuitry86may include one or more filters and amplifiers for filtering and amplifying a signal received from electrodes52and60. The resulting cardiac electrical signal may be passed to cardiac event detection circuitry that detects a cardiac event when the cardiac electrical signal crosses a sensing threshold. The cardiac event detection circuitry may include a rectifier, filter and/or amplifier, a sense amplifier, comparator, and/or analog-to-digital converter. Sensing circuitry86outputs an indication to processing circuitry80in response to sensing of a cardiac event (e.g., detected P-waves or R-waves). In this manner, processing circuitry80may receive detected cardiac event signals corresponding to the occurrence of detected R-waves and P-waves in the respective chambers of heart26. Indications of detected R-waves and P-waves may be used for detecting ventricular and/or atrial tachyarrhythmia episodes, e.g., ventricular or atrial fibrillation episodes. Some detection channels may be configured to detect cardiac events, such as P- or R-waves, and provide indications of the occurrences of such events to processing circuitry80, e.g., as 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 incorporated herein by reference in its entirety.

Sensing circuitry86may also include a switch module to select which of the available electrodes (or electrode polarities) are used to sense the heart activity. In examples with several electrodes, processing circuitry80may select the electrodes that function as sense electrodes, i.e., select the sensing configuration, via the switch module within sensing circuitry86. Sensing circuitry86may also pass one or more digitized EGM signals to processing circuitry80for analysis, e.g., for use in cardiac rhythm discrimination.

Processing circuitry80may implement programmable counters. If IPD16is configured to generate and deliver pacing pulses to heart26, such counters may control the basic time intervals associated with bradycardia pacing (e.g., DDD, VVI, DVI, VDD, AAI, DDI, DDDR, VVIR, DVIR, VDDR, AAIR, DDIR pacing) and other modes of pacing. Intervals defined by processing circuitry80may 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, and the pulse widths of the pacing pulses. The durations of these intervals may be determined by processing circuitry80in response to pacing mode parameters90in memory82.

Interval counters implemented by processing circuitry80may be reset upon sensing of R-waves and P-waves with detection channels of sensing circuitry86. In examples in which IPD16provides pacing, therapy delivery circuitry84may include pacer output circuits that are coupled to electrodes52and60, for example, and are appropriate for delivery of a bipolar or unipolar pacing pulse to one of the chambers of heart26. In such examples, processing circuitry80may reset the interval counters upon the generation of pacing pulses by therapy delivery circuitry84, and thereby control the basic timing of cardiac pacing functions, including baseline or bradycardia pacing, ATP, or post-shock pacing.

The value of the count present in the interval counters when reset by sensed R-waves and P-waves may be used by processing circuitry80to measure the durations of R-R intervals, P-P intervals, P-R intervals and R-P intervals, which are measurements that may be stored in memory82. Processing circuitry80may use the count in the interval counters to detect a tachyarrhythmia event, such as atrial fibrillation (AF), atrial tachycardia (AT), VF, or VT. These intervals may also be used to detect the overall heart rate, ventricular contraction rate, and heart rate variability. A portion of memory82may be configured as a plurality of recirculating buffers, capable of holding series of measured intervals, which may be analyzed by processing circuitry80in response to the occurrence of a pace or sense interrupt to determine whether the patient's heart26is presently exhibiting atrial or ventricular tachyarrhythmia.

In some examples, an arrhythmia detection method may include any suitable tachyarrhythmia detection algorithms. In one example, processing circuitry80may 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. U.S. Pat. No. 5,755,736 to Gillberg et al. is incorporated herein by reference in their entireties. However, other arrhythmia detection methodologies, such as those methodologies that utilize timing and morphology of the electrocardiogram, may also be employed by processing circuitry80in other examples.

In some examples, processing circuitry80may determine that tachyarrhythmia has occurred by identification of shortened R-R (or P-P) interval lengths. Generally, processing circuitry80detects tachycardia when the interval length falls below 220 milliseconds and fibrillation when the interval length falls below 180 milliseconds. In other examples, processing circuitry80may detect ventricular tachycardia when the interval length falls between 330 milliseconds and ventricular fibrillation when the interval length falls below 240 milliseconds. These interval lengths are merely examples, and a user may define the interval lengths as desired, which may then be stored within memory82. This interval length may need to be detected for a certain number of consecutive cycles, for a certain percentage of cycles within a running window, or a running average for a certain number of cardiac cycles, as examples. In other examples, additional physiological parameters may be used to detect an arrhythmia. For example, processing circuitry80may analyze one or more morphology measurements, impedances, or any other physiological measurements to determine that patient14is experiencing a tachyarrhythmia.

In addition to detecting and identifying specific types of cardiac events, e.g., cardiac depolarizations, sensing circuitry86may also sample the detected intrinsic signals to generate an electrogram or other time-based indication of cardiac events. Sensing circuitry86may include an analog-to-digital converter or other circuitry configured to sample and digitize the electrical signal sensed via electrodes52and60. Processing circuitry80may analyze the digitized signal for a variety of purposes, including morphological identification or confirmation of tachyarrhythmia of heart26, and detection of evoked responses to pacing pulses to determine whether the pacing pulses captured heart26.

Processing circuitry80may also analyze the digitized signal to detect delivery of an anti-tachyarrhythmia shock by another medical device, e.g., extracardiovascular ICD system30aor30b. In the example ofFIG. 4, processing circuitry80includes shock detection circuitry88configured to analyze the digitized signal to detect delivery of an anti-tachyarrhythmia shock by another medical device. In some examples, the shock detection functionality attributed to shock detection circuitry88may be a functional module executed by processing circuitry80.

Shock detection circuitry88may be used to detect anti-tachyarrhythmia shocks delivered by ICD system30aor30b, or another device. For example, processing circuitry80may enable shock detection circuitry88in response to detecting a tachyarrhythmia or receiving a communication indicating that an arrhythmia has been detected or a shock is imminent. Processing circuitry80may also disable shock detection circuitry88after a predetermined time period has elapsed or when a shock is otherwise not (or no longer) anticipated. When shock detection circuitry88is enabled, shock detection circuitry88may identify when an electrical signal received by sensing circuitry86is representative of a cardioversion or defibrillation pulse.

In response to detecting a shock via shock detection circuitry88, processing circuitry80may begin post-shock pacing according to a post-shock pacing mode when such functionality has been enabled for therapy. Processing circuitry80may also re-start post-shock pacing in response to detecting additional shocks via shock detection circuitry88. In some examples, processing circuitry80may terminate ATP upon detection of a shock.

Shock detection circuitry88may detect an anti-tachyarrhythmia shock, e.g., a defibrillation or cardioversion pulse, delivered by ICD systems30aor30b, or an external defibrillator, based on the detection of an electrical signal across two or more electrodes, such as electrodes52and60. In order to detect the anti-tachyarrhythmia shock, shock detection circuitry88may detect one or more signal characteristics of an anti-tachyarrhythmia shock in the signal including: detection of the high amplitude level of an anti-tachyarrhythmia shock, detection of a high slew rate of the leading and trailing edges, and detection of a large post-shock polarization change. Detection of more than one signal characteristic may improve sensitivity and/or specificity of the shock anti-tachyarrhythmia shock detection.

In general, IPD16may detect an anti-tachyarrhythmia shock by detecting an amplitude of the digitized version of the electrical signal sensed by sensing circuitry86that is above a shock threshold. An amplitude above the shock threshold may reflect, for example, a high amplitude level of the electrical signal and/or polarization across electrodes associated with delivery of an anti-tachyarrhythmia shock by another medical device. An amplitude of the signal may include an amplitude of a derivative of the signal, and a high derivative amplitude may indicate the high slew rate of the leading and trailing edges of the shock waveform. In some examples, IPD16(e.g., shock detection circuitry88and/or processing circuitry80) may implement any of the anti-tachyarrhythmia shock detection techniques described in commonly-assigned U.S. Pat. No. 9,278,229 to Reinke et al., titled, “ANTI-TACHYARRHYTHMIA SHOCK DETECTION,” and issued Mar. 8, 2016, the entire content of which is incorporated by reference herein. One or more shock thresholds or other shock detection parameters92used by shock detection circuitry88and processing circuitry80to detect shocks may be stored in memory92.

Processing circuitry80is also configured to detect asystole of heart26. Processing circuitry80is configured to determine, without detecting the delivery of the anti-tachyarrhythmia shock, that the other medical device, e.g., extracardiovascular ICD systems30aor30b, delivered the anti-tachyarrhythmia shock based on the detection of asystole. Asystole of heart26may result from delivery of the anti-tachyarrhythmia shock and, accordingly, detection of asystole may indicate the other device has delivered the anti-tachyarrhythmia shock.

Processing circuitry80may detect asystole based on an absence of a cardiac depolarization, e.g., the absence of an indication of a cardiac depolarization from sensing circuitry86, for at least a threshold period of time, which may be referred to as an asystole threshold, and stored as part of shock detection parameters92in memory82. The asystole threshold may be between 1 and 10 seconds, such as 2 to 5 seconds, as examples. Processing circuitry80may compare the asystole threshold to a period of time beginning upon a most recent depolarization of heart26, detection of a tachyarrhythmia, or termination of delivery of ATP by IPD16, as examples, and the asystole threshold may vary depending on which event triggered initiation of the time period to which the threshold will be compared.

In some examples, processing circuitry80detects a tachyarrhythmia, e.g., as described above, and, in response to detecting the tachyarrhythmia, starts a timer to compare to the asystole threshold and controls shock detection circuitry88to begin shock detection. In some examples in which processing circuitry80controls therapy delivery circuitry84to deliver ATP in response to detecting the tachyarrhythmia, processing circuitry80initiates the shock detection and asystole detection in response to end the delivery of ATP. In either of these examples, processing circuitry80determines that a shock was delivered by another medical device based on detecting asystole within a threshold period of time following detection of a tachyarrhythmia. In examples in which IPD16does not detect a tachyarrhythmia and delivers bradycardia pacing, processing circuitry80may control therapy delivery circuitry84to suspend bradycardia pacing for one or more cardiac cycles to facilitate detection of prolonged asystole.

In response to determining that another medical device delivered an anti-tachyarrhythmia shock, processing circuitry80controls therapy delivery circuitry84to deliver post-shock pacing via electrodes52and60according to a post-shock pacing mode stored in pacing mode parameters90within memory82. Pacing mode parameters90stored in memory82may include a baseline value of a pacing pulse magnitude for delivery of pacing pulses according to a baseline pacing mode, e.g., bradycardia pacing, and a post-shock value of the pacing pulse magnitude for delivery of pacing pulses according to a post-shock pacing mode. The post-shock value of the pacing pulse magnitude is greater than the baseline value. Again, pacing pulse magnitude may include one or both of pacing pulse amplitude and pacing pulse width. Pacing mode parameters90for the post-shock pacing mode may also include a length of time and/or number of pulses for delivery of post-shock pacing according to the post-shock pacing mode.

Processing circuitry80may also revert IPD16from the post-shock pacing mode to the baseline pacing mode, e.g., after the length of time or number of pulses. For the reversion, processing circuitry80may control therapy delivery circuitry84to deliver a plurality of pacing pulses to heart26via electrodes52and60. The values of the pacing pulse magnitude for the plurality of pacing pulses are configured to perform a downward capture threshold test by iteratively testing a plurality of values a pacing pulse magnitude that decrease from an initial reversion value, which may be greater than the baseline value and less than the post-shock value. The initial reversion value may be stored as part of pacing mode parameters90in memory82. Processing circuitry80may control therapy delivery circuitry84to test decreasing values of the pacing pulse magnitude until loss of capture is detected. To determine whether the pacing pulses captured heart26, processing circuitry80may, based on the electrical signal sensed by sensing circuitry86via electrodes52and60, determine whether an evoked response of heart26was caused by the pacing pulses, e.g., by each of the pacing pulses.

During the iterative testing of decreasing pacing pulse magnitude values, processing circuitry80may control therapy delivery circuitry84to increase the rate at which pacing pulses are delivered, thereby suppressing intrinsic depolarizations, and ensuring that detected cardiac activity is in response to the pacing pulses. In some examples, processing circuitry80controls therapy delivery circuitry to decrease the pacing pulse magnitude every cardiac cycle, or every N cardiac cycles. The frequency and size of pacing pulse magnitude reductions during reversion may be stored as pacing mode parameters90in memory82.

In other examples of iteratively testing decreasing magnitude values, one or more test pacing pulses at a next, lower test value of pacing pulse magnitude are preceded and/or followed, in one or more preceding or subsequent cardiac cycles, by one or more support pulses at the current value of pacing pulse magnitude. If the test pacing pulses capture heart26, the successful test value becomes the current value, and another lower, test value of pacing pulse magnitude may be similarly tested. If a test pacing pulse fails to capture heart26, processing circuitry80may control therapy deliver circuitry84to deliver, within the same cardiac cycle, a hack-up pacing pulse with at least the current value of pacing pulse magnitude, to ensure that heart26is paced. In the event that a test pacing pulse failed to capture heart26, processing circuitry80may control therapy delivery circuitry to re-attempt one or more test pacing pulses at the test value of pacing pulse magnitude, or end the iterative testing of decreasing magnitude values with a determination that the test value failed to capture heart26.

Based on the detection of loss of capture of one of the plurality of values of pacing pulse magnitude, processing circuitry80may update the baseline value of the pacing pulse magnitude for the baseline pacing mode stored as one of pacing mode parameters90in memory82. For example, processing circuitry80may determine the pacing pulse magnitude that preceded the one of the plurality of pacing pulses that failed to capture the heart, and update the baseline value based on the determined value of the pacing pulse magnitude. For example, processing circuitry80may update the baseline value to be a predetermined or programmable margin above the magnitude that preceded loss of capture of heart26. Processing circuitry80may control therapy delivery circuitry84to deliver pacing pulse having the updated baseline value of magnitude according to the baseline pacing mode, e.g., a bradycardia pacing mode.

In some examples, in response to determining that the initial reversion value of the pacing pulse magnitude failed to capture the heart, processing circuitry80may suspend the reversion to the baseline pacing mode. The failure of the initial reversion magnitude pacing pulse to capture heart26may indicate that heart26is not ready for pacing according to the baseline pacing mode and/or would benefit from further pacing according to the post-shock pacing mode. Processing circuitry80may control therapy delivery circuitry84to stop iterative testing of decreasing magnitudes, and then deliver one or more pacing pulses having the post-shock value of the pacing magnitude. The return to post-shock pacing may be for a period of time or number of pulses, which may be stored as a pacing mode parameter90in memory82. Processing circuitry80may then restart the reversion, e.g., by controlling therapy delivery circuitry84to deliver pacing pulses configured to iterative test the decreasing magnitudes.

Communication circuitry94includes any suitable hardware, firmware, software or any combination thereof for communicating with another device, such as external device21or ICD system30aor30b. Under the control of processing circuitry80, communication circuitry94may receive downlink telemetry from and send uplink telemetry to external device21with the aid of an antenna, which may be internal and/or external. Processing circuitry80may provide the data to be uplinked to device21and the control signals for the telemetry circuitry within communication circuitry94, e.g., via an address/data bus. In some examples, communication circuitry94may provide received data to processing circuitry80via a multiplexer. In some examples, communication circuitry94may communicate with a local external device, and processing circuitry80may communicate with a networked computing device via the local external device and a computer network, such as the Medtronic CareLink® Network developed by Medtronic, plc, of Dublin, Ireland.

A clinician or other user may retrieve data from IPD16using external device21or another local or networked computing device configured to communicate with processing circuitry80via communication circuitry94. The clinician may also program parameters of IPD16using external device21or another local or networked computing device. In some examples, the clinician may program any of the magnitude values, thresholds, time periods, number of pulses, or other parameters discussed herein, such as those stored in memory as pacing mode parameters90and shock determination parameters92.

FIG. 5is a flow diagram illustrating an example technique for transitioning from a baseline pacing mode to a post-shock pacing mode in response to determining that an anti-tachyarrhythmia shock was delivered, and reverting from the post-shock pacing mode to the baseline pacing mode. The flowchart ofFIGS. 5-7are intended to illustrate the functional operation of IPD16, medical systems8aand8b, and other devices and systems described herein, and should not be construed as reflective of a specific form of software or hardware necessary to practice the methods described. Methods described in conjunction with flow diagrams presented herein may be implemented in a non-transitory computer-readable medium that includes instructions for causing a programmable processor to carry out the methods described. A non-transitory computer-readable medium includes but is not limited to any volatile or non-volatile media, such as a RAM, ROM, CD-ROM, NVRAM, EEPROM, flash memory, or other computer-readable media, with the sole exception being a transitory, propagating signal. The instructions may be implemented by processing circuitry hardware as execution of one or more software modules, which may be executed by themselves or in combination with other software.

The example methods illustrated byFIGS. 5-7may be performed, by any one or more devices described herein, and may be performed, in part, by processing circuitry of any one or more devices described herein, such as by processing circuitry80of IPD16, processing circuitry of ICD9, and processing circuitry of external device21. For ease of description, the methods ofFIGS. 5-7will be described hereafter as being performed by processing circuitry80of IPD16.

According to the example method ofFIG. 5, processing circuitry80controls therapy delivery circuitry84of IPD16to deliver pacing pulses according to a baseline pacing mode, e.g., a bradycardia pacing mode (100). The baseline pacing mode may specify a baseline value of a pacing pulse magnitude, e.g., pulse amplitude and/or pulse width.

The processing circuitry80determines whether an anti-tachyarrhythmia shock was delivered to patient14(102). For example, shock detection circuitry88may detect a shock delivered by another medical device, such as extracardiovascular ICD system30aor30b, based on an electrical signal sensed by sensing circuitry86via electrodes52and60, as described herein. In some examples, processing circuitry80determines that the shock was delivered, without detecting the shock itself, by detecting asystole, as described herein. In some examples, processing circuitry80detects a tachyarrhythmia of heart26, e.g., based on the electrical signal sensed by sensing circuitry86via electrodes52and60, and determines whether an anti-tachyarrhythmia shock was delivered to patient14within a predetermined interval beginning at the detection of the tachyarrhythmia. In examples in which an IMD that delivers anti-tachyarrhythmia shocks performs the example method ofFIG. 5, the IMD will know when it has delivered a shock.

Processing circuitry80may continue to control therapy delivery circuitry84to deliver pacing pulses according to the baseline pacing mode until processing circuitry80determines that a shock was delivered (NO of102). In response to determining that a shock was delivered (YES of102), processing circuitry80controls therapy delivery circuitry84to deliver post-shock pacing according to a post shock pacing mode, as described herein (104). After delivery of post-shock pacing, processing circuitry80may revert IPD16to the baseline pacing mode (106).

FIG. 6is a flow diagram illustrating an example technique for determining whether an anti-tachyarrhythmia shock was delivered. The example technique described inFIG. 6may be used, for example, by IPD16in block102ofFIG. 5. In some examples, processing circuitry80detects a tachyarrhythmia of heart26, e.g., based on the electrical signal sensed by sensing circuitry86via electrodes52and60, and, in response the detection of the tachyarrhythmia, determines whether an anti-tachyarrhythmia shock was delivered according to the example technique ofFIG. 6.

In other examples, the technique described inFIG. 6may be employed by any medical device to determine that another medical device delivered an anti-tachyarrhythmia shock based on either detecting the shock itself or, if the shock is not (e.g., cannot be) detected, detecting asystole of heart26. The example technique described inFIG. 6may be performed by the medical device for any purpose. For example, a medical device performing the example technique ofFIG. 6need not deliver cardiac pacing according to a baseline pacing mode (100ofFIG. 5) prior to determining whether a shock was delivered, deliver post-shock pacing according to a post-shock pacing mode in response to determining that the shock was delivered (104ofFIG. 5), or deliver any cardiac pacing or other therapy.

According to the example ofFIG. 6, sensing circuitry86senses an electrical signal via electrodes52and60(110). The electrical signal may include the electrical activity, e.g., depolarizations, of heart26, as well as any other signal across electrodes52and60, such as those caused by delivery of an anti-tachyarrhythmia shock to patient14. Processing circuitry80determines whether an amplitude of the signal, such as an amplitude of a derivative of the signal (e.g., first derivative indicating slope), is above a shock threshold (112). If the amplitude is above the shock threshold (YES of112), processing circuitry80detects an anti-tachyarrhythmia shock delivered by another medical device, e.g., extracardiovascular ICD system30aor30b(114).

Processing circuitry80is also configured, e.g., when the amplitude of the signal is not above the shock threshold (NO of112), to determine whether asystole of heart26is detected based on the electrical signal, e.g., based on the absence of cardiac depolarizations in the signal, as described herein (116). Processing circuitry80may be configured to detect asystole (YES of116) if sensing circuitry86has not indicated detection of a cardiac depolarization for at least an asystole threshold period of time. Processing circuitry80may implement an asystole timer, which may begin and/or be reset upon detection of tachyarrhythmia, termination of ATP, or detection of a cardiac depolarization, as examples. Processing circuitry80may detect asystole when a value of the timer meets and/or exceeds the asystole threshold. In response to detecting asystole (YES of116), processing circuitry80determines that the other medical device delivered an anti-tachyarrhythmia shock (118). Absent detection of asystole (NO of116), processing circuitry80may continue to monitor the sensed electrical signal (110).

FIG. 7is a flow diagram illustrating an example technique for reverting from a post-shock pacing mode to a baseline pacing mode. The example technique described inFIG. 7may be used, for example, by IPD16in block106ofFIG. 5. In other examples, the technique described inFIG. 7may be employed by any medical device to revert from a post-shock pacing mode to a baseline, e.g., bradycardia, pacing mode. For example, the technique described inFIG. 7may be employed by an ICD configured to deliver both cardiac pacing and anti-tachyarrhythmia shock therapies, such as an extracardiovascular ICD system, or an ICD coupled to intracardiac leads. The like-numbered block inFIG. 7is described above in further detail with reference toFIG. 5.

According to the example technique ofFIG. 7, processing circuitry80controls IPD16to deliver pacing pulse to iteratively test decreasing values of pacing pulse magnitude to identify a capture threshold of heart26. As illustrated by the example ofFIG. 7, processing circuitry sets an initial test pulse magnitude for one or more test pacing pulses delivered by IPD16to an initial reversion value, which is greater than a baseline value, but less than a post-shock pacing value, of the pacing pulse magnitude (130). Processing circuitry80controls therapy delivery circuitry84to deliver one or more test pacing pulses at the initial reversion pulse magnitude value (132). In some examples, as described in greater detail above, the one or more test pacing pulses at the initial reversion pulse magnitude value may be preceded and/or followed by support pacing pulses at a higher pulse magnitude value, such as the post-shock value of pacing pulse magnitude. Processing circuitry80determines whether the one or more pulses at the initial reversion value captured heart26(134).

If the one or more pulses at the initial reversion value failed to capture heart26(NO of134), processing circuitry80suspends the reversion to the baseline pacing mode (136). As described above, suspending the reversion may include delivering one or more additional pulses at the post-shock pacing value of the pulse magnitude prior to re-starting the reversion from the post-shock pacing mode to the baseline pacing mode.

If the one or more pulses at the initial reversion value captured heart26(YES of134), processing circuitry80decrements the test pulse magnitude (138), and controls therapy delivery circuitry84to deliver one or more test pacing pulse at the decremented test magnitude value (140). Processing circuitry80determines whether the one or more test pulses at the decremented magnitude value captured heart26(142). Processing circuitry80may iteratively decrement the test magnitude value (138), and control delivery of the one or more test pacing pulses at the decremented magnitude value (140), so long as the decremented test magnitude values capture heart26(YES of142). In some examples, as described in greater detail above, the one or more test pacing pulses at the decremented pulse magnitude value may be preceded and/or followed by support pacing pulses at a higher pulse magnitude value, such as the previous test pulse magnitude value.

In response to determining that one or more of the pacing pulses having a decremented test magnitude fails to capture heart26(NO of142), processing circuitry80updates the baseline pacing pulse magnitude value for the baseline pacing mode (144). For example, processing circuitry80may update the baseline value to be a predetermined or programmable margin above the magnitude that preceded the magnitude that failed to capture heart26.

In some examples, as illustrated inFIG. 7, processing circuitry80determines whether updating the baseline value of pacing pulse magnitude resulted in an increase of the baseline value by at least a threshold amount (146). If the baseline value increased by at least the threshold amount (YES of146), processing circuitry may provide an alert, e.g., store a flag in memory82and/or provide an alert to external device21or another computing device or system via communication circuitry94(148). Whether or not the baseline value increased by at least the threshold amount, processing circuitry80controls therapy delivery circuitry84to deliver pacing pulses having the updated baseline value of the pacing pulse magnitude according to the baseline pacing mode (100).

The baseline value having increased by at least the threshold may indicate a pacing threshold change due to the tachyarrhythmia, or delivery of anti-tachyarrhythmia therapies in response to the tachyarrhythmia. A clinician may consider such a change clinically significant, and providing the alert when the baseline value increased by at least the threshold amount may inform the clinician of such a change. The increased baseline value of pacing magnitude may also impact the useful life of a power source of IPD16, and the alert may notify the clinician of this possibility.

In one or more examples, the functions described in this disclosure may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on, as one or more instructions or code, a computer-readable medium and executed by a hardware-based processing unit. Computer-readable media may include computer-readable storage media forming a tangible, non-transitory medium. Instructions may be executed by one or more processors, such as one or more DSPs, ASICs, FPGAs, general purpose microprocessors, or other equivalent integrated or discrete logic circuitry. Accordingly, the term “processor,” as used herein may refer to one or more of any of the foregoing structure or any other structure suitable for implementation of the techniques described herein.

In addition, in some aspects, the functionality described herein may be provided within dedicated hardware and/or software modules. Depiction of different features as modules or units is intended to highlight different functional aspects and does not necessarily imply that such modules or units must be realized by separate hardware or software components. Rather, functionality associated with one or more modules or units may be performed by separate hardware or software components, or integrated within common or separate hardware or software components. Also, the techniques could be fully implemented in one or more circuits or logic elements. The techniques of this disclosure may be implemented in a wide variety of devices or apparatuses, including an IMD, an external programmer, a combination of an IMD and external programmer, an integrated circuit (IC) or a set of ICs, and/or discrete electrical circuitry, residing in an IMD and/or external programmer.