Cardiac medical device and method for avoiding t-wave oversensing

Abstract

A medical device includes a sensing circuit configured to sense a cardiac electrical signal and sense a cardiac event signal in response to the cardiac electrical signal crossing an adaptive cardiac event sensing threshold. The medical device includes a control circuit configured to determine if high sensing threshold criteria are met and control the sensing circuit to apply the adaptive cardiac event sensing threshold by applying a high cardiac event sensing threshold when the high sensing threshold criteria are met and a low cardiac event sensing threshold when the high sensing threshold criteria are not met.

Description

CARDIAC MEDICAL DEVICE AND METHOD FOR AVOIDING T-WAVEOVERSENSING

[0001] This application claims the benefit of US Provisional application no. 63 / 675,720 filed on July 25, 2024, the entire content of which is incorporated herein.TECHNICAL FIELD

[0002] The disclosure relates generally to a cardiac medical device and method for sensing cardiac electrical signals and avoiding T-wave oversensing.BACKGROUND

[0003] During normal sinus rhythm (NSR), the heartbeat is regulated by electrical signals produced by the sino-atrial (SA) node located in the right atrial wall. Each depolarization signal produced by the SA node spreads across the atria, causing the depolarization and contraction of the atria, and arrives at the atrioventricular (AV) node. The AV node responds by propagating a depolarization signal through the bundle of His of the atrioventricular septum and thereafter to the left and right bundle branches and the Purkinje fibers of the right and left ventricles, sometimes referred to as the “His-Purkinje system” and referred to herein as the “conduction system.”

[0004] Patients with poor SA node function, poor AV node conduction (referred to as AV block), or conduction system abnormalities of the His bundle or left and / or right bundle branches (referred to as bundle branch block) or other conduction system abnormalities may receive a pacemaker to restore a more normal heart rhythm and heart chamber synchrony. Atrial pacing may be performed to provide a regular atrial rate in a patient having SA node dysfunction. Ventricular pacing may be performed to promote a regular ventricular rate in a patient having AV conduction abnormalities or bundle branch block. A single chamber ventricular pacemaker may be coupled to a transvenous ventricular lead carrying electrodes, which may be placed in the right ventricle (RV) for instance. The pacemaker itself is generally implanted in a subcutaneous pocket with the transvenous lead tunneled to the subcutaneous pocket. The pacemaker may sense cardiac electrical signals via electrodes carried by the transvenous lead and deliver ventricular pacing asneeded. Intracardiac pacemakers have been introduced or proposed for implantation entirely within a patient’s heart, eliminating the need for transvenous leads. An intracardiac pacemaker may provide sensing and pacing from within a chamber of the patient’s heart, e.g., from within the right ventricle in a patient having AV conduction block.

[0005] Dual chamber pacemaker systems are available which may include a transvenous atrial lead carrying electrodes which are placed in the right atrium and a transvenous ventricular lead carrying electrodes that are placed in the right ventricle via the right atrium. Some leadless dual chamber pacemaker systems have been proposed for implantation within a patient’s heart, without requiring transvenous leads. A dual chamber pacemaker system senses atrial electrical signals and ventricular electrical signals and can provide both atrial pacing and ventricular pacing as needed to promote a normal atrial and ventricular rhythm and promote AV synchrony when SA node, AV node, bundle branch block or other conduction abnormalities are present.SUMMARY

[0006] In general, this disclosure is directed to a medical device capable of monitoring the heart rhythm by sensing cardiac electrical signals and provides techniques for avoiding oversensing of cardiac event signals. The medical device may apply a sensing threshold, e.g., an R-wave sensing threshold, to a sensed cardiac electrical signal for sensing cardiac event signals, e.g., R-waves. Sensing of R-waves attendant to the depolarizations of the ventricles, for example, can be performed to determine the ventricular rate for controlling ventricular pacing and / or cardioversion or defibrillation (CV / DF) shock delivery. In some instances, T-waves, attendant to the repolarization of the ventricles, may be falsely sensed as R-waves, e.g., when the T-wave of the cardiac electrical signal crosses the R-wave sensing threshold. This false sensing of T-waves as R-waves is referred to as “T-wave oversensing” (TWOS).

[0007] A medical device operating according to the techniques disclosed herein may adjust the R-wave sensing threshold by adaptively increasing or “boosting” the R-wave sensing threshold to avoid or reduce the likelihood of TWOS. In some examples, the adaptive increase in the R-wave sensing threshold may be applied following a delivered pacing pulse to avoid oversensing of the post-pace T-wave that accompanies myocardialrepolarization following a pacing-evoked ventricular depolarization. By avoiding T-wave oversensing, reliable sensing of the ventricular rate and rhythm can be performed for controlling cardiac electrical stimulation therapies.

[0008] In one example, the disclosure provides a medical device including a sensing circuit configured to sense at least one cardiac electrical signal, a memory configured to store high sensing threshold criteria and a therapy delivery circuit configured to deliver pacing pulses. The medical device further includes a control circuit configured to determine from at least one cardiac electrical signal sensed by the sensing circuit if the high sensing threshold criteria are met. The control circuit may be further configured to select a starting value of a cardiac event sensing threshold based on whether the high sensing threshold criteria are met by selecting a low starting value of the cardiac event sensing threshold when the high sensing threshold criteria are not met or selecting a high starting value of the cardiac event sensing threshold when the high sensing threshold criteria are met, the high starting value greater than the low starting value. The sensing circuit may be further configured to apply the cardiac event sensing threshold having the selected starting value to a first cardiac electrical signal of the at least one cardiac electrical signal sensed by the sensing circuit and sense a cardiac event signal in response to the first cardiac electrical signal crossing the cardiac event sensing threshold. The control circuit may be further configured to start a pacing interval in response to the sensed cardiac event signal to schedule a pacing pulse for delivery by the therapy delivery circuit.

[0009] In another example, the disclosure provides a method including sensing at least one cardiac electrical signal, determining from at least one sensed cardiac electrical signal if high sensing threshold criteria are met, and selecting a starting value of a cardiac event sensing threshold based on whether the high sensing threshold criteria are met by selecting a low starting value of the cardiac event sensing threshold when the high sensing threshold criteria are not met or selecting a high starting value of the cardiac event sensing threshold when the high sensing threshold criteria are met, the high starting value greater than the low starting value. The method may further include applying the cardiac event sensing threshold having the selected starting value to a first cardiac electrical signal of the at least one sensed cardiac electrical signals and sensing a cardiac event signal in response to the first cardiac electrical signal crossing the cardiac event sensing threshold. The method mayfurther include starting a pacing interval in response to the sensed cardiac event signal to schedule a pacing pulse.

[0010] In yet another example, the disclosure provides a non-transitory, computer readable medium storing a set of instructions that, when executed by control circuitry of a medical device, cause the medical device to sense at least one cardiac electrical signal, determine from at least one sensed cardiac electrical signal if high sensing threshold criteria are met and select a starting value of a cardiac event sensing threshold based on whether the high sensing threshold criteria are met by selecting a low starting value of the cardiac event sensing threshold when the high sensing threshold criteria are not met or selecting a high starting value of the cardiac event sensing threshold when the high sensing threshold criteria are met, the high starting value being greater than the low starting value. The instructions may further cause the medical device to apply the cardiac event sensing threshold having the selected starting value to a first cardiac electrical signal of the at least one sensed cardiac electrical signals, sense a cardiac event signal in response to the first cardiac electrical signal crossing the cardiac event sensing threshold and start a pacing interval in response to the sensed cardiac event signal to schedule a pacing pulse.

[0011] This summary is intended to provide an overview of the subject matter described in this disclosure. It is not intended to provide an exclusive or exhaustive explanation of the apparatus and methods described in detail within the accompanying drawings and description below. Further details of one or more examples are set forth in the accompanying drawings and the description below.BRIEF DESCRIPTION OF DRAWINGS

[0012] FIG. l is a diagram of a medical device system for delivering cardiac electrical stimulation therapies and sensing cardiac electrical signals according to the methods disclosed herein in some examples.

[0013] FIG. 2 is a diagram of a leadless pacemaker that may be configured to operate according to the methods disclosed herein in some examples.

[0014] FIG. 3 is a diagram of a medical device system including the leadless pacemaker of FIG. 2 implanted at a different ventricular pacing site than the position shown in FIG. 2.

[0015] FIG. 4 is a diagram of circuitry that may be enclosed within an implantable medical device, e.g., the pacemakers shown in FIGs. 1, 2 or 3, configured to delivercardiac electrical stimulation therapies and sense cardiac signals according to the techniques disclosed herein.

[0016] FIG. 5 is a flow chart of a method for performing R-wave sensing by the pacemaker of FIG. 4 according to some examples.

[0017] FIG. 6 is a diagram of an adaptive R-wave sensing threshold that may be applied to a ventricular EGM signal by a medical device according to some examples.

[0018] FIG. 7 is a flow chart of a method that may be performed by a medical device for controlling an adaptive R-wave sensing threshold according to some examples.

[0019] FIG. 8 is a flow chart of a method for determining when high sensing threshold criteria are met after enabling adaptive sensing control of the R-wave sensing threshold according to some examples.

[0020] FIG. 9 is a diagram of a pacing rate dependent high starting value of the adaptive R-wave sensing threshold according to some examples.

[0021] FIG. 10 is a flow chart of a method for selecting the high starting value of an adaptively controlled R-wave sensing threshold according to another example.

[0022] FIG. 11 is a flow chart of a method for controlling the adaptive R-wave sensing threshold according to another example.

[0023] FIG. 12 is a diagram of a ventricular electrical signal that may be sensed by a medical device for sensing R-waves according to methods disclosed herein in some examples.DETAILED DESCRIPTION

[0024] A medical device capable of sensing cardiac electrical signals in a manner that reduces the likelihood of TWOS is disclosed herein. In some instances, the T-wave that is attendant to myocardial repolarization can be falsely sensed as an R-wave if the T-wave crosses the R-wave sensing threshold. TWOS may cause a pacemaker to inhibit ventricular pacing when a pacing pulse may actually be needed because the TWOS results in falsely sensing a faster ventricular rate than the true ventricular rate. TWOS could lead to false tachyarrhythmia detection. T-waves following a delivered ventricular pacing pulse and the subsequent pacing-evoked depolarization may have a relatively higher amplitude than T-waves that following intrinsic depolarizations (e.g., conducted via the AV node when a ventricular pacing pulse is not delivered). TWOS may be more likely to occur insome patients depending on the characteristics of the post-pace T-waves, the pacing site, the sensing electrode vector and other factors. TWOS, however, may occur following delivered ventricular pacing pulses and / or sensed intrinsic R-waves. Using the techniques disclosed herein, post-pace and / or post-sense TWOS can be avoided while promoting high sensitivity to detecting fast intrinsic ventricular rates by adaptively controlling the R-wave sensing threshold applied to the cardiac electrical signal sensed following ventricular pacing pulses and / or sensed intrinsic R-waves.

[0025] In various examples, the starting value of the R-wave sensing threshold and / or the decay rate of the R-wave sensing threshold may be adaptively controlled by a medical device operating according to the techniques disclosed herein. In some examples, the adaptive control of the R-wave sensing threshold may be enabled when the medical device detects an adaptive sensing control condition, which may be associated with a relatively greater likelihood of TWOS than when the adaptive sensing control condition is not met. When adaptive sensing control is enabled, the medical device may adaptively control the post-pace and / or post-sense R-wave sensing threshold based at least in part on the ventricular rate, which may be a paced rate or a sensed rate or a combination of both.

[0026] While several illustrative examples presented herein refer to an adaptive R-wave sensing threshold that is applied to a sensed ventricular electrical signal following a delivered ventricular pacing pulse (e.g., post-pace R-wave sensing threshold), it is to be understood that techniques described herein can be used for controlling an adaptive postsense R-wave sensing threshold. An adaptive post-sense R-wave sensing threshold may be selected as a high post-sense R-wave sensing threshold or a low post-sense R-wave sensing threshold depending on whether high sensing threshold criteria are met or not, as generally described in the examples relating to the post-pace adaptive R-wave sensing threshold in the following description and accompanying drawings.

[0027] FIG. 1 is a diagram of a medical device system 10 for sensing and analyzing cardiac electrical signals and delivering cardiac electrical stimulation therapies according to some examples. Medical device system 10 includes a pacemaker 14 connected to an atrial lead 16 and a ventricular lead 18 in this example. Pacemaker 14 includes a housing 15, which may be hermetically sealed, to enclose internal circuitry corresponding to the various circuits and components for sensing cardiac signals from heart 8 and controlling cardiac pacing delivered to heart 8 by pacemaker 14. The housing 15 may be formed of aconductive material, such as titanium or titanium alloy. The housing 15 may function as an electrode (sometimes referred to as a “can” electrode). In some examples, housing 15 may be available as a return anode electrode for delivering unipolar pacing pulses and / or in a sensing electrode vector for sensing cardiac electrical signals in combination with electrodes carried by lead 16 and / or lead 18.

[0028] Pacemaker 14 includes a connector assembly 13 (sometimes referred to as a “connector block” or “header”), coupled to housing 15, having connector bores configured to receive the proximal lead connectors (not shown) of atrial lead 16 and ventricular lead 18. Connector block 13 may have one or more additional connector bores for receiving one or more additional leads, e.g., for receiving a coronary sinus lead for providing pacing and sensing in the left ventricle (LV) of heart 8 from a location in a cardiac vein along the left lateral free wall in some examples.

[0029] Atrial lead 16 is shown advanced transvenously into the right atrial chamber of a patient’s heart 8 for sensing atrial signals, e.g., P-waves attendant to atrial depolarizations, and for delivering atrial pacing pulses. Atrial lead 16 includes pacing and sensing electrodes 20 and 22. Electrode 20 is shown as a screw-in, helical tip electrode at the distal end of atrial lead 16. Electrode 22 is shown as a ring electrode (e.g., circumscribing the atrial lead body 17) spaced proximally from tip electrode 20. Electrodes 20 and 22 can form a bipolar pair for sensing atrial signals and delivering atrial pacing pulses via tip electrode 20 as a cathode electrode and ring electrode 22 as the return anode electrode, for example. Atrial lead 16 includes an elongated lead body 17 through which insulated electrical conductors extend from the respective electrodes 20 and 22 to the proximal lead connector (not shown) connected to the pacemaker 14 via connector assembly 13. The electrodes 20 and 22 are thereby connected to internal electronics of pacemaker 14 via respective electrical feedthroughs in connector assembly 13 that cross pacemaker housing 15.

[0030] Ventricular lead 18 is shown advanced transvenously into the right atrial chamber of a patient’s heart 8 and further into the right ventricle (RV) for positioning tip electrode 32 within the interventricular septum 12. Tip electrode 32 may be positioned in the vicinity of the heart’s conduction system, e.g., at a His bundle pacing site, a left bundle branch area pacing (LBBAP) site or at a right bundle branch area pacing (RBBAP) site. Delivery of ventricular pacing via the conduction system, e.g., His bundle pacing, LBBAPor RBBAP, may promote a relatively more normal electrical activation pattern of the ventricles than pacing the ventricular myocardium. Myocardial ventricular pacing via electrodes at or near the right ventricular apex, for example, has been found to be associated with increased risk of atrial fibrillation and heart failure. Delivery of ventricular pacing at sites along the His-Purkinje conduction system of the heart, for capturing at least a portion of the conduction system, may promote a more physiological electrical activation pattern of the heart because the pacing-evoked depolarizations can be propagated along the native conduction system, e.g., along the bundle branches and Purkinje fibers. Pacing the ventricles via the His bundle, the RBB and / or the LBB for example, allows recruitment along the heart’s natural conduction system, including the Purkinje fibers, and subsequent propagation of the depolarization wavefronts through the ventricular myocardium.

[0031] Ventricular lead 18 is positioned for sensing ventricular event signals and for delivering ventricular pacing pulses. Ventricular lead 18 includes pacing and sensing electrodes 32 and 34 for sensing ventricular event signals, e.g., R-waves attendant to intrinsic depolarizations of the ventricular myocardium and, in some instances, pacing- evoked ventricular depolarizations. Electrode 32 is shown as a screw-in, helical tip electrode at the distal end of ventricular lead 18. Electrode 34 is shown as a ring electrode spaced proximally from tip electrode 32 and circumscribing ventricular lead body 19. Electrodes 32 and 34 can form a bipolar pair for sensing ventricular signals and delivering pacing pulses via tip electrode 32 as a cathode electrode and ring electrode 34 as the return anode electrode, for example. While the electrodes 20, 22, 32 and 34 are represented as either helical screw-in electrodes or ring electrodes in FIG. 1, it is to be understood that other electrode types may be used such as button electrodes, hook electrodes, segmented electrodes, short coil electrodes, or the like. Tip electrode 32 of ventricular lead 18 may be a tissue-piercing electrode, which may or may not have a helical shape, to facilitate advancement of tip electrode 32 into the interventricular septum 12 to a conduction system pacing (CSP) site in the area of the His bundle, LBB or RBB in some examples.

[0032] In some instances, pacemaker 14 may be capable of delivering cardioversion / defibrillation (CV / DF) shocks for treating ventricular tachyarrhythmias. In this case, ventricular lead 18 (and / or another lead coupled to pacemaker 14) may carry one or more coil electrodes 36 and 38 for use in delivering high voltage CV / DF shocks. As such, while pacemaker 14 is referred to as a “pacemaker” herein, it could be referred to as“implantable cardioverter defibrillator” or “ICD” when capable of delivering high voltage CV / DF shocks in addition to the pacing functionality as disclosed herein.

[0033] Ventricular lead 18 includes an elongated lead body 19 through which insulated electrical conductors extend from the respective electrodes 32 and 34 (and coil electrodes 36 and 38 if present) to a proximal lead connector (not shown) connected to the pacemaker 14 via connector assembly 13. The electrodes 32 and 34 (and coil electrodes 36 and 38 if present) are thereby connected to internal electronics of pacemaker 14 via respective electrical feedthroughs in connector assembly 13 that cross pacemaker housing 15.

[0034] Electrodes 20, 22, 32, 34 (and 36 and 38 if present) may be formed from titanium, platinum, iridium or alloys thereof, as examples with no limitation intended, and may include a low polarizing coating, such as titanium nitride, iridium oxide, ruthenium oxide, platinum black, among others. Lead bodies 17 and 19 may each be formed from a non- conductive material, including silicone, polyurethane, fluoropolymers, mixtures thereof, and / or other appropriate materials. Each lead body may be shaped to form one or more lumens within which one or more insulated electrical conductors extend between the proximal lead connectors and the distal electrodes 20, 22, 32, 34, 36 and 38 carried by the respective lead 16 or 18.

[0035] While ventricular lead 18 is shown advanced into the RV for positioning tip electrode 32 in the interventricular septum 12 for delivering ventricular pacing pulses in the septum 12, e.g., in the area of the LBB or the RBB for delivering CSP, it is to be understood that the distal end of ventricular lead 18 may be positioned at other locations for delivering ventricular pacing to heart 8 for causing depolarizations of the tissue of the conduction system and / or ventricular myocardium thereby pacing the ventricles. For instance, ventricular lead tip electrode 32 may be positioned along or in the area of the His bundle and / or the RBB or LBB in a basal portion of the interventricular septum 12. In other examples, ventricular lead 18 may be advanced into the right atrium with tip electrode 32 advanced into the interatrial septum toward the His bundle, e.g., at the inferior end of the interatrial septum. The tip electrode 32 of ventricular lead 18 may be advanced toward the His bundle from a location beneath the AV node and near the tricuspid valve annulus, generally in the Triangle of Koch, to position tip electrode 32 near the His bundle from a right atrial approach. The techniques disclosed herein are not limited to a particular ventricular pacing and sensing location and may be practiced in avariety of medical device systems including at least one electrode that can be positioned at a ventricular sensing site, including leadless pacemakers and / or pacemakers or ICDs coupled to one or more leads.

[0036] Ventricular lead 18 is shown as an example “true bipolar lead,” including tip electrode 32 and ring electrode 34 for sensing ventricular electrical signals from the bipolar sensing electrode vector between tip electrode 32 and ring electrode 34. Pacemaker 14 may additionally or alternatively sense ventricular signals using the tip electrode 32 and the coil electrode 36 in an integrated bipolar sensing electrode pair. The ventricular sensing electrode vector can be “true bipolar” between the tip electrode 32 and a ring electrode 34 or “integrated-bipolar” between tip electrode 32 and coil electrode 36. In some examples, ventricular lead 18 may be an “integrated bipolar lead,” e.g., having tip electrode 32 and at least one high voltage coil electrode 36, without ring electrode 34 such that ventricular signal sensing is performed using an integrated bipolar sensing electrode vector. The techniques disclosed herein for avoiding TWOS can be implemented in conjunction with true bipolar sensing or integrated bipolar sensing, the latter of which can be associated with a higher likelihood of TWOS.

[0037] Factors that can lead to a relatively greater incidence of TWOS may include the selected sensing electrode vector and type of pacing being delivered. For example, though TWOS can occur during true bipolar sensing, instances of TWOS may be relatively more prevalent during integrated bipolar sensing of ventricular event signals than during true bipolar sensing of ventricular event signals. In other examples, post-pace TWOS may be relatively more prevalent during CSP than during ventricular pacing delivered to the ventricular myocardium that does not capture the His-Purkinje conduction system. As further described below, pacemaker 14 may be configured to sense R-waves by applying a post-pace R-wave sensing threshold, to a sensed ventricular electrical signal, that is adaptively controlled according to the techniques disclosed herein to avoid or reduce the likelihood of post-pace TWOS.

[0038] Pacemaker 14 includes therapy delivery circuitry for generating pacing pulses delivered via the atrial lead 16 and ventricular lead 18. As described below, cardiac electrical signal sensing circuitry included in pacemaker 14 may receive an atrial electrical signal sensed from electrodes carried by atrial lead 16 and a ventricular electrical signal sensed from electrodes carried by ventricular lead 18 for use in sensing cardiac eventsignals and controlling the timing and delivery of atrial pacing pulses and ventricular pacing pulses.

[0039] While pacemaker 14 is shown as a dual chamber pacemaker receiving both atrial lead 16 and ventricular lead 18, it is to be understood that in other examples, pacemaker 14 may be a single chamber device, e.g., configured to receive one lead for sensing cardiac electrical signals and delivering ventricular pacing without necessarily having atrial pacing capabilities. A lead and electrode configuration for delivering ventricular pacing may be configured to enable dual chamber (atrial and ventricular) sensing by the pacemaker, e.g., when ventricular lead 18 is advanced to a His bundle pacing site from the right atrium such that atrial signals and ventricular signals can be sensed by electrodes carried by ventricular lead 18. In still other examples, pacemaker 14 may be a multi-chamber pacemaker configured to sense cardiac signals and deliver atrial pacing via atrial lead 16, ventricular pacing via ventricular lead 18, and left ventricular pacing via a third lead that may be advanced via the coronary sinus ostium of the right atrium into the coronary sinus and further into a cardiac vein to a left ventricular pacing site, e.g., for delivering cardiac resynchronization therapy (CRT).

[0040] Medical device system 10 is shown including an external medical device 50 for receiving data from pacemaker 14 and for transmitting programming commands to pacemaker 14, which may include various sensing and pacing control parameters used by pacemaker 14. External device 50 may receive data from pacemaker 14 which may include atrial and / or ventricular electrical signal episodes, sensed cardiac event signal data, and therapy delivery data logged by pacemaker 14.

[0041] External device 50 may be embodied as a programmer used in a hospital, clinic or physician’s office to program pacemaker 14 and to acquire data from pacemaker 14. External device 50 may alternatively be embodied as a handheld device, such as a tablet or cell phone. In some examples, external device 50 is a home monitor configured to interrogate pacemaker 14 to receive signals or data from pacemaker 14 and transmit data to pacemaker 14 via a wireless communication link 48. An example programmer that may be configured to program pacemaker 14 and included in medical device system 10 configured to perform the techniques disclosed herein is the CARELINK® Programmer, commercially available from Medtronic, Inc., Dublin, Ireland.

[0042] External device 50 may include a processor 52, memory 53, display unit 54, user interface unit 56, and telemetry unit 58. Processor 52 is coupled to the other components and units of external device 50, e.g., via a data bus, for controlling the functions attributed to external device 50 herein. Processor 52 may execute instructions stored in memory 53. Processor 52 may include any one or more of a microprocessor, a controller, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field- programmable gate array (FPGA), or equivalent discrete or analog logic circuitry. In some examples, processor 52 may include multiple components, such as any combination of one or more microprocessors, one or more controllers, one or more DSPs, one or more ASICs, or one or more FPGAs, as well as other discrete or integrated logic circuitry. The functions attributed to processor 52 herein may be embodied as software, firmware, hardware or any combination thereof. Memory 53 may 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. Memory 53 may include non- transitory computer-readable media that may store instructions that, when executed by processor 52, cause medical device system 10 to perform various methods and functions attributed to medical device system 10 as disclosed herein.

[0043] User interface unit 56 may include a mouse, touch screen, keypad or the like to enable a user to interact with external device 50, e.g., to initiate and terminate an interrogation session for retrieving data from pacemaker 14, adjust settings of display unit 54, enter programming commands or selections or make other user requests. Display unit 54, which may include a liquid crystal display, light emitting diodes (LEDs) and / or other visual display components, may generate a display of cardiac electrical signals received from pacemaker 14 and / or data derived therefrom. Display unit 54 may be configured to generate a graphical user interface (GUI) including various windows, icons, user selectable menus, etc. to facilitate interaction by a user with the external device 50. Display unit 54 may display various windows to a user, e.g., in a GUI, for enabling a clinician or other user to review cardiac event signal sensing and therapy delivery related data retrieved from pacemaker 14.

[0044] Display unit 54 may function as an input and / or output device using technologies including liquid crystal displays (LCD), quantum dot display, dot matrix displays, lightemitting diode (LED) displays, organic light-emitting diode (OLED) displays, cathode ray tube displays, e-ink, or monochrome, color, or any other type of display capable of generating tactile, audio, and / or visual output. In some examples, display unit 54 is a presence-sensitive display. Display unit 54 may serve as a user interface device that operates both as one or more input devices and one or more output devices.

[0045] External device 50 may receive data, via telemetry unit 58, from pacemaker 14 via the wireless communication link 48. Data received from pacemaker 14 may include cardiac signals, e.g., intracardiac electrogram (EGM) signals sensed by pacemaker 14, marker channel data indicating the timing of pacing pulses delivered by pacemaker 14 and sensed cardiac event signals (e.g., sensed P-waves and sensed R-waves), and data relating to the pacing history.

[0046] Telemetry unit 58 includes a transceiver and antenna configured for bidirectional communication with a communication circuit included in an implantable pacemaker 14, e.g., in response to user requests. Telemetry unit 58 includes communication circuitry configured to operate in conjunction with processor 52 for sending and receiving data relating to pacemaker functions via a wireless communication link 48 with the implantable pacemaker 14. Communication link 48 may be established using a radio frequency (RF) link such as BLUETOOTH®, Wi-Fi, Medical Implant Communication Service (MICS) or other communication bandwidth. In some examples, external device 50 may include a programming head that is placed proximate pacemaker 14 to establish and maintain communication link 48, and in other examples external device 50 and pacemaker 14 may be configured to communicate using a distance telemetry algorithm and circuitry that does not require the use of a programming head and does not require user intervention to maintain a communication link 48.

[0047] It is contemplated that external device 50 may be in wired or wireless connection to a communications network via telemetry unit 58 that includes a transceiver and antenna or via a hardwired communication line for transferring data to a centralized database or computer to allow remote management of the patient. External device telemetry unit 58 may be coupled to a communication network / cloud (not shown in FIG. 1) for receiving and transmitting data to a remote computing device (not shown in FIG. 1), which may be a personal computer, personal mobile device or other computing device at a remote location from the patient to enable remote monitoring of data obtained from pacemaker 14 by aclinician or other user. The CARELINK™ network available from Medtronic, Inc., Dublin, Ireland, is an example of a remote patient monitoring system and database that may collect and display data retrieved from a patient’s pacemaker for review by a clinician or other user.

[0048] FIG. 2 is a diagram of a leadless pacemaker 114 that may be configured to operate according to the methods disclosed herein in some examples. The pacemaker 114 may be positioned within the right atrium for providing ventricular pacing via the conduction system in the area of the His bundle. Pacemaker 114 may include a distal tip electrode 132 extending away from a distal end 112 of the pacemaker housing 115. Leadless pacemaker 114 is shown implanted in the right atrial chamber of the patient’s heart for advancing distal tip electrode 132 to a His bundle pacing site from a right atrial approach. For example, the distal tip electrode 132 may be inserted into the inferior end of the interatrial septum, beneath the AV node and near the tricuspid valve annulus, generally in the Triangle of Koch, to advance tip electrode 132 to a His bundle pacing site. As described above in conjunction with FIG. 1, in other examples, a tip electrode 32 of ventricular lead 18 may be advanced to a His bundle pacing site from a right atrial approach to deliver CSP via a pacing lead, e.g., ventricular lead 18, and pacemaker 14 instead of the leadless pacemaker 114 as shown here.

[0049] In other examples, intracardiac leadless pacemaker 114 may be implanted within the right ventricle, e.g., high along the interventricular septum, for positioning distal tip electrode 132 in the basal portion of the interventricular septum in the vicinity of the His bundle or in another interventricular septal location along the His-Purkinje system for delivering CSP, e.g., in the area of the RBB or LBB. However, leadless pacemaker 114 is not necessarily limited to being implantable at CSP sites and may be implanted at another cardiac site within or on the heart for sensing cardiac signals and delivering pacing pulses.

[0050] Distal tip electrode 132 may be a helical electrode providing fixation to anchor the pacemaker 114 at the implant position. In other examples, pacemaker 114 may include a fixation member that includes one or more tines, hooks, barbs, helices or other fixation member(s) that anchor the distal end of the pacemaker 114 at the implant site. A proximal portion of the distal tip electrode 132 may be electrically insulated such that only the most distal end of tip electrode 132, furthest from housing distal end 112, is exposed to providetargeted pacing at a tissue site, which may include a portion of the conduction system in some examples.

[0051] One or more housing-based electrodes 120 and 134 may be carried on the surface of the housing 115 of pacemaker 114. Electrodes 120 and 134 are shown as ring electrodes circumscribing the longitudinal sidewall of pacemaker housing 115 that extends from the housing distal end 112 to housing proximal end 110. In other examples, a return anode electrode used in sensing and pacing may be positioned on housing proximal end 110. Ventricular pacing may be achieved using the distal tip electrode 132 as the cathode electrode and either of the housing-based electrodes 120 or 134 as the return anode. In some examples, pacing of atrial tissue may be achieved by delivering atrial pacing pulses via the distal ring electrode 120 using proximal ring electrode 134 as the return anode electrode. In other examples, distal ring electrode 120 shown circumscribing the lateral sidewall of housing 115 for the sake of clarity in FIG. 2 may be located on the pacemaker distal end 112 for providing atrial pacing and atrial sensing, e.g., in combination with proximal ring electrode 134. Ventricular pacing pulses may be delivered in the area of the His bundle via tip electrode 132 with proximal ring electrode 134 as the return anode. In this way, dual chamber pacing of the atria and the ventricles may be delivered by leadless pacemaker 114. In other examples more than two ring electrodes (or other types of electrodes) may be provided on housing 115, e.g., to provide two distinct atrial and ventricular pacing and sensing electrode vectors.

[0052] Cardiac electrical signals may be sensed by pacemaker 114 using one or more sensing electrode pairs selected from electrodes 120, 132 and 134. For example, a ventricular electrical signal may be sensed using distal tip electrode 132 and distal ring electrode 120 or proximal ring electrode 134. Intrinsic R-waves may be sensed by sensing circuitry of pacemaker 114 via the ventricular electrical signal sensing electrode pair for use in inhibiting a scheduled ventricular pacing pulse and scheduling the next ventricular pulse. Pacemaker 114 may sense intrinsic R-waves from the ventricular electrical signal using an adaptive R-wave sensing threshold according to the techniques disclosed herein.

[0053] An atrial electrical signal may be sensed using electrodes 120 and 134, for example. Intrinsic P-waves may be sensed by the atrial electrical signal sensing electrode pair for use in inhibiting and scheduling atrial pacing pulses and / or for scheduling atrial synchronous ventricular pacing pulses. The cardiac electrical signals sensed by pacemaker114 may be used for determining the atrial rate, ventricular rate, and / or for detecting atrial and / or ventricular tachyarrhythmias.

[0054] While external device 50 is not shown in FIG. 2, it is to be understood that pacemaker 114 can be included in a medical device system including external device 50 configured to communicate with pacemaker 114 and in some cases, as described above, with a network / cloud based patient database and / or a remote computing device. Pacemaker 114 may be configured to communicate via a communication circuit with external device 50 for receiving programming commands and transmitting data to external device 50 as generally described above in conjunction with FIG. 1. Leadless pacemaker 114 may be configured to transmit data to external device 50, which may be further analyzed by external device processor 52 and / or used in generating a graphical user interface of data acquired by pacemaker 114 for review by a clinician.

[0055] FIG. 3 is a diagram of a medical device system 200 including leadless pacemaker 114 implanted at a different ventricular pacing site than the position shown in FIG. 2. In this example, tip electrode 132 may be advanced into the interventricular septum 12 from a right ventricular approach for delivering CSP pulses in the area of the LBB or the area of the RBB, for example, for capturing at least a portion of the conduction system, with or without capturing local myocardial tissue. In other examples, ventricular pacing may be delivered that captures septal myocardial tissue without necessarily capturing a portion of the His-Purkinje conduction system. Pacemaker 114 may sense a ventricular electrical signal using tip electrode 132 and ring electrode 134 for sensing R-waves based on R- wave sensing threshold crossings by the ventricular electrical signal. Pacemaker 114 may apply a post-pace and / or post-sense R-wave sensing threshold that is adaptively adjusted according to the techniques disclosed herein to avoid TWOS.

[0056] In some cases, the medical device system 200 may include a second leadless pacemaker 214 implanted in the right atrium for delivering atrial pacing pulses and sensing atrial electrical signals. In this example, pacemaker 214 includes a tip electrode 232 that may be paired with a proximal ring electrode 234 circumscribing the lateral sidewall of cylindrical housing 215 of pacemaker 214. Tip electrode 232 is shown as a non-tissue piercing button electrode in this example but may be provided as a tissue piercing or non-tissue piercing electrode and may be any of the types of example electrodes listed herein. Pacemaker 214 may include a fixation member 213, e.g., providedas one or more fixation tines, extending from distal end 212 of pacemaker housing 215 to provide fixation of pacemaker 214 at an atrial pacing site.

[0057] In some examples, atrial pacemaker 214 can provide atrial pacing and sensing and ventricular pacemaker 114 can provide ventricular pacing (via the conduction system and / or ventricular myocardium) and sensing in a dual chamber leadless pacemaker system 200. Atrial pacemaker 214 and ventricular pacemaker 114 may communicate wirelessly, as shown by arrow 218, to coordinate dual chamber pacing delivery. For example, atrial pacemaker 214 may transmit a signal to ventricular pacemaker 114 when an atrial pacing pulse is delivered or an atrial P-wave is sensed so that ventricular pacemaker 114 can deliver an atrial synchronous ventricular pacing pulse at a desired atrioventricular (AV) pacing interval. In other examples, ventricular pacemaker 114 may sense atrial systolic event signals, e.g., from an electrical signal sensed by pacemaker 114 or from an acceleration signal sensed by an accelerometer included in pacemaker 114, for use in synchronizing ventricular pacing pulses to the atrial event signals. While not shown in FIG. 3, it is to be understood that external device 50 as shown in FIG. 1, which may be in communication with a network / cloud and / or remote computing device, may be included in the medical device system 200 and may be configured to send data to and receive data from pacemaker 114 and pacemaker 214, if present.

[0058] While several examples of medical device systems are shown and described in conjunction with FIGs. 1 — 3, it is to be understood that the methods for controlling an adaptively adjusted cardiac event sensing threshold, e.g., an R-wave sensing threshold, as described herein are not limited to a particular cardiac device system. The methods disclosed herein may be practiced in any medical device system that includes a medical device that is capable of sensing cardiac electrical signals and delivering pacing pulses.

[0059] FIG. 4 is a diagram of circuitry that may be enclosed within implantable pacemaker 14 of FIG. 1 configured to deliver cardiac electrical stimulation therapies and sense cardiac electrical signals according to the techniques disclosed herein. The diagram of FIG. 4 is described with reference to pacemaker 14 connected to atrial lead 16 carrying electrodes 20 and 22 and ventricular lead 18 carrying electrodes 32, 34, 36 and 38. It is to be understood, however, that the functionality attributed to the various circuits and components shown in FIG. 4 may correspond to circuitry enclosed in a pacemaker configured to perform techniques disclosed herein when connected to other pacing leadand electrode configurations or in a leadless pacemaker. For instance, when pacemaker 14 is configured as an implantable cardioverter defibrillator (ICD) with an integrated bipolar lead, one or both of coil electrodes 36 and / or 38 may be present and coupled to therapy delivery circuit 84 for delivering CV / DF shocks and may be coupled to sensing circuit 86 for use in sensing cardiac electrical signals, e.g., in an integrated bipolar sensing electrode vector including tip electrode 32 and ring electrode 34 may be omitted. Pacemaker 14 may be configured to receive one or more leads for electrical connection to circuitry enclosed by housing 15 to enable selection of a variety of pacing and / or sensing electrode configurations for sensing cardiac electrical signals and delivering cardiac pacing therapies. Housing 15 is depicted in FIG. 4 as an electrode coupled to pacemaker circuitry, e.g., for use in a unipolar pacing and / or sensing electrode vector.

[0060] Furthermore, a pacemaker configured to perform the techniques disclosed herein may be a leadless pacemaker, e.g., pacemaker 114 shown in FIG. 2, including housingbased electrodes for sensing atrial signals, delivering atrial pacing pulses, sensing ventricular signals and delivering ventricular pulses. In this case, the multiple housing based electrodes, e.g., electrodes 120, 132 and 134 shown in FIG. 2, can be coupled to sensing circuit 86 and therapy delivery circuit 84. In still other examples, circuitry generally described in conjunction with FIG. 4 may be included in pacemaker 114 implanted in the right ventricle as shown in FIG. 3 for sensing cardiac signals and delivering ventricular pacing pulses to a pacing site, e.g., in the interventricular septum. The circuitry and functionality of pacemaker 14 described in conjunction with FIG. 4 may be adapted for implementation in a leadless pacemaker or in pacemakers configured to receive one or more pacing leads for performing cardiac signal sensing using an R-wave sensing threshold that is adaptively adjusted to reduce the likelihood of TWOS as described herein.

[0061] The electronic circuitry enclosed within housing 15 (shown conceptually as an electrode in FIG. 4) includes software, firmware and hardware that cooperatively monitor cardiac electrical signals, determine when a pacing pulse is necessary, and deliver electrical pacing pulses to the patient’s heart as needed according to a programmed pacing mode and other pacing control parameters. The electronic circuitry may include a control circuit 80, memory 82, therapy delivery circuit 84, cardiac electrical signal sensing circuit 86 (also referred to herein as “sensing circuit” 86), communication circuit 88 and powersource 98. In some examples, pacemaker 14 may include one or more other sensors 90 for sensing physiological signals. For instance, pacemaker 14 may include a motion sensor such as an accelerometer for sensing patient physical activity, monitoring patient posture, and / or sensing cardiac motion (e.g., when the pacemaker is implanted within the heart such as in the examples of FIGs. 2 or 3). Other examples of physiological sensors that may be included in pacemaker 14 include heart sound sensors, pressure sensors, temperature sensors, oxygen sensors, impedance measurement circuitry or the like.

[0062] Power source 98 provides power to the circuitry of pacemaker 14 including each of the components 80, 82, 84, 86, 88 and 90 as needed. Power source 98 may include one or more energy storage devices, such as one or more rechargeable or non-rechargeable batteries. The connections between power source 98 and each of the other components 80, 82, 84, 86, 88 and 90 are to be understood from the general block diagram of FIG. 4 but are not shown for the sake of clarity. For example, power source 98 may be coupled to one or more charging circuits included in therapy delivery circuit 84 for providing the power needed to charge holding capacitors included in therapy delivery circuit 84 that are discharged at appropriate times under the control of control circuit 80 for delivering pacing pulses. Power source 98 is also coupled to components of sensing circuit 86 (such as sense amplifiers, analog-to-digital converters, switching circuitry, etc.), communication circuit 88, sensors 90 and memory 82 to provide power to the various components and circuits as needed.

[0063] The components shown in FIG. 4 represent functionality included in pacemaker 14 (or pacemaker 114) and may include any discrete and / or integrated electronic circuit components that implement analog and / or digital circuits capable of producing the functions attributed to pacemaker 14 (and pacemaker 114) herein. The various components may include an application specific integrated circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and memory that execute one or more software or firmware programs, a combinational logic circuit, state machine, or other suitable components or combinations of components that provide the described functionality. Providing software, hardware, and / or firmware to accomplish the described functionality in the context of any modem medical device, given the disclosure herein, is within the abilities of one of skill in the art.

[0064] Control circuit 80 communicates, e.g., via a data bus, with therapy delivery circuit 84 and sensing circuit 86 for cooperatively sensing cardiac electrical signals and controlling delivery of cardiac electrical stimulation pulses in response to sensed cardiac event signals (or absence thereof), e.g., R-waves attendant to ventricular depolarization and / or P-waves attendant to atrial depolarization, in accordance with a pacing mode. Electrodes 20, 22, 32, 34, 36 and 38 and housing 15 may be electrically coupled to therapy delivery circuit 84 for delivering electrical stimulation pulses generated by therapy delivery circuit 84. Electrodes 20, 22, 32, 34, 36 and 38 and housing 15 may be electrically coupled to sensing circuit 86 for sensing cardiac electrical signals produced by the heart. Sensing circuit 86 may sense intrinsic signals (such as intrinsic P-waves and intrinsic R-waves) produced by the heart in the absence of a pacing pulse that captures the heart. Sensing circuit 86 may sense evoked response signals, e.g., pacing-evoked P-waves and pacing evoked R-waves, following a delivered pacing pulse of sufficient energy to cause cardiac capture. As further described below, a post-pace R-wave sensing threshold may be applied to a sensed cardiac electrical signal for sensing an intrinsic R-wave following a delivered ventricular pacing pulse. In order to avoid oversensing the T-wave following the pacing-evoked R-wave (thus falsely sensing the T-wave as an intrinsic R- wave), the sensing circuit 86 may increase or “boost” the starting value of the post-pace R- wave sensing threshold. As further described below, the post-pace R-wave sensing threshold may be adaptively adjusted by sensing circuit 86 based on when high sensing threshold criteria are met as determined by control circuit 80. In some examples, a postsense R-wave sensing threshold may be adaptively adjusted by sensing circuit 86 based on when high sensing threshold criteria are met.

[0065] Sensing circuit 86 may include an input pre-filter and amplifier 140 for receiving a cardiac electrical signal from a pair of sensing electrodes, e.g., atrial lead electrodes 20 and 22 and ventricular lead electrodes 32 and 34 or ventricular lead electrodes 32 and 36, as non-limiting examples. The filtered and amplified signal may be passed to an analog-to- digital converter and wide bandpass filter (ADC) 141 for producing a multi -bit digital cardiac electrical signal that may be passed to control circuit 80 and is referred to herein as a cardiac electrogram or “EGM” signal when the raw signal is sensed from electrodes on or within a heart chamber.

[0066] Sensing circuit 86 may further include a rectifier and narrowband filter / amplifier142 for receiving the ADC signal and passing a rectified, filtered signal to cardiac event detector circuit 143. Cardiac event detector circuit 143 may produce a cardiac sensed event signal, e.g., a sensed ventricular event (Vsense) signal or a sensed atrial event (Asense) signal, in response to the respective rectified ventricular EGM signal or atrial EGM signal crossing a sensing threshold amplitude, e.g., an R-wave sensing threshold or a P-wave sensing threshold, respectively. The sensed event signal is passed to control circuit 80 for use in controlling pacing pulses. For example, in response to receiving an Asense signal from sensing circuit 86, pace timing and control circuit 147 included in control circuit 80 may set a pacing escape interval timer for scheduling a ventricular pacing pulse at an AV pacing interval (when pacemaker 14 is operating in an atrial synchronous ventricular pacing mode). Control circuit 80 may inhibit an atrial pacing pulse in response to the Asense signal and schedule a subsequent atrial pacing pulse by starting an atrial lower rate interval (LRI) to provide bradycardia pacing of the atria when the LRI expires without an Asense signal being received from sensing circuit 86. The LRI may correspond to a programmed base pacing rate and is used by control circuit 80 to control the minimum heart rate of the patient to be at least the base pacing rate. At other times, the LRI may be a temporary rate response pacing interval based on a patient activity metric determined by control circuit 80 from a patient activity signal received from sensors 90.

[0067] In response to receiving a Vsense signal, a scheduled ventricular pacing pulse may be inhibited and a ventricular pacing interval, e.g., a ventricular LRI, may be started for scheduling a ventricular pacing pulse. If the ventricular LRI expires before a Vsense signal is received and before an Asense signal is received or an atrial pacing pulse is delivered for triggering an atrial synchronous ventricular pacing pulse at the AV pacing interval, therapy delivery circuit 84 may deliver the scheduled ventricular pacing pulse to pace the ventricles. The techniques disclosed herein can reduce the likelihood of control circuit 80 receiving a false Vsense signal due to TWOS by reducing the likelihood that a post-pace T-wave (that corresponds to myocardial repolarization after a pacing-evoked R-wave) crosses the post-pace R-wave sensing threshold applied by cardiac event detector circuit143 to the ventricular EGM signal.

[0068] Pace timing and control circuit 147 may include various timers or counters for performing timing related functions of control circuit 80 including, but not limited to,counting down various pacing escape intervals set according to a permanent or temporary pacing mode. The pacing modes of pacemaker 14 may include various bradycardia pacing modes such as single chamber atrial pacing, dual chamber atrial synchronous ventricular pacing, dual chamber atrial asynchronous ventricular pacing, and single chamber ventricular pacing, as non-limiting examples, and may include bradycardia pacing with rate response pacing in some examples. A sensed event signal received from sensing circuit 86 by control circuit 80 may cause pace timing and control circuit 147 to trigger or inhibit a pacing pulse depending on the particular pacing mode in effect.

[0069] The time expired of a pacing escape interval started by pace timing and control circuit 147 when a sensed event signal is received from sensing circuit 86 may be passed to processor 148 as a cardiac event interval for use in determining the heart rhythm, e.g., for detecting tachycardia and / or fibrillation. For example, the time expired of a ventricular pacing escape interval (started in response to a Vsense signal or a delivered ventricular pacing pulse) when the next Vsense signal is received may be determined as an RR interval (RRI). Processor 148 may compare RRIs to a ventricular tachycardia (VT) detection interval and / or a ventricular fibrillation (VF) detection interval for detecting VT and / or VF intervals (VT / VF intervals). Control circuit 80 may include one or more counters used for counting VT / VF intervals, e.g., a VT interval counter, a VF interval counter and / or a combined VT / VF interval counter. When a counter, which may be an X of Y counter, reaches a required number of intervals to detect (NID) VT or VF, control circuit 80 may detect a VT / VF episode and control therapy delivery circuit to deliver a cardiac electrical stimulation therapy, e.g., anti-tachycardia pacing (ATP) or a cardioversion or defibrillation (CV / DF) shock. As further described below, control circuit 80 may determine when high sensing threshold criteria are met based on a count of VT / VF intervals for adaptively controlling the R-wave sensing threshold applied to a sensed ventricular EGM signal by sensing circuit 86.

[0070] Sensing circuit 86 may include multiple sensing channels, e.g., a ventricular sensing channel and an atrial sensing channel, and in some examples a far field morphology sensing channel. For example, sensing circuit 86 may include an atrial sensing channel configured to receive an atrial signal from atrial electrodes 20 and 22, which may be filtered, amplified, rectified and passed to an atrial event detector circuit included in cardiac event detector circuit 143. Cardiac event detector circuit 143 maygenerate an Asense signal in response to the atrial signal crossing a P-wave sensing threshold. A ventricular sensing channel of sensing circuit 86 may receive a ventricular signal from ventricular electrodes 32 and 34 for bipolar sensing, from electrode 32 and either of coil electrodes 36 or 38 (e.g., in an integrated bipolar sensing electrode pair), electrode 34 and either of coil electrodes 36 or 38, or any of ventricular lead electrodes 32, 34, 36 or 38 paired with housing 15, as examples. The ventricular sensing channel may include the same or a different narrowband filter than the atrial sensing channel. A ventricular event detector circuit of cardiac event detector circuit 143 can be configured to generate a Vsense signal in response to the narrowband filtered ventricular signal crossing an R-wave sensing threshold. Each atrial sensing channel and ventricular sensing channel may include separate pre-filter / amplifiers 140, ADC 141, rectifier and narrowband filter / amplifier 142 and cardiac event detector circuit 143 or some components may be shared between the different sensing channels. Cardiac event detector circuit 143 may include one or more sense amplifiers, comparators and / or other components configured to receive the filtered, amplified and (at least in some cases) rectified atrial and ventricular signals, compare the signals to respective P-wave and R-wave sensing thresholds, and generate respective Asense and Vsense signals passed to control circuit 80.

[0071] In some examples, a wideband filtered EGM signal may be passed to control circuit 80, e.g., from the ADC 141 of a ventricular sensing channel prior to narrowband filtering of the EGM signal that is passed to cardiac event detector circuit 143. The wideband filtered EGM signal may be used for performing morphology analysis of the P- wave, R-wave, and / or T-wave. For instance, in some examples, an analysis of the R-wave peak amplitude and T-wave peak amplitude in the EGM signal may be performed for use in controlling the adaptively adjusted post-pace R-wave sensing threshold for reducing the likelihood of TWOS.

[0072] Morphology analysis of a sensed signal waveform corresponding in time to a Vsense signal received from sensing circuit 86 may be performed by control circuit 80 for detecting evidence of TWOS. The sensed signal waveform may be a true QRS signal correctly sensed as an R-wave resulting in a true Vsense signal. However, in some instances, the sensed signal waveform may be a T-wave falsely sensed as an R-wave resulting in a false Vsense signal. Control circuit 80 may determine one or more features of the sensed signal waveform for comparison to respective thresholds or ranges expectedwhen the sensed signal waveform is a true R-wave. For instance, the peak amplitude, peak polarity pattern, maximum slope, signal width, signal area or other features or combinations of features of a sensed signal waveform may be determined and compared to the analogous feature(s) of a known R-wave, a previously established R-wave template, and / or to a consecutively sensed signal waveform for detecting evidence of TWOS.

[0073] In some examples, control circuit 80 may determine a waveform morphology matching score between a sensed signal waveform and an R-wave template, which may be stored in memory 82. One method for determining a waveform morphology matching score includes performing a wavelet transform, e.g., a Haar wavelet transform, for determining wavelet coefficients that can be compared to the wavelet coefficients of the R-wave template. A computed distance or difference between the coefficients, which may be weighted, may be determined as a morphology matching score. When the morphology matching score does not meet a match threshold, evidence of TWOS may be detected by control circuit 80 because the sensed signal waveform may not be a true R-wave. Other waveform correlation or matching methods may be performed by control circuit 80 for detecting evidence of TWOS.

[0074] The detection of evidence of TWOS may include an analysis of time intervals between consecutively received Vsense signals, in addition to or alternatively to analyzing sensed signal waveform morphology. For example, when the time intervals between consecutively received Vsense signals and / or intervals between ventricular pacing pulses and Vsense signals (which can be referred to collectively as “RR intervals” or “RRIs”) are alternating in length, e.g., short-long-short-long, the received Vsense signals may correspond to alternating false Vsense and true Vsense signals (or alternating ventricular pacing pulses and false Vsense signals) produced at R-T and T-R intervals. An alternating pattern of RRIs, alternating pattern peak amplitudes or other signal features of the sensed signal waveforms, alternating waveform morphology matching scores or any combination thereof may be detected by control circuit 80 as evidence of TWOS.

[0075] When control circuit 80 detects evidence of TWOS, an adaptive control condition may be met. Sensing circuit 86 may adaptively control the post-pace R-wave sensing threshold when an adaptive control condition is met. The R-wave sensing threshold may be adaptively controlled to have a relatively higher amplitude when high sensing threshold criteria are met compared to the R-wave sensing threshold amplitude when the highsensing threshold criteria are not met. The high sensing threshold criteria may be met when a ventricular pacing rate is less than a rate threshold and / or when less than a threshold number of VT / VF intervals are detected, as examples. Methods for adaptively adjusting the post-pace R-wave sensing threshold applied by cardiac event detector circuit 143 to a sensed ventricular EGM signal based on when high sensing threshold criteria are met (or not met) are further described below.

[0076] Control circuit 80 may be configured to control therapy delivery circuit 84 to deliver atrial and ventricular pacing pulses according to a programmed or automatically selected pacing mode and programmed or automatically adjusted pacing control parameters. Therapy delivery circuit 84 is configured to generate pacing pulses and includes a charging circuit 144 including one or more charge storage devices such as one or more holding capacitors, an output circuit 146, and switching circuitry 145. Switching circuitry 145 can be controlled by control signals from control circuit 80 to control when the holding capacitor(s) of charging circuit 144 are charged and when the charged holding capacitor(s) are discharged through the output circuit 146 to deliver pacing pulses via a selected pacing electrode vector for pacing the atria and / or the ventricles (which may be paced via the Elis-Purkinje conduction system) according to the programmed pacing mode.

[0077] Output circuit 146 may include switching circuitry for selecting the pacing electrode vector(s) and associated pacing electrode polarities coupled to a holding capacitor of charging circuit 144 via switching circuitry 145. For instance, output circuit 146 may include switching circuitry for selecting the ventricular lead tip electrode 32 as a pacing cathode electrode with return anode ring electrode 34 for bipolar CSP in the area of the His bundle, LBB or RBB or at a myocardial pacing site. Alternatively, ring electrode 34 may be selected as a cathode electrode with tip electrode 32 selected as the return anode in a bipolar pacing electrode vector for delivering ventricular pacing via the conduction system and / or ventricular myocardium. The atrial lead electrodes 20 and 22 may be selected by switching circuitry included in output circuit 146 in an atrial pacing electrode vector for delivering atrial pacing pulses.

[0078] Charging of a holding capacitor to a programmed pacing voltage amplitude and discharging of the capacitor for a programmed pacing pulse width may be performed by therapy delivery circuit 84 according to control signals received from control circuit 80. For example, pace timing and control circuit 147 included in control circuit 80 mayinclude programmable digital counters set by processor 148 for controlling the basic pacing time intervals, which can also be referred to as “escape intervals,” associated with various single chamber and dual chamber pacing modes. Control circuit 80 may also set the amplitude, pulse width, polarity, or other characteristics of the cardiac pacing pulses, which may be based on programmed values stored in memory 82.

[0079] Therapy delivery circuit 84 may include multiple pacing channels for delivering pacing pulses, e.g., an atrial pacing channel and a ventricular pacing channel. Each pacing channel may be coupled to selected electrodes via switching circuitry included in output circuit 146 for selecting various unipolar or bipolar pacing electrode combinations for delivering pacing pulses. In some examples, multiple pacing channels may include an additional left ventricular pacing channel, e.g., when pacemaker 14 is coupled to a coronary sinus lead to facilitate delivery of CRT.

[0080] When pacemaker 14 is configured to deliver high voltage CV / DF shocks, therapy delivery circuit 84 may include a high voltage therapy circuit for generating high voltage CV / DF shock pulses in addition to a low voltage therapy circuit that generates cardiac pacing pulses. Therapy delivery circuit 84 may operate under the control of control circuit 80 to deliver a variety of cardiac electrical stimulation pulses, which may include bradycardia pacing pulses, ATP pulses, induction pulses for defibrillation testing, CV / DF shock pulses, post-shock pacing pulses, and impedance measurement drive signals, as examples.

[0081] Sensor(s) 90 may include a patient activity sensor provided for sensing a signal correlated to patient physical activity for use by control circuit 80 in controlling rate response pacing. In one example, the activity sensor is an accelerometer, e.g., a single or multi-axis piezoelectric sensor or MEMS device, for sensing an acceleration signal. The accelerometer may produce an electrical signal correlated to motion or vibration of the accelerometer, e.g., when subjected to patient body motion. The activity sensor may include one or more filter, amplifier, rectifier, anal og-to-digi tai converter (ADC) and / or other components for producing an acceleration signal that may be passed to control circuit 80 for use in determining a patient physical activity metric for controlling rate response pacing.

[0082] In various examples, an acceleration signal received from sensor(s) 90 by control circuit 80 may be filtered by a band pass or low pass filter, e.g., a 1-10 Hz bandpass filteror a 10 Hz low pass filter, digitized by an ADC and rectified for use by processor 148 of control circuit 80 for determining a patient physical activity metric. Various activity metrics may be derived from the acceleration signal by control circuit 80 that are correlated to patient physical activity. For instance, the activity metric derived from the acceleration signal may be obtained by integrating the absolute value of an acceleration signal received from activity sensor 90 over a predetermined time duration (such as 2 seconds). The amplitude of the sampled data points over a two-second interval may be summed to obtain the activity metric. This activity metric may be referred to as an “activity count” and is correlated to the acceleration due to patient body motion imparted on the pacemaker 14 during the predetermined time interval. The 2-second (or other time interval) activity counts may be used by control circuit 80 for determining a sensor indicated pacing rate (SIR) for use in controlling rate response pacing. A patient activity metric or SIR may be used to control the rate of atrial or ventricular pacing pulses according to a temporary rate response pacing interval, based on the SIR, that is shortened by control circuit 80 from the programmed LRI.

[0083] Communication circuit 88 may include a transceiver and antenna for communicating with external device 50 (shown in FIG. 1) using radio frequency communication as described above. Control parameters utilized by control circuit 80 for sensing cardiac event signals, analyzing EGM signals, and controlling cardiac pacing may be programmed into memory 82 via communication circuit 88 for retrieval and execution by processor 148 of control circuit 80. Under the control of control circuit 80, communication circuit 88 may receive downlink telemetry from and send uplink telemetry to the external device 50. As described above in conjunction with pacemaker 114 in FIG. 3, in some examples, communication circuit 88 may be configured to communicate with another implanted device, e.g., the atrial pacemaker 214 shown in FIG. 3, for coordinating dual chamber pacing in a two device system. In some examples, inter-device communication performed by communication circuit 88 may include tissue conductance communication.

[0084] FIG. 5 is a flow chart 300 of a method for performing R-wave sensing by pacemaker 14 according to some examples. For the sake of illustration, FIG. 5 and other flow charts presented herein are described with reference to pacemaker 14 of FIG. 1 and FIG. 4. It is to be understood, however, that the disclosed techniques attributed topacemaker 14 and components of FIG. 4 may be implemented in other medical devices, including the leadless pacemaker 114 shown in FIGs. 2 and 3.

[0085] At block 302, control circuit 80 may determine the starting value of the post-pace R-wave sensing threshold. The starting value may be based on the programmed ventricular sensitivity in some examples. The programmed ventricular sensitivity is the minimum amplitude of the R-wave sensing threshold and is the minimum amplitude of the ventricular EGM signal that can be sensed as an R-wave by sensing circuit 86. Thus, the lower the ventricular sensitivity setting is in millivolts (mV), the more sensitive sensing circuit 86 is in sensing R-waves. As the programmed ventricular sensitivity setting in mV is increased, sensing circuit 86 becomes less sensitive to sensing small amplitude R- waves. As described below in conjunction with FIG. 6, the post-pace R-wave sensing threshold applied to the ventricular EGM signal by sensing circuit 86 may have a starting value, determined at block 302, that decays or decreases over time until the ventricular sensitivity is reached or an R-wave sensing threshold crossing by the ventricular EGM signal occurs, whichever comes first.

[0086] As further described below, e.g., in conjunction with FIG. 7, control circuit 80 may determine the starting value of a post-pace R-wave sensing threshold at block 302 by determining whether high sensing threshold criteria are met. The high sensing threshold criteria may include one or more criteria that, when met, cause control circuit 80 to select a high starting value of the post-pace R-wave sensing threshold. When the high sensing threshold criteria are not met, control circuit 80 may set the starting value of the post-pace R-wave sensing threshold to a low starting value, that is lower than the high starting value. The post-pace low starting value may be a multiple or offset greater than the programmed ventricular sensitivity, e.g., 2 to 10 times greater than the programmed ventricular sensitivity. For example, the low starting value of the post-pace R-wave sensing threshold may be 2.5 to 5 times the programmed ventricular sensitivity or about 3.5 times the programmed ventricular sensitivity. The high starting value of the post-pace R-wave sensing threshold selected when the high sensing threshold criteria are met may be a higher multiple of the programmed ventricular sensitivity, e.g., 2 to 25 times the programmed ventricular sensitivity, 3 to 20 times the programmed ventricular sensitivity or 5 to 10 times the programmed ventricular sensitivity in various examples.

[0087] As such, control circuit 80 may determine the starting value of the post-pace Il- wave sensing threshold at block 302 by first determining if the high sensing threshold criteria are met. If so, control circuit 80 selects the high starting value. The high starting value may be determined by control circuit 80 based on the programmed ventricular sensitivity, a determined T-wave amplitude, a determined R-wave amplitude and / or a pacing rate in various examples, as further described below. If the high sensing threshold criteria are not met, control circuit 80 may select the low starting value. Example methods for determining if the high sensing threshold criteria are met are described below. Briefly, high sensing threshold criteria may be if Vsense signals are being received at RRIs that are not ventricular tachycardia or ventricular fibrillation (VT / VF) intervals (e.g., less than M VT / VF interval out the most recent N RRIs). Additionally or alternatively, control circuit 80 may determine that the high sensing threshold criteria are met when the ventricular rate is less than a threshold rate, which may be a paced ventricular rate. In some examples, the high starting value of the post-pace R-wave sensing threshold may be selected at block 302 and remain selected as long as the high sensing threshold criteria are met. If the high sensing threshold criteria become unmet, e.g., a threshold number of sensed VT / VF intervals are detected or the ventricular pacing rate exceeds a threshold rate, control circuit 80 may select the low starting value of the R-wave sensing threshold.

[0088] In some examples, in addition to or alternatively to determining the post-pace starting sensing threshold at block 302, a post-pace decay rate of the R-wave sensing threshold may be selected by control circuit 80 when high sensing threshold criteria are met. The post-pace decay rate selected when high sensing threshold criteria are met may be selected to promote an R-wave sensing threshold amplitude that is greater than an expected T-wave amplitude at the time of the expected T-wave. The post-pace decay rate may be determined by determining a T-wave amplitude and / or timing of the post-pace T- wave following a delivered ventricular pacing pulse. Control circuit 80 may determine an adjusted post-pace decay rate that is different than a post-sense decay rate of the R-wave sensing threshold applied by sensing circuit 86 following a Vsense signal and / or different than the post-pace decay rate applied following a ventricular pacing pulse when the high sensing threshold criteria are not met.

[0089] In this way, the adjusted decay rate of the R-wave sensing threshold from the selected starting value to the programmed ventricular sensitivity may be tailored to thepatient in a manner that both reduces the likelihood of TWOS while still promoting a relatively high sensitivity for sensing R-waves, e.g., by starting at a high R-wave sensing threshold and decaying as quickly as possible to the programmed ventricular sensitivity without reaching an R-wave sensing threshold value that is lower than the T-wave amplitude at the expected time of the post-pace T-wave time.

[0090] In some examples, control circuit 80 may be configured to select a post-sense starting value and / or post-sense decay rate of the R-wave sensing threshold amplitude, which may be different than the post-pace starting value and / or post-pace decay rate. When the high sensing threshold criteria are met at block 302, control circuit 80 may determine a relatively higher starting value of the post-sense R-wave sensing threshold and / or a relatively slower adjusted decay rate of the post-sense R-wave sensing threshold than the post-sense starting value and decay rate used when the high sensing threshold criteria are not met. For example, the post-sense R-wave sensing threshold may be determined as a percentage of the maximum peak amplitude of the sensed signal. A higher percentage (of the sensed signal peak amplitude) may be selected by control circuit 80 for determining the post-sense starting value of the R-wave sensing threshold when the high sensing threshold criteria are met at block 302 than when the high sensing threshold criteria are not met. In other examples, a multiple of the programmed ventricular sensitivity may be selected as the starting value of the post-sense R-wave sensing threshold when the high sensing threshold criteria are met. A percentage of the peak amplitude of the most recently sensed waveform may be selected as the starting value of the post-sense R-wave sensing threshold when the high sensing threshold criteria are not met.

[0091] After control circuit 80 has established the starting value(s) and / or decay rate(s) of the post-pace and / or post-sense R-wave sensing threshold, therapy delivery circuit 84 may deliver a ventricular pacing pulse at block 304 according to programmed pacing mode, e.g., upon expiration of an AV pacing interval or a ventricular LRI (which may be a base pacing rate LRI, a rate smoothing interval, or a shorter, temporary LRI during rate response pacing). In some instances, the ventricular pacing pulse delivered at block 304 could be a post-shock pacing pulse or an ATP pulse. At block 306, sensing circuit 86 may apply a post-pace blanking period. The post-pace blanking period may be applied to allow the post-pace artifact to decay prior to applying the R-wave sensing threshold to theventricular EGM signal. The post-pace blanking period may be 50-450 milliseconds (ms), as examples, starting from the time of the ventricular pacing pulse. A nominal post-pace blanking period may be 200 to 250 ms as examples.

[0092] Upon expiration of the post-pace blanking period, sensing circuit 86 may apply the post-pace R-wave sensing threshold amplitude to the ventricular EGM signal. As further described below, e.g., in conjunction with FIG. 6 and 12, the R-wave sensing threshold may have a starting value, selected at block 302, that decays toward the programmed ventricular sensitivity (e.g., according to an adjusted or programmed decay rate) until the ventricular EGM signal crosses the R-wave sensing threshold or a ventricular pacing escape interval expires, whichever comes first.

[0093] If an escape interval expires (“yes” branch of block 310) before a Vsense signal is received from sensing circuit 86 (“no” branch of block 312), therapy delivery circuit 84 may deliver another ventricular pacing pulse at block 304. Control circuit 80 may restart a ventricular pacing interval in response to therapy delivery circuit 84 delivering the ventricular pacing pulse at block 304. Sensing circuit 86 may restart the post-pace sensing sequence of applying a post-pace blanking period (block 306) and the post-pace R-wave sensing threshold (block 308). It is to be understood that in some instances, an AV pacing interval may be started when a P-wave is sensed or an atrial pacing pulse is delivered during a ventricular LRI. The escape interval that expires at block 310 may be an AV pacing interval that can expire before a Vsense signal is received by control circuit 80 at block 312 from sensing circuit 86.

[0094] If a ventricular pacing escape interval has not expired (“no” branch of block 310), control circuit 80 continues to wait for a Vsense signal from sensing circuit 86. If the ventricular EGM signal crosses the R-wave sensing threshold before the escape interval expires, sensing circuit 86 generates a Vsense signal that is received by control circuit 80 (“yes” branch of block 312). In response to the Vsense signal, control circuit 80 may restart the ventricular pacing escape interval that was running at the time of the Vsense signal (and inhibit the scheduled ventricular pacing pulse).

[0095] Following the Vsense signal, sensing circuit 86 may start a post-sense sensing sequence, which may include a post-sense ventricular blanking period applied at block 314 and applying a post-sense R-wave sensing threshold to the ventricular EGM signal atblock 316. The post-sense R-wave sensing threshold may have a starting value that is determined differently than the post-pace R-wave sensing threshold starting value.

[0096] For instance, the post-sense R-wave sensing threshold may be determined by control circuit 80 based on the maximum peak amplitude of the signal waveform sensed as an R-wave by sensing circuit 86, resulting in the Vsense signal at block 312. The cardiac event detector circuit 143 (FIG. 4) may detect the maximum peak amplitude of the ventricular EGM signal following an R-wave sensing threshold crossing. For instance, the cardiac event detector circuit 143 may include a peak track and hold circuit for determining the maximum peak amplitude during a peak tracking window. The peak tracking window may be the same as the post-sense ventricular blanking period or a portion thereof, e.g., extending from the R-wave sensing threshold crossing and expiring earlier than the post-sense ventricular blanking period. Sensing circuit 86 may pass the maximum peak amplitude of the sensed waveform to control circuit 80. The starting value of the post-sense R-wave sensing threshold may be determined by control circuit 80 as a percentage of the maximum peak amplitude of the sensed waveform. As such, the starting value of the post-sense R-wave sensing threshold and the starting value of the post-pace R-wave sensing threshold may be determined according to different techniques by pacemaker 14.

[0097] The post-sense sensing threshold applied at block 316 may decay according to a programmed post-sense decay rate from the post-sense starting value to the programmed ventricular sensitivity. The post-sense decay rate may be the same or different than the decay rate of the post-pace R-wave sensing threshold and may be a programmed decay rate that is used post-sense and, in some examples, post-pace when the high sensing threshold criteria are not met.

[0098] Control circuit 80 may return to block 310 to wait for a ventricular pacing interval to expire at block 310 or a Vsense signal to be received again at block 312, whichever comes first. Sensing circuit 86 applies the post-pace sensing sequence as indicated at blocks 306 and 308 in response to a delivered ventricular pacing pulse when a ventricular pacing interval expires. Sensing circuit 86 applies the post-sense sensing sequence as indicated at blocks 314 and 316 in response to a Vsense signal produced when the ventricular EGM signal crosses the R-wave sensing threshold.

[0099] It is noted that as long as the high sensing threshold criteria continue to be met (as determined at block 302), the post-pace R-wave sensing threshold (applied at block 308) may be controlled by sensing circuit 86 according to the high starting value and / or an adjusted decay rate. When the high sensing threshold criteria become unmet (as determined at block 302), the post-pace R-wave sensing threshold may be controlled by sensing circuit 86 according to the low starting value and a non-adjusted decay rate. The low starting value and non-adjusted decay rate may be used to control the post-pace R- wave sensing threshold at block 308 until control circuit 80 determines that the high sensing threshold criteria are met again (block 302). In this way, the post-pace R-wave sensing threshold may be adaptively controlled according to whether the high sensing threshold criteria are met or not.

[0100] Furthermore, when the high sensing threshold criteria are met (as determined at block 302), the post-sense R-wave sensing threshold (applied at block 314) may be adaptively controlled by sensing circuit 86 according to a high post-sense starting value and / or an adjusted post-sense decay rate. When the high sensing threshold criteria become unmet (as determined at block 302), the post-sense R-wave sensing threshold may be controlled by sensing circuit 86 according to the low post-sense starting value and a nonadjusted decay rate. The low starting value and non-adjusted decay rate may be used to control the post-sense R-wave sensing threshold at block 314 until control circuit 80 determines that the high sensing threshold criteria are met again (block 302). In other examples, the post-pace R-wave sensing threshold may be adaptively controlled based on whether the high sensing threshold criteria are met, and the post-sense R-wave sensing threshold may not be adaptively adjusted by applying the post-sense R-wave sensing threshold having a starting value determined as a specified (non-adapted) percentage of the sensed event peak amplitude and a programmed (non-adjusted) decay rate independent of whether the high sensing threshold criteria are met.

[0101] While not shown explicitly in the flow chart 300, it is to be understood that at any time during the process of flow chart 300, control circuit 80 may re-determine whether the high sensing threshold criteria are met or unmet for updating the selected post-pace R- wave sensing threshold starting value and / or post-pace decay rate and / or the selected postsense R-wave sensing threshold starting value and / or post-sense decay rate. The process of determining whether the high sensing threshold criteria are met and selecting the R-wavesensing threshold starting value and / or decay rate at block 302 may be performed in parallel or concomitantly with the process of blocks 304 through 316. For example, the counts of VT / VF intervals and / or the ventricular pacing rate may be updated on a beat by beat basis and compared to the high sensing threshold criteria on a beat by beat or less frequent basis for updating the selected starting value and / or decay rate of the post-pace Il- wave sensing threshold (and in some examples the post-sense R-wave sensing threshold) based on whether the high sensing threshold criteria are met or unmet. Furthermore, while the method of FIG. 5 presumes a ventricular pacing pulse is delivered at block 304, prior to control circuit 80 receiving a Vsense (block 312), it is to be understood that a Vsense may be received prior to a ventricular pacing pulse after determining if the high sensing threshold criteria are met or not at block 302.

[0102] FIG. 6 is a diagram 400 of the high R-wave sensing threshold 408 and low R-wave sensing threshold 418 that may be adaptively applied to the ventricular EGM signal 401 by sensing circuit 86 according to some examples. A ventricular pacing pulse (VP) 402, also referred to herein as a “Vpace”) is delivered at time 0 ms. The rectified ventricular EGM signal 401, sensed by sensing circuit 86 following Vpace 402, is shown and may include the pacing-evoked QRS waveform 403 and the post-pace T-wave 420. Sensing circuit 86 may apply a post-pace blanking period 404 following the Vpace 402. Vsense signals are not produced by sensing circuit 86 during the post-pace blanking period 404. It is noted that while the rectified evoked response QRS waveform 403 is shown in FIG. 6 for the sake of illustration, sensing circuit 86 may blank ADC 141, amplifiers and / or other components of sensing circuit 86 during the blanking period 404 so that the high amplitude pacing artifact does not saturate the sensing circuitry.

[0103] Control circuit 80 may determine whether the high sensing threshold criteria are met for selecting either a high starting value 406 or low starting value 416 of the R-wave sensing threshold applied to the post-pace ventricular EGM signal 401. When the high sensing threshold criteria are met, the high starting value 406 may be selected, and the R- wave sensing threshold 408 may decay from the high starting value 406 to the programmed ventricular sensitivity 410. When the high sensing threshold criteria are not met, the low starting value 416 may be selected so that the R-wave sensing threshold 418 decays from the low starting value 416 to the programmed ventricular sensitivity 410.

[0104] When the low starting value 416 is selected and R-wave sensing threshold 418 exponentially decays to the programmed ventricular sensitivity 410, the post-pace T-wave 412 may cross the R-wave sensing threshold 418. In this instance, sensing circuit 86 may oversense the T-wave 412 and produce a false Vsense signal that is passed to control circuit 80.

[0105] When the high starting value 406 is selected, and the R-wave sensing threshold 408 decays exponentially to the programmed ventricular sensitivity 410, T-wave 412 does not cross the R-wave sensing threshold 408. TWOS is avoided by selecting the high starting value 406 of R-wave sensing threshold 408. Control circuit 80 may select the high starting value 406 when the high sensing threshold criteria are met to reduce the likelihood of TWOS.

[0106] However, while it is desirable to avoid TWOS, it is undesirable to undersense true R-waves due to the R-wave sensing threshold remaining greater than an intrinsic R-wave amplitude until the expiration of a ventricular pacing escape interval. In the example of FIG. 6, the high post-pace R-wave sensing threshold 408 and the low post-pace R-wave sensing threshold 418 may decay exponentially at the same decay rate. Because the high post-pace R-wave sensing threshold 408 starts at the high starting value 406, it arrives at the programmed ventricular sensitivity 410 at a later time (as indicated by arrow 405) after the Vpace 402 than the low post-pace R-wave sensing threshold 418. When the ventricular rate is relatively fast, sensing circuit 86 may be less sensitive to sensing R-waves, e.g., low amplitude R-waves during ventricular tachycardia or low amplitude fibrillation waves. Therefore, in order to reduce the likelihood of post-pace TWOS while still promoting a high sensitivity to detecting fast intrinsic ventricular rates, the high sensing threshold criteria may be unmet when the intrinsic ventricular rate and / or the paced ventricular rate is relatively fast. In this way, the low post-pace R-wave sensing threshold 418 may be used during relatively faster ventricular rates so that the R-wave sensing threshold is at or near the programmed ventricular sensitivity 410 more quickly during the relatively short RRI (sensed or paced). Relatively low amplitude intrinsic R-waves may be sensed with a higher sensitivity using the low post-pace R-wave sensing threshold 418 to promote reliable detection of VT / VF and inhibition of ventricular pacing when not needed. As such, the high sensing threshold criteria may include requirements relating to paced and / or sensed ventricular rate limits or paced and / or sensed ventricular event intervals (e.g.,paced or sensed RRIs). If a fast sensed rate is detected, e.g., one or more sensed RRIs are VT / VF intervals, or if the ventricular pacing rate is faster than a threshold rate, the high sensing threshold criteria may be unmet so that the low R-wave sensing threshold 418 is applied by sensing circuit 86 to promote quicker decay to the programmed ventricular sensitivity 410.

[0107] In the example of FIG. 6, the decay rate of the high post-pace R-wave sensing threshold 408 and the low post-pace R-wave sensing threshold is the same. The decay rate may correspond to programmed decay rate and may or may not be the same as a postsense decay rate. In some examples, control circuit 80 may determine an adjusted decay rate for the high post-pace R-wave sensing threshold 408. For instance, sensing circuit 86 may be configured to determine the maximum peak amplitude 420 of the T-wave 412 and the T-wave peak time 422 (e.g., the time interval from Vpace 402 to peak amplitude 420 of T-wave 412). Control circuit 80 may receive the maximum peak amplitude 420 from sensing circuit 86 that follows Vpace 402 after blanking period 404 and store the peak amplitude 420 and corresponding peak time 422 in memory 82. In some examples, control circuit 80 may determine the high starting value 406 and / or adjusted decay rate of high post-pace R-wave sensing threshold 408 based on the maximum peak amplitude 420 and peak time 422. In this way, a starting value 406 may be selected for a given decay rate that results in an R-wave sensing threshold 408 that is expected to be greater than the T-wave peak amplitude 420 at the peak time 422 to reduce the likelihood of oversensing T-wave 420. Alternatively, for a selected starting value 406, an adjusted decay rate may be determined to promote an R-wave sensing threshold 408 that is greater than the peak amplitude 420 at peak time 422. Example methods for determining an adjusted decay rate are further described below, e.g., in conjunction with FIGs. 10 — 12.

[0108] FIG. 7 is a flow chart 450 of a method that may be performed by a medical device for controlling the adaptive R-wave sensing threshold according to some examples. In some examples, the adaptive post-pace and / or post-sense sensing control parameters, e.g., selectable high starting value, adjustable decay rate, and high sensing threshold criteria, may be enabled all the time. In this case, control circuit 80 may analyze the high sensing threshold criteria beat by beat or less often (e.g., at scheduled time intervals, scheduled time(s) of day, or after every N ventricular cycles, etc.) for use in selecting the post-pace starting value (e.g., high or low starting value) and / or decay rate (e.g., adjusted or non-adjusted decay rate) of the post-pace R-wave sensing threshold. In the example of FIG. 7, however, an adaptive sensing control condition may be required to be met (block 452) in order for the control circuit 80 to proceed with analyzing the high sensing threshold criteria and selecting between the high and low starting value and / or an adjusted or nonadjusted decay rate for use by sensing circuit 86 in controlling the post-pace R-wave sensing threshold.

[0109] With continued reference to pacemaker 14 of FIG. 4, control circuit 80 may determine if an adaptive sensing condition is detected at block 452. An adaptive sensing condition may be a condition that, if detected, is an indication that TWOS may be more likely to occur than if the condition is not detected. In some instances, the adaptive control of the post-pace and / or post-sense R-wave sensing threshold may be enabled or disabled by a programming command received via communication circuit 88 from external device 50 (see FIG. 1). A clinician may program the adaptive sensing control on or off, for example. Control circuit 80 may determine that the adaptive sensing condition is met at block 452 at least when an “enable adaptive sensing” programming command is received by communication circuit 88. Control circuit 80 may determine that the adaptive sensing condition is not met at block 452 when a “disable adaptive sensing” programming command is received by communication circuit 88. Post-pace and post-sense adaptive sensing may be individually enabled or disabled by user entered programming commands.

[0110] Additionally or alternatively, control circuit 80 may determine that the adaptive sensing condition is met at block 452 when the programmed ventricular sensitivity setting is greater than a specified threshold value (which may be stored in memory 82). In an illustrative example, a default or nominal ventricular sensitivity setting may be 0.45 mV but may be programmable to lower settings (higher sensitivity for sensing R-waves) or higher settings (lower sensitivity for sensing R-waves). If the ventricular sensitivity setting is programmed to a higher value in mV than the default or nominal setting, which may be stored in memory 82 as threshold value, control circuit 80 may determine that the adaptive sensing condition is met at block 452.

[0111] Additionally or alternatively, control circuit 80 may determine that an adaptive sensing condition is met when TWOS evidence is detected. Control circuit 80 may be configured to determine and analyze ventricular event intervals (e.g., RRIs defined by two consecutive Vsense signals and / or RRIs defined by a Vsense signal and Vpace that areconsecutive in either order). Control circuit 80 may be configured to determine and analyze sensed ventricular event amplitudes, sensed ventricular event morphology, and / or other cardiac signal features for determining when TWOS evidence is detected. For instance, post-pace TWOS evidence may be detected based on at least Vpace to Vsense intervals. For example, if Vpace to Vsense intervals are consistently within an expected T- wave time range and / or the Vpace to Vsense and consecutive Vsense to Vpace intervals are consistently alternating short-long intervals, control circuit 80 may determine that post-pace TWOS evidence is detected at block 452 as an adaptive sensing condition.

[0112] Other example methods for detecting evidence of TWOS are described above in conjunction with FIG. 4. For instance, TWOS evidence may be detected by analyzing the sensed event signal waveform morphology by comparing the sensed signal waveform to a morphology template of a known waveform. For instance, control circuit 80 may perform a waveform correlation or matching analysis to determine if a sensed event waveform matches a previously established T-wave morphology template stored in memory 82 and / or does not match a previously established R-wave morphology template stored in memory 82. In some examples, control circuit 80 may determine one or more features of the sensed waveform, e.g., amplitude, slope, width, area, number and polarity of peaks or other waveform features for comparison to analogous T-wave features stored in memory 82.

[0113] Evidence for T-wave oversensing may be determined from morphology or signal feature analysis of another cardiac electrical signal that is different than the ventricular signal that the R-wave sensing threshold is applied to. For instance, if the R-wave sensing threshold is applied to a bipolar ventricular signal sensed from tip electrode 32 to ring electrode 34, a morphology analysis may be performed using a different cardiac electrical signal sensed from a coil electrode 36 or 38 to housing 15 or another available sensing electrode vector. Analysis of a combination of cardiac electrical signals sensed by sensing circuit 86 may be performed for detecting evidence of TWOS, such as the bipolar ventricular tip electrode to ring electrode signal and a tip electrode to can (housing 15), ring electrode to can, or coil electrode to can signal.

[0114] Furthermore, in some instances evidence of TWOS may be detected by control circuit 80 based on receipt of a user confirmation signal, e.g., transmitted from external device 50. Techniques performed by a medical device configured to determine when anadaptive sensing condition is met by determining when TWOS is suspected at block 452 may generally correspond to methods disclosed in U.S. Patent No. 11,654,291 (Cao, et al., filed November 27, 2020) or in U.S. Patent No. 8,942,795 (Gunderson, et al., filed March 31, 2005), both of which incorporated herein by reference in their entirety. Determining that an adaptive sensing condition is met based on evidence of TWOS is not dependent on a particular method for detecting TWOS. It is recognized that a variety of techniques for detecting evidence of TWOS may be performed by control circuit 80 for determining that the adaptive sensing condition is met at block 452.

[0115] Additionally or alternatively, control circuit 80 may determine that an adaptive sensing condition is met at block 452 when pacemaker 14 is programmed to deliver CSP, which may be confirmed by a user initiated command transmitted to pacemaker 14 via external device 50. Higher T-wave amplitudes may be expected during ventricular pacing via the conduction system than during ventricular pacing delivered to ventricular myocardium, for example. When CSP is being delivered, adaptive control of at least the post-pace R-wave sensing threshold may be enabled, with or without enabling the adaptive control of the post-sense R-wave sensing threshold.

[0116] Additionally or alternatively, control circuit 80 may determine that an adaptive sensing condition is met at block 452 based on the programmed ventricular sensing electrode vector. For instance, when pacemaker 14 is programmed to sense the ventricular EGM signal for R-wave sensing using an integrated bipolar sensing electrode vector, an adaptive sensing condition may be met at block 452. For example, when the ventricular sensing electrode vector is programmed to include a CV / DF coil electrode and a tip electrode or ring electrode, control circuit 80 may determine that an adaptive sensing condition is met at block 452. Higher T-wave amplitudes may be expected during ventricular sensing via an integrated bipolar sensing electrode vector than during ventricular sensing via a true bipolar sensing electrode vector, for example.

[0117] Additionally or alternatively, control circuit 80 may determine that an adaptive sensing condition is met at block 452 when a CV / DF pulse has been delivered. Post-shock T-waves may be higher in amplitude for a period of time following delivery of the CV / DF shock than prior to shock delivery. When a CV / DF shock is delivered, adaptive control of at least the post-sense R-wave sensing threshold may be enabled, with or without enabling the adaptive control of the post-pace R-wave sensing threshold in some examples.

[0118] Control circuit 80 may determine that the adaptive sensing control condition is met at block 452 when one or a combination of two or more adaptive sensing control conditions are met. For example, if adaptive sensing control is programmed on and at least one of: the ventricular sensitivity is programmed to a setting higher than a specified threshold, TWOS evidence is detected, ventricular pacing is being delivered as CSP, or the ventricular sensing electrode vector is an integrated bipolar pair or any combination of two or more of these conditions are met, control circuit 80 may determine that the adaptive sensing control condition is met at block 452. If control circuit 80 determines that one or more required adaptive sensing conditions are not met at block 452, control circuit 80 may disable the adaptive control of the R-wave sensing threshold at block 453. Control circuit 80 may select the low starting value of the R-wave sensing threshold (and a non-adjusted decay rate) at block 454. As described above, the low starting value of the post-pace R- wave sensing threshold may be a specified multiple or offset greater than the programmed ventricular sensitivity in some examples.

[0119] Control circuit 80 may disable determination of whether the high sensing threshold criteria are met when the adaptive sensing control is disabled at block 453. In other examples, control circuit 80 may evaluate the high sensing threshold criteria even though the adaptive sensing control is disabled. Control circuit 80 may update the status of the high sensing threshold criteria in memory 82 as being met or not met on a beat by beat or less frequent basis so that if the adaptive sensing condition is met and adaptive sensing control becomes enabled, control circuit 80 may select between the high and low starting values and / or adjusted or non-adjusted decay rate for controlling the post-pace (or postsense) R-wave sensing threshold following the next Vpace (or Vsense) without delay.

[0120] When an adaptive sensing condition is met at block 452, control circuit 80 enables the adaptive sensing control at block 455. By enabling the adaptive sensing control, control circuit 80 may select between a high starting value and a low starting value and / or between an adjusted and non-adjusted decay rate of the post-pace (and / or post-sense) R- wave sensing threshold. Control circuit 80 determines if the high sensing threshold criteria are met at block 456. The high starting value and / or adjusted decay rate of the post-pace (and / or post-sense) R-wave sensing threshold may be selected

[0121] When the high sensing threshold criteria are determined to be met at block 456 by control circuit 80, according to any of the examples described herein, control circuit 80may select the high starting value and / or an adjusted decay rate at block 458. When the high sensing threshold criteria are not met (“no” branch of block 456), control circuit 80 may select the low starting value and / or non-adjusted decay rate at block 454.

[0122] Accordingly, when conditions for enabling the adaptive sensing control of the Il- wave sensing threshold are not met (“no” branch of block 452), sensing circuit 86 may set the starting value of the R-wave sensing threshold to a relatively low starting value, e.g., a first multiple of the ventricular sensitivity, that decays according to a specified, nonadjusted decay rate toward the programmed ventricular sensitivity. When conditions for enabling the adaptive sensing control of the R-wave sensing threshold are met (“yes” branch of block 452), control circuit 80 may select between the low starting value and a relatively high starting value (e.g., a second multiple greater than the first multiple of the programmed ventricular sensitivity) and / or between the non-adjusted decay rate and an adjusted, e.g., faster, decay rate. Sensing circuit 86 is configured to apply the R-wave sensing threshold to the ventricular EGM signal for sensing R-waves according to the sensing control parameter selections made by control circuit 80.

[0123] Control circuit 80 may select the high starting value of the R-wave sensing threshold to be in effect until the high sensing threshold criteria are re-checked, which may be on a beat-to-beat or less frequent basis. In some instances, the high sensing threshold criteria may be met for one pacing cycle and become unmet on a subsequent pacing cycle such that control circuit 80 may switch between the high starting value and / or adjusted decay rate selection and the low starting value and / or non-adjusted decay rate selection as the high sensing threshold criteria become met and unmet as long as the adaptive sensing condition is met (block 452).

[0124] In some examples, when control circuit 80 determines that the adaptive sensing condition is met at block 452, control circuit 80 may enable both post-pace adaptive control of the R-wave sensing threshold and post-sense adaptive control of the R-wave sensing threshold. In other examples, control circuit 80 may separately and distinctly determine when a post-pace adaptive sensing condition is met at block 452 and when a post-sense adaptive sensing condition is met at block 452. Control circuit 80 may enable or disable post-pace adaptive sensing control and post-sense adaptive sensing control independently based on respective adaptive sensing conditions. Post-sense adaptive sensing conditions may be different than post-pace adaptive sensing conditions. Forexample, control circuit 80 may determine that post-sense adaptive sensing conditions are met when a CV / DF shock has been delivered and / or an integrated bipolar sensing electrode vector is selected. Control circuit 80 may determine that a post-pace adaptive sensing condition is met when any one of a CV / DF shock has been delivered, CSP is being delivered, evidence of TWOS is detected or an integrated bipolar sensing electrode vector is selected. These illustrative examples are non-limiting and other adaptive sensing conditions may be defined, including any combination of the example conditions listed herein, that can be detected by control circuit 80 for separately enabling or disabling postpace adaptive sensing control and post-sense adaptive sensing control.

[0125] FIG. 8 is a flow chart 500 of a method for determining when the high sensing threshold criteria are met after enabling the adaptive sensing control of the R-wave sensing threshold according to some examples. As described above in conjunction with FIG. 7, control circuit 80 of IMD 14 may enable the adaptive sensing control of the R-wave sensing threshold when one or more adaptive sensing conditions are met (block 502). For instance, adaptive sensing control may be enabled when one or more conditions associated with an increased likelihood of TWOS are present, such as CSP, integrated bipolar sensing, or detected evidence of TWOS. In other instances, adaptive sensing control may be programmably enabled by a clinician or be enabled by default unless programmably disabled by a clinician. FIG. 8 is described in conjunction with controlling the post-pace R-wave sensing threshold for the sake of illustration.

[0126] When the adaptive sensing control is enabled, control circuit 80 may determine if criteria for selecting the high post-pace R-wave sensing threshold are met. At block 504, control circuit 80 may determine if a ventricular pacing rate is less than a pacing rate threshold. Therapy delivery circuit 84 may be delivering ventricular pacing pulses synchronously with atrial events (sensed P-waves and / or delivered atrial pacing pulses). In other instances, therapy delivery circuit 84 may be delivering ventricular pacing pulses at a rate response rate, e.g., a temporary pacing rate that is faster than a programmed ventricular lower rate to provide rate support during increased patient physical activity. In other instances, therapy delivery circuit 84 may be delivering ventricular pacing pulses according to the programmed ventricular lower rate (e.g., at LRIs). As such, at any given time, the ventricular rate may be at the programmed lower rate or faster than the programmed lower rate.

[0127] The high sensing threshold criteria evaluated by control circuit 80 for selecting the high R-wave sensing threshold may include a rate threshold applied to the ventricular rate at block 504. When the ventricular rate is faster than (or equal to) a rate threshold (“no” branch of block 504), control circuit 80 may determine that the high sensing threshold criteria are not met and select the low R-wave sensing threshold at block 510. When the pacing rate is relatively fast, the high R-wave sensing threshold may not reach the programmed ventricular sensitivity prior to an expiration of a pacing escape interval. Depending on the decay rate of the high R-wave sensing threshold and the ventricular pacing rate, the high R-wave sensing threshold may not decay from the high starting value to the ventricular sensitivity prior to the next ventricular pacing pulse. In order to promote time for sensing R-waves at (or at least near) the programmed ventricular sensitivity, e.g., to promote sensing of relatively low amplitude R-waves or fibrillation waves, control circuit 80 may select the low R-wave sensing threshold at block 510 when the pacing rate is not less than the rate threshold.

[0128] The rate that is compared to the rate threshold at block 504 may be a scheduled pacing rate, e.g., a the programmed lower rate or a rate response rate. In other instances, the pacing rate that is compared to the rate threshold at block 504 may be an actual delivered pacing rate, e.g., determined from RRIs between consecutively delivered ventricular pacing pulses (with no intervening Vsense signal). The actual delivered pacing rate of ventricular pacing pulses delivered as atrial synchronous ventricular pacing pulses at the expiration of AV pacing intervals, for example, may be faster than the programmed ventricular lower rate. In still other examples, the rate that is compared to the rate threshold at block 504 may be an actual ventricular rate determined from RRIs that may include both ventricular pacing pulses and Vsense signals.

[0129] Additionally or alternatively, the high sensing threshold criteria for selecting the high R-wave sensing threshold at block 508 may include a threshold number of ventricular tachyarrhythmia intervals. Control circuit 80 may determine sensed RRIs as the time intervals between consecutive Vsense signals received from sensing circuit 86. Control circuit 80 may compare the sensed RRIs to a VT interval range and / or to a VF interval for counting VT / VF intervals. In some cases, a sensed RRI may be an RRI that ends with a Vsense signal but may begin with a Vsense signal or a Vpace. When a VT / VF interval counter reaches a threshold number of intervals to detect (NID), control circuit 80 maydetect a ventricular tachyarrhythmia episode. When the adaptive sensing control is enabled, control circuit 80 may compare the VT / VF interval counters to a threshold value at block 506 for determining if high sensing threshold criteria are met. If less than a specified threshold number of VT / VF intervals have been counted, control circuit 80 may select the high R-wave sensing threshold at block 508 (e.g., high starting value and / or adjusted decay rate). If at least a specified threshold number of VT / VF intervals have been counted, control circuit 80 may select the low R-wave sensing threshold (e.g., low starting value and / or non-adjusted decay rate) at block 510. When a VT / VF interval counter has started increasing but not yet reached the NID, control circuit 80 may determine that the high sensing threshold criteria are not met and select the low R-wave sensing threshold at block 510 in order to promote a high sensitivity for sensing of low amplitude R- waves or fibrillation waves.

[0130] If control circuit 80 has not counted at least N VT / VF intervals, e.g., out of the most recent M VT / VF intervals, control circuit 80 may select the high R-wave sensing threshold at block 508. In this way, when at least some VT / VF intervals have been detected, control circuit 80 may control the post-pace R-wave sensing threshold to have a low starting value that decreases toward the programmed ventricular sensitivity relatively more quickly than when the high R-wave sensing threshold is selected. TWOS can be minimized or avoided following delivered ventricular pacing pulses by selecting the high R-wave sensing threshold when the ventricular rate is relatively slow, and undersensing of low amplitude R-waves or fibrillation waves can be avoided by selecting the low R-wave sensing threshold when the ventricular rate is relatively fast to promote a high sensitivity for ventricular tachyarrhythmia detection.

[0131] At block 512, control circuit 80 may wait for the next ventricular pacing pulse to be delivered. Sensing circuit 86 may apply the selected high R-wave sensing threshold or low R-wave sensing threshold to the ventricular EGM signal sensed post-pace. Control circuit 80 may return to block 502 to confirm that the adaptive sensing control parameters remain enabled (based on one or more adaptive sensing conditions still being met). Prior to the expiration of the next post-pace blanking period following the next delivered ventricular pacing pulse, control circuit 80 may determine whether the high sensing threshold criteria are met or not (blocks 504 and 506) for selecting the high R-wavesensing threshold (block 508) or the low R-wave sensing threshold (block 510), respectively.

[0132] FIG. 9 is a diagram 530 of a ventricular rate dependent high starting value of the adaptive R-wave sensing threshold according to some examples. Control circuit 80 may determine the high starting level of the R-wave sensing threshold based on a ventricular rate in some examples, instead of or in addition to applying a rate threshold when determining if high sensing threshold criteria are met. With continued reference to FIG. 8, in some examples, block 504 may be optional. Control circuit 80 may determine if the high sensing threshold criteria are met based on the VT / VF interval count without comparing the ventricular rate to a rate threshold. Instead, the ventricular rate may be used at block 508 to select a high starting value when less than a threshold number of VT / VF intervals have been detected. The high starting value may be scaled to the ventricular rate as shown in FIG. 9 and further described below.

[0133] In other examples, control circuit 80 may apply a rate threshold to the ventricular rate at block 504 for determining when high sensing threshold criteria are met. When the high sensing threshold criteria are met, e.g., by the pacing rate and the count of VT / VF intervals both being less than respective thresholds, the high starting value of the high R- wave sensing threshold may be selected at block 508 based on the ventricular rate, which may be an actual paced ventricular rate, a scheduled pacing rate in effect (e.g., based on a rate response rate), a sensed ventricular rate or a rate determined from a combination of paced and sensed RRIs.

[0134] In FIG. 9, a boost level is shown in mV on the y-axis as a function of pacing rate shown in beats per minute (bpm) on the x-axis for the sake of example. The boost level may be the value of the high starting value of the R-wave sensing threshold. For instance, if the high sensing threshold criteria are met, control circuit 80 may select the high starting value of the R-wave sensing threshold to be 3 mV when the pacing rate is 100 bpm. In other examples, the boost level plotted as a function of pacing rate in FIG. 9 may be an offset that is added to the programmed ventricular sensitivity to select the high starting value. For example, if the programmed ventricular sensitivity is 1 mV and the pacing rate is 100 bpm, the high starting value may be selected to be 4 mV, the sum of the ventricular sensitivity (1 mV) and the boost level offset (3 mV) that is scaled according to pacing rate. In still other examples, the boost level scaled according to pacing rate (in an inverserelationship such that the boost level decreases with pacing rate) may be defined as a multiple of the programmed ventricular sensitivity. For instances, a higher multiple of the ventricular sensitivity may be used to select the high starting value when the pacing rate is lower and a lower multiple of the ventricular sensitivity may be used to select the high starting value when the pacing rate is relatively higher. Generally, the higher the pacing rate (or actual ventricular rate) the lower the high starting value so that the high R-wave sensing threshold is likely to reach (or at least be near) the programmed ventricular sensitivity before the pacing rate interval expires. In this way, low amplitude R-waves or fibrillation waves may be sensed to inhibit pacing pulse delivery and avoid pacing into a fast intrinsic heart rate.

[0135] The boost level used to select the high starting value of the R-wave sensing threshold may decrease linearly with increasing pacing rate, e.g., as shown by the plotted boost levels 532. In other examples, the boost level may be scaled to the pacing rate in a stepwise manner (e.g., as shown by the scaled boost levels 534) or other non-linear manner. For instance, when the pacing rate is in the range of 84 bpm to 98 bpm, the boost level may be 3.5 mV. Thus, control circuit 80 may maintain the selected high starting value of the R-wave sensing threshold over a range of pacing rates, which can avoid frequent changes in the starting value of the R-wave sensing threshold with relatively small fluctuations in pacing rate.

[0136] The values of boost levels and pacing rates shown in FIG. 9 are intended to be illustrative in nature with no limitations intended. For instance, the boost level may range between 1 mV and 5 mV, between 1.5 mV and 4.5 mV, between 2 mV and 4 mV, between 2.0 mV and 5 mV, or other maximum and minimum limits. In some examples, the boost level ranges may be a function of the programmed ventricular sensitivity such that for a given programmed ventricular sensitivity, a unique range of boost levels may be defined. For example, a higher range of multiples or offsets may be used as the pacing rate dependent boost levels when a relatively lower ventricular sensitivity setting is programmed, and a lower range of multiples or offsets may be used as the pacingdependent boost levels when the ventricular sensitivity is programmed to a relatively higher value.

[0137] The change in boost level with increasing pacing rate may be linear, stepwise with two or more boost levels defined over the range of pacing rates, exponentially decreasingor other function of pacing rate. The pacing rates over which the adjustable boost level may be applied may be the programmed lower rate to the maximum upper rate for rate response pacing (e.g., 50 bpm to 140 bpm in the example shown). The pacing rates over which the adjustable boost level may be applied may be the programmed lower rate to a rate threshold above which high sensing threshold criteria are not met. For instance, if the rate threshold is 120 bpm, the boost level may be adjustable and scaled according to the ventricular pacing rate up to the pacing rate threshold, above which high sensing threshold criteria are not met and the low R-wave sensing threshold may be selected by control circuit 80 (see “no” branch of block 504 and block 510 of FIG. 8).

[0138] The pacing rates shown in FIG. 9 may include scheduled pacing rates and / or actual delivered pacing rates. A scheduled pacing rate may be the programmed ventricular lower rate that controls the minimum ventricular rate. Ventricular pacing pulses may be scheduled by control circuit 80 by starting a ventricular pacing escape interval according to the programmed ventricular lower rate. If IMD 14 is configured to deliver rate response pacing, the ventricular pacing escape interval may be set shorter, according to a temporary LRI according to the rate response rate, to schedule ventricular pacing pulses. These scheduled pacing rates, the programmed lower rate or the temporary rate response rate or other pacing rates used to schedule ventricular pacing pulses by starting a corresponding pacing escape interval may be used by control circuit 80 to select the pacing-rate dependent boost level according to a function or values stored in memory 82. For instance, when therapy delivery circuit 84 is operating in an asynchronous ventricular pacing mode, e.g., a VVI(R) or VDI(R) pacing mode, ventricular pacing pulses that are delivered by therapy delivery circuit 84 may be scheduled at the programmed lower rate or temporary rate response rate. Control circuit 80 may use the ventricular pacing rate which is in effect for scheduling ventricular pacing pulses for selecting the boost level and corresponding high starting value of the high R-wave sensing threshold that is applied post-pace.

[0139] In other instances, the ventricular pacing rate used for determining the boost level may be an actual delivered pacing rate determined by control circuit 80 based on the timing of actual delivered ventricular pacing pulses, e.g., based on paced RRIs. For instance, depending on the pacing mode, ventricular pacing pulses may be actually delivered at a different rate than a programmed lower rate or a temporary rate response rate that is used by control circuit 80 for scheduling ventricular pacing pulses by starting aventricular pacing escape interval. For instance, when therapy delivery circuit 84 is delivering ventricular pacing pulses in an atrial synchronous pacing mode, e.g., a DDD(R) or VDD(R) pacing mode, the actual ventricular pacing rate may vary depending on the rate of sensed P-waves and / or delivered atrial pacing pulses because ventricular pacing pulses may be delivered by therapy delivery circuit 84 at an AV interval following an atrial event (sensed or paced) before the ventricular pacing escape interval expires. Therefore, in some instances, the pacing rate used by control circuit 80 when selecting a pacing-rate dependent boost level may be a determined actual rate of delivered pacing pulses as opposed to a programmed or scheduled rate. Control circuit 80 may determine the time interval between two consecutive ventricular pacing pulses delivered by therapy delivery circuit 84 with no intervening Vsense signal (e.g., a Vpace-Vpace interval) or between a Vsense signal and a subsequent Vpace (e.g., Vsense-Vpace interval), which may be collectively referred to as “paced RRIs”. One or more paced RRIs (each ending with a Vpace) may be determined by control circuit 80 to determine the actual delivered pacing rate that is used by control circuit 80 to determine the corresponding boost level and the selected high starting value of the R-wave sensing threshold at block 508 of FIG. 8.

[0140] In an illustrative example, the programmed ventricular lower rate may be 60 bpm such that control circuit 80 may start ventricular pacing escape intervals that are 1 second long. If pacemaker 14 is operating in an atrial synchronous ventricular pacing mode (e.g., DDI or VDI pacing mode), however, and the intrinsic atrial rate is 80 bpm, as an example, the rate of delivered ventricular pacing pulse can be 80 bpm. Control circuit 80 may determine this actual delivered pacing rate from the time intervals between consecutively delivered ventricular pacing pulses (e.g., paced RRIs) and use this determined actual delivered pacing rate for selecting the corresponding boost level and high starting value of the R-wave sensing threshold when the high sensing threshold criteria are met.

[0141] FIG. 10 is a flow chart 550 of a method for selecting the high starting value of an adaptively controlled R-wave sensing threshold according to another example. With reference to FIG. 6, control circuit 80 may log in memory 82 the maximum peak amplitude 420 and peak time 422 of the post-pace cardiac electrical signal. The maximum peak amplitude 420 and peak time 422 may be identified by a peak track and hold circuit of sensing circuit 86 during a T-wave window following the post-pace blanking period404 and passed to control circuit 80. In other examples, the maximum peak amplitude 420 and peak time 422 may be determined by control circuit 80 from the ventricular EGM signal received from sensing circuit 86. Control circuit 80 may log multiple post-pace maximum peak amplitudes and corresponding peak times in memory 82, each of which may be determined from the sensed ventricular signal during a T-wave time window defined relative to the delivered Vpace. Control circuit 80 may determine a representative T-wave amplitude and peak time at block 552 from the logged values. For instance, control circuit 80 may determine a greatest one of the maximum peak amplitudes or a mean, median, specified percentile or other representative value of the maximum peak amplitudes logged in memory 82 as the T-wave amplitude at block 552. Control circuit 80 may determine a corresponding peak time as the T-wave time at block 552. The T-wave peak time may be the time of the greatest one of the maximum peak amplitudes, the greatest one of the peak times stored in memory 82, or a mean, median or specified percentile of the stored peak times.

[0142] At block 554, control circuit 80 may calculate, for a given decay rate, the starting value of the R-wave sensing threshold that is required at the time of the post-pace blanking period so that the R-wave sensing threshold is greater than the maximum peak amplitude at the peak time. For instance, control circuit 80 may calculate a minimum starting value that decays to the T-wave peak amplitude at the peak time for a specified decay rate (e.g., the decay rate of the low R-wave sensing threshold applied post-pace when high sensing threshold criteria are not met). Control circuit 80 may calculate the high starting value as an offset or multiple greater than the calculated minimum starting value to promote a high R-wave sensing threshold that is higher than the post-pace T-wave peak amplitude at the peak time. Sensing circuit 84 may apply the calculated high starting value and specified decay rate to the cardiac electrical signal sensed after a delivered ventricular pacing pulse for sensing an R-wave at block 556 when the high sensing threshold criteria are met according to any of the examples described above.

[0143] In another example, for a selected high starting value, control circuit 80 may calculate an adjusted decay rate at block 554 that results in a value of the R-wave sensing threshold at the T-wave time that is greater than the T-wave amplitude. The selected high starting value may be a specified high starting value, a specified multiple of the programmed ventricular sensitivity, or a specified offset greater than the programmedventricular sensitivity and may be pacing rate dependent as described above in conjunction with FIG. 9. Control circuit 80 may calculate an adjusted decay rate at block 554 that results in the high R-wave sensing threshold decaying from the specified high starting value to at least an offset or multiple greater than the T-wave amplitude at the T-wave time. Sensing circuit 84 may apply the selected high starting value and the calculated decay rate at block 556 to the post-pace cardiac electrical signal for sensing an R-wave.

[0144] In yet another example, control circuit 80 may calculate a maximum decay rate that results in the R-wave sensing threshold being equal to the T-wave peak amplitude at the T-wave time at block 554 for a specified high starting value. Control circuit 80 may then select a high starting value that is an offset greater than the specified high starting value and / or select an adjusted decay rate that is slower than the maximum decay rate to increase the likelihood of the R-wave sensing threshold being at a value that is greater than the T-wave amplitude at the T-wave time. Sensing circuit 84 may apply the selected high starting value and the adjusted decay rate at block 556 to the post-pace cardiac electrical signal for sensing an R-wave (when high sensing threshold criteria are met).

[0145] It is recognized that a variety of methods for determining a T-wave amplitude and T-wave time and for calculating a high starting value and / or adjusted decay rate based on the determined T-wave amplitude and T-wave time may be conceived based on the techniques disclosed herein for controlling the post-pace R-wave sensing threshold. The foregoing examples are not exhaustive and other methods may be conceived and used for selecting a high starting value and / or adjusted decay rate of an R-wave sensing threshold based on a determined or expected T-wave amplitude and T-wave time so that the R-wave sensing threshold is greater than the T-wave amplitude at the T-wave time following a ventricular pacing pulse.

[0146] FIG. 11 is a flow chart 560 of a method for controlling the adaptive R-wave sensing threshold according to another example. The method of flow chart 560 is described with reference to adaptive control of the post-pace R-wave sensing threshold. The method of flow chart 560, however, may be used in conjunction with the adaptive control of the post-sense R-wave sensing threshold in other examples. At block 562, control circuit 80 may determine a T-wave amplitude and T-wave time, e.g., using any of the example methods described above in conjunction with FIG. 10. At block 563, control circuit 80 may determine an R-wave amplitude. The maximum peak amplitude of thesensed cardiac electrical signal following an R-wave sensing threshold crossing may be determined by sensing circuit 86 for one or more R-wave sensing threshold crossings. The maximum peak amplitude may be determined from the cardiac electrical signal sensed during a peak tracking window, which may be all or a portion of a post-sense blanking period applied by sensing circuit 86 following an R-wave sensing threshold. Control circuit 80 may receive a corresponding Vsense signal and the maximum peak amplitude from sensing circuit 86. Control circuit 80 may use the maximum peak amplitude for determining the high starting value and / or the adjusted decay rate of the post-pace high R- wave sensing threshold at block 564. The maximum peak amplitudes of sensed R-waves may be buffered in memory 82 by control circuit 80 as Vsense signals received from sensing circuit 86.

[0147] The maximum peak amplitude corresponding to the most recent Vsense signal may be used as an R-wave amplitude for determining the post-pace high starting value used by sensing circuit 86. The maximum peak amplitude may be determined on a beat by beat basis as Vsense signals are received for use in determining the high starting value of the post-pace R-wave sensing threshold when a ventricular pacing pulse is delivered. In other examples, a representative R-wave amplitude may be determined from multiple maximum peak amplitudes determined from sensed signal waveforms and stored in memory 82. For example, the lowest maximum peak amplitude, a median, mean or specified percentile of the post-sense maximum peak amplitudes may be determined as a representative R-wave amplitude. Control circuit 80 may use the R-wave amplitude for determining the high starting value and / or adjusted decay rate at block 564 used by sensing circuit 86 for controlling the post-pace (and / or post-sense) R-wave sensing threshold.

[0148] At block 564, control circuit 80 may determine the high starting value of the postpace R-wave sensing threshold using the T-wave amplitude, the T-wave time, the R-wave amplitude and an expected R-wave time in some examples. Control circuit 80 may compute the high starting value for the non-adjusted decay rate that results in an R-wave sensing threshold value that is greater than the T-wave amplitude at the T-wave time according to any of the examples described above in conjunction with FIG. 10. Control circuit 80 may verify that the R-wave sensing threshold is less than the R-wave amplitude at an expected R-wave time after the Vpace. For example, control circuit 80 may verify that the R-wave sensing threshold at an expected R-wave time (which may be based on arate of Vsense and / or Vpace events) is at least a specified margin less than the R-wave amplitude to promote R-wave sensing while avoiding TWOS. A specified margin may be defined as a percentage of the R-wave peak amplitude, e.g., 60%, 50%, 40%, or 30% of the R-wave peak amplitude. Additionally or alternatively, the specified margin may be defined as a difference in millivolts between the R-wave sensing threshold and the R-wave amplitude at the expected R-wave time.

[0149] For instance, if the R-wave sensing threshold at the expected R-wave time is not 50% or less of the R-wave amplitude and / or at least a specified margin (e.g., 0.1 to 2.0 mV) less than the R-wave amplitude, one or both of the high starting value and / or the decay rate may be adjusted by control circuit 80 to achieve the specified margin less than the R-wave amplitude at an expected R-wave time when the R-wave sensing threshold value at the T-wave time is greater than the T-wave amplitude. For example, the decay rate may be increased to achieve the desired margin between the R-wave amplitude and the R-wave sensing threshold at the expected R-wave time.

[0150] In some examples, control circuit 80 may calculate the high starting value and / or adjusted decay rate at block 564 by performing a curve fitting operation using a first point defined by the T-wave peak amplitude and T-wave time, a second point defined by the R- wave amplitude and expected R-wave time, and / or a third point defined by the programmed ventricular sensitivity and a maximum post-pace time for reaching the programmed ventricular sensitivity. Using one, two or all three of these points and the known post-pace blanking interval as a starting time of the post-pace R-wave sensing threshold, the adjusted decay rate may be determined as a best fit curve as further described below in conjunction with FIG. 12.

[0151] At block 566, sensing circuit 86 can apply the post-pace R-wave sensing threshold to a sensed cardiac electrical signal in accordance with a selected starting value and decay rate. When high sensing threshold criteria are met, control circuit 80 may control sensing circuit 86 to use the high starting value, which may be a computed value determined at block 564 and the non-adjusted or an adjusted decay rate. When the high sensing threshold criteria are not met, control circuit 80 may control sensing circuit 86 to use the low starting value and the non-adjusted decay rate for controlling the post-pace R-wave sensing threshold. It is to be understood that the methods described here for controlling the post-pace R-wave sensing threshold can additionally or alternatively be performed for selecting and applying the post-sense R-wave sensing threshold.

[0152] FIG. 12 is a diagram 600 of a ventricular electrical signal 601 that may be sensed by sensing circuit 86 for sensing R-waves. Cardiac electrical signal 601 is shown as a rectified ventricular EGM signal, which may be sensed by a ventricular sensing channel of sensing circuit 86. Cardiac electrical signal 601 includes an intrinsic R-wave 602 that is sensed by sensing circuit 86 in response to an R-wave sensing threshold crossing 603. Sensing circuit 86 may pass a Vsense signal 606 to control circuit 80, produced in response to the R-wave sensing threshold crossing 603. Sensing circuit 86 may start a post-sense blanking period 608 in response to the R-wave sensing threshold crossing 603. During the blanking period 608, sensing circuit 86 may identify the maximum peak amplitude 605 of the sensed signal waveform (R-wave 602) and pass the maximum peak amplitude 605 to control circuit 80.

[0153] In some examples, control circuit 80 may determine a post-sense starting value 622 of the post-sense R-wave sensing threshold 620 based on the maximum peak amplitude 605 received from sensing circuit 86. The post-sense starting value 622 may be a specified percentage of the maximum peak amplitude 605, e.g., 40% to 80% or 50% to 60% of the maximum peak amplitude 605. The post-sense R-wave sensing threshold 620 may decay from the starting value 622 to the programmed ventricular sensitivity 624 according to a specified decay rate (as shown) or according to two or more different decay rates and / or one or more drop time intervals and corresponding step drops in the R-wave sensing threshold amplitude. The post-pace R-wave sensing threshold 620 may be applied according to a number of control parameters that define how the post-pace R-wave sensing threshold 620 decreases from the starting value 622 to the programmed ventricular sensitivity 624. The cardiac electrical signal 601 includes a post-sense T-wave 604 that has a maximum peak amplitude that is less than the post-sense R-wave sensing threshold 620.

[0154] As indicated above, while illustrative examples presented here refer to an adaptive post-pace R-wave sensing threshold, the techniques disclosed herein may be applied to the post-sense R-wave sensing threshold. For instance, when the adaptive sensing control is enabled for adaptively controlling the post-sense R-wave sensing threshold, control circuit 80 may select between a high post-sense R-wave sensing threshold and a low post-senseR-wave sensing threshold based on whether high sensing threshold criteria are met. As an example, when an adaptive sensing condition is met (e.g., adaptive sensing programmed on, sensing using an integrated bipolar lead, evidence of TWOS detected, post CV / DF shock, or other condition), control circuit 80 may compare the sensed ventricular rate and / or VT / VF interval counts to respective threshold values for determining if high sensing threshold criteria are met. If so, control circuit 80 may select the post-sense starting value 622 of post-sense R-wave sensing threshold 620 to be a high value, e.g., a relatively high percentage of the R-wave peak amplitude 605. When the high sensing threshold criteria are not met, control circuit 80 may select the post-sense starting value 622 to be a low value, e.g., a relatively lower percentage of the R-wave peak amplitude 605.

[0155] The decay rate of post-sense R-wave sensing threshold 620 may be a non-adjusted decay rate or an adjusted decay rate. The adjusted decay rate may be determined based on a post-sense T-wave amplitude and T-wave time and / or the sensed R-wave amplitude. The techniques described above in conjunction with FIGs. 10 and 11 for determining a postpace adjusted decay rate may be adapted for determining a post-sense adjusted decay rate, e.g., by determining a post-sense T-wave amplitude and T-wave time, which may include applying a post-sense T-wave window to the sensed ventricular EGM signal.

[0156] In FIG. 12, a Vpace 610 delivered by therapy delivery circuit 84 is shown following the Vsense signal 606. The Vpace 610 may be delivered in response to an expired ventricular pacing interval, e.g., an AV pacing interval or a ventricular lower rate interval, which may be a base pacing rate interval or a temporary rate response pacing interval, in various examples. Cardiac electrical signal 601 includes a post-pace waveform 612 which may include pacing artifact and the pacing evoked R-wave. Sensing circuit 86 starts a post-pace blanking period 618 in response to the delivered Vpace 610, under the control of control circuit 80. The post-pace blanking period 618 may be different than the post-sense blanking period 608, e.g., longer than post-sense blanking period 608, to avoid saturation of the sensing circuit components by the post-pace artifact and to avoid sensing of the pacing-evoked R-wave (post-pace waveform 612).

[0157] According to the methods described above, control circuit 80 may determine if high sensing threshold criteria are met for selecting a low starting value 632 or a high starting value 642 of the low post-pace R-wave sensing threshold 630 or high post-pace R-wave sensing threshold 640, respectively. Furthermore, control circuit 80 may determine the high starting value 642 based on a previously determined post-pace T-wave amplitude, T-wave time and / or R-wave amplitude and expected R-wave time as described above in conjunction with FIGs. 10 and 11. For example, when the high sensing threshold criteria are met, the high starting value 642 may be determined for the non-adjusted decay rate that results in post-pace R-wave sensing threshold 640 being greater than the T-wave amplitude 615 at T-wave time 616 of the post-pace T-wave 614. As illustrated in FIG. 12, the post-pace T-wave 614 can have a higher peak amplitude and higher frequency than the post-sense T-wave 604, which may lead to a greater likelihood of post-pace TWOS by sensing circuit 86 than post-sense TWOS by sensing circuit 86. As such, adaptive sensing control post-sense may be optional or omitted in some examples. Adaptive sensing control post-sense and adaptive sensing control post-pace may be separately enabled and disabled based on adaptive sensing control conditions and each may be separately programmable on or off by a clinician.

[0158] Control circuit 80 may receive the post-pace maximum peak amplitude 615 (that follows the post-pace blanking period 618) and the peak time 616 from sensing circuit 86 for buffering in memory 82 for use in determining a T-wave amplitude and T-wave time. The maximum peak amplitude 615 and peak time 617 may be determined by sensing circuit 86 during a T-wave window 650. T-wave window 650 may extend from the expiration of the post-pace blanking period 618 through an expected time of the T-wave 614. T-wave window 650 may be 200 ms to 500 ms long, as examples, and may begin 50 to 200 ms after the Vpace 610. In an example, the T-wave window 650 may begin upon expiration of the post-pace blanking period 618 and have a duration of 350 ms. As described above, the T-wave amplitude and T-wave time may be used for calculating a high starting value and / or adjusted decay rate of the high post-pace R-wave sensing threshold 640 applied following subsequent Vpaces. For example, the high starting value 642 of the high post-pace R-wave sensing threshold 640 may be updated each time a new post-pace T-wave maximum peak amplitude and T-wave peak time are determined or on a less frequent basis, e.g., after buffering a specified number of post-pace T-wave maximum peak amplitudes and T-wave peak times. For example, the high starting value 642 may be redetermined using recent post-pace T-wave maximum peak amplitude(s) and corresponding peak time(s), once per minute, once per hour, once per day or at otherspecified time intervals. The high R-wave sensing threshold 640 may decay to the programmed ventricular sensitivity 624 at an adjusted or a non-adjusted decay rate.

[0159] As illustrated in FIG. 12, if the low starting value 632 is selected by control circuit 80 when high sensing threshold criteria are not met, the post-pace T-wave 614 may be oversensed by sensing circuit 86 resulting in a false Vsense signal 616 being produced by sensing circuit 86 due to the T-wave 614 crossing the low post-pace R-wave sensing threshold 630. Using the techniques disclosed herein, TWOS is avoided by enabling adaptive sensing control and applying a high R-wave sensing threshold 640 at least postpace. However, a relatively high sensitivity to sensing fast ventricular rates is promoted by applying high sensing threshold criteria before using the high R-wave sensing threshold.

[0160] In some examples, control circuit 80 may perform a curve fitting operation using points 654 and 656. Point 654 may be defined as a specified margin greater than the postpace T-wave peak amplitude (determined from one or more previous cardiac cycles) at the corresponding post-pace T-wave time. For example, control circuit 80 may determine a first point 654 of the high post-pace R-wave sensing threshold 640 as at least 25% (or other specified margin) greater than a previously determined post-pace T-wave peak amplitude at the post-pace T-wave peak time. Control circuit 80 may determine a second point 656 as being a specified margin less than a previously determined R-wave peak amplitude, e.g., intrinsic R-wave peak amplitude 605, at the expected R-wave time 652. For instance, control circuit 80 may determine the second point 656 of the high post-pace R-wave sensing threshold amplitude 640 as having an amplitude that is 50% (or other specified margin) of a determined R-wave peak amplitude 605 at an expected R-wave time 652. The expected R-wave time 652 may be the time after Vpace 610 that corresponds to a recently determined ventricular rate interval (e.g., an expected RRI based on recently determined RRIs ending on Vsense signals).

[0161] Control circuit 80 may determine the adjusted decay rate of the high post-pace R- wave sensing threshold 640 by curve fitting the two points 654 and 656 and computing the starting value 642 at the time of the expiration of post-pace blanking period 618. In some examples, control circuit 80 may perform the curve fitting operation using a third point 658 that is equal to the programmed ventricular sensitivity 624 at a maximum specified time point after the Vpace 610 that the high post-pace R-wave sensing threshold 640 is required to reach the programmed ventricular sensitivity 624. Control circuit 80 mayperform an exponential, linear or a piecewise linear curve fitting operation or a combination thereof. For example, a linear decay rate may extend from starting value 642 to the first point 654 followed by an exponential decay rate from point 654 to point 658 passing through or below point 656. In some examples, control circuit 80 may select exponential and / or linear decay rates from a table or list of available decay rates stored in memory 82 for selecting a best fit adjusted decay rate of the high post-pace R-wave sensing threshold 640 based on points 654 and 656 and, in some examples, point 658. In some instances, when the specified T-wave margin (greater than the T-wave peak amplitude) and the specified R-wave margin (less than the R-wave amplitude 605) cannot both be met by the curve fitting operation, the post-pace blanking interval 618 and / or the programmed ventricular sensitivity 624 may be adjusted (increased or decreased) by control circuit 80 to achieve the desired margins to promote R-wave sensing without TWOS.

[0162] Further disclosed herein is the subject matter of the following examples:

[0163] Example 1. A medical device including a sensing circuit configured to sense at least one cardiac electrical signal, a memory configured to store high sensing threshold criteria and a control circuit configured to determine from at least one cardiac electrical signal sensed by the sensing circuit if the high sensing threshold criteria are met. The control circuit may be further configured to select a starting value of a cardiac event sensing threshold based on whether the high sensing threshold criteria are met by selecting a low starting value of the cardiac event sensing threshold when the high sensing threshold criteria are not met or selecting a high starting value of the cardiac event sensing threshold when the high sensing threshold criteria are met, where the high starting value is greater than the low starting value. The sensing circuit may be further configured to apply the cardiac event sensing threshold having the selected starting value to a first cardiac electrical signal of the at least one cardiac electrical signal sensed by the sensing circuit and sense a cardiac event signal in response to the first cardiac electrical signal crossing the cardiac event sensing threshold. The medical device may further include a therapy delivery circuit configured to deliver pacing pulses. The control circuit may be further configured to start a pacing interval in response to the sensed cardiac event signal to schedule a pacing pulse for delivery by the therapy delivery circuit.

[0164] Example 2. The medical device of example 1 wherein the memory is further configured to store a sensitivity as the minimum value of the cardiac event sensing threshold. The control circuit may be further configured to determine the low starting value as a first multiple of the sensitivity and determine the high starting value as a second multiple of the sensitivity, the second multiple greater than the first multiple.

[0165] Example 3. The medical device of any one of examples 1 — 2 wherein the control circuit is further configured to determine from at least one cardiac electrical signal sensed by the sensing circuit if the high sensing threshold criteria are met by determining cardiac event intervals from the cardiac event signals sensed by the sensing circuit, comparing the cardiac event intervals to a tachyarrhythmia detection interval and determining that the high sensing threshold criteria are met when less than a threshold number of the cardiac event intervals meet the tachyarrhythmia detection interval.

[0166] Example 4. The medical device of any one of examples 1 — 3 wherein the control circuit is further configured to control the therapy delivery circuit to deliver pacing pulses based on the at least one cardiac electrical signal sensed by the sensing circuit and determine from at least one cardiac electrical signal sensed by the sensing circuit if the high sensing threshold criteria are met by determining an actual rate of pacing pulses that are delivered by the therapy delivery circuit and determining that the high sensing threshold criteria are met when the actual rate of pacing pulses that are delivered by the therapy delivery circuit is less than a threshold rate.

[0167] Example 5. The medical device of any one of examples 1 — 4 wherein the control circuit is further configured to determine a ventricular rate from at least one of delivered pacing pulses or senses cardiac event signals and determine the high starting value scaled to the ventricular rate.

[0168] Example 6. The medical device of example 5 wherein the control circuit is further configured to determine the high starting value scaled to the ventricular rate over a range of high starting values that is scaled to a programmed ventricular sensitivity.

[0169] Example 7. The medical device of any one of examples 1 — 6 wherein the control circuit is further configured to determine that an adaptive sensing condition is met and, in response to determining that the adaptive sensing condition is met, determine if the high sensing threshold criteria are met.

[0170] Example 8. The medical device of example 7 wherein the memory is further configured to store a sensitivity as the minimum value of the cardiac event sensing threshold. The control circuit may be further configured to determine that the adaptive sensing condition is met by determining that the sensitivity is greater than a specified sensitivity setting.

[0171] Example 9. The medical device of any one of examples 7 — 8 wherein the control circuit is further configured to detect evidence of T-wave oversensing from at least one cardiac electrical signal sensed by the sensing circuit and determine that the adaptive sensing condition is met in response to detecting the evidence of T-wave oversensing.

[0172] Example 10. The medical device of any one of examples 7 — 9 further comprising a communication circuit configured to receive a programming command transmitted from another medical device. The control circuit may be further configured to determine that the adaptive sensing condition is met in response to the communication circuit receiving the programming command.

[0173] Example 11. The medical device of any one of examples 7 — 10 wherein the therapy delivery circuit is further configured to deliver a cardioversion or defibrillation shock pulse. The control circuit may be further configured to determine that the adaptive sensing condition is met in response to the therapy delivery circuit delivering the cardioversion or defibrillation shock pulse.

[0174] Example 12. The medical device of any one of examples 1 — 11 wherein the control circuit is further configured to determine a T-wave amplitude from the first cardiac electrical signal, determine a T-wave time corresponding to the T-wave amplitude and determine the high starting value based on at least the T-wave amplitude and the T-wave time.

[0175] Example 13. The medical device of any one of examples 1 — 12 wherein the control circuit is further configured to determine an R-wave amplitude from the first cardiac electrical signal, determine an expected R-wave time from at least one of the first cardiac electrical signal or the pacing pulses delivered by the therapy delivery circuit and determine the high starting value based on at least the R-wave amplitude and the expected R-wave time.

[0176] Example 14. The medical device of any one of examples 1 — 13 wherein the sensing circuit is further configured to apply the cardiac event sensing threshold havingthe selected starting value to the first cardiac electrical signal by one of decreasing the cardiac event sensing threshold from the low starting value according to a first decay rate or decreasing the cardiac event sensing threshold from the high starting value according to a second decay rate different than the first decay rate.

[0177] Example 15. The medical device of example 14 wherein the control circuit is further configured to determine a T-wave amplitude from the first cardiac electrical signal, determine a T-wave time corresponding to the T-wave amplitude and determine the second decay rate based on at least the T-wave amplitude and the T-wave time.

[0178] Example 16. The medical device of any one of examples 14 — 15 wherein the control circuit is further configured to determine an R-wave amplitude from the first cardiac electrical signal, determine an expected R-wave time from at least one of the first cardiac electrical signal or the pacing pulses delivered by the therapy delivery circuit and determine the second decay rate based on at least the R-wave amplitude and the expected R-wave time.

[0179] Example 17. The medical device of any one of examples 1 — 16 wherein the therapy delivery circuit is further configured to deliver the pacing pulses as conduction system pacing pulses for capturing at least a portion of the conduction system.

[0180] Example 18. The medical device of any one of examples 1 — 17 further comprising a connector block configured to receive an integrated bipolar lead. The sensing circuit may be further configured to receive the first cardiac electrical signal via a sensing electrode pair of the integrated bipolar lead.

[0181] Example 19. The medical device of any one of examples 1 — 18 wherein the control circuit is further configured to select the starting value of the cardiac event sensing threshold by selecting a starting post-pace value of the cardiac event sensing threshold. The sensing circuit is further configured to apply the cardiac event sensing threshold having the selected post-pace starting value to the first cardiac electrical signal in response to a pacing pulse delivered by the therapy delivery circuit.

[0182] Example 20. The medical device of any one of examples 1 — 19 wherein the control circuit is further configured to select the starting value of the cardiac event sensing threshold by selecting a starting post-sense value of the cardiac event sensing threshold by determining a peak amplitude of a cardiac event sensed by the sensing circuit, determine the low starting value as a first percentage of the peak amplitude and determine the highstarting value as a second percentage of the peak amplitude greater than the first percentage. The sensing circuit can be further configured to apply the cardiac event sensing threshold having the selected post-sense starting value to the first cardiac electrical signal in response to sensing the cardiac event from the first cardiac electrical signal.

[0183] Example 21. A method comprising sensing at least one cardiac electrical signal, determining from at least one sensed cardiac electrical signal if high sensing threshold criteria are met, and selecting a starting value of a cardiac event sensing threshold based on whether the high sensing threshold criteria are met by selecting a low starting value of the cardiac event sensing threshold when the high sensing threshold criteria are not met or selecting a high starting value of the cardiac event sensing threshold when the high sensing threshold criteria are met, the high starting value greater than the low starting value. The method may further include applying the cardiac event sensing threshold having the selected starting value to a first cardiac electrical signal of the at least one sensed cardiac electrical signals, sensing a cardiac event signal in response to the first cardiac electrical signal crossing the cardiac event sensing threshold and starting a pacing interval in response to the sensed cardiac event signal to schedule a pacing pulse.

[0184] Example 22. The method of example 21 further including determining the low starting value as a first multiple of a sensitivity that is a minimum value of the cardiac event sensing threshold and determining the high starting value as a second multiple of the sensitivity, where the second multiple is greater than the first multiple.

[0185] Example 23. The method of any one of examples 21 — 22 further including determining, from at least one sensed cardiac electrical signal, if the high sensing threshold criteria are met by determining cardiac event intervals from the sensed cardiac event signals, comparing the cardiac event intervals to a tachyarrhythmia detection interval and determining that the high sensing threshold criteria are met when less than a threshold number of the cardiac event intervals meet the tachyarrhythmia detection interval.

[0186] Example 24. The method of any one of examples 21 — 23 further including determining, from at least one sensed cardiac electrical signal, if the high sensing threshold criteria are met by delivering pacing pulses based on at least one sensed cardiac electrical signal, determining an actual rate of delivered pacing pulses and determiningthat the high sensing threshold criteria are met when the actual rate of delivered pacing pulses is less than a threshold rate.

[0187] Example 25. The method of any one of examples 21 — 24 further including determining a ventricular rate from at least one of delivered pacing pulses or sense cardiac event signals and determining the high starting value scaled to the ventricular rate.

[0188] Example 26. The method of example 25 further including determining the high starting value scaled to the ventricular rate over a range of high starting values that is scaled to a programmed ventricular sensitivity that is a minimum value of the cardiac event sensing threshold.

[0189] Example 27. The method of any one of examples 21 — 26 further including determining that an adaptive sensing condition is met and, in response to determining that the adaptive sensing condition is met, determining if the high sensing threshold criteria are met.

[0190] Example 28. The method of example 27 further including determining that the adaptive sensing condition is met by determining that a sensitivity that is a minimum value of the cardiac event sensing threshold is greater than a specified sensitivity setting.

[0191] Example 29. The method of any one of examples 27 — 28 further comprising detecting evidence of T-wave oversensing from at least one sensed cardiac electrical signal and determining that the adaptive sensing condition is met in response to detecting the evidence of T-wave oversensing.

[0192] Example 30. The method of any one of examples 27 — 29 further including receiving a programming command transmitted from another medical device and determining that the adaptive sensing condition is met in response to receiving the programming command.

[0193] Example 31. The method of any one of examples 27 — 30 further including delivering a cardioversion or defibrillation shock pulse and determining that the adaptive sensing condition is met in response to delivering the cardioversion or defibrillation shock pulse.

[0194] Example 32. The method of any one of examples 21 — 31 further including determining a T-wave amplitude from the first cardiac electrical signal, determining a T- wave time corresponding to the T-wave amplitude, and determining the high starting value based on at least the T-wave amplitude and the T-wave time.

[0195] Example 33. The method of any one of examples 21 — 32 further including determining an R-wave amplitude from the first cardiac electrical signal, determining an expected R-wave time from at least one of the first cardiac electrical signal or delivered pacing pulses and determining the high starting value based on at least the R-wave amplitude and the expected R-wave time.

[0196] Example 34. The method of any one of examples 21 — 33 further including applying the cardiac event sensing threshold having the selected starting value to the first cardiac electrical signal by one of: decreasing the cardiac event sensing threshold from the low starting value according to a first decay rate or decreasing the cardiac event sensing threshold from the high starting value according to a second decay rate different than the first decay rate.

[0197] Example 35. The method of example 34 further including determining a T-wave amplitude from the first cardiac electrical signal, determining a T-wave time corresponding to the T-wave amplitude and determining the second decay rate based on at least the T-wave amplitude and the T-wave time.

[0198] Example 36. The method of any one of examples 34 — 35 further including determining an R-wave amplitude from the first cardiac electrical signal, determining an expected R-wave time from at least one of the first cardiac electrical signal or delivered pacing pulses and determining the second decay rate based on at least the R-wave amplitude and the expected R-wave time.

[0199] Example 37. The method of any one of examples 21 — 36 further comprising delivering the pacing pulses as conduction system pacing pulses for capturing at least a portion of the conduction system.

[0200] Example 38. The method of any one of examples 21 — 37 further comprising receiving the first cardiac electrical signal via a sensing electrode pair of an integrated bipolar lead.

[0201] Example 39. The method of any one of examples 21 — 38 further comprising selecting the starting value of the cardiac event sensing threshold by selecting a starting post-pace value of the cardiac event sensing threshold and applying the cardiac event sensing threshold having the selected post-pace starting value to the first cardiac electrical signal in response to a delivered pacing pulse.

[0202] Example 40. The method of any one of examples 21 — 39 further comprising selecting the starting value of the cardiac event sensing threshold by selecting a starting post-sense value of the cardiac event sensing threshold by determining a peak amplitude of a cardiac event sensed by the sensing circuit, determining the low starting value as a first percentage of the peak amplitude and determining the high starting value as a second percentage of the peak amplitude, where the second percentage is greater than the first percentage. The method may include applying the cardiac event sensing threshold having the selected post-sense starting value to the first cardiac electrical signal in response to sensing the cardiac event from the first cardiac electrical signal.

[0203] Example 41. A non-transitory computer readable medium storing instructions that, when executed by a control circuit of a medical device, cause the medical device to sense at least one cardiac electrical signal, determine from at least one sensed cardiac electrical signal if high sensing threshold criteria are met and select a starting value of a cardiac event sensing threshold based on whether the high sensing threshold criteria are met by selecting a low starting value of the cardiac event sensing threshold when the high sensing threshold criteria are not met or selecting a high starting value of the cardiac event sensing threshold when the high sensing threshold criteria are met, the high starting value greater than the low starting value. The instructions may further cause the medical device to apply the cardiac event sensing threshold having the selected starting value to a cardiac electrical signal of the at least one sensed cardiac electrical signals, sense a cardiac event signal in response to the cardiac electrical signal crossing the cardiac event sensing threshold and start a pacing interval in response to the sensed cardiac event signal to schedule a pacing pulse.

[0204] It should be understood that, depending on the example, certain acts or events of any of the methods described herein can be performed in a different sequence, in parallel, may be added, merged, or left out altogether (e.g., not all described acts or events are necessary for the practice of the method). Moreover, in certain examples, acts or events may be performed concurrently, e.g., through multi -threaded processing, interrupt processing, or multiple processors, rather than sequentially. In addition, while certain aspects of this disclosure are described as being performed by a single processor, circuit or unit for purposes of clarity, it should be understood that the techniques of this disclosuremay be performed by a combination of processors, units or circuits associated with, for example, a medical device system.

[0205] In one or more examples, the functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored as one or more instructions or code on a computer-readable medium and executed by one or more hardware-based processing units. Computer- readable media may include computer-readable storage media, which corresponds to a tangible medium such as data storage media (e.g., RAM, ROM, EEPROM, flash memory, or any other medium that can be used to store desired program code in the form of instructions or data structures and that can be accessed by a computer).

[0206] Instructions may be executed by one or more processors, such as one or more digital signal processors (DSPs), general purpose microprocessors, application specific integrated circuits (ASICs), field programmable logic arrays (FPGAs), or other equivalent integrated or discrete logic circuitry. Accordingly, the term “processor,” as used herein may refer to any of the foregoing structure or any other structure suitable for implementation of the techniques described herein. Also, the techniques could be fully implemented in one or more circuits or logic elements.

[0207] Thus, a medical device system has been presented in the foregoing description with reference to specific examples. It is to be understood that various aspects disclosed herein may be combined in different combinations than the specific combinations presented in the accompanying drawings. It is appreciated that various modifications to the referenced examples may be made without departing from the scope of the disclosure and the following claims.

Claims

WHAT IS CLAIMED IS:

1. A medical device, comprising: a sensing circuit configured to sense at least one cardiac electrical signal; a memory configured to store high sensing threshold criteria; and a control circuit configured to: determine from at least one cardiac electrical signal sensed by the sensing circuit if the high sensing threshold criteria are met; select a starting value of a cardiac event sensing threshold based on whether the high sensing threshold criteria are met by: selecting a low starting value of the cardiac event sensing threshold when the high sensing threshold criteria are not met; or selecting a high starting value of the cardiac event sensing threshold when the high sensing threshold criteria are met, the high starting value greater than the low starting value; a therapy delivery circuit configured to deliver pacing pulses; the sensing circuit being further configured to: apply the cardiac event sensing threshold having the selected starting value to a first cardiac electrical signal of the at least one cardiac electrical signal sensed by the sensing circuit; and sense a cardiac event signal in response to the first cardiac electrical signal crossing the cardiac event sensing threshold; and the control circuit being further configured to start a pacing interval in response to the sensed cardiac event signal to schedule a pacing pulse for delivery by the therapy delivery circuit.

2. The medical device of claim 1 wherein: the memory is further configured to store a sensitivity as the minimum value of the cardiac event sensing threshold; and the control circuit is further configured to: determine the low starting value as a first multiple of the sensitivity; and determine the high starting value as a second multiple of the sensitivity, the second multiple being greater than the first multiple.

3. The medical device of any one of claims 1 — 2 wherein the control circuit is further configured to determine from at least one cardiac electrical signal sensed by the sensing circuit if the high sensing threshold criteria are met by: determining cardiac event intervals from the cardiac event signals sensed by the sensing circuit; comparing the cardiac event intervals to a tachyarrhythmia detection interval; and determining that the high sensing threshold criteria are met when less than a threshold number of the cardiac event intervals meet the tachyarrhythmia detection interval.

4. The medical device of any one of claims 1 — 3 wherein the control circuit is further configured to: control the therapy delivery circuit to deliver the pacing pulses based on the at least one cardiac electrical signal sensed by the sensing circuit; and determine if the high sensing threshold criteria are met by: determining an actual rate of pacing pulses that are delivered by the therapy delivery circuit; determining that the high sensing threshold criteria are met when the actual rate of pacing pulses that are delivered by the therapy delivery circuit is less than a threshold rate.

5. The medical device of any one of claims 1 — 4 wherein the control circuit is further configured to: determine a ventricular rate from at least one of delivered pacing pulses or sensed cardiac event signals; and determine the high starting value scaled to the ventricular rate.

6. The medical device of claim 5 wherein the control circuit is further configured to determine the high starting value scaled to the ventricular rate over a range of high starting values that is scaled to a programmed ventricular sensitivity.

7. The medical device of any one of claims 1 — 6 wherein: the control circuit is further configured to determine that an adaptive sensing condition is met; and in response to determining that the adaptive sensing condition is met, determine if the high sensing threshold criteria are met.

8. The medical device of claim 7 wherein: the memory is further configured to store a sensitivity as the minimum value of the cardiac event sensing threshold; and the control circuit is further configured to determine that the adaptive sensing condition is met by determining that the sensitivity is greater than a specified sensitivity setting.

9. The medical device of any one of claims 7 — 8 wherein the control circuit is further configured to: detect evidence of T-wave oversensing from at least one cardiac electrical signal sensed by the sensing circuit; and determine that the adaptive sensing condition is met in response to detecting the evidence of T-wave oversensing.

10. The medical device of any one of claims 7 — 9 further comprising a communication circuit configured to receive a programming command transmitted from another medical device; and wherein the control circuit is further configured to determine that the adaptive sensing condition is met in response to the communication circuit receiving the programming command.

11. The medical device of any one of claims 7 — 10 wherein: the therapy delivery circuit is further configured to deliver a cardioversion or defibrillation shock pulse; andthe control circuit is further configured to determine that the adaptive sensing condition is met in response to the therapy delivery circuit delivering the cardioversion or defibrillation shock pulse.

12. The medical device of any one of claims 1 — 11 wherein the control circuit is further configured to: determine a T-wave amplitude from the first cardiac electrical signal; determine a T-wave time corresponding to the T-wave amplitude; determine the high starting value based on at least the T-wave amplitude and the T- wave time.

13. The medical device of any one of claims 1 — 12 wherein the control circuit is further configured to: determine an R-wave amplitude from the first cardiac electrical signal; determine an expected R-wave time from at least one of the first cardiac electrical signal or the pacing pulses delivered by the therapy delivery circuit; and determine the high starting value based on at least the R-wave amplitude and the expected R-wave time.

14. The medical device of any one of claims 1 — 13 wherein the sensing circuit is further configured to apply the cardiac event sensing threshold having the selected starting value to the first cardiac electrical signal by one of: decreasing the cardiac event sensing threshold from the low starting value according to a first decay rate; or decreasing the cardiac event sensing threshold from the high starting value according to a second decay rate different than the first decay rate.

15. The medical device of claim 14 wherein the control circuit is further configured to: determine at least one of: a T-wave amplitude and a T-wave time corresponding to the T-wave amplitude from the first cardiac electrical signal; oran R-wave amplitude and an expected R-wave time from at least one of the first cardiac electrical signal or the pacing pulses delivered by the therapy delivery circuit; and determine the second decay rate based on at least one of: the T-wave amplitude and the T-wave time; or the R-wave amplitude and the expected R-wave time.

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