Reduction of oversensing related short interval counts in medical devices

Abstract

Example systems, devices, and techniques are disclosed. An example system includes an implantable medical device (IMD) configured to obtain the cardiac EGM of the patient. The IMD is configured to determine, based on the cardiac EGM, a first event and a second ventricular event. The IMD is configured to determine a first time interval between the first event and the second ventricular event satisfies a first time interval threshold, indicating a short interval event pair. The IMD is configured to determine whether the short interval event pair is a result of oversensing. The IMD is configured to increment or refrain from incrementing a counter based on the determination of whether the short interval event pair is the result of oversensing. The IMD is configured to determine, based at least in part on a count of the counter, whether to send a lead integrity alert.

Description

REDUCTION OF OVERSENSING RELATEDSHORT INTERVAL COUNTS IN MEDICAL DEVICES

[0001] This application claims the benefit of U.S. Provisional Patent Application Serial No. 63 / 675,837, filed July 26, 2024, the entire content of which is incorporated herein by reference.TECHNICAL FIELD

[0002] The disclosure relates generally to medical device systems and, more particularly, cardiac monitoring by medical devices.BACKGROUND

[0003] Some types of implantable medical devices, such as cardiac pacemakers or implantable cardioverter defibrillators, provide electrical therapy to a heart of a patient via electrodes of one or more implantable leads. The electrical therapy may be delivered to the heart in the form of pulses for pacing or shocks for cardioversion or defibrillation. In some cases, an implantable medical device may sense the presence arrhythmias of the heart and control the delivery of electrical therapy to the heart based on the sensing. Other medical devices may detect arrhythmias, but do not themselves deliver responsive therapy.SUMMARY

[0003] In general, this disclosure describes example techniques related to determining whether a sensed arrythmia episode or detected rhythms leading up to an episode is a true arrhythmia episode detection or a false arrhythmia episode detection due to oversensing and, in some examples, controlling the delivery of therapy based on the determination. Oversensing can be a problem with implantable cardiac devices like ICDs. For example, ICDs that use with integrated bipolar electrodes, which are more widely separated than traditional dedicated short bipole sensing electrodes, are more vulnerable to receiving far- field electrical activity (e.g., P-waves) which may lead to oversensing and possible overdetection of arrythmia episodes. Implantable or external defibrillators and / or monitors including cutaneous, subcutaneous, substemal, and / or extravascular electrodes may be similarly vulnerable to receiving far-field electrical activity. Therefore, it may be desirableto discriminate or detect oversensing in a detected tachyarrhythmia episode in such devices, especially when detecting on-device (e.g., on the ICD), to avoid delivery of inappropriate therapy.

[0004] In one example, this disclosure describes a system comprising: sensing circuitry configured to sense a cardiac electrogram (EGM) of a patient; and processing circuitry configured to: obtain the cardiac EGM of the patient; determine, based on the cardiac EGM, a first ventricular event; determine, based on the cardiac EGM, a second ventricular event; determine a first time interval between the first ventricular event and the second ventricular event; determine that the first time interval satisfies a first time interval threshold; determine, based on the first time interval satisfying the first time interval threshold, that the first ventricular event and the second ventricular event are a short interval event pair; determine whether the short interval event pair is a result of oversensing; increment or refrain from incrementing a counter based on the determination of whether the short interval event pair is the result of oversensing; and determine, based at least in part on a count of the counter, whether to send a lead integrity alert.

[0005] In another example, this disclosure describes a method comprising: sensing, by sensing circuitry, a cardiac electrogram (EGM) of a patient; obtaining, by processing circuitry, the cardiac EGM of the patient; determining, by the processing circuitry and based on the cardiac EGM, a first ventricular event; determining, by the processing circuitry and based on the cardiac EGM, a second ventricular event; determining, by the processing circuitry, a first time interval between the first ventricular event and the second ventricular event; determining, by the processing circuitry, that the first time interval satisfies a first time interval threshold; determining, by the processing circuitry and based on the first time interval satisfying the first time interval threshold, that the first ventricular event and the second ventricular event are a short interval event pair; determining, by the processing circuitry, whether the short interval event pair is a result of oversensing; incrementing or refraining from incrementing, by the processing circuitry, a counter based on the determination of whether the short interval pair is the result of oversensing; and determining, by the processing circuitry and based at least in part on a count of the counter, whether to send a lead integrity alert.

[0006] In another example, this disclosure describes an implantable medical device comprising: An implantable medical device comprising: sensing circuitry configured tosense a cardiac electrogram (EGM) of a patient; and processing circuitry configured to: obtain the cardiac EGM of the patient; determine, based on the cardiac EGM, a first ventricular event; determine, based on the cardiac EGM, a second ventricular event; determine a first time interval between the first ventricular event and the second ventricular event; determine that the first time interval satisfies a first time interval threshold; determine, based on the first time interval satisfying the first time interval threshold, that the first ventricular event and the second ventricular event are a short interval event pair; determine whether the short interval event pair is a result of oversensing; increment or refrain from incrementing a counter based on the determination of whether the short interval event pair is the result of oversensing; and determine, based at least in part on a count of the counter, whether to send a lead integrity alert.

[0007] This summary is intended to provide an overview of the subject matter described in this disclosure. It is not intended to provide an exclusive or exhaustive explanation of the methods and systems described in detail within the accompanying drawings and description below. The details of one or more aspects of the disclosure are set forth in the accompanying drawings and the description below.BRIEF DESCRIPTION OF DRAWINGS

[0008] The details of one or more examples of this disclosure are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of this disclosure will be apparent from the description and drawings, and from the claims.

[0009] FIG. 1 is conceptual diagram illustrating an example medical device system, in accordance with some examples of the current disclosure.

[0010] FIG. 2 is a conceptual diagram further illustrating the implantable medical device (IMD) of FIG. 1, in accordance with some examples of the current disclosure.

[0011] FIG. 3 is a functional block diagram illustrating an example configuration of implantable medical device of FIGS. 1 and 2, in accordance with some examples of the current disclosure.

[0012] FIG. 4 is a conceptual diagram illustrating example atrial sensed events and ventricle sensed events according to one or more aspects of this disclosure.

[0013] FIG. 5 is a conceptual diagram illustrating example windows around sensed events according to one or more aspects of this disclosure.

[0014] FIG. 6 is a functional block diagram illustrating an example configuration of the external device of the medical system of FIG. 1, in accordance with some examples of the current disclosure.

[0015] FIG. 7 is a block diagram illustrating an example system that includes an external device, such as a server, and one or more computing devices that are coupled to the IMD and external device shown in FIG. 1 via a network, in accordance with some examples of the current disclosure.

[0016] FIG. 8 is a flow diagram illustrating an example technique for reducing oversensing related short interval counts according to one or more aspects of this disclosure.

[0017] Like reference characters denote like elements throughout the description and figures.DETAILED DESCRIPTION

[0018] An implantable medical system includes an implantable medical device (IMD), such as a pacemaker, implantable cardioverter defibrillator (ICD), or implantable cardiac resynchronization therapy (CRT) device, that may provide therapies for maintaining and restoring normal cardiac rhythms by pacing and / or by delivering electrical shock therapy for cardioverting or defibrillating the heart. One or more electrical leads connected to the IMD may be inserted into or in proximity to the heart of the patient. The leads carry therapeutic current from the IMD to the heart tissue to either stimulate the heart using low energy pacing pulses or cardiovert / defibrillate the heart using relatively higher energy shocks. The IMD also uses the leads for sensing electrical activity, such as electrogram (EGM) signals, from the heart. Using the EGM signals, the IMD may detect cardiac depolarizations, repolarizations, or other activity, and detect arrhythmias responsive to which the IMD may deliver the electrical therapy. In some examples, within the IMD, sense amplifiers may amplify EGM signals from electrodes on the leads, and the amplified EGM signals may be used by the IMD to sense intrinsic depolarizations of the atria (referred to as P-waves) and the ventricles (referred to as R-waves).

[0019] The implantable medical systems may also include one or more leads that are wholly or partially implanted within the patient and are configured to couple to the IMDs. In some examples, the implantable leads include an integrated bipolar lead, in which an electrode used to deliver relatively higher energy shock therapy, e.g., a coil electrode, servesas either an anode or cathode of a sensing vector, such as a sensing bipole. The sensing bipole of an integrated bipolar lead may have larger (e.g., wider) spacing than a traditional bipolar lead that includes, for example, two relatively more closely spaced electrodes, such as a tip electrode and a ring electrode or two closely spaced ring electrodes. Because of the larger interelectrode spacing and the length of the coil electrode, the integrated bipolar lead may capture more of far-field signals. In some examples, an integrated bipolar lead may include a defibrillator coil electrode connected to a ring electrode with the combination of the defibrillator coil electrode and the ring electrode acting as an anode or cathode of a sensing bipole of the integrated bipolar lead. In some examples, integrated bipolar leads may include any lead configured to provide an integrated bipole for sensing, e.g., whether or not the lead is also configured to provide or more traditional bipoles, e.g., includes more closely spaced ring and tip electrodes.

[0020] Integrated bipolar leads that are implanted in the ventricle or ventricular septum consequently may have a higher chance of atrial oversensing, particularly for integrated bipolar leads that are implanted in the left bundle branch area, septal area, or other location higher up / closer to the atrium than conventional apical implantation. In some examples, a position of an integrated bipolar lead may be adjusted, such as by an implanter, at implant to reduce the chance of a ventricularly-implanted integrated bipolar lead oversensing atrial far-field activity. However, in some cases over time, the ventricularly-implanted integrated bipolar lead may sense atrial far-field activity which may lead to atrial oversensing. For example, after the leads are implanted, a position of the leads may change, such as due to patient movement, which may cause an increase in sensed atrial far-field activity by an integrated bipolar lead implanted in a ventricle, which can lead to atrial oversensing, e.g., misidentification of features in the EGM associated with atrial depolarizations as ventricular depolarizations. Atrial oversensing may lead to a variety of undesired outcomes, such as over-detection of tachyarrhythmias, inhibition of cardiac resynchronization therapy (CRT) and / or loss of optimal AV interval for CRT or other synchronous ventricular pacing.

[0021] Oversensing may occur with implantable cardiac devices like ICDs. For example, ICDs with integrated bipolar electrodes more widely separated from each other than traditional short bipole sensing electrodes are more vulnerable to receiving far-field electrical activity (e.g., P-waves) which may lead to oversensing and possible over-detection of arrythmia episodes. Oversensing may lead an IMD to overcount a number of shortventri cl e-to- ventricle (V-V) intervals. For example, oversensing may lead to a single beat appearing as two closely spaced beats with a short V-V interval therebetween, as one of the ventricular events, for example the first or the second of such ventricular events, may be an oversensed event.

[0022] IMDs may include a sensing integrity counter (SIC) to count short V-V intervals and may use a short V-V interval count for triggering a lead integrity alert (LIA). In some examples, a count in the SIC is one of a plurality of inputs that may trigger an LIA. An integrated bipolar sensing vector may be associated with a higher count of short V-V intervals due to reasons such as oversensing of far-field activity, such as atrial activity, as ventricular activity. With leads placed higher up in the septum, there is a higher chance of an increased short V-V interval count in the SIC and therefore, a trigger of a false positive LIA. Therefore, it may be desirable to determine when atrial oversensing leads to short V- V intervals and exclude such events from the SIC counter.

[0023] In general, this disclosure describes example techniques relating to reduction of oversensing related short interval counts. False sensed ventricular events due to oversensing can end up triggering an LIA.

[0024] When an IMD sends an LIA, a clinician typically will attempt to determine what causes the LIA. Even if the IMD does not send the LIA, but sends a count of the SIC, the clinician may still be concerned about the high count and spend time investigating what may be causing the high count. If the high count is due to oversensing rather than an issue with the integrity of the lead, this is a time investment that may be avoided. It may be desirable to avoid clinical burden in which a clinician attempts to determine whether a lead has become dislodged or is failing. For example, a clinician may try to determine a source of the oversensing, perform an x-ray or other imaging to determine if a lead is dislodged, employ a Holter monitor on the patient, change pacing of a pacemaker, or employ other techniques in an attempt to discover the cause of the oversensing. By refraining from incrementing an SIC when a sensed short V-V interval is due to oversensing, the techniques of this disclosure may free up the clinician for more important medical activities.

[0025] For example, when a T-wave or P-wave is sensed as a ventricular depolarization, the IMD may determine that the V-V interval is a short interval even though the actual beat is not a short beat.

[0026] According to the techniques of this disclosure, an IMD may obtain the cardiac EGM of the patient. The IMD may determine, based on the cardiac EGM, a first ventricular event. The IMD may determine, based on the cardiac EGM, a second ventricular event. The IMD may determine a first time interval between the first ventricular event and the second ventricular event. The IMD may determine that the first time interval satisfies (e.g., is less than or less than or equal to) a first time interval threshold (e.g., 130 milliseconds (ms), 140ms, etc.). For example, the IMD may classify the first ventricular event and the second ventricular event as a short interval pair (or a potential short interval pair) if the first time interval satisfies the first time interval threshold. In other words, the IMD may classify the V-V interval as a short V-V interval.

[0027] If the V-V interval is a short V-V interval, the IMD may determine that the first ventricular event and the second ventricular event are a short interval event pair. The IMD may determine whether the short interval event pair is a result of oversensing (e.g., whether either the first ventricular event or the second ventricular event is an oversensed event). For example, if there is an atrial lead, the IMD may determine the time interval between the first ventricular event of the short interval pair and the nearest atrial event. If this time interval is less than a predetermined threshold (e.g., 80ms, 100ms, etc.), the IMD may determine that the short interval event pair is a result of atrial oversensing. In absence of an atrial lead (e.g., single chamber IMD), the IMD may compare one or more characteristics and / or morphologic features (e.g., the peak to peak amplitudes) of the cardiac EGM within a first time window around the first ventricular event to one or more characteristics and / or morphologic features (e.g., the peak to peak amplitudes) of the cardiac EGM within a second time window around the second ventricular event. The IMD may, based on that comparison, determine whether the short interval event pair is a result of oversensing (e.g., atrial oversensing on the ventricular channel).

[0028] The IMD may increment or refrain from incrementing a counter based on the determination of whether the short V-V interval (e.g., the short interval event pair) is the result of oversensing. The IMD may determine, based at least in part on a count of the counter, whether to send a lead integrity alert. As used herein something may satisfy a threshold by a value or property of the something being one of greater than, greater than or equal to, less than, or less than or equal to, depending on the circumstances.

[0029] FIG. 1 illustrates example medical device system 10 in conjunction with patient 14. Medical device system 10 is an example of a medical device system that is configured to implement the example techniques described herein for reducing oversensing related short interval counts. In some examples, medical device system 10 includes an implantable medical device (IMD) 16 in communication with external device 24. In the illustrated example, IMD 16 may be coupled to leads 18, 20, and 22. IMD 16 may be, for example, an implantable cardioverter, an implantable defibrillator, an implantable pacemaker, and / or other implantable medical device that provides electrical signals to heart 12 and senses electrical activity of heart 12 via electrodes coupled to one or more of leads 18, 20, and 22. In some examples, the techniques described herein may be implemented in medical devices that do not deliver therapy, medical devices that are not coupled to their electrodes via leads, and / or medical devices that are not implanted.

[0030] Leads 18, 20, 22 extend into heart 12 of patient 14 to sense electrical activity of heart 12 and to deliver electrical therapy to heart 12. In the example shown in FIG. 1, right ventricular (RV) lead 18 extends through one or more veins (not shown), the superior vena cava (not shown), and right atrium (RA) 26, and into RV 28. Left ventricular (LV) coronary sinus lead 20 extends through one or more veins, the vena cava, right atrium 26, and into the coronary sinus 30 to a region adjacent to the free wall of LV 32 of heart 12. Right atrial (RA) lead 22 extends through one or more veins and the vena cava, and into the RA 26 of heart 12.

[0031] In some examples, lead 18 may be referred to as a ventricularly-implanted integrated bipolar lead. In some examples, lead 22 may be referred to as an atrial lead. Although an apical implantation location of lead 18 is illustrated in FIG. 1, ventricularly- implanted integrated bipolar lead 18 may be implanted in other locations in some examples, such as proximate the left bundle branch, ventricular septum, or more generally closer to the right atrium. In some examples, lead 18 may be a conduction system pacing (CSP) lead positioned along a portion of the ventricular septum for stimulating a portion of the heart’s natural conduction system.

[0032] IMD 16 may sense electrical signals attendant to the depolarization and repolarization of heart 12 via electrodes (not shown in FIG. 1) coupled to at least one of the leads 18, 20, 22. In some examples, IMD 16 may also sense electrical signals attendant to the depolarization and repolarization of heart 12 via extravascular electrodes (e.g.,electrodes positioned outside the vasculature of patient 14), such as epicardial electrodes, external surface electrodes, subcutaneous electrodes, and the like. The configurations of electrodes used by IMD 16 for sensing and pacing may be unipolar or bipolar.

[0033] The natural electrical activation system of a human heart 12 involves several sequential conduction pathways starting with the sino-atrial (SA) node, and continuing through the atrial conduction pathways of Bachmann's bundle and intemodal tracts at the atrial level, followed by the atrio-ventricular (AV) node, Common Bundle of His, right and left bundle branches, and a final distribution to the distal myocardial terminals via the Purkinje fiber network. In a normal electrical activation sequence, the cardiac cycle commences with the generation of a depolarization wave at the SA Node in the wall of RA 26. The depolarization wave is transmitted through the atrial conduction pathways of Bachmann's Bundle and the Internodal Tracts at the atrial level into the left atrium (LA) 33 septum. When the atrial depolarization wave has reached the AV node, the atrial septum, and the furthest walls of the right and left atria 26, 33, respectively, the atria 26, 33 may contract as a result of the electrical activation. The aggregate right atrial and left atrial depolarization wave appears as the P-wave of the PQRST complex of a cardiac EGM. When the amplitude of the atrial depolarization wave passing between a pair of unipolar or bipolar pace / sense electrodes located on or adjacent RA 26 and / or LA 33 exceeds a threshold, it is detected as a sensed P-wave. The sensed P-wave may also be referred to as an atrial intrinsic event.

[0034] During or after the atrial contractions, the AV node distributes the depolarization wave inferiorly down the Bundle of His in the intraventricular septum. The depolarization wave may travel to the apical region of heart 12 and then superiorly though the Purkinje Fiber network. The aggregate right ventricular and left ventricular depolarization wave and the subsequent T-wave accompanying re-polarization of the depolarized myocardium may appear as the QRST portion of the PQRST cardiac cycle complex. When the amplitude of the QRS ventricular depolarization wave passing between a bipolar or unipolar pace / sense electrode pair located on or adjacent RV 28 and / or LV 32 exceeds a threshold, it is detected as a sensed R-wave. The sensed R-wave may also be referred to as a ventricular intrinsic event, an RV sensing event (RVs), or an LV sensing event (LVs) depending upon the ventricle in which the electrodes of one or more of leads 18, 20, 22 are configured to sense in a particular case.

[0035] In some examples, IMD 16 provides defibrillation therapy and / or cardioversion therapy via electrodes located on at least one of the leads 18, 20, 22. Based on signals sensed via one or more of leads 18, 20, 22, e.g., the detection of R-waves, IMD 16 may detect arrhythmia of heart 12, such as fibrillation or other tachyarrhythmia of ventricles 28 and 32, and deliver antitachyarrhythmia therapy to heart 12 in the form of electrical shocks. In some examples, IMD 16 is programmed to deliver a progression of therapies, e.g., shocks with increasing energy levels, until a tachyarrhythmia of heart 12 is stopped. In examples in which IMD 16 provides antitachyarrhythmia shock therapy, IMD 16 may detect tachyarrhythmia by employing any one or more tachyarrhythmia detection techniques known in the art.

[0036] In some examples, external device 24 may be a handheld computing device or a computer workstation. External device 24 may include a user interface that receives input from a user. The user interface may include, for example, a keypad and a display, which may for example, be a liquid crystal display (LCD) or light emitting diode (LED) display. The keypad may take the form of an alphanumeric keypad or a reduced set of keys associated with particular functions. External device 24 can additionally or alternatively include a peripheral pointing device, such as a mouse, via which a user may interact with the user interface. In some examples, a display of external device 24 may include a touch screen display, and a user may interact with external device 24 via the display.

[0037] A user, such as a physician, technician, or other clinician, may interact with external device 24 to communicate with IMD 16. For example, the user may interact with external device 24 to retrieve physiological or diagnostic information from IMD 16. In some examples, a clinician may interact with external device 24 to receive or retrieve an LIA or a count of a SIC of IMD 16. A user may also interact with external device 24 to program IMD 16, e.g., to select values for operational parameters of the IMD 16.

[0038] For example, the user may use external device 24 to retrieve information from IMD 16 regarding the rhythm of heart 12, trends therein over time, or arrhythmia episodes. As another example, the user may use external device 24 to retrieve information from IMD 16 regarding other sensed physiological parameters of patient 14, such as sensed electrical activity, activity, posture, respiration, or thoracic impedance. As another example, the user may use external device 24 to retrieve information from IMD 16 regarding the performance or integrity of IMD 16 or other components of system 10, such as leads 18, 20, and 22, or apower source of IMD 16. In such examples, physiological parameters of patient 14 and data regarding IMD 16 may be stored in a memory of IMD 16 for retrieval by the user. The user may use external device 24 to program parameters of therapy delivery by IMD 16 and / or parameters used for depolarization and / or arrhythmia detection by IMD 16. In some examples, the user may activate certain features of IMD 16 by entering a single command via external device 24, such as depression of a single key or combination of keys of a keypad or a single point-and-select action with a pointing device.

[0039] IMD 16 and external device 24 may communicate via wireless communication using any techniques known in the art. Examples of communication techniques may include, for example, include radiofrequency (RF) telemetry, which may be an RF link established via an antenna according to Bluetooth®, WiFi, or medical implant communication service (MICS), though other techniques are also contemplated. In some examples, external device 24 may include a programming head that may be placed proximate to the patient’s body near the IMD 16 implant site in order to improve the quality or security of communication between IMD 16 and external device 24.

[0040] FIG. 2 is a conceptual diagram further illustrating an example configuration of IMD 16 in conjunction with heart 14. In the example of FIG. 2, IMD 16 is coupled to leads 18 and 22. IMD 16 may be coupled to two leads as illustrated in FIG. 2, three leads as illustrated in FIG. 1, or other numbers of leads. Furthermore, the leads coupled to IMD 16 may be configured differently than those illustrated herein, but IMD 16 may nevertheless implement the techniques of this disclosure.

[0041] As shown in FIG. 2, the proximal ends of leads 18 and 22 are connected to a connector block 34 of IMD 16 to electrically couple the electrodes on the leads to circuitry within the housing 60 of IMD 16. In some examples, proximal ends of leads 18 and 22 may include electrical contacts that electrically couple to respective electrical contacts within connector block 34 of IMD 16. Each of the leads 18 and 22 includes an elongated insulative lead body, which may carry a number of conductors, e.g., a conductor for each electrode on the lead, each of which may be connected to a respective contact at the proximal end of the lead. Bipolar electrode 42 is located adjacent to a distal end of lead 18 in right ventricle 28. In addition, bipolar electrodes 48 and 50 are located adjacent to a distal end of lead 22 in right atrium 26.

[0042] In some examples, lead 18 may be referred to as a ventricularly-implanted integrated bipolar lead 18 or a ventricular integrated bipolar lead 18. As will be described in greater detail below, lead 18 may be configured to facilitate sensing of a ventricular EGM by IMD 16 via an integrated bipolar pair including tip electrode 42 and elongated electrode 62. In some examples, lead 22 may be referred to as an atrial lead 22.

[0043] Electrode 48 may take the form of ring electrodes, and electrodes 42 and 50 may take the form of helix tip electrodes mounted, e.g., with a fixed screw, within insulative electrode heads 52 and 56, respectively. Some helix tip electrodes can include a mechanism for an extendable / retractable helix. In other examples, one or more of electrodes 42 and 50 may take the form of small circular electrodes at the tip of a tined lead or other fixation element. Leads 18 and 22 also include elongated electrodes 62 and 66, respectively, each of which may take the form of a coil, and may be configured for delivery of relatively high energy therapeutic shocks. Each of the electrodes 42, 48, 50, 62 and 66 may be electrically coupled to a respective one of the conductors within the lead body of its associated lead 18 and 22, and thereby coupled to respective ones of the electrical contacts on the proximal end of leads 18 and 22.

[0044] In the example of FIG. 2, IMD 16 includes a housing electrode 58, which may be formed integrally with an outer surface of hermetically-sealed housing 60 of IMD 16, or otherwise coupled to housing 60. In some examples, housing electrode 58 is defined by an uninsulated portion of an outward facing portion of housing 60 of IMD 16. Other division between insulated and uninsulated portions of housing 60 may be employed to define two or more housing electrodes. In some examples, housing electrode 58 comprises substantially all of housing 60.

[0045] IMD 16 may sense electrical signals attendant to the depolarization and repolarization of heart 12 via electrodes 42, 48, 50, 62, and 66. The electrical signals are conducted to IMD 16 from the electrodes via the respective leads 18 and 22. IMD 16 may sense such electrical signals via any bipolar combination of electrodes 40, 42, 48, 50, 62, and 66. For example, IMD 16 may sense a ventricular EGM via an integrated bipolar pair including tip electrode 42 and elongated electrode 62. Furthermore, any of the electrodes 42, 48, 50, 62, and 66 may be used for unipolar sensing in combination with housing electrode 58. The combination of electrodes used for sensing may be referred to as a sensing configuration or electrode vector.

[0046] In some examples, IMD 16 delivers pacing pulses via bipolar combinations of electrodes 42, 48, 50, 62, and 66 to produce depolarization of cardiac tissue of heart 12. In some examples, IMD 16 delivers pacing pulses via any of electrodes 42, 48 and 50 in combination with housing electrode 58 in a unipolar configuration. Furthermore, IMD 16 may deliver antitachyarrhythmia shocks, e.g., defibrillation shocks, to heart 12 via any combination of elongated electrodes 62 and 66, and housing electrode 58. IMD 16 may also use electrodes 58, 62, and 66 to deliver cardioversion shocks to heart 12. Electrodes 62 and 66 may be fabricated from any suitable electrically conductive material, such as, but not limited to, platinum, platinum alloy or other materials known to be usable in implantable defibrillation electrodes.

[0047] The configurations of system 10 illustrated in FIGS. 1 and 2 are merely examples. In other examples, a system may include extravascular leads and electrodes instead of or in addition to the illustrated transvenous leads 18 and 22. Further, IMD 16 need not be implanted within the patient. In examples in which IMD 16 is not implanted in the patient, IMD 16 may sense electrical signals and / or deliver antitachyarrhythmia shocks and other therapies to heart 12 via percutaneous leads that extend through the skin of a patient to a variety of positions within or outside of heart 12.

[0048] FIG. 3 is a functional block diagram of one example configuration of IMD 16 of FIGS. 1 and 2. In the illustrated example, IMD 16 includes memory 70, processing circuitry 80, sensing circuitry 82, one or more accelerometers 84, therapy delivery circuitry 86, telemetry circuitry 88, and power source 90, one or more of which may be disposed within housing 60 of IMD 16. In some examples, memory 70 includes computer-readable instructions that, when executed by processing circuitry 80, cause IMD 16 and processing circuitry 80 to perform various functions attributed to IMD 16 and processing circuitry 80 herein. Memory 70 may include any volatile, non-volatile, magnetic, optical, or electrical media, such as a random access memory (RAM), read-only memory (ROM), non-volatile RAM (NVRAM), electrically-erasable programmable ROM (EEPROM), flash memory, or any other digital media. Sensed physiological parameters of patient 14 (e.g., EGM or ECG signals or atrial events) may be stored by memory 70. Memory 70 may store include SIC 72, may store EGM 74, and may store any thresholds discussed herein in thresholds 76.

[0049] Processing circuitry 80 may include one or more of a microprocessor, a controller, digital signal processing circuitry (DSP), an application specific integrated circuit(ASIC), a field-programmable gate array (FPGA), or equivalent discrete or integrated logic circuitry. In some examples, processing circuitry 80 may include multiple components, such as any combination of one or more microprocessors, one or more controllers, one or more DSPs, one or more ASICs, or one or more FPGAs, as well as other discrete or integrated logic circuitry. The functions attributed to processing circuitry 80 herein may be embodied as software, firmware, hardware or any combination thereof. According to the techniques described herein, processing circuitry 80 may be configured to obtain the cardiac EGM of the patient. Processing circuitry 80 may be configured to determine, based on the cardiac EGM, a first ventricular event. Processing circuitry 80 may be configured to determine, based on the cardiac EGM, a second ventricular event. Processing circuitry 80 may be configured to determine a first time interval between the first ventricular event and the second ventricular event. Processing circuitry 80 may be configured to determine that the first time interval satisfies a first time interval threshold. If the first time interval satisfies the first time interval threshold, processing circuitry 80 may determine that the first ventricular event and the second ventricular event are a short interval event pair. Processing circuitry 80 may be configured to determine whether the short interval event pair is a result of oversensing. For example, processing circuitry 80 may determine whether the first ventricular event or the second ventricular event is an oversensed event. Processing circuitry 80 may be configured to increment or refrain from incrementing a counter based on the determination of whether the short interval event pair is the result of oversensing. Processing circuitry 80 may be configured to determine, based at least in part on a count of the counter, whether to send a lead integrity alert.

[0050] Sensing circuitry 82 is configured to monitor signals from at least one of electrodes 42, 48, 50, 58, 62, or 66 in order to monitor electrical activity of heart 12, e.g., via EGM signals. For example, sensing circuitry 82 may sense atrial intrinsic events (e.g., a P-wave) with electrodes 48, 50, 66 within RA 26. In some examples, sensing circuitry 82 includes switching circuitry to select which of the available electrodes are used to sense the electrical activity of heart 12. For example, processing circuitry 80 may select the electrodes that function as sense electrodes via the switching circuitry within sensing circuitry 82, e.g., by providing signals via a data / address bus. In some examples, sensing circuitry 82 includes one or more sensing channels, each of which may comprise an amplifier. In response to thesignals from processing circuitry 80, the switching circuitry of sensing circuitry 82 may couple the outputs from the selected electrodes to one of the sensing channels.

[0051] In some examples, one channel of sensing circuitry 82 may include an R-wave amplifier that receives signals from selected pairs of electrodes 42, 62, and 58, which are used for pacing and sensing in RV 28 of heart 12. In accordance with the techniques of this disclosure, sensing circuitry 82 may include an R-wave amplifier that receives a signal from an integrated bipolar pair of electrodes 42 and 62, i.e., an integrated bipolar ventricular EGM signal, and detects R- waves within the signal. In some examples, the R-wave amplifiers may take the form of an automatic gain controlled amplifier that provides an adjustable sensing threshold as a function of the measured R-wave amplitude of the heart rhythm. In accordance with the techniques of this disclosure, processing circuitry 80 may adjust a parameter of the adjustable sensing threshold, e.g., to increase the threshold and make the threshold less sensitive to waves in the integrated bipolar ventricular EGM signal, in response to a windowed portion of the integrated bipolar ventricular EGM signal satisfying a far-field activity threshold.

[0052] In addition, in some examples, one channel of sensing circuitry 82 may include a P-wave amplifier that receives signals from electrodes 48 and 50, which are used for pacing and sensing in RA26 of heart 12. In some examples, the P-wave amplifier may take the form of an automatic gain controlled amplifier that provides an adjustable sensing threshold as a function of the measured P-wave amplitude of the heart rhythm. Examples of R-wave and P-wave amplifiers are described in U.S. Patent No. 5,117,824 to Keimel et al., which issued on June 2, 1992 and is entitled, “APPARATUS FOR MONITORING ELECTRICAL PHYSIOLOGIC SIGNALS,” and is incorporated herein by reference in its entirety. Other amplifiers may also be used. Furthermore, in some examples, one or more of the sensing channels of sensing circuitry 82 may be selectively coupled to housing electrode 58, or elongated electrodes 62, or 66, with or instead of one or more of electrodes 42, 48 or 50, e.g., for unipolar or integrated bipolar sensing of R-waves or P-waves in any of chambers 26, 28, or 32 of heart 12.

[0053] In some examples, sensing circuitry 82 includes a channel that comprises an amplifier with a relatively wider pass band than the R-wave or P-wave amplifiers. Signals from the selected sensing electrodes that are selected for coupling to this wide-band amplifier may be provided to a multiplexer, and thereafter converted to multi-bit digitalsignals by an analog-to-digital converter for storage in memory 70 as an EGM 74. In some examples, the storage of such EGMs in memory 70 may be under the control of a direct memory access circuit. Processing circuitry 80 may employ digital signal analysis techniques to characterize the digitized signals stored in memory 70 to detect and classify the patient's heart rhythm from the electrical signals. Processing circuitry 80 may detect and classify the heart rhythm of patient 14 by employing any of the numerous signal processing methodologies known in the art. In some examples, sensing 82 stores the integrated bipolar EGM, e.g., the ventricular integrated bipolar EGM 74, in memory 70 for windowing and further processing by processing circuitry 80 in accordance with the techniques of this disclosure.

[0054] Signals generated by sensing circuitry 82 may include, for example: an RA-event signal, which indicates a detection of a P-wave via electrodes implanted within RA26 (FIG. 1); an LA-event signal, which indicates a detection of a P-wave via electrodes implanted within LA 33 (FIG. 1); an RV-event signal, which indicates a detection of an R-wave via electrodes implanted within RV 28; or an LV-event signal, which indicates a detection of an R-wave via electrodes implanted within LV 32.

[0055] In some examples, IMD 16 may include one or more additional sensors, such as accelerometers 84. In some examples, accelerometers 84 may comprise one or more three- axis accelerometers. Signals generated by accelerometers 84 may be indicative of, for example, gross body movement of patient 14, such as a patient posture or activity level. Regardless of the configuration of accelerometers 84, processing circuitry 80 may determine patient parameter values based on the signals obtained therefrom. Accelerometers 84 may produce and provide signals to processing circuitry 80 for a determination as to the posture and activity level of patient 14 at a given time. Processing circuitry 80 may then use the determined posture and activity level to further determine whether patient 14 is awake or asleep, and, if patient 14 is determined to be awake, to further determine whether patient 14 is at rest or exercising.

[0056] Therapy delivery circuitry 86 is electrically coupled to electrodes 42, 48, 50, 58, 62, and 66, e.g., via conductors of the respective lead 18, 20, 22, or, in the case of housing electrode 58, via an electrical conductor disposed within housing 60 of IMD 16. Therapy delivery circuitry 86 is configured to generate and deliver electrical therapy.

[0057] In some examples, therapy delivery circuitry 86 is configured to deliver cardioversion or defibrillation shocks to heart 12. The pacing stimuli, cardioversion shocks, and defibrillation shocks may be in the form of pulses. In other examples, therapy delivery circuitry 86 may deliver one or more of these types of therapy in the form of other signals, such as sine waves, square waves, or other substantially continuous time signals.

[0058] Therapy delivery circuitry 86 may include a switching circuitry, and processing circuitry 80 may use the switching circuitry to select, e.g., via a data / address bus, which of the available electrodes are used to deliver shock pulses or pacing pulses. The switching circuitry may include a switch array, switch matrix, multiplexer, or any other type of switching device suitable to selectively couple therapeutic energy to selected electrodes. In other examples, processing circuitry 80 may select a subset of electrodes 42, 48, 50, 58, 62, and 66 with which therapy is delivered to heart 12 without a switching circuitry.

[0059] Processing circuitry 80 may include pacer timing and control circuitry, which may be embodied as hardware, firmware, software, or any combination thereof. Pacer timing and control circuitry may comprise a dedicated hardware circuit, such as an ASIC, separate from other processing circuitry 80 components, such as a microprocessor, or a software module executed by a component of processing circuitry 80 (e.g., a microprocessor or ASIC).

[0060] In some examples, an arrhythmia detection method may include any suitable tachyarrhythmia detection algorithms. In one example, processing circuitry 80 may utilize all or a subset of the rule-based detection methods described in U.S. Patent No. 5,545,182 to Olson et al., entitled, “PRIORITIZED RULE BASED METHOD AND APPARATUS FOR DIAGNOSIS AND TREATMENT OF ARRHYTHMIAS,” which issued on August 13, 1996, or in U.S. Patent No. 5,755,736 to Gillberg et al., entitled, “PRIORITIZED RULE BASED METHOD AND APPARATUS FOR DIAGNOSIS AND TREATMENT OF ARRHYTHMIAS,” which issued on May 26, 1998. U.S. Patent No. 5,545,182 to Olson et al. and U.S. Patent No. 5,755,736 to Gillberg et al. are incorporated herein by reference in their entireties. However, other arrhythmia detection methodologies may also be employed by processing circuitry 80 in other examples.

[0061] In some examples, processing circuitry 80 may employ an M of N rule based technique for determining a suspected arrhythmia. For example, if processing circuitry 80 detects at least M fast beats within N consecutive beats, processing circuitry 80 maydetermine that there is a suspected arrhythmia episode within the N consecutive beats. A fast beat may be a beat having a sensed interval from a last beat (e.g., a sensed ventricular event from a last sensed ventricular event) of a period less than (or less than or equal to) a threshold time, for example, less than 140ms.

[0062] Each fast beat within the N consecutive beats may be considered an event, such that all of the fast beats within the N consecutive beats make up or are part of the suspected arrhythmia episode. When determining whether a suspected arrhythmia episode is a true arrhythmia episode or a false arrhythmia episode due to oversensing as described herein, in some examples, processing circuitry 80 may ignore the non-fast beats occurring within the suspected arrhythmia episode. The values of M and / or N may be programmable. In some examples, M may equal 20 and N may equal 30.

[0063] If IMD 16 is configured to generate and deliver defibrillation shocks to heart 12, therapy delivery circuitry 86 may include a high voltage charge circuit and a high voltage output circuit. In the event that processing circuitry 80 determines that generation of a cardioversion or defibrillation shock is required, processing circuitry 80 may employ the escape interval counter to control timing of such cardioversion and defibrillation shocks, as well as associated refractory periods. In response to the detection of atrial or ventricular fibrillation or tachyarrhythmia requiring a cardioversion pulse, processing circuitry 80 may activate a cardioversion / defibrillation control circuitry (not shown), which may be a hardware component of processing circuitry 80 and / or a firmware or software module executed by one or more hardware components of processing circuitry 80. The cardioversion / defibrillation control circuitry may initiate charging of the high voltage capacitors of the high voltage charge circuit of therapy delivery circuitry 86 under control of a high voltage charging control line.

[0064] Processing circuitry 80 may monitor the voltage on the high voltage capacitor, e.g., via a voltage charging and potential (VCAP) line. In response to the voltage on the high voltage capacitor reaching a predetermined value set by processing circuitry 80, processing circuitry 80 may generate a logic signal that terminates charging. Thereafter, timing of the delivery of the defibrillation or cardioversion pulse by therapy delivery circuitry 86 is controlled by a cardioversion / defibrillation control circuitry (not shown) of processing circuitry 80. Following delivery of the fibrillation or tachycardia therapy, processing circuitry 80 may return therapy delivery circuitry 86 to a cardiac pacing functionand await the next successive interrupt due to pacing or the occurrence of a sensed atrial or ventricular depolarization.

[0065] Therapy delivery circuitry 86 may deliver cardioversion or defibrillation shock with the aid of an output circuit that determines whether a monophasic or biphasic pulse is delivered, whether housing electrode 58 serves as cathode or anode, and which electrodes are involved in delivery of the cardioversion or defibrillation pulses. Such functionality may be provided by one or more switches or a switching circuitry of therapy delivery circuitry 86.

[0066] Telemetry circuitry 88 includes any suitable hardware, firmware, software or any combination thereof for communicating with another device, such as external device 24 (FIG. 1). Under the control of processing circuitry 80, telemetry circuitry 88 may receive downlink telemetry from and send uplink telemetry to external device 24 with the aid of an antenna, which may be internal and / or external. Processing circuitry 80 may provide the data to be uplinked to external device 24 and the control signals for the telemetry circuit within telemetry circuitry 88, e.g., via an address / data bus. In some examples, telemetry circuitry 88 may provide received data to processing circuitry 80 via a multiplexer.

[0067] In some examples, processing circuitry 80 may transmit atrial and ventricular heart signals (e.g., EGM signals) produced by atrial and ventricular sense amplifier circuits within sensing circuitry 82 to external device 24. Other types of information may also be transmitted to external device 24, such as a count in SIC 72, an LIA, or the like.

[0068] Telemetry circuitry 88 includes any suitable hardware, firmware, software or any combination thereof for communicating with another device, such as external device 24 (FIG. 1). Under the control of processing circuitry 80, telemetry circuitry 88 may receive downlink telemetry from and send uplink telemetry to external device 24 with the aid of an antenna, which may be internal and / or external. Processing circuitry 80 may provide the data to be uplinked to external device 24 and the control signals for the telemetry circuit within telemetry circuitry 88, e.g., via an address / data bus. In some examples, telemetry circuitry 88 may provide received data to processing circuitry 80 via a multiplexer.

[0069] The various components of IMD 16 are coupled to power source 90, which may include a rechargeable or non-rechargeable battery. A non-rechargeable battery may be selected to last for several years, while a rechargeable battery may be inductively charged from an external device, e.g., on a daily or weekly basis.

[0070] Short V-V interval counts (e.g., counts of short interval event pairs) may be an input used by processing circuitry 80 to determine whether to send a lead integrity alert (LIA). An LIA may be an alert sent by IMD 16 to external device 24 to indicate that a lead may be failing or may have become dislodged. Such an alert may cause a clinician to investigate whether there is a failing or dislodged lead.

[0071] An integrated bipolar sensing (IBS) vector of an integrated bipolar lead may be associated with a higher count of short V-V intervals in SIC 72 due to reasons such as oversensing of far-field activity, such as atrial activity. With leads placed higher up in the septum, there is a higher chance of an increased SIC count and a false positive LIA trigger. Incidences of an increase in short V-V interval counts have been observed more for IBS devices where the sensing electrodes (e.g., tip and coil) have greater separation than short bipolar leads. As a result, IBS is associated with greater SIC counts often as a result of P- wave oversensing. This can occur in both single chamber and dual chamber devices. Therefore, it may be desirable to determine when oversensing causes a determination of short V-V intervals and exclude such events when incrementing SIC 72.

[0072] For example, IMD 16 may include SIC 72 which records a count of V-V intervals that are relatively very short (e.g., 120ms - 130ms, less than 140ms, or the like). The count of SIC 72 may be used to trigger a LIA. For example, processing circuitry 80 may determine whether to send an LIA based, at least in part, on the count of SIC 72. Sometimes, due to atrial oversensing on a ventricular lead, short V-V intervals may be incorrectly registered which may cause an exaggerated SIC count and possibly trigger a false LIA. To eliminate or reduce the likelihood of such a false LIA, processing circuitry 80 may prevent certain short V-V intervals from being registered (e.g., counted) by SIC 72.

[0073] To determine a short V-V interval, processing circuitry 80 may determine a first ventricular event (e.g., a first VS) and a second ventricular event (e.g., a second VS) in EGM 74. Processing circuitry 80 may determine a time interval between the first ventricular event and the second ventricular event (e.g., a V-V interval length). Processing circuitry 80 may then determine whether the time interval satisfies a time interval threshold. For example, processing circuitry 80 may determine whether the time interval is less than (or less than or equal to) 140ms or is within the range of 120ms -130ms, or the like. If the time interval satisfies the time interval threshold, processing circuitry 80 may determine the V-V intervalis a short V-V interval and / or the first ventricular event and the second ventricular event are a short interval event pair.

[0074] This disclosure describes techniques for reducing oversensing related short V-V interval counts for IMDs including both dual chamber devices and single chamber devices. Techniques for use with IMDs which include an atrial sense capability, such as dual chamber devices, are first discussed.

[0075] In some examples where IMD 16 is a device capable of performing an atrial sense (e.g., a dual chamber device), processing circuitry 80 may determine if short V-V intervals are associated with atrial oversensing during normal atrial rhythm, and eliminate such events from incrementing a count of SIC 72 so as to prevent or reduce the occurrence of false lead integrity alerts. For example, processing circuitry 80 may determine whether an atrial rhythm is a normal rate (e.g., within a predetermined range) without atrial tachycardia or fibrillation events. This atrial rhythm may be a sinus rhythm or a paced rhythm. In some examples, processing circuitry 80 may determine whether a pattern of events are sensed by sensing circuitry 82 corresponding to the short V-V interval: A-VS- VS, where A is either atrial pacing (AP) event or an trial sensing (AS) event, and VS is a ventricular sensing event. For example, processing circuitry 80 may determine whether an atrial sense or pace precedes a first VS event and a second VS event without an intervening atrial event between the first VS event and the second VS event (e.g., an A-VS-VS pattern). In some examples, processing circuitry 80 may determine whether, in the A-VS-VS sequence, an A-VS interval between the A event and the first VS in the VS-VS sequence is less than (or less than or equal to) a threshold (e.g., 130ms, 100ms, or the like). In such examples, processing circuitry 80 may determine that the short V-V interval is due to oversensing if a) the atrial rhythm is a normal rate without atrial tachycardia or fibrillation events, b) an A-VS-VS pattern corresponds to the short V-V interval, and / or c) the A-VS interval is less than (or less than or equal to a threshold). In some examples, processing circuitry 80 may determine that the short V-V interval (e.g., the short interval event pair) is due to oversensing if all three conditions (a-c above) are true.

[0076] If the above conditions are true, processing circuitry 80 may refrain from incrementing the count of SIC 72 because the short VS-VS interval is likely a result of atrial oversensing by the ventricular lead. This may prevent SIC 72 from registering a largenumber of oversensed events and potentially avoid a false LIA trigger. This may be especially true for integrated bipolar sensing devices.

[0077] FIG. 4 is a conceptual diagram illustrating example atrial sensed events and ventricle sensed events according to one or more aspects of this disclosure. A first atrial sensed event AS 1 and a second atrial sensed event AS2 are shown on graph 400. Ventricular events VS1 and VS2 are shown on graph 410. In the example of FIG. 4, there is an atrial event followed by two ventricular events. For example, AS1 is followed by VS1 and VS2, with no atrial event (e.g., AS2) occurring (or being sensed) between VS1 and VS2. So the examples of FIG. 4 meets the A-VS-VS pattern discussed above.

[0078] Processing circuitry 80 may determine an atrial event interval 402 which may be indicative of an atrial rhythm. Processing circuitry 80 may determine whether the atrial rhythm, based on atrial event interval 402, is within a predetermined range without atrial tachycardia or fibrillation events. Additionally, or alternatively, processing circuitry 80 may determine an A-VS interval 412 is less than (or less than or equal to) a threshold.

[0079] Techniques are now discussed which may be used by single chamber devices. These techniques may be used by devices capable of an atrial sense as well, in lieu of, or in addition to the techniques discussed above.

[0080] In some examples, processing circuitry 80 may determine whether a short V-V interval is due to oversensing by the ventricular lead and treat such a short interval accordingly (e.g., not increase the count of SIC 72) through the use of EGM characteristics. For example, sensing circuitry 82 may sense an EGM between tip to coil or can to coil electrodes. Based on differences in EGM characteristics, processing circuitry 80 may determine that the short V-V interval events are a result of oversensing and may not increment the count of SIC 72 corresponding to those events. This may affect more accurate lead monitoring and may be useful in avoiding false positive LIAs.

[0081] For example, processing circuitry 80 may determine a peak-to-peak amplitude corresponding to each event for a given short V-V interval, which may be an event pair registered by processing circuitry 80 as a ventricular sense (VS) - fibrillation sense (FS). For example, processing circuitry 80 may create a window to capture the EGM signal around the VS / FS event. This window may start at a first time (e.g., 100ms) prior to the event and extend up to a second time (e.g., 64ms) following the event. In some examples, the length of the first time and the length of the second time are different, such that the window is notcentered around the event. In other examples, the length of the first time and the length of the second time are the same. It should be noted that 100ms and 64ms are provided as examples and other lengths of time may be used to generate the window around an event, so long as the length of the window does not capture both the VS and the FS event. In some examples, the length of the window is shorter, e.g., between 80ms and 120ms.

[0082] FIG. 5 is a conceptual diagram illustrating example windows around sensed events according to one or more aspects of this disclosure. Ventricular sensed events VS1 and VS2 are shown in graph 500. VS2 may be an FS event. Processing circuitry 80 may generate window 502 around VS1 and generate window 504 around VS2. In some examples, VS1 and VS2 constitute a short interval pair.

[0083] In some examples, processing circuitry 80 may determine the maximum amplitude of the EGM within window 502 and the minimum amplitude of the EGM within window 502. Processing circuitry 80 may determine the difference between the maximum amplitude of the EGM within window 502 and the minimum amplitude of the EGM within window 502 to determine a peak-to-peak amplitude (PAMP) associated with first ventricular event (e.g., VS1). Similarly, processing circuitry 80 may determine the maximum amplitude of the EGM within window 504 and the minimum amplitude of the EGM within window 504. Processing circuitry 80 may determine the difference between the maximum amplitude of the EGM within window 504 and the minimum amplitude of the EGM within window 504 to determine a peak-to-peak amplitude (PAMP) associated with second ventricular event (e.g., VS2). If the PAMP associated with the VS1 event is less than (or less than or equal to) a predetermined percentage (e.g., 50%) of the PAMP associated with the corresponding FS event (e.g., VS2), then processing circuitry 80 may determine that the short V-V interval event is likely the result of oversensing and exclude the short V-V interval event from the count of SIC 72. For example, processing circuitry 80 may refrain from incrementing SIC 72 based on determining that the short V-V interval event is likely the result of oversensing. In addition to, or in lieu of, using PAMP, in some examples, processing circuitry 80 may use other EGM characteristics, such as maximum amplitude, minimum amplitude, timing of maximum and / or minimum amplitude, maximum slope, minimum slope, and / or the like, of the event pair within corresponding windows when determining whether a short interval event should be included in the SIC count.

[0084] FIG. 6 is functional block diagram of an example external device 24. As shown in FIG. 6, external device 24 includes processing circuitry 100, a memory 102, a user interface 104, telemetry circuitry 106, and a power source 108. External device 24 may be a dedicated hardware device with dedicated software for interacting with IMD 16. Alternatively, external device 24 may be an off-the-shelf computing device running an application that enables external device 24 to interact with IMD 16.

[0085] A user may use external device 24 to select programmable parameters that control the monitoring and delivery of therapy by IMD 16, and to retrieve information collected by IMD regarding the condition of patient 14 or the performance of IMD 16. The user may interact with external device 24 via user interface 104, which may include display to present graphical user interface to a user, and a keypad or another mechanism for receiving input from a user.

[0086] Processing circuitry 100 can take the form one or more microprocessors, DSPs, ASICs, FPGAs, programmable logic circuitry, or the like, and the functions attributed to processing circuitry 100 herein may be embodied as hardware, firmware, software or any combination thereof. Memory 102 may store instructions that cause processing circuitry 100 to provide the functionality ascribed to external device 24 herein, and information used by processing circuitry 100 to provide the functionality ascribed to external device 24 herein. Memory 102 may include one or more of any fixed or removable magnetic, optical, or electrical media, such as RAM, ROM, CD-ROM, hard or floppy magnetic disks, EEPROM, or the like. Memory 102 may also include one or more removable memory portions that may be used to provide memory updates or increases in memory capacities. A removable memory may also allow patient data to be easily transferred to another computing device, or to be removed before external device 24 is used to program therapy for another patient. Memory 102 may also store information that controls therapy delivery by IMD 16, such as stimulation parameter values.

[0087] External device 24 may communicate wirelessly with IMD 16, such as using RF communication or proximal inductive interaction. This wireless communication is possible through the use of telemetry circuitry 106, which may be coupled to an internal antenna or an external antenna. An external antenna that is coupled to external device 24 may correspond to the programming head that may be placed over heart 12, as described above with reference to FIG. 1.

[0088] Telemetry circuitry 106 may be similar to telemetry circuitry 88 of IMD 16 (FIG. 3). Telemetry circuitry 106 may also be configured to communicate with another computing device via wireless communication techniques, or direct communication through a wired connection. Examples of local wireless communication techniques that may be employed to facilitate communication between external device 24 and another computing device include RF communication according to the 802.11 or Bluetooth specification sets, infrared communication, e.g., according to the IrDA standard, or other standard or proprietary telemetry protocols. In this manner, other external devices may be capable of communicating with external device 24 without needing to establish a secure wireless connection.

[0089] Power source 108 is configured to deliver operating power to the components of external device 24. Power source 108 may include a battery and a power generation circuit to produce the operating power. In some embodiments, the battery may be rechargeable to allow extended operation. Recharging may be accomplished by electrically coupling power source 108 to a cradle or plug that is connected to an alternating current (AC) outlet. In addition or alternatively, recharging may be accomplished through proximal inductive interaction between an external charger and an inductive charging coil within external device 24. In other embodiments, traditional batteries (e.g., nickel cadmium or lithium ion batteries) may be used. In addition, external device 24 may be directly coupled to an alternating current outlet to power external device 24. Power source 108 may include circuitry to monitor power remaining within a battery. In this manner, user interface 104 may provide a current battery level indicator or low battery level indicator when the battery needs to be replaced or recharged. In some cases, power source 108 may be capable of estimating the remaining time of operation using the current battery.

[0090] In some examples, processing circuitry 100 and memory 102 of external device 24 may be configured to provide some or all of the functionality ascribed to processing circuitry 80 and memory 70 of IMD 16. In some examples, processing circuitry 100 may be configured to perform one or more of the techniques as described herein with respect to processing circuitry 80 of IMD 16.

[0091] FIG. 7 is a block diagram illustrating a system 110 that includes an external device 112, such as a server, and one or more computing devices 114A-114N that are coupled to IMD 16 and external device 24 shown in FIG. 1 via a network 120, according toone example. In this example, IMD 16 uses telemetry circuitry 88 (FIG. 3) to communicate with external device 24 via a first wireless connection, and to communicate with an access point 122 via a second wireless connection. In the example of FIG. 7, access point 122, external device 24, external device 112, and computing devices 114A-114N are interconnected, and able to communicate with each other, through network 120. In some cases, one or more of access point 122, external device 24, external device 112, and computing devices 114A-114N may be coupled to network 120 through one or more wireless connections. IMD 16, external device 24, external device 112, and computing devices 114A-114N may each comprise one or more processing circuitries, such as one or more microprocessors, DSPs, ASICs, FPGAs, programmable logic circuitry, or the like, that may perform various functions and operations, such as those described herein.

[0092] Access point 122 may comprise a device that connects to network 120 via any of a variety of connections, such as telephone dial-up, digital subscriber line (DSL), or cable modem connections. In other examples, access point 122 may be coupled to network 120 through different forms of connections, including wired or wireless connections. In some examples, access point 122 may communicate with external device 24 and / or IMD 16. Access point 122 may be co-located with patient 14 (e.g., within the same room or within the same site as patient 14) or may be remotely located from patient 14. For example, access point 122 may be a home monitor that is located in the patient’s home or is portable for carrying with patient 14.

[0093] During operation, IMD 16 may collect, measure, and store various forms of diagnostic data. For example, as described previously, IMD 16 may collect EGM signals, generate a time window of an integrated bipolar EGM signal, determine values of one or more features of the integrated bipolar EGM signal during the time window, and adjust a sensitivity threshold used to detect R-waves or other near field depolarizations. In certain cases, IMD 16 may directly analyze collected diagnostic data and generate any corresponding reports or alerts. In some cases, however, IMD 16 may send diagnostic data to external device 24, access point 122, and / or external device 112, either wirelessly or via access point 122 and network 120, for remote processing and analysis.

[0094] IMD 16 may provide external device 112 with collected EGM data, system integrity indications, and any other relevant physiological or system data via access point 122 and network 120. External device 112 includes one or more processing circuitries 118.In some cases, external device 112 may request such data, and in some cases, IMD 16 may automatically or periodically provide such data to external device 112. Upon receipt of the diagnostic data via input / output device 116, external device 112 is capable of analyzing the data and generating reports or alerts upon determination that there may be a possible condition with one or more of leads 18, 20, and 22, or with patient 14.

[0095] In one example, external device 112 may comprise a secure storage site for information that has been collected from IMD 16 and / or external device 24. In this example, network 120 may comprise an Internet network; and trained professionals, such as clinicians, may use computing devices 114A-114N to securely access stored data on external device 112. For example, the trained professionals may need to enter usernames and passwords to access the stored information on external device 112. In one embodiment, external device 112 may be a CareLink™ server provided by Medtronic, Inc., of Minneapolis, Minnesota.

[0096] In some examples, processing circuitry and memory of one or more of access point 122, server 112, or computing devices 114, e.g., processing circuitry 118 and memory of server 112, may be configured to provide some or all of the functionality ascribed to processing circuitry 80 and memory 70 of IMD 16.

[0097] FIG. 8 is a flow diagram illustrating an example technique for reducing oversensing related short interval counts according to one or more aspects of this disclosure. Sensing circuitry 82 may sense a cardiac EGM of a patient. Processing circuitry 80 may obtain the cardiac EGM of the patient (800). For example, processing circuitry 80 may obtain the cardiac EGM from sensing circuitry 82 or read the cardiac EGM from memory 70.

[0098] Processing circuitry 80 may determine, based on the cardiac EGM, a first ventricular event (802). For example, processing circuitry 80 may determine a VS in the cardiac EGM. Processing circuitry 80 may determine, based on the cardiac EGM, a second ventricular event (804). For example, processing circuitry 80 may determine a second VS event, which, in some cases, may be a FS event.

[0099] Processing circuitry 80 may determine a first time interval between the first ventricular event and the second ventricular event (806). For example, processing circuitry 80 may determine a length of time between the first ventricular event and the second ventricular event.

[0100] Processing circuitry 80 may determine that the first time interval satisfies a first time interval threshold (808). For example, processing circuitry 80 may compare the first time interval to the interval threshold to determine that the first time interval satisfies the first time threshold. In some examples, by the first time interval satisfying the first time threshold, processing circuitry 80 may classify the V-V interval between the first ventricular event and the second ventricular event as a short V-V interval. Processing circuitry 80 may determine, based on the first time interval satisfying the first time interval threshold, that the first ventricular event and the second ventricular event are a short interval event pair (810). For example, because the first time interval satisfies the first time interval threshold, processing circuitry 80 may classify the first ventricular event and the second ventricular event as a short interval event pair.

[0101] Processing circuitry 80 may determine whether the short interval event pair is a result of oversensing (812). For example, if the V-V interval is a short V-V interval, processing circuitry 80 may determine that the short interval event pair is the result of oversensing based on a determination that an atrial heart rate is within a predetermined range, an atrial sense or pace precedes the first ventricular event and the second ventricular event without an intervening atrial event between the first ventricular event and the second ventricular event, and a second time interval between an atrial event and the first ventricular event satisfies a second time interval threshold. In another example, processing circuitry 80 may determine whether the short interval event pair is the result of oversensing based on determining that a comparison of a first characteristic of a first window around the first ventricular event to a second characteristic of a second window around the second ventricular event satisfies a comparison threshold.

[0102] Processing circuitry 80 may increment or refrain from incrementing a counter based on the determination of whether the short interval event pair is the result of oversensing (814). For example, if the short interval event pair is the result of oversensing, processing circuitry 80 may refrain from incrementing SIC 72. If the short interval event pair is not the result of oversensing, processing circuitry 80 may increment SIC 72.

[0103] Processing circuitry 80 may determine, based at least in part on a count of the counter, whether to send a lead integrity alert (814). For example, processing circuitry 80 increments a count of SIC 72 and that incrementing of the count causes the count of SIC 72to now satisfies a threshold, processing circuitry 80 may determine to send a lead integrity alert.

[0104] In some examples, the short interval event pair is the result of oversensing, and processing circuitry 80 may refrain from incrementing the counter based on the determination that the short interval event pair is the result of oversensing. In some examples, the short interval event pair is not the result of oversensing, and processing circuitry 80 may increment the counter based on the determination that the short interval event pair is not the result of oversensing.

[0105] In some examples, to determine whether the short interval event pair is the result of oversensing, processing circuitry 80 is configured to determine at least one of whether an atrial heart rate is within a predetermined range, whether an atrial sense or pace precedes the first ventricular event and the second ventricular event without an intervening atrial event between the first ventricular event and the second ventricular event, or whether a second time interval between an atrial event and the first ventricular event satisfies a second time interval threshold. In some examples, to determine whether the short interval event pair is the result of oversensing, processing circuitry 80 is configured to determine whether the atrial heart rate is within the predetermined range, whether the atrial sense or pace precedes the first ventricular event and the second ventricular event without the intervening atrial event between the first ventricular event and the second ventricular event, and whether the second time interval between the atrial event and the first ventricular event satisfies the second time interval threshold.

[0106] In some examples, to determine whether the short interval event pair is the result of oversensing, processing circuitry 80 may determine a first window in the cardiac EGM around the first ventricular event and determine a second window in the cardiac EGM around the second ventricular event. Processing circuitry 80 determine at least one first characteristic in the first window. Processing circuitry 80 may determine at least one second characteristic in the second window, the at least one second characteristic corresponding to the at least one first characteristic. For example, if a first characteristic is a peak-to-peak amplitude, a second characteristic is also a peak-to-peak amplitude. Processing circuitry 80 may compare the at least one first characteristic to the at least one second characteristic. Processing circuitry 80 may determine, based on whether the comparison satisfies a comparison threshold, whether the short interval event pair is the result of oversensing.

[0107] In some examples, the comparison satisfies the comparison threshold, the short interval event pair is the result of oversensing, and processing circuitry 80 refrains from incrementing the counter based on the short interval event pair is the result of oversensing. In some examples, the first window and the second window have a same duration. In some examples, the first window is not centered around the first ventricular event and wherein the second window is not centered around the second ventricular event.

[0108] In some examples, the one or more characteristics include at least one of a peak- to-peak amplitude, a maximum amplitude, a minimum amplitude, a timing of a maximum amplitude, a timing of a minimum amplitude, a maximum slope, or a minimum slope. In some examples, the comparison threshold is 50%.

[0109] In some examples, the system includes an implantable medical device. In some examples, the implantable medical device includes an implantable cardioverter defibrillator.

[0110] In one or more examples, the functions described in this disclosure may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on, as one or more instructions or code, a computer- readable medium and executed by a hardware-based processing unit. Computer-readable media may include computer-readable storage media forming a tangible, non-transitory medium. Instructions may be executed by one or more processing circuitries, such as one or more DSPs, ASICs, FPGAs, general purpose microprocessors, or other equivalent integrated or discrete logic circuitry. Accordingly, the term “processing circuitry,” as used herein may refer to one or more of any of the foregoing structure or any other structure suitable for implementation of the techniques described herein.

[0111] The techniques described in this disclosure may be implemented, at least in part, in hardware, software, firmware, or any combination thereof. For example, various aspects of the techniques may be implemented within one or more microprocessors, DSPs, ASICs, FPGAs, or any other equivalent integrated or discrete logic QRS circuitry, as well as any combinations of such components, embodied in external devices, such as physician or patient programmers, stimulators, or other devices. The terms “processor” and “processing circuitry” may generally refer to any of the foregoing logic circuitry, alone or in combination with other logic circuitry, or any other equivalent circuitry, and alone or in combination with other digital or analog circuitry.

[0112] For aspects implemented in software, at least some of the functionality ascribed to the systems and devices described in this disclosure may be embodied as instructions on a computer-readable storage medium such as RAM, DRAM, SRAM, magnetic discs, optical discs, flash memories, or forms of EPROM or EEPROM. The instructions may be executed to support one or more aspects of the functionality described in this disclosure.

[0113] In addition, in some aspects, the functionality described herein may be provided within dedicated hardware and / or software modules. Depiction of different features as modules or units is intended to highlight different functional aspects and does not necessarily imply that such modules or units must be realized by separate hardware or software components. Rather, functionality associated with one or more modules or units may be performed by separate hardware or software components, or integrated within common or separate hardware or software components. Also, the techniques could be fully implemented in one or more circuits or logic elements. The techniques of this disclosure may be implemented in a wide variety of devices or apparatuses, including an IMD, an external programmer, a combination of an IMD and external programmer, an integrated circuit (IC) or a set of ICs, and / or discrete electrical circuitry, residing in an IMD and / or external programmer.

[0114] Various aspects of the techniques may enable the following examples.

[0115] Example 1. A system comprising: sensing circuitry configured to sense a cardiac electrogram (EGM) of a patient; and processing circuitry configured to: obtain the cardiac EGM of the patient; determine, based on the cardiac EGM, a first ventricular event; determine, based on the cardiac EGM, a second ventricular event; determine a first time interval between the first ventricular event and the second ventricular event; determine that the first time interval satisfies a first time interval threshold; determine, based on the first time interval satisfying the first time interval threshold, that the first ventricular event and the second ventricular event are a short interval event pair; determine whether the short interval event pair is a result of oversensing; increment or refrain from incrementing a counter based on the determination of whether the short interval event pair is the result of oversensing; and determine, based at least in part on a count of the counter, whether to send a lead integrity alert.

[0116] Example 2. The system of example 1, wherein the short interval pair is the result of oversensing, and wherein the processing circuitry is configured to refrain fromincrementing the counter based on the determination that the short interval pair is the result of oversensing.

[0117] Example 3. The system of example 1, wherein the short interval pair is not the result of oversensing, wherein the processing circuitry is configured to increment the counter based on the determination that the short interval pair is not the result of oversensing.

[0118] Example 4. The system of any of examples 1-3, wherein the first ventricular event and the second ventricular event follow an atrial event and wherein to determine whether the short interval event pair is the result of oversensing, the processing circuitry is configured to determine at least one of whether an atrial heart rate is within a predetermined range, whether the atrial event precedes the first ventricular event and the second ventricular event without an intervening atrial event between the first ventricular event and the second ventricular event, or whether a second time interval between the atrial event and the first ventricular event satisfies a second time interval threshold.

[0119] Example 5. The system of example 4, wherein the first ventricular event and the second ventricular event follow an atrial event and wherein to determine whether the short interval event pair is the result of oversensing, the processing circuitry is configured to determine whether the atrial heart rate is within the predetermined range, whether the atrial event precedes the first ventricular event and the second ventricular event without the intervening atrial event between the first ventricular event and the second ventricular event, and whether the second time interval between the atrial event and the first ventricular event satisfies the second time interval threshold.

[0120] Example 6. The system of any of examples 1-3, wherein to determine whether the short interval event pair is the result of oversensing, the processing circuitry is configured to: determine a first window in the cardiac EGM around the first ventricular event; determine a second window in the cardiac EGM around the second ventricular event; determine at least one first characteristic in the first window; determine at least one second characteristic in the second window, the at least one second characteristic corresponding to the at least one first characteristic;compare the at least one first characteristic to the at least one second characteristic; and determine, based on whether the comparison satisfies a comparison threshold, whether the short interval event pair is the result of oversensing.

[0121] Example 7. The system of example 6, wherein the comparison satisfies the comparison threshold, the short interval event pair is the result of oversensing, and the processing circuitry is configured to refrain from incrementing the counter based on the short interval event pair being the result of oversensing.

[0122] Example 8. The system of example 6 or example 7, wherein the first window and the second window have a same duration.

[0123] Example 9. The system of example 8, wherein the first window is not centered around the first ventricular event and wherein the second window is not centered around the second ventricular event.

[0124] Example 10. The system of any of examples 6-9, wherein the one or more characteristics comprise at least one of a peak-to-peak amplitude, a maximum amplitude, a minimum amplitude, a timing of a maximum amplitude, a timing of a minimum amplitude, a maximum slope, or a minimum slope.

[0125] Example 11. The system of any of examples 6-10, wherein the comparison threshold comprises 50%.

[0126] Example 12. The system of any of examples 1-11, wherein the system comprises an implantable medical device comprising the sensing circuitry and the processing circuitry.

[0127] Example 13. The system of example 12, wherein the implantable medical device comprises an implantable cardioverter defibrillator.

[0128] Example 14. The system of example 13, further comprising an integrated bipolar lead coupled to the implantable cardioverter defibrillator, wherein the sensing circuitry is configured to sense the EGM via the integrated bipolar lead.

[0129] Example 15. A method comprising: sensing, by sensing circuitry, a cardiac electrogram (EGM) of a patient; obtaining, by processing circuitry, the cardiac EGM of the patient; determining, by the processing circuitry and based on the cardiac EGM, a first ventricular event; determining, by the processing circuitry and based on the cardiac EGM, a second ventricular event; determining, by the processing circuitry, a first time interval between the first ventricular event and the second ventricular event; determining, by theprocessing circuitry, that the first time interval satisfies a first time interval threshold; determining, by the processing circuitry and based on the first time interval satisfying the first time interval threshold, that the first ventricular event and the second ventricular event are a short interval event pair; determining, by the processing circuitry, whether the short interval event pair is a result of oversensing; incrementing or refraining from incrementing, by the processing circuitry, a counter based on the determination of whether the short interval pair is the result of oversensing; and determining, by the processing circuitry and based at least in part on a count of the counter, whether to send a lead integrity alert.

[0130] Example 16. The method of example 15, wherein the short interval pair is the result of oversensing, and wherein the method comprises refraining from incrementing the counter based on the determination that the short interval pair is the result of oversensing.

[0131] Example 17. The method of example 15, wherein the short interval pair is not the result of oversensing, and wherein the method comprises incrementing the counter based on the determination that the short interval pair is not the result of oversensing.

[0132] Example 18. The method of any of examples 15-17, wherein the first ventricular event and the second ventricular event follow an atrial event and wherein determining whether the short interval pair is the result of oversensing comprises determining at least one of whether an atrial heart rate is within a predetermined range, whether the atrial event precedes the first ventricular event and the second ventricular event without an intervening atrial event between the first ventricular event and the second ventricular event, or whether a second time interval between the atrial event and the first ventricular event satisfies a second time interval threshold.

[0133] Example 19. The method of any of examples 15-18, wherein to determine whether the short interval pair is the result of oversensing, and wherein the method further comprises: determining, by the processing circuitry, a first window in the cardiac EGM around the first ventricular event; determining, by the processing circuitry, a second window in the cardiac EGM around the second ventricular event; determining, by the processing circuitry, at least one first characteristic in the first window; determining, by the processing circuitry, at least one second characteristic in the second window, the at least one second characteristic corresponding to the at least one first characteristic; comparing, by the processing circuitry, the at least one first characteristic to the at least one second characteristic; and determining, by the processing circuitry and based on whether thecomparison satisfies a comparison threshold, whether the short interval pair is the result of oversensing.

[0134] Example 20. An implantable medical device comprising: sensing circuitry configured to sense a cardiac electrogram (EGM) of a patient; and processing circuitry configured to: obtain the cardiac EGM of the patient; determine, based on the cardiac EGM, a first ventricular event; determine, based on the cardiac EGM, a second ventricular event; determine a first time interval between the first ventricular event and the second ventricular event; determine that the first time interval satisfies a first time interval threshold; determine, based on the first time interval satisfying the first time interval threshold, that the first ventricular event and the second ventricular event are a short interval event pair; determine whether the short interval event pair is a result of oversensing; increment or refrain from incrementing a counter based on the determination of whether the short interval event pair is the result of oversensing; and determine, based at least in part on a count of the counter, whether to send a lead integrity alert.

[0135] Various examples have been described. These and other examples are within the scope of the following claims.

Claims

CLAIMS:

1. A system comprising: sensing circuitry configured to sense a cardiac electrogram (EGM) of a patient; and processing circuitry configured to: obtain the cardiac EGM of the patient; determine, based on the cardiac EGM, a first ventricular event; determine, based on the cardiac EGM, a second ventricular event; determine a first time interval between the first ventricular event and the second ventricular event; determine that the first time interval satisfies a first time interval threshold; determine, based on the first time interval satisfying the first time interval threshold, that the first ventricular event and the second ventricular event are a short interval event pair; determine whether the short interval event pair is a result of oversensing; increment or refrain from incrementing a counter based on the determination of whether the short interval event pair is the result of oversensing; and determine, based at least in part on a count of the counter, whether to send a lead integrity alert.

2. The system of claim 1, wherein the short interval pair is the result of oversensing, and wherein the processing circuitry is configured to refrain from incrementing the counter based on the determination that the short interval pair is the result of oversensing.

3. The system of claim 1, wherein the short interval pair is not the result of oversensing, wherein the processing circuitry is configured to increment the counter based on the determination that the short interval pair is not the result of oversensing.

4. The system of any of claims 1-3, wherein the first ventricular event and the second ventricular event follow an atrial event and wherein to determine whether the shortinterval event pair is the result of oversensing, the processing circuitry is configured to determine at least one of whether an atrial heart rate is within a predetermined range, whether the atrial event precedes the first ventricular event and the second ventricular event without an intervening atrial event between the first ventricular event and the second ventricular event, or whether a second time interval between the atrial event and the first ventricular event satisfies a second time interval threshold.

5. The system of claim 4, wherein the first ventricular event and the second ventricular event follow an atrial event and wherein to determine whether the short interval event pair is the result of oversensing, the processing circuitry is configured to determine whether the atrial heart rate is within the predetermined range, whether the atrial event precedes the first ventricular event and the second ventricular event without the intervening atrial event between the first ventricular event and the second ventricular event, and whether the second time interval between the atrial event and the first ventricular event satisfies the second time interval threshold.

6. The system of any of claims 1-3, wherein to determine whether the short interval event pair is the result of oversensing, the processing circuitry is configured to: determine a first window in the cardiac EGM around the first ventricular event; determine a second window in the cardiac EGM around the second ventricular event; determine at least one first characteristic in the first window; determine at least one second characteristic in the second window, the at least one second characteristic corresponding to the at least one first characteristic; compare the at least one first characteristic to the at least one second characteristic; and determine, based on whether the comparison satisfies a comparison threshold, whether the short interval event pair is the result of oversensing.

7. The system of claim 6, wherein the comparison satisfies the comparison threshold, the short interval event pair is the result of oversensing, and the processingcircuitry is configured to refrain from incrementing the counter based on the short interval event pair being the result of oversensing.

8. The system of claim 6 or claim 7, wherein the first window and the second window have a same duration.

9. The system of claim 8, wherein the first window is not centered around the first ventricular event and wherein the second window is not centered around the second ventricular event.

10. The system of any of claims 6-9, wherein the one or more characteristics comprise at least one of a peak-to-peak amplitude, a maximum amplitude, a minimum amplitude, a timing of a maximum amplitude, a timing of a minimum amplitude, a maximum slope, or a minimum slope.

11. The system of any of claims 6-10, wherein the comparison threshold comprises 50%.

12. The system of any of claims 1-11, wherein the system comprises an implantable medical device comprising the sensing circuitry and the processing circuitry.

13. The system of claim 12, wherein the implantable medical device comprises an implantable cardioverter defibrillator.

14. A method comprising: sensing, by sensing circuitry, a cardiac electrogram (EGM) of a patient; obtaining, by processing circuitry, the cardiac EGM of the patient; determining, by the processing circuitry and based on the cardiac EGM, a first ventricular event; determining, by the processing circuitry and based on the cardiac EGM, a second ventricular event, the first ventricular event and the second ventricular event forming an event pair;determining, by the processing circuitry, a first time interval between the first ventricular event and the second ventricular event; determining, by the processing circuitry, that the first time interval satisfies a first time interval threshold; determining, by the processing circuitry and based on the first time interval satisfying the first time interval threshold, that the first ventricular event and the second ventricular event are a short interval event pair; determining, by the processing circuitry, whether the short interval event pair is a result of oversensing; incrementing or refraining from incrementing, by the processing circuitry, a counter based on the determination of whether the short interval pair is the result of oversensing; and determining, by the processing circuitry and based at least in part on a count of the counter, whether to send a lead integrity alert.

15. An implantable medical device comprising: sensing circuitry configured to sense a cardiac electrogram (EGM) of a patient; and processing circuitry configured to: obtain the cardiac EGM of the patient; determine, based on the cardiac EGM, a first ventricular event; determine, based on the cardiac EGM, a second ventricular event, the first ventricular event and the second ventricular event forming an event pair; determine a first time interval between the first ventricular event and the second ventricular event; determine that the first time interval satisfies a first time interval threshold; determine, based on the first time interval satisfying the first time interval threshold, that the first ventricular event and the second ventricular event are a short interval event pair; determine whether the short interval event pair is a result of oversensing;increment or refrain from incrementing a counter based on the determination of whether the short interval event pair is the result of oversensing; and determine, based at least in part on a count of the counter, whether to send a lead integrity alert.

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