Systems and methods for identifying and responding to P-wave oversensing in a cardiac system

Abstract

A cardiac medical system, such as an implantable cardioverter-defibrillator (ICD) system, receives cardiac electrical signals and senses a cardiac event when the signals cross an R-wave sensing threshold. The system determines at least one sensed event parameter from the cardiac electrical signals for consecutive cardiac events sensed by the sensing circuitry and compares the sensed event parameter to a P-wave oversensing criterion. The system detects P-wave oversensing in response to the sensed event parameter meeting the P-wave oversensing criterion; and adjusts at least one of an R-wave sensing control parameter or a therapy delivery control parameter in response to detecting the P-wave oversensing.

Description

[0001] This application is a divisional application of an invention patent application with an international application date of 2017-06-01, international application number PCT / US2017 / 035417, and application number 201780035927.0 entering the Chinese national phase, entitled “System and method for identifying and responding to P-wave oversensing in a cardiac system”. Technical Field

[0002] The present disclosure generally relates to a cardiac system and method for identifying and responding to P-wave oversensing (PWOS). Background Art

[0003] Medical devices such as pacemakers and ICDs provide therapeutic electrical stimulation to a patient's heart via electrodes carried by one or more medical electrical leads and / or electrodes on the housing of the medical device. The electrical stimulation may include signals such as pacing pulses, or cardioversion or defibrillation shocks. In some cases, the medical device can sense cardiac electrical signals associated with intrinsic depolarization of the heart or depolarization induced by pacing, and control the delivery of stimulation signals to the heart based on the sensed cardiac electrical signals. Upon detecting an abnormal rhythm such as bradycardia, tachycardia, or fibrillation, one or more appropriate electrical stimulation signals can be delivered to restore or maintain a more normal rhythm of the heart. For example, an ICD can deliver a pacing pulse to a patient's heart upon detecting bradycardia or tachycardia, or deliver a cardioversion or defibrillation shock to the heart upon detecting tachycardia or fibrillation. An ICD can sense cardiac electrical signals in the heart chambers and use electrodes carried by transvenous medical electrical leads to deliver electrical stimulation therapy to the heart chambers. Cardiac signals sensed within the heart typically have high signal strength and quality for reliable sensing of cardiac electrical events, such as R-waves. In other examples, non-transvenous leads may be coupled to an ICD, in which case cardiac signal sensing presents new challenges for accurately sensing cardiac electrical events. Summary of the Invention

[0004] Generally, the present disclosure relates to techniques for identifying P-wave oversensing (PWOS) by an implantable cardioverter-defibrillator (ICD) and responding to the PWOS, for example, by adjusting R-wave sensing control parameters and / or adjusting therapy control parameters. An ICD operating according to the techniques disclosed herein detects PWOS based on analysis of cardiac electrical signals received by extracardiovascular sensing electrode vectors. In some examples, clusters of sensed cardiac events are detected as evidence of PWOS.

[0005] In one example, the present disclosure provides an extracardiovascular ICD system comprising: a sensing circuit, a therapy delivery circuit, and a control circuit. The sensing circuit is configured to receive an electrocardiogram (ECG) signal from an electrode coupled to the ICD and sense a cardiac event in response to the ECG signal crossing an R-wave sensing threshold. The therapy delivery circuit is configured to deliver electrical stimulation therapy to the patient's heart via electrodes coupled to the ICD. The control circuit is configured to: determine at least one sensing event parameter based on the ECG signal for each of a plurality of consecutive cardiac events sensed by the sensing circuit; compare the sensing event parameter with a P-wave oversensing criterion; detect P-wave oversensing in response to the sensing event parameter satisfying the P-wave oversensing criterion; and adjust the R-wave sensing control parameter and / or therapy delivery control parameter in response to detecting P-wave oversensing.

[0006] In another example, the present disclosure provides a method performed by a cardiovascular implantable cardioverter-defibrillator (ICD) system. The method includes: receiving a cardiac electrical signal via an electrode coupled to the ICD by a sensing circuit; sensing a cardiac event in response to the cardiac electrical signal crossing an R-wave sensing threshold; determining, by a control circuit of the ICD, at least one sensed event parameter based on the cardiac electrical signal for each of consecutive cardiac events sensed by the sensing circuit; comparing the sensed event parameter with a P-wave oversensing criterion; detecting P-wave oversensing in response to the sensed event parameter satisfying the P-wave oversensing criterion; and adjusting at least one of an R-wave sensing control parameter or a therapy delivery control parameter in response to detecting the P-wave oversensing.

[0007] In another example, the present disclosure provides a non-transitory computer-readable storage medium comprising a set of instructions that, when executed by a control circuit of an ICD system, causes the system to: receive a cardiac electrical signal via an electrode coupled to the ICD through a sensing circuit; sense a cardiac event in response to the cardiac electrical signal crossing an R-wave sensing threshold; determine at least one sensing event parameter based on the cardiac electrical signal through the control circuit of the ICD for each of a plurality of consecutive cardiac events sensed by the sensing circuit; compare the sensing event parameter with a P-wave oversensing criterion; detect P-wave oversensing in response to the sensing event parameter satisfying the P-wave oversensing criterion; and adjust R-wave sensing control parameters and / or therapy delivery control parameters in response to detecting the P-wave oversensing.

[0008] This summary is intended to provide an overview of the subject matter described in this disclosure. This summary is not intended to provide an exclusive or exhaustive explanation of the devices and methods described in detail in the following figures and the specification. Further details of one or more examples are set forth in the following figures and the specification. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1A and Figure 1B is a conceptual diagram of an extracardiovascular ICD system according to one example.

[0010] Figures 2A to 2C Different implant configurations are used to implant Figure 1A Conceptual diagram of a patient with an extracardiac ICD system.

[0011] Figure 3 is a conceptual diagram of a distal portion of a cardiovascular external lead having an electrode configuration according to another example.

[0012] Figure 4 Based on an example Figures 1A to 2C Schematic diagram of an ICD.

[0013] Figure 5A During PWOS Figure 4 Conceptual diagram of the R-wave sense event signal generated by the ICD's sensing circuitry.

[0014] Figure 5B Conceptual diagram of a bandpass-filtered and rectified cardiac electrical signal depicting cardiac events and R-wave sensing thresholds.

[0015] Figure 5C is a conceptual diagram of a bandpass filtered and rectified cardiac electrical signal, showing an example of PWOS when the R-wave amplitude is relatively small.

[0016] Figure 6 is a conceptual diagram of a bandpass filtered and rectified cardiac electrical signal, illustrating another example of a PWOS.

[0017] Figure 7 is a conceptual diagram of a bandpass filtered and rectified cardiac electrical signal, illustrating yet another example of PWOS.

[0018] Figure 8 is a flow chart of a method for identifying and responding to a PWOS according to one example.

[0019] Figure 9 Based on an example Figure 1A Flowchart of a method performed by an ICD to detect clusters of perception events.

[0020] Figure 10 is a flow chart of a method for analyzing clustered event waveforms to identify sensory event clusters as PWOS.

[0021] Figure 11 According to another example Figure 1A Flowchart of a method an ICD performs to identify and respond to PWOS.

[0022] Figure 12 is a flow chart of a method for identifying PWOS by an ICD according to another example.

[0023] Figure 13 is a flow chart of a method for confirming an R wave after identifying PWOS.

[0024] Figure 14 is a timing diagram of sense event signals that may be generated by an ICD sensing circuit and received by an ICD control circuit, and illustrates a technique for detecting PWOS. DETAILED DESCRIPTION

[0025] In general, the present disclosure describes techniques for sensing cardiac electrical signals using implantable extra-cardiovascular electrodes. As used herein, the term "extra-cardiovascular" refers to a location outside the blood vessels, heart, and pericardium surrounding the patient's heart. The implantable electrodes carried by the extra-cardiovascular leads can be positioned extra-thoracic (outside the chest cavity and sternum) or intra-thoracic (below the chest cavity or sternum), but generally not in close contact with myocardial tissue. The technology disclosed herein provides a method for identifying PWOS in an extra-cardiovascular ICD system. As used herein, the term "P-wave oversensing" or "PWOS" refers to the erroneous sensing of an R-wave by the sensing circuitry of an extra-cardiovascular ICD or pacemaker when an intrinsic P-wave occurs. The P-wave that accompanies atrial depolarization is typically smaller in amplitude than the R-wave that accompanies ventricular depolarization, and therefore typically has a peak amplitude that is less than the R-wave sensing threshold and does not interfere with reliable R-wave sensing. However, when using external cardiovascular electrodes to acquire cardiac electrical signals, PWOS may occur, especially when the amplitude of the R wave is relatively small or the heart rate is slow. Reliable R-wave sensing is very important in detecting ventricular arrhythmias.

[0026] If a P wave is over-sensed as an R wave, the heart rate may be over-estimated, which leads to an erroneous rhythm determination. For example, if a patient's heart rate is very slow and bradycardia pacing is required, PWOS may cause the ventricular rate to appear within the normal range for the ICD, resulting in the cessation of bradycardia pacing pulses that may be needed to maintain a normal heart rate without hemodynamic insufficiency. If the patient's heart is within the normal range but PWOS is occurring, the heart rate may appear faster than it actually is, and the ICD may detect a ventricular tachyarrhythmia, which may result in unnecessary tachyarrhythmia therapy being delivered, such as anti-tachycardia pacing (ATP) or one or more cardioversion / defibrillation shocks. The techniques disclosed herein for identifying PWOS enable the identified PWOS to be rejected or ignored when determining the heart rhythm, thereby allowing the ICD to provide an appropriate therapy delivery response.

[0027] The PWOS detection techniques are described in conjunction with an ICD coupled to an implantable medical lead carrying an extracardiac electrode for sensing cardiac electrical signals. However, the aspects disclosed herein for identifying and responding to PWOS can be used in conjunction with various implantable or external devices that use other cardiac electrical sensing lead or electrode systems. For example, the techniques for PWOS as described in conjunction with the accompanying figures can be implemented in any implantable or external medical device that is enabled to sense cardiac electrical signals, including: an implantable pacemaker, ICD, CRT-P, CRT-D, or cardiac monitor coupled to a transvenous or epicardial lead carrying a sensing electrode; a leadless pacemaker, ICD, CRT-P, CRT-D, or cardiac monitor with a housing-based sensing electrode; and an external pacemaker, defibrillator, or cardiac monitor coupled to an external electrode, a body surface electrode, or a skin electrode.

[0028] Figure 1A and Figure 1B is a conceptual diagram of an extracardiovascular ICD system 10 according to one example. Figure 1A is a front view of ICD system 10 implanted in patient 12. ICD system 10 includes ICD 14 connected to extracardiovascular electrical stimulation and sensing leads 16. Figure 1B is a side view of the distal portion 25 of the lead 16 implanted in the patient 12. The ICD system 10 is described in the context of providing a defibrillation shock and / or a cardioversion shock as well as a pacing pulse. Figure 1A and Figure 1B .

[0029] ICD 14 includes a housing 15 that forms an airtight seal that protects the internal components of ICD 14. Housing 15 of ICD 14 can be formed of a conductive material such as titanium or a titanium alloy. Housing 15 can serve as a housing electrode (sometimes referred to as a metal shell electrode). In the examples described herein, housing 15 can serve as an active metal shell electrode used when delivering cardioversion / defibrillation (CV / DF) shocks or other high-voltage pulses delivered using a high-voltage therapy circuit. In other examples, housing 15 can be combined with a lead-based cathode electrode for delivering unipolar low-voltage cardiac pacing pulses. In other instances, housing 15 of ICD 14 can include multiple electrodes located on an external portion of the housing. The external portion(s) of housing 15 that serve as the electrode(s) can be coated with a material such as titanium nitride.

[0030] ICD 14 includes a connector assembly 17 (also referred to as a connector block or connector header) that includes electrical feedthroughs that intersect with housing 15 and are used to provide electrical connections between conductors extending within lead bodies 18 of leads 16 and electronic components included within housing 15 of ICD 14. As will be described in further detail herein, housing 15 may house one or more processors, memory, transceivers, sensors, cardiac electrical signal sensing circuitry, therapy delivery circuitry, a power supply, and other components for sensing cardiac electrical signals, detecting cardiac rhythms, and controlling and delivering electrical stimulation pulses to treat abnormal cardiac rhythms.

[0031] Lead 16 includes an elongated lead body 18 having a proximal end 27 including a lead connector (not shown) configured to connect to the ICD connector assembly 17 and a distal end 25 including one or more electrodes. Figure 1A and Figure 1B , distal end 25 of lead 16 includes defibrillation electrodes 24 and 26 and pace / sense electrodes 28, 30, and 31. In some cases, defibrillation electrodes 24 and 26 may together form a defibrillation electrode because they can be configured to be activated simultaneously. Alternatively, defibrillation electrodes 24 and 26 may form separate defibrillation electrodes, in which case each of electrodes 24 and 26 can be activated independently. In some instances, defibrillation electrodes 24 and 26 are coupled to electrically isolated conductors, and ICD 14 may include a switching mechanism to allow electrodes 24 and 26 to be used as a single defibrillation electrode (e.g., activated simultaneously to form a common cathode or anode) or as separate defibrillation electrodes (e.g., activated individually, one as a cathode and one as an anode; or activated one at a time, one as an anode or cathode and the other remains inactive, with housing 15 acting as the active electrode).

[0032] Electrodes 24 and 26 (and in some examples, housing 15) are referred to herein as defibrillation electrodes because they are used, alone or collectively, to deliver high-voltage stimulation therapy (e.g., cardioversion or defibrillation shocks). Electrodes 24 and 26 can be elongated coil electrodes and typically have a relatively high surface area for delivering high-voltage electrical stimulation pulses compared to low-voltage pacing and sensing electrodes 28, 30, and 31. However, electrodes 24 and 26 and housing 15 can also be used to provide pacing functions, sensing functions, or both pacing and sensing functions in addition to or in lieu of high-voltage stimulation therapy. In this sense, the use of the term "defibrillation electrodes" herein should not be construed as limiting electrodes 24 and 26 to use only for high-voltage cardioversion / defibrillation shock therapy applications. Electrodes 24 and 26 can be used in a pacing electrode vector to deliver extracardiovascular pacing pulses such as ATP pulses, post-shock pacing pulses, or bradycardia pacing pulses, and / or in a sensing electrode vector to sense cardiac electrical signals and detect ventricular tachycardia (VT) and ventricular fibrillation (VF).

[0033] Electrodes 28, 30, and 31 are relatively small surface area electrodes (compared to defibrillation electrodes 24 and 26) used to deliver low-voltage pacing pulses and to sense cardiac electrical signals. Electrodes 28, 30, and 31 are referred to as pacing / sensing electrodes because they are generally configured for low-voltage applications, e.g., serving as either cathodes or anodes for delivering pacing pulses and / or sensing cardiac electrical signals. In some instances, electrodes 28, 30, and 31 may provide only pacing functionality, only sensing functionality, or both.

[0034] exist Figure 1A and Figure 1B , electrode 28 is positioned proximal to defibrillation electrode 24, and electrode 30 is positioned between defibrillation electrodes 24 and 26. A third pace / sense electrode 31 may optionally be positioned distal to defibrillation electrode 26. In other examples, one or more pace / sense electrodes may be carried by lead 16 and located proximal to defibrillation electrode 24, between defibrillation electrodes 24 and 26, and / or distal to defibrillation electrode 26.

[0035] exist Figure 1A and Figure 1B In the example shown, electrodes 28 and 30 are illustrated as ring electrodes, and electrode 31 is illustrated as a hemispherical tip electrode. However, electrodes 28, 30, and 31 may comprise any of a variety of different types of electrodes, including ring electrodes, short coil electrodes, hemispherical electrodes, directional electrodes, segmented electrodes, and the like, and may be positioned anywhere along distal portion 25 of lead 16. Further, electrodes 28, 30, and 31 may be of similar type, shape, size, and material or may be different from one another.

[0036] Lead 16 extends subcutaneously or submuscularly above chest cavity 32 from the middle of connector assembly 27 of ICD 14 toward the center of patient 12's torso (e.g., toward xiphoid process 20 of patient 12). At a location near xiphoid process 20, lead 16 bends or turns and extends subcutaneously or submuscularly above the chest cavity and / or sternum, substantially parallel to sternum 22. Although Figure 1A and Figure 1B While shown in FIG1 as being laterally offset from and extending substantially parallel to sternum 22, lead 16 may also be implanted at other locations, such as above sternum 22, offset to the right or left of sternum 22, angled laterally to the left or right of sternum 22, etc. Alternatively, lead 16 may be placed along other subcutaneous or submuscular routes. The path of lead 16 may depend on the location of ICD 14, the arrangement and location of electrodes carried by lead distal portion 25, and / or other factors.

[0037] Electrical conductors (not shown) extend from the lead connector at the proximal lead end 27 through one or more lumens of the elongated lead body 18 of the lead 16 to electrodes 24, 26, 28, 30, and 31 positioned along the distal end 25 of the lead body 18. The lead body 18 can have a tubular or cylindrical shape. In other examples, the distal portion 25 (or all) of the elongated lead body 18 can have a flat, ribbon-like, or paddle-like shape. The lead body 18 of the lead 16 can be formed of a non-conductive material (including silicone, polyurethane, fluoropolymer, mixtures thereof, and other suitable materials) and shaped to form one or more lumens within which the one or more conductors extend. However, the technology disclosed herein is not limited to this configuration or to any particular lead body design.

[0038] Each elongated electrical conductor contained within lead body 18 is electrically coupled to a corresponding defibrillation electrode 24 and 26 and a pacing / sense electrode 28, 30, and 31. Each of the pacing and sensing electrodes 28, 30, and 31 is coupled to a corresponding electrical conductor, which can be a separate corresponding conductor within the lead body. The corresponding conductors electrically couple electrodes 24, 26, 28, 30, and 31 to circuitry within ICD 14, such as therapy delivery circuitry and / or sensing circuitry as described below, via connections within connector assembly 17, including associated electrical feedthroughs that intersect with housing 15. The electrical conductors transmit therapy from therapy circuitry within ICD 14 to one or more of defibrillation electrodes 24 and 26 and / or pacing / sense electrodes 28, 30, and 31, and transmit sensed electrical signals from defibrillation electrodes 24 and 26 and / or one or more of pacing / sense electrodes 28, 30, and 31 to sensing circuitry within ICD 14.

[0039] ICD 14 can obtain electrical signals corresponding to the electrical activity of heart 8 via a combination of sensing vectors including a combination of electrodes 28, 30, and / or 31. In some examples, housing 15 of ICD 14 is used in combination with one or more of electrodes 28, 30, and / or 31 in the sensing electrode vector. ICD 14 can even obtain cardiac electrical signals using a sensing electrode vector that includes one or both of defibrillation electrodes 24 and / or 26 (e.g., between electrodes 24 and 26) or one of electrodes 24 or 26 in combination with one or more of electrodes 28, 30, 31 and / or housing 15.

[0040] The ICD 14 analyzes cardiac electrical signals received from one or more of the sensing vectors to detect abnormal rhythms, such as bradycardia, ventricular tachycardia (VT), or ventricular fibrillation (VF). The ICD 14 can analyze the heart rate and / or the morphology of the cardiac electrical signals to detect tachyarrhythmias based on any of a variety of tachyarrhythmia detection techniques. An example technique for detecting tachyarrhythmias is described in U.S. Patent No. 7,761,150 (Ghanem et al.).

[0041] The ICD 14 generates and delivers electrical stimulation therapy in response to detection of a tachyarrhythmia (e.g., VT or VF). The ICD 14 can deliver ATP in response to VT detection, and in some cases, can deliver ATP before a CV / DF shock or during charging of a high-voltage capacitor to attempt to avoid the need to deliver a CV / DF shock. ATP can be delivered using an extracardiac pacing electrode vector selected from any one of electrodes 24, 26, 28, 30, 31, and / or housing 15. The pacing electrode vector can be different from the sensing electrode vector. In one example, cardiac electrical signals are sensed between pacing / sense electrodes 28 and 30, and ATP pulses and other pacing pulses are delivered between the pacing / sense electrode 30, which is used as the cathode electrode, and the defibrillation electrode 24, which is used as the return anode electrode. In other examples, pacing pulses can be delivered between the pacing / sense electrode 28 and either (or both) of the defibrillation electrodes 24 or 26, or between the defibrillation electrode 24 and the defibrillation electrode 26. These examples are not intended to be limiting, and it will be appreciated that other sensing electrode vectors and pacing electrode vectors may be selected based on individual patient needs.

[0042] If ATP does not successfully terminate VT, or when VF is detected, ICD 14 may deliver one or more cardioversion or defibrillation (CV / DF) shocks via one or both of defibrillation electrodes 24 and 26 and / or housing 15. ICD 14 may use electrodes 24 and 26, alone or together, as cathodes (or anodes) and housing 15 as anodes (or cathodes) to deliver CV / DF shocks. ICD 14 may generate and use a pacing electrode vector comprising one or more of electrodes 24, 26, 28, 30, and 31 and housing 15 of ICD 14 to deliver other types of electrical stimulation pulses, such as post-shock pacing pulses or bradycardia pacing pulses.

[0043] Figure 1A and Figure 1B The invention is illustrative in nature and should not be considered as limiting the practice of the technology disclosed herein. Various example configurations of cardiovascular external leads and electrodes and sizes that can be implemented in conjunction with the extracardiovascular sensing technology disclosed herein are described in U.S. Publication No. 2015 / 0306375 (Marshall et al.) and U.S. Publication No. 2015 / 0306410 (Marshall et al.).

[0044] ICD 14 is shown as being implanted subcutaneously on the left side of patient 12's body along thorax 32. In some instances, ICD 14 may be implanted between the left posterior axillary line and the left anterior axillary line of patient 12. However, ICD 14 may be implanted at other subcutaneous or submuscular locations within patient 12. For example, ICD 14 may be implanted in a subcutaneous pocket in the pectoral region. In this case, lead 16 may extend subcutaneously or submuscularly from ICD 14 toward the manubrium of sternum 22 and bend or turn downward from the manubrium subcutaneously or submuscularly and extend to a desired location. In yet another example, ICD 14 may be placed in the abdomen. Lead 16 may also be implanted in other extracardiac locations. For example, as described with respect to Figures 2A to 2C As depicted, the distal portion 25 of the lead 16 may be implanted beneath the sternum / sternum of the chest cavity in the substernal space.

[0045] External device 40 is shown in telemetric communication with ICD 14 via communication link 42. External device 40 may include a processor, a display, a user interface, a telemetry unit, and other components for communicating with ICD 14 for transmitting and receiving data via communication link 42. A radio frequency (RF) link (e.g., Wi-Fi or Medical Implant Communications Service (MICS) or other RF or communications band) establishes a communication link 42 between the ICD 14 and the external device 40.

[0046] The external device 40 can be implemented as a programmer used in a hospital, clinic, or doctor's office to retrieve data from the ICD 14 and program operating parameters and algorithms in the ICD 14 for controlling ICD functions. The external device 40 can alternatively be implemented as a home monitor or handheld device. The external device 40 can be used to program cardiac rhythm detection parameters and therapy control parameters used by the ICD 14. The control parameters used to identify PWOS according to the techniques disclosed herein can be programmed into the ICD 14 using the external device 40. Data stored or acquired by the ICD 14 (including physiological signals or associated data derived therefrom, device diagnostics, and a history of detected rhythm events and delivered therapies) can be retrieved from the ICD 14 by the external device 40 following an interrogation command.

[0047] Figures 2A to 2C Is to use Figure 1A to Figure 1B A conceptual diagram of a patient 12 having an extracardiovascular ICD system 10 arranged in different implant configurations is shown in FIG. Figure 2A is a front view of patient 12 having ICD system 10 implanted therein. Figure 2B is a side view of patient 12 having ICD system 10 implanted therein. Figure 2C is a lateral view of patient 12 implanted with ICD system 10. In this arrangement, leads 16 of system 10 are at least partially implanted beneath sternum 22 of patient 12. Leads 16 extend subcutaneously or submuscularly from ICD 14 toward xiphoid process 20 and bend or turn near xiphoid process 20 and extend upward within anterior mediastinum 36 in a substernal position.

[0048] The anterior mediastinum 36 can be viewed as being bounded laterally by the pleura 39, posteriorly by the pericardium 38, and anteriorly by the sternum 22. In some instances, the anterior wall of the anterior mediastinum 36 can also be formed by the transverse thoracic muscle and one or more costal cartilages. The anterior mediastinum 36 includes a certain amount of loose connective tissue (e.g., cellulite), adipose tissue, some lymphatic vessels, lymph glands, substernal musculature, small side branches of the internal thoracic artery or vein, and the thymus gland. In one example, the distal portion 25 of the lead 16 extends substantially along the posterior side of the sternum 22 within the loose connective tissue and / or substernal musculature of the anterior mediastinum 36.

[0049] Leads that are implanted so that the distal portion 25 is substantially within the anterior mediastinum 36 may be referred to as "substernal leads." Figures 2A to 2C, lead 16 is positioned substantially centrally below sternum 22. However, in other examples, lead 16 can be implanted such that it is laterally offset from the center of sternum 22. In some examples, lead 16 can extend laterally such that distal portion 25 of lead 16 is below / under thoracic cavity 32 (in addition to or in lieu of sternum 22). In other examples, distal portion 25 of lead 16 can be implanted in other extracardiovascular intrathoracic locations (including the pleural space) or around and near, but generally not within, the pericardium 38 of heart 8. Other implant locations and lead and electrode arrangements that may be used in conjunction with the techniques described herein are generally disclosed in the above-referenced patent applications.

[0050] Figure 3 is a conceptual diagram showing a curved distal end portion 25' having a lead body 18' Figures 1A to 2C FIG20 is another example of a distal portion 25' of a cardiovascular external lead 16. The lead body 18' can be formed to have a curved, bent, serpentine, or zigzag shape along the distal portion 25'. In the example shown, the defibrillation electrodes 24' and 26' are carried along the curved portion of the lead body 18'. The pacing / sense electrode 30' is carried between the defibrillation electrode 24' and the defibrillation electrode 26'. The pacing / sense electrode 28' is carried proximal to the proximal defibrillation electrode 24'. In this example, no electrode is provided at the distal end of the defibrillation electrode 26'.

[0051] like Figure 3 As shown in FIG, lead body 18' can be formed to have a curved distal portion 25' including two "C"-shaped curves, which together can resemble the Greek letter epsilon "ε". Defibrillation electrodes 24' and 26' are each carried by the two corresponding C-shaped portions of lead body distal portion 25', which extend or curve in the same direction away from a central axis 33 of lead body 18'. In the example shown, pace / sense electrode 28' is proximal to the C-shaped portion carrying electrode 24', and pace / sense electrode 30' is proximal to the C-shaped portion carrying electrode 26'. In some instances, pace / sense electrodes 28' and 30' can be generally aligned with the central axis 33 of the straight proximal portion of lead body 18' such that the midpoints of defibrillation electrodes 24' and 26' are laterally offset from electrodes 28' and 30'. Other examples of cardiovascular external leads that can be implemented with the pacing technology described herein are generally disclosed in U.S. patent application Ser. No. 14 / 963,303, which include one or more defibrillation electrodes and one or more pacing and sensing electrodes carried by a curved, serpentine, undulating, or zigzag-shaped distal portion of the lead body.

[0052] Figure 4 is a schematic diagram of an ICD 14 according to an example. Figure 4 The electronic circuit system within the ICD 14 (schematically shown as electrodes in FIG) includes software, firmware, and hardware that collaboratively monitor one or more cardiac electrical signals, determine when electrical stimulation therapy is needed, and deliver therapy as needed according to programmed therapy delivery algorithms and control parameters. The software, firmware, and hardware are configured to detect ventricular tachyarrhythmias and can distinguish between VT and VF to determine when ATP or CV / DF shocks are required. In some cases, the ICD 14 can be configured to deliver bradycardia pacing when the heart rate drops below a programmed lower rate. The ICD 14 is coupled to external cardiovascular leads, such as those carrying external cardiovascular electrodes 24, 26, 28, 30, and 31 (if available). Figure 1A The lead 16 shown in Figure 3 Leads 16' are provided for delivering electrical stimulation pulses to the patient's heart and for sensing cardiac electrical signals.

[0053] ICD 14 includes control circuitry 80, memory 82, therapy delivery circuitry 84, sensing circuitry 86, and telemetry circuitry 88. Power supply 98 provides power to the circuitry of ICD 14 (including each of components 80, 82, 84, 86, and 88) as needed. Power supply 98 may include one or more energy storage devices, such as one or more rechargeable or non-rechargeable batteries. Connections between power supply 98 and each of the other components 80, 82, 84, 86, and 88 will be based on the power supply 98. Figure 4 The overall block diagram of FIG84 is shown, but is not shown for clarity. For example, power supply 98 can be coupled to a low-voltage (LV) charging circuit and a high-voltage (HV) charging circuit included in therapy delivery circuit 84 to charge a low-voltage capacitor and a high-voltage capacitor, respectively, included in therapy delivery circuit 84 for generating corresponding low-voltage pacing pulses, such as bradycardia pacing pulses, post-shock pacing pulses, or ATP pulses, or for generating high-voltage pulses, such as CV / DF shock pulses. In some examples, the high-voltage capacitors, rather than the low-voltage capacitors, are charged and used to deliver cardiac pacing pulses, ATP pulses, and / or post-shock pacing pulses.

[0054] Figure 4The functional blocks shown in the are representative of the functionality contained in the ICD 14 and may include any discrete and / or integrated electronic circuit components that implement analog and / or digital circuitry capable of producing the functionality attributable to the ICD 14 herein. These various components may include application specific integrated circuits (ASICs), electronic circuits, processors (shared, dedicated, or groups) 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. The particular form of software, hardware, and / or firmware used to implement the functionality disclosed herein will be determined primarily by the particular system architecture employed in the ICD and the particular detection and therapy delivery methods employed by the ICD. It is within the ability of one skilled in the art to provide software, hardware, and / or firmware to implement the described functionality in the context of any modern ICD system, given the disclosure herein.

[0055] The memory 82 may include any volatile, nonvolatile, magnetic, or electrical non-transitory computer-readable storage medium, such as random access memory (RAM), read-only memory (ROM), non-volatile RAM (NVRAM), electrically erasable programmable ROM (EEPROM), flash memory, or any other storage device. Furthermore, the memory 82 may include a non-transitory computer-readable medium that stores instructions that, when executed by one or more processing circuits, cause the control circuitry 80 or other ICD components to perform various functions attributed to the ICD 14 or those ICD components. The non-transitory computer-readable medium that stores these instructions may include any of the media listed above.

[0056] The functionality attributed herein to ICD 14 may be implemented as one or more integrated circuits. Depicting different features as components (e.g., circuits) is intended to highlight different functional aspects and does not necessarily imply that such components (e.g., circuits or modules) must be implemented by separate hardware or software components. Rather, the functionality associated with one or more components may be performed by separate hardware, firmware, or software components, or integrated within a common hardware, firmware, or software component. For example, sensing operations may be performed by sensing circuit 86 under the control of control circuit 80, and identification of PWOS operations may be implemented in a processor of control circuit 80 executing instructions stored in memory 82.

[0057] Control circuitry 80 communicates, for example, via a data bus, with therapy delivery circuitry 84 and sensing circuitry 86 to sense cardiac electrical activity, detect cardiac rhythm, and control the delivery of cardiac electrical stimulation therapy in response to sensed cardiac signals. Therapy delivery circuitry 84 and sensing circuitry 86 are electrically coupled to electrodes 24, 26, 28 and 30, 31 carried by leads 16 and housing 15, which may serve as a common or ground electrode or as an active metal shell electrode for delivering CV / DF shock pulses or cardiac pacing pulses.

[0058] Sensing circuit 86 can be selectively coupled to electrodes 28, 30, 31, and / or housing 15 to monitor the electrical activity of the patient's heart. Sensing circuit 86 can also be selectively coupled to defibrillation electrodes 24 and / or 26 for use in a sensing electrode vector. Sensing circuit 86 is configured to selectively monitor one or more sensing vectors selected at a time from among the available electrodes 24, 26, 28, 30, 31, and housing 15. For example, sensing circuit 86 can include switching circuitry for selecting which of electrodes 24, 26, 28, 30, 31, and housing 15 are coupled to a sense amplifier or other cardiac event detection circuitry included in one or more sensing channels of sensing circuit 86. The switching circuitry can include a switch array, a switch matrix, a multiplexer, or any other type of switching device suitable for selectively coupling components of sensing circuit 86 to selected electrodes. In some examples, control circuit 80 can control the switching circuitry to selectively couple sensing circuit 86 to one or more sensing electrode vectors. Cardiac event detection circuitry within sensing circuit 86 may include one or more sense amplifiers, filters, rectifiers, threshold detectors, comparators, analog-to-digital converters (ADCs), or other analog or digital components.

[0059] In some examples, sensing circuitry 86 includes multiple sensing channels for acquiring cardiac electrical signals from a plurality of sensing vectors selected from electrodes 24, 26, 28, 30, 31, and housing 15. Each sensing channel can be configured to amplify, filter, and rectify the cardiac electrical signals received from the selected electrodes coupled to the corresponding sensing channel to improve the signal quality for sensing cardiac events (e.g., R-waves). For example, each sensing channel can include a pre-filter and amplifier for filtering and amplifying the signals received from the selected pair of electrodes. The resulting raw cardiac electrical signals can be passed from the pre-filter and amplifier to cardiac event detection circuitry for sensing cardiac events from the received cardiac electrical signals. The cardiac event detection circuitry can include a pre-filter and amplifier, an analog-to-digital converter, a bandpass filter, a rectifier, a sense amplifier, and / or a comparator for detecting cardiac events when the cardiac electrical signals cross a sensing threshold. For example, the R-wave sensing threshold can be automatically adjusted by sensing circuitry 86 under the control of control circuitry 80. The R-wave sensing threshold can have a starting threshold set to a percentage of the maximum peak amplitude of the immediately preceding sensed R-wave. The R-wave sensing threshold may be decreased from a starting value in a decaying or stepwise manner over a predetermined time period. Parameters for determining and controlling the R-wave sensing threshold may be stored in memory 82 and controlled by hardware or firmware of control circuitry 80 and / or sensing circuitry 86. Some sensing threshold control parameters may be user programmable and communicated from control circuitry 80 to sensing circuitry 86 via a data bus.

[0060] The sensing circuit 86 can sense the R-wave according to an automatically adjusted sensing threshold. For example, the R-wave sensing threshold can be attenuated from a certain starting percentage, such as 60% of the maximum peak amplitude of the most recently sensed R-wave. In other examples, as disclosed in U.S. patent application Ser. No. 15 / 142,171 (Attorney Docket No. C00012942.USU1, Cao et al.), the R-wave sensing threshold can be adjusted to multiple threshold levels in a stepwise manner at a specified time after the sensing threshold is crossed.

[0061] Upon detecting a cardiac event based on a sensing threshold crossing, sensing circuitry 86 may generate a sensed event signal, such as an R-wave sensed event signal, that is transmitted to control circuitry 80. Control circuitry 80 uses the sensed event signal to detect cardiac rhythm and determine the need for treatment. Sensing circuitry 86 may also transmit the digitized cardiac electrical signal to control circuitry 80 for waveform morphology analysis to detect and distinguish cardiac rhythms.

[0062] The signal from the selected sensing vector may be passed through a bandpass filter and amplifier, provided to a multiplexer, and converted to a multi-bit digital signal by an analog-to-digital converter for storage in random access memory included in memory 82 under the control of direct memory access circuitry via a data / address bus. The bandpass filter, amplifier, multiplexer, and analog-to-digital converter are all included in sensing circuitry 86. Control circuitry 80 may be a microprocessor-based controller that employs digital signal analysis techniques to characterize the digitized signals stored in the random access memory of memory 82 in order to employ any of a number of signal processing methods for analyzing cardiac signals and cardiac event waveforms (e.g., R waves) to identify and classify the patient's cardiac rhythm. Examples of algorithms that may be executed by the ICD 14 to detect, distinguish, and treat tachyarrhythmias, and that may be adapted to include the PWOS identification techniques described herein, are generally disclosed in U.S. Pat. No. 5,354,316 (Keimel), U.S. Pat. No. 5,545,186 (Olson et al.), U.S. Pat. No. 6,393,316 (Gillberg et al.), U.S. Pat. No. 7,031,771 (Brown et al.), U.S. Pat. No. 8,160,684 (Ghanem et al.), and U.S. Pat. No. 8,437,842 (Zhang et al.).

[0063] The therapy delivery circuit 84 includes charging circuitry, one or more charge storage devices, such as one or more high-voltage capacitors and, in some examples, one or more low-voltage capacitors, and switching circuitry that controls when to discharge the capacitor(s) across a selected pacing electrode vector or CV / DF shock vector. Charging the capacitors to a programmed pulse amplitude and discharging the capacitors for a programmed pulse width can be performed by the therapy delivery circuit 84 based on control signals received from the control circuit 80. The control circuit 80 may include various timers or counters that control when to deliver ATP or other cardiac pacing pulses.

[0064] For example, control circuitry 80 may include pacemaker timing and control circuitry having a programmable digital counter that is set by a microprocessor of control circuitry 80 to control the fundamental time intervals associated with various pacing modes or anti-tachycardia pacing sequences delivered by ICD 14. The microprocessor of control circuitry 80 may also set the amplitude, pulse width, polarity, or other characteristics of cardiac pacing pulses, which parameters may be based on programmed values stored in memory 82.

[0065] During pacing, an escape interval counter within the pacemaker timing and control circuit system is reset when an R wave is sensed as indicated by a signal from sensing circuit 86. Depending on the selected pacing mode, when the escape interval counter expires, a pacing pulse is generated by the pulse output circuit of the therapy delivery circuit 84. The pacing output circuit is coupled to the desired electrode via a switch matrix to discharge one or more capacitors across the pacing load. The escape interval counter is reset when the pacing pulse is generated and thereby controls the basic timing of cardiac pacing functions (including anti-tachycardia pacing, bradycardia pacing, or post-shock pacing). The duration of the escape interval is determined by the control circuit 80 via the data / address bus. The count value present in the escape interval counter when the escape interval counter is reset by a sensed R wave can be used to measure the RR interval (RRI) for detecting the occurrence of various arrhythmias. The RRI is the time interval between two consecutive sensed R waves.

[0066] As described below, the control circuit 80 can monitor the RRI for detecting an RRI pattern that is evidence of PWOS. The pattern can be a pattern of alternating long and short RRIs, such as long-short-long-short, or a cluster of sensory events occurring in short intervals separated by a long interval, such as short-short-long or short-short-short-long. When an RRI pattern indicating PWOS is detected, for example, when a predetermined number of sensory event clusters are detected based on RRI criteria, the waveform of the digitized cardiac electrical signal corresponding to the RRI pattern of clustered sensory events can be analyzed by the control circuit 80 for identifying PWOS. When the RRI pattern and waveform morphology analysis meet the PWOS detection criteria, PWOS can be identified. If PWOS is identified and a tachyarrhythmia is being detected, the tachyarrhythmia attack detection can be rejected, or the scheduled tachyarrhythmia treatment can be canceled or stopped. If PWOS is identified and a tachyarrhythmia is not being detected, analysis of sensing events can be enabled (e.g., on a beat-by-beat basis) to allow oversensed P waves to be identified as they occur and ignored for purposes of resetting the pacing escape interval counter so that the oversensed P waves do not inhibit pacing pulse delivery. Additionally or alternatively, if PWOS is identified, cardiac signal segments can be stored and / or R-wave sensing control parameters can be adjusted to reduce the likelihood of PWOS in the future.

[0067] The memory 82 comprises a read-only memory (ROM) or other memory device in which resides a stored program that controls the operation of the control circuit 80. The memory 82 may further comprise a random access memory (RAM) or flash memory configured as a plurality of recirculating buffers capable of holding a series of measured RRIs, cardiac signal segments, counts, or other data for analysis by the control circuit 80 to predict or diagnose arrhythmias.

[0068] In response to detecting a ventricular tachycardia, ATP can be delivered by loading a protocol from a microprocessor included in control circuit 80 into the pacing timing and control circuitry based on the type and frequency of the detected tachycardia. If the tachycardia is not terminated by ATP, or if VF is detected and a higher voltage cardioversion or defibrillation pulse is required, the control circuitry activates the cardioversion and defibrillation control circuitry included in control circuit 80 to initiate charging of a high-voltage capacitor via a charging circuit under the control of a high-voltage charge control line. Both the charging circuit and the high-voltage capacitor are included in therapy delivery circuit 84. The voltage on the high-voltage capacitor is monitored via a voltage capacitor line transmitted to control circuit 80. When the voltage reaches a predetermined value set by the microprocessor of control circuit 80, a logic signal is generated on a capacitor charge line transmitted to therapy delivery circuit 84, thereby terminating charging. A defibrillation or cardioversion pulse is delivered to the heart via a control bus by the output circuitry of therapy delivery circuit 84 under the control of the pacemaker timing and control circuitry. The output circuitry, which may include multiple switches and may take the form of an H-bridge circuit, determines the electrodes used to deliver the cardioversion or defibrillation pulse and the pulse waveform. The therapy delivery charging and output circuitry and control circuitry generally disclosed in any of the above-referenced patents may be implemented in ICD 14 .

[0069] The control parameters used by control circuit 80 to detect cardiac rhythm and control therapy delivery can be programmed into memory 82 via telemetry circuit 88. Telemetry circuit 88 includes a circuit for communicating with external device 40 ( Figure 1A 12 ). Under the control of control circuitry 80, telemetry circuitry 88 can receive downlink telemetry from external device 40 and send uplink telemetry to an external device. In some cases, telemetry circuitry 88 can be used to transmit and receive communication signals to / from another medical device implanted in patient 12.

[0070] Figure 5A 1 is a conceptual diagram 100 of an R-wave sense event signal 102 that may be generated by sensing circuitry 86 during a PWOS. Event 102 is labeled "P" for a P wave and "R" for an R wave, with "r" designating a sensed R wave twice. In this designation, an uppercase "R" followed by a lowercase "r" indicates that the sense event signal is generated by sensing the same QRS complex twice. When using extracardiac electrodes to acquire cardiac electrical signals, the QRS waveform in some patients may be relatively wide compared to the QRS waveform of signals received using transvenous, intracardiac, or epicardial electrodes. Because of this, when a single R-wave signal exceeds the R-wave sense threshold a second time outside of a blanking period, there may be a higher probability of sensing an R-wave twice.

[0071] When the R wave is sensed for the second time, the cardiac signal peak amplitude may be lower than the actual peak amplitude of the R wave. When the R wave sensing threshold is set to a certain percentage of the maximum R wave amplitude, the attenuated or reduced R wave sensing threshold that begins at a relatively low amplitude may be crossed by the subsequent P wave. In other cases, in some instances, the amplitude of the R wave sensed by the external cardiovascular electrode may be lower. A relatively small amplitude R wave may still be larger than a P wave or T wave and be properly sensed as an R wave. However, when the starting R wave sensing threshold is set to a certain percentage of the maximum peak amplitude of the sensed R wave, the starting threshold can be set relatively low when the R wave peak amplitude is low. In some instances, a P wave may be over-sensed after a lower amplitude R wave, especially when the heart rate is low.

[0072] Figure 5B 1 is a conceptual diagram of a bandpass filtered and rectified cardiac electrical signal 150, including an R wave 152, followed by a T wave 154 and a P wave 156, without PWOS. Following a blanking period 172 following the sensing of the R wave 152, the R wave sensing threshold 160 is set to a starting threshold 166. The R wave 152 is sensed at time 171, and the blanking period 172 begins.

[0073] During the blanking period 172, the maximum peak amplitude 164 of the R-wave 152 is determined and used to set a starting R-wave sensing threshold 166, e.g., approximately 60% of the maximum peak amplitude 164. The R-wave sensing threshold 160 decreases from the starting value 166 over time. In the illustrated example, the R-wave sensing threshold 160 is shown decreasing from the starting value 166 at a predetermined decay rate 168 until a predetermined time interval 173 expires, or until a minimum sensing threshold 170 is reached, whichever occurs first. If the time interval 173 expires, the R-wave sensing threshold 160 drops to the minimum sensing threshold 170, which may be equal to the programmed sensitivity setting. In other examples, the R-wave sensing threshold 160 may decrease linearly and / or according to one or more step-downs or other R-wave sensing threshold control parameters, including the multi-level R-wave sensing threshold example disclosed in the above-referenced U.S. Patent Application No. 15 / 142,171 (Attorney Docket No. C00012942.USU1, Cao et al.).

[0074] When the R-wave amplitude 164 is relatively high, the starting value 166 based on the amplitude 164 is relatively high, so that the decaying R-wave sensing threshold 160 remains greater than the amplitude of the P-wave 156 (and the T-wave 154), thereby preventing PWOS from occurring. The next R-wave 153 is sensed at time 175 when the cardiac electrical signal crosses the R-wave sensing threshold 160, which has been reduced to the minimum value 170. The time interval 165 is determined as the RRI between the consecutively sensed R-waves 152 and 153 and can be used by the control circuit 80 to detect a pattern of PWOS. For example, the RRI 165 can represent a long RRI in an RRI analysis performed to detect a pattern including long and short RRIs that can be evidence of PWOS.

[0075] exist Figure 5C , an R-wave 158 is followed by a T-wave and an over-sensed P-wave 162. When an R-wave 158 of relatively small amplitude occurs, or when the ratio of the R-wave amplitude 174 to the P-wave amplitude 184 is relatively small, the starting R-wave sensing threshold 176 based on the R-wave maximum peak amplitude 174 is relatively low compared to the P-wave maximum peak amplitude 184. As the R-wave sensing threshold decreases from the starting value 176 at the decay rate 168, it drops below the amplitude 184 of the P-wave 162. The over-sensing of the P-wave 162 at time 178 causes the sensing circuit 86 to generate a false R-wave sensing event signal. The R-wave sensing threshold 160 is set to the starting value 186 based on the peak amplitude 184 of the P-wave 162, which was falsely detected as an R-wave. This causes the R-wave sensing threshold 160 to return to the minimum sensing threshold 170 as it rapidly decreases at the decay rate 168.

[0076] The time interval 179 between the sensed R wave 158 at time 177 and the sensed P wave 162 at time 178 is determined to be an RRI, but a relatively short RRI and can be identified by the control circuit 80 as an RRI pattern that is evidence of PWOS. In the presence of an atrial tachyarrhythmia (such as atrial fibrillation or atrial flutter), multiple P waves may occur between R waves. When a P wave 162 is over-sensed and followed by a relatively low R wave sensing threshold based on the lower peak amplitude 184 of the P wave 162, multiple P waves may be sequentially over-sensed, resulting in a cluster of sensed events occurring at shorter intervals.

[0077] like Figure 5C As shown, subsequent PWOS may occur when a relatively small amplitude R-wave 158 occurs, particularly when the R-wave sensing threshold starting value is set based on the maximum peak amplitude of the most recently sensed event. PWOS may recur until a relatively large amplitude R-wave is sensed, which resets the R-wave sensing threshold to a higher proportional starting value. The higher starting value can maintain the R-wave sensing threshold above the P-wave amplitude and interrupt the sequence of sensed events that includes PWOS.

[0078] Relatively small R waves can occur during normal or faster ventricular rates, leading to PWOS and an overestimation of the ventricular rate. VT or VF can be erroneously detected, leading to unwanted therapy, such as unnecessary cardioversion / defibrillation shocks. Small R waves can also occur during slower ventricular rates when the patient may be experiencing bradycardia, leading to PWOS and an overestimation of the ventricular rate. In this case, due to PWOS, appropriate bradycardia pacing may be discontinued because the R-wave sense event signal causes the pacing escape interval to be reset before expiration and pacing pulse delivery. As such, PWOS can lead to erroneous detection of ventricular tachyarrhythmias and unnecessary therapy, and PWOS can result in missed detection of bradycardia intervals and discontinuation of appropriate bradycardia pacing therapy.

[0079] Figure 6 is a conceptual illustration of a bandpass filtered and rectified cardiac electrical signal 250, including R-waves 252 and 260 with an intermediate T-wave 254 and P-wave 256. In this example, double sensing of the R-wave 252 and oversensing of the P-wave 256 occur, resulting in clusters of sensed events occurring in relatively short RRIs 265, 267, and 269 at times 251, 253, 259, and 261, respectively.

[0080] An R-wave 252 is first sensed at time 251, and a blanking interval 172 begins. Following blanking interval 172, R-wave sensing threshold 160 is set to a starting threshold 262. R-wave sensing threshold 160 decays at a decay rate 168. In this example, R-wave 252 has a relatively wide signal width, such that when the first blanking interval 172, which begins at time 251, expires, the rectified R-wave 252 crosses R-wave sensing threshold 160 a second time at time 253, outside of blanking interval 172, beginning another blanking interval 172. Control circuit 80 determines an RRI 265 between the R-wave sensing event signals received at time 251 and time 253.

[0081] The R-wave sensing threshold 160 is set to a starting value 264 based on a percentage of the maximum peak amplitude 257 detected during the blanking interval 172 beginning at time 253 corresponding to the second sensing of the R-wave 252. The starting value 264 of the R-wave sensing threshold 160 is lower than the starting threshold 262 based on a percentage of the true maximum peak amplitude 255 of the R-wave 252. The R-wave sensing threshold 160 can decrease at a decay rate 168 or another linear or step-wise decrease. The P-wave 256 crosses the R-wave sensing threshold 160 at time 259, starting a new blanking interval 172. The control circuit 80 determines the RRI 267 as the time interval between the R-wave sensing event signals received at time 253 and time 259.

[0082] After the blanking interval 172 begins when the P wave 256 is sensed at time 259, the R-wave sensing threshold is set to a starting value 266 that is based on a percentage of the maximum peak amplitude 258 of the P wave 256. The R-wave sensing threshold decreases at a decay rate 168 until it reaches a minimum sensing threshold 170, e.g., a programmed sensitivity setting. An R-wave 260 is sensed at time 261 when the cardiac electrical signal 250 crosses the R-wave sensing threshold 160. The control circuit 80 determines the next RRI 269 as the time interval between the R-wave sensing event signals received from the sensing circuit 86 at time 259 and time 261.

[0083] All of these RRIs 265, 267, and 269 are relatively short compared to the true RRI 270 between consecutive R waves 252 and 260. This cluster of R-wave perception events at times 251, 253, 259, and 261 defining relatively short RRIs can be identified and detected by the control circuit 80 as evidence of PWOS. In this example, additional analysis of the perception events, two sensings of the R-wave 252, the P-wave 256, and the R-wave 260, can be performed in response to detecting the perception event cluster, for example, as combined with Figure 8 described.

[0084] Figure 7 2 is a conceptual diagram of a bandpass filtered and rectified cardiac electrical signal 280, including R-waves 282 and 290 with an intermediate T-wave 284 and P-wave 286. In this example, the heart rate is very slow, for example, less than 60 beats per minute, or even slower, less than 40 beats per minute. The R-wave 282 is properly sensed at time 295 when the cardiac electrical signal 280 crosses the R-wave sensing threshold 160. After the blanking interval 172, the R-wave sensing threshold 160 is set to a starting value 276 based on a percentage of the maximum peak amplitude 285 of the R-wave 282. The R-wave sensing threshold 160 decreases at a decay rate 168 and is adjusted to a minimum sensing threshold 170 after a predetermined fall time interval 173. In some examples, the fall time interval may be, for example, 1.5 seconds or 2 seconds. Because the heart rate is very slow in this example, a P wave 286 occurs after the fall time interval 173 expires, and the cardiac electrical signal 280 crosses the R-wave sensing threshold 160 , which is set to the minimum value 170 .

[0085] A P wave 286 is sensed at time 297, and a new blanking period 172 begins. The R-wave sensing threshold 160 is adjusted to a starting value 288 based on the peak amplitude of the P wave 286 and decays to a minimum threshold 170. An R-wave 290 is sensed at time 299 when the cardiac electrical signal 270 crosses the R-wave sensing threshold 160. The control circuit 80 determines an RRI 277 between the R-wave sensing event signals received from the sensing circuit 86 at time 295 and time 297, and determines an RRI 279 between the R-wave sensing event signals received at time 297 and time 299. These RRIs 277 and 279 are both shorter than the true RRI 292. The true RRI 292 can be longer than the programmed lower pacing rate interval. For example, the lower pacing rate interval can be programmed to 1.0 second for a pacing rate of 60 pulses per minute, or to 1.5 seconds for a pacing rate of 40 pulses per minute. If the RRI 277 is shorter than the programmed lower frequency interval, then when the R wave 282 is sensed, the pacing escape interval that began at time 295 may be reset at time 297 in response to the R wave sense event signal at time 297. When the actual heart rate is slower than the rate corresponding to the programmed lower frequency interval, PWOS may occur during the slower heart rate and result in inhibition of pacing pulses.

[0086] return Figure 5A , a cluster of sensed events 104 may include multiple events sensed at a relatively short RRI 106 due to PWOS. Each vertical line represents an event sensed as an R wave by the sensing circuit 86, such that an R wave sensed event signal is transmitted to the control circuit 80. As such, intervals between consecutive sensed events, such as interval 106 and interval 108, are measured by the control circuit 80 as RRIs, as the time intervals between consecutively received R wave sensed event signals. In this example, due to an atrial tachyarrhythmia, multiple P waves are sensed for each R wave, with or without a degree of atrioventricular block. The degree of AV block (e.g., no AV block, first degree, second degree, or third degree complete AV block) affects how many P waves are conducted to the ventricles, and therefore affects how many P waves occur during one RR interval and the regularity of the PR interval during an atrial tachyarrhythmia. Each cluster of sensed events 104 is separated from the next consecutive cluster 110 by a relatively long RRI 108. The control circuit 80 may apply PWOS detection criteria to the R-wave sensed event signals and cardiac electrical signal waveforms occurring during the sensed event clusters to detect PWOS as described herein, for example, in conjunction with Figures 8 to 14 .

[0087] like Figure 5C 、 Figure 6 and Figure 7 As shown in the example of , the number of over-sensed P waves in each sensed event cluster 104, 110, etc. and the relative RRI during and between clusters can vary depending on a number of factors, such as intrinsic ventricular rate, R wave amplitude, P wave amplitude, underlying AV conduction, and intrinsic atrial rhythm (e.g., presence of atrial arrhythmias such as atrial flutter, atrial fibrillation, atrial tachyarrhythmias, etc.). Cluster detection criteria for detecting sensed event clusters and identifying PWOS can be established based on the specific rhythm history and cardiac electrical signal characteristics of these cluster patterns as observed or expected in individual patients. Although Figure 5A The RRI pattern during PWOS is depicted as a cluster of multiple sensory events separated by relatively long RRIs, but in other cases, e.g. Figure 7 In the example of , during slower heart rates, PWOS can result in alternating long and short RRIs when a single P wave 286 is over-perceived during each true RRI 292.

[0088] Figure 8 FIG2 is a flow chart of a method 200 for identifying and responding to a PWOS according to an example. At block 202, the control circuit 80 monitors RRI for clustered sensing events. Figure 7 A method for detecting clusters of sensory events is described. Briefly, an RRI is determined based on the time or count that has elapsed when the escape interval timer is reset due to control circuit 80 receiving an R-wave sensory event signal from sensing circuit 86, for example. Long and short RRI thresholds can be applied to continuously determined RRIs to detect patterns of clustered sensory events. Figure 5A As shown, the pattern of clustered sensed events may include two or more short RRIs 106 followed by a long RRI 108. In other examples, PWOS may be characterized by an SLSL interval when a single P wave is sensed during each true RRI. This may occur during slower heart rates when the R wave amplitude is low and AV conduction is intact. Because of this, in some examples, a cluster of sensed events may include only two sensed events separated from each other by a short RRI and separated from other clusters of sensed events by one long RRI. In other examples, a cluster of sensed events may include 3, 4, 5 or more sensed events separated by short RRIs. Multiple short RRIs within a cluster may be different from each other, but all less than the short RRI threshold. Clustered sensed events may include at least one P wave, and will typically include at least one PR or RP interval, such as Figure 5C 、 Figure 6 and Figure 7 In other examples, clustered sensing events may include twice-sensed R waves, multiple over-sensed P waves, and over-sensed T waves.

[0089] If a cluster is detected based on the cluster detection criteria, the control circuit 80 may increment a cluster counter at block 206, as determined at block 204. The cluster counter may be compared to a threshold at block 208. If the counter reaches a predetermined number of sensed event clusters, such as 3, 4, 5, or other threshold number of clusters, the waveform of the sensed event for each cluster is analyzed by the control circuit 80 at block 210. Based on the waveform analysis, the cluster is identified or not identified as a PWOS. The waveform analysis may include event amplitude analysis, waveform morphology analysis, waveform slope analysis, or other analysis of the event waveform. Figure 8 An example of the analysis performed at block 210 is described below.

[0090] If a PWOS is not identified and all predetermined number of clusters have not been identified, the "No" branch of box 216, the control circuit 80 analyzes the next cluster by returning to box 210. If the cluster is determined to be a PWOS, the "Yes" branch of box 212, the PWOS counter can be incremented by the control circuit 80 at box 214. Once all predetermined number of clusters have been evaluated, the "Yes" branch of box 216, the PWOS count adjusted at box 214 is compared to the PWOS rejection threshold at box 218. If the PWOS counter does not reach the rhythm rejection threshold, a PWOS is not identified, as indicated by box 220. The rhythm being sensed or detected by the ICD is considered valid. For example, if VT or VF is being detected, the rhythm detection is acceptable and therapy can be delivered according to the programmed tachyarrhythmia therapy. If VT or VF is not being detected and an RRI that is less than the programmed bradycardia lower pacing rate interval is being determined, the RRI is considered correct. No bradycardia treatment was required.

[0091] If the number of clusters identified as PWOS does reach the rejection threshold at box 218, then at box 222, PWOS is identified and the current sensed rhythm is rejected. If a VT or VF episode is being detected, VT or VF detection may be rejected at box 222, or ventricular tachyarrhythmia therapy may be discontinued. If a normal sinus rhythm is being sensed, for example, if the RRI is being determined to be less than the bradycardia lower pacing rate interval, and no bradycardia pacing is being delivered, then the sensed rhythm is rejected. The ICD 14 may adjust therapy control parameters by enabling monitoring of event amplitude, for example, as combined with Figure 13 As described, other corrective actions may be taken to identify oversensed P waves as they occur so that they may be ignored for purposes of controlling the ventricular pacing escape interval timer and ventricular pacing pulse delivery. Figure 11An example of a PWOS-based rhythm rejection response is described below.

[0092] Figure 9 is a flowchart 300 of a method that may be performed by the ICD 14 to detect clusters of sensory events according to one example. The method of flowchart 300 may be used in conjunction with Figure 8 206, wherein the RRI is monitored to detect a cluster of sensed events and a cluster counter is incremented when a cluster is detected. At block 302, the control circuit 80 receives an R-wave sensed event signal from the sensing circuit 86. This sensed event signal is referred to as an "R-wave sensed event signal" because it is a signal generated in response to the cardiac electrical signal crossing an R-wave sensing threshold. However, the actual event of crossing the R-wave sensing threshold may correspond to an R-wave, a P-wave, or even a T-wave or other non-cardiac electrical noise, and thus may be a false R-wave sensed event signal.

[0093] At box 304, the control circuit 80 determines the RRI (N) as the time interval ending with the currently received R wave sensed event signal and starting with the most immediately previous R wave sensed event signal. At box 306, this RRI (N) is compared with a short interval threshold (TH1). The short interval threshold TH1 can be set to a fixed interval, such as approximately 210ms, 200ms, 190ms, 180ms, 150ms or other predetermined time interval, which can be based on the normal expected PR interval for the patient. The PR interval - for example, the time interval from the sensed P wave or its maximum peak amplitude to the next sensed R wave or its maximum peak amplitude - can be automatically determined by the ICD 14 or measured by the clinician. The short interval threshold TH1 can be automatically set or programmed to be slightly larger than the expected PR interval for the patient.

[0094] In some examples, the RRI(N) (and subsequent RRIs) can be compared to an interval range. When non-cardiac noise, such as electromagnetic interference, is present, very short RRIs can occur when the non-cardiac noise is mistakenly perceived as an R wave. Therefore, the criteria for identifying PWOS can include a minimum RRI threshold and a maximum RRI threshold for identifying short intervals between R-wave perception event signals that may be caused by PWOS. The minimum RRI threshold can correspond to the minimum expected PR interval, and the maximum RRI can correspond to the maximum expected PR interval. The normal PR interval range can be approximately 120 ms to 200 ms. This range can be adjusted up or down or widened or narrowed according to the needs of the individual patient.

[0095] If the RRI(N) is not less than the short interval threshold, the control circuit 80 returns to block 302 to wait for the next R-wave sensing event signal. However, the RRI(N) is stored in the memory 82 for use in evaluating a series of RRIs. For example, a series of up to three, four, six, or more consecutive RRIs required to detect a cluster pattern according to the cluster detection criteria can be stored in the memory 82 in a circular buffer.

[0096] If the RRI (N) is less than the short interval threshold at box 306, the most recent previous RRI - RRI (N-1) - can be compared with the long interval threshold (TH2) at box 308. When the heart rate is lower than the tachyarrhythmia frequency, the long interval threshold TH2 can be set to the minimum expected RP interval. For example, the long interval threshold TH2 can be set to approximately 250ms, 300ms, 350ms, 400ms or other predetermined time interval. A short RRI followed by a long RRI can be the beginning of a cluster of sensing events. If the previous interval is not longer than the long interval threshold, the control circuit 80 waits for the next R wave sensing event signal at box 302. If the previous RRI (N-1) is longer than the long interval threshold, the event defining the start and end of RRI (N) can be a clustered event. The cluster interval counter is set to one at box 310 to start counting the number of RRIs less than the short interval threshold after the longer RRI (N-1).

[0097] At box 312, the control circuit 80 determines the next RRI, RRI(N+i), where i was initially set to 1 at box 311. At box 314, the next RRI(N+1) is compared to the short interval threshold. If the comparison at box 314 is true, the cluster interval counter is increased again at box 316. At box 318, the cluster interval counter is compared to the maximum number of short intervals. If the maximum number of intervals has not been reached, but the cluster interval counter has been increased, a cluster is being detected at box 320. In this example, a perception event cluster is being detected if there are at least two consecutive short intervals following a long interval based on the short and long interval thresholds or ranges. In other examples, in order to detect a cluster, the cluster interval counter can be compared to a cluster detection threshold that requires a predetermined number of short intervals. In some cases, only one short interval (preceded and followed by a long interval) can be detected as a perception event cluster. In other examples, at least two or at least three short intervals may be required to detect a sensory event cluster, such that at least three sensory events or at least four sensory events are clustered together with a short interval.

[0098] At block 318, the cluster interval counter is compared to a maximum limit so that events occurring at a sustained faster rate are not detected as very long clusters that would result in PWOS detection. Events occurring at a sustained faster rate could be true ventricular tachyarrhythmias. Thus, when the cluster interval counter exceeds the maximum number of short intervals, cluster detection can be canceled at block 328. At block 326, the cluster interval counter is cleared, and control circuit 80 returns to block 302 to repeat the process starting with the next R wave.

[0099] If a cluster is being detected (at box 320), then at box 322, i is incremented by 1, where i is used to identify the next RRI(N+i) interval. At box 312, RRI(N+i) is determined and compared to the short interval threshold at box 314. If RRI(N+i) is not less than the short interval threshold, and a cluster is being detected based on one or more previous short RRIs as determined at box 324, then at box 330, the cluster counter is incremented by one. If a cluster is not being detected, for example, if the cluster interval counter has not been incremented the required number of times based on a comparison of the RRI with the short interval threshold or range, then at box 326, the cluster interval counter is cleared. A cluster of sensing events is not detected, and the cluster interval counter is not incremented. The control circuit 80 returns to box 302 to continue monitoring the RRI.

[0100] If the cluster counter is incremented at block 330, then as previously described, the cluster counter may be incremented at block 330 in the flowchart 200 ( Figure 8 ) at block 208 of the control circuit 80. Once a threshold number of sensory event clusters are identified based on the RRIs, the clustered event waveforms may be analyzed at block 210 to identify a PWOS. In some examples, based on the long and short RRI thresholds or ranges, only one cluster of two sensory events occurring with a short RRI preceded and followed by a long RRI may result in a cluster being detected and the cluster counter reaching the counter threshold at block 208, causing the control circuit 80 to perform additional analysis at block 210 to identify a PWOS.

[0101] Figure 10 It is a kind of Figure 8 Flowchart 400 of a method for analyzing clustered event waveforms at block 210 of FIGURE 400 to identify a sensed event cluster as a PWOS at block 212. After the cluster counter reaches a threshold number of clusters (e.g., 1, 2, 3, 4, 5, or other predetermined number of clusters), analysis of the event waveform for each cluster begins at block 402. The control circuit 80 may receive digitized, filtered, and rectified cardiac electrical currents from the sensing circuit 86, which are buffered in the memory 82 in a circular buffer to be available for waveform analysis when the cluster counter reaches the threshold.

[0102] Each cluster can be defined as starting on a first R-wave perception event signal that defines the start of a first short RRI (N) that is less than a short interval threshold (and defines the end of an immediately preceding long RRI (N-1) that is greater than a long interval threshold). A perception event cluster can also be defined as ending on a last R-wave perception event signal that defines the first RRI (N+i) that is not less than a short interval threshold after the cluster interval counter starts counting short RRIs. Alternatively, a perception event cluster can end on a previous perception event that defines the start of the last short RRI. The last R wave that defines the end of the last short RRI after one or more short RRIs and the start of the first long RRI can be as follows Figure 5A The R wave is shown.

[0103] In one example, the maximum peak amplitude of each sensed event for a given cluster (including a start event and an end event) can be determined during the blanking interval following the crossing of the R-wave sensing threshold. The maximum peak amplitude can be stored in the memory 82 in the circular buffer along with the timing of the corresponding R-wave sensed event signal. When the cluster counter reaches the threshold, the control circuit 80 can determine the largest maximum peak amplitude stored for each corresponding R-wave sensed event during the given cluster at block 402. Alternatively, the largest maximum peak amplitude of all events during the cluster can be determined based on the buffered digitized cardiac electrical signal.

[0104] At block 404, the largest peak amplitude of the sensed event cluster is compared to an amplitude threshold. In some patients, PWOS may be most likely to occur when R-waves of relatively small amplitude occur, resulting in the R-wave sensing threshold starting value being set to a relatively low amplitude, such as Figure 5C As such, one criterion for identifying a cluster of sensed events as PWOS can be that the largest maximum peak amplitude is less than a threshold amplitude, indicating that if the cluster of events includes a true R-wave, it is a smaller amplitude R-wave, and that all sensed events otherwise have amplitudes no greater than the expected P-wave amplitude. The amplitude threshold can be approximately 200 millivolts or set based on determining baseline P-wave and R-wave amplitudes.

[0105] At block 404, the amplitude criterion for identifying a PWOS may require that the largest maximum peak amplitude of all sensed events of the cluster be less than an amplitude threshold. In other examples, a certain percentage or portion of all sensed events of the cluster may be required to be less than the amplitude threshold. For example, if a cluster includes four sensed events, three of the four events may be required to have a maximum amplitude less than the amplitude threshold. Figure 5ANormal R waves may be sensed during the sequence of oversensed P waves shown, for example, when an atrial arrhythmia is occurring and the ventricular rate is slow and / or the ratio of R-wave amplitude to P-wave amplitude is relatively small. As such, the amplitude criteria for detecting PWOS may allow one or more larger amplitude sensed events to occur as long as a predetermined percentage or portion of the sensed event waveform has a maximum amplitude less than an amplitude threshold.

[0106] In other examples, the last sensed event of a cluster of events can be excluded from comparison with the amplitude threshold at block 404. A relatively large amplitude R-wave can reset the starting R-wave sensing threshold to a relatively high value that prevents PWOS on the next heartbeat. The last sensed event of an event cluster that initiates an RRI greater than a short interval threshold, ending a series of short RRIs, can be a true R-wave. As long as all or at least a predetermined portion of the sensed events preceding the last sensed event of the cluster are less than the amplitude threshold, the cluster of sensed events can meet the amplitude criteria required for identifying PWOS at block 404.

[0107] If the amplitude criteria for identifying a PWOS are not met at block 404, the cluster is not identified as a PWOS at block 412. If the amplitude criteria are met, additional waveform morphology analysis can be performed at block 406. In one example, a morphology matching score is determined for each sensed event waveform of the cluster by comparing the waveform to a known R-wave template. The R-wave template can be pre-generated and stored in memory 82, for example, by aligning and averaging multiple R-wave signals acquired during normal sinus rhythm. The waveform of each sensed event can be aligned with the R-wave template, and the difference between each aligned pair of samples can be determined to determine a morphology matching score for each waveform. Various morphology matching algorithms can be used, including wavelet transforms or other transform methods. Examples of methods for generating R-wave templates and determining morphology matching scores are generally disclosed in U.S. Pat. No. 6,393,316 (Gillberg et al.), U.S. Pat. No. 8,825,145 (Zhang et al.), U.S. Pat. No. 8,965,505 (Charlton et al.), and U.S. Pat. No. 8,983,586 (Zhang et al.).

[0108] At block 408, the control circuit 80 determines whether the morphology criteria for identifying a PWOS are met. In one example, the morphology match score for each event of the cluster determined at block 406 is compared to a match threshold. As long as all or a predetermined percentage or number of all perceived event waveforms of the cluster have a match score less than the match threshold, the PWOS morphology criteria are met at block 408. A lower match score indicates a relatively poor correlation between the perceived event waveform and the R-wave template, indicating that the waveform perceived as an R-wave is unlikely to be a true R-wave. For example, if the morphology match score has possible values between 0 and 100, a morphology match score of 30 or less can indicate that the event is unlikely to be a true R-wave. In some cases, at least one true R-wave is expected to occur within the event cluster, such as, for example, Figure 5A In this case, at least one event in the detected perception event cluster may be required to have a morphological matching score greater than a matching threshold, for example, greater than 30, and all remaining events (which may be one or more) may be required to have a morphological matching score less than the threshold.

[0109] If the PWOS morphology criteria are not met at block 408, the cluster of sensed events is not identified as PWOS. The cluster of sensed events may be a true arrhythmia, or may be caused by other cardiac oversensing (e.g., T-wave oversensing) or other non-cardiac oversensing (e.g., oversensing of electromagnetic interference, muscle noise, or other non-cardiac noise). If the PWOS morphology criteria are met at block 408, the cluster of sensed events is identified as PWOS at block 410. This may be repeated for each cluster in the cluster counted toward reaching the cluster threshold. Figure 10 In other examples, after identifying a cluster as a PWOS, clusters of sensory events are identified forward in time. Figure 8 At block 214 of FIG. 1 , each cluster identified as a PWOS is counted, and if the PWOS counter reaches a threshold number of clusters identified as PWOS, then the PWOS counter is closed as described above in conjunction with FIG. Figure 8 As described and in combination with Figure 11 A response to identifying a PWOS is provided as described.

[0110] Figure 11FIG5 is a flow chart 500 of a method performed by the ICD 14 to identify and respond to a PWOS according to one example. At block 502, bradycardia PWOS criteria are established and stored in memory 82 for access by the control circuit 80 when detecting clusters of sensed events and identifying a PWOS during a bradycardia rhythm. At block 504, tachyarrhythmia PWOS criteria are established and stored for use in detecting clusters of sensed events and identifying a PWOS during a tachyarrhythmia. The PWOS may exhibit a different pattern of clusters of sensed events when the heart rhythm is slow during bradycardia than when the heart rhythm is faster during tachycardia or fibrillation.

[0111] For example, when the sensed event pattern is an alternation of over-sensed P waves and sensed R waves in a PRPR pattern, a cluster of sensed events during bradycardia may include a single short RRI that may persist for many cardiac cycles (multiple sequential 2-event clusters) or for a number of cardiac cycles with a series of correctly sensed R waves at normal RRIs and no over-sensed intermediate cardiac cycles. During faster sensed heart rates, for each true R wave, multiple P waves may be over-sensed with zero, one, or more true R waves sensed between the sensed event clusters. Thus, two or more different sets of PWOS detection criteria may be defined, including: different short and / or long interval thresholds for detecting clustered events, the number of short intervals required to detect a cluster, the number of sensed event clusters that need to be identified before analyzing the sensed event waveform, amplitude and / or morphology criteria for identifying PWOS in a sensed event cluster, and / or the number of clusters identified as PWOS required to provide a response to PWOS. Different criteria can be defined for detecting PWOS in the presence of bradycardia, in the presence of tachyarrhythmias, in the presence of AV block, or other conditions that the patient may know or anticipate experiencing, and these criteria may influence the pattern of perceived events during PWOS.

[0112] After establishing at least two different sets of criteria (which may include establishing thresholds, R-wave templates, and other criteria based on analysis of the patient's cardiac electrical signals), the control circuit 80 monitors the sensed event clusters according to these two (or more) sets of PWOS criteria. In order to detect different PWOS patterns, the sensed event signals and cardiac electrical signal waveforms can be monitored for the sensed event clusters simultaneously according to multiple PWOS criteria. Alternatively, the sensed event frequency can be used to determine which set of PWOS criteria is being actively used. For example, if the sensed event frequency for more than a predetermined number of sensed events (such as the most recent 8, 12, 18, 22, or other number of sensed events) is greater than the tachyarrhythmia detection frequency, the PWOS criteria for tachyarrhythmias established at box 504 are used. For example, if the running average RRI is less than 500 ms, less than the tachycardia detection interval, or if the tachyarrhythmia interval detection counter is greater than a predetermined number (such as 3), the tachyarrhythmia PWOS criteria are used. The bradycardia PWOS criteria may be used if the heart rate is less than 120 beats per minute or the running average RRI is longer than the tachycardia detection interval and / or the tachyarrhythmia interval detection counter is inactive (counts zero).

[0113] If PWOS is detected according to the bradycardia PWOS criteria, the "yes" branch at box 510 may provide one or more PWOS responses at boxes 512, 514, and / or 516. In response to identifying PWOS based on the bradycardia PWOS criteria, bradycardia pacing may be enabled at box 512. A triggered pacing mode (e.g., a VVT pacing mode) may be initiated to enable ventricular pacing at a rate faster than the intrinsic heart rate, and the triggered pacing mode may be triggered starting with the next sensed event, which may be a P wave or an R wave. The triggered pacing pulse is delivered by the therapy delivery circuit within the physiological refractory period of the sensed event, for example, within 100 ms or no more than 200 ms of the sensed event, without setting a pacing escape interval when the event is sensed.

[0114] An inhibited pacing mode (e.g., a VVI pacing mode) can be initiated at box 512, during which the sensed event signal inhibits the scheduled pacing pulse only when the sensed event is confirmed to be an R wave. In the inhibited pacing mode, a pacing escape interval is initiated at each sensed event (which occurs outside of any device blanking period or refractory period). If the pacing escape interval expires without being restarted due to another sensed event, a pacing pulse is scheduled for delivery. When PWOS is identified and bradycardia pacing is enabled, R-wave sensed event confirmation can be enabled at box 512 as part of bradycardia pacing control. Before restarting the pacing escape interval in response to the sensed event, one or more morphological features can be determined to confirm each sensed event as an R wave. For example, the peak amplitude, positive slope, morphology match score, or other morphological features of each sensed event can be determined and compared to R-wave confirmation criteria. If the sensed event is confirmed to be an R-wave based on confirmation criteria being met, the ongoing pacing escape interval is restarted in response to the confirmed R-wave, thereby stopping the scheduled pacing pulse at the expiration of the escape interval. If the sensed event is not confirmed to be an R-wave, the ongoing pacing escape interval is not restarted, but is allowed to continue running until either the sensed event is confirmed to be an R-wave and the pacing escape interval is restarted, or the pacing escape interval expires and the scheduled pacing pulse is delivered, whichever occurs first.

[0115] Alternatively or additionally, one or more parameters controlling the R-wave sensing threshold may be adjusted at block 514. For example, the R-wave sensing threshold starting value may be increased, the decay rate may be decreased, the time interval during which the sensing threshold drops to a lower value may be increased, the minimum sensing threshold may be increased, or other parameters may be adjusted to effectively increase the R-wave sensing threshold when a P-wave is expected to avoid PWOS in a subsequent heartbeat.

[0116] If PWOS is not being identified based on bradycardia PWOS criteria but is being identified based on tachyarrhythmia PWOS criteria, the "yes" branch at box 518, the ICD 14 may provide one or more responses to the identification of PWOS. For example, if tachyarrhythmia episode detection is ongoing, as determined at box 520, then detection of tachyarrhythmia episodes may be discontinued and / or VT or VF therapy may be discontinued at box 522. Tachyarrhythmia episode detection may be determined at box 520 if at least one tachyarrhythmia detection interval counter (e.g., a counter for counting the number of RRIs that fall within a tachycardia interval or a counter for counting the number of RRIs that fall within a fibrillation interval) is active, e.g., has a count greater than zero or another predetermined count.

[0117] Whenever PWOS is identified, control circuitry 80 may respond at block 514 by adjusting the R-wave sensing threshold control parameter to reduce the likelihood of P-wave oversensing in the future. At block 516, data related to the identified PWOS may be stored in memory 82 for transmission to external device 40 via telemetry circuitry 88. Figure 1A ), the ICD 14 can respond to it whenever PWOS is identified. The stored data can include cardiac electrical signals including one or more clusters of sensed events identified as PWOS, RRI data, morphology data, subsequent therapies that were delivered or withheld, etc. The storage and transmission of data related to the identified PWOS can enable the clinician to adjust programmed sensing parameters, PWOS detection criteria, tachyarrhythmia detection criteria, bradycardia pacing control parameters, and / or tachyarrhythmia therapy control parameters to optimize the performance of the ICD 14 in reliably determining cardiac rhythms and delivering or withholding therapy as needed.

[0118] Figure 12 is a flow chart of a method for identifying PWOS by ICD 14 according to another example. At block 602, a sense event signal generated by sensing circuit 86 is received by control circuit 80. When the sense event signal is received, the maximum peak amplitude of each sense event is determined at block 604. In some examples, the blanking interval begins when the cardiac electrical signal crosses the R-wave sensing threshold, such as Figure 5B The control circuit 80 can determine the maximum sampling point amplitude during the blanking interval 172 as the maximum peak amplitude of the corresponding perception event.

[0119] At block 606, the control circuitry 80 determines a morphology matching score for each sensed event based on an implemented morphology matching scheme, such as any of the examples provided above and in the references cited above. The morphology matching score is determined for each sensed event by comparing a waveform morphology feature, or one or more morphology features, of the cardiac signal waveform corresponding to the respective sensed event with a predetermined normal R-wave morphology template or normal R-wave features.

[0120] At block 608, the sensed event interval is determined as the time interval between two consecutive sensed event signals received at block 602. It should be appreciated that when the process of flowchart 600 is first initiated, a sensed event interval that ends on the initial event sensed by sensing circuit 86 will not be determined because the immediately preceding sensed event will not exist. Therefore, the initial time stamp of the first sensed event can be set using the initial event sensed by ICD 14 to enable determination of the first sensed event interval that ends with the second sensed event signal at block 608. The sensed event intervals determined at block 608 may be referred to herein as "RRIs" because they are determined based on R-wave sensed event signals, but the sensed event intervals may not be true "RRIs" because one (or both) of the two sensed events defining the start and end of the sensed event interval may not be true R waves. For example, one or both of the two sensed events may be an over-sensed P wave or other over-sensed event.

[0121] These parameters (event magnitude, event morphology, and inter-event duration) may be determined for each sensed event at blocks 604, 606, and 608 and stored in memory 82 at block 610. These three parameters determined for each sensed event may be used to determine whether the sensed event likely includes a PWOS based on the determined pattern of consecutive event magnitudes, event morphologies, and inter-event durations of sensed events.

[0122] At block 612, the control circuit 80 performs a comparative analysis of the perceived event parameters. In some examples, the event parameters for each event are first compared to a predetermined amplitude threshold, a predetermined morphology matching threshold, and a predetermined RRI threshold. In other examples, similar event parameters determined for each perceived event can be compared to each other. A comparative analysis is performed to determine whether the parameter values for consecutive perceived events represent a possible PWOS pattern. For example, a comparative analysis can be performed to determine whether consecutive perceived events include multiple groups of events that exhibit an alternating pattern of low and high amplitudes, R-wave and non-R-wave morphologies, and / or short and long RRIs (which would be evidence of an alternating pattern of over-perceived P waves and true R waves).

[0123] In one example, at block 612, the maximum peak amplitude determined for each sensed event can be compared to a maximum P-wave amplitude threshold (e.g., 1.5 mV). The maximum P-wave amplitude threshold can be a predetermined value based on empirical data or selected for the patient based on actual P-wave peak amplitude measurements (and / or R-wave peak amplitude measurements). If the event amplitude is less than the maximum P-wave amplitude threshold, the event can be labeled or marked as a low-amplitude event, "L." If the event amplitude is greater than the maximum P-wave amplitude threshold, the event can be labeled or marked as a high-amplitude event, or "H."

[0124] At block 612, each sensed event interval can be compared to an RRI threshold. The RRI threshold can be a predetermined minimum event interval that is considered a valid RRI when no tachyarrhythmia is occurring, such as 300 ms. If the sensed event interval is less than the RRI threshold, the sensed event interval can be labeled as short or "S," and otherwise labeled as long or "L."

[0125] Additionally or alternatively, at block 612, the morphology match score for each event can be compared to an R-wave match threshold. For example, when the maximum possible match score is 100, the R-wave match threshold can be 30. If the morphology match score is less than the R-wave match threshold, the event can be labeled or marked as having a non-matching morphology, or "N," indicating that the perceived event is unlikely to be an R-wave. If the morphology match score is greater than 30, the event can be labeled or marked as having a matching morphology, "M," indicating that the perceived event is likely a true R-wave. Once at least three consecutive sensed events have been labeled based on the three event parameters of amplitude, morphology, and the perceived event interval between occurrences of the events, the three labels can be compared to determine, at block 614, whether a pattern of events indicative of PWOS is present.

[0126] Figure 14 FIG7 is a timing diagram 700 of a sense event signal 702 that may be generated by the sensing circuit 86 and received by the control circuit 80. The sense event signal 702 arrives at a plurality of sense event clusters 711, 712, 713, 714, 715, and 716. Each cluster includes at least one over-sense P wave (e.g., cluster 713) or a plurality of over-sense P waves (e.g., cluster 714).

[0127] In response to each sensed event, the control circuit 80 analyzes the digitized cardiac electrical signal and the time interval between consecutive sensed event signals to determine the maximum absolute peak amplitude, morphology matching score and sensed event interval of each event, as described above in conjunction with Figure 12 The control circuit 80 may then label each event as having a high (H) or low (L) amplitude 704, a non-matching (N) or matching (M) morphology match score (MMS) 706, and as an end event labeled as a short (S) or long (L) RRI 708. This event parameter labeling may be based on comparisons with predetermined thresholds, as described above in conjunction with Figure 12 described.

[0128] Alternatively, event labels can be determined based on comparing event parameters to each other. For example, the perception event signal can be analyzed as a pair of two consecutive events, three consecutive events, or multiple groups of three or more consecutive perception events (such as a group of four consecutive perception events 720). The event with the highest amplitude within the group of consecutive perception events can be identified, and the amplitude of each other event can be compared with the highest amplitude. Other event amplitudes that are less than a predetermined percentage of the highest amplitude are labeled "L" for low amplitude. Other event amplitudes that are greater than a predetermined percentage of the highest event amplitude are labeled "H" for high amplitude.

[0129] The highest morphology match score can be identified and compared to the morphology match scores of each other sensed event in a selected set of consecutive events (e.g., set 720). If the other morphology match scores are greater than a predetermined percentage of the highest morphology match score, the corresponding event is labeled "M" to indicate a morphology that is likely an R-wave. Any event in the selected set having a morphology match score that is less than a predetermined percentage of the highest morphology match score is labeled as a non-match or "N."

[0130] The longest RRI of a selected set of sensory events can be identified and compared to the other RRIs of the selected set. Events that end with an RRI that is at least a predetermined percentage of the longest RRI are labeled "L" (long). Events that end with an RRI that is less than a predetermined percentage of the longest RRI are labeled "S" (short).

[0131] In some examples, perceived events can be labeled based on a combination of comparisons of event parameters to predetermined thresholds and comparisons of event parameters to each other. For example, the RRI can be compared to a predetermined threshold to label an event as occurring with a long or short interval. The highest morphology match score can be determined, and as long as it is greater than a predetermined threshold, the corresponding event can be labeled M (matched to R-wave morphology). Other event morphology match scores can be compared to the same predetermined threshold or to a certain percentage of the highest morphology match score. The maximum peak amplitude of the perceived event with the highest morphology match score can be determined, and the maximum P-wave sensing threshold can be set to a certain percentage of the maximum peak amplitude. The maximum peak amplitude of other perceived events of a selected set of events can be compared to the maximum P-wave sensing threshold determined based on the maximum amplitude of the event with the highest morphology match score. Events with a peak amplitude less than the P-wave sensing threshold are labeled "L", and events with a peak amplitude greater than the P-wave sensing threshold are labeled "H". It should be understood that other variations or combinations of comparisons of event parameters to each other and / or to predetermined thresholds can be contemplated and utilized to label sensed events as being relatively low or high in amplitude, as having a relatively low R-wave morphology match score or a relatively high R-wave morphology match score, and / or as ending on a relatively short RRI or a relatively long RRI. Event labeling allows the control module 80 to determine whether a PWOS pattern is present.

[0132] Event tags for the amplitude 704, morphology match score (MMS) 706, and RRI 708 parameters are shown in the timing diagram 700 for each sensory event signal 702. The control circuit 80 can analyze the sensory event tags for the amplitude 704, MMS 706, and RRI 708 in multiple sets of four sensory events in progress to identify alternating patterns of LHL amplitude, NMN morphology match score, and SLS RRI. For example, the first set of four sensory events 720 is selected for pattern analysis, and each of the parameters of amplitude, MMS, and RRI is determined for each of these events. For the initial sensory event signal 701, the RRI is not determined. As such, a set of four consecutive sensory events 720 allows the first three amplitude and morphology tags of the set of four sensory events to be examined, and the last three event interval tags to be examined for an alternating PWOS pattern.

[0133] The amplitude labels and MMS labels of the first three sensory event signals of the first set of four sensory events 720 are shown in dashed boxes 705 and 707, respectively. The patterns of the amplitude labels and MMS labels are analyzed to determine whether the first three sensory events of the set of four sensory events 720 occur in an alternating LHL and NMN pattern, respectively.

[0134] The RRI tags of the last three perception events of the group of four perception events 720 are shown in the dashed box 709. The RRI tags of the last three perception events of the group of four perception events 720 correspond to the three corresponding RRIs starting with the first three perception events of the group of four perception events 720. For the alternating mode of SLS, the control circuit 80 analyzes the RRI tags of the last three perception events of the group of four perception events 720.

[0135] As in Figure 14 As can be seen in the example of , the first group of four sensory events 720 meets the criteria of the LHL amplitude pattern of the first three sensory events, the NMN morphology matching score pattern of the first three sensory events, and the SLS pattern of the RRI labels of the last three sensory events. As such, this group of four sensory events 720 is identified by the control circuit 80 as evidence of the sensory event cluster 711 (and 712). In this example, the evidence of the LHL amplitude pattern, the NMN morphology pattern, and the SLS RRI pattern corresponds to the last short interval of the sensory event cluster 711, the first short interval of the sensory event cluster 712, and the intermediate long sensory event interval 703 separating the two sensory event clusters 711 and 712. In response to identifying the evidence of the sensory event clusters 711 and 712, the PWOS cluster interval counter included in the control circuit 80 can be increased by 1. When the count of the PWOS cluster interval counter reaches a threshold, the control circuit 80 can provide a PWOS response, for example, in combination with the above. Figure 8 and Figure 11 And the following combination Figure 13 Any response described.

[0136] After determining whether the first group of four sensory event intervals 720 exhibits a PWOS pattern as evidence of a sensory event cluster, the control module 80 can advance the sensory event signal by one to the next group of four sensory events for analysis of the next group of four consecutive sensory events, which in this example exhibit an HLL amplitude pattern, an MNN morphological matching score pattern, and an LSS RRI pattern. The next group of four sensory events is not appropriately identified as evidence of a new sensory event cluster because these events are still part of sensory event clusters 711 and / or 712. In some examples, when a group of four sensory events is identified as evidence of a sensory event cluster, the control module 80 can advance two sensory events, rather than just one, to select the next group of four sensory events for analysis for a PWOS pattern. Advancing by only one sensory event may result in the selection of four sensory events that still occur within the same two sensory event clusters that were just identified.

[0137] This process of selecting multiple groups of four consecutive sensory events and analyzing the amplitude labels, MMS labels, and RRI labels can continue until a threshold number of these groups of four sensory events are identified as evidence of sensory event clusters. In the example shown, the groups of four sensory events 720, 722, 724, 726, and 728 are each identified as evidence of sensory event clusters 711 to 716 based on the LHL amplitude pattern, NMN MMS pattern, and SLS RRI pattern (each of which is highlighted by a corresponding dashed box for each group of four sensory events 720 to 728).

[0138] In each case, the perception event clusters 701 to 716 are identified based on the last short interval of a cluster, the first short interval of the immediately following cluster, and the intermediate long RRIs. This analysis performed by the control circuit 80 identifies the perception event clusters 711 to 716 regardless of the number of over-perception events and short RRIs that occur within each cluster 711 to 716. Figure 14 As shown in , when the number of oversensing events and short RRIs within each cluster is variable, the presence of a cluster of sensing events is still identified without detecting a threshold number of short RRIs within the cluster. Figure 5B 、 Figure 5C 、 Figure 6 and Figure 7 As shown in the various examples of FIG, PWOS patterns can vary between patients and within a given patient. Figure 12 and Figure 14 A technique is presented to identify clusters of perceived events due to PWOS without first knowing the expected or predicted number of events within the event cluster when PWOS occurs.

[0139] return Figure 12 If, based on the comparison performed at block 612, the sense event parameters do not meet the PWOS mode criteria, the “NO” branch of block 614, then when the next sense event signal is received from the sensing circuit 86, the control circuit 80 proceeds to block 616 to determine and store the next set of sense event parameters.

[0140] If the comparison of the sensed event parameters performed at block 612 does satisfy the PWOS pattern criteria, the "yes" branch of block 614 allows detection of sensed event clusters at block 618. The PWOS pattern criteria may require alternating patterns of all three sensed event parameters determined for multiple groups of consecutive events, such as in combination with Figure 14As described. In some cases, in order to meet the PWOS pattern criteria at block 614, two of the three perception event parameters may be required to exhibit an alternating pattern. For example, if the set of four consecutive perception events exhibits at least two of the LHL amplitude pattern, the NMN morphology match score pattern, and the SLS RRI pattern, the PWOS pattern criteria may be met at block 614. In some cases, as long as the SLS RRI pattern is detected, either the LHL amplitude pattern or the NMN morphology match score pattern (or both) will meet the PWOS pattern criteria at block 614. In still other examples, at block 614, an alternating pattern of only one of the three perception event parameters within the set of four consecutive perception events may meet the PWOS pattern criteria.

[0141] exist Figure 12 In the example shown, if the PWOS mode criteria are met a single time, a cluster of sensing events is detected at block 618, and the control circuit 80 enables R-wave confirmation for controlling therapy delivery at block 620. In other examples, a threshold number of sensing event cluster detections may be required based on multiple times that the PWOS mode criteria are met before enabling R-wave confirmation at block 620.

[0142] Figure 13 is a continuation of the flowchart 600. If Figure 12 If R wave confirmation is enabled at block 620 of Figure 14 The control circuit 80 proceeds to block 652 (as indicated by connector "B") to wait for the next sensing event signal at block 652. Figure 12 and Figure 14 The monitoring of PWOS described above is switched to Figure 13 The method of FIG. 80 is shown to perform R wave confirmation to identify PWOS events on a beat-by-beat basis and reduce the possibility of inappropriate therapy withholding or delivery due to PWOS. As indicated by block 651, the pacemaker timing and control circuit system of the control circuit 80 may run the escape interval timer or counter that was started when the immediately preceding sensed event signal was detected. As described above in conjunction with Figure 4 As described above, an escape interval timer can be started to count down the pacing time interval to control the timing of pacing pulse delivery. The escape interval timer can be restarted in response to a sense event signal from the sensing circuit 86, and the timer value can be used to determine the sense event interval since the immediately preceding sense event. The sense event interval can be used as described in conjunction with Figure 12 and Figure 14 The described PWOS detection can also be used to detect tachyarrhythmias, for example, based on VT and VF detection algorithms.

[0143] At block 654, the control circuit 80 determines the maximum peak amplitude of the current sensed event sensed at block 652 after enabling R-wave confirmation. At block 656, the peak amplitude is compared to the P-wave amplitude threshold. If the peak amplitude of the sensed event is less than the P-wave amplitude threshold ("yes" branch of block 656), the control circuit 80 may identify the sensed event as a PWOS event at block 658, or at least not confirm the sensed event as an R-wave. Resetting of the currently running escape interval is stopped at block 660. The currently running escape interval timer is allowed to continue running at block 651 without being reset due to the sensed event signal. In this manner, the PWOS event does not interfere with the scheduling and timing of pacing pulses or the detection of tachyarrhythmias.

[0144] For example, a bradycardia pacing escape interval may be initiated by the control circuit 80 in response to the most recent previous sensed event signal. This ongoing escape interval is allowed to continue running without being reset so that a PWOS event does not prevent bradycardia pacing when bradycardia pacing is required. PWOS does not cause the escape interval to be reset, which could result in an erroneous RRI determination that may be less than the pacing interval and cause cessation of pacing pulses, or the erroneous RRI may be in the tachycardia or fibrillation interval range and result in an erroneous tachyarrhythmia detection.

[0145] If the peak amplitude is greater than the P-wave amplitude threshold, the "No" branch at block 656 is taken, and the sensed event is confirmed to be an R-wave at block 662. In response to confirming the R-wave, the pacing escape interval timer is reset at block 664. It should be understood that when the escape interval timer is reset, the time that expires on the escape interval timer is used to determine the RRI that ends on the confirmed R-wave, and this RRI can be used by the tachyarrhythmia detection algorithm implemented in the ICD 14. It should also be understood that if the escape interval expires before the confirmed R-wave causes the escape interval to be restarted, a pacing pulse can be delivered by the ICD 14.

[0146] In some examples, the control circuit 80 may determine whether a PWOS event has not been identified for a predetermined maximum time period at block 666. If a PWOS has not been identified for a predetermined maximum time period (e.g., 1 minute, 5 minutes, 1 hour, 24 hours, or other desired period), the control circuit may return to the default state by returning to the default state. Figure 12 The process switches back to PWOS monitoring mode (as indicated by connector "A") at block 602. In this manner, if PWOS has not been detected for a predetermined maximum time interval that is set to control how long R-wave confirmation occurs on a beat-by-beat basis in the absence of PWOS detection, then no beat-by-beat confirmation of the R-wave occurs.

[0147] Alternatively, before or after enabling R-wave confirmation, if at least one PWOS is detected, the ICD 14 may remain in a monitoring mode in which all sensed events are analyzed to confirm whether the event is a true R-wave until the ICD 14 is reprogrammed by the user. In some examples, the ICD 14 may be entered directly at block 652 as in conjunction with Figure 13 The R wave pattern described does not need to be combined with Figure 12 PWOS monitoring was performed as described.

[0148] Only PWOS monitoring mode is enabled ( Figure 12 ), enable only R-wave confirmation mode ( Figure 13 ) and enable PWOS monitoring mode by automatically switching to R-wave confirmation mode ( Figure 12 and Figure 13 A combination of (a) and (b) may be a user programmable feature of the ICD 14. When enabled in response to identifying one or more predetermined number of sensory event clusters, the sensory event cluster may be activated. Figure 12 and Figure 14 In the described PWOS monitoring mode without automatically switching to the R-wave confirmation mode, the ICD 14 may respond to identification of a predetermined number of clusters of sensed events during the monitoring mode by recording cardiac electrical signal segments that include the identified PWOS, adjusting R-wave sensing threshold control parameters, discontinuing tachyarrhythmia episode detection and / or treatment, delivering one or more triggered pacing pulses to provide bradycardia pacing support, if needed, within the physiological refractory period of one or more corresponding sensed events, or any combination of these responses or other PWOS responses described herein.

[0149] Thus, in the foregoing description, a method and apparatus for identifying and responding to PWOS in an extracardiovascular ICD system has been presented with reference to specific examples. In other examples, the various methods described herein may include steps performed in a different order or combination than the illustrative examples shown and described herein. It should be understood that various modifications may be made to the referenced examples without departing from the scope of the present disclosure and the following claims.

Claims

1. A medical device comprising: A sensing circuit configured to: Receive cardiac electrical signals, and sensing a first plurality of consecutive cardiac events from the cardiac electrical signals; A control circuit configured to: determining at least one sensed event parameter for each of the first plurality of consecutive cardiac events; determining that the at least one sensed event parameter determined for each of the first plurality of consecutive cardiac events satisfies a P-wave oversensing criterion; determining, based on satisfying the P-wave oversensing criteria, that at least one of the first plurality of consecutive cardiac events corresponds to a P-wave that was incorrectly sensed by the sensing circuit as an R-wave; determining one or more ventricular tachyarrhythmia intervals from the cardiac electrical signal; as well as responsive to determining that at least one of the first plurality of consecutive cardiac events corresponds to a P wave that was erroneously sensed as an R wave, suppressing ventricular tachyarrhythmia detection based on the one or more ventricular tachyarrhythmia intervals; as well as Therapy delivery circuitry is configured to deliver electrical stimulation therapy when the control circuitry detects a ventricular tachyarrhythmia.

2. The medical device according to claim 1, wherein The control circuit is further configured to: determining the at least one sensed event parameter by determining a maximum peak amplitude of each of the first plurality of consecutive cardiac events; comparing the maximum peak amplitude to the P-wave oversensing criterion; as well as Satisfaction of the P-wave oversensing criterion is determined based at least on the maximum peak amplitude.

3. The medical device according to claim 1, wherein The control circuit is further configured to: determining the at least one sensed event parameter by determining a morphology matching score of each of the first plurality of consecutive cardiac events to a predetermined R-wave template; comparing the morphology matching score to the P-wave oversensing criterion; as well as The P-wave oversensing criterion is determined to be satisfied based at least on the morphology matching score.

4. The medical device according to claim 1, wherein The control circuit is further configured to: The at least one perception event parameter is determined by: determining a morphology matching score for each of the first plurality of consecutive cardiac events to a predetermined R-wave template; as well as determining a maximum peak amplitude for each of the first plurality of consecutive cardiac events; identifying an alternating pattern of the morphology matching scores and an alternating pattern of the maximum peak amplitudes; as well as Satisfaction of the P-wave oversensing criterion is determined based at least on the alternating pattern of the morphology match scores and the alternating pattern of the maximum peak amplitudes.

5. The medical device according to claim 1, wherein The control circuit is further configured to: determining the at least one sensed event parameter by determining an inter-event interval for each of the first plurality of consecutive cardiac events; comparing the event interval to the P wave oversensing criterion; as well as The P-wave oversensing criterion is satisfied based on at least the event interval.

6. The medical device according to claim 1, wherein The control circuit is further configured to determine that the P-wave oversensing criterion is satisfied based at least on the event interval by: determining that at least a first one of the inter-event intervals is less than a first time interval threshold; as well as A second one of the inter-event intervals is determined to be greater than a second time interval threshold.

7. The medical device according to claim 1, wherein The control circuit is further configured to: determining a sensing event interval from the cardiac electrical signal; determining that at least a threshold number of the sensed event intervals fall within a tachyarrhythmia interval region; and In response to determining that at least the threshold number of the sensed event intervals fall within the tachyarrhythmia interval region, the at least one sensed event parameter is compared to the P-wave oversensing criterion.

8. The medical device according to claim 1, wherein The control circuit is further configured to: responsive to the at least one sensed event parameter determined for each of the first plurality of consecutive cardiac events satisfying the P-wave oversensing criterion, incrementing a P-wave oversensing cluster count; determining that the P-wave oversensing cluster count reaches a threshold; as well as In response to determining that the P wave oversensing cluster count reaches the threshold, the ventricular tachyarrhythmia detection is suppressed.

9. The medical device according to claim 8, wherein: The sensing circuit is further configured to sense a second plurality of consecutive cardiac events from the cardiac electrical signal, the second plurality of consecutive cardiac events overlapping with the first plurality of consecutive cardiac events; and The control circuit is further configured to: determining that the second plurality of consecutive cardiac events meets the P-wave oversensing criteria; and In response to the second plurality of consecutive cardiac events satisfying the P-wave oversensing criteria, the P-wave oversensing cluster count is incremented.

10. The medical device according to claim 1, wherein: The sensing circuit is further configured to: adjusting the R-wave sensing threshold according to at least one control parameter; and sensing the first plurality of consecutive cardiac events based on the R-wave sensing threshold adjusted according to the at least one control parameter; and The control circuit is further configured to adjust the at least one control parameter in response to determining that at least one of the first plurality of consecutive cardiac events corresponds to a P wave that was incorrectly sensed as an R wave.

11. A method for identifying and responding to P-wave oversensing, the method comprising: Receiving cardiac electrical signals by a sensing circuit; sensing, by the sensing circuit, a first plurality of consecutive cardiac events from the cardiac electrical signal; for each of said first plurality of consecutive cardiac events, determining at least one sensed event parameter; determining that the at least one sensed event parameter determined for each of the first plurality of consecutive cardiac events satisfies a P-wave oversensing criterion; determining, based on satisfying the P-wave oversensing criteria, that at least one of the first plurality of consecutive cardiac events corresponds to a P-wave that was incorrectly sensed by the sensing circuit as an R-wave; determining one or more ventricular tachyarrhythmia intervals from the cardiac electrical signal; as well as In response to determining that at least one of the first plurality of consecutive cardiac events corresponds to a P wave that was incorrectly sensed as an R wave, ventricular tachyarrhythmia detection is suppressed based on the one or more ventricular tachyarrhythmia intervals.

12. The method of claim 11, further comprising: determining the at least one sensed event parameter by determining a maximum peak amplitude of each of the first plurality of consecutive cardiac events; comparing the maximum peak amplitude to the P-wave oversensing criterion; as well as Satisfaction of the P-wave oversensing criterion is determined based at least on the maximum peak amplitude.

13. The method of claim 11, further comprising: determining the at least one sensed event parameter by determining a morphology matching score of each of the first plurality of consecutive cardiac events to a predetermined R-wave template; comparing the morphology matching score to the P-wave oversensing criterion; as well as The P-wave oversensing criterion is determined to be satisfied based at least on the morphology matching score.

14. The method of claim 11, further comprising: The at least one perception event parameter is determined by: determining a morphology matching score for each of the first plurality of consecutive cardiac events to a predetermined R-wave template; as well as determining a maximum peak amplitude for each of the first plurality of consecutive cardiac events; identifying an alternating pattern of the morphology matching scores and an alternating pattern of the maximum peak amplitudes; as well as Satisfaction of the P-wave oversensing criterion is determined based at least on the alternating pattern of the morphology match scores and the alternating pattern of the maximum peak amplitudes.

15. The method of claim 11, further comprising: determining the at least one sensed event parameter by determining an inter-event interval for each of the first plurality of consecutive cardiac events; comparing the event interval to the P wave oversensing criterion; as well as The P-wave oversensing criterion is satisfied based on at least the event interval.

16. The method according to claim 11, wherein Determining that the P-wave oversensing criterion is satisfied based at least on the event interval includes: determining that at least a first one of the inter-event intervals is less than a first time interval threshold; and A second one of the inter-event intervals is determined to be greater than a second time interval threshold.

17. The method of claim 11, further comprising: determining a sensing event interval from the cardiac electrical signal; determining that at least a threshold number of said sensed event intervals fall within a tachyarrhythmia interval region; as well as In response to determining that at least the threshold number of the sensed event intervals fall within the tachyarrhythmia interval region, the at least one sensed event parameter is compared to the P-wave oversensing criterion.

18. The method of claim 11, further comprising: responsive to the at least one sensed event parameter determined for each of the first plurality of consecutive cardiac events satisfying the P-wave oversensing criterion, incrementing a P-wave oversensing cluster count; determining that the P-wave oversensing cluster count reaches a threshold; as well as In response to determining that the P wave oversensing cluster count reaches the threshold, the ventricular tachyarrhythmia detection is suppressed.

19. The method of claim 18, further comprising: sensing a second plurality of consecutive cardiac events from the cardiac electrical signals, the second plurality of consecutive cardiac events overlapping with the first plurality of consecutive cardiac events; determining that the second plurality of consecutive cardiac events meets the P-wave oversensing criteria; as well as In response to the second plurality of consecutive cardiac events satisfying the P-wave oversensing criteria, the P-wave oversensing cluster count is incremented.

20. The method of claim 11, further comprising: adjusting an R-wave sensing threshold according to at least one control parameter; sensing the first plurality of consecutive cardiac events based on the R-wave sensing threshold adjusted according to the at least one control parameter; as well as In response to determining that at least one of the first plurality of consecutive cardiac events corresponds to a P wave that was incorrectly sensed as an R wave, the at least one control parameter is adjusted.

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