Inhibiting noise reversion

Abstract

This disclosure generally relates to systems, devices, and methods for initiating or inhibiting noise reversion pacing therapy based on a morphology analysis to determine whether monitored cardiac electrical activity is indicative of a ventricular tachycardia / ventricular fibrillation (VT / VF). Specifically, if the morphology analysis indicates that a VT / VF episode is occurring, then noise reversion pacing therapy is inhibited.

Description

INHIBITING NOISE REVERSION

[0001] This application claims the benefit of U.S. Provisional Patent Application Serial No. 63 / 639,055, filed April 26, 2024, the entire content of which is incorporated herein by reference.

[0002] This disclosure generally relates to initiating or inhibiting noise reversion pacing therapy based on a morphology analysis to determine whether monitored cardiac electrical activity is indicative of a ventricular tachycardia / ventricular fibrillation (VT / VF).

[0003] Implantable medical devices (IMDs) may include multi -programmable, multimode implantable pacemakers, and any other implantable cardiac stimulators, monitors, or the like, and may be equipped with sense amplifiers that are designed to detect depolarizations of myocardial tissue constituting features of the electrogram (EGM) as a “sense event” and record data related to the sense event and / or affect the operation of such devices. For example, to detect P-waves (e.g., indicative of atrial contractions or depolarizations) and / or R-waves (e.g., indicative of ventricular contractions or depolarizations) and so that the various pacing intervals such as the A-V delay can be timed such that certain operations may be initiated on detection of the P-waves or R- waves.

[0004] In practice, the detection of P-waves and R-waves may be complicated by a number of factors or abnormal conditions which mask, elevate, or diminish the signal amplitudes, so that the signals, even if present may not be sensed (referred to as “undersensing”) or too many sensed events may be triggered (referred to as “oversensing”). For example, noise can cause oversensing, and such oversensing can lead to inhibition of pacing, which can be problematic in pacemaker-dependent patients. To detect this noise, IMDs can use a combination of analog noise filter (ANF) and “quiet timer” features. When noise is detected by these features, the IMDs may switch into noise reversion pacing therapy, which is pacing without tracking and without inhibition (e.g., VOO mode), so continuous pacing is delivered even when the sense amplifier is swamped by noise. In other words, noise reversion pacing therapy may be designed to revert thepacemaker to an asynchronous pacing mode when noise is suspected to avoid pacing inhibition, which could be problematic in pacemaker-dependent patients.

[0005] In practice, the detection of P-waves and R-waves may be complicated by a number of factors or abnormal conditions that mask, elevate, or diminish the signal amplitudes, so that the signals, even if present may not be sensed (referred to as “undersensing”) or too many sensed events may be triggered (referred to as “oversensing”). For example, noise can cause oversensing, and such oversensing can lead to inhibition of pacing, which can be problematic in pacemaker-dependent patients. To detect this noise, IMDs can use a combination of analog noise filter (ANF) and “quiet timer” functionality. The ANF functionality may be generally described as measuring the peaks of monitored ventricular electrical activity and applying filtering to it as a decay time constant. The resultant signal decays fast enough that if the only peak present is the normal QRS complex, it will not change the signal behavior substantially. However, if continuous noise is present, the peak value will not decay as peaks are received repeatedly from the continuous noise. The level of this filtered peak value may be compared against a noise level high (NLH) parameter to determine if the noise threshold has been crossed or not. When noise is detected by these features, the IMDs may switch into noise reversion pacing therapy (e.g., pacing without tracking and without inhibition such as VOO mode) so continuous pacing is delivered even when the sense amplifier is swamped by noise. In other words, the ANF may effectively process the monitored ventricular electrical activity such that only spontaneous events whose magnitude is greater than that of the noise source (e.g., cardiac events such as atrial and ventricular depolarizations) will be passed along.

[0006] The quiet timer functionality may be described as a quiet time interval, or period, that is started in response to a cardiac electrical signal crossing a noise threshold so as to avoid noise following detection of a R-wave (i.e., a ventricular activation or depolarization). In some examples, the quiet timer is started in response to each R-wave sensing threshold crossing that occurs outside a post-sense blanking period. When a quiet timer is active (e.g., during the quiet time interval), the threshold detectors will not detect a further pace pulse. In this manner, quiet timer functionality may be described as inhibiting further detection of ventricular paces or intrinsic activations until the quiet timer deactivates (e.g., the quiet time interval expires). Additionally, despite inhibiting sensingof ventricular paces or intrinsic activations until the quiet timer deactivates, if sensing threshold is crossed during the quiet timer interval, the signal may be considered to be at a frequency characteristic of noise. Crossing the sensing threshold during the quiet timer interval will cause the quiet timer interval to be reset. If the quiet timer interval is continuously reset (e.g., noise present) until the next scheduled pace, then that pace may be delivered as a noise reversion pace. If the sensing threshold is not crossed during a quiet timer interval, the quiet timer interval will expire and the atrial or ventricular sense channel is available for a P-wave or R-wave sensing, which occurs when the sensing threshold is crossed. The quiet time interval may be between 10 milliseconds (ms) and 50 ms. In one embodiment, the quiet time interval is 40 ms. Illustrative quiet timer functionality may be described in U.S. Patent No. 10,226,197 to Reinke, et al. issued on March 12, 2019, which is incorporated herein by reference in its entirety.

[0007] These noise functionality, or features, may be designed to be sensitive with a bias to provide noise reversion pacing rather than inappropriately withholding delivery of life-sustaining pacing to a pacemaker-dependent patient. The noise reversion pacing therapy may be designed to revert the pacemaker to an asynchronous pacing mode when noise is suspected to avoid pacing inhibition, which could be problematic in pacemakerdependent patients.

[0008] Conventional implantable defibrillators may not apply noise reversion pacing to avoid unintentionally initiating pacing during a ventricular tachyarrhythmia / ventricular fibrillation (VT / VF) episode. If noise reversion pacing therapy delivers pacing during a VT / VF episode, a device may fail to detect such arrhythmias.SUMMARY

[0009] One illustrative implantable medical device includes a plurality of electrodes to sense cardiac electrical activity of a patient’s heart and to deliver cardiac pacing therapy to the patient’s heart and a processing circuitry operably coupled to one or more of the plurality of electrodes. The processing circuitry is configured to monitor ventricular electrical activity using the one or more electrodes in the plurality of electrodes, perform a pacing therapy comprising controlling delivery of the cardiac pacing therapy using the oneor more electrodes based on at least the monitored ventricular electrical activity, determine that the monitored ventricular electrical activity comprises an unacceptable amount of noise, determine that the monitored ventricular electrical activity is indicative of a ventricular tachycardia / ventricular fibrillation (VT / VF) episode based on morphology analysis of the monitored ventricular electrical activity in response to determination that the monitored ventricular electrical activity comprises the unacceptable amount of noise, and initiate noise reversion pacing therapy in response to determining that the monitored ventricular electrical activity comprises the unacceptable amount of noise and the monitored ventricular electrical activity not being indicative of the VT / VF episode. The noise reversion pacing therapy comprises controlling delivery of the cardiac pacing therapy independent of the monitored ventricular electrical activity. The processing circuitry is further configured to initiate a VT / VF response in response to determining that the monitored ventricular electrical activity is indicative of the VT / VF episode.

[0010] One illustrative method includes monitoring ventricular electrical activity of a patient’s heart using one or more of a plurality of electrodes, performing pacing therapy comprising controlling delivery of the cardiac pacing therapy using the one or more of the plurality of electrodes based on at least the monitored ventricular electrical activity, determining that the monitored ventricular electrical activity comprises an unacceptable amount of noise, determining that the monitored ventricular electrical activity is indicative of a ventricular tachycardia / ventricular fibrillation (VT / VF) episode based on morphology analysis of the monitored ventricular electrical activity in response to determination that the monitored ventricular electrical activity comprises the unacceptable amount of noise, and initiating noise reversion pacing therapy in response to determining that the monitored ventricular electrical activity comprises the unacceptable amount of noise and the monitored ventricular electrical activity not being indicative of the VT / VF episode. The noise reversion pacing therapy comprises controlling delivery of the cardiac pacing therapy independent of the monitored ventricular electrical activity. The method further includes initiating a VT / VF response in response to determining that the monitored ventricular electrical activity is indicative of the VT / VF episode.

[0011] One illustrative system includes an external device configured to analyze the monitored ventricular activity to confirm VT / VF episodes and an implantable medicaldevice that includes a plurality of electrodes to sense cardiac electrical activity of a patient’s heart and to deliver cardiac pacing therapy to the patient’s heart, a telemetry apparatus comprising an antenna and a processing circuitry, operably coupled to one or more electrodes in the plurality of electrodes and the telemetry apparatus. The processing circuitry is configured to monitor ventricular electrical activity using the one or more electrodes in the plurality of electrodes, perform a pacing therapy comprising controlling delivery of the cardiac pacing therapy based on at least the monitored ventricular electrical activity, determine that the monitored ventricular electrical activity comprises an unacceptable amount of noise, determine that the monitored ventricular electrical activity is indicative of a ventricular tachycardia / ventricular fibrillation (VT / VF) episode based on morphology analysis of the monitored ventricular electrical activity in response to determination that the monitored ventricular electrical activity comprises the unacceptable amount of noise, and initiate noise reversion pacing therapy in response to determining that the monitored ventricular electrical activity comprises the unacceptable amount of noise and the monitored ventricular electrical activity not being indicative of the VT / VF episode. The noise reversion pacing therapy includes controlling delivery of the cardiac pacing therapy independent of the monitored ventricular electrical activity. The processing circuitry is further configured to initiate a VT / VF response in response to determining that the monitored ventricular electrical activity is indicative of the VT / VF episode. The VT / VF response includes transmitting the monitored ventricular activity to the external device using the telemetry apparatus.

[0012] In one or more embodiments, systems, devices, and methods may be described as improvements to specificity of noise detection in order to avoid delivery of noise reversion pacing therapy during a tachyarrhythmia episode. For example, prior to initiation of noise reversion pacing (such as, for example, when either or both of ANF or quiet timer criteria may be met), an IMD may initiate a morphology analysis of monitored cardiac electrical activity to determine whether the monitored cardiac electrical activity comprises a VT / VF episode. If the morphology analysis indicates that a VT / VF episode is occurring, then noise reversion pacing therapy is inhibited.

[0013] The morphology analysis may comprise estimating frequency content (e.g., through counting zero crossings), estimating mean frequency of monitored cardiacelectrical activity (e.g., according to a sum of an absolute value of derivative monitored cardiac electrical activity divided by the sum of an absolute value of the monitored cardiac electrical activity), detecting and counting a number of inflection points of the monitored cardiac electrical activity, or detecting and counting occurrences of signal clipping in monitored cardiac electrical activity. Other indicators of VT / VF morphology may also be included in the morphology analysis.

[0014] After at least one of the above measurements are performed, determination may be made regarding whether the monitored cardiac electrical activity is indicative of a monomorphic ventricular tachycardia (MVT) / polymorphic ventricular tachycardia (PVT) / ventricular fibrillation (VF) tachyarrhythmia or if the signal is noise. If the signal is noise or if the signal comprises noisy signals, then ANF and quiet timer are activated to determine whether standard noise reversion pacing should be initiated. If, however, the signal is indicative of MVT / P VT / VF, the noise reversion pacing is inhibited. If noise reversion pacing is inhibited, the morphology analysis can be periodically repeated to determine whether noise reversion pacing therapy should be initiated. Accordingly, detection of MVT / P VT / VF can proceed without oversensing of noise reversion pacing therapy. The morphology analysis as described herein may alternately or additionally include a rapid alert functionality feature, wherein IMDs implementing morphology analysis work in conjunction with an edge artificial intelligence (Al) on an external user interface device, such as, for example, a mobile phone, to detect tachyarrhythmias and trigger notifications for emergency assistance. Alternately or additionally, the rapid alert functionality feature may be configured to implement morphology analysis and work in conjunction with an Al on the IMD.

[0015] Alternately, or in addition, the described morphology analysis can be used to improve discrimination between noise and MVT / P VT / VF sensing in IMDs such as, for example, implantable defibrillators. Conventional implantable defibrillators may not apply noise reversion pacing therapy and may instead be configured to undersense noise such that noise reversion pacing therapy is not unintentionally initiated during an MVT / PVT / VF episode. As an example, because implantable cardioverter-defibrillators (ICDs) generally utilize high sensitivity to VT / VF, ICDs may be configured to inhibit pacing if noise is sensed rather than to initiate any noise reversion pacing therapy.

[0016] Implementing the morphology analysis as described herein may allow improvements to noise reversion pacing therapy in defibrillators without risking undersensing of MVT / PVT / VF. Additionally or alternately, implementation of the morphology analysis as described herein in ICDs may potentially reduce occurrences of unintentional or inappropriate shocks.

[0017] The details of one or more aspects of the disclosure are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the techniques described in this disclosure will be apparent from the description and drawings, and from the claims.BRIEF DESCRIPTION OF DRAWINGS

[0018] FIG. 1 is an illustrative system including an IMD and an external user interface device.

[0019] FIG. 2 is the IMD of FIG. 1.

[0020] FIG. 3 is a block diagram of the IMD of FIGS. 1-2.

[0021] FIG. 4 is a diagram of the external user interface device of the system of FIG.1.

[0022] FIG. 5 is a diagram of an illustrative system including the IMD and the external user interface device of FIG. 1 and additional devices coupled thereto via a network.

[0023] FIG. 6 is an illustrative method of initiating or inhibiting noise reversion pacing therapy based on a morphology analysis.

[0024] FIG. 7 is an illustrative method of the VT / VF morphology analysis of FIG. 6.DETAILED DESCRIPTION

[0025] In the following detailed description of illustrative embodiments, reference is made to the accompanying figures of the drawing which form a part thereof, and in which are shown, by way of illustration, specific embodiments which may be practiced. It is tobe understood that other embodiments may be utilized, and structural changes may be made without departing from (e.g., still falling within) the scope of the disclosure presented hereby.

[0026] Illustrative systems, devices, and methods shall be described with reference to Figures 1-7. It will be apparent to one skilled in the art that elements or processes from one embodiment may be used in combination with elements or processes of the other embodiments, and that the possible embodiments of such systems, devices, and methods using combinations of features set forth herein is not limited to the specific embodiments shown in the Figures and / or described herein. Further, it will be recognized that the embodiments described herein may include many elements that are not necessarily shown to scale. Still further, it will be recognized that timing of the processes and the size and shape of various elements herein may be modified but still fall within the scope of the present disclosure, although certain timings, one or more shapes and / or sizes, or types of elements, may be advantageous over others.

[0027] FIG. 1 is a conceptual drawing of an illustrative therapy system 10 (further detailed in FIG. 2) that may be used to deliver pacing therapy, such as noise reversion pacing therapy, bradycardia pacing therapy, biventricular pacing therapy, cardiac resynchronization therapy, etc., to a patient 14, to determine noise used to initiate noise reversion pacing therapy, and to determine VT / VF. It may be described that noise reversion pacing therapy is a subset of bradycardia pacing therapy and that initiation of noise reversion pacing therapy is effectively informing how bradycardia pacing should operate. While a patient 14 is shown as a human, the patient 14 may also be a variety of other types of animals. The therapy system 10 may include an implantable medical device 16 (IMD), which may be coupled to leads 18, 20, 22, and an external user interface user interface device 24. The IMD 16 may be, e.g., an implantable pacemaker, cardioverter, and / or defibrillator, that delivers, or provides, electrical signals (e.g., paces, etc.) to and / or senses electrical signals from the heart 12 of the patient 14 via electrodes coupled to one or more of the leads 18, 20, 22.

[0028] The leads 18, 20, 22 extend into the heart 12 of the patient 14 to sense electrical activity of the heart 12 and / or to deliver electrical stimulation to the heart 12. In the example shown in FIG. 1, the right ventricular (RV) lead 18 extends through one ormore veins (not shown), the superior vena cava (not shown), and the right atrium 26, and into the right ventricle 28. The right atrial (RA) lead 22 extends through one or more veins and the vena cava, and into the right atrium 26 of the heart 12. Further, the left ventricular (LV) coronary sinus lead 20 extends through one or more veins, the vena cava, the right atrium 26, and into the coronary sinus 30 to a region adjacent to the free wall of the left ventricle 32 of the heart 12.

[0029] The IMD 16 may sense, among other things, electrical signals attendant to the depolarization and repolarization of the heart 12 via electrodes coupled to at least one of the leads 18, 20, 22. In some examples, the IMD 16 provides pacing therapy (e.g., pacing pulses) to the heart 12 based on the electrical signals sensed within the heart 12. The IMD 16 may be operable to adjust one or more parameters associated with the pacing therapy such as, e.g., pacing rate, R-R interval, A-V delay and other various timings, pulse width, amplitude, voltage, burst length, etc. Further, the IMD 16 may be operable to use various electrode configurations to deliver pacing therapy, which may be unipolar, bipolar, quadripolar, or further multipolar. Hence, a multipolar lead system may provide, or offer, multiple electrical vectors to pace from. A pacing vector may include at least one cathode, which may be at least one electrode located on at least one lead, and at least one anode, which may be at least one electrode located on at least one lead (e.g., the same lead, or a different lead) and / or on the casing, or can, of the IMD 16, or electrode apparatus. The IMD 16 may be operable to adjust one or more sensing or detection parameters associated with detection of VT / VF and noise using the electrical signals monitored by electrodes located on the leads 18, 20, 22. The IMD 16 may also provide defibrillation therapy and / or cardioversion therapy via electrodes located on at least one of the leads 18, 20, 22. Further, the IMD 16 may detect arrhythmia of the heart 12, such as fibrillation of the ventricles 28, 32, and deliver defibrillation therapy to the heart 12 in the form of electrical pulses. In some examples, the IMD 16 may be programmed to deliver a progression of therapies, e.g., pulses with increasing energy levels, until an arrythmia, such as atrial fibrillation, of the heart 12 is stopped.

[0030] In some examples, the external user interface device 24 may be a mobile computing device or a computer workstation. The external user interface device 24 may include a user interface that receives input from a user. The user interface may include, forexample, 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. The external user interface 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 embodiments, a display of the external user interface device 24 may include a touch screen display, and a user may interact with the external user interface device 24 via the display.

[0031] A user, such as a physician, technician, patient, or other user, may interact with the external user interface device 24 to communicate with the IMD 16. For example, a user may interact with the external user interface device 24 to retrieve physiological or diagnostic information from the IMD 16. A user may also interact with the external user interface device 24 to program the IMD 16, e.g., select values for operational parameters of the IMD.

[0032] Further, for example, a user may use the external user interface device 24 to retrieve information from IMD 16 regarding the rhythm of heart 12, trends therein over time, or tachyarrhythmia episodes. More specifically, for example, the external user interface device 24 may receive sensed cardiac signals, such as ventricular electrical activity, that the IMD 16 has initially determined may be indicative of VT / VF, and may further analyze the sensed cardiac signals to confirm whether the sensed cardiac signals are indicative of VT / VF or not indicative of VT / VF. In one or more embodiments, the external user interface device 24 may utilize conventional processing and / or artificial intelligence to analyze the sensed cardiac signals to determine and / or confirm VT / VF. As another example, a user may use the external user interface device 24 to retrieve information from the IMD 16 regarding other sensed physiological or diagnostic parameters of the patient 14, such as intracardiac or intravascular pressure, activity, posture, respiration, or thoracic impedance. As another example, the user may use the external user interface device 24 to retrieve information from the IMD 16 regarding the performance or integrity of the IMD 16 or other components of the system 10, such as the leads 18, 20, and 22, or a power source of the IMD 16.

[0033] A user may use the external user interface device 24 to program a therapy progression, select electrodes used to deliver defibrillation shocks, select waveforms for the defibrillation shock, or select or configure a tachyarrhythmia and / or fibrillation detection algorithm for the IMD 16. A user may also use the external user interface device 24 to program aspects of other therapies provided by the IMD 16, such as cardioversion or pacing therapies. In some examples, a user may activate certain features of the IMD 16 by entering one or more commands via the external user interface 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.

[0034] The IMD 16 and the external user interface device 24 may communicate via wireless communication using any techniques known in the art. Examples of communication techniques may include, for example, low frequency or radiofrequency (RF) telemetry (e.g., BLUETOOTH), but other techniques are also contemplated. In some examples, the external user interface 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 the IMD 16 and the external user interface device 24.

[0035] FIG. 2 is a conceptual drawing of the IMD 16 and the leads 18, 20, 22 of therapy system 10 of FIG. 1 in more detail. The leads 18, 20, 22 may be electrically coupled to a therapy delivery (e.g., for delivery of bradycardia pacing therapy, for delivery of cardiac resynchronization therapy, etc.), a sensing (e.g., for sensing one or more signals from one or more electrodes), and / or any other s of the IMD 16 via a connector block 34. In some examples, the proximal ends of the leads 18, 20, 22 may include electrical contacts that electrically couple to respective electrical contacts within the connector block 34 of the IMD 16. In addition, in some examples, the leads 18, 20, 22 may be mechanically coupled to the connector block 34 with the aid of set screws, connection pins, or another suitable mechanical coupling mechanism.

[0036] Each of the leads 18, 20, 22 includes an elongated insulative lead body, which may carry a number of conductors (e.g., concentric coiled conductors, straight conductors, etc.) separated from one another by insulation (e.g., tubular insulative sheaths). In the illustrated example, bipolar electrodes 40, 42 are located proximate to a distal end of thelead 18. In addition, bipolar electrodes 44, 45, 46, 47 are located proximate to a distal end of the lead 20 and bipolar electrodes 48, 50 are located proximate to a distal end of the lead 22.

[0037] The electrodes 40, 44, 45, 46, 47, 48 may take the form of, or define, ring electrodes, and the electrodes 42, 50 may take the form of, or define, extendable helix tip electrodes mounted retractably within the insulative electrode heads 52, 54, 56, respectively. Each of the electrodes 40, 42, 44, 45, 46, 47, 48, 50 may be electrically coupled to a respective one of the conductors (e.g., coiled and / or straight) within the lead body of its associated lead 18, 20, 22, and thereby coupled to a respective one of the electrical contacts on the proximal end of the leads 18, 20, 22.

[0038] The electrodes 40, 42, 44, 45, 46, 47, 48, 50 may further be used to sense electrical signals (e.g., morphological waveforms within electrograms (EGM)) attendant to the depolarization and repolarization of the heart 12. The electrical signals are conducted to the IMD 16 via the respective leads 18, 20, 22. In some examples, the IMD 16 may also deliver pacing pulses via the electrodes 40, 42, 44, 45, 46, 47, 48, 50 to cause depolarization of cardiac tissue of the patient's heart 12. In some examples, as illustrated in FIG. 2, the IMD 16 includes one or more housing electrodes, such as housing electrode 58, which may be formed integrally with an outer surface of a housing 60 (e.g., hermetically sealed housing) of the IMD 16 or otherwise coupled to the housing 60. Any of the electrodes 40, 42, 44, 45, 46, 47, 48, 50 may be used for unipolar sensing or pacing in combination with the housing electrode 58. It is generally understood by those skilled in the art that other electrodes can also be selected to define, or be used for, pacing and sensing vectors. Further, any of electrodes 40, 42, 44, 45, 46, 47, 48, 50, 58, when not being used to deliver pacing therapy, may be used to sense electrical activity during pacing therapy.

[0039] As described in further detail with reference to FIG. 2, the housing 60 may enclose a therapy delivery that may include a stimulation generator for generating cardiac pacing pulses and defibrillation or cardioversion shocks, as well as a sensing for monitoring the electrical signals of the patient’s heart (e.g., the patient's heart rhythm). The leads 18, 20, 22 may also include elongated electrodes 62, 64, 66, respectively, which may take the form of a coil. The IMD 16 may deliver defibrillation shocks to the heart 12 viaany combination of the elongated electrodes 62, 64, 66 and the housing electrode 58. The electrodes 58, 62, 64, 66 may also be used to deliver cardioversion pulses to the heart 12. Further, the electrodes 62, 64, 66 may be fabricated from any suitable electrically conductive material, such as, but not limited to, platinum, platinum alloy, and / or other materials known to be usable in implantable defibrillation electrodes. Since electrodes 62, 64, 66 are not generally configured to deliver pacing therapy, any of electrodes 62, 64, 66 may be used to sense electrical activity and may be used in combination with any of electrodes 40, 42, 44, 45, 46, 47, 48, 50, 58. In at least one embodiment, the RV elongated electrode 62 may be used to sense electrical activity of a patient's heart during the delivery of pacing therapy (e.g., in combination with the housing electrode 58, or defibrillation electrode-to-housing electrode vector).

[0040] The configuration described herein of the therapy system 10 is merely one example. In other examples, the therapy system may include epicardial leads and / or patch electrodes instead of, or in addition to, the transvenous leads 18, 20, 22 illustrated in FIG.1. In further embodiments, the therapy system 10 may be implanted in / around the cardiac space without transvenous leads (e.g., leadless / wireless pacing systems) or with leads implanted (e.g., implanted transvenously or using approaches) into the left chambers of the heart (in addition to or replacing the transvenous leads placed into the right chambers of the heart as illustrated in FIG. 1). In one example, the left ventricular (LV) coronary sinus lead 20 extends through one or more veins, the vena cava, the right atrium 26, and into the coronary sinus 30 to a region adjacent to the free wall of the left ventricle 32 of the heart 12. Further, in one or more embodiments, the IMD 16 may not be implanted within the patient 14. For example, the IMD 16 may deliver various cardiac therapies to the heart 12 via percutaneous leads that extend through the skin of the patient 14 to a variety of positions within or outside of the heart 12. In one or more embodiments, the system 10 may utilize wireless pacing (e.g., using energy transmission to the intracardiac pacing component(s) via ultrasound, inductive coupling, RF, etc.) and sensing cardiac activation using electrodes on the can / housing and / or on subcutaneous leads.

[0041] Other example therapy systems that provide electrical stimulation therapy to the heart 12 may include any suitable number of leads coupled to the IMD 16, and each of the leads may extend to any location within or proximate to the heart 12. Such othertherapy systems may include three transvenous leads located as illustrated in FIGS. 1-2. Still further therapy systems may include a single lead that extends from the IMD 16 into the right atrium 26 or two leads that extend into a respective one of the right atrium 26 and the left atrium.

[0042] FIG. 3 is a functional block diagram of an illustrative configuration of the IMD 16. As shown, the IMD 16 may include a control module 81, a therapy delivery module 84 (e.g., which may include a stimulation generator), a sensing module 86, and a power source 90. The control module, or apparatus, 81 may include a processing circuitry, or computing apparatus, 80, memory 82, and a telemetry module, or apparatus, 88. The memory 82 may include computer-readable instructions that, when executed, e.g., by the processing circuitry 80, cause the IMD 16 and / or the control module 81 to perform various functions attributed to the IMD 16 and / or the control module 81 described herein. Further, the memory 82 may include any volatile, non-volatile, magnetic, optical, and / 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, and / or any other digital media.

[0043] The processing circuitry 80 of the control module 81 may include any processing circuitry such as, e.g., one or more of a microprocessor, a controller, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field- programmable gate array (FPGA), and / or equivalent discrete or integrated logic circuitry. In some examples, the 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, and / or one or more FPGAs, as well as other discrete or integrated logic circuitry. The functions attributed to the processing circuitry 80 herein may be embodied as software, firmware, hardware, or any combination thereof.

[0044] The control module 81 may control the therapy delivery module, or apparatus, 84 to deliver therapy (e.g., electrical stimulation therapy such as cardiac remodeling pacing) to the heart 12 according to a selected one or more therapy programs, which may be stored in the memory 82, and based on algorithms, or methods, described further below. More, specifically, the control module 81 (e.g., the processing circuitry 80) may control various parameters of the electrical stimulus delivered by the therapy deliverymodule 84 such as, e.g., A-V delays, pacing vectors, pacing pulses with the amplitudes, pulse widths, frequency, or electrode polarities, etc., which may be specified by one or more selected therapy programs (e.g., A-V delay adjustment programs, pacing therapy programs, pacing recovery programs, capture management programs, etc.). The therapy delivery module 84 is electrically coupled to electrodes 40, 42, 44, 45, 46, 47, 48, 50, 58, 62, 64, 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 module 84 may be configured to generate and deliver electrical stimulation therapy such as pacing therapy to the heart 12 using one or more of the electrodes 40, 42, 44, 45, 46, 47, 48, 50, 58, 62, 64, 66.

[0045] For example, the therapy delivery module 84 may deliver pacing stimulus (e.g., pacing pulses) via ring electrodes 40, 44, 45, 46, 47, 48 coupled to leads 18, 20, 22 and / or helical tip electrodes 42, 50 of leads 18, 22. Further, for example, therapy delivery module 84 may deliver defibrillation shocks to the heart 12 via at least two of electrodes 58, 62, 64, 66. In some examples, therapy delivery module 84 may be configured to deliver pacing, cardioversion, or defibrillation stimulation in the form of electrical pulses. In other examples, therapy delivery module 84 may be configured to deliver one or more of these types of stimulation in the form of other signals, such as sine waves, square waves, and / or other substantially continuous time signals.

[0046] The IMD 16 may further include a switch module, or apparatus, 85 and the control module 81 (e.g., the processing circuitry 80) may use the switch module 85 to select, e.g., via a data / address bus, which of the available electrodes are used to deliver therapy such as pacing pulses for pacing therapy, or which of the available electrodes are used for sensing. The switch module 85 may include a switch array, switch matrix, multiplexer, or any other type of switching device suitable to selectively couple the sensing module, or apparatus, 86 and / or the therapy delivery module 84 to one or more selected electrodes. More specifically, the therapy delivery module 84 may include a plurality of pacing output circuits. Each pacing output circuit of the plurality of pacing output circuits may be selectively coupled, e.g., using the switch module 85, to one or more of the electrodes 40, 42, 44, 45, 46, 47, 48, 50, 58, 62, 64, 66 (e.g., a pair of electrodes for delivery of therapy to a bipolar or multipolar pacing vector). In other words,each electrode can be selectively coupled to one of the pacing output circuits of the therapy delivery module using the switch module 85.

[0047] The sensing module 86 is coupled (e.g., electrically coupled) to sensing apparatus, which may include, among additional sensing apparatus, the electrodes 40, 42, 44, 45, 46, 47, 48, 50, 58, 62, 64, 66 to monitor electrical activity of the heart 12, e.g., electrocardiogram (ECG) / electrogram (EGM) signals, etc. The ECGZEGM signals may be used to determine a noisy signal and to determine whether a patient is undergoing a VT / VF episode. In one embodiment, the morphology of the ECGZEGM signals may be analyzed to determine whether a patient is undergoing a VT / VF episode. The ECGZEGM signals may be used to measure or monitor activation times (e.g., ventricular activations times, etc.), heart rate (HR), heart rate variability (HRV), heart rate turbulence (HRT), deceleration / accel eration capacity, deceleration sequence incidence, T-wave altemans (TWA), P-wave to P-wave intervals (also referred to as the P-P intervals or A-A intervals), R-wave to R-wave intervals (also referred to as the R-R intervals or V-V intervals), P- wave to QRS complex intervals (also referred to as the P-R intervals, A-V intervals, or P- Q intervals), QRS-complex morphology, ST segment (i.e., the segment that connects the QRS complex and the T-wave), T-wave changes, QT intervals, electrical vectors, etc.

[0048] The switch module 85 may also be used with the sensing module 86 to select which of the available electrodes are used, or enabled, to, e.g., sense electrical activity of the patient's heart (e.g., one or more electrical vectors of the patient's heart using any combination of the electrodes 40, 42, 44, 45, 46, 47, 48, 50, 58, 62, 64, 66). Likewise, the switch module 85 may also be used with the sensing module 86 to select which of the available electrodes are not to be used (e.g., disabled) to, e.g., sense electrical activity of the patient's heart (e.g., one or more electrical vectors of the patient's heart using any combination of the electrodes 40, 42, 44, 45, 46, 47, 48, 50, 58, 62, 64, 66), etc. In some examples, the control module 81 may select the electrodes that function as sensing electrodes via the switch module within the sensing module 86, e.g., by providing signals via a data / address bus.

[0049] In some examples, sensing module 86 includes a channel that includes an amplifier with a relatively wider pass band than the R-wave or P-wave amplifiers. Signals from the selected sensing electrodes may be provided to a multiplexer, and thereafterconverted to multi-bit digital signals by an analog-to-digital converter for storage in memory 82, e.g., as an electrogram (EGM). In some examples, the storage of such EGMs in memory 82 may be under the control of a direct memory access circuit.

[0050] In some examples, the control module 81 may operate as an interrupt-driven device and may be responsive to interrupts from pacer timing and control module, where the interrupts may correspond to the occurrences of sensed P-waves and R-waves and the generation of cardiac pacing pulses. Any mathematical calculations may be performed by the processing circuitry 80 and any updating of the values or intervals controlled by the pacer timing and control module may be executed, or take place, following such interrupts. A portion of memory 82 may be configured as a plurality of recirculating buffers, capable of holding one or more series of measured intervals or sensed signals, which may be analyzed by, e.g., the processing circuitry 80 in response to the occurrence of a pace or sense interrupt to determine whether the patient's heart 12 is presently exhibiting atrial or ventricular tachyarrhythmia. The pacer timing and control module may include programmable counters which control the basic time intervals associated with DDD, VVI, DVI, VDD, AAI, DDI, DDDR, VVIR, DVIR, VDDR, AAIR, DDIR, AAO, AVO, ADO, WO, VAO, VDO, DDO, DAO, or DVO and other modes of single and dual chamber pacing. In the aforementioned pacing modes, “D” may indicate dual chamber, “V” may indicate a ventricle, “I” may indicate inhibited pacing (e.g., no pacing), and “A” may indicate an atrium. The first letter in the pacing mode may indicate the chamber that is paced, the second letter may indicate the chamber in which an electrical signal is sensed, the third letter may indicate the chamber in which the response to sensing is provided, and the fourth letter describes whether rate response is active (R) or disabled.

[0051] Further, the processing circuitry 80 of IMD 16 may detect a tachyarrhythmia episode, such as a ventricular fibrillation, ventricular tachycardia, or fast ventricular tachyarrhythmia episode, based on electrocardiographic activity of heart 12 (e.g., using one or more of conventional processing, artificial intelligence (Al) algorithms, and machine learning (ML) models) that is monitored via sensing module 86. For example, sensing module 86, with the aid of at least some of the electrodes 40, 42, 44, 46, 48, 50, 58, 62, 64, and 66 (shown in FIGS. 1-2), may generate an electrocardiogram (ECG) or electrogram (EGM) signal that indicates the electrocardiographic activity. Alternatively,sensing module 86 may be coupled to sense electrodes that are separate from the stimulation electrodes that deliver electrical stimulation to heart 12 (shown in FIGS. 1-2), and may be coupled to one or more different leads than leads 18, 20, 22 (shown in FIGS. 1-2). The ECG signal may be indicative of the depolarization of heart 12.

[0052] For example, in some examples, the processing circuitry 80 may identify the presence of a tachyarrhythmia episode by detecting a threshold number of tachyarrhythmia events (e.g., R-R or P-P intervals having a duration less than or equal to a threshold). In some examples, the processing circuitry 80 may also identify the presence of the tachyarrhythmia episode by detecting a variable coupling interval between the R-waves of the heart signal.

[0053] The telemetry module 88 of the control module 81 may include any suitable hardware, firmware, software, or any combination thereof for communicating with another device, such as an external user interface device 24 (e.g., a programmer or a mobile computing device such as a smartphone). For example, under the control of the processing circuitry 80, the telemetry module 88 may receive downlink telemetry from and send uplink telemetry to a programmer or mobile computing device with the aid of an antenna, which may be internal and / or external. The processing circuitry 80 may provide the data to be uplinked to a programmer or a mobile computing device and the control signals for the telemetry circuit within the telemetry module 88, e.g., via an address / data bus. In some examples, the telemetry module 88 may provide received data to the processing circuitry 80 via a multiplexer.

[0054] The various components of the IMD 16 are further coupled to a 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.

[0055] FIG. 4 is an illustrative external user interface device 24. As shown, the external user interface device 24 includes a processor 100, a memory 102, a user interface 104, a telemetry module 106, and a power source 108. The external user interface device 24 may be a dedicated hardware device with dedicated software for programming of IMD 16. Alternatively, the external user interface device 24 may be an off-the-shelf computingdevice (e.g., mobile compute device such as a smartphone) running an application that enables external user interface device 24 to program IMD 16.

[0056] A user may use the external user interface device 24 to receive alerts from the IMD 16, to receive data including cardiac electrical activity or signals to be used to confirm VT / VF, to analyze the cardiac electrical data to confirm VT / VF, to utilize artificial intelligence (Al) to analyze the cardiac electrical data to confirm VT / VF, to select therapy programs (e.g., sets of stimulation parameters), generate new therapy programs, modify therapy programs through individual or global adjustments or transmit the new programs to a medical device, such as the IMD 16 (FIG. 1). The clinician may interact with the external user interface device 24 via the 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.

[0057] The processor 100 can take the form one or more microprocessors, DSPs, ASICs, FPGAs, programmable logic circuitry, or the like, and the functions attributed to processor 100 herein may be embodied as hardware, firmware, software or any combination thereof. The memory 102 may store instructions that cause processor 100 to provide the functionality ascribed to the external user interface device 24 herein, and information used by processor 100 to provide the functionality ascribed to the external user interface device 24 herein. The memory 102 may include any fixed or removable magnetic, optical, or electrical media, such as RAM, ROM, CD-ROM, hard or floppy magnetic disks, EEPROM, or the like. The memory 102 may also include a removable memory portion that may be used to provide memory updates or increases in memory capacities. A removable memory may also allow IMD and / or patient data to be easily transferred to another computing device, or to be removed before the external user interface device 24 is used to program therapy for another patient. The memory 102 may also store cardiac electrical activity or signals or analysis thereof to determine and / or confirm VT / VF. Additionally, the memory 102 may also store information that controls therapy delivery by the IMD 16, such as stimulation parameter values.

[0058] The external user interface device 24 may communicate wirelessly with the IMD 16, such as using RF communication (e.g., BLUETOOTH) or proximal inductive interaction. This wireless communication is possible through the use of the telemetrymodule 106, which may be coupled to an internal antenna or an external antenna. An external antenna that is coupled to external user interface device 24 may correspond to the programming head that may be placed over the heart 12, as described above with reference to FIG. 1. The telemetry module 106 may be similar to telemetry module 88 of the IMD 16.

[0059] The telemetry module 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 the external user interface 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 the external user interface device 24 without needing to establish a secure wireless connection.

[0060] The power source 108 delivers operating power to the components of external user interface device 24. The 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 user interface device 24. In other embodiments, traditional batteries (e.g., nickel cadmium or lithium-ion batteries) may be used. In addition, external user interface device 24 may be directly coupled to an alternating current outlet to power the external user interface device 24. The power source 108 may include circuitry to monitor power remaining within a battery. In this manner, a 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.

[0061] FIG. 5 is a block diagram illustrating a system 190 that includes an external device 192, such as a server, and one or more computing devices 194A-194N that arecoupled to the IMD 16 and the external user interface device 24 shown in FIGS. 1-4 via a network 196, according to one embodiment. In this embodiment, the IMD 16 may use its telemetry module 88 to communicate with the external user interface device 24 via a first wireless connection, and to communicate with an access point 198 via a second wireless connection. In the example of FIG. 5, the access point 198, the external user interface device 24, the external device 192, and the computing devices 194A-194N are interconnected, and able to communicate with each other, through a network 196. In some cases, one or more of the access point 198, the external user interface device 24, the external device 192, and the computing devices 194A-194N may be coupled to the network 196 through one or more wireless connections. The IMD 16, the external user interface device 24, the external device 192, and the computing devices 194A-194N may each include, or comprise, one or more processors, 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.

[0062] The access point 198 may include, or comprise, a device that connects to the network 196 via any of a variety of connections, such as cellular data connection, telephone dial-up, digital subscriber line (DSL), or cable modem connections. In other examples, the access point 198 may be coupled to the network 196 through different forms of connections, including wired or wireless connections. In some examples, the access point 198 may communicate with the external user interface device 24 and / or the IMD 16. The access point 198 may be co-located with the patient 14 (e.g., within the same room or within the same site as the patient 14) or may be remotely located from the patient 14. For example, the access point 198 may be a home monitor that is located in the patient’s home or is portable for carrying with the patient 14.

[0063] During operation, the IMD 16 may collect, measure, and store various forms of diagnostic data such as, e.g., cardiac electrical activity that may be utilized by the illustrative systems, methods, and processes to determine or confirm VT / VF. In certain cases, the IMD 16 may directly analyze collected diagnostic data, such as cardiac electrical activity, and generate any corresponding reports or alerts, such as a VT / VF alert. In some cases, however, the IMD 16 may send diagnostic data such as the diagnostic parameters including a monitored ventricular electrical activity, to the external userinterface device 24, the access point 198, and / or the external device 192, either wirelessly or via the access point 198 and the network 196, for remote processing and analysis (e.g., to determine or confirm VT / VF). One or more of the external user interface device 24, the access point 198, and / or the external device 192 may utilize artificial intelligence (Al) to process and analyze the diagnostic data to confirm whether the data indicates a VT / VF, for example.

[0064] In another example, the IMD 16 may send diagnostic data such as the diagnostic parameters to the external user interface device 24 for remote processing and analysis (e.g., to determine or confirm VT / VF). In some instances, the processing circuitry of the user interface device 24 may employ various artificial intelligence (Al) algorithms and / or machine learning (ML) models that are configured to process the monitored ventricular electrical activity and conduct a morphology analysis in order to determine whether to permanently or temporary modify or disable initiating noise reversion pacing therapy based on processing.

[0065] In another example, the IMD 16 may provide the external device 192 with collected diagnostic data or parameters via the access point 198 and the network 196. The external device 192 includes one or more the processors 200. In some cases, the external device 192 may request such data, and in some cases, the IMD 16 may automatically or periodically provide such data to the external device 192. Upon receipt of the diagnostic data via the input / output device 202, the external device 192 may be capable of analyzing the data and generating reports, alerts (e.g., VT / VF alerts), or other values.

[0066] One or more of the computing devices 194A-194N may access the diagnostic data or parameters through the network 196 for use in determining or confirming VT / VF. In some cases, the external device 192 may automatically send VT / VF confirmations via the input / output device 202 to one or more of the computing devices 194A-194N. In some cases, the external device 192 may send the VT / VF confirmations and / or diagnostic data to another device, such as the external user interface device 24, either automatically or upon request.

[0067] In one embodiment, the external device 192 may comprise a secure storage site for diagnostic data or information that has been collected from the IMD 16 and / or the external user interface device 24. In this embodiment, the network 196 may comprise anInternet network, and trained professionals, such as clinicians, may use the computing devices 194A-194N to securely access stored diagnostic data or parameters or lower pacing rate limits on the external device 192. For example, the trained professionals may utilize secure usernames and passwords to access the stored information on the external device 192. In one embodiment, the external device 192 may be a CareLink server provided by Medtronic, Inc., of Minneapolis, Minnesota.

[0068] An illustrative method 600 of initiating or inhibiting noise reversion pacing therapy, for example, including a focused look at VT / VF morphology analysis, using the system and devices of FIGS. 1-5, is depicted in FIG. 6. It is to be understood that the method 600 may be performed, at least in part, automatically by an implantable medical device and system as described herein with respect to FIGS. 1-5.

[0069] The method 600 includes monitoring ventricular electrical activity 602 using a plurality of electrodes. Ventricular electrical activity may be monitored using one or more electrodes positioned or placed in proximity to ventricular tissue of the left or right ventricles to provide electrical signals indicative of the depolarization and repolarization of the ventricular tissue. In at least one embodiment, the ventricular electrical activity may be measured, or monitored, using one or more electrodes positioned inside of the right ventricle using, e.g., the RV lead 18 of the therapy system 10 of FIGS 1-4 or one or more electrodes positioned proximate of the left ventricle using, e.g., the LV coronary sinus lead 20 of the therapy system 10 of FIGS 1-4. Additionally, the ventricular electrical activity may be monitored using a combination of electrodes utilized by an IMD and associated devices or systems. In other words, the ventricular electrical activity may be monitored using various vectors using two or more electrodes that are part of an IMD and associated devices or systems. Further, it is to be understood that a particular vector used to deliver ventricular paces to a patient’s heart may be the same or a different vector that it used to sense ventricular electrical activity. In at least one embodiment, the ventricular electrical activity may be monitored using a bipolar sensing vector, for example, using the tip electrode 42 and the ring electrode 44 of the RV lead 18 of the therapy system 10 of FIGS 1-4. In at least one embodiment, the ventricular electrical activity may be monitored using a unipolar sensing vector, for example, using the tip electrode 42 of the RV lead 18 and the housing electrode 58 of the therapy system 10 of FIGS 1-4. In at least oneembodiment, the ventricular electrical activity may be monitored using a bipolar sensing vector, for example, using the ring electrode 47 and the ring electrode 46 of the LV coronary sinus lead 20 of the therapy system 10 of FIGS 1-4. In at least one embodiment, the ventricular electrical activity may be monitored using a unipolar sensing vector, for example, using the ring electrode 47 of the LV coronary sinus lead 20 and the housing electrode 58 of the therapy system 10 of FIGS 1-4. The ventricular electrical activity may be monitored continuously and stored, or saved, using a circulating buffer.

[0070] The method 600 further includes performing pacing therapy 604. The pacing therapy 604 may include any type of pacing therapy configured to providing pacing therapy to a patient’s heart. For example, the pacing therapy 604 may be bradycardia pacing therapy, e.g., to maintain a patient’s heart rate above a minimum heart rate. Further, for example, the pacing therapy 604 may be cardiac resynchronization therapy configured to maintain synchrony of the patient’s heart. Still further, for example, the pacing therapy 604 may be biventricular pacing therapy or right ventricle only pacing therapy. The cardiac pacing therapy delivered during process 604 is different than the noise reversion pacing therapy delivered during process 614 as described herein.

[0071] The pacing therapy 604 includes controlling delivery of the cardiac pacing therapy based on at least monitored ventricular electrical activity 602. For example, the atrial and / or ventricular paces of the pacing therapy may be delivered in response to sensed events within the monitored cardiac electrical activity such as, e.g., ventricular depolarizations or contractions, atrial depolarizations or contractions, etc.

[0072] As described herein, simultaneously with determining ventricular tachycardia / ventricular fibrillation (VT / VF) episodes 608 as well as monitoring ventricular electrical activity 602 and performing conventional cardiac pacing therapy 604, the method 600 includes determining that the monitored ventricular electrical activity comprises, or includes, an unacceptable amount of noise 606. The noise detection may include detecting electromagnetic interference (EMI), noise due to muscle or other motion artifacts, lead fractures or disconnections, magnetic resonance imaging, other non- physiological noise, and any other type of noise. In one or more embodiments, determining that the monitored ventricular electrical activity comprises, or includes, an unacceptable amount of noise 606 may include performing filtering, rectifying, and anyother signal processing to the monitored ventricular activity to help facilitate noise recognition, monitoring one or more characteristics of the monitored ventricular activity, providing an indication of a signal amplitude of the monitored ventricular activity (e.g., filtered and rectified ventricular electrical activity), and utilized a noise counter that increments based on fluctuations in the signal amplitude.

[0073] In one example, a moving average of the monitored ventricular activity (e.g., filtered and rectified ventricular electrical activity) may be utilized to help facilitate noise recognition. For example, the monitored ventricular electrical activity may be monitored, or sampled, at approximately 1024 Hz and a moving average may be computed based on approximately 16 data points. When a rising (or falling) edge of the monitored ventricular electrical activity crosses a threshold value (e.g., approximately one half of the moving average), a noise counter may be incremented each time this occurs. In this manner, the noise counter may provide an indication of the number of signal fluctuations that may be attributed to noise, such as EMI. Additionally, the value of the monitored ventricular electrical activity may also need to exceed a lower limit, such as one-fourth of a sensitivity setting, in order to increment the noise counter to help prevent noise counter from counting very low amplitude noise or non-noise signal fluctuations.

[0074] In other examples, peaks of the monitored ventricular activity (e.g., filtered and rectified ventricular electrical activity) may be detected and the noise counter may be incremented based on the peak detection. The amplitude of the detected peaks may also be monitored to ensure that only signal peaks that exceed a threshold value increment the noise counter. In other examples, the monitored ventricular electrical activity may be filtered to determine a threshold for noise recognition, and the monitored ventricular electrical activity may be compared to the threshold determined based on low pass filtering to increment noise counter.

[0075] Further, a characteristic of the monitored ventricular electrical activity may be monitored within a sensing window to help facilitate noise recognition. For example, computing apparatus may monitor the ventricular electrical activity for a period of time corresponding to a sensing window upon detection of a specified type of cardiac event, e.g., a P- or R-wave. The sensing window may correspond to a blanking period. The blanking period may follow a detected cardiac event, e.g., a P-wave or R-wave. Detectionof cardiac events and delivery of therapy during the blanking period may be withheld. Therefore, noise detected during the blanking period may be due to sources other than therapy delivery. Furthermore, the sensing window, e.g., blanking period, may be sufficiently short such that signal fluctuations would not be physiologic, e.g., due to a subsequent normal or tachyarrhythmic cardiac depolarization, and instead would more likely be due to noise. For example, the sensing window may expire prior to a subsequent cardiac depolarization, e.g., a next cardiac event. Thus, the sensing window may be activated, or initiated, subsequent to each sensed cardiac event of a specified type, e.g., subsequent to each R-wave. As one example, the sensing window may be less than or equal to approximately 120 milliseconds (ms).

[0076] Still further, determining that the monitored ventricular electrical activity comprises, or includes, an unacceptable amount of noise 606 may be based on the count of the noise counter upon expiration of a sensing window. For example, determination of whether there is an unacceptable amount of noise may be based on the noise count obtained during one sensing window associated with one heartbeat. If the count within the noise counter is greater than or equal to a noise threshold, e.g., is greater than or equal to approximately 10 counts, then it may be determined that the monitored ventricular electrical activity comprises, or includes, an unacceptable amount of noise.

[0077] In some examples, determination of whether the monitored ventricular electrical activity comprises, or includes, an unacceptable amount of noise 606 may be based on a cumulative noise count obtained over a plurality of consecutive sensing windows. For example, it may be determined that the monitored ventricular electrical activity comprises, or includes, an unacceptable amount of noise if the cumulative noise count over two consecutive heartbeats, e.g., R-waves, is greater than or equal to approximately 14 counts, and the interval between the two consecutive heartbeats, e.g., R- R interval, is less than 160 ms. As another example, it may be determined that the monitored ventricular electrical activity comprises, or includes, an unacceptable amount of noise if the cumulative noise count over three consecutive heartbeats, e.g., R-waves, is greater than or equal to approximately 19 counts, and the interval from the first heartbeat to the third heartbeat is less than approximately 380 ms.

[0078] The various noise count rules, e.g., for one, two, and three heartbeats, may account for various types of high frequency noise. The most common EMI signals within monitored cardiac electrical activity are at frequencies of approximately 50 Hz and approximately 60 Hz. The noise count gathered for one heartbeat may be sufficient to detect this type of noise. Intermittent noise or other types of noise may be detected by monitoring the noise count over a plurality of heartbeats. The count within the noise counter may be reset to zero upon expiration of a sensing window, and the noise count values may be stored for previous heartbeats.

[0079] In some examples, it may be determined that the monitored ventricular electrical activity comprises, or includes, an unacceptable amount of noise for a heartbeat if the monitored ventricular activity (e.g., filtered and rectified ventricular electrical activity) has an amplitude outside of a physiological range. For example, if the amplitude of the monitored ventricular electrical activity exceeds a physiological threshold, e.g., 30 millivolts, it may be determined that the signal is non-physiological and that noise is present for that heartbeat. In this manner, noise detection based on a physiological threshold may supplement noise detection based on the noise count of signal fluctuations.

[0080] In response to a determination that the monitored ventricular electrical activity does not comprise an unacceptable amount of noise, the method 600 may proceed to monitor ventricular electrical activity 602 and to perform conventional cardiac pacing therapy 604.

[0081] In response to a determination that the monitored ventricular electrical activity comprises an unacceptable amount of noise 606, the method 600 may proceed to determine whether the monitored ventricular electrical activity comprises, or is indicative of, a ventricular tachycardia / ventricular fibrillation (VT / VF) episode 612. Determination of whether the monitored ventricular electrical activity comprises, or is indicative of, a ventricular tachycardia / ventricular fibrillation (VT / VF) may employ, or be executed by, one or more of conventional processing, artificial intelligence (Al) algorithms, and machine learning (ML) models by the processing circuitry 80 on the IMD 16.

[0082] For example, using the VT / VF morphology analysis process 612, one or more different morphological features of the monitored ventricular activity may be monitored, and subsequently, analyzed to determine whether or not the monitored ventricular activityis indicative of VT / VF or not indicative of VT / VF. The one or more different morphological features within the monitored ventricular activity may include inflection points, clippings (e.g., segments of monitored ventricular electrical activity which exceed a dynamic range of amplifying circuitry and are clipped), estimated mean frequency, estimated frequency content, quantifying energy contained in various frequency bands, quantifying slope of the monitored ventricular electrical activity waveform, classifying regularity of occurrence of inflection points, classifying regularity of occurrence of clipped monitored ventricular electrical activity segments, detecting difference between calculated mean frequency and estimated fundamental frequency obtained from a rate of occurrence of sensed events, determining slope of each sample of the monitored ventricular electrical activity, plotting a histogram of the slopes and comparing the occurrence of samples with low slope to the occurrence of samples with high slope, comparison of energy contained in high frequencies to energy contained in low frequencies, comparison of morphological features in a first monitored ventricular electrical activity (e.g., obtained between two electrodes) to the morphological features in a second monitored ventricular electrical activity (e.g., obtained between at least one electrode that is different than used to monitor the first ventricular electrical activity), area and width of monitored ventricular electrical activity, template matching of prior VT depolarization morphology templates, zero crossings, and utilization of a deep neural network to analyze monitored ventricular electrical activity.

[0083] After the one or more different morphological features are monitored, analysis of the one or more different morphological features may include one or more of comparing the morphological features to various thresholds, and parameters. One illustrative method including multiple processes that may be used themselves or in conjunction with one another to determine that the monitored ventricular electrical activity is indicative of a ventricular tachycardia / ventricular fibrillation (VT / VF) episode based on morphology analysis 612 is shown in FIG. 7.

[0084] If VT / VF morphology analysis process 612 determines that the monitored ventricular electrical activity is indicative of a VT / VF episode, then the method 600 will proceed with initiating a VT / VF response via VT / VF Response 610. A VT / VF response may include defibrillation, cardioversion, anti-tachycardia pacing, alerting a patient, alerting a caregiver, alerting or connecting to emergency services, and sending GPScoordinates of the patient to any appropriate connected resource (such as, for example, emergency services).

[0085] If, however, the VT / VF morphology analysis 612 determines that the monitored ventricular electrical activity is not indicative of VT / VF (and potentially, also confirming that the monitored ventricular electrical activity is noise), then noise reversion pacing therapy 614 will be initiated. Noise reversion pacing may include controlling delivery of the cardiac pacing therapy without being based on the monitored ventricular electrical activity. In other words, when either of processing circuitry on the control module 81 or in the external user interface device 24 indicates that the monitored ventricular electrical activity includes noise-induced signals that may have an amplitude that is large enough to be sensed by the sensing threshold, then noise features, such as, for example, ANF and / or quiet timer may be activated in order for the noise features to determine whether noise is sensed. If either of ANF and / or quiet timer determines that the monitored ventricular electrical activity includes noise-induced signals, asynchronous pacing independent of sensed electrical signals may be initiated. Noise reversion pacing therapy 614 does not monitor atrial or ventricular electrical activity for use in timing the delivery of pacing pulses to the atria and / or ventricles. Further, it may be described that noise reversion pacing therapy may not be based on sensed cardiac events, such as sensed atrial depolarizations or sensed ventricular depolarizations. Instead, noise reversion pacing therapy may be delivered at a fixed rate that is independent of sensed cardiac events. The noise reversion pacing therapy may be implemented for a defined time period or until the presence of noise is no longer detected. Noise reversion pacing therapy may be further described as being asynchronous pacing independent of sensed electrical signals. In asynchronous pacing mode, pacing therapy is provided but not relative to any function of sensing electrical activity. As asynchronous pacing does not rely on sensing to provide pacing therapy, asynchronous pacing can include pacing modes such as VOO, AAO, AVO, ADO, WO, VAO, VDO, DDO, DAO, or DVO pacing mode.

[0086] During delivery of conventional cardiac pacing therapy 604, the method 600 may further include determining ventricular tachycardia / ventricular fibrillation (VT / VF) episodes based on the monitored ventricular electrical activity 602 and determining that the monitored ventricular electrical activity comprises, or includes, an unacceptableamount of noise 606. It is to be understood that process 602 604, 606, and 608 may be performed simultaneously or in parallel.

[0087] Determining ventricular tachycardia / ventricular fibrillation (VT / VF) episodes based on the monitored ventricular electrical activity 608 may be generally described as analyzing one or more characteristics or properties of the monitored ventricular electrical activity for indications of VT / VF. It to be understood that such analyzing one or more characteristics or properties of the monitored ventricular electrical activity for indications of VT / VF may performed, or executed, by one or more of conventional processing, artificial intelligence (Al) algorithms, and machine learning (ML) models by the processing circuitry 80 on the IMD 16. In one or more embodiments, VT / VF episodes may be detected based on a selected number of consecutive “fast” cardiac cycles or a ratio of “fast” cardiac cycles over a selected number of cardiac cycles. A “fast” cardiac cycle may be a cardiac cycle less than or equal to a VT / VF threshold, such as 230 milliseconds (ms), and thus, potentially indicative of VT / VF. The VT / VF threshold may be between about 200 ms and about 550 ms. In one or more embodiments, the VT / VF threshold may be greater than or equal to 200 ms, greater than or equal to 225 ms, greater than or equal to 250 ms, greater than or equal to 275 ms, greater than or equal to 300 ms, or greater than or equal to 325 ms, and / or less than or equal to 550 ms, less than or equal to 500 ms, less than or equal to 450 ms, less than or equal to 400 ms, less than or equal to 375 ms, less than or equal to 350 ms, less than or equal to 340 ms, or less than or equal to 260 ms. For example, the selected number of consecutive “fast” cardiac cycles may be 16, and thus, if 16 consecutive cardiac cycles are less than or equal to the VT / VF threshold, then a VT / VF episode may be detected. Further, for example, a ratio of “fast” cardiac cycles over 40 cardiac cycles may be 75%, and thus, if 30 or more cardiac cycles out of the 40 cardiac cycles are less than or equal to the VT / VF threshold, then a VT / VF episode may be detected. In one or more embodiments, ventricular tachycardia episodes may be detected based on atrioventricular (AV) timing. For example, if the ventricular rate is greater than the atrial rate, then it may indicate ventricular tachycardia (and not any atrial arrythmia or supraventricular tachycardia). In one or more embodiments, VT / VF episodes may be detected based upon a template matching score to assess whether the waveform of suspected arrhythmia looks the same or different than a regular sinus beat. In one or more embodiments, R-R interval onset may be used to detect a ventricular tachycardia. Forexample, a “fast” R interval onset typically indicates a tachyarrhythmia as opposed to exercise which has a slower R-R interval onset. In one or more embodiment, R-R interval stability may be used to detect VT / VF. For example, R-R interval stability during atrial fibrillation is typically variable (as well as ventricular fibrillation), but R-R interval stability during monomorphic ventricular tachycardia is more stable.

[0088] If a VT / VF episode is detected 608 then the method 600 may proceed to a VT / VF response 610, and conversely, if a VT / VF episode is not detected 608, then the method 600 may continue monitoring ventricular electrical activity 602 and providing conventional cardiac pacing therapy 604. Generally, the VT / VF response 610 may include one or more of providing an alert to the patient, transmitting an alert to an external device, providing therapy to terminate the VT / VF, transmitting data including the monitored ventricular electrical activity indicative of VT / VF (which was used to detect the VT / VF episode) to an external device, receiving confirmation from an external device of the VT / VF, and adjusting or disabling in noise reversion pacing therapy response to VT / VF confirmation.

[0089] FIG. 7 provides a detailed illustration of the VT / VF morphology analysis 612 of method 600. As described herein, the morphology analysis 612 may be configured to determine whether the monitored ventricular electrical activity is indicative of a VT / VF episode based on one or more or a plurality of difference morphological features. As shown in this embodiment, the morphology analysis 612 may monitor four different morphological features that each may be utilized independently as well as in conjunction with each other to determine whether or not the monitored ventricular electrical activity is indicative of VT / VF. In particular, the morphology analysis 612 monitors inflection points, clippings, mean frequency, and frequency content as will be described further herein.

[0090] Generally, an inflection point may be determined, and thus counted, by detecting each time the monitored ventricular activity waveform slope shifts from positive to negative or from negative to positive. Alternately or additionally, an inflection point may be determined, and thus counted, by detecting each time the monitored ventricular activity waveform slope shifts from convex to concave or from concave to convex. Because noise is more variable than cardiac events (such as, for example, VT / VFepisodes), it is expected that monitored ventricular electrical activity with numerous inflection points will indicate noise. By contrast, cardiac events such as, for example, VT / VF episodes, will have a less variable waveform and, accordingly, fewer inflection points. In one embodiment, to detect and count inflection points 702, a first order derivative filter may be applied the monitored ventricular electrical activity.

[0091] For example, the VT / VF morphology analysis 612 is configured to count inflection points 702 in the monitored ventricular electrical activity and to determine, based on the counted number of inflection points, whether the monitored ventricular electrical activity is indicative of a VT / VF episode 710. In an embodiment, to count inflection points 702, a first order derivative filter is applied to the monitored ventricular electrical activity to provide each instance where inflection points in the monitored ventricular electrical activity is present. More specifically, the first order derivative filter generates a signal that indicates when each of the inflection points occurs over time, e.g., when the signal changes slope.

[0092] In another embodiment, to detect and count inflection points 702, a second order derivative filter may be applied to the monitored ventricular electrical activity to determine instances of shifting concavity (e.g., when shape shifts from concave to convex or convex to concave). More specifically, the second order derivative filter generates a signal that indicates when shape of the original waveform shifts concavity, e.g., when an inflection point occurs.

[0093] Additionally, it shall be understood that the process 702 may filter out low amplitude signals that would result in false inflection points. In one embodiment, to do so, the process 702 may be configured to determine the maximum and minimum signal amplitude between each pair of successive inflection points and set a low amplitude threshold based on the observed amplitude of signal deviations that occur between pairs of inflection points. Any inflection points occurring in the monitored ventricular electrical activity that bound periods of signal where the maximum amplitude fluctuation (i.e., the difference between the maximum and minimum extent) is below the low amplitude threshold may be filtered out and not identified as an inflection points. In other words, in order to avoid any false inflection point detections and increase overall robustness, ahysteresis may be utilized such that low amplitude noise signals are not conflated as inflection points.

[0094] Accordingly, if the counted number of inflection points is fewer than an inflection point threshold over an inflection count time period 710, then the method 612 may proceed to providing an indication of VT / VF 718. The inflection point threshold may be between about 12 and about 100. In one embodiment, the inflection point threshold is 24. In one or more embodiments, the inflection point threshold may be greater than or equal to about 12, greater than or equal to about 18, greater than or equal to about 24, greater than or equal to about 30, greater than or equal to about 36, greater than or equal to about 42, greater than or equal to about 50, or greater than or equal to about 60, and / or less than or equal to about 100, less than or equal to about 95, less than or equal to about 85, less than or equal to about 75, less than or equal to about 65, less than or equal to about 55, less than or equal to about 45, or less than or equal to about 35. The inflection point time period is between about 0.5 seconds and about 4 seconds. In one embodiment, the inflection point time period may be 1 second. In one or more embodiments, the inflection point time period may be greater than or equal to about 0.5 seconds, greater than or equal to about 0.75 seconds, greater than or equal to about 1 seconds, greater than or equal to about 1.5 seconds, greater than or equal to about 2 seconds, or greater than or equal to about 2.5 seconds, and / or less than or equal to about 4 seconds, less than or equal to about 3.5 seconds, less than or equal to about 3.0 seconds, less than or equal to about 2.75 seconds, less than or equal to about 2.25 seconds, less than or equal to about 1.75 seconds, or less than or equal to about 1.25 seconds.

[0095] If the counted number of inflection points is less than or equal to the inflection point threshold over the inflection point time period 710, then VT / VF may be determined or detected. Alternately, if the counted number of inflection points is greater than the inflection point threshold over the inflection point time period 710, then VT / VF may not be determined or detected that, in turn, will allow method 600 to proceed to delivering noise reversion pacing therapy 614 as shown in FIG. 6.

[0096] The morphology analysis process 612 may include other techniques for determining whether the monitored ventricular electrical activity is indicative of VT / VF. For example, the morphology analysis process 612 may further include counting clippingsin the monitored ventricular electrical activity 704 to determine whether, based on the counted number of clippings, the monitored ventricular electrical activity is indicative of a VT / VF episode 712.

[0097] Signal clipping is a form of distortion that limits a signal once the signal exceeds a threshold. In this case, if a signal amplitude of the monitored ventricular electrical activity exceeds an acceptable ceiling threshold signal, the signal amplitude may be intentionally distorted or shortened after the accepted threshold ceiling (e.g., “clipped”). Further explained, there is a physiologic amplitude range in which cardiac electrical activity, such as for example, ventricular electrical activity, occurs. Any signal exceeding the physiologic amplitude range may be considered to be noise or at least comprising noise signals.

[0098] Generally, as noise is unpredictable and is more likely to have variable amplitudes, noise signals are more likely to cause clipping than cardiac events (such as, for example, a VT / VF episode). Accordingly, counting clippings in the monitored ventricular electrical activity 704 may be useful to determine whether the monitored ventricular electrical activity is indicative of VT / VF.

[0099] More specifically, if the counted number of clippings is below, or less than or equal to, a clippings threshold over a clippings count time period 712, then the method 612 may proceed to providing an indication of VT / VF 718. The clippings threshold may be between about 0 and about 10 clippings. In one embodiment, the clippings threshold is 2. In one or more embodiments, the clippings threshold may be greater than or equal to about 1, greater than or equal to about 3, greater than or equal to about 5, greater than or equal to about 7, greater than or equal to about 8, greater than or equal to about 9, and / or less than or equal to about 10, less than or equal to about 9, less than or equal to about 7, less than or equal to about 5, less than or equal to about 3, less than or equal to about 2, or less than or equal to about 1.

[0100] The clippings time period may be between about 0.5 and about 4 seconds. In one embodiment, the clippings time period may be 1 second. In one or more embodiments, the clippings time period may be greater than or equal to about 1 second, greater than or equal to about 1.5 seconds, greater than or equal to about 2 seconds, greater than or equal to about 2.5 seconds, greater than or equal to about 3 seconds, greater than or equal toabout 3.5 seconds, and / or less than or equal to about 4 seconds, less than or equal to about3.75 seconds, less than or equal to about 3 seconds, less than or equal to about 2.5 seconds, less than or equal to about 2 seconds, less than or equal to about 1 second.

[0101] Alternately, if the number of clippings over the clippings time period is greater than to a clippings threshold, then VT / VF may not be determined or detected and, in turn, will allow method 600 to proceed to delivering noise reversion pacing therapy 614 as shown in FIG. 6. For example, where the clippings threshold is 5 and the clippings time period is 1 second, if there are greater than 5 instances of clipping per second in the monitored ventricular electrical activity, then the method 600 may exit the VT / VF morphology analysis 612 and initiate noise reversion pacing therapy at 614 as shown in FIG. 6, as the monitored ventricular electrical activity comprises a clippings count over the clippings time period that meets or surpasses the clippings threshold and therefore is not indicative of VT / VF.

[0102] Additionally, while it is possible that initially, clipping may be observed on the monitored ventricular electrical activity in cases of VT / VF, such clipping may naturally decrease over time. Therefore, in addition to counting instances of clipping per clippings time period, the VT / VF morphology analysis may additionally or alternately be configured to detect clipping trends over time. If clipping is present at a beginning of a given period but decreases over time, then such a trend may be indicative of VT / VF and the VT / VF morphology analysis 612 may proceed to providing an indication of VT / VF 718.

[0103] In addition to the processes already discussed herein, morphology analysis process 612 may include additional techniques for determining whether the monitored ventricular electrical activity is indicative of VT / VF. For example, the VT / VF morphology analysis 612 may be further configured to estimate a mean frequency 706 of the monitored ventricular electrical activity and to determine, based on the estimated mean frequency, whether a VT / VF episode is indicated.

[0104] In one embodiment, to determine the mean frequency of monitored ventricular electrical activity 706, the VT / VF morphology analysis process 612 may estimate the mean frequency by first estimating the mean period. As disclosed in Equation 1 below, mean period can be estimated by dividing the sum of the absolute value of the original monitored ventricular electrical activity signal by the sum of the first difference (i.e., anapproximation of the first derivative) of the original waveform of the monitored ventricular electrical activity,

[0105] EQ(1) = , where V(J) is an amplitude of the Jth sample point of the monitored ventricular electrical activity. The mean frequency is then estimated as an inverse of the mean period estimated in Equation 1. Further, discussions regarding mean frequency and mean period estimation and / or calculation can be found in “Computer Detection of Ventricular Fibrillation” (S. Kuo, S.M.; R. Dillman, M.S.) (September 1978), which is herein incorporated by reference in its entirety.

[0106] After determining the mean frequency, if the calculated mean frequency is less than or equal to a mean frequency threshold value 714, then VT / VF is indicated 718. The mean frequency threshold value may be between about 10 and about 15 Hertz (Hz). In one embodiment, the mean frequency threshold value is 12 Hz. For instance, a mean frequency between 2 Hz and 10 Hz is often indicative of VT / VF.

[0107] If, however, the calculated mean frequency is not less than or equal to mean frequency threshold value (in other words, greater than mean frequency threshold value), then noise reversion therapy 614 may be initiated, as shown in FIG. 6.

[0108] Another technique for morphological analysis of the monitored ventricular electrical activity to determine whether VT / VF is indicated may include measuring zero crossings in order to estimate frequency content of the monitored ventricular electrical activity 708. Generally, frequency content may be determined by detecting and counting each time the monitored ventricular electrical activity waveform shifts across the X axis, e.g., “crosses zero.” Because noise is more variable than cardiac events (such as, for example, VT / VF episodes), it is expected that monitored ventricular electrical activity with a high density of zero crossings will indicate noise. By contrast, cardiac events such as, for example, a VT / VF episode, will have a less variable waveform and, accordingly, fewer instances of zero crossings. In one embodiment, to estimate the frequency content 708, the monitored ventricular electrical activity is observed to determine each instance when the original waveform slope changes from negative to positive or positive to negative as the monitored ventricular electrical activity waveform crosses the X-axis.

[0109] For example, the VT / VF morphology analysis 612 is configured to estimate frequency content 708 by counting zero crossings in the monitored ventricular electrical activity and to determine, based on the counted number of zero crossings over a zero crossings time period 716, whether the monitored ventricular electrical activity is indicative of a VT / VF episode 718. In one embodiment, the VT / VF morphology analysis may further include determining that the monitored ventricular electrical activity is indicative of a VT / VF episode 718 in response to the obtained number of zero crossings being below, or less than or equal to, a zero crossings threshold. The zero crossings thresholds may be between about 12 and about 100. In one embodiment, the zero crossings threshold is 24. In one or more embodiments, the zero crossings threshold may be greater than or equal to about 12, greater than or equal to about 15, greater than or equal to about 25, greater than or equal to about 35, greater than or equal to about 45, greater than or equal to about 55, greater than or equal to 65, greater than or equal to 75, and / or less than or equal to about 100, less than or equal to about 90, less than or equal to about 80, less than or equal to about 70, less than or equal to about 60, less than or equal to about 50, or less than or equal to about 35.

[0110] The zero crossings time period may be between about 0.5 and about 4 seconds. In one embodiment, the zero crossings time period is 1 second. The zero crossings time period may be between about 0.5 and about 4 seconds. In one embodiment, the clippings time period may be 1 second. In one or more embodiments, the zero crossings time period may be greater than or equal to about 1 second, greater than or equal to about 1.5 seconds, greater than or equal to about 2 seconds, greater than or equal to about 2.5 seconds, greater than or equal to about 3 seconds, greater than or equal to about 3.5 seconds, and / or less than or equal to about 4 seconds, less than or equal to about 3.75 seconds, less than or equal to about 3 seconds, less than or equal to about 2.5 seconds, less than or equal to about 2 seconds, less than or equal to about 1 second.

[0111] Alternately or additionally, the VT / VF morphology analysis 612 may be generally configured to count each instance of a general threshold crossing when the general threshold crossing results in a minimum directional change in order to estimate frequency content 708 over a general threshold crossings time period 716. The minimum directional change is representative of the minimum change needed to count a generalthreshold crossing. In one embodiment, the VT / VF morphology analysis may further include determining that the monitored ventricular electrical activity is indicative of a VT / VF episode 718 in response to the obtained number of general threshold crossings being below, or less than or equal to, a general crossings threshold.

[0112] The general crossings thresholds may be between about 12 and about 100. In one embodiment, the general crossings threshold is 24. In one or more embodiments, the general crossings threshold may be greater than or equal to about 12, greater than or equal to about 15, greater than or equal to about 25, greater than or equal to about 35, greater than or equal to about 45, greater than or equal to about 55, greater than or equal to 65, greater than or equal to 75, and / or less than or equal to about 100, less than or equal to about 90, less than or equal to about 80, less than or equal to about 70, less than or equal to about 60, less than or equal to about 50, or less than or equal to about 35.

[0113] The general crossings time period may be between about 0.5 and about 4 seconds. In one embodiment, the general crossings time period is 1 second. In one embodiment, the general crossings time period may be 1 second. In one or more embodiments, the zero crossings time period may be greater than or equal to about 1 second, greater than or equal to about 1.5 seconds, greater than or equal to about 2 seconds, greater than or equal to about 2.5 seconds, greater than or equal to about 3 seconds, greater than or equal to about 3.5 seconds, and / or less than or equal to about 4 seconds, less than or equal to about 3.75 seconds, less than or equal to about 3 seconds, less than or equal to about 2.5 seconds, less than or equal to about 2 seconds, less than or equal to about 1 second.

[0114] Additionally, it shall be understood that the process 708 may filter out low amplitude signals that would result in false zero crossings. In one embodiment, to do so, the process 708 may be configured to determine the maximum and minimum signal amplitude between each pair of successive zero crossings and set a low amplitude threshold based on the observed amplitude of signal deviations that occur between pairs of zero crossings. Any two neighboring zero crossings observed in the monitored ventricular electrical activity wherein a signal between the two neighboring zero crossings does not exceed a threshold absolute amplitude value will cause the prior zero crossing to be ignored. In other words, in order to avoid any zero crossing detections and increase overallrobustness, a hysteresis may be utilized such that low amplitude noise signals are not conflated as zero crossings.

[0115] If VT / VF morphology analysis makes a determination that the monitored ventricular electrical activity is indicative of VT / VF 612, then a VT / VF response may be initiated 610. The VT / VF response 610 may include any appropriate response to a VT / VF detection, such as, for example, initiating antitachycardia pacing therapy using the plurality of electrodes and initiating defibrillation therapy using the plurality of electrodes. For example, antitachycardia pacing therapy may include any type of pacing therapy configured to providing antitachycardia pacing therapy to a patient’s heart. The antitachycardia pacing therapy may be ventricular antitachycardia pacing therapy, e.g., to deliver pacing stimuli to the patient’s heart at a rate faster than the tachycardia for a short time period to attempt to terminate the tachycardia.

[0116] The VT / VF response 610 may further include transmitting an alert to the user interface device 24. The transmitted alert can be any signal type which can be transmitted such that the processing circuitry of the device 24 may process the transmitted signal. As an example, a sample transmitted signal may be any type of analog signal, such as for example at least an analog audio signal.

[0117] The VT / VF response 610 may also include transmitting the sensed signals of the monitored ventricular activity to device 24 such that the device 24 is configured to analyze the received data in order to confirm the VT / VF episode by processing the received data using either conventionally known methods and / or methods as described herein. For example, device 24 may process the received data in order to determine if the received data is indicative of VT / VF by estimating frequency content of the received data by detecting zero crossings, calculating mean frequency of the received data, counting clippings present in the received data, counting inflection points in the received data, etc. The device 24 may alternately or additionally process the received data in order to determine if the received data is indicative of VT / VF based on a selected number of consecutive “fast” cardiac cycles or a ratio of “fast” cardiac cycles over a selected number of cardiac cycles. It shall be understood that the device 24 may additionally or alternately be configured to use any known methods of conventionally processing data and determining whether the data is indicative of VT / VF.

[0118] The VT / VF response 610 may further include using the computing apparatus of IMD 16 to receive confirmation from the user interface device 24 of the VT / VF episode based on analysis of the transmitted monitored ventricular activity performed by the device 24 and disable or modify noise reversion pacing therapy settings in response to receipt of the confirmation of the VT / VF episode. Processing circuitry in the device 24 may include conventionally known algorithms to confirm VT / VF episodes as well as approaches as described herein. Analysis of the monitored ventricular electrical activity as performed on the processing circuitry of the device 24 may therefore be understood to be robust to the extent that permanently disabling or modifying noise reversion pacing therapy in response to its determination is deemed appropriate.ILLUSTRATIVE EXAMPLES

[0119] Example Exl : An implantable medical device comprising: a plurality of electrodes to sense cardiac electrical activity of a patient’s heart and to deliver cardiac pacing therapy to the patient’s heart; and a processing circuitry operably coupled to one or more of the plurality of electrodes, wherein the processing circuitry is configured to: monitor ventricular electrical activity using the one or more of the plurality of electrodes; perform pacing therapy comprising controlling delivery of the cardiac pacing therapy using the one or more of the plurality of electrodes based on at least the monitored ventricular electrical activity; determine that the monitored ventricular electrical activity comprises an unacceptable amount of noise; determine that the monitored ventricular electrical activity is indicative of a ventricular tachycardia / ventricular fibrillation (VT / VF) episode based on morphology analysis of the monitored ventricular electrical activity in response to determination that the monitored ventricular electrical activity comprises the unacceptable amount of noise; initiate noise reversion pacing therapy in response to determining that the monitored ventricular electrical activity comprises the unacceptable amount of noise and the monitored ventricular electrical activity not being indicative of the VT / VF episode, wherein the noise reversion pacing therapy comprises controlling delivery of the cardiac pacing therapy independent of the monitored ventricular electrical activity; and initiate a VT / VF response in response to determining that the monitored ventricular electrical activity is indicative of the VT / VF episode.

[0120] Example Ex2: A method comprising: monitoring ventricular electrical activity of a patient’s heart using one or more of a plurality of electrodes; performing pacing therapy comprising controlling delivery of the cardiac pacing therapy using the one or more of the plurality of electrodes based on at least the monitored ventricular electrical activity; determining that the monitored ventricular electrical activity comprises an unacceptable amount of noise; determining that the monitored ventricular electrical activity is indicative of a ventricular tachycardia / ventricular fibrillation (VT / VF) episode based on morphology analysis of the monitored ventricular electrical activity in response to determination that the monitored ventricular electrical activity comprises the unacceptable amount of noise; initiating noise reversion pacing therapy in response to determining that the monitored ventricular electrical activity comprises the unacceptable amount of noise and the monitored ventricular electrical activity not being indicative of the VT / VF episode, wherein the noise reversion pacing therapy comprises controlling delivery of the cardiac pacing therapy independent of the monitored ventricular electrical activity; and initiating a VT / VF response in response to determining that the monitored ventricular electrical activity is indicative of the VT / VF episode.

[0121] Example Ex3 : The device as in Example Exl or the method as in Example Ex2, wherein determining that the monitored ventricular electrical activity is indicative of a VT / VF episode based on morphology analysis comprises: estimating a frequency content of the monitored ventricular electrical activity; and determining that the monitored ventricular electrical activity is indicative of a VT / VF episode based on the estimated frequency content of the monitored ventricular electrical activity.

[0122] Example Ex4: The device or method as in any of Examples Ex 1 - 3, wherein estimating the frequency content of the monitored ventricular electrical activity comprises counting zero crossings.

[0123] Example Ex5: The device or method as in any of Examples Ex 3 - 4, wherein determining that the monitored ventricular electrical activity is indicative of a VT / VF episode based on the estimated frequency content of the monitored ventricular electrical activity comprises determining that the monitored ventricular electrical activity is indicative of a VT / VF episode in response to estimated frequency content of the monitored ventricular electrical activity being below 15 hertz.

[0124] Example Ex6: The device or method as in any of Examples Ex. 1 - 5, wherein determining that the monitored ventricular electrical activity is indicative of a VT / VF episode based on morphology analysis comprises: estimating a mean frequency of the monitored ventricular electrical activity; and determining that the monitored ventricular electrical activity is indicative of a VT / VF episode based on the estimated mean frequency of the monitored ventricular electrical activity.

[0125] Example Ex7: The device or method as in Example Ex6, wherein estimating the mean frequency of the monitored ventricular electrical activity comprises calculating a sum of an absolute value of a derivative of the monitored ventricular electrical activity divided by a sum of the absolute value of the monitored ventricular electrical activity.

[0126] Example Ex8: The device or method as in any one of Examples Exl - 7 , wherein determining that the monitored ventricular electrical activity is indicative of a VT / VF episode based on the estimated mean frequency of the monitored ventricular electrical activity comprises determining that the monitored ventricular electrical activity is indicative of a VT / VF episode in response to the estimated mean frequency being below 15 hertz.

[0127] Example Ex9: The device or method as in any of Examples Exl - 8, wherein determining that the monitored ventricular electrical activity is indicative of a VT / VF episode based on the morphology analysis comprises: counting each inflection point in the monitored ventricular electrical activity to obtain a number of inflection points; and determining that the monitored ventricular electrical activity is indicative of a VT / VF episode based on the number of inflection points.

[0128] Example ExlO: The device or method as in Example Ex9, wherein determining that the monitored ventricular electrical activity is indicative of a VT / VF episode based on the obtained number of inflection points comprises determining that the monitored ventricular electrical activity is indicative of a VT / VF episode in response to the obtained number being fewer than 100.

[0129] Example Exl 1 : The device or method as in any one of Examples Exl - 10, wherein determining that the monitored ventricular electrical activity is indicative of a VT / VF episode based on the morphology analysis comprises: counting each occurrence ofclipping during the monitored ventricular electrical activity resulting in a number of occurrences of clipping; and determining that the monitored ventricular electrical activity is indicative of VT / VF based on the number of occurrences of clipping.

[0130] Example Exl2: The device or method as in Example Exl 1, wherein determining that the monitored ventricular electrical activity is indicative of a VT / VF episode based on the number of occurrences of clipping comprises determining that the monitored ventricular electrical activity is indicative of VT / VF in response to the number of occurrences of clipping being fewer than 5 times per second.

[0131] Example Exl3: The device or method as in any one of Examples Ex 1 - 12, wherein the VT / VF response comprises one or more of: initiating antitachycardia pacing therapy using one or more of the plurality of electrodes; and initiating defibrillation therapy using the one or more of the plurality of electrodes.

[0132] Example Exl4: The device or method as in any one of Examples Exl - 13, wherein the VT / VF response comprises transmitting an alert to an external device.

[0133] Example Exl 5: The device or method as in any one of Examples Exl - 14, wherein the VT / VF response comprises transmitting the monitored ventricular activity to an external device configured to further analyze to the monitored ventricular activity to confirm the VT / VF episode.

[0134] Example Exl6: The device or method as in Example Exl5, wherein the processing circuitry is further configured to execute and / or the method further comprises: receiving confirmation from the external device of the VT / VF episode based on analysis of the transmitted monitored ventricular activity performed by the external device; and disabling or modifying the noise reversion pacing therapy in response to receipt of the confirmation of the VT / VF episode.

[0135] Example Exl7: A system comprising: an external device configured to analyze to monitored ventricular activity to confirm VT / VF episodes; and an implantable medical device comprising: a plurality of electrodes to sense cardiac electrical activity of a patient’s heart and to deliver cardiac pacing therapy to the patient’s heart; a telemetry apparatus comprising an antenna; and a processing circuitry operably coupled to the one or more of the plurality of electrodes and the telemetry apparatus, wherein the processingcircuitry is configured to: monitor ventricular electrical activity using one or more of the plurality of electrodes; perform pacing therapy comprising controlling delivery of the cardiac pacing therapy based on at least the monitored ventricular electrical activity; determine that the monitored ventricular electrical activity comprises an unacceptable amount of noise; determine that the monitored ventricular electrical activity is indicative of a ventricular tachycardia / ventricular fibrillation (VT / VF) episode based on morphology analysis of the monitored ventricular electrical activity in response to determination that the monitored ventricular electrical activity comprises the unacceptable amount of noise; initiate noise reversion pacing therapy in response to determining that the monitored ventricular electrical activity comprises the unacceptable amount of noise and the monitored ventricular electrical activity not being indicative of the VT / VF episode, wherein the noise reversion pacing therapy comprises controlling delivery of the cardiac pacing therapy independent of the monitored ventricular electrical activity; and initiate a VT / VF response in response to determining that the monitored ventricular electrical activity is indicative of the VT / VF episode, wherein the VT / VF response comprises transmitting the monitored ventricular activity to the external device using the telemetry apparatus.

[0136] All references and publications cited herein are expressly incorporated herein by reference in their entirety for all purposes, except to the extent any aspect directly contradicts this disclosure.

[0137] Unless otherwise indicated, all numbers expressing feature sizes, amounts, and physical properties used in the specification and claims may be understood as being modified either by the term “exactly” or “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the foregoing specification and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by those skilled in the art utilizing the teachings disclosed herein or, for example, within typical ranges of experimental error.

[0138] As used herein, the term “configured to” may be used interchangeably with the terms “adapted to” or “structured to” unless the content of this disclosure clearly dictates otherwise.

[0139] The singular forms “a,” “an,” and “the” encompass embodiments having plural referents unless its context clearly dictates otherwise.

[0140] As used herein, “have,” “having,” “include,” “including,” “comprise,” “comprising” or the like are used in their open-ended sense, and generally mean “including, but not limited to.” It will be understood that “consisting essentially of,” “consisting of,” and the like are subsumed in “comprising,” and the like.

[0141] Reference to “one embodiment,” “an embodiment,” “certain embodiments,” or “some embodiments,” etc., means that a particular feature, configuration, composition, or characteristic described in connection with the embodiment is included in at least one embodiment of the disclosure. Thus, the appearances of such phrases in various places throughout are not necessarily referring to the same embodiment of the disclosure.Furthermore, the particular features, configurations, compositions, or characteristics may be combined in any suitable manner in one or more embodiments.

[0142] The words “preferred” and “preferably” refer to embodiments of the disclosure that may afford certain benefits, under certain circumstances. However, other embodiments may also be preferred, under the same or other circumstances. Furthermore, the recitation of one or more preferred embodiments does not imply that other embodiments are not useful and is not intended to exclude other embodiments from the scope of the disclosure.

Claims

CLAIMSWhat is claimed is:

1. An implantable medical device comprising: a plurality of electrodes to sense cardiac electrical activity of a patient’s heart and to deliver cardiac pacing therapy to the patient’s heart; and a processing circuitry operably coupled to the plurality of electrodes, wherein the processing circuitry is configured to: monitor ventricular electrical activity using one or more of the plurality of electrodes; perform pacing therapy comprising controlling delivery of the cardiac pacing therapy using the one or more of the plurality of electrodes based on at least the monitored ventricular electrical activity; determine that the monitored ventricular electrical activity comprises an unacceptable amount of noise; determine that the monitored ventricular electrical activity is indicative of a ventricular tachycardia / ventricular fibrillation (VT / VF) episode based on morphology analysis of the monitored ventricular electrical activity in response to determination that the monitored ventricular electrical activity comprises the unacceptable amount of noise; initiate noise reversion pacing therapy in response to determining that the monitored ventricular electrical activity comprises the unacceptable amount of noise and the monitored ventricular electrical activity not being indicative of the VT / VF episode, wherein the noise reversion pacing therapy comprises controlling delivery of the cardiac pacing therapy independent of the monitored ventricular electrical activity; and initiate a VT / VF response in response to determining that the monitored ventricular electrical activity is indicative of the VT / VF episode.

2. A method comprising: monitoring ventricular electrical activity of a patient’s heart using one or more of a plurality of electrodes;performing pacing therapy comprising controlling delivery of the cardiac pacing therapy using one or more of the plurality of electrodes based on at least the monitored ventricular electrical activity; determining that the monitored ventricular electrical activity comprises an unacceptable amount of noise; determining that the monitored ventricular electrical activity is indicative of a ventricular tachycardia / ventricular fibrillation (VT / VF) episode based on morphology analysis of the monitored ventricular electrical activity in response to determination that the monitored ventricular electrical activity comprises the unacceptable amount of noise; initiating noise reversion pacing therapy in response to determining that the monitored ventricular electrical activity comprises the unacceptable amount of noise and the monitored ventricular electrical activity not being indicative of the VT / VF episode, wherein the noise reversion pacing therapy comprises controlling delivery of the cardiac pacing therapy independent of the monitored ventricular electrical activity; and initiating a VT / VF response in response to determining that the monitored ventricular electrical activity is indicative of the VT / VF episode.

3. The implantable medical device as in claim 1 or the method as in claim 2, wherein determining that the monitored ventricular electrical activity is indicative of a VT / VF episode based on morphology analysis comprises: estimating a frequency content of the monitored ventricular electrical activity; and determining that the monitored ventricular electrical activity is indicative of a VT / VF episode based on the estimated frequency content of the monitored ventricular electrical activity.

4. The implantable medical device or method as in claim 3, wherein estimating the frequency content of the monitored ventricular electrical activity comprises counting zero crossings.

5. The implantable medical device or method as in any one of claims 3-4, wherein determining that the monitored ventricular electrical activity is indicative of a VT / VF episode based on the estimated frequency content of the monitored ventricular electricalactivity comprises determining that the monitored ventricular electrical activity is indicative of a VT / VF episode in response to estimated frequency content of the monitored ventricular electrical activity being below 10 Hertz.

6. The implantable medical device or method as in any of claims 1-5, wherein determining that the monitored ventricular electrical activity is indicative of a VT / VF episode based on morphology analysis comprises: estimating a mean frequency of the monitored ventricular electrical activity; and determining that the monitored ventricular electrical activity is indicative of a VT / VF episode based on the estimated mean frequency of the monitored ventricular electrical activity.

7. The implantable medical device or method as in claim 6, wherein estimating the mean frequency of the monitored ventricular electrical activity comprises calculating a sum of an absolute value of a derivative of the monitored ventricular electrical activity divided by a sum of the absolute value of the monitored ventricular electrical activity.

8. The implantable medical device or method as in any one of claims 6-7, wherein determining that the monitored ventricular electrical activity is indicative of a VT / VF episode based on the estimated mean frequency of the monitored ventricular electrical activity comprises determining that the monitored ventricular electrical activity is indicative of a VT / VF episode in response to the estimated mean frequency being below 15 Hertz.

9. The implantable medical device or method as in any one of claims 1-8, wherein determining that the monitored ventricular electrical activity is indicative of a VT / VF episode based on the morphology analysis comprises: counting each inflection point in the monitored ventricular electrical activity to obtain a number of inflection points; and determining that the monitored ventricular electrical activity is indicative of a VT / VF episode based on the number of inflection points.

10. The implantable medical device or method as in claim 9, wherein determining that the monitored ventricular electrical activity is indicative of a VT / VF episode based on the obtained number of inflection points comprises determining that the monitored ventricular electrical activity is indicative of a VT / VF episode in response to the obtained number being fewer than 100.

11. The implantable medical device or method as in any one of claims 1-10, wherein determining that the monitored ventricular electrical activity is indicative of a VT / VF episode based on the morphology analysis comprises: counting each occurrence of clipping during the monitored ventricular electrical activity resulting in a number of occurrences of clipping; and determining that the monitored ventricular electrical activity is indicative of VT / VF based on the number of occurrences of clipping.

12. The implantable medical device or method as in any one of claims 1-11, wherein the VT / VF response comprises one or more of: initiating antitachycardia pacing therapy using one or more of the plurality of electrodes; and initiating defibrillation therapy using one or more of the plurality of electrodes.

13. The implantable medical device or method as in any one of claims 1-12, wherein the VT / VF response comprises transmitting an alert to an external device.

14. The implantable medical device or method as in any one of claims 1-13, wherein the VT / VF response comprises transmitting the monitored ventricular activity to an external device configured to further analyze to the monitored ventricular activity to confirm the VT / VF episode.

15. The implantable medical device or method as in claim 14, wherein the processing circuitry is further configured to execute and / or the method further comprises: receiving confirmation from the external device of the VT / VF episode based on analysis of the transmitted monitored ventricular activity performed by the external device; anddisabling or modifying the noise reversion pacing therapy in response to receipt of the confirmation of the VT / VF episode.

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