Medical devices and methods for delivering backup cardiac pacing

Abstract

A medical device system is configured to: sense a ventricular event signal accompanied by ventricular depolarization; deliver an atrial pacing pulse; and, in response to the delivery of the atrial pacing pulse, initiate a standby atrial pacing interval to schedule the standby atrial pacing pulse. The medical device system may be configured to determine whether a ventricular event signal is sensed during the standby atrial pacing interval. In response to sensing a ventricular event signal during the standby atrial pacing interval, the medical device system may determine, at least based on the timing of the sensed ventricular event signal, the atrial capture outcome of the delivered atrial pacing pulse, and cancel the scheduled standby atrial pacing pulse.

Description

[0001] This application claims the benefit of U.S. Provisional Patent Application Serial No. 63 / 613,009, filed December 20, 2023, the entire contents of which are incorporated herein by reference. Technical Field

[0002] This disclosure relates to a medical device and method for delivering a backup cardiac pacing pulse. Background Technology

[0003] During normal sinus rhythm (NSR), the heartbeat is regulated by electrical signals generated by the sinoatrial (SA) node located in the wall of the right atrium. Each atrial depolarization signal generated by the SA node propagates through the atrium, causing atrial depolarization and contraction, and reaches the atrioventricular (AV) node. The AV node responds by propagating the ventricular depolarization signal through the His bundle in the interventricular septum and subsequently to the bundle branches of the right and left ventricles and Purkinje muscle fibers (sometimes referred to as the "His-Purkinje system").

[0004] Patients with conduction system abnormalities, such as SA node dysfunction or AV node conduction malfunction, bundle branch block, or other conduction anomalies, may receive pacemakers to restore a more normal heart rhythm. A single-chamber pacemaker, connected to a transvenous lead with an electrode located in the right atrium, can provide atrial pacing to treat patients with SA node dysfunction. When the AV node is functioning normally, single-chamber atrial pacing can adequately correct the rhythm. Pacing-induced atrial depolarization can conduct normally to the ventricle via the AV node and the His-Purkinje system, maintaining normal AV synchrony. However, some patients may experience AV node conduction abnormalities, such as partial or complete AV block. AV block can be intermittent and can evolve over time. In cases of high AV block, atrial depolarization may not conduct to the ventricle in every atrial cycle, or it may conduct with prolonged AV conduction time, resulting in poor AV synchrony of the native rhythm. In such cases, patients may benefit from a single-chamber ventricular pacemaker or a dual-chamber pacemaker.

[0005] Dual-chamber pacemakers can be implanted in certain patients to sense atrial and ventricular electrical signals associated with atrial and ventricular depolarization, and to pace both the atrial and ventricular chambers as needed to promote and maintain AV synchronization. The dual-chamber pacemaker can be coupled to transvenous atrial and transvenous ventricular leads to place electrodes for sensing and pacing in both chambers. The pacemaker itself can be implanted in a subcutaneous pouch, with the transvenous lead tunneling into the pouch.

[0006] It has been proposed or suggested that intracardiac pacemakers be implanted entirely within a patient's heart, eliminating the need for transvenous leads. For example, intracardiac pacemakers can provide sensing and pacing from within the heart chambers of patients with conduction abnormalities to promote a more normal heart rhythm. Summary of the Invention

[0007] The present disclosure relates generally to a medical device configured to sense cardiac event signals (e.g., P waves and R waves) associated with myocardial depolarization, deliver cardiac pacing pulses, and in some cases deliver alternative cardiac pacing pulses to promote a regular heart rhythm. The medical device can receive cardiac electrical signals from electrodes implanted in or on the heart chambers and sense cardiac event signals from these electrical signals. The medical device may be a pacemaker configured to sense P waves associated with atrial depolarization and R waves associated with ventricular depolarization. The medical device may be a dual-chamber pacemaker configured to deliver both atrial and ventricular pacing pulses. The timing of the generated cardiac pacing pulses can be controlled by the medical device based on the sensed cardiac event signals.

[0008] A medical device operating according to the techniques disclosed herein can be configured to deliver atrial pacing pulses for verifying atrial capture via the atrial pacing pulses. The medical device can deliver atrial pacing pulses and schedule a backup atrial pacing pulse by initiating a backup atrial pacing interval. The medical device can determine the atrial pacing capture outcome based on whether and when a ventricular R wave is sensed during the backup atrial pacing interval. The medical device can apply a capture verification window during the backup atrial pacing interval. This capture verification window may have an end time that occurs after the delivered atrial pacing pulse but earlier than the expiration time of the backup atrial pacing interval.

[0009] In one example, this disclosure provides a medical device comprising: a sensing circuit configured to sense a ventricular event signal accompanied by ventricular depolarization; a pulse generation circuit configured to generate a pacing pulse; and a control circuit configured to control the pulse generation circuit to deliver an atrial pacing pulse. In response to generating the atrial pacing pulse, a backup atrial pacing interval is initiated to schedule the backup atrial pacing pulse, the backup atrial pacing interval having an expiration time. The control circuit may also be configured to: determine whether the sensing circuit senses a ventricular event signal during the backup atrial pacing interval; and, in response to the sensing circuit sensing a ventricular event signal during the backup atrial pacing interval, determine an atrial capture result of the delivered atrial pacing pulse based at least on the time of the sensed ventricular event signal, and cancel the scheduled backup atrial pacing pulse. The control circuit can also be configured to, in response to the sensing circuit not sensing a ventricular event signal during the standby atrial pacing interval: determine the atrial capture result of the delivered atrial pacing pulse as a capture loss; and control the pulse generation circuit to deliver the scheduled standby atrial pacing pulse at the end of the interval.

[0010] In another example, this disclosure provides a method comprising: sensing a ventricular event signal accompanied by ventricular depolarization; delivering an atrial pacing pulse; and initiating a standby atrial pacing interval to schedule a standby atrial pacing pulse in response to the delivery of the atrial pacing pulse, the standby atrial pacing interval having an expiration time. The method may further include determining whether a ventricular event signal is sensed during the standby atrial pacing interval. The method may include, in response to sensing a ventricular event signal during the standby atrial pacing interval, determining an atrial capture outcome of the delivered atrial pacing pulse based at least on the time of the sensed ventricular event signal, and canceling the scheduled standby atrial pacing pulse. The method may further include, in response to not sensing a ventricular event signal during the standby atrial pacing interval, determining the atrial capture outcome of the delivered atrial pacing pulse as a capture loss, and delivering the scheduled standby atrial pacing pulse at the expiration time.

[0011] In another example, this disclosure provides a non-transitory computer-readable storage medium including a set of instructions that, when executed by control circuitry of a medical device, cause the medical device to: sense a ventricular event signal accompanied by ventricular depolarization; deliver an atrial pacing pulse; and, in response to the delivery of the atrial pacing pulse, initiate a backup atrial pacing interval to schedule a backup atrial pacing pulse, the backup atrial pacing interval having an expiration time. The instructions may also cause the medical device to: determine whether a ventricular event signal is sensed during the backup atrial pacing interval; and, in response to the sensed ventricular event signal during the backup atrial pacing interval, cause the medical device to determine, at least based on the time of the sensed ventricular event signal, the atrial capture result of the delivered atrial pacing pulse, and cancel the scheduled backup atrial pacing pulse. The instruction can also cause the medical device to determine the atrial capture result of the delivered atrial pacing pulse as a capture loss in response to the absence of a ventricular event signal during the standby atrial pacing interval, and to deliver the scheduled standby atrial pacing pulse at the end of the interval.

[0012] Details of one or more aspects of this disclosure are set forth in the following drawings and description. Other features, objects, and advantages of the technology described in this disclosure will be apparent from the description, drawings, and claims. Attached Figure Description

[0013] Figure 1 This is a conceptual diagram illustrating an implantable medical device (IMD) system that can be configured to sense cardiac signals and provide cardiac pacing according to the technology disclosed herein.

[0014] Figure 2 It is based on an example Figure 1 The diagram shown is a conceptual representation of a pacemaker.

[0015] Figure 3 Examples include a medical device system comprising two leadless pacemakers for providing dual-chamber pacing and sensing, the medical device system being configured to perform the techniques disclosed herein.

[0016] Figure 4 This is a conceptual diagram of another example of a medical device system that can be configured to determine atrial capture and control the delivery of standby atrial pacing pulses according to the technology disclosed herein.

[0017] Figure 5 This is another example of a medical device system that can realize the currently disclosed methods for delivering atrial pacing pulses, determining atrial capture results, and controlling backup pacing pulses.

[0018] Figure 6This is a conceptual diagram of an example configuration of a medical device configured to perform the atrial pacing, capture determination, and backup pacing methods disclosed herein.

[0019] Figure 7 This is a flowchart, based on some examples, of a method that can be performed by a medical device system for determining atrial pacing capture and controlling the delivery of standby atrial pacing pulses and ventricular pacing pulses.

[0020] Figure 8 This is a flowchart of another method, based on some examples, that can be performed by a medical device system for determining atrial pacing capture and controlling the delivery of standby atrial pacing pulses and ventricular pacing pulses.

[0021] Figure 9 It can be executed Figure 8 The control circuit of the medical device system uses atrial and ventricular pacing pulses and timing diagrams of various time intervals.

[0022] Figure 10 It is a timing diagram based on some examples of medical device systems that can be controlled to schedule standby atrial pacing pulses, schedule ventricular pacing pulses, and determine the atrial pacing capture result after the delivered atrial pacing pulse.

[0023] Figure 11 This is a flowchart of a method for performing an atrial capture threshold search, based on some examples.

[0024] Figure 12 It is a timing diagram, according to yet another example, which can be controlled by control circuit 206 to schedule standby atrial pacing pulses, schedule ventricular pacing pulses, and determine the time interval of atrial pacing capture results.

[0025] Figure 13 This is a flowchart of a method, which can be performed by a medical device according to yet another example, for determining atrial capture results and controlling atrial and ventricular pacing pulses. Detailed Implementation

[0026] Generally, this disclosure describes a medical device and method for determining cardiac pacing capture and for controlling the delivery of backup cardiac pacing pulses. Examples disclosed herein provide a medical device and method for delivering atrial pacing pulses, determining atrial pacing capture outcome (e.g., atrial capture, capture loss, or indeterminate capture outcome) after delivery of the atrial pacing pulses, and controlling the delivery of backup atrial and ventricular pacing pulses.

[0027] Figure 1This is a conceptual diagram illustrating an implantable medical device (IMD) system 10 configured to sense cardiac signals and provide cardiac pacing according to the technology disclosed herein. The IMD system 10 is shown as including a pacemaker 14 implanted in the right atrium (RA) of a patient's heart 8. In some examples, the pacemaker 14 is a catheter-directed, leadless pacemaker that can be fully implanted within the heart chambers. The size of the pacemaker 14 can be reduced compared to a subcutaneously implanted pacemaker, and its shape can be generally cylindrical to facilitate transvenous implantation via a delivery catheter. The pacemaker 14 can be a leadless pacemaker comprising electrodes carried on a pacemaker housing without the need for medical leads extending from the pacemaker 14 for sensing cardiac electrical signals and delivering cardiac pacing pulses.

[0028] Pacemaker 14 can sense atrial and ventricular event signals, such as P waves accompanied by atrial depolarization and R waves accompanied by ventricular depolarization. Pacemaker 14 can be configured as a dual-chamber pacemaker capable of sensing both atrial and ventricular event signals and delivering atrial and ventricular pacing pulses as needed based on the sensed atrial and / or ventricular event signals. In other examples, pacemaker 14 can be configured as a single-chamber pacemaker capable of delivering only atrial pacing pulses but still capable of dual-chamber sensing of both atrial and ventricular event signals.

[0029] In the example shown, pacemaker 14 is implanted in the RA for delivering ventricular pacing from an atrial location. Pacemaker 14 can be configured to deliver ventricular pacing pulses via the heart's natural conduction system and / or ventricular myocardium from a right atrial approach. For example, the distal end 12 of pacemaker 14 can be positioned at the lower end of the atrial septum, below the AV node, and near the tricuspid annulus to position the tip electrode 32 for advancement toward the His bundle towards the natural His-Purkinje system into the atrial septum. A second electrode (e.g., a loop electrode 34 or loop electrode 36) can be proximally spaced from the tip electrode 32 to, together with the tip electrode 32, provide bipolar pacing of the right and left ventricles via the His-Purkinje system and / or ventricular myocardium. The ventricular pacing pulses delivered by pacemaker 14 can capture at least a portion of the His bundle and / or ventricular myocardium for delivering ventricular pacing from the atrial implantation site of pacemaker 14 to the ventricles (e.g., the right ventricle (RV) and / or the left ventricle (LV)). However, the techniques disclosed herein are not necessarily limited to a specific implantation site of pacemaker 14 and can be practiced in pacemakers implanted in various surgical sites to provide cardiac signal sensing of atrial and ventricular electrical events and deliver cardiac pacing to at least one atrial chamber.

[0030] The pacemaker 14 may be capable of bidirectional wireless communication with an external device 50 for programming sensing and pacing control parameters. The external device 50, which may be referred to as a "programmer," is used by a physician, technician, nurse, clinician, or other qualified user to program the operating parameters in the pacemaker 14. The external device 50 may be located in a clinic, hospital, or other medical facility. Alternatively, the external device 50 may be embodied as a home monitor or handheld device that can be used in a medical facility, a patient's home, or another location. Operating parameters, including sensing and therapy delivery control parameters, can be programmed into the pacemaker 14 through user interaction with the external device 50.

[0031] External device 50 may include processor 52, memory 53, display unit 54, user interface 56, and telemetry unit 58. Processor 52 controls the operation of external device and processes data and signals received from pacemaker 14. Display unit 54 may generate a display (which may include a graphical user interface) of data and information related to pacemaker function for the user to review pacemaker operation and programming parameters. Display unit 54 may generate a display including cardiac signals and / or data derived therefrom that can be stored by pacemaker 14 and transmitted to external device 50 during an inquiry session, cardiac pacing timing markers, cardiac pacing history and / or other physiological data, patient data, or device-related data. For example, pacemaker 14 may generate outputs for transmission to external device 50, including, for example, pacing and sensing event history, capture test results, capture threshold test results, device operating parameters, and device diagnostic data.

[0032] User interface 56 may include a mouse, touchscreen, keyboard, etc., enabling a user to interact with external device 50 to initiate a telemetry session with pacemaker 14 to retrieve and / or transmit data to pacemaker 14, including programmable parameters for controlling sensing and pacing functions. Telemetry unit 58 includes a transceiver and antenna configured to communicate bidirectionally with telemetry circuitry included in pacemaker 14, and is configured to operate in conjunction with processor 52 to send and receive data related to pacemaker functionality via communication link 48.

[0033] The telemetry unit 58 can establish a wireless two-way communication link 48 with the pacemaker 14. The communication link 48 can use technologies such as Bluetooth. ® The communication link 48 can be established using a radio frequency (RF) link with bandwidths such as Wi-Fi, Medical Implantable Communication Service (MICS), or other communication bandwidths. In some examples, the external device 50 may include a programming head placed close to the pacemaker 14 to establish and maintain the communication link 48, and in other examples, the external device 50 and the pacemaker 14 may be configured to communicate using distance telemetry algorithms and circuitry that do not require the use of a programming head and do not require user intervention to maintain the communication link.

[0034] It is conceivable that the external device 50 can be connected to a communication network, either wired or wirelessly, via telemetry circuitry including a transceiver and antenna, or via hardwired communication lines for transmitting data to a centralized database or computer, to allow for remote patient management. A remote patient management system that includes a centralized patient database can enable clinicians to view data related to the sensing and pacing functions performed by the pacemaker 14.

[0035] Figure 2 It is based on an example Figure 1 The diagram shows a conceptual representation of a pacemaker 14. The pacemaker 14 includes a housing 15 having a distal end 12 and a proximal end 16. The transverse sidewalls 17 of the housing 15 extending from the distal end 12 to the proximal end 16 may be generally cylindrical to facilitate transvenous delivery, for example, via a catheter. The distal end 12 is referred to as “distal” because it is expected to be the tip when the pacemaker 14 is advanced through a delivery tool (such as a catheter) and placed against a target pacing site. In other examples, the housing 15 may have a generally prismatic shape. The housing 15 encloses the electronics and power supply for sensing cardiac signals, generating pacing pulses, controlling therapy delivery, and other functions of the pacemaker 14 as described herein.

[0036] The pacemaker 14 is shown as including electrodes 32, 34, and 36 spaced apart along the housing 15 of the pacemaker 14 for sensing cardiac electrical signals and delivering pacing pulses. Electrode 32 is shown as including a tip electrode extending from the distal end 12 of the housing 15. Electrodes 34 and 36 are shown as annular electrodes along the transverse sidewall 17 of the housing 15. Electrodes 34 and 36 may be annular electrodes surrounding the transverse sidewall 17, for example, adjacent to the proximal end 16 and adjacent to the distal end 12, respectively.

[0037] like Figure 1 As shown, the tip electrode 32 can be advanced from within the right atrial cavity to a ventricular pacing site, for example, for delivering pacing to the His-Purkinje conduction system and / or for pacing of the interventricular septal myocardial tissue. The tip electrode 32 is shown as a screw-in helical electrode that can provide fixation of the pacemaker 14 at the implantation site and also serve as a pacing and sensing electrode. In other examples, the tip electrode 32 may have a straight, hook-shaped, or other shape and may have a distal tip that pierces tissue to facilitate advancement of the pacemaker 14 to a ventricular pacing site (e.g., within the septum of the heart 8) when implanted in the RA. In some examples, the pacemaker 14 may include fixation members configured to engage atrial endocardial tissue to anchor the pacemaker 14 at the implantation site, such as one or more curved or angled fangs. Various types of active and / or passive fixation members can be employed to anchor or securely stabilize the pacemaker 14 at the implantation site.

[0038] The tip electrode 32 can be used as a cathode electrode, while the ring electrode 34 serves as a return anode for delivering ventricular pacing pulses. The tip electrode 32 and the ring electrode 34 can serve as a bipolar pair for ventricular pacing and for receiving ventricular electrical signals, from which R waves can be sensed by a sensing circuit enclosed by the housing 15. The ring electrodes 34 and 36 can form a second anode and cathode pair for bipolar atrial pacing and sensing atrial electrical signals, from which P waves can be sensed by a sensing circuit enclosed by the housing 15.

[0039] Although electrodes 34 and 36 are shown as annular electrodes surrounding the cylindrical sidewall 17 of housing 15, in other examples, the atrial cathode electrode may be positioned as one or more button-shaped, hemispherical, hook-shaped, segmented, short coil-shaped, or other types of electrodes, or combinations thereof, on the distal end 12 and / or along the longitudinal sidewall 17. The proximal annular electrode 34, serving as the return anode electrode for the ventricular and atrial pacing pairs, may alternatively be positioned as a button-shaped, hemispherical, hook-shaped, segmented, short coil-shaped, or other types of electrodes, or combinations thereof, along the proximal end 16 and / or longitudinal sidewall 17 of housing 15. Electrodes 32, 34, and 36 may be, but are not limited to, titanium, platinum, iridium, or alloys thereof, and may include low-polarization coatings such as titanium nitride, iridium oxide, ruthenium oxide, platinum black, etc.

[0040] Electrodes 32, 34, and 36 may be positioned along pacemaker 14 rather than as shown. While pacemaker 14 is shown as a leadless pacemaker comprising three housing-based electrodes, in other examples pacemaker 14 may be provided with a different number of electrodes, such as more than three. For example, a second anode electrode may be carried by pacemaker 14 to provide dedicated ventricular pacing and sensing cathode and anode pairs, as well as dedicated atrial pacing and sensing cathode and anode pairs, which do not necessarily share a common anode between ventricular and atrial pacing and sensing electrode pairs. Examples of various leadless dual-chamber pacemakers and pacing electrode arrangements in which the currently disclosed technology may be implemented are generally disclosed in U.S. Patent No. 11,426,578 (Yang et al.), the entire contents of which are incorporated herein by reference.

[0041] The housing 15 is formed of a biocompatible material, such as stainless steel or titanium alloy. In some examples, the housing 15 may include an insulating coating. Examples of insulating coatings include parylene, polyurethane, PEEK, or polyimide. The entire housing 15 may be insulating, except for electrodes 32, 34, and 36, which are not insulating. The tip electrode 32 may be coupled to internal circuitry (e.g., a pacemaker pulse generator and cardiac electrical signal sensing circuitry) enclosed by the housing 15 via an electrical feedthrough across the housing 15. Electrodes 34 and 36 may be formed as conductive portions of the housing 15 defining corresponding annular electrodes, which are electrically isolated from each other and from other portions of the housing 15, such as... Figure 2 The overall picture is shown in the middle.

[0042] The pacemaker 14 may include features for facilitating deployment and fixation at the implantation site. For example, the pacemaker 14 may optionally include a delivery tool interface 18. The delivery tool interface 18 may be located at the proximal end 16 of the pacemaker 14 and is configured to connect to a delivery device (such as a catheter) for positioning the pacemaker 14 in the implantation site during implantation procedures. The delivery tool interface 18 allows a clinician to advance, retract, and guide the pacemaker 14 to the implantation site and rotate the pacemaker 14 to advance the helical tip electrode 32 into the cardiac tissue (and / or, when included on the pacemaker housing 15, deploy other fixation components).

[0043] As an illustrative example, the exemplary technique disclosed herein for determining atrial pacing capture and controlling a backup atrial pacing pulse during capture testing is described as being implemented in and performed by a leadless pacemaker 14. However, it should be understood that aspects of the methods disclosed herein can be implemented in various leadless pacemaker configurations, including two device systems and a pacemaker or implantable cardioverter-defibrillator system including one or more medical electrical leads for positioning electrodes in or on the heart 8, such as transvenous and / or epicardial leads and electrode systems. Figures 3 to 5 Other example medical device systems that can be configured to practice the techniques disclosed herein are described.

[0044] Figure 3 This is an example of a medical device system 110 including two leadless pacemakers 114 and 116 for providing dual-chamber pacing and sensing. Pacemaker 114 may be configured for implantation in RA for pacing and sensing within the atrial cavity. Pacemaker 114 may include a distal tip electrode 132 and a proximal annular electrode 134 serving as a bipolar atrial pacing and sensing electrode pair. In other examples, pacemaker 114 may include more than two electrodes for sensing cardiac electrical signals and delivering atrial pacing. Electrodes 132 and 134 are carried on a pacemaker housing 115. For example, electrode 134 may be an annular electrode surrounding a cylindrical longitudinal sidewall of housing 115. Pacemaker 114 may include one or more retaining teeth 118 for engaging with atrial tissue to securely anchor pacemaker 114 at the implantation site. As an example, pacemaker 114 is shown as being implanted at an implantation site near the atrial septum above the tricuspid valve, but pacemaker 114 may be located at other locations on or within the RA.

[0045] The atrial pacemaker housing 115 can enclose the sensing circuit, pulse generation circuit, communication circuit, control circuit, and power supply, and in some cases, enclose other physiological sensors (as described below). Figure 6(Generally described herein), for performing sensing and pacing functions. Pacemaker 114 may be configured to deliver atrial pacing pulses according to the techniques disclosed herein, determine a capture outcome following the atrial pacing pulse (e.g., atrial capture, indeterminate capture, or capture loss), and control the delivery of a backup atrial pacing pulse. As described below, the control circuitry of pacemaker 114 may use the timing of a ventricular event signal sensed after the delivered atrial pacing pulse to determine the capture outcome. In some examples, pacemaker 114 may be configured to sense a far-field R wave from cardiac electrical signals sensed by electrodes 132 and 134. In other examples, pacemaker 114 may receive a communication signal (indicating the timing of the sensed R wave) from pacemaker 116 implanted in the right ventricle (RV) for determining the atrial capture outcome and for controlling the delivery of a backup atrial pacing pulse according to the techniques described below.

[0046] Atrial pacemaker 114 may be configured to: wirelessly communicate with ventricular pacemaker 116 (as indicated by arrow 148) to coordinate AV synchronous dual-chamber pacing in some examples; and to communicate timing of cardiac events to perform atrial capture management and backup atrial pacing according to the methods disclosed herein. Atrial pacemaker 114 and ventricular pacemaker 116 may each include communication circuitry for transmitting and / or receiving communication signals, which may be radio frequency signals, tissue conductance communication signals, or other forms of communication signals. In various examples, atrial pacemaker 114 may transmit a communication signal to ventricular pacemaker 116 to indicate the timing of a sensed P wave or a delivered atrial pacing pulse. In response to receiving the communication signal, ventricular pacemaker 116 may be triggered to deliver a ventricular pacing pulse at the AV pacing interval. In some examples, ventricular pacemaker 116 may transmit a signal to atrial pacemaker 114 indicating the timing of a sensed R wave or a delivered ventricular pacing pulse. As noted above, the atrial pacemaker 114 can use the timing of the sensed R wave to determine the atrial pacing capture outcome and control the delivery of the backup atrial pacing pulse. When the atrial pacemaker 114 delivers the backup atrial pacing pulse, a communication signal transmitted from the atrial pacemaker 114 to the ventricular pacemaker 116 can trigger the ventricular pacemaker 116 to deliver the ventricular pacing pulse synchronously with the backup atrial pacing pulse.

[0047] The ventricular pacemaker 116 is shown as including a housing 125 that carries at least two housing-based electrodes 136 and 138 for providing a bipolar electrode pair to sense ventricular electrical signals and deliver ventricular pacing pulses. In other examples, the ventricular pacemaker 116 may include another annular electrode (e.g., positioned near the distal end of the tip electrode 136 from which it extends) for setting a second pacing and / or sensing electrode pair. The tip electrode 136 may be a helical electrode, which can serve as a cathode electrode and a fixation member for anchoring the pacemaker 116 at the implantation site. In other examples, electrodes 136 and 138 may be other types of electrodes (e.g., according to any of the examples listed herein). The ventricular pacemaker housing 125 may enclose sensing circuitry, pulse generation circuitry, communication circuitry, and control circuitry, as well as a power supply, and in some cases, enclose other physiological sensors (as described below). Figure 6 (General description), used to perform sensing and pacing functions.

[0048] The ventricular pacemaker 116 is shown implanted along the interventricular septum 9, such that a tip electrode 136 can be advanced within the septum to reach a pacing site in the conduction system for delivering ventricular pacing via the His-Purkinje system. For example, the tip electrode 136 can be advanced to a pacing site in the region of the left bundle branch, right bundle branch, or His bundle. In other examples, the tip electrode 136 can be positioned (e.g., along the septum 9) at other pacing site locations for pacing the septal myocardium, or positioned at the apex for myocardial pacing.

[0049] The methods disclosed herein are advantageously applicable in medical devices with reduced housing size and volumetric capacity, such as in Figure 1 Leadless intracardiac pacemaker 14 or Figure 2 The method disclosed herein is applicable to devices capable of delivering atrial pacing using a reduced number of holding capacitors included in the pulse generation circuitry, wherein the reduced number of holding capacitors is used to deliver cardiac pacing pulses. This is further illustrated below. Figure 6 Further described, the pulse generation circuitry included in pacemaker 14 or pacemaker 114 may include holding capacitors that are charged to the pacing pulse voltage amplitude and discharged to the pacing pulse width for pacing pulse delivery. By reducing the number of holding capacitors required to deliver the primary and backup pacing pulses, the overall size of the medical device can be reduced, and / or space can be provided within the medical device housing (e.g., housing 15 or 115) for a larger power supply or other electronic circuitry.

[0050] In past practice, a backup atrial pacing pulse could be delivered during the atrial absolute refractory period following the primary or test atrial pacing pulse. Thus, if the primary or test atrial pacing pulse captures atrial myocardium, the backup atrial pacing pulse has no effect (e.g., it fails to capture atrial myocardium) because the tissue is in the absolute refractory period. However, when the primary or test atrial pacing pulse fails to capture atrial myocardium, a backup atrial pacing pulse delivered within a time interval shorter than the atrial absolute refractory period from the primary or test atrial pacing pulse can capture atrial myocardium and promote a regular atrial (and ventricular) rate.

[0051] To deliver a backup atrial pacing pulse during the physiological atrial refractory period following the primary atrial pacing pulse or a test atrial pacing pulse, a different capacitor than the one discharged to deliver the primary atrial pacing pulse is typically required to generate the backup atrial pacing pulse. Recharging the same capacitor used to deliver the primary atrial pacing pulse may not be fast enough to deliver the backup atrial pacing pulse within the physiological absolute refractory period of the atrium (e.g., within 50 to 100 milliseconds after the primary atrial pacing pulse). The same capacitor that was charged and discharged to deliver the primary atrial pacing pulse can be recharged for use in delivering the backup atrial pacing pulse by scheduling the backup atrial pacing pulse over a longer backup pacing interval (e.g., at least 300 ms or longer, or at least 400 ms or longer). A single holding capacitor (or a combination of holding capacitors) can be charged to the atrial pacing pulse voltage amplitude for generating and delivering the atrial pacing pulse. Using the techniques disclosed herein, the same single capacitor or combination of capacitors can be recharged to deliver a spare atrial pacing pulse scheduled at a spare atrial pacing interval that is longer than the atrial absolute refractory period and the atrial vulnerable period (e.g., during the atrial relative refractory period or the atrial repolarization phase).

[0052] Therefore, by implementing the methods disclosed herein, at least one capacitor typically included in the pulse generation circuitry for generating a backup atrial pacing pulse can be eliminated, thereby allowing for a reduction in the overall size of the pacemaker. While such size reduction is particularly advantageous in pacemakers fully implanted within RA, size reduction in any implantable medical device can be beneficial, for example, by promoting greater patient comfort and ease of implantation and removal. Additionally or alternatively, eliminating at least one capacitor typically included for generating a backup pacing pulse can allow for an increase in the size of the pacemaker's power supply or other electronic circuitry within the same or smaller medical device housing size. Therefore, the techniques disclosed herein can be implemented as medical device systems including a pacemaker or implantable cardioverter defibrillator (ICD) implanted inside or outside the heart (e.g., subcutaneously or submuscularly) and can be leadless pacemakers or connected to medical leads for positioning pacing electrodes and sensing electrodes in an operational position relative to the patient's heart.

[0053] Figure 4 This is a conceptual diagram of another example of a medical device system 150 configured to determine atrial capture and control the delivery of a backup atrial pacing pulse according to the technology disclosed herein. In this example, the pacemaker 154 includes a housing 155 for closure of interval device circuitry and a connector assembly 153 (sometimes referred to as a “connector block” or “head”) connected to the housing 155. The connector assembly 153 may be provided with one or more connector holes configured to receive proximal lead connectors for one or more medical electrical leads (e.g., atrial pacing and sensing leads 156 and ventricular pacing and sensing leads 158). Figure 4 (Not shown in the image).

[0054] The pacemaker 154 may be a dual-chamber pacemaker configured to receive atrial electrical signals and deliver atrial pacing pulses via electrodes 166 and 168 of atrial pacing and sensing leads 156. Electrical conductors extending through the atrial lead body 157 electrically connect the respective electrodes 166 and 168 to the sensing and pacing circuitry enclosed by the housing 155, for example via contacts within the connector assembly 153 and through electrical feedthroughs through the housing 155.

[0055] The pacemaker 154 can be configured to receive ventricular electrical signals and deliver ventricular pacing pulses via electrodes 162 and 164 of the ventricular pacing and sensing leads 158. Electrical conductors extending through the ventricular lead body 159 electrically connect the respective electrodes 162 and 164 to the sensing and pacing circuitry enclosed by the housing 155, for example via contacts within the connector assembly 153 and through electrical feedthroughs through the housing 155.

[0056] In the illustrated example, the atrial pacing and sensing lead 156 is advanced into the RA via a vein, and the atrial tip electrode 166 may be anchored at the atrial pacing and sensing site, for example, along the atrial septum or another atrial endocardial location. The atrial tip electrode 166 may be a helical electrode, serving as both a cathode electrode and a fixation member for anchoring the lead 156 at the atrial pacing and sensing site. In other examples, the atrial lead 156 may include a non-tissue-puncture distal tip electrode and one or more fixation teeth or other fixation members for anchoring the lead 156 at the atrial pacing and sensing site. Electrode 168 may be a ring electrode surrounding the lead body 157 and spaced proximally from the distal tip electrode 166 along the lead body 157.

[0057] The ventricular pacing and sensing lead 158 is advanced into the RA via a vein, and its ventricular tip electrode 162 can be advanced from a right atrial approach to the pacing site of the conduction system. For example, the tip electrode 162 can be advanced from an insertion point in the Koch triangle into the interventricular septum 9 to position the ventricular tip electrode 162 along or near the His bundle for delivering ventricular pacing pulses via the native conduction system. The ventricular tip electrode 162 can be a helical electrode, which serves as a cathode electrode and a fixation member for anchoring the ventricular pacing and sensing lead 158 at the desired implantation site. Electrode 164 can be a ring electrode surrounding the lead body 159 and spaced proximally from the distal tip electrode 162 along the lead body 159.

[0058] Pacemaker 154 can be configured to deliver atrial pacing pulses via atrial pacing and sensing lead 156 and sense ventricular R waves via ventricular pacing and sensing lead 158 for determining atrial pacing capture results and for controlling the delivery of backup atrial pacing pulses according to the techniques disclosed herein, as further described below. The lead and electrode configuration of medical device system 150 is an example of a transvenous dual-lumen medical device system. As noted above, the techniques disclosed herein are not limited to practice in conjunction with a particular medical device system or any particular lead and electrode configuration or electrode implantation site. Various lead and / or electrode configurations and electrode implantation sites can be used in conjunction with the techniques disclosed herein. For example, instead of Figure 4 The two lead systems shown allow a single lead carrying multiple electrodes to be connected to pacemaker 154 to provide atrial pacing and sensing electrode pairs and ventricular pacing and sensing electrode pairs carried by the same lead (e.g., lead 158). A single lead may carry three or more electrodes, which may be selectively coupled to the sensing and pacing circuitry of pacemaker 154, for example via a switching circuit, to select an atrial sensing electrode, an atrial pacing electrode, a ventricular sensing electrode, and / or a ventricular pacing electrode.

[0059] Figure 5This is another example of a medical device system 170 that enables the currently disclosed methods for delivering atrial pacing pulses, determining atrial capture outcomes, and controlling backup atrial pacing pulses. The medical device system 170 includes a pacemaker 174 coupled to atrial leads 176 and ventricular leads 178 via a connector assembly 173, which provides connections of atrial pacing electrodes 186 and sensing electrodes 188, and ventricular pacing electrodes 182 and sensing electrodes 184, to pacing and sensing circuitry enclosed by a housing 175.

[0060] In this example, pacemaker 174 is capable of dual-chamber sensing and pacing, as well as the delivery of high-voltage cardioversion / defibrillation (CV / DF) impulses, and may be referred to as an ICD. Therefore, at least one electrode with a relatively high surface area for delivering high-voltage CV / DF impulses may be carried by at least one of leads 176 and / or 178. In the illustrated example, ventricular lead 178 includes an RV coil electrode 190 and a superior vena cava (SVC) coil electrode 192, which are configured to deliver high-voltage CV / DF impulses together with and / or in combination with pacemaker housing 175, which serves as an active canister electrode. Electrodes 190 and 192 may be configured as elongated coil electrodes and may be referred to as “defibrillation electrodes,” but in some examples they may also be used individually or in combination in the sensing electrode vector for sensing cardiac electrical signals.

[0061] In this example, the ventricular lead 178 is shown being advanced into the RV of the patient's heart 8 to position the ventricular pacing electrode 182 and sensing electrode 184 at the desired ventricular pacing and sensing sites. As shown, the tip electrode 182 may be advanced into the interventricular septum 12 to position it at a location for pacing the ventricle via the His-Purkinje conduction system. For example, as an example, the tip electrode 182 may be advanced into the interventricular septum 12 to reach a left bundle branch pacing site, a right bundle branch pacing site, or from an insertion point near the base of the interventricular septum 9 to a His bundle pacing site. In other examples, the tip electrode 182 may be advanced and anchored (e.g., in or along the interventricular septum, or at or near the apex of the RV) to a ventricular myocardial pacing site.

[0062] Pacemaker 174 may be configured to perform the techniques described herein for delivering atrial pacing pulses via atrial electrodes 186 and 188, sensing atrial P waves via atrial electrodes 186 and 188, delivering ventricular pacing pulses via ventricular electrodes 182 and 184, sensing ventricular R waves via ventricular electrodes 182 and 184, and determining an atrial capture outcome based on whether and when a ventricular R wave is sensed after delivery of the atrial pacing pulse. Pacemaker 174 may schedule a standby atrial pacing pulse at a standby atrial pacing interval longer than the physiological refractory period of the atrium. As further described below, the control circuitry of pacemaker 174 or any other example pacemaker described herein may determine whether to deliver or cancel the standby atrial pacing pulse based on whether an atrial P wave or a ventricular R wave is sensed during the standby atrial pacing interval. The control circuitry can determine whether or not to deliver the ventricular pacing pulse during or after the standby atrial pacing interval based on whether and when an atrial P wave is sensed, or whether and when a standby atrial pacing interval is delivered if the pacemaker's sensing circuitry does not sense a ventricular R wave.

[0063] Figure 6 This is a conceptual diagram of an example configuration of a medical device configured to perform the atrial pacing, capture determination, and backup pacing methods disclosed herein. For convenience, refer to... Figure 1 The leadless intracardiac pacemaker 14 describes Figure 6 However, it should be understood that the circuitry and functionality attributable to pacemaker 14 for practicing the technology disclosed herein may be applicable to other medical device systems (including those combined with...). Figures 3 to 5 Implemented in any of the medical device systems described in the example medical device system.

[0064] The pacemaker 14 may include a pulse generator 202, a cardiac electrical signal sensing circuit 204, a control circuit 206, a telemetry circuit 208, a memory 210, a sensor 212, and a power supply 214. Figure 6 The various circuits represented herein can be combined on one or more integrated circuit boards, which include: application-specific integrated circuits (ASICs), electronic circuits, processors (shared, dedicated, or grouped) and memories that execute one or more software or firmware programs, combinational logic circuits, state machines, or other suitable components that provide the described functionality.

[0065] The cardiac electrical signal sensing circuit 204 (hereinafter referred to as "sensing circuit" 204) is configured to receive at least one cardiac electrical signal via electrodes coupled to pacemaker 14 (e.g., via tip electrode 32 and proximal ring electrode 34). A second cardiac electrical signal may be received via ring electrodes 34 and 36 (and / or electrode tip 32 and distal ring electrode 36). Therefore, sensing circuit 204 may have multiple sensing channels, such as atrial sensing channel 203 and ventricular sensing channel 205. Although pacemaker 14 is shown as having three electrodes in the example illustrated herein, in other examples, pacemaker 14 may be provided with two or more electrodes that may be coupled to sensing circuit 204 (and / or pulse generator 202) to form a selected sensing (and / or pacing) electrode vector. Sensing circuit 204 may include switching circuitry for coupling sensing electrode pairs to corresponding sensing channels 203 or 205. For example, by switching the distal ring electrode 36 and the proximal ring electrode 34 to the atrial sensing channel 203 in the bipolar atrial sensing electrode pair, the sensing circuit 204 can receive atrial signals. By switching the tip electrode 32 and the proximal ring electrode 34 to the ventricular sensing channel 205 in the bipolar ventricular sensing electrode pair, the sensing circuit 204 can receive ventricular signals.

[0066] Sensing channels 203 and 205 may include filters, amplifiers, analog-to-digital converters (ADCs), rectifiers, sensing amplifiers, comparators, and / or other circuitry for sensing cardiac event signals (e.g., P waves and R waves, respectively) and generating sensed cardiac event signals (e.g., atrial sensing event signals (Asense signals) and ventricular sensing event signals (Vsense signals)) that are passed from the respective sensing channels 203 and 205 to control circuitry 206. Sensing circuitry 204 may be configured to, for example, pass filtered and amplified multi-bit digital electrocardiogram (EGM) signals from one or both of atrial sensing channel 203 and ventricular sensing channel 205 to control circuitry 206. The EGM signals may be processed and analyzed by control circuitry 206 to determine heart rhythm and / or stored as cardiac signal segments in memory 210, which may be transmitted by telemetry circuitry 208 to, for example, an external device 50. Figure 1 (As shown in the image).

[0067] Each of the atrial sensing channel 203 and the ventricular sensing channel 205 can receive a raw cardiac electrical signal from a selected sensing electrode vector as input to a pre-filter and amplifier circuit for filtering and amplifying the raw signal. Each pre-filter and amplifier circuit includes a high-pass filter to remove DC offset, such as a 2.5Hz to 5Hz high-pass filter, or a broadband filter with a narrow bandpass of 2.5Hz to 100Hz or less to remove DC offset and high-frequency noise. The pre-filter and amplifier circuit can then pass the filtered and amplified signal to the ADC of the corresponding sensing channel 203 or 205.

[0068] Each ADC can individually pass a rectified digital signal to a narrowband filter in its respective sensing channel 203 or 205. The atrial sensing channel 203 may include a bandpass filter with a bandpass cutoff frequency to allow the P wave signal to pass through and attenuate other cardiac event signals, such as R and T waves. As an example, the low-pass cutoff frequency of the narrowband filter in the atrial sensing channel 203 may be between 25 Hz and 100 Hz or between 50 Hz and 80 Hz, and the high-pass cutoff frequency may be between 5 Hz and 25 Hz or between 15 Hz and 20 Hz. In this example, the atrial sensing channel 203 includes a bandpass filter with a low-pass frequency of 70 Hz and a high-pass frequency of 17 Hz.

[0069] Atrial sensing channel 203 may include atrial event detector circuitry, which may include a sensing amplifier, a comparator, or other event detection circuitry that compares an incoming rectified, filtered, and amplified atrial EGM signal with a P-wave sensing threshold. For example, when an incoming signal crosses the P-wave sensing threshold, atrial sensing channel 203 may generate an Asense signal, which may be transmitted to control circuitry 206 to indicate the timing of the sensed P wave. The P-wave sensing threshold may be an automatically adjusting threshold, which is automatically reduced from an initial value to a minimum value by sensing circuitry 204 or until a P-wave sensing threshold crossing occurs. The P-wave sensing threshold amplitude is initially set to a starting value applied to the atrial EGM signal at the end of the atrial post-silence period and may be adjusted to be equal to a minimum sensing threshold or "sensing limit" of programmed atrial sensitivity.

[0070] Atrial sensing channel 203 may include peak tracking and hold circuitry or other circuitry for detecting the maximum peak amplitude of the atrial EGM signal during a portion of the post-atrial blanking period. The initial value of the P-wave sensing threshold may be set based on the maximum peak amplitude, for example, as a percentage of the maximum peak amplitude after the P-wave sensing threshold is crossed. In some examples, the P-wave sensing threshold may be set to 50% to 80% of the maximum peak amplitude. The P-wave sensing threshold may be decreased according to one or more decay rates and corresponding decay intervals until the atrial EGM signal crosses the P-wave sensing threshold or reaches atrial sensitivity. Atrial sensitivity defines the maximum atrial EGM signal amplitude that can be sensed as a P wave. In other examples, the P-wave sensing threshold may be a fixed value that does not decay over time and may be applied as a percentage of the maximum peak amplitude of the atrial EGM signal during the post-atrial blanking period or based on a programmed atrial sensitivity. If the atrial pacing interval (which may be set to a programmed LRI) expires before the control circuitry 206 receives the Asense signal, the pulse generator 202 may deliver an atrial pacing pulse.

[0071] Ventricular sensing channel 205 may include an ADC for receiving a filtered and amplified input signal. The ADC of ventricular sensing channel 205 may pass the rectified signal to a narrow bandpass filter having a bandpass cutoff frequency to allow the R-wave signal to pass through and attenuate other cardiac event signals, such as P and T waves. As an example, the low-pass cutoff frequency of the bandpass filter included in ventricular sensing channel 205 may be between 25 Hz and 100 Hz or between 40 Hz and 80 Hz, and the high-pass cutoff frequency may be between 5 Hz and 25 Hz or between 15 Hz and 20 Hz. In an example, ventricular sensing channel 205 is provided with a bandpass filter having a low-pass frequency of 70 Hz and a high-pass frequency of 17 Hz. The bandpass cutoff frequencies of atrial sensing channel 203 and ventricular sensing channel 205 may be the same or different cutoff frequencies. In some examples, the cutoff frequency is user-programmable.

[0072] Ventricular sensing channel 205 may include ventricular event detector circuitry, which may include a sensing amplifier, a comparator, or other event detection circuitry that compares an incoming rectified, filtered, and amplified ventricular EGM signal with an R-wave sensing threshold. For example, when the incoming signal crosses the R-wave sensing threshold, sensing circuitry 204 may generate a Vsense signal that can be passed to control circuitry 206. The R-wave sensing threshold may be an automatically adjusting threshold that is automatically reduced by sensing circuitry 204 from a starting value until the ventricular EGM signal crosses the threshold. The R-wave sensing threshold amplitude is initially set to a starting value applied to the ventricular EGM signal at the end of the post-ventricular blanking period and may be adjusted to be equal to a minimum sensing threshold or "sensing limit" of the programmed ventricular sensitivity.

[0073] Sensing circuitry 204 may include peak tracking and hold circuitry or other circuitry for detecting the maximum peak amplitude of the ventricular EGM signal after the R-wave sensing threshold has been crossed during the peak tracking portion of the post-ventricular blanking period. The initial value of the R-wave sensing threshold may be set based on the maximum peak amplitude, for example, as a percentage of the maximum peak amplitude. In some examples, the R-wave sensing threshold may be set to 50% to 80% of the maximum peak amplitude. The R-wave sensing threshold may be decreased according to one or more decay rates and corresponding decay intervals until the ventricular EGM signal crosses the R-wave sensing threshold or reaches ventricular sensitivity. Ventricular sensitivity defines the maximum amplitude of the ventricular EGM signal that can be sensed as an R-wave. In other examples, the R-wave sensing threshold may be a fixed, non-decaying value, for example, a fixed percentage of the maximum peak amplitude or a fixed value based on programmed ventricular sensitivity. If the ventricular pacing interval or AV pacing interval expires before control circuitry 206 receives the Vsense signal, pulse generator 202 may deliver a ventricular pacing pulse.

[0074] Control circuit 206 can provide sensing control signals to sensing circuit 204. Sensing control parameters may include R-wave sensing threshold adjustment parameters, such as a percentage of the maximum peak amplitude of the initial R-wave sensing threshold and ventricular sensitivity, and P-wave sensing threshold adjustment parameters, such as a percentage of the maximum peak amplitude of the initial P-wave sensing threshold and atrial sensitivity. Sensing control parameters may include various blanking periods and refractory periods applied to atrial EGM signals, such as post-sensing atrial blanking period, post-pacing atrial blanking period, atrial refractory period, and post-ventricular atrial blanking period. Sensing control parameters may include various blanking periods and refractory periods applied to ventricular EGM signals, such as post-sensing ventricular blanking period, post-pacing ventricular blanking period, ventricular refractory period, and post-ventricular blanking period.

[0075] When sensing circuit 204 is configured to receive raw atrial and ventricular electrical signals, in various examples, components included in atrial sensing channel 203 and ventricular sensing channel 205 may be separate or shared between the two sensing channels 203 and 205. For example, a pre-filter / amplifier and / or ADC may be shared by both atrial sensing channel 203 and ventricular sensing channel 205, wherein separate outputs are passed to both the atrial channel bandpass filter and atrial event detector circuitry and to the ventricular channel bandpass filter and ventricular event detector circuitry. Different filtering and amplification processes may be applied to the ADC outputs before passing the separate signals to the respective atrial and ventricular event detector circuitry.

[0076] Control circuit 206 may include pacing timing circuit 242 and processor 244. Control circuit 206 may receive Vsense and Asense signals from sensing circuit 204 for controlling the timing of cardiac pacing pulses. In response to a ventricular event signal sensed by ventricular sensing channel 205, the Vsense signal may be transmitted from sensing circuit 204 to control circuit 206 to indicate the timing of sensed R waves. In response to an atrial event signal sensed by atrial sensing channel 203, the Asense signal may be transmitted from sensing circuit 204 to control circuit 206 to indicate the timing of sensed P waves.

[0077] Processor 244 can transmit sensing control parameters to sensing circuitry 204 for sensing cardiac event signals from cardiac electrical signals. Processor 244 may include one or more clocks for generating clock signals, which are used by pacing timing circuitry 242 to time out various pacing intervals to provide atrial and / or ventricular pacing according to the operating pacing mode. Depending on the operating pacing mode of control circuitry 206, pacing timing circuitry 242 may initiate various pacing intervals to schedule pacing pulses. Control circuitry 206 may be configured to operate in a variety of programmable and / or automatically switchable pacing modes. During atrial-ventricular pacing modes (e.g., which may be represented as DDD or VDD pacing modes), ventricular pacing pulses may be delivered synchronously with atrial pacing pulses and received Asense signals. For example, in response to receiving an Asense signal, pacing timing circuitry 242 may initiate an AV pacing interval to control the timing of atrial-ventricular pacing pulses. When the pulse generator 202 delivers a ventricular pacing pulse at the end of the AV pacing interval, the pacing timing circuit 242 can initiate the ventricular pacing interval to schedule the ventricular pacing pulse according to the programmed lower ventricular limit rate. During atrial-synchronized ventricular pacing, if no Asense signal is received or no atrial pacing pulse is delivered before the end of the ventricular pacing interval, the pulse generator 202 can deliver an asynchronous ventricular pacing pulse to prevent ventricular pacing from stopping and restart the ventricular pacing interval. If an Asense signal is received (or an atrial pacing pulse is delivered) before the end of the ventricular pacing interval, the scheduled ventricular pacing pulse can be suppressed. Pending pacing pulses can be cancelled, and atrial-synchronized ventricular pacing pulses can be delivered at the AV pacing interval from the Asense signal (or the delivered atrial pacing pulse).

[0078] In response to receiving a Vsense signal from sensing circuit 204, pacing timing circuit 242 may suppress pending ventricular pacing pulses scheduled at the ventricular pacing interval (or scheduled at the AV pacing interval) and restart the ventricular pacing interval. The ventricular pacing interval may be a lower limit rate interval (LRI) corresponding to a programmed minimum or baseline lower limit ventricular pacing rate. In other cases, the ventricular pacing interval may be a temporary ventricular pacing interval set as a rate smoothing interval to avoid sudden changes in ventricular rate. In still other cases, the ventricular pacing interval may be a temporary rate-responsive pacing interval set to provide rate-responsive pacing during periods of increased patient physical activity, which may be determined based on signals from sensor 212, as further described below.

[0079] The pacing timing circuit 242 can activate the pacing escape interval timer upon receiving an Asense or Vsense signal from the sensing circuit 204. The value reached by the escape interval timer between two consecutive Asense signals or between an Asense signal and a preceding atrial pacing pulse can be determined as the PP interval (PPI) for determining the atrial rate. The value reached by the escape interval timer between two consecutive Vsense signals or between a Vsense signal and a preceding ventricular pacing pulse can be determined as the RR interval (RRI) for determining the ventricular rate. The atrial rate and / or ventricular rate can be determined by the control circuit 206 for storing cardiac data in the memory 210, controlling pacing mode switching, or other pacemaker functions in some examples.

[0080] The pacing timing circuit 242 may include a timer or counter for determining the time from the atrial pacing pulse delivered by the pulse generator 202 to the Vsense signal received from the sensing circuit 204. This time interval may be referred to as the pacing AV interval or "Apace-Vsense interval" and may be measured by the control circuit 206 for determining the capture result of the delivered atrial pacing pulse according to the techniques disclosed herein, as further described below. The pacing timing circuit 242 may include a timer or counter for determining the time from the Asense signal received from the sensing circuit 204 to the Vsense signal received from the sensing circuit 204. This time interval may be referred to as the sensed AV interval or "Asense-Vsense interval" and may be measured by the control circuit 206 for determining the capture result of the delivered atrial pacing pulse when an Asense is received during the standby atrial pacing interval according to the techniques disclosed herein.

[0081] As further described below, control circuit 206 can perform atrial capture management by determining the capture outcome after an atrial pacing pulse delivered by pulse generator 202. The capture outcome can be determined based on the timing of any Asense and / or Vsense signals received after the atrial pacing pulse. Pacing timing circuit 242 can initiate a standby atrial pacing interval upon delivery of the atrial pacing pulse, and control circuit 206 can determine the capture outcome based on any Asense and / or Vsense signals received during the standby atrial pacing interval, and cancel the delivery of the standby atrial pacing pulse when an Asense or Vsense signal is received during the standby atrial pacing interval. As described below, when no Vsense signal is received during the standby atrial pacing interval or during an AV pacing interval extending from the end of the standby atrial pacing interval, control circuit 206 can control pulse generator 202 to deliver a ventricular pacing pulse.

[0082] Pulse generator 202 generates electrical pacing pulses that can be delivered via cathode electrode 32 and return anode electrode 34 to pace the ventricles of a patient's heart. Pulse generator 202 can, for example, use electrodes 36 and 34 to generate electrical pacing pulses for pacing the atria. In addition to providing control signals to pacing timing circuit 242 and pulse generator 202 for controlling the timing and delivery of pacing pulses, processor 244 can also retrieve programmable pacing control parameters (such as pacing pulse amplitude and pacing pulse width) from memory 210, which are passed to pulse generator 202 for controlling pacing pulse delivery.

[0083] The pulse generator 202 may include a charging circuit 230, a switching circuit 232, and an output circuit 234. The charging circuit 230 is configured to receive current from a power supply 214 and may include at least one holding capacitor, which may be charged to the pacing pulse amplitude, for example, under the control of a voltage regulator included in the charging circuit 230. The pacing pulse amplitude may be set based on a control signal from the control circuit 206. In the illustrated example, the charging circuit 230 includes an atrial holding capacitor 235, which may be charged to the atrial pacing pulse amplitude and discharged via the switch 232 and the output circuit 234 through an atrial pacing electrode vector including electrodes 34 and 36. The charging circuit 230 includes a ventricular holding capacitor 236, which may be charged to the ventricular pacing pulse amplitude and discharged via the switch 232 and the output circuit 234 through a ventricular pacing electrode vector including electrodes 32 and 34. It should be understood that in some examples, the atrial retention capacitor 235 and the ventricular retention capacitor 236 may each be a single capacitor, or one or both of the atrial retention capacitor and the ventricular retention capacitor may be a combination of retention capacitors configured to be charged to the respective atrial pacing amplitude and ventricular pacing pulse amplitude. Although the above is combined with... Figures 1 to 5 Some pacemakers described as examples may include at least one additional holding capacitor (which can be charged to deliver a backup pacing pulse), but in some examples, the backup pacing holding capacitor is omitted in pacemaker 14 to facilitate miniaturization of pacemaker 14 for easy implantation (e.g., implantation in the atrium).

[0084] Switching circuit 232 controls when the holding capacitors 235 or 236 of charging circuit 230 are connected to output circuit 234 to deliver atrial pacing pulses or ventricular pacing pulses, respectively. For example, switching circuit 232 may include a switch activated by a timing signal received from pacing timing circuit 242 at the end of the pacing escape interval and held closed for a programmed pacing pulse width to allow the holding capacitors of charging circuit 230 to discharge. The ventricular holding capacitor 236 or atrial holding capacitor 235, previously charged to the ventricular or atrial pacing pulse voltage amplitude, may discharge across the respective ventricular pacing electrodes 32 and 34 or across the atrial pacing electrodes 36 and 34 via the output capacitors of output circuit 234 for the programmed pacing pulse duration. Although the switching circuit 232 and the output circuit 234 are shown as a shared circuit for an atrial pacing channel including an atrial holding capacitor 235 and a ventricular pacing channel including a ventricular holding capacitor 236, in other examples, each atrial pacing channel and ventricular pacing channel may include separate charging circuits, switching circuits, and output circuits operating under the control of the control circuit 206 to deliver atrial pacing pulses and ventricular pacing pulses, respectively.

[0085] The pacemaker 14 may include one or more sensors 212 for sensing physiological signals, including cardiac mechanical signal sensors. For example, sensor 212 may include an accelerometer for sensing patient motion and / or cardiac motion. Sensor 212 may include a single-axis or multi-axis accelerometer for generating acceleration signals in one or more dimensions, which can be used to determine the relative level of the patient's physical activity. In some examples, the pacemaker 14 may be able to deliver rate-responsive pacing based on a measure of the patient's physical activity determined according to the acceleration signals generated by sensor 212. Control circuitry 206 may receive rectified acceleration signals from sensor 212 and determine the measure of the patient's physical activity based on the acceleration signals, for example, by summing the amplitudes of acceleration signal sampling points within the activity measurement time interval. The activity measure may be converted into a target heart rate to meet the patient's metabolic needs. The target heart rate may be converted into an SIR based on a sensor-indicated rate (SIR) transfer function, which may include, for example, a lower rate setpoint and an activity of daily living (ADL) range, as well as a maximum higher rate. During rate response pacing mode, the pulse generator 202 can be controlled by the control circuit 206 to deliver atrial or ventricular pacing pulses at a rate response pacing rate determined based on SIR.

[0086] Additionally or alternatively, sensor 212 may include a pressure sensor, impedance sensor, heart sound sensor, accelerometer, or gyroscope, or other sensors for sensing cardiac mechanical signals accompanying atrial and / or ventricular contraction and / or diastole and / or opening and closing of heart valves. While the exemplary examples described herein involve sensing cardiac electrical signals by sensing circuitry 204 for pacing Asense and Vsense signals to control circuitry 206, it is contemplated that control circuitry 206 may be configured to receive one or more signals from sensor 212 that generates signals in response to cardiac mechanical function, and detect ventricular event signals and / or atrial event signals corresponding to ventricular systole or atrial systole, respectively. During the atrial standby pacing interval, the ventricular event signals and / or atrial event signals detected by control circuitry 206 from one or more cardiac mechanical signals can be used to determine the atrial capture outcome and control the standby pacing pulse according to the methods described herein. For example, control circuit 206 may be configured to detect a ventricular event signal from an accelerometer signal according to the method described below and determine an atrial capture outcome based on at least the timing of the ventricular event signal.

[0087] Memory 210 may include computer-readable instructions that, when executed by control circuitry 206, cause control circuitry 206 to perform various functions attributed to pacemaker 14 throughout this disclosure. The computer-readable instructions may be encoded within memory 210. Memory 210 may include any non-transitory computer-readable storage medium, including any volatile, non-volatile, magnetic, optical, or electrical medium, such as random access memory (RAM), read-only memory (ROM), non-volatile RAM (NVRAM), electrically erasable programmable ROM (EEPROM), flash memory, or other digital media, with the sole exception of transient propagation signals.

[0088] Memory 210 may store sensed event data based on Vsense and Asense signals received from sensing circuit 204 for use in determining atrial pacing capture results and controlling the delivery of backup atrial pacing pulses and ventricular pacing pulses according to the techniques disclosed herein. In some examples, memory 210 includes a buffer storing one or more EGM signal segments received from sensing circuit 204. When control circuit 206 determines that atrial capture has been lost or performs an atrial pacing threshold search, memory 210 may store one or more segments of the EGM signal for transmission via telemetry circuit 208.

[0089] Telemetry circuit 208 includes a transceiver 209 and an antenna 211 for transmitting and receiving data via a radio frequency (RF) communication link. As described above, telemetry circuit 208 may be able to communicate with external device 50 ( Figure 1 Two-way communication is enabled. Cardiac electrical signals and / or data derived therefrom, atrial and ventricular pacing history, capture thresholds, etc., can be transmitted by telemetry circuit 208 to external device 50. Programmable control parameters and algorithms for sensing cardiac event signals and controlling pacing therapy delivered by pulse generator 202 can be received by telemetry circuit 208 and stored in memory 210 for access by control circuit 206. In some examples, pacemaker 14 can be configured to communicate with a second implantable medical device via telemetry circuit 208 or via tissue conduction communication signals, which can be transmitted by pulse generator via electrodes 32, 34, and / or 36. For example, in... Figure 3 In the example shown, the two leadless pacemakers 114 and 116 may be configured to communicate with each other via respective telemetry circuits (e.g., via RF communication or tissue conduction communication) for coordinating dual-chamber pacing and for transmitting the timing of the Vsense signal for determining the atrial capture outcome and controlling the delivery of the backup atrial pacing pulse according to the techniques disclosed herein.

[0090] Power source 214 supplies power to each of the other circuits and components of pacemaker 14 when needed. Power source 214 may include one or more energy storage devices, such as one or more rechargeable or non-rechargeable batteries. For clarity, the connections between power source 214 and other pacemaker circuits and components are not shown in the diagram. Figure 6 As shown in the text, but should be from Figure 6 The overall block diagram is for understanding. Power supply 214 can supply power to pulse generator 202, sensing circuit 204, telemetry circuit 208, memory 210 and sensor 212 as needed.

[0091] The functions attributed herein to pacemaker 14 can be embodied in one or more processors, controllers, hardware, firmware, software, or any combination thereof. Describing different features as specific circuits is intended to highlight different functional aspects and does not necessarily imply that such functions must be implemented by separate hardware, firmware, or software components or by any particular circuit architecture. Rather, the functionality associated with one or more circuits described herein can be performed by separate hardware, firmware, or software components, or integrated within general-purpose hardware, firmware, or software components. For example, the process for confirming cardiac event signals can be implemented in control circuitry 206, which executes instructions stored in memory 210 and depends on input from sensing circuitry 204. Given the disclosure herein, providing software, hardware, and / or firmware to accomplish the described functionality in the context of any modern medical device is within the capabilities of those skilled in the art.

[0092] Figure 7 This is a flowchart 250, based on some examples of methods for determining atrial capture outcomes and controlling backup pacing pulses by a medical device. For convenience, refer to... Figure 1 and Figure 6 The pacemaker 14 shown illustrates the method of flowchart 250, as well as other flowcharts and timing diagrams described below. It should be understood that the processes presented in the flowcharts and timing diagrams can be implemented in any of the example medical device systems described above.

[0093] At block 252, pulse generator 202 delivers an atrial pacing pulse (apace). As described below, the apace can be a test apace during capture management testing or capture threshold search. In other examples, the apace can be delivered based on the currently valid pacing mode and pacing pulse parameters, for which control circuitry 206 can verify capture of the apace. In response to the delivered apace, control circuitry 206 can schedule a backup apace at block 254 by activating a backup atrial pacing interval.

[0094] At box 256, control circuitry 206 determines whether a Vsense signal has been received before the expiration of the spare atrial pacing interval. If not, pulse generator 202 may deliver the spare Apace at box 258 and determine capture loss at box 260. Control circuitry 206 may control the pulse generator to deliver a ventricular pacing pulse at the AV pacing interval following the Apace at box 258.

[0095] If control circuit 206 receives a Vsense signal at block 256 before the expiration of the standby atrial pacing interval, control circuit 206 may cancel the scheduled standby Apace at block 262. At block 264, control circuit 206 may determine the atrial capture outcome based at least on the time of the Vsense signal (e.g., the time interval from the delivered Apace to the Vsense signal). As further described below, control circuit 206 may determine the capture outcome by applying at least one capture verification window that expires before the standby atrial pacing interval to the Apace-Vsense interval for verifying the capture of the Apace. In some examples, if control circuit 206 receives an Asense signal during the standby atrial pacing interval before the Vsense signal, control circuit 206 may determine the capture outcome based at least on the time of the Vsense signal relative to the Apace (e.g., the Apace-Vsense interval) and the time of the Vsense signal relative to the Asense signal (e.g., the Asense-Vsense interval). The control circuit 206 can execute a response to the capture result, as described below. Figure 8 and Figure 11 The flowchart is described further.

[0096] Figure 8 This is a flowchart 300 of a method, which can be executed by pacemaker 14, for determining the outcome of atrial capture and controlling the delivery of standby atrial pacing pulses. Figure 9 It can be used by the control circuitry of pacemaker 14 for execution Figure 8 The method of atrial and ventricular pacing pulses and timing diagrams of various time intervals 400.

[0097] refer to Figure 8At block 302, control circuitry 206 controls pulse generator 202 to generate and deliver an Apace. The Apace may be a test pulse delivered to confirm atrial capture during a capture test. In other cases, the Apace may be delivered during an atrial capture threshold search. In some cases, the Apace may be delivered according to a programmed pacing pattern, for example, as a bradycardia pacing pulse delivered at a programmed lower atrial rate limit interval. The Apace may be delivered at a shortened pacing interval (in some cases, e.g., shorter than the sensed intrinsic atrial rate) to facilitate earlier delivery of the Apace than intrinsic atrial depolarization. In various examples, control circuitry 206 may be configured to verify the capture of the delivered Apace and, according to… Figure 8 The method schedules backup apaces on a beat-by-beat or less frequent basis. For example, capture tests can be performed at a frequency of once per minute, once per hour, once per day, or other scheduled frequencies. Atrial capture threshold searches can be performed daily or according to a specified schedule, and can be performed in response to a capture loss detected by control circuitry 206 during a capture test. Atrial capture threshold searches can be performed when a user-input command is received via telemetry circuitry 208 (e.g., during a telemetry session with external device 50).

[0098] At block 304, control circuit 206 can schedule a standby Apace by activating a standby atrial pacing interval in response to the delivery of an atrial pacing pulse by pulse generator 202 at block 302. Control circuit 206 can determine the atrial capture outcome based on whether and when a Vsense signal is received after the Apace during the standby atrial pacing interval. It should be noted that when the current pacing mode is AV synchronous dual-chamber mode, in order to determine the capture outcome of the Apace delivered at block 302 based on when and whether a Vsense signal is received from sensing circuit 204 after the Apace, a ventricular pacing pulse is not scheduled during the AV pacing interval after the Apace. When Apace is delivered at box 302, control circuit 206 may not activate the AV pacing interval, and the pacing mode may temporarily change from AV synchronous dual-chamber mode to prevent the delivery of AV synchronous ventricular pacing pulses. Alternatively, control circuit 206 may activate an extended AV pacing interval longer than the spare atrial pacing interval when Apace is delivered at box 202 (as described below). Figure 9 (As described).

[0099] Control circuit 206 determines the time interval from the Apace delivered at block 302 to the Vsense received during the spare atrial pacing interval, and compares this Apace-Vsense time interval with a capture verification window that completes earlier than the spare atrial pacing interval. (Reference) Figure 9The control circuit 206 can initiate the standby atrial pacing interval 404, for example, by setting a pacing escape interval timer or counter, during the delivery of Apace 402. The control circuit 206 can apply the capture verification window 416 during the standby atrial pacing interval 404.

[0100] The capture verification window 416 may have a start time 414 and an end time 420, both of which are earlier than the expiration time 406 of the spare atrial pacing interval 404. Therefore, in some examples, the control circuit 206 may simultaneously (or sequentially in order of the start / end times of various time periods) start multiple timers or counters (for counting clock cycles) during the delivery of the Apace 402 to control the delivery (or suppression) of the spare atrial pacing pulse 430 and to determine whether the Apace 402 has captured the atrium. For example, the capture verification start time interval 412 (also referred to herein as the “indeterminate time interval” 412), the capture verification end time interval 418, and the spare atrial pacing interval 404 may each be started by the control circuit 206 during the delivery of the Apace 402.

[0101] In other examples, control circuitry 206 may start a timer or counter upon delivery of Apace 402 to measure the pacing AV time interval from Apace 402 until the receipt of a Vsense signal. Control circuitry 206 may initiate a backup atrial pacing interval 404, which may terminate upon receipt of an Asense or Vsense. If an Asense or Vsense is received before the backup atrial pacing interval 404 expires, the backup Apace 430 may be cancelled. If control circuitry 206 receives an Asense from sensing circuitry 204 before the backup atrial pacing interval 404 expires and before the receipt of a Vsense, the time when the backup atrial pacing interval 404 expires may be determined as the PPI from Apace 402 to the Asense. If Vsense is received before Asense and before the delivery of the backup Apace 430, the control circuit 206 can determine the time when the backup atrial pacing interval 404 expires as the pacing AV interval from Apace to Vsense. This pacing AV interval can be compared with various timing thresholds (e.g., the start time 414 and end time 420 of the capture verification window 416) to determine the atrial capture outcome.

[0102] As an illustrative example, the spare atrial pacing interval 404 may be at least 350 ms, at least 400 ms, or at least 450 ms. In one example, the spare atrial pacing interval 404 is 420 ms, such that if no Asense or Vsense signal is received before the expiration time 406 of the spare atrial pacing interval 404, the pulse generator 202 delivers a spare Apace (BAP) 430.

[0103] As an example and not intended to be limiting, the capture verification window 416 may have an activation time 414 between 80 ms and 180 ms after Apace 402. In some examples, control circuitry 206 may determine the capture verification window activation time 414 based on previously measured AV conduction time in the patient (e.g., measured Apace-Vsense interval or Asense-Vsense interval). The capture verification window activation time 414 may be, for example, the measured AV conduction time minus an offset, such as subtracting 20 ms to 50 ms. In one example, the activation time 414 is approximately 24 ms less than the measured AV conduction time.

[0104] As an example and not intended to be limiting, the capture verification window 416 may have an end time 420 between 180 ms and 330 ms. Control circuitry 206 may determine the end time 420 of the capture verification window based on previously measured AV conduction time. For example, in this example, the end time 420 may be equal to the previously measured AV conduction time plus an offset of 10 ms to 80 ms, or approximately 24 ms longer than the measured AV conduction time. Using an example where the start time 414 is 24 ms shorter than the measured AV conduction time and the end time 420 is 24 ms longer than the measured AV conduction time, the duration of the capture verification window 416 is 48 ms. In some examples, the capture verification window 416 may have an adjustable start time 414 based on the pacing rate of the delivery Apace 402, since AV conduction time can be heart rate dependent.

[0105] In some examples, control circuitry 206 may initiate a post-atrial ventricular blanking period 410 when pulse generator 202 delivers Apace 402. As an example, post-atrial ventricular blanking period 410 may be 20 ms to 100 ms or approximately 30 ms to 60 ms. The ventricular sensing channel 205 of sensing circuitry 204 may be disabled during post-atrial ventricular blanking period 410, or control circuitry 206 may ignore any Vsense signals received during post-atrial ventricular blanking period 410. This post-atrial ventricular blanking period 410 prevents oversensitization of atrial pacing artifacts in the sensed cardiac electrical signal from being erroneously sensed as an R wave.

[0106] Control circuit 206 may initiate a post-atrial pacing blanking period 408 in response to the delivered Apace 402. During the post-atrial pacing blanking period 408, atrial sensing channel 203 of sensing channel 204 may be disabled or blanked to avoid oversensing of post-atrial pacing signal artifacts. In some examples, control circuit 206 may apply an atrial refractory period that is equal to or greater than the post-atrial pacing blanking period. Control circuit 206 may ignore any Asense signals received by control circuit 206 during the atrial refractory period, at least for the purpose of scheduling atrial or ventricular pacing pulses. In some examples, an Asense signal received by control circuit 206 during the atrial refractory period may cause control circuit 206 to cancel standby Apace 430. However, as further described below, control circuit 206 may still wait for a Vsense signal to determine the atrial capture outcome.

[0107] In some examples, if no Vsense signal is received before the expiration time 406 of the spare atrial pacing interval 404, control circuitry 206 may initiate ventricular pacing interval 432 in response to the delivered Apace 402 to schedule ventricular pacing pulses (Vpace) 434 for delivery by pulse generator 202. As will be described below, in some cases, control circuitry 206 may receive an Asense signal during the spare atrial pacing interval 404, but may not receive a Vsense signal during the spare atrial pacing interval 404. Control circuitry 206 may schedule Vpace 434 at the expiration of ventricular pacing interval 432 to prevent ventricular arrest. In other examples, if no Vsense signal is received during the spare atrial pacing interval 404, control circuitry 206 may initiate AV pacing interval 436 at the expiration of the spare atrial pacing interval, regardless of whether a spare Apace 430 is delivered.

[0108] Refer again Figure 8 And continue to refer to Figure 9 Control circuit 206 can wait at block 308 for the spare atrial pacing interval 404 to expire, while monitoring for a Vsense signal (block 312) or an Asense signal (block 310) from sensing circuit 204 before the spare atrial pacing interval 404 expires. If a Vsense is received at block 312 before the spare atrial pacing interval 404 expires, control circuit 206 can cancel the scheduled spare Apace 430 at block 330. At block 332, control circuit 206 can determine the capture result of the Apace delivered at block 302 based on the timing of the Vsense signal. For example, if the capture verification window 416 (see...) Figure 9If a Vsense signal is received during the capture period, control circuit 206 can determine that Apace 402 has successfully captured the atrium (as confirmed by conduction depolarization of the ventricle), thereby generating a Vsense signal during the expected AV conduction time range represented by capture verification window 416. Control circuit 206 can respond to the capture determination at block 334 by continuing to deliver atrial pacing at the current atrial pacing pulse output. However, if control circuit 206 is performing an atrial capture threshold search, control circuit 206 can adjust the atrial pacing pulse output and deliver another Apace at block 302 with the adjusted atrial pacing pulse output until control circuit 206 identifies the lowest atrial pacing pulse output at which atrial capture is still detected as the atrial pacing capture threshold.

[0109] If, for example, the Vsense signal is received at box 312 earlier than the capture verification window 416 during the indeterminate time interval 412 that expires after the capture verification window 414, then the Vsense signal is received too early to be caused by the conduction of paced atrial depolarization associated with Apace 402. In this case, control circuit 206 can... Figure 8 At box 332, the capture result is determined to be uncertain. Control circuit 206 can respond to the uncertain capture result at box 334 by delivering another Apace with the same atrial pacing output at box 302 and repeating the process of flowchart 300. In some examples, when the uncertain capture result is the nth uncertain capture result for the same Apace output (where n can be a specified threshold, for example, 1, 2, 3, 4, or 5), control circuit 206 can respond to the uncertain capture result by aborting or delaying subsequent capture determinations (e.g., by aborting or delaying atrial capture management test or atrial capture threshold search).

[0110] If a Vsense signal is received at box 308 after the capture verification window 416 (e.g., the Apace-Vsense interval is longer than the end time 420 of the capture verification window), control circuit 206 can determine that the Apace 402 delivered at box 302 failed to capture the atrium. Control circuit 206 can determine capture loss at box 332. In some examples, a second indeterminate time window may be included after the capture verification window 416, as described below. Figure 10 Further description. In Figure 9 In the example shown, if the Vsense signal is received after the end time 420 of the capture verification window 416, the control circuit 206 will... Figure 8Capture loss is identified at frame 332. The time interval 422 from the end of the capture verification window 420 to the expiration of either the ventricular pacing interval 432 or the AV pacing interval 436 (regardless of which one the control circuit 206 uses to schedule Vpace 434) can be referred to as the "capture loss" window. During the capture loss window 422, the Vsense signal received by the control circuit 206 may be received too late after Apace 402 to allow conduction pacing-induced atrial depolarization associated with Apace 402 to occur.

[0111] However, if control circuit 206 receives a Vsense signal before the expiration time 406 of the standby atrial pacing interval 404, control circuit 206 may cancel the scheduled standby Apace 430 and will not schedule Vpace 434 by not initiating AV pacing interval 436. In other examples, if control circuit 206 initiates ventricular pacing interval 432 when Apace 402 is delivered, control circuit 206 may terminate ventricular pacing interval 432 and cancel the scheduled Vpace 434.

[0112] If the spare atrial pacing interval of 404 periods has expired ( Figure 8 If the control circuit 206 does not receive a Vsense signal (the "No" branch of box 312) or an Asense signal (the "No" branch of box 310), then the pulse generator 202 may deliver a backup Apace 430 (box 314) and schedule Vpace 434 at AV pacing interval 436 according to the backup Apace 402 (or allow ventricular pacing interval 432 to continue operating if it was previously activated during the delivery of Apace 430). It should be noted that the control circuit 206 may control the pulse generator 202 (see [link to relevant documentation]). Figure 6 The atrial holding capacitor 235 is charged to the atrial pacing pulse amplitude to deliver Apace 402, and during the standby atrial pacing interval 404, the pulse generator 202 recharges the atrial holding capacitor 235 to the standby atrial pacing pulse amplitude. The standby atrial pacing pulse amplitude (of the standby Apace 430) may be greater than the pacing pulse amplitude of Apace 402. The atrial holding capacitor 235 may be discharged to deliver the standby Apace 430 at the end of the standby atrial pacing interval 404 at time 406.

[0113] Pulse generator 202 can deliver a backup Apace 430 by maximizing the programmable atrial pacing pulse output or by adding an offset (e.g., adding 2 volts, 2.5 volts, or 3.0 volts) to the currently programmed atrial pacing pulse output up to the maximum available atrial pacing pulse output. In other examples, pulse generator 202 can deliver a backup Apace 430 by a user-programmable backup atrial pacing pulse output. In other examples, pulse generator 202 can deliver the backup Apace 430 by the lower of: a user-programmable backup atrial pacing pulse output or the currently programmed atrial pacing pulse output plus a specified offset. Figure 8 After the spare Apace 430 is delivered at frame 314, the atrial holding capacitor 235 can be recharged to deliver the next Apace (which may be at a lower pulse amplitude than the spare Apace 430).

[0114] The capture loss window 422 may be extended from the end time 420 of the capture verification window 416 until the Vsense signal is received or Vpace 434 is delivered (whichever occurs first). If the Vsense signal is received during the capture loss window 422 before the expiration of the spare atrial pacing interval 404, Figure 8 If the backup Apace 402 is delivered (e.g., during the AV pacing interval 436, or if running, before the expiration of the ventricular pacing interval 432) during the capture loss window 422, the control circuit 206 can detect the capture loss of Apace 430 and cancel the delivery of the scheduled Vpace 434.

[0115] Refer again Figure 8 And continue to refer to Figure 9If no Asense or Vsense is received from sensing circuitry 204 at box 308 before the expiration of the spare atrial pacing interval, pulse generator 202 delivers the scheduled spare atrial pacing pulse 430 at box 314. At box 318, control circuitry 206 can schedule Vpace 434. Control circuitry 206 can schedule Vpace 434 by initiating AV pacing interval 436 at box 314 upon delivery of spare Apace 430. In other examples, ventricular pacing interval 432, which is set to be longer than the desired AV pacing interval 404, can continue to operate. AV pacing interval 436, or the AV pacing interval added to spare atrial pacing interval 404 for scheduling Vpace 434, can be 50ms to 150ms or 60ms to 100ms, and as an example, it can be 80ms. If no Vsense signal is received at box 320 before the expiration of AV pacing interval 436 (or ventricular pacing interval 432), pulse generator 202 may deliver the scheduled Vpace 434 (box 324) at the expiration of AV pacing interval 436 (or ventricular pacing interval 432). In other examples, instead of canceling Vpace at box 322 in response to a Vsense signal received at box 320 during AV pacing interval 436, pulse generator 202 may be controlled to deliver the scheduled Vpace at AV pacing interval 436 (regardless of whether a Vsense signal is received during AV pacing interval 436). In this case, Vpace may be delivered during the absolute refractory period of ventricular tissue following the intrinsic R wave sensed by sensing circuitry 204, and this Vpace is unlikely to capture the ventricle.

[0116] If control circuit 206 does not receive an Asense or Vsense from sensing circuit 204 before the expiration of the spare atrial pacing interval 404, control circuit 206 determines a capture loss at block 326. If a spare Apace is delivered at block 314 due to the absence of an Asense or Vsense signal during the spare atrial pacing interval 404, and a Vpace is delivered at block 324 (regardless of whether a Vsense signal is received during the AV pacing interval 436), control circuit 206 may determine a capture loss at block 326. Control circuit 206 may execute a response to a capture loss determined at block 334.

[0117] The response could be to increase the atrial pacing pulse output. The response could also trigger an atrial pacing capture threshold search. If the process of flowchart 300 is performed as part of an atrial pacing capture threshold search, control circuitry 206 can increase the atrial pacing pulse output and deliver another Apace at block 302 to search for the lowest atrial pacing pulse output to verify capture. In some cases, control circuitry 206 can perform an atrial pacing capture threshold search by starting with a relatively high atrial pacing pulse output and decreasing the atrial pacing pulse output until a capture loss is detected. In this case, when a capture loss is detected at block 326 (or block 332 based on the timing of the received Vsense signal), control circuitry 206 can determine the atrial pacing capture threshold as the preceding higher atrial pacing pulse output that leads to atrial capture. At block 334, control circuitry 206 can set the atrial pacing pulse output to a safety margin (e.g., 0.25V to 2.0V) larger than the atrial pacing capture threshold. Control circuit 206 can control pulse generator 202 to deliver atrial pacing using an atrial pacing pulse output set at block 334 based on an atrial pacing capture threshold, according to a programmed pacing mode.

[0118] In some cases, control circuit 206 may receive an Asense signal during the standby atrial pacing interval 404 without ever receiving a Vsense signal. The Asense signal could be evidence of atrial capture loss or it could be atrial premature contractions. If no Vsense signal is received before the Asense signal is received at box 310 (the "No" branch of box 312), control circuit 206 may cancel the standby Apace at box 316 in response to the Asense signal and schedule the Vpace at box 318 (or allow the ventricular pacing interval 432 to continue if previously activated). In some examples, even if the standby Vpace is canceled, control circuit 206 may schedule the Vpace to occur during, for example, a period of time when the standby Vpace is not yet activated. Figure 9 The event shown occurs at AV pacing interval 436 after the expiration of the spare atrial pacing interval 404. In other examples, control circuitry 206 may schedule Vpace to occur at the expiration time 406 of the spare atrial pacing interval 404. In yet another example, Vpace may be scheduled at the AV pacing interval based on an Asense signal.

[0119] If control circuit 206 does not receive the Vsense signal at block 320 before the scheduled Vpace time, pulse generator 202 may deliver the scheduled Vpace 434 (at block 324). When the Vsense signal is not received, control circuit 206 may determine a capture loss at block 326 and perform a capture loss response at block 334 as described above.

[0120] However, if the control circuit 206 receives the Vsense signal at block 320 before the scheduled Vpace time, the control circuit 206 can cancel the scheduled Vpace at block 322. The control circuit 206 can determine the capture result at block 332 based on the timing of the Vsense signal and, at least in some examples, based on the relative timing of the Asense signal and the Vsense signal (received at blocks 310 and 320, respectively).

[0121] Control circuit 206 can determine the Asense-Vsense interval and the Apace-Vsense interval at block 332. If the Asense-Vsense interval is less than the minimum AV conduction time threshold, control circuit 206 can determine the capture outcome based on the Vsense interval. The Asense signal can be an oversensitized far-field R wave. In this case, when the Asense-Vsense interval is shorter than the minimum AV conduction time threshold, the Vsense signal can be associated with conduction depolarization after Apace 402. If a Vsense signal is received during the capture verification window 416 and the time between the Vsense signal and the Asense signal is less than the minimum AV conduction time, control circuit 206 can determine atrial pacing capture. If a Vsense signal is received before the capture verification window 416, the capture outcome can be indeterminate. If a Vsense signal is received after the capture verification window 416, control circuit 206 can determine capture loss. Based on any of the examples given above, control circuit 206 can execute a response to the determined atrial capture result at block 334.

[0122] However, if the Asense-Vsense interval is at least the minimum AV conduction time threshold, the Vsense signal can be associated with the Asense signal as conduction depolarization following the intrinsic atrial P wave, rather than with Apace 402. The capture outcome can be determined based on the timing of both the Asense and Vsense signals. When within the capture loss window 422 (or as...) Figure 10 If a Vsense signal is received before the capture loss window 452 (shown and described below) and the Vsense signal reaches at least the minimum AV conduction time threshold after the Asense signal, the control circuit 206 may determine the capture result to be indeterminate. For example, a Vsense signal received at any time before the capture loss window 422 (which has at least the minimum AV conduction time after the Asense signal) could be an atrial premature contraction conducting to the ventricle. Therefore, at box 328, the capture result may be indeterminate.

[0123] If the Asense-Vsense time interval is at least the minimum AV conduction time threshold, and the control circuit 206 captures the lost window 422 (or Figure 10 If a Vsense signal is received during the capture-loss window (452) shown, the control circuit 206 can determine the atrial capture result as a capture loss at block 328. In this case, a relatively later Asense signal, followed by a Vsense signal that satisfies the minimum AV conduction time, can be an indication that Apace 402 failed to capture and that an intrinsic beat has occurred. According to any of the examples described above, the control circuit 206 can execute a response to the determined capture result at block 334.

[0124] Figure 10 Figure 450 illustrates a time period, controllable by control circuitry 206, for scheduling a backup atrial pacing pulse, scheduling a ventricular pacing pulse, and determining the outcome of atrial pacing capture after pacemaker 14 delivers Apace, according to another example. Figure 10 The elements with the same number shown correspond to Figure 9 The elements shown and described above have the same numbering. However, in this example, control circuitry 206 may set the capture-loss window start time interval 440 upon delivery of Apace 402. The expiration time 456 of the capture-loss window start time interval 440 marks the start time of the capture-loss window 452. In other examples, control circuitry 206 starts one or more timers upon delivery of Apace 402 to time out the Apace-Vsense interval and the Apace-Asense interval and / or the Asense-Vsense interval (as the difference between the first two intervals). The capture-loss start time interval 440 may be a threshold time interval after which control circuitry 206 may determine the capture-loss result in response to a Vsense signal received after the threshold time interval (equal to the start time 456 of the capture-loss window 452). Instead of... Figure 9 In the example shown, the capture loss window 452 is initiated at the end time 420 of the capture verification window 416. In this example, the capture verification window 416 and the capture loss window 452 are separated by a second indeterminate window 454. The capture loss window 452 may extend from the capture loss window initiation time 456 until Vsense is received or until Vpace 434 is delivered (e.g., at the AV pacing interval 436 after the expiration time 406 of the spare atrial pacing interval 404) (whichever occurs first).

[0125] The time interval 454 between the end time 420 of the capture verification window 416 and the start time 456 of the capture loss window can be referred to as the second "ignore" window or the second "uncertain" window. When a Vsense signal is received during the second uncertain time interval 454, the control circuit 206 may ignore the Vsense signal for the purpose of determining the capture result. The timing of the Vsense signal in the second uncertain time interval 454 may be nonspecific, and the capture or capture loss of Apace 402 cannot be reliably determined. In some cases, heart rate-dependent AV block may result in varying AV conduction times. The Vsense signal in the uncertain window 454 may be due to conduction depolarization generated by Apace 402, but with a relatively long AV conduction time due to heart rate-dependent AV block. In other cases, the Vsense signal in the second uncertain time interval 454 may be unrelated to Apace 402. Therefore, to account for rate-dependent AV blockade, control circuit 206 can apply an indeterminate time interval 454 to the Vsense signal time to prevent erroneous capture-loss determination due to prolonged AV conduction time. In this case, erroneous capture-loss determination could lead to an unnecessary increase in atrial pacing pulse output.

[0126] Therefore, in Figure 10 In the example, control circuit 206 may apply two time windows (a first uncertain time interval 412 and a second uncertain time interval 454) as uncertain windows because a Vsense signal received during either of these time intervals 412 or 454 could result in an unknown or uncertain capture outcome. When the capture outcome is uncertain, control circuit 206 may control pulse generator 202 to repeat the delivery of Apace with the same pacing pulse output as a second attempt to determine capture or capture loss based on the timing of the Vsense signal in the capture verification window 416 or the capture loss window 452. A Vsense signal received by control circuit 206 at any time during the spare atrial pacing interval 404 may result in the cancellation of the scheduled spare Apace 430 and Vpace 434.

[0127] As described above, if an Asense signal and a Vsense signal are received during the standby atrial pacing interval 404 and the Asense-Vsense interval is less than the minimum AV conduction time, the control circuit 206 can determine the capture result based on the timing of the Vsense signal, according to the uncertain time intervals 412 and 454, the capture verification window 416, and the capture loss window 452. An Asense signal less than the minimum AV conduction time before the Vsense signal can be a far-field R wave, which is oversensed as a spurious P wave by the sensing circuit 204. If the Asense-Vsense interval is at least the minimum AV conduction time, the control circuit 206 can determine the capture result as uncertain if the Vsense signal is received before the capture loss window initiation time 452, and determine capture loss if the Vsense signal is received within the capture loss window 456.

[0128] Figure 11 This is a flowchart 600 of a method for performing an atrial capture threshold search, based on some examples. At block 602, control circuitry 206 can confirm a stable atrial rate by performing an atrial rate stability check. Control circuitry 206 can verify that the atrial rate is stable before delivering the first test Apace for the atrial pacing capture threshold search. For example, control circuitry 206 can determine whether a specified number of consecutive atrial cycles are within each other's threshold intervals and whether no atrial premature contractions or ventricular premature contractions are sensed. For example, when an Asense signal is received from the preceding Asense signal or from the delivered Apace at a short PPI interval (where there is no intermediate Vpace or Vsense signal in the short PPI), control circuitry 206 can determine that an atrial premature contraction is sensed. When a Vsense signal is received from the preceding Vsense signal or from the delivered Vpace at a short RRI interval (where there is no intermediate Apace or Asense signal in the short RRI), control circuitry 206 can detect a ventricular premature contraction. As an example, control circuit 206 can verify that the atrial rate is a stable rate over at least 6 to 12 atrial cycles or 8 atrial cycles. It should be understood that if the atrial rate stability check fails, for example, by detecting irregular atrial phases and / or premature beats, the atrial pacing capture threshold search can be suspended or delayed until the atrial rate stability check fails at box 602.

[0129] At block 604, control circuitry 206 can confirm that AV conduction is intact by performing an AV conduction stability check. For example, control circuitry 206 can suppress ventricular pacing (e.g., by prolonging the AV pacing interval or changing the pacing mode) and measure the AV conduction time from the Asense signal or the delivered Apace to the subsequent Vsense over a specified number of atrial cycles. In some examples, control circuitry 206 can control pulse generator 202 to deliver one or more “support” Apaces prior to the test Apace to facilitate stable pacing rates and confirmed stable AV conduction before the test Apace is delivered. One or more support Apaces can be delivered with high pacing output (e.g., higher pulse amplitude and / or pulse width than the subsequent test Apace) to facilitate capture and rate support, wherein AV conduction stability is confirmed prior to the test Apace delivery at block 605. If the AV conduction time determined after a specified number of consecutive atrial events (e.g., Apace) is within each other's threshold ranges and / or meets other stability criteria, control circuitry 206 may confirm AV conduction stability at block 604. It should be understood that if AV conduction stability is not confirmed at block 604, control circuitry 206 may abort or delay the atrial pacing capture threshold search until the AV conduction stability criteria are met at block 604 (and the atrial rate stability criteria are met at block 602).

[0130] When atrial rate stability and AV conduction stability criteria are met at blocks 602 and 604, respectively, control circuit 206 can control pulse generator 202 to deliver a first test Apace for pacing threshold search at block 605. At block 606, control circuit 206 schedules a backup Apace by initiating a backup atrial pacing interval as described in the examples given above. The backup atrial pacing interval is set to expire later than the capture verification window, which can be applied to the timing of the Vsense signal received by control circuit 206 during the backup atrial pacing interval to determine the atrial capture outcome according to any of the examples given above. When delivering the test Vpace, control circuit 206 can schedule the Vpace at block 606, for example, by initiating a ventricular pacing interval that is a longer AV pacing interval than the backup atrial pacing interval (e.g., 80 ms).

[0131] At block 608, control circuit 206 waits to receive a Vsense signal from sensing circuit 204. If the Vsense signal is received before the expiration of the standby atrial pacing interval, as determined at block 608, control circuit 206 may cancel the scheduled standby Apace at block 610. If the Vpace has been scheduled by initiating a ventricular pacing interval (which is an AV pacing interval longer than the standby atrial pacing interval), control circuit 206 may cancel the Vpace. If the Vpace has not been scheduled, control circuit 206 does not schedule the Vpace because the Vsense signal has been received, thus prohibiting Vpace delivery. Control circuit 206 proceeds to block 630 to determine the atrial capture outcome based at least on the timing of the Vsense signal, according to any of the examples given above. For example, control circuit 206 may initiate a timer when a test Apace is delivered at block 605. The timer value reached when the Vsense signal is received can be compared with the capture verification window start time, the capture verification window end time, and the capture loss window start time. If the Vsense signal occurs before the capture verification window start time or between the capture verification window end time and the capture loss start time, the capture result at block 630 may be indeterminate. Control circuitry 206 can repeat the test Apace with the same pulse output by advancing to block 632 (determining that another test Apace is needed) and returning to block 604 (to reconfirm AV conduction stability by delivering a specified number of support Apaces with a higher pulse output) without performing test Apace pulse amplitude or pulse width adjustment. In other examples, control circuitry 206 may return to block 602 to reconfirm a stable rhythm and verify AV conduction stability before the next test Apace (block 604). When the capture result is indeterminate, another test Apace can be delivered with the same pulse output at block 605.

[0132] If the Vsense signal received at block 608 occurs at or after the start time of the capture verification window and before or during the end time of the capture verification window, control circuitry 206 may determine atrial capture at block 630. Control circuitry 206 may proceed to block 632 to determine if another test pulse is needed. Control circuitry 206 may control pulse generator 202 to sequentially decrease the pacing pulse amplitude or pulse width every n test apaces delivered (where n can be 1, 2, 3, 5, or other specified numbers). In some cases, capture results are determined for at least two apaces delivered with the same pacing pulse output until at least a threshold number of capture or capture loss results match. When a capture loss is detected for a given apace pulse output, the preceding higher pulse output is identified as the atrial pacing capture threshold. In other examples, control circuitry 206 may control pulse generator 202 to sequentially increase the amplitude or width of the pacing pulse as a test Apace is delivered, such that when capture is first detected (for at least a specified number of test Apaces at the same pulse output), control circuitry 206 may identify the corresponding pacing pulse output as the atrial pacing capture threshold. Control circuitry 206 may determine at block 630 that another test Apace is needed until a minimum test Apace pulse output is determined to have captured the atrium for at least a specified threshold number of test Apaces (which may be one or more test Apaces).

[0133] If no Vsense is received before the expiration of the spare atrial pacing interval (the "No" branch of box 608), and no Asense is received during the spare atrial pacing interval (the "No" branch of box 612), pulse generator 202 may deliver the spare Apace at box 614. If an Asense is received during the spare atrial pacing interval (the "Yes" branch of box 612), the Apace may be canceled at box 615. Control circuitry 206 may schedule the Vpace at box 616 (if it has not yet been scheduled). In some examples, the Vpace is scheduled at the AV pacing interval after the scheduled (but canceled) spare Apace. After the expiration of the spare atrial pacing interval, the Vpace may be scheduled at the AV pacing interval (e.g., 80 ms). If no Vsense signal is received before the scheduling time of the Vpace (the "No" branch of box 618), pulse generator 202 may deliver the scheduled Vpace at box 620. When no Vsense signal is received, control circuit 206 can determine atrial capture loss at block 622. Control circuit 202 can then proceed to block 632 to determine whether another test phase is required based on the capture threshold test protocol.

[0134] If a Vsense signal is received at box 618 before the expiration of the AV pacing interval (which can be initiated at the expiration of the spare atrial pacing interval, even if the Apace was not delivered due to the Asense signal), the scheduled Vpace can be cancelled at box 624. In other examples, the scheduled Vpace can still be delivered because it will be delivered from the Vsense signal during the absolute refractory period without ventricular capture. The scheduling time of the Vpace can define the expiration of the capture loss window, as described above. Figure 9 and Figure 10 As described above. Therefore, when Vsense occurs before the scheduled Vpace during the capture loss window, control circuit 206 determines atrial capture loss at block 622. Figure 8 As described, if the Vsense signal is received at block 618 earlier than the capture loss window, control circuitry 206 can determine the capture outcome at block 630 based on the time of the Vsense signal and / or the Asense-Vsense interval. For example, if the Vsense signal time is before the capture loss window and less than the minimum AV conduction time, the Asense signal can be an oversensitized far-field R-wave, and the Vsense signal can be a valid R-wave conducted in response to the test Apace. Therefore, at block 630, control circuitry 206 can use the time of the Vsense signal relative to the Apace (Apace-Vsense interval) and the time relative to any Asense signal sensed before the Vsense signal (Asense-Vsense signal) to determine the capture outcome.

[0135] After determining the capture result as a capture, a loss of capture, or an indeterminate outcome at box 630, control circuitry 206 determines at box 632 whether another test Apace is required. If not, control circuitry 206 may identify the lowest test Apace output that results in atrial capture as the atrial pacing capture threshold at box 634. At box 634, control circuitry 206 may set the atrial pacing pulse output to a safety margin greater than the capture threshold (e.g., 0.25 volts to 2.0 volts greater than the capture threshold). After completing the atrial pacing capture threshold search, control circuitry 206 may control pulse generator 202 to deliver atrial (and ventricular) pacing according to a programmed (or temporary) pacing mode for delivering cardiac pacing therapy using the atrial pacing pulse output selected at box 634.

[0136] Figure 12 It is a timing diagram 700, which can be controlled by control circuit 206 according to another example, for scheduling standby atrial pacing pulses, scheduling ventricular pacing pulses and determining the time interval of atrial pacing capture results after pacemaker 14 delivers Apace. Figure 12The elements with the same number shown correspond to Figure 10 The elements shown and described above are the same numbered elements. However, in this example, control circuitry 206 may activate ventricular safety pacing (VSP) window 460 upon delivery of Apace 402. VSP window 460 may be longer than the post-atrial ventricular blanking period 410. VSP window 460 may be shorter than or equal to the indeterminate time interval 412.

[0137] If control circuit 206 receives a Vsense signal from sensing circuit 204 during VSP window 460, control circuit 206 may deliver VSP pulse 464 at the end of VSP window 460. In response to pulse generator 202 delivering VSP pulse 464, control circuit 206 may cancel both standby Apace 430 and Vpace 434 (scheduled at AV pacing interval 436 after the scheduling time of standby Apace 430). Since the Vsense received during VSP window 460 falls within the indeterminate time interval 412, control circuit 206 may determine the atrial pacing capture result as indeterminate. If control circuit 206 does not receive Vsense during VSP window 460, control circuit 206 may cancel or suppress pulse generator 202's delivery of VSP pulse 464. Control circuit 206 can monitor any Asense and Vsense signals received during the standby atrial pacing interval 404 to determine the atrial capture outcome and control the delivery of standby Apace 430 and Vpace 434 according to any of the methods described above.

[0138] Figure 13 This is a flowchart 750 of a method, which can be performed by pacemaker 14 according to another example, for determining atrial capture outcome and controlling atrial and ventricular pacing pulses. At block 752, pulse generator 202 delivers an atrial pacing pulse (Apace). As described above, the Apace may be a test Apace during capture management testing or capture threshold search. In other examples, the Apace may be delivered based on the currently valid pacing mode and pacing pulse parameters, for which control circuitry 206 can verify capture. In response to the delivered Apace, control circuitry 206 may schedule a backup Apace at block 754 by initiating a backup atrial pacing interval.

[0139] At box 756, control circuit 206 can activate the VSP window, for example, Figure 12The VSP window 460 is shown. At box 758, control circuitry 206 can wait for the VSP window to expire while monitoring the Vsense signal (and, if the atrial pacing blanking period has expired, monitoring the Asense signal). If a Vsense signal is received during the VSP window, control circuitry 206 can control pulse generator 202 to deliver a VSP pulse at box 760 when the VSP window expires. In this way, pacemaker 14 can reduce the likelihood of ventricular arrest if the Vsense signal is an oversensitized (false) signal. If the Vsense signal is a false signal, the VSP pulse will capture the ventricle. However, if the Vsense signal received during the VSP window is a true R wave, the VSP pulse will be delivered during the physiological absolute refractory period of the ventricle, and this VSP pulse will not capture the ventricle. When a VSP pulse is delivered at block 760, control circuit 206 can cancel the standby Apace at block 762 and suppress or cancel the Vpace that can be scheduled at the AV pacing interval after the standby Apace.

[0140] At box 764, when a Vsense signal is received and a VSP pulse is delivered during the VSP window, control circuit 206 can determine the atrial capture result as uncertain. When the VSP window 460 is equal to or shorter than the uncertain time interval 412, the result is determined to be uncertain during the uncertain time interval 412 (see [link to relevant documentation]). Figure 12 During this period, the Vsense signal received during the VSP window is received. According to any of the examples described above, control circuitry 206 can perform a deterministic response to an indeterminate capture at block 764.

[0141] Referring again to block 758, if the VSP window expires without a Vsense signal being received from sensing circuit 204, control circuit 206 may control pulse generator 202 to suppress the VSP pulse at block 759. Control circuit 206 may proceed to block 766 to determine whether a Vsense signal is received during the spare atrial pacing interval (after the VSP window). If no Vsense signal is received during the spare atrial pacing interval, control circuit 206 may control pulse generator 202 to deliver a spare Apace at block 768 upon the expiration of the spare atrial pacing interval, and Vpace may be delivered at the AV pacing interval after the spare Apace, as described above. At block 770, control circuit 206 determines the atrial capture result as capture loss.

[0142] If the control circuit 206 receives a Vsense signal at block 766 before the expiration of the standby atrial pacing interval, the control circuit 206 may cancel the scheduled standby Apace at block 762. At block 764, the control circuit 206 may determine the atrial capture outcome based at least on the time of the Vsense signal (e.g., the time interval from the delivered Apace to the Vsense signal). As described above, the control circuit 206 may determine the capture outcome by applying at least one capture verification window that expires before the standby atrial pacing interval to the time of the Vsense signal for verifying the capture of the Apace. As described above, if the control circuit 206 receives an Asense signal before the Vsense signal during the standby atrial pacing interval, the control circuit 206 may determine the capture outcome based at least on the time of the Vsense signal relative to the Apace and the time of the Vsense signal relative to the Asense signal. The control circuit 206 may determine the atrial capture outcome according to either the timing diagram and the flowchart described above. The control circuit 206 can execute a response to the capture result according to any of the examples described above.

[0143] The following embodiments are also disclosed in this article: Example 1. A medical device system comprising: a sensing circuit configured to sense a ventricular event signal accompanied by ventricular depolarization; a pulse generation circuit configured to generate a pacing pulse; and a control circuit configured to control the pulse generation circuit to deliver an atrial pacing pulse. In response to generating the atrial pacing pulse, the control circuit may be configured to activate a standby atrial pacing interval to schedule a standby atrial pacing pulse, the standby atrial pacing interval having an expiration time. The control circuit may also be configured to determine whether the sensing circuit senses a ventricular event signal during the standby atrial pacing interval. In response to the sensing circuit sensing a ventricular event signal during the standby atrial pacing interval, the control circuit may be configured to determine, at least based on the time of the sensed ventricular event signal, the atrial capture result of the delivered atrial pacing pulse, and to cancel the scheduled standby atrial pacing pulse. The control circuit can also be configured to, in response to the sensing circuit not sensing a ventricular event signal during the standby atrial pacing interval: determine the atrial capture result of the delivered atrial pacing pulse as a capture loss; and control the pulse generation circuit to deliver the scheduled standby atrial pacing pulse at the end of the interval.

[0144] Example 2. The medical device system according to Example 1, wherein the control circuit is further configured to determine the atrial capture result as uncertain, captured, or captured but lost.

[0145] Example 3. A medical device system according to any one of Examples 1 to 2, wherein the control circuit is further configured to: apply a capture verification window to the time of the sensed ventricular event signal, the capture verification window having an end time earlier than the expiration time of the spare atrial pacing interval after the delivered atrial pacing pulse; and determine the atrial capture result as atrial capture based on the time of the sensed ventricular event signal during the capture verification window.

[0146] Example 4. The medical device system according to Example 3, wherein the control circuit is further configured to: apply the capture verification window having an activation time after the delivered atrial pacing pulse; and when the time of the sensed ventricular event signal is earlier than the activation time of the capture verification window, determine the atrial capture result as uncertain based on the time of the sensed ventricular event signal.

[0147] Example 5. A medical device system according to any one of Examples 2 to 3, wherein the control circuit is further configured to: apply a capture-loss threshold time to the time of the sensed ventricular event signal, the capture-loss threshold time being at least as long as the end time of the capture verification window after the delivered atrial pacing pulse; and determine the capture result as a capture-loss in response to the time of the sensed ventricular event signal satisfying the capture-loss threshold time.

[0148] Example 6. The medical device system according to Example 5, wherein the control circuit is further configured to determine the atrial capture result of the delivered atrial pacing pulse based on the time of the sensed ventricular event signal by: applying the capture loss threshold time as a threshold time greater than the end time of the capture verification window; and determining the capture result as uncertain in response to the time of the sensed ventricular event signal being between the end time of the capture verification window and the capture loss threshold time.

[0149] Example 7. A medical device system according to any one of Examples 1 to 6, wherein the control circuit is further configured to: schedule ventricular pacing pulses at the atrioventricular pacing interval starting from the expiration time of the spare atrial pacing interval; and cancel the scheduled ventricular pacing pulses in response to the sensing circuit sensing the ventricular event signal during the spare atrial pacing interval.

[0150] Example 8. A medical device system according to any one of Examples 1 to 7, wherein the sensing circuit is further configured to: sense an atrial event signal accompanied by atrial depolarization. The control circuit may also be configured to: determine that the sensing circuit senses the atrial event signal during the standby atrial pacing interval; determine that the sensing circuit senses a ventricular event signal after the atrial event signal and during the standby atrial pacing interval; and determine the atrioventricular time interval from the sensed atrial event signal to the sensed ventricular event signal. The control circuit may also be configured to: determine the atrial capture result of the delivered atrial pacing pulse based on the time of the sensed ventricular event signal from the delivered atrial pacing pulse and the atrioventricular time interval.

[0151] Example 9. The medical device system according to Example 8, wherein the control circuit is further configured to: compare the atrioventricular time interval with a minimum atrioventricular conduction time threshold; and when the atrioventricular time interval does not meet the minimum conduction time interval, determine the atrial capture result based on the time of the sensed ventricular event signal from the atrial pacing pulse. When the atrioventricular time interval meets the minimum conduction time interval, the control circuit may be configured to determine the atrial capture result as either uncertain or lost capture.

[0152] Example 10. The medical device system according to Example 9, wherein the control circuit is further configured to: determine the atrial capture result as a capture loss when the time of the sensed ventricular event signal from the delivered atrial pacing pulse meets the capture loss threshold time.

[0153] Example 11. A medical device system according to any one of Examples 1 to 10, wherein the sensing circuit is further configured to: sense an atrial event signal accompanied by atrial depolarization, and the control circuit is further configured to: schedule a pending ventricular pacing pulse at an atrioventricular pacing interval starting from the expiration time of the spare atrial pacing interval. The control circuit may also be configured to: determine that the sensing circuit senses an atrial event signal before the expiration time of the spare atrial pacing interval; cancel the scheduled spare atrial pacing pulse in response to the atrial event signal sensed by the sensing circuit; determine that the sensing circuit does not sense a ventricular event signal before the expiration time of the atrioventricular pacing interval; and determine the atrial capture result as a capture loss in response to the failure to sense the ventricular event signal before the expiration time of the atrioventricular pacing interval. The pulse generation circuit may also be configured to: deliver the pending ventricular pacing pulse in response to the failure to sense a ventricular event signal before the expiration time of the spare atrial pacing interval.

[0154] Example 12. A medical device system according to any one of Examples 1 to 11, wherein the control circuit is further configured to: activate a ventricular safety pacing window in response to the pulse generation circuit delivering the atrial pacing pulse, the ventricular safety pacing window extending during the spare atrial pacing interval and expiring earlier than the spare atrial pacing interval; and determine whether the sensing circuit senses a ventricular event signal during the ventricular safety pacing window. The control circuit may also be configured to: control the pulse generator to deliver a ventricular safety pacing pulse at the expiration of the ventricular safety pacing window in response to the sensing circuit sensing a ventricular event signal during the ventricular safety pacing window.

[0155] Example 13. A medical device system according to any one of Examples 1 to 12, wherein the pulse generation circuit includes a charging circuit and an atrial holding capacitor. The pulse generation circuit may be configured to: charge the atrial holding capacitor for delivering the atrial pacing pulse; and recharge the atrial holding capacitor during the standby atrial pacing interval for generating a scheduled standby atrial pacing pulse.

[0156] Example 14. The medical device system according to any one of Examples 1 to 13, the medical device system further includes a housing that encloses the sensing circuit, the pulse generating circuit and the control circuit.

[0157] Example 15. The medical device system according to Example 14, the medical device system further includes an atrial pacing electrode pair and a ventricular pacing electrode pair located on the housing, the ventricular pacing electrode pair including a tissue puncture electrode.

[0158] Example 16. A method comprising: sensing a ventricular event signal accompanied by ventricular depolarization; delivering an atrial pacing pulse; and initiating a standby atrial pacing interval to schedule a standby atrial pacing pulse in response to the delivery of the atrial pacing pulse, the standby atrial pacing interval having an expiration time. The method further comprises: determining whether a ventricular event signal is sensed during the standby atrial pacing interval; and, in response to sensing a ventricular event signal during the standby atrial pacing interval, determining an atrial capture outcome of the delivered atrial pacing pulse based at least on the time of the sensed ventricular event signal, and canceling the scheduled standby atrial pacing pulse. The method may further comprise: in response to not sensing a ventricular event signal during the standby atrial pacing interval, determining the atrial capture outcome of the delivered atrial pacing pulse as a capture loss, and delivering the scheduled standby atrial pacing pulse at the expiration time.

[0159] Example 17. The method according to Example 16, further comprising: determining the atrial capture result as uncertain, captured, or captured but lost.

[0160] Example 18. The method according to any one of Examples 16 to 17, further comprising: applying a capture verification window to the time of the sensed ventricular event signal, the capture verification window having an end time earlier than the expiration time of the standby atrial pacing interval after the delivered atrial pacing pulse. The method may further comprise: determining an atrial capture result as atrial capture based on the time of the sensed ventricular event signal during the capture verification window.

[0161] Example 19. The method according to Example 18, further comprising: applying the capture verification window having an activation time after the delivered atrial pacing pulse; and determining the atrial capture result as uncertain based on the time of the sensed ventricular event signal when the time of the sensed ventricular event signal is earlier than the activation time of the capture verification window.

[0162] Example 20. The method according to any one of Examples 17 to 19, further comprising: applying a capture-loss threshold time to the time of the sensed ventricular event signal, the capture-loss threshold time being at least as long as the end time of the capture verification window following the delivered atrial pacing pulse. The method further comprises: determining the capture result as a capture-loss in response to the time of the sensed ventricular event signal satisfying the capture-loss threshold time.

[0163] Example 21. The method according to Example 20, wherein determining the atrial capture result of the delivered atrial pacing pulse based on the time of the sensed ventricular event signal includes: applying the capture loss threshold time as a threshold time greater than the end time of the capture verification window; and determining the capture result as uncertain in response to the time of the sensed ventricular event signal being between the end time of the capture verification window and the capture loss threshold time.

[0164] Example 22. The method according to any one of Examples 16 to 21, further comprising: scheduling a ventricular pacing pulse at the atrioventricular pacing interval starting from the expiration time of the spare atrial pacing interval; and canceling the scheduled ventricular pacing pulse in response to the sensing circuit sensing the ventricular event signal during the spare atrial pacing interval.

[0165] Example 23. The method according to any one of Examples 16 to 22, further comprising: sensing an atrial event signal accompanied by atrial depolarization; determining that the atrial event signal was sensed during the standby atrial pacing interval; determining that a ventricular event signal was sensed after the atrial event signal and during the standby atrial pacing interval; determining the atrioventricular time interval from the sensed atrial event signal to the sensed ventricular event signal; and determining the atrial capture result of the delivered atrial pacing pulse based on the time of the sensed ventricular event signal from the delivered atrial pacing pulse and the atrioventricular time interval.

[0166] Example 24. The method according to Example 23, further comprising: comparing the atrioventricular time interval with a minimum atrioventricular conduction time threshold. When the atrioventricular time interval does not meet the minimum conduction time interval, the method may further comprise determining the atrial capture result based on the time of the sensed ventricular event signal from the atrial pacing pulse. When the atrioventricular time interval meets the minimum conduction time interval, the method may further comprise determining the atrial capture result as either indeterminate or lost capture.

[0167] Example 25. According to the method of Example 24, the method further includes: when the time of the sensed ventricular event signal from the delivered atrial pacing pulse meets the capture loss threshold time, determining the atrial capture result as a capture loss.

[0168] Example 26. The method according to any one of Examples 16 to 25, further comprising: sensing an atrial event signal accompanied by atrial depolarization; scheduling a pending ventricular pacing pulse at an atrioventricular pacing interval starting from the expiration time of the spare atrial pacing interval; determining that the sensing circuit sensed the atrial event signal before the expiration time of the spare atrial pacing interval; and canceling the scheduled spare atrial pacing pulse in response to the atrial event signal sensed by the sensing circuit. The method may further comprise: determining that the sensing circuit did not sense a ventricular event signal before the expiration time of the atrioventricular pacing interval; and determining the atrial capture result as a capture loss in response to the lack of sensing of the ventricular event signal before the expiration time of the atrioventricular pacing interval. The method may further comprise delivering the pending ventricular pacing pulse in response to the lack of sensing of the ventricular event signal before the expiration time of the spare atrial pacing interval.

[0169] Example 27. The method according to any one of Examples 16 to 26, further comprising: activating a ventricular safety pacing window in response to a delivered atrial pacing pulse, the ventricular safety pacing window extending during the spare atrial pacing interval and expiring earlier than the spare atrial pacing interval. The method may further comprise: determining whether a ventricular event signal is sensed during the ventricular safety pacing window; and delivering a ventricular safety pacing pulse at the expiration of the ventricular safety pacing interval in response to a ventricular event signal sensed during the ventricular safety pacing window.

[0170] Example 28. The method according to any one of Examples 16 to 27, further comprising: charging an atrial holding capacitor for delivering the atrial pacing pulse; and recharging the atrial holding capacitor during the standby atrial pacing interval for generating a scheduled standby atrial pacing pulse.

[0171] Example 29. A non-transitory computer-readable medium storing a set of instructions, which, when executed by a medical device system, causes the medical device system to: sense a ventricular event signal accompanied by ventricular depolarization; deliver an atrial pacing pulse; initiate a standby atrial pacing interval to schedule a standby atrial pacing pulse in response to the delivery of the atrial pacing pulse, the standby atrial pacing interval having an expiration time; and determine whether a ventricular event signal is sensed during the standby atrial pacing interval. The instructions may also cause the medical device system, in response to sensing a ventricular event signal during the standby atrial pacing interval, to determine an atrial capture result of the delivered atrial pacing pulse, at least based on the time of the sensed ventricular event signal, and to cancel the scheduled standby atrial pacing pulse. The instructions may also cause the medical device, in response to not sensing a ventricular event signal during the standby atrial pacing interval, to determine the atrial capture result of the delivered atrial pacing pulse as a capture loss, and to deliver the scheduled standby atrial pacing pulse at the expiration time.

[0172] It should be understood that, depending on the example, certain actions or events in any of the methods described herein may be performed in a different order, and may be added, combined, or omitted entirely (e.g., not all described actions or events are necessary for practicing the method). Furthermore, in some examples, actions or events may be performed simultaneously, for example, through multithreading, interrupt handling, or multiple processors, rather than sequentially. In addition, for clarity, although some aspects of this disclosure are described as being performed by a single circuit or unit, it should be understood that the techniques of this disclosure may be performed by a combination of units or circuits associated with, for example, a medical device.

[0173] In one or more examples, the described functionality may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functionality may be stored as one or more instructions or code on a computer-readable medium and executed by a hardware-based processing unit. A computer-readable medium may include a computer-readable storage medium, which corresponds to a tangible medium, such as a data storage medium (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 is accessible by a computer).

[0174] Instructions can 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 (FPLAs), or other equivalent integrated or discrete logic circuits. Therefore, as used herein, the term "processor" can refer to any of the foregoing structures or any other structure suitable for implementing the techniques described herein. Furthermore, these techniques can be fully implemented in one or more circuit or logic elements.

[0175] Therefore, a medical device system has been presented in the foregoing description with reference to specific examples. It should be understood that the various aspects disclosed herein can be combined in combinations different from the specific combinations presented in the accompanying drawings. It should be understood that various modifications may be made to the referenced examples without departing from the scope of this disclosure and the following claims.

Claims

1. A medical device system, the medical device system comprising: A sensing circuit configured to sense ventricular event signals accompanied by ventricular depolarization; A pulse generation circuit configured to generate pacing pulses; and Control circuit, the control circuit being configured to: The pulse generation circuit is controlled to deliver atrial pacing pulses; In response to the generation of the atrial pacing pulse, a standby atrial pacing interval is initiated to schedule the standby atrial pacing pulse, the standby atrial pacing interval having an expiration time; Determine whether the sensing circuit senses a ventricular event signal during the standby atrial pacing interval; In response to the sensing circuit sensing a ventricular event signal during the spare atrial pacing interval: The atrial capture outcome of the delivered atrial pacing pulse is determined at least based on the timing of the sensed ventricular event signal; and Cancel the scheduled backup atrial pacing pulse; as well as In response to the sensing circuit not sensing a ventricular event signal during the spare atrial pacing interval: The atrial capture result of the delivered atrial pacing pulse is determined to be a capture loss; as well as The pulse generation circuit is controlled to deliver the scheduled standby atrial pacing pulse at the expiration time.

2. The medical device system according to claim 1, wherein the control circuit is further configured to: Determine that the sensing circuit senses the ventricular event signal during the spare atrial pacing interval; and In response to the sensing circuit sensing the ventricular event signal during the standby atrial pacing interval, the atrial capture result is determined to be one of uncertain, captured, or captured and lost.

3. The medical device system according to any one of claims 1 to 2, wherein the control circuit is further configured to: The sensing circuit is determined to detect the ventricular event signal during the standby atrial pacing interval. In response to the sensing circuit sensing the ventricular event signal during the spare atrial pacing interval, a capture verification window is applied to the time of the sensed ventricular event signal, the capture verification window having an end time earlier than the expiration time of the spare atrial pacing interval after the delivered atrial pacing pulse; and When the time of the sensed ventricular event signal is during the capture verification window, the atrial capture result is determined to be atrial capture.

4. The medical device system according to claim 3, wherein the control circuit is further configured to: The application has the capture verification window having a start time following the delivered atrial pacing pulse; and When the time of the sensed ventricular event signal is earlier than the start time of the capture verification window, the atrial capture result is determined to be uncertain.

5. The medical device system according to any one of claims 3 to 4, wherein the control circuit is further configured to: The capture loss threshold time is applied to the time of the sensed ventricular event signal, the capture loss threshold time being at least as long as the end time of the capture verification window following the delivered atrial pacing pulse; and When the time of the sensed ventricular event signal meets the capture-loss threshold time, the capture result is determined to be a capture-loss.

6. The medical device system according to claim 5, wherein the control circuit is further configured to: The capture loss threshold time is applied as a threshold time greater than the end time of the capture verification window; and When the time of the sensed ventricular event signal is between the end time of the capture verification window and the capture loss threshold time, the capture result is determined to be uncertain.

7. The medical device system according to any one of claims 1 to 6, wherein the control circuit is further configured to: Starting from the expiration time of the spare atrial pacing interval, ventricular pacing pulses are scheduled at the atrioventricular pacing interval; and The scheduled ventricular pacing pulse is canceled in response to the sensing circuit sensing the ventricular event signal during the standby atrial pacing interval.

8. The medical device system according to any one of claims 1 to 7, wherein: The sensing circuit is also configured to sense atrial event signals accompanied by atrial depolarization; and The control circuit is also configured to: The sensing circuit is determined to detect an atrial event signal during the standby atrial pacing interval; The sensing circuit is determined to sense the ventricular event signal after the atrial event signal and during the standby atrial pacing interval; The atrioventricular time interval is defined as the time from the sensed atrial event signal to the sensed ventricular event signal. as well as The atrial capture result of the delivered atrial pacing pulse is determined based on the time of the sensed ventricular event signal from the delivered atrial pacing pulse and the atrioventricular time interval.

9. The medical device system of claim 8, wherein the control circuit is further configured to: Compare the atrioventricular time interval with the minimum atrioventricular conduction time threshold; When the atrioventricular time interval does not meet the minimum conduction time interval, the atrial capture result is determined based on the time of the sensed ventricular event signal from the atrial pacing pulse; and When the atrioventricular time interval meets the minimum conduction time interval, the atrial capture result is determined to be either uncertain or captured and lost.

10. The medical device system according to any one of claims 1 to 9, wherein: The sensing circuit is also configured to sense atrial event signals accompanied by atrial depolarization; The control circuit is further configured to: Starting from the expiration time of the spare atrial pacing interval, the undetermined ventricular pacing pulse is scheduled at the atrioventricular pacing interval; The sensing circuit detects an atrial event signal before the expiration time of the standby atrial pacing interval; The scheduled standby atrial pacing pulse is cancelled in response to the atrial event signal sensed by the sensing circuit. It is determined that the sensing circuit did not detect a ventricular event signal before the expiration of the atrioventricular pacing interval; as well as The atrial capture result is determined as a capture loss if no ventricular event signal is sensed before the expiration of the atrioventricular pacing interval; and The pulse generation circuit is also configured to deliver the pending ventricular pacing pulse in response to the absence of a ventricular event signal before the expiration of the standby atrial pacing interval.

11. The medical device system according to any one of claims 1 to 10, wherein the control circuit is further configured to: In response to the delivery of the atrial pacing pulse by the pulse generation circuit, a ventricular safety pacing window is activated, which extends during the spare atrial pacing interval and reaches its end earlier than the spare atrial pacing interval; Determine whether the sensing circuit senses a ventricular event signal during the ventricular safe pacing window; as well as In response to the sensing circuit sensing a ventricular event signal during the ventricular safe pacing window, the pulse generator is controlled to deliver a ventricular safe pacing pulse when the ventricular safe pacing window expires.

12. The medical device system according to any one of claims 1 to 11, wherein the pulse generating circuit includes a charging circuit and an atrial holding capacitor, and the pulse generating circuit is configured to: The atrial holding capacitor is charged to deliver the atrial pacing pulse; and The atrial holding capacitor is recharged during the standby atrial pacing interval to generate the scheduled standby atrial pacing pulse.

13. The medical device system according to any one of claims 1 to 12, the medical device system further comprising a housing enclosing the sensing circuit, the pulse generating circuit and the control circuit.

14. The medical device system of claim 13, further comprising an atrial pacing electrode pair and a ventricular pacing electrode pair located on the housing, the ventricular pacing electrode pair comprising a tissue puncture electrode.

15. The medical device system according to any one of claims 1 to 14, wherein the control circuit is further configured to: The atrial capture threshold should be determined at least based on the determined atrial capture outcome; and The pulse generation circuit is controlled to deliver atrial pacing pulses according to the atrial capture threshold.

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