Atrioventricular node stimulation for pacing therapy

Abstract

The illustrative systems, devices, and methods described herein may be configured to deliver and adjust atrioventricular (AV) node stimulation to regularize a patient's heart rate and slow down, or decrease, the patient's heart and to deliver pacing therapy (e.g., cardiac resynchronization therapy, left ventricle only pacing therapy, biventricular pacing therapy, left bundle branch pacing therapy, etc.) in cooperation with the AV node stimulation.

Description

ATRIOVENTRICULAR NODE STIMULATION FOR PACING THERAPY

[0001] This application claims the benefit of U.S. Provisional Patent Application Serial No. 63 / 639,189, filed April 26, 2024, the entire content of which is incorporated herein by reference.

[0002] The disclosure herein relates to systems, devices, and methods for use in treating heart conditions by delivering electrical stimulation to the atrioventricular (AV) node or nerves innervating the AV node in conjunction with pacing therapy such as, for example, cardiac resynchronization therapy, left ventricle only pacing therapy, biventricular pacing therapy, left bundle branch pacing therapy, and atrial pacing therapy.

[0003] Implantable medical devices (IMDs), such as implantable pacemakers, cardioverters, defibrillators, or pacemaker-cardioverter-defibrillators, provide therapeutic electrical stimulation to the heart. IMDs may provide pacing to address bradycardia, or pacing or shocks in order to terminate tachyarrhythmia, such as tachycardia or fibrillation. In some cases, the medical device may sense intrinsic depolarizations of the heart, detect arrhythmia based on the intrinsic depolarizations (or absence thereof), and control delivery of electrical stimulation to the heart if arrhythmia is detected based on the intrinsic depolarizations. Conventional pacing techniques involve pacing one or more of the four chambers of patient’s heart 12 — left atrium (LA) 33, right atrium (RA) 26, left ventricle (LV) 32 and right ventricle (RV) 28, all of which are shown in FIG. 1.

[0004] The cardiac conduction system includes sinoatrial node (SA node) 1, atrial internodal tracts 2, 4, 5 (i.e., anterior intemodal 2, middle internodal 4, and posterior internodal 5), AV node 3, His bundle 13 (also known as atrioventricular bundle or bundle of His), and right and left bundle branches 8a, 8b. FIG. 1 also shows the arch of aorta 6 and Bachman’s bundle 7. The SA node, located at the junction of the superior vena cava and right atrium, is considered to be the natural pacemaker of the heart since it continuously and repeatedly emits electrical impulses. The electrical impulse spreads through the muscles of right atrium 26 to left atrium 33 to cause synchronous contraction of the atria. Electrical impulses are also carried through atrial internodal tracts to atrioventricular (AV) node 3 — connection of the cardiac conduction system between theatria and the ventricles. Conduction through the AV nodal tissue takes longer than through the atrial tissue, resulting in a delay between atrial contraction and the start of ventricular contraction. The AV delay, which is the delay between atrial contraction and ventricular contractor, allows the atria to empty blood into the ventricles. Then, the valves between the atria and ventricles close before causing ventricular contraction via branches of the bundle of His. His bundle 13 is located in the membranous atrioventricular septum near the annulus of the tricuspid valve. His bundle 13 splits into right and left bundle branches 8a, 8b and are formed of specialized fibers called “Purkinje fibers” 9. Purkinje fibers 9 may be described as rapidly conducting an action potential down the ventricular septum (VS), spreading the depolarization wavefront quickly through the remaining ventricular myocardium, and producing a coordinated contraction of the ventricular muscle mass.

[0005] The use of nerve stimulation, e.g., stimulation of the vagus nerve innervating the AV node 3, stimulation of the parasympathetic nerves including vagus nerve, etc. for treating and controlling a variety of medical, psychiatric, and neurological disorders has seen significant growth over the last several decades, e.g., including the treatment of heart conditions. The vagus nerve is composed of somatic and visceral afferent fibers (which, e.g., convey impulses toward the brain) and efferent fibers (which, e.g., convey impulses to an effector to regulate activity such as muscle contraction or glandular secretion). The rate of the heart may be restrained in part by parasympathetic stimulation from the right and left vagus nerves. Low vagal nerve activity may be related to various arrhythmias, including tachycardia, ventricular accelerated rhythm, and rapid atrial fibrillation.

[0006] Atrial fibrillation occurs a large percentage, e.g., 40% of patients, receiving cardiac resynchronization therapy (CRT) at the time of implantation of an implantable medical device (IMD). Device-detected atrial tachyarrhythmias often predict adverse outcomes in real-world patients with implantable biventricular defibrillators. Further, atrial fibrillation often prevents the delivery of optimal CRT therapy due to the irregular conduction to the ventricles. Patients with atrial fibrillation may have a higher long-term mortality after CRT implant compared to those in sinus rhythm.SUMMARY

[0007] The illustrative systems, devices, and methods described herein may be configured to deliver and adjust atrioventricular (AV) node stimulation to regularize a patient’s heart rate and slow down, or decrease, the patient’s heart and to deliver pacing therapy (e.g., cardiac resynchronization therapy, left ventricle only pacing therapy, biventricular pacing therapy, left bundle branch pacing therapy, etc.) in cooperation with the AV node stimulation. If the AV node stimulation regularizes the heart rate, the illustrative systems, devices, and methods may then determine whether the patient’s heart rate exceeds a heart rate threshold such as, e.g., 100 beats per minute (bpm), if the patient’s heart rate exceeds the heart rate threshold, then biventricular pacing therapy be delivered in conjunction with the AV node stimulation, and if the patient’s heart rate is less than or equal to the heart rate threshold, then left ventricle only pacing therapy may be delivered in conjunction with the AV node stimulation. Further, if the AV node stimulation does not regularize the heart rate, then the illustrative systems, devices, and methods may deliver left ventricle only pacing therapy or left bundle branch pacing therapy. In one embodiment, the AV node stimulation may continue to be delivered along with the left ventricle only pacing therapy or left bundle branch pacing therapy in response to determining that AV node stimulation did not regularize the heart rate. In one embodiment, the AV node stimulation may not be delivered along with the left ventricle only pacing therapy or left bundle branch pacing therapy in response to determining that AV node stimulation did not regularize the heart rate. Additionally, in one or more embodiments, right bundle branch pacing therapy may be delivered if the AV node stimulation does not regularize the heart rate in situations, or conditions, where the right ventricular activation is failing more than the left ventricular activation.

[0008] Further, the illustrative systems, devices, and methods described herein may be configured regularize heart rate, or ventricular rate, using atrioventricular (AV) node stimulation to obtain a seemingly normal conduction during atrial tachycardia / atrial fibrillation (AT / AF). In one or more embodiments, the AV node stimulation could be performed using a lead targeting a vagal nerve branch about 5 millimeters (mm) to about 30 mm from the coronary sinus ostium in the posterior septum, which innervates the AV node. In one or more embodiments, the AV node stimulation may include pulses of about 40 Hertz (Hz) to about 60 Hz delivered to the AV node during the refractory period of theventricles or atria or both. Further, the output (e.g., pulses, pulse width, current, etc.) of the AV node stimulation may be optimized to regularize the heart rate in the ventricle without delaying the heart rate too much and provide as much intrinsic conduction as possible.

[0009] Additionally, the AV node stimulation processes described herein may be described as optimizing battery life as energy is saved when the heart rate, or ventricular rate, can be lowered below 100 beats per minute (bpm) thereby reducing an amount of biventricular pacing. Further, a low and regular rate that can be provided by the illustrative systems, devices, and methods may facilitate optimization of CRT since left ventricular pacing timed to fuse with intrinsic conduction improves left ventricular contractile function better than biventricular pacing. In other words, the illustrative systems, devices, and methods may allow CRT to be delivered using left ventricle only pacing (i.e., no right ventricular pacing), which may be beneficial because, as the intrinsic right ventricular activation is more physiologic, it may result in better hemodynamics with left ventricular pre-activation if heart rate is below 100 bpm, and it may save device energy.

[0010] When intrinsic conduction is prolonged, however, biventricular pacing may be utilized. The biventricular pacing can be adjusted to intrinsic electrical conduction (e.g., adaptive biventricular pacing). For example, the AV pacing delay may be adjusted to pace after the end of the P-wave to provide effective left ventricular filling. Further, a higher % biventricular pacing may be utilized if the AV pacing delay is adjusted to pace in advance of intrinsic QRS complex. Still further, biventricular pacing may promote better left ventricle hemodynamics if intraventricular (VV) delay is adjusted to promote intrinsic right ventricular activation when it is sufficiently preserved.

[0011] The illustrative systems, devices, and methods may be further described as providing AV node stimulation during atrial fibrillation to enable left bundle branch pacing or adaptive left ventricle only pacing and to enable lowering of the heart rate so that adaptive biventricular pacing can be avoided or circumvented. The ability to provide CRT therapy may slow down the progression of atrial fibrillation.

[0012] One illustrative system includes a therapy delivery circuit to deliver therapy to the patient’s heart, a sensing circuit to sense electrical activity of the patient’s heart, and a computing apparatus comprising processing circuitry operably coupled to the therapy delivery circuit and the sensing circuit. The computing apparatus is configured to monitor cardiac electrical activity of the patient using a plurality of electrodes operably coupled tothe therapy delivery circuit and the sensing circuit, determine an irregular cardiac rhythm or a regular cardiac rhythm based on the monitored cardiac electrical activity, deliver AV node stimulation using the neural electrode to regularize the patient’s heart rhythm and decrease the patient’s heart rate in response to determining the irregular cardiac rhythm, determine that the patient’s heart rhythm has not been regularized in response to the AV node stimulation based on the monitored cardiac electrical activity, and deliver left ventricular pacing therapy in response to determining that the patient’s heart rhythm has not been regularized in response to the AV node stimulation.

[0013] One illustrative method includes monitoring cardiac electrical activity of the patient using a plurality of electrodes, determining an irregular cardiac rhythm or a regular cardiac rhythm based on the monitored cardiac electrical activity, delivering AV node stimulation using the neural electrode to regularize the patient’s heart rhythm and decrease the patient’s heart rate in response to determining the irregular cardiac rhythm, determining that the patient’s heart rhythm has not been regularized in response to the AV node stimulation based on the monitored cardiac electrical activity, and delivering left ventricular pacing therapy in response to determining that the patient’s heart rhythm has not been regularized in response to the AV node stimulation.

[0014] One illustrative implantable medical system includes a therapy delivery circuit to deliver therapy to the patient’s heart, a sensing circuit to sense electrical activity of the patient’s heart, and a computing apparatus comprising processing circuitry operably coupled to the therapy delivery circuit and the sensing circuit. The computing apparatus is configured to monitor cardiac electrical activity of the patient using a plurality of electrodes operably coupled to the therapy delivery circuit and the sensing circuit, determine an irregular cardiac rhythm or a regular cardiac rhythm based on the monitored cardiac electrical activity, deliver AV node stimulation using the neural electrode to regularize the patient’s heart rhythm and decrease the patient’s heart rate in response to determining the irregular cardiac rhythm, determine that the patient’s heart rhythm has been regularized in response to the AV node stimulation based on the monitored cardiac electrical activity, and deliver adaptive left ventricular pacing therapy or adaptive biventricular pacing therapy in response to determining that the patient’s heart rhythm has been regularized in response to the AV node stimulation.

[0015] One illustrative method includes monitoring cardiac electrical activity of the patient using a plurality of electrodes, determining an irregular cardiac rhythm or a regular cardiac rhythm based on the monitored cardiac electrical activity, delivering AV node stimulation using the neural electrode to regularize the patient’s heart rhythm and decrease the patient’s heart rate in response to determining the irregular cardiac rhythm, determining that the patient’s heart rhythm has been regularized in response to the AV node stimulation based on the monitored cardiac electrical activity, and delivering adaptive left ventricular pacing therapy or adaptive biventricular pacing therapy in response to determining that the patient’s heart rhythm has been regularized in response to the AV node stimulation.

[0016] The above summary is not intended to describe each embodiment or every implementation of the present disclosure. A more complete understanding will become apparent and appreciated by referring to the following detailed description and claims taken in conjunction with the accompanying drawings.BRIEF DESCRIPTION OF THE DRAWINGS

[0017] FIG. l is a schematic diagram of a heart of patient.

[0018] FIG. 2A is a conceptual diagram depicting an illustrative therapy system that is configured to provide AV node stimulation and cardiac resynchronization therapy (CRT) using four leads.

[0019] FIG. 2B is a conceptual diagram depicting an illustrative therapy system similar to that of FIG. 2A that is configured to provide AV node stimulation and biventricular pacing therapy using three leads.

[0020] FIG. 2C is a conceptual diagram depicting an illustrative therapy system similar to that of FIG. 2A that is configured to provide AV node stimulation and cardiac conduction system pacing therapy using three leads.

[0021] FIG. 3 is a functional block diagram illustrating an example of a configuration of an implantable medical device of FIGS. 2A-2C.

[0022] FIG. 4 is a conceptual diagram depicted a distal end of AV node stimulation lead usable with the implantable medical device of FIGS. 2A-2C.

[0023] FIG. 5 depicts an illustrative method delivering AV node stimulation and pacing therapy that may be utilized by the devices of FIGS. 1-5.DETAILED DESCRIPTION

[0024] In the following detailed description of illustrative embodiments, reference is made to the accompanying figures of the drawing which form a part hereof, and in which are shown, by way of illustration, specific embodiments which may be practiced. It is to be 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.

[0025] Illustrative systems, devices, and methods shall be described with reference to FIGS. 1-5. 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.

[0026] FIG. 1 depicts a schematic diagram of a heart 12 and FIGS. 2A-2C depict conceptual diagrams showing illustrative therapy systems that may be used to provide therapy to the heart 12 of a patient 14. The patient 14 ordinarily, but not necessarily, will be a human. As shown in FIGS. 2A-2C, the therapy system 10 may include an implantable medical device (IMD) 16, which is coupled to four leads 18, 20, 21, 23, and a user interface device 24. The IMD 16 may be, for example, an implantable pacemaker, cardioverter, and / or defibrillator that provides electrical pulses to the heart 12 via electrodes coupled to one or more of the leads 18, 20, 21, 23. Further non-limiting examples of the IMD 16 be a pacemaker with a medical lead, an implantable cardioverterdefibrillator (ICD), an intracardiac device, a leadless pacing device (LPD), a subcutaneous ICD (S-ICD), and a subcutaneous medical device (e.g., nerve stimulator, inserted monitoring device, etc.).

[0027] The leads 18, 20, 21, 23 may extend into the heart 12 of the patient 14 to sense electrical activity of the heart 12 and / or deliver electrical stimulation to the heart 12. In the example shown in FIG. 2A, the right ventricular lead 18 extends through one or more 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 23 extends through one or more veins and the vena cava, and into the right atrium 26 of the heart 12 to a region near the atrial septum. The left ventricular 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. The neural, or AV node stimulation, lead 21 extends through one or more veins and the vena cava, and into the right atrium 26 of the heart 12 to a posterior septal position to deliver stimulation to a vagal nerve branch innervating the AV node.

[0028] One or more elongated conductors of any of the leads 18, 20, 21, 23 may extend through a hermetic feedthrough assembly, and within an insulative tubular member of the respective lead, and may electrically couple an electrical pulse generator (contained within housing) to one or more electrodes such as, e.g., ring electrodes, tips electrodes, helical electrodes, etc. The conductors may be formed by one or more electrically conductive wires comprising, for example, MP35N alloy known to those skilled in the art, in a coiled or cabled configuration, and the insulative tubular member may be any suitable medical grade polymer, for example, polyurethane, silicone rubber, or a blend thereof. According to one or more illustrative embodiments, the flexible lead body may extend a pre-specified length (e.g., about 10 centimeters (cm) to about 20 cm, or about 15 to 20 cm) from a proximal end to a distal end. The lead body may be less than about 7 French (FR) but typically in the range of about 3 FR to 4 FR in size. In one or more embodiments, about 2 FR size to about 3 FR size lead body is employed.

[0029] In some embodiments, the IMD 16 may be an intracardiac pacemaker as shown or leadless pacing device (LPD), although not shown herein. As used herein, “leadless” refers to a device being free of a lead extending out of the heart 12. In other words, a leadless device may have a lead that does not extend from outside of the heart to inside of the heart. Some leadless devices may be introduced through a vein, but once implanted, the leadless devices are free of, or may not include, any transvenous lead and may be configured to provide cardiac therapy without using any transvenous lead. Aleadless electrode may be leadlessly coupled to the housing of the medical device without using a lead between the electrode and the housing.

[0030] The IMD 16 may sense electrical signals attendant to the depolarization and repolarization of the heart 12 via various electrodes as shown in FIG. 2 A coupled to at least one of leads 18, 20, 21, 23. In some examples, the IMD 16 provides pacing pulses to the heart 12 based on the electrical signals sensed within the heart 12. The configurations of the electrodes used by the IMD 16 for sensing and pacing may be unipolar or bipolar. The IMD 16 may also provide defibrillation therapy and / or cardioversion therapy via electrodes located on at least one of the leads 18, 20, 21, 23. For example, the IMD 16 may detect atrial arrhythmias of heart 12, such as atrial fibrillation of the atria 26, 33, and then may deliver defibrillation therapy to the heart 12 in the form of electrical pulses. Also, the IMD 16 may detect ventricular arrhythmias of the heart 12, such as ventricular fibrillation of the ventricles 28, 32, and then may 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 fibrillation of the heart 12 is stopped. The IMD 16 may detect fibrillation employing one or more fibrillation detection techniques known in the art.

[0031] In some examples, the user interface device 24 diagrammatically shown in FIG. 2A may be a handheld computing device or a computer workstation or a mobile phone. The user interface device 24 may include a user interface that receives input from a user. The user interface may include, for example, a keypad and a display, which may for example, be a cathode ray tube (CRT) display, 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 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 user interface device 24 may include a touch screen display, and a user may interact with the user interface device 24 via the display. Through the graphical user interface on the user interface device 24, a user may configure one or more pacing therapies, select one or more pacing modes, etc.

[0032] Additionally, various pacing settings may be adjusted, or configured, based on various sensed signals. For example, various near-field and far-field signals may besensed by one or more of the electrodes of the IMD 16 and / or other devices operatively coupled thereto. For example, P-wave-to-R-wave interval may be monitored or measured within a near-field or far-field signal and then may be used to adjust, configure, and select cardiac conduction system pacing therapy. Further, for example, QRS width may be monitored or measured within a near-field or far-field signal and then may be used to adjust, configure, and select cardiac conduction system pacing therapy.

[0033] The illustrative therapy systems described herein including IMD 16 may be utilized to deliver AV node stimulation and various pacing therapies such as, e.g., adaptive left ventricle only pacing therapy, adaptive biventricular pacing, left bundle branch pacing therapy, etc. To do so, the IMD 16 may sense one or more cardiac electrical signals. As used herein, the term “far-field” electrical signal refers to the result of measuring cardiac activity using a sensor, such as an electrode, positioned outside of an area of interest. For example, a far-field electrical signal representing electrical activity of a chamber of interest of the patient’s heart may be measured from an electrode positioned in an adjacent chamber (i.e., a chamber different from than that of the chamber of interest that is next to or near the chamber of interest). More specifically, for example, atrial electrical activity, or electrical activity originating one or more both atria, representative of depolarization of the one or both atria may be monitored in a far-field electrical signal measured using an electrode positioned outside of the right atrium such as in the right or left ventricle, or in the ventricular septum. As used herein, the term “near-field” electrical signal refers to the result of measuring cardiac activity using a sensor, such as an electrode, positioned near an area of interest. For example, an electrical signal measured from an electrode positioned on the left side of the patient’s ventricular septum is one example of a near-field electrical signal of the patient’s LV.

[0034] P-wave timing may be described as the time at which a P-wave is detected. Typically, P-wave timing includes using the maximal first derivative of a P-wave upstroke (or the time of the maximal P-wave value). P-wave timing is also used in the device marker channel to indicate the time of the P-wave or the time of atrial activation. P-wave timing may be determined using near-field signals obtained by sensors (e.g., electrodes, accelerometers, heart sound sensors, etc.) positioned in the atria (e.g., the right atrium) and / or far-field near-field signals obtained by sensors (e.g., electrodes, accelerometers,heart sound sensors, etc.) positioned outside of the atria (e.g., the right atrium) such as in the right ventricle and / or ventricular septum.

[0035] R-wave timing is the time at which the QRS complex is detected. Typically, R-wave timing includes using the maximal first derivative of an R-wave upstroke (or the time of the maximal R-wave value). R-wave timing is also used in the device marker channel to indicate the time of the R-wave or the time of ventricular activation.

[0036] A user, such as a physician, technician, or other clinician, may interact with the user interface device 24 to communicate with the IMD 16. For example, the user may interact with the user interface device 24 to retrieve physiological or diagnostic information from the IMD 16. Additionally, a user may also interact with the user interface device 24 to program the IMD 16, e.g., select values for operational parameters of the IMD 16. The IMD 16 and 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, but other techniques are also contemplated. In some examples, the 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 user interface device 24.

[0037] The system 10 of FIG. 2 A may be described as a triple-chamber system that may be used for cardiac rhythm therapy and defibrillation or cardioversion therapy (CRT-D). The leads 18, 20, 21, 23 may be electrically coupled to a stimulation generator, a sensing module, or other modules of IMD 16 via connector block 34. In some examples, proximal ends of leads 18, 20, 21, 23 may include electrical contacts that electrically couple to respective electrical contacts within the connector block 34. In addition, in some examples, the leads 18, 20, 21, 23 may be mechanically coupled to the connector block 34 with the aid of set screws, connection pins, or another suitable mechanical coupling mechanism.

[0038] Each of the leads 18, 20, 21, 23 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, an optional pressure sensor 38 and bipolar electrodes40 and 42 are located proximate to a distal end of the right ventricular lead 18. In addition, the bipolar electrodes 44 and 46 are located proximate to a distal end of the left ventricular lead 20 and bipolar electrodes 48 and 50 are located proximate to a distal end of right atrial lead 23. The neural, or AV node stimulation, electrode 51 located on a distal end of the neural lead 21 may be used for delivering nerve stimulation to a vagal nerve branch from the right atria. The neural electrode 51 may be positioned between about 5 millimeters and about 30 millimeters from the coronary sinus ostium into the posterior septum of the right atrium to deliver the AV node stimulation to the vagal nerve branch innervating the AV node.

[0039] The pressure sensor 38 is disposed in right ventricle 28 and may respond to an absolute pressure inside right ventricle 28. The pressure sensor 38 may be, for example, a capacitive or piezoelectric absolute pressure sensor. In other examples, the pressure sensor 38 may be positioned within other regions of the heart 12 and may monitor pressure within one or more of the other regions of the heart 12, or the pressure sensor 38 may be positioned elsewhere within or proximate to the cardiovascular system of the patient 14 to monitor cardiovascular pressure associated with mechanical contraction of the heart. Optionally, a pressure sensor in the pulmonary artery can be used that is in communication with the IMD 16.

[0040] The electrodes 40, 44, 48 may take the form of ring electrodes, and the electrodes 42, 46, 50 may take the form of extendable and / or fixed helix tip electrodes mounted within the insulative electrode heads 52, 54, 56, respectively. Each of the electrodes 40, 42, 44, 46, 48, 50, 51 may be electrically coupled to a respective one of the coiled conductors within the lead body of its associated lead 18, 20, 21 23, and thereby coupled to respective ones of the electrical contacts on the proximal end of the leads 18, 20, 21, 23. The neural, or AV node stimulation, electrode 51 may take the form of extendable and / or fixed helix tip electrode mounted in a insulative electrode head of the lead 21. An illustrative neural electrode 51 is described further herein with respect to FIG. 4.

[0041] The electrodes 40, 42, 44, 46, 48, 50, 51 may sense electrical signals 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, 21, 23. In some examples, the IMD 16 also delivers pacing pulses via the electrodes 40, 42, 44, 46, 48, 50 to causedepolarization of cardiac tissue of heart 12 and AV node stimulation via the neural electrode 51. In some examples, the IMD 16 may include one or more housing electrodes, such as housing electrode 58, which may be formed integrally with an outer surface of a hermetically sealed housing 60 of the IMD 16 or otherwise coupled to the housing 60. In some examples, the housing electrode 58 may be defined by an uninsulated portion of an outward facing portion of the housing 60 of the IMD 16. Other divisions between insulated and uninsulated portions of housing 60 may be employed to define two or more housing electrodes. In some examples, the housing electrode 58 includes substantially all of the housing 60. Any of the electrodes 40, 42, 44, 46, 48, 50, 51 may be used for unipolar sensing or pacing in combination with the housing electrode 58 or for bipolar sensing with two electrodes in the same pacing lead. In one or more embodiments, the housing 60 may enclose a stimulation generator that generates cardiac pacing pulses and defibrillation or cardioversion shocks, as well as a sensing module for monitoring the patient’s heart rhythm.

[0042] The leads 18, 20, 23 may also include elongated electrodes 62, 64, 66, respectively, which may take the form of a coil. Additionally, although not depicted, it is to be understood that lead 21 may also include an elongated electrode similar to elongated electrodes 62, 64, 66. The IMD 16 may deliver defibrillation shocks to the heart 12 via any 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. The electrodes 62, 64, 66 may be fabricated from any suitable electrically conductive material, such as, but not limited to, platinum, platinum alloy or other materials known to be usable in implantable defibrillation electrodes.

[0043] The pressure sensor 38 may be coupled to one or more coiled conductors within the lead 18. As shown, the pressure sensor 38 is located more distally on the lead 18 than elongated electrode 62. In other examples, the pressure sensor 38 may be positioned more proximally than the elongated electrode 62, rather than distal to the electrode 62. Further, the pressure sensor 38 may be coupled to another one of the leads 20, 21, 23 in other examples, or to a lead other than the leads 18, 20, 21, 23 carrying stimulation and sense electrodes. In addition, in some examples, the pressure sensor 38 may be self-contained device that is implanted within the heart 12, such as within the ventricular septum separating the right ventricle 28 from the left ventricle 32, or the atrialseptum separating the right atrium 26 from the left atrium 33. In such an example, the pressure sensor 38 may wirelessly communicate with the IMD 16.

[0044] It is to be understood that the illustrative system 10 and IMD 16 is one example that may utilizes the illustrative processes and methods described further. As shown, the system 10 includes four leads. It is to be understood that the illustrative processes and methods may be performed by systems including less than four leads, more than four leads, or leadless embodiments so as long as the systems are capable over delivering AV node stimulation, performing cardiac sensing (e.g., atrial and / or ventricular activations and timing associated therewith), and at least some form of ventricular pacing. Two illustrative embodiments that utilize three leads are depicted in FIGS. 2B-2C. The illustrative system 11 of FIG. 2B is substantially similar to the system 10 of FIG. 2A except that it does not include the right atrial lead 21. Further, the illustrative system 15 of FIG. 2B is substantially similar to the system 10 of FIG. 2A except that it does not include the left ventricular coronary sinus lead 20 or right ventricular lead 18 and includes a cardiac conduction system lead 25.

[0045] The cardiac conduction system pacing lead 25 may be include an electrode 29 in the form of a helix (also referred to as a helical electrode) that may be positioned proximate to, near, adjacent to, or in, area or portions of the cardiac conduction system such as, e.g., ventricular septum, the His bundle, left bundle branch, and / or right bundle branch. In particular, as shown in FIG. 2C, the cardiac conduction system pacing lead 25 is configured to delivery cardiac conduction system pacing therapy to at least the left bundle branch using the electrode 29 implanted in the ventricular septum from the right ventricle 28.

[0046] More specifically, the cardiac conduction system pacing lead 25 may be implanted in the septal wall, or ventricular septum, from the right ventricle 28 toward the left ventricle 32. In one or more embodiments, the cardiac conduction system pacing lead 25 may not pierce through the wall of the left ventricle 32 or extend into the left ventricular chamber. The electrode 29 may be disposed on a distal end portion of the cardiac conduction system pacing lead 25 and may be described as a tissue-piercing electrode. The electrode 29 may be implanted near right bundle branch 8b or near the left bundle branch 8a.

[0047] Although a single electrode is depicted, it is to be understood that the cardiac conduction system pacing lead 25 may be a bipolar lead or a quadripolar lead including multiple types of electrodes for sensing, pacing, and delivering defibrillation shocks. Additionally, the helix of the lead 25 implanted in the ventricular septum may configured to carry, or include, more than one electrode such as two electrodes so as to delivery cardiac conduction system pacing therapy to both the right and left bundle branches, which may be referred to as dual bundle branch pacing. During dual bundle branch pacing, the electrodes may each deliver a cathodal pulse to achieve synchronized activation, or excitation, of the right bundle branch 8b and the left bundle branch 8a, which may result in synchronized activation of the right ventricle 28 and the left ventricle 32. In some embodiments, the pulses may be delivered at the same time to achieve synchrony. In other embodiments, the pulses may be delivered with a delay to achieve synchrony.

[0048] The configuration of the therapy systems 10, 11, 15 illustrated in FIGS. 2A-2C are merely a few examples that may be configured to perform the illustrative methods and processes described herein. In other examples, a therapy system may include epicardial leads and / or patch electrodes instead of or in addition to the transvenous leads 18, 20, 21, 23, 25 illustrated in FIGS. 2A-2C or other configurations shown or described herein or incorporated by reference. Further, the IMD 16 may not be implanted within patient 14. As such, it is to be understood that the illustrative therapy systems 10, 11, 15 described herein 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. For example, illustrative therapy systems may include four transvenous leads located as illustrated in FIG. 2A or three transvenous leads located as illustrated in FIGS. 2B-2C.

[0049] 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. One or more components of the IMD 16, such as the control module 81, may be contained within a housing of the IMD 16 (e.g., within a housing of a pacemaker). 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 processingcircuitry 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.

[0050] 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. The processing circuitry 80 controls the therapy delivery module, or stimulation generator, 84 to select a therapy mode such as, for example, select one or more of left ventricular only pacing therapy, biventricular pacing therapy, left bundle branch pacing therapy, right bundle branch pacing therapy, AV node stimulation, etc., and deliver stimulation therapy to the heart 12 according to the selected one or more pacing modes, which may be stored in the memory 82, and various sensing (e.g., atrial depolarizations or activations, ventricular atrial depolarizations or activations, heartrate, P-wave-to-R-wave intervals, etc.). Specifically, the processing circuitry 80 may control the therapy delivery module 84 to deliver electrical pulses with amplitudes, pulse widths, frequency, or electrode polarities for pacing and neural, or nerve, stimulation (e.g., vagus nerve stimulation, AV node stimulation, etc.) specified by the selected one or more therapy programs and therapy modes.

[0051] 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 herein. More, specifically, the control module 81 (e.g., the processing circuitry 80) maycontrol various parameters of the electrical stimulus delivered by the therapy delivery module 84 such as, e.g., AV delays, pacing vectors, pacing pulses amplitude, pacing pulse widths, pacing pulse frequency, AV node stimulation pulse amplitude, AV node stimulation pulse pacing pulse widths, AV node stimulation pulse frequency, or electrode polarities, etc., which may be specified by one or more selected therapy programs (e.g., AV delay adjustment programs, AV node stimulation programs, pacing therapy programs, pacing recovery programs, capture management programs, etc.). The therapy delivery module 84 is electrically coupled to electrodes 29, 40, 42, 44, 45, 46, 47, 48, 50, 51, 58, 62, 64, 66, e.g., via conductors of the respective lead 18, 20, 21, 22, 25, 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 29, 40, 42, 44, 45, 46, 47, 48, 50, 51, 58, 62, 64, 66.

[0052] For example, the therapy delivery module 84 may deliver pacing stimulus (e.g., pacing pulses) via the ring electrodes 40, 44, 45, 46, 47, 48 coupled to leads 18, 20, 22 and / or the helical tip electrodes 42, 50 of the leads 18, 22. Further, for example, the therapy delivery module 84 may deliver AV node stimulus via the vagus nerve (e.g., nerve stimulation) via the neural electrode 51 coupled to the lead 21. Still further, for example, the therapy delivery module 84 may deliver cardiac conduction system pacing via electrode 29 coupled to the lead 25. And 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, nerve stimulation, 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.

[0053] 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 thesensing 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 29, 40, 42, 44, 45, 46, 47, 48, 50, 51, 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.

[0054] The sensing module 86 is coupled (e.g., electrically coupled) to sensing apparatus, which may include, among additional sensing apparatus, the electrodes 29, 40, 42, 44, 45, 46, 47, 48, 50, 51, 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 whether a patient is undergoing various cardiac conditions such as AT / AF or VT / VF. The ECGZEGM signals may be used to determine lynwhether the patient’s heart rate or ventricular rate is regularized as will be described further herein. The ECGZEGM signals may be used to measure or monitor the patient’s intrinsic AV delay or conduction to assist in adjusting pacing therapy such as adaptive left ventricular only or biventricular pacing therapy. Moreover, 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 / acceleration capacity, deceleration sequence incidence, T-wave alternans (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.

[0055] 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 29, 40, 42, 44, 45, 46, 47, 48, 50, 51, 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., senseelectrical activity of the patient's heart (e.g., one or more electrical vectors of the patient's heart using any combination of the electrodes 29, 40, 42, 44, 45, 46, 47, 48, 50, 51, 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.

[0056] 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 thereafter converted 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.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] A conceptual diagram of a distal end 92 of an illustrative neural, or AV node stimulation, lead 21 usable with the implantable medical device 16 of FIGS. 2A-2C is depicted in FIG. 4. The neural lead 21 may define lead body 91 extending from a proximal end operably coupled to the IMD 16 to a distal end 92 shown in FIG. 4. A fixation helix 95 may be coupled to and extend from the distal end 92 of the lead body 91 to be implanted and fixated at a target implantation site to, e.g., stimulate the vagus nerve innervating the AV node, and in particular, nerve fibers of the vagus nerve having parasympathetic function. As described herein, stimulation of the vagus nerve (e.g., the parasympathetic fibers of the vagus nerve) may be used to control ventricular rate during arrhythmias. In particular, the parasympathetic tone of the vagus nerve may be increased by stimulating intracardiac parasympathetic neurons of vagus nerve between about 5millimeters (mm) and about 30 mm from the coronary sinus ostium into the posterior septum of the right atrium. In other embodiments, the AV node may be stimulating in other areas or regions such as, for example, the fat pads near the superior vena cava (SVC) and inferior vena cava (IVC), tissue near the AV node, the base of the right ventricle, and other vagal nerves near the heart.

[0062] The fixation helix 95 extends from an insulated proximal end region, coupled to the lead body 91, to a distal end region. The distal end region may include, or define, the neural, or AV node stimulation, electrode 51. In one embodiment, the neural electrode 51 is defined at, or as part of, a distal area or tip of the fixation helix 95. To avoid stimulating non-nerve tissue such as the right atrial myocardial tissue in the embodiments of systems 10, 11, 15 shown in FIGS. 2A-2C, the fixation helix 95 may be insulated 97 from the distal end 92 of the lead body 91 to the neural electrode 51, which may be referred to as the insulated proximal region. In other words, the fixation helix 95 may include an insulated portion or region 97. The fixation helix 95 may define a length 96 between about 1 millimeter (mm) and about 8 mm. In one embodiment, the length 96 of the fixation helix 95 is 5 mm. In one or more embodiments, the length 96 of the fixation helix 95 is greater than or equal to 0.25 mm, greater than or equal to 0.5 mm, greater than or equal to 1 mm, greater than or equal to 1.5 mm, greater than or equal to 2 mm, greater than or equal to 2.5 mm, greater than or equal to 3 mm, greater than or equal to 3.5 mm, greater than or equal to 4.5 mm, or greater than or equal to 5 mm, and / or less than or equal to 8 mm, less than or equal to 7.5 mm, less than or equal to 7 mm, less than or equal to 6.5 mm, less than or equal to 6 mm, less than or equal to 5.5 mm, less than or equal to 4.75 mm, or less than or equal to 4.25 mm.

[0063] The neural electrode 51, which, in one or more embodiments, may be described as the uninsulated distal end region of the fixation helix 95, may define a length 98 between about 1 mm and about 4 mm. In one embodiment, the length 98 of the neural electrode 51 is 2 mm. In this way, the AV node stimulation may be delivered to the desired location, i.e., the vagus nerve, as opposed to undesired locations such myocardial tissue.

[0064] FIG. 5 depicts an illustrative method 100 of delivering AV node stimulation and pacing therapy that may be utilized by the illustrative systems and devices of FIGS. 1-4. The method 100 includes monitoring cardiac electrical activity of a patientusing one or more implantable electrodes 102. The cardiac electrical activity may be monitored using one or more electrodes positioned or placed in proximity to atrial of the right atrium and ventricular tissue of the left or right ventricles to provide one or more 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 FIGS. 2A-2B, or one or more electrodes positioned proximate of the left ventricle using, e.g., the LV coronary sinus lead 20 of FIGS. 2A-2B. In at least one embodiment, the atrial electrical activity may be measured, or monitored, using one or more electrodes positioned inside of the right atria using, e.g., the RA lead 23 of FIGS. 2A and 2C. Additionally, the cardiac electrical activity may be monitored using a combination of electrodes. In other words, the cardiac electrical activity may be monitored using various vectors using two or more electrodes that are operably coupled to the IMD 16 and associated devices or systems.

[0065] The method 100 further includes evaluating the patient’s intrinsic cardiac conduction or activation 102 for arrythmias such as, for example, atrial fibrillation or atrial tachycardia or for an abnormally high heart rate during rest (e.g., greater than 100 beats per minute). Determination of atrial tachycardias including atrial fibrillation, atrial tachycardia, and atrial flutter may be performed using a variety of different processes and techniques. One example is described in U.S. Pat. App. Pub. No. 2020 / 0196899 entitled “Atrial Arrhythmia Episode Detection in a Cardiac Medical Device” published on February 14, 2023, to Higgins et al., which is hereby incorporated by reference in its entirety.

[0066] If the patient’s intrinsic cardiac conduction or activation 102 indicates an arrythmia or an abnormally high heart rate, then the method 100 may proceed to determining whether the patient has an irregular cardiac rhythm or a regular cardiac rhythm 106 based on the monitored cardiac electrical activity. Determination of an irregular or regular rhythm may be described as determining whether atrial tachyarrhythmia or atrial fibrillation (AT / AF) is causing lack of regularization of ventricular contraction or activation, e.g., heartbeat or ventricular rate. In atrial fibrillation, the atria depolarize at an elevated rate that is highly irregular, and the atrial depolarizationsare typically conducted intermittently to the ventricles, so that the ventricles beat synchronously at times and asynchronously at other times with the atrial depolarizations.

[0067] Determination of an irregular or regular cardiac rhythm may be performed various way using one or more metrics and processes. One illustrative example of determination of an irregular or regular cardiac rhythm may be based on the consistency of R-R interval lengths. For example, the regularity may be determined based on the cumulative differences between consecutive R-R intervals. More particularly, the sum of the absolute values of the differences between the consecutive intervals prior to detection may be compared to one or more thresholds to classify the episode as regular, irregular, or very regular. In one example, the sum must be less than or equal to a first threshold to be classified as regular, and less than or equal to a second, lower threshold to be classified as very regular. The sum of the absolute values of the differences may be called a factor. For example, a factor of 6 would indicate that the sum of the difference for the intervals examined is 6 milliseconds (ms). In addition, in some examples, each consecutive change in interval length may not be greater than a threshold, such as 40 ms, for the episode to be considered regular. To be considered extremely regular, 10 consecutive intervals are examined and the threshold to be considered extremely regular is a factor of 6. That is, for at least 10 consecutive intervals the sum of the absolute values of the differences between the consecutive intervals is less than 6 ms. For very regular episodes, 12 consecutive intervals are used and a factor of 14 is used as the threshold. For regular episodes, 10 consecutive intervals are used along with a factor of 25 for the threshold. Additionally details and examples of determination of an irregular or regular cardiac rhythm may be described in U.S. Pat. No. 8,521,281 entitled “Electrogram Classification Algorithm” and issued on August 27, 2023, to Patel, et al., which is hereby incorporated by reference in its entirety.

[0068] One illustrative example of determination of an irregular or regular cardiac rhythm may be based atrial depolarizations. For example, regularity may be determined by measuring time intervals between a number of recent atrial depolarizations and comparing the difference between the largest time interval between successive atrial depolarizations and the smallest time interval between successive atrial depolarizations. If the difference between the two is greater than a predetermined reference value, then it may be determined the arrhythmia is irregular. Likewise, if the difference between the two is lessthan the predetermined reference value, then it may be determined the arrhythmia is regular. Additionally details and examples of determination of an irregular or regular cardiac rhythm may be described in U.S. Pat. No. 6,922,584 entitled “Method and apparatus for discrimination atrial fibrillation using ventricular rate detection” and issued on July 26, 2005, to Wang et al., which is hereby incorporated by reference in its entirety.

[0069] If an irregular cardiac rhythm is determined, then the method 100 may proceed to delivering AV node stimulation 108 to regularize the patient’s heart rhythm and decrease the patient’s heart rate. The AV node stimulation may be delivered using a neural electrode such as the neural electrode 51 described herein with respect to FIGS. 2A-2C. Further, the AV node stimulation may be delivered during refractory periods of one or more of the atria and ventricles (i.e., the periods between depolarizations of the aria and ventricles) according to variety of parameters. Such parameters of the AV node stimulation may include time (e.g., the vagal stimulation may be delivered for a selected time period for each cardiac cycle), voltage (e.g., within a range of about 1 volt and about 8 volts), frequency of the pulses within a burst of pulses (e.g., within a range of about 1 hertz to about 150 hertz), pulse width of each pulse (e.g., within a range of about 0.05 milliseconds (ms) to about 1.5 ms), electrode configuration (e.g., bipolar or unipolar), and number of pulses per burst (e.g., within a range of about 3 pulses to about 20 pulses). In at least one embodiment, the AV node stimulation may include 40 hertz to 60 hertz pulses delivered during refractory periods of one or both of the atria and ventricles.

[0070] As earlier mentioned, the AV node stimulation 108 is delivered to regularize the patient’s heart rhythm and decrease the patient’s heart rate. Thus, the method 100 will continuously or periodically determine whether an irregular cardiac rhythm or a regular cardiac rhythm is occurring 106. When determined periodically, the irregular cardiac rhythm or a regular cardiac rhythm determination 106 may occur between about every 2 seconds and about every 10 seconds. In other words, the time period triggering, or initiating, the irregular cardiac rhythm or a regular cardiac rhythm determination 106 may be between about 2 seconds and about 10 seconds.

[0071] If, following initial delivery of AV node stimulation 108, there are adjustments available to be made to the AV node stimulation, then the method 100 may make such adjustments so that the AV node stimulation achieves the goal of regularizing the cardiac rhythm. Such process is show in FIG. 5 has determining whether the AV nodestimulation adjustments have been exhausted 110. For example, if no more adjustments to any of the AV node stimulation parameters may be adjusted any further, then it may be determined that the AV node stimulation adjustments have been exhausted 110.Conversely, if adjustments are available the AV node stimulation parameters 110, then the node stimulation adjustments will be to not have been exhausted 110 and the method 100 may adjust one or more parameters of the AV node stimulation 112.

[0072] In general, to adjust the AV node stimulation 112, the energy and / or aggressiveness of the AV node stimulation may be increased to attempt to affect the parasympathetic function of the vagus nerve innervating the AV node. For example, the frequency of the AV node stimulation may be increased by a selected step or percentage when adjusting the AV node stimulation 112. For instance, if the frequency of the AV node stimulation is 40 Hz, it may be increased by a step of 5 Hz resulting in 45 Hz. Subsequently, the frequency of the AV node stimulation may be increased by the same 5 Hz step during each adjustment cycle until the cardiac rhythm is regularized or until the frequency of the AV node stimulation reaches a maximum frequency of, for example, 80 Hz. If the AV node stimulation is being delivered at the maximum frequency and the patient’s cardiac rhythm has still not been regularized, then it may be determined that adjustments to the frequency parameter of the AV node stimulation has been exhausted 110.

[0073] Further, for example, the pulse width of the AV node stimulation may be increased by a selected step or percentage when adjusting the AV node stimulation 112. For instance, if the pulse width of the AV node stimulation is .1 ms, it may be increased by a step of 0.1 ms resulting in 0.2 Hz. Subsequently, the pulse width of the AV node stimulation may be increased by the same 0.1 ms step during each adjustment cycle until the cardiac rhythm is regularized or until the pulse width of the AV node stimulation reaches a maximum pulse width of, for example, 1.5 ms. If the AV node stimulation is being delivered at the maximum pulse width and the patient’s cardiac rhythm has still not been regularized, then it may be determined that adjustments to the pulse width parameter of the AV node stimulation has been exhausted 110.

[0074] Still further, for example, the voltage, or amplitude, of the AV node stimulation may be increased by a selected step or percentage when adjusting the AV node stimulation 112. For instance, if the voltage of the is AV node stimulation is 2 Volts (V), itmay be increased by a step of 0.25 V resulting in 2.25 V. Subsequently, the voltage of the AV node stimulation may be increased by the same 0.25 V step during each adjustment cycle until the cardiac rhythm is regularized or until the voltage of the AV node stimulation reaches a maximum voltage of, for example, 8 V. If the AV node stimulation is being delivered at the maximum voltage and the patient’s cardiac rhythm has still not been regularized, then it may be determined that adjustments to the voltage, or amplitude, parameter of the AV node stimulation have been exhausted 110. Further, it is to be understood that more than one AV node stimulation parameter may be adjusted at the same time or during the same the irregular cardiac rhythm or a regular cardiac rhythm determination 106 cycle.

[0075] The AV node stimulation adjustment 112 may be described as being configured to stimulate with enough energy to delay and regularize cardiac rhythm but maintain intrinsic conduction from the atria to ventricles as much as possible and not increase the AV delay too much. In other words, the energy and aggressiveness of the AV node stimulation may be increased to provide the regularity being sought but then not further increased so as to result in loss of intrinsic conduction or too long of intrinsic conduction. Thus, the method 100 may adjust the AV node stimulation 112 to decrease heart rate while maintaining intrinsic atrioventricular activation and without exceeding an intrinsic atrioventricular delay threshold. The intrinsic atrioventricular delay threshold may be between about 50 milliseconds (ms) and about 250 ms. In one embodiment, the intrinsic atrioventricular delay threshold is 150 ms. In one or more embodiments, the intrinsic atrioventricular delay threshold may be greater than or equal to 50 ms, greater than or equal to 70 ms, greater than or equal to 90 ms, greater than or equal to 110 ms, greater than or equal to 130 ms, greater than or equal to 150 ms, or greater than or equal to 170 ms, and / or less than or equal to 250 ms, less than or equal to 230 ms, less than or equal to 210 ms, less than or equal to 190 ms, less than or equal to 180 ms, or less than or equal to 160 ms. If the intrinsic atrioventricular delay threshold is exceeded while the adjusting the AV node stimulation 112, then it may be determined that the cardiac rhythm cannot be regularized by the AV node stimulation.

[0076] Additionally, while the AV node stimulation parameters are being adjusted in an attempt to provide cardiac rhythm regularization, changes in lead impedance may be monitored to determine micro-dislodgments of the lead.

[0077] In response to determination that the AV node stimulation adjustments have been exhausted 110 and that the cardiac rhythm has not been regularized 106 using AV node stimulation, the method 100 may then proceed to providing left ventricular pacing therapy 120, 122. In other words, the method 100 may deliver left ventricular pacing therapy 120, 122 in response to determining that the patient’s heart rhythm has not been regularized 106 in response to the AV node stimulation 108. Since the cardiac rhythm has not been regularized, the timing to deliver pacing, such as left ventricular pacing based on an AV delay may be challenging, because atrial and ventricular sensing may be intermittent or inconsistent. Thus, prior to delivering left ventricular pacing therapy 120, 122, the method 100 includes estimating heartbeat timing 114, and in particular, may estimate intrinsic atrial and / or ventricular activations. In one embodiment, “missed” atrial or ventricular activations or contractions may be “filled in” to when such activations or contractions are expected based on previously measured activations or contractions. In this way, the left ventricular pacing therapy 120, 122 may have appropriate timing to base the timing of the delivery of left ventricular pacing thereon.

[0078] The left ventricular pacing therapy may include one or both of left bundle branch pacing therapy 120 and adaptive left ventricular only pacing therapy 122 (e.g., depending upon what the therapy system supports and a patient’s physician prescribes). For example, the left ventricular pacing therapy may be left bundle branch-optimized cardiac resynchronization (LOT-CRT). The left bunch branch pacing therapy 120 may be delivered using systems including a left bundle lead such as illustrative system 15 of FIG. 2C. The left ventricular only pacing therapy 122 may be delivered using systems including a left ventricular coronary sinus leads such as illustrative systems 10, 11 of FIGS. 2A-2B. It is noted that one or both of the left bundle branch pacing therapy 120 or left ventricular only pacing therapy 122 may be adaptive pacing therapy, which means that the AV timing of the ventricular pacing pulses may be periodically adjusting atrioventricular delay based on one or more of the patient’s activity level and intrinsic atrioventricular delay. In particular, for example, the adaptive left ventricular pacing pulses may be configured to be delivered at 70% of a patient’s intrinsic AV delay and at least 40 milliseconds prior to intrinsic right ventricular activation or contraction.

[0079] If patient’s cardiac rhythm has determined to have been regularized 106 in response to the AV node stimulation, the method 100 may proceed to determining whetherto provide left ventricular pacing therapy 122 or biventricular pacing therapy 124. To do so, the method 100 may determine whether the patient has a high heart rate 116. If the patient is determined to have a high heart rate, then biventricular pacing therapy may be delivered 124, and conversely, if the patient is not determined to have a high heart rate, then left ventricular only pacing therapy may be delivered 122. Similar to as previously described, the left ventricular only pacing therapy 122 and the biventricular pacing therapy 124 may be adaptive. Adaptive left ventricular only pacing therapy includes periodically adjusting atrioventricular delay based one or more of the patient’s activity level and intrinsic atrioventricular delay. Adaptive biventricular pacing therapy includes periodically adjusting atrioventricular delay and interventricular delay based one or more of the patient’s activity level, intrinsic atrioventricular delay, and intrinsic interventricular delay.

[0080] In one embodiment, determination of a high heart rate may be determined by comparing the patient’s heart rate to a threshold value. The patient’s heart rate may be the patient’s instantaneous heart rate or a statistical metric of the patient’s heart rate of a period of time. For example, the patient’s heart rate may be an average of the patient’s heart rate over the most recent 30 seconds. The heart rate threshold value may be between about 90 beats per minute (bpm) to about 120 bpm. In one embodiment, the heart rate threshold value is 100 bpm. In one or more embodiments, the heart rate threshold value may be greater than or equal to 90 bpm, greater than or equal to 95 bpm, greater than or equal to 100 bpm, greater than or equal to 105 bpm, or greater than or equal to 110 bpm, and / or less than or equal to 120 bpm, less than or equal to 115 bpm, less than or equal to 112 bpm, less than or equal to 107 bpm, or less than or equal to 102 bpm.

[0081] Thus, if the patient’s heart rate is less than or equal to the heart rate threshold value 116, then the method 100 may proceed to delivering left ventricular only pacing therapy 122. And further, if the patient’s heart rate is greater than the heart rate threshold value 116, then the method 100 may proceed to delivering biventricular pacing therapy 124.ILLUSTRATIVE EXAMPLES

[0082] While the present disclosure is not so limited, an appreciation of various aspects of the disclosure will be gained through a discussion of the specific illustrativeexamples provided below. Various modifications of the illustrative examples, as well as additional examples of the disclosure, will become apparent herein.

[0083] Example Exl : A system comprising: a therapy delivery circuit to deliver therapy to the patient’s heart; a sensing circuit to sense electrical activity of the patient’s heart; and a computing apparatus comprising processing circuitry operably coupled to the therapy delivery circuit and the sensing circuit, the computing apparatus configured to: monitor cardiac electrical activity of the patient using a plurality of electrodes operably coupled to the therapy delivery circuit and the sensing circuit; determine an irregular cardiac rhythm or a regular cardiac rhythm based on the monitored cardiac electrical activity; deliver AV node stimulation using the neural electrode to regularize the patient’s heart rhythm and decrease the patient’s heart rate in response to determining the irregular cardiac rhythm; determine that the patient’s heart rhythm has not been regularized in response to the AV node stimulation based on the monitored cardiac electrical activity; and deliver left ventricular pacing therapy in response to determining that the patient’s heart rhythm has not been regularized in response to the AV node stimulation:

[0084] Example Ex2: A method comprising: monitoring cardiac electrical activity of the patient using a plurality of electrodes; determining an irregular cardiac rhythm or a regular cardiac rhythm based on the monitored cardiac electrical activity; delivering AV node stimulation using the neural electrode to regularize the patient’s heart rhythm and decrease the patient’s heart rate in response to determining the irregular cardiac rhythm; determining that the patient’s heart rhythm has not been regularized in response to the AV node stimulation based on the monitored cardiac electrical activity; and delivering left ventricular pacing therapy in response to determining that the patient’s heart rhythm has not been regularized in response to the AV node stimulation.

[0085] Example Ex3: The system as in Example Exl or method as in Example Ex2, wherein the left ventricular pacing therapy comprises one or more of left bunch branching pacing therapy and adaptative left ventricular pacing therapy, wherein the adaptative left ventricular pacing therapy comprises periodically adjusting atrioventricular delay based on the patient’s intrinsic atrioventricular delay.

[0086] Example Ex4: The system as in Example Exl or the method as in Example Ex2, wherein the computing apparatus is further configured to execute or the method further comprises: determining that the patient’s heart rate is less than or equal to a heartrate threshold in response to determination of the irregular cardiac rhythm; and delivering adaptive left ventricular pacing therapy in response to determining that the patient’s heart rate is less than or equal to the heart rate threshold, wherein the adaptative left ventricular pacing therapy comprises periodically adjusting atrioventricular delay based at least on the patient’s intrinsic atrioventricular delay.

[0087] Example Ex5: The system or method as in Example Ex4, wherein the computing apparatus is further configured to execute or the method further comprises delivering adaptative biventricular pacing therapy in response to determining that the patient’s heart rate is greater than the heart rate threshold, wherein the adaptative biventricular pacing therapy comprises periodically adjusting atrioventricular delay and interventricular delay based at least on the patient’s activity level and intrinsic atrioventricular delay.

[0088] Example Ex6: The system or method as in any one of Examples Ex4-Ex5, wherein the heart rate threshold is greater than or equal to 100 beats per minute (bpm).

[0089] Example Ex7: The system or method as in any one of Examples Exl-Ex6, wherein the computing apparatus is further configured to execute or the method further comprises adjusting the AV node stimulation to decrease heart rate while maintaining intrinsic atrioventricular activation and without exceeding an intrinsic atrioventricular delay threshold.

[0090] Example Ex8: The system or method as in Example Ex7, wherein the intrinsic atrioventricular delay threshold is 150 milliseconds.

[0091] Example Ex9: The system or method as in any one of Examples Exl-Ex8, wherein delivering left ventricular pacing therapy in response to determining that the patient’s heart rhythm has not been regularized in response to the AV node stimulation comprises: delivering left ventricular pacing based on right ventricle activation; and estimating right ventricle activation when intrinsic right ventricle activation is not sensed.

[0092] Example ExlO: The system or method as in any one of Examples Exl-Ex9, wherein the computing apparatus is further configured to execute or the method further comprises determining atrial fibrillation based on the monitored cardiac electrical activity, wherein determining an irregular cardiac rhythm or a regular cardiac rhythm based on the monitored cardiac electrical activity is in response to determining atrial fibrillation.

[0093] Example Exl 1 : The system or method as in any one of Examples Exl- ExlO, wherein determining the irregular cardiac rhythm based on the monitored cardiac electrical activity comprises ventricular tachyarrhythmia or fibrillation.

[0094] Example Exl2: The system as in any one of Examples Exl and Ex3-Exl 1, wherein the system further comprises a plurality of electrodes operably coupled to the sensing circuit and the therapy delivery circuit, wherein the plurality of electrodes comprises: a neural electrode implantable in right atrium of a patient’s heart to deliver therapy of one or both of the atrioventricular (AV) node or nerves innervating the AV node of the patient’s heart; a right ventricular electrode configured to deliver pacing therapy to the right ventricle of the patient’s heart; and a left ventricular electrode configured to deliver pacing therapy to the left ventricle of the patient’s heart.

[0095] Example Exl3: The system as in any one of Examples Exl and Ex3-Exl2, wherein system further comprises AV node pacing lead comprising: a lead body; and a fixation helix coupled to the lead body and extending from an insulated proximal end region to a distal end region, wherein the fixation helix comprises a neural electrode positioned at the distal end region of the fixation helix.

[0096] Example Exl4: The system as in Example Exl3, wherein the fixation helix defines a length of greater than or equal to 2 millimeters.

[0097] Example Exl5: The system or method as in any one of Examples Exl- Exl4, wherein the AV node stimulation is delivered to a vagal nerve branch from the right atrium between 5 millimeters and 30 millimeters from the coronary sinus ostium in the posterior septum.

[0098] Example Exl6: The system or method as in any one of Examples Exl- Exl5, wherein the AV node stimulation comprises 40 hertz to 60 hertz pulses delivered during refractory periods of one or both of the atria and ventricles.

[0099] Example Exl 7: A system comprising: a therapy delivery circuit to deliver therapy to the patient’s heart; a sensing circuit to sense electrical activity of the patient’s heart; and a computing apparatus comprising processing circuitry operably coupled to the therapy delivery circuit and the sensing circuit, the computing apparatus configured to: monitor cardiac electrical activity of the patient using a plurality of electrodes operably coupled to the therapy delivery circuit and the sensing circuit; determine an irregular cardiac rhythm or a regular cardiac rhythm based on the monitored cardiac electricalactivity; deliver AV node stimulation using the neural electrode to regularize the patient’s heart rhythm and decrease the patient’s heart rate in response to determining the irregular cardiac rhythm; determine that the patient’s heart rhythm has been regularized in response to the AV node stimulation based on the monitored cardiac electrical activity; and deliver adaptive left ventricular pacing therapy or adaptive biventricular pacing therapy in response to determining that the patient’s heart rhythm has been regularized in response to the AV node stimulation.

[0100] Example Exl8: A method comprising: monitoring cardiac electrical activity of the patient using a plurality of electrodes; determining an irregular cardiac rhythm or a regular cardiac rhythm based on the monitored cardiac electrical activity; delivering AV node stimulation using the neural electrode to regularize the patient’s heart rhythm and decrease the patient’s heart rate in response to determining the irregular cardiac rhythm; determining that the patient’s heart rhythm has been regularized in response to the AV node stimulation based on the monitored cardiac electrical activity; and delivering adaptive left ventricular pacing therapy or adaptive biventricular pacing therapy in response to determining that the patient’s heart rhythm has been regularized in response to the AV node stimulation.

[0101] Example Exl9: The system as in Example Exl7 or the method as in Example Exl8, wherein the computing apparatus is further configured to execute or the method further comprises determining that the patient’s heart rate is less than or equal to a heart rate threshold in response to determining the irregular cardiac rhythm, wherein adaptive left ventricular pacing therapy is delivered in response to determining that the patient’s heart rhythm has been regularized in response to the AV node stimulation and determining that the patient’s heart rate is less than or equal to the heart rate threshold.

[0102] Example Ex20: The system or method as in Example Exl9, wherein adaptive biventricular pacing therapy is delivered in response to determining that the patient’s heart rhythm has been regularized in response to the AV node stimulation and determining that the patient’s heart rate is greater than the heart rate threshold.

[0103] Example Ex21 : The system or method as in any one of Examples Exl9- Ex20, wherein the heart rate threshold is greater than or equal to 100 beats per minute (bpm).

[0104] Example Ex22: The system or method as in any one of Examples Exl7- Ex21, wherein the computing apparatus is further configured to execute or the method further comprises adjusting the AV node stimulation to decrease heart rate while maintaining intrinsic atrioventricular activation and without exceeding an intrinsic atrioventricular delay threshold.

[0105] Example Ex23 : The system or method as in Example Ex22, wherein the intrinsic atrioventricular delay threshold is 150 milliseconds.

[0106] Example Ex24: The system or method as in any one of Examples Exl7- Ex23, wherein the computing apparatus is further configured to execute or the method further comprises determining atrial fibrillation based on the monitored cardiac electrical activity, wherein determining an irregular cardiac rhythm or a regular cardiac rhythm based on the monitored cardiac electrical activity is in response to determining atrial fibrillation.

[0107] Example Ex25: The system or method as in any one of Examples Exl7- Ex24, wherein determining the irregular cardiac rhythm based on the monitored cardiac electrical activity comprises ventricular tachyarrhythmia or fibrillation.

[0108] Example Ex26: The system as in any one of Examples Exl7 and Exl9- Ex25, wherein the system further comprises a plurality of electrodes operably coupled to the sensing circuit and the therapy delivery circuit, wherein the plurality of electrodes comprises: a neural electrode implantable in right atrium of a patient’s heart to deliver therapy of one or both of the atrioventricular (AV) node or nerves innervating the AV node of the patient’s heart; a right ventricular electrode configured to deliver pacing therapy to the right ventricle of the patient’s heart; and a left ventricular electrode configured to deliver pacing therapy to the left ventricle of the patient’s heart.

[0109] Example Ex27: The system as in any one of Examples Exl7 and Exl9- Ex26, wherein system further comprises AV node pacing lead comprising: a lead body; and a fixation helix coupled to the lead body and extending from an insulated proximal end region to a distal end region, wherein the fixation helix comprises a neural electrode positioned at the distal end region of the fixation helix.

[0110] Example Ex28: The system as in Example Ex27, wherein the fixation helix defines a length of greater than or equal to 2 millimeters.

[0111] Example Ex29: The system or method as in any one of Examples Exl7- Ex28, wherein the AV node stimulation is delivered to a vagal nerve branch from the right atrium between 5 millimeters and 30 millimeters from the coronary sinus ostium in the posterior septum.

[0112] Example Ex30: The system or method as in any one of Examples Exl7- Ex29, wherein the AV node stimulation comprises 40 hertz to 60 hertz pulses delivered during refractory periods of one or both of the atria and ventricles.

[0113] This disclosure has been provided with reference to illustrative embodiments and examples and is not meant to be construed in a limiting sense. As described previously, one skilled in the art will recognize that other various illustrative applications may use the techniques as described herein to take advantage of the beneficial characteristics of the systems, devices, and methods described herein. Various modifications of the illustrative embodiments and examples will be apparent upon reference to this description.

[0114] In one or more examples, the described techniques may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored as one or more instructions or code on a computer-readable medium and executed by a hardware-based processing unit. Computer-readable media may include non-transitory computer-readable media, which corresponds to a tangible medium such as data storage media (e.g., RAM, ROM, EEPROM, flash memory, or any other medium that can be used to store desired program code in the form of instructions or data structures and that can be accessed by a computer).

[0115] Instructions may be executed by one or more processors, such as one or more digital signal processors (DSPs), general purpose microprocessors, application specific integrated circuits (ASICs), field programmable logic arrays (FPGAs), or other equivalent integrated or discrete logic circuitry. Accordingly, the term “processor” as used herein may refer to any of the foregoing structure or any other physical structure suitable for implementation of the described techniques. Also, the techniques could be fully implemented in one or more circuits or logic elements.

[0116] 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.

[0117] All scientific and technical terms used herein have meanings commonly used in the art unless otherwise specified. The definitions provided herein are to facilitate understanding of certain terms used frequently herein and are not meant to limit the scope of the present disclosure.

[0118] 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.

[0119] The recitation of numerical ranges by endpoints includes all numbers subsumed within that range (e.g., 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, and 5) and any range within that range. Herein, the terms “up to” or “no greater than” a number (e.g., up to 50) includes the number (e.g., 50), and the term “no less than” a number (e.g., no less than 5) includes the number (e.g., 5).

[0120] The terms “coupled” or “connected” refer to elements being attached to each other either directly (in direct contact with each other) or indirectly (having one or more elements between and attaching the two elements). Either term may be modified by “operatively” and “operably,” which may be used interchangeably, to describe that the coupling or connection is configured to allow the components to interact to carry out at least some functionality (for example, a mobile user device may be operatively coupled to a cellular network transmit data to or receive data therefrom).

[0121] 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.

[0122] As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” encompass embodiments having plural referents, unless the contentclearly dictates otherwise. As used in this specification and the appended claims, the term “or” is generally employed in its sense including “and / or” unless the content clearly dictates otherwise.

[0123] 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.

[0124] The term “and / or” means one or all of the listed elements or a combination of at least two of the listed elements.

[0125] The phrases “at least one of,” “comprises at least one of,” and “one or more of’ followed by a list refers to any one of the items in the list and any combination of two or more items in the list.

Claims

CLAIMSWhat is claimed:

1. A system comprising: a therapy delivery circuit to deliver therapy to a patient’s heart; a sensing circuit to sense electrical activity of the patient’s heart; and a computing apparatus comprising processing circuitry operably coupled to the therapy delivery circuit and the sensing circuit, the computing apparatus configured to: monitor cardiac electrical activity of the patient using a plurality of electrodes operably coupled to the therapy delivery circuit and the sensing circuit; determine an irregular cardiac rhythm or a regular cardiac rhythm based on the monitored cardiac electrical activity; deliver atrioventricular (AV) node stimulation using a neural electrode operably coupled to the therapy delivery circuit to regularize the patient’s heart rhythm and decrease the patient’s heart rate in response to determining the irregular cardiac rhythm; determine that the patient’s heart rhythm has not been regularized in response to the AV node stimulation based on the monitored cardiac electrical activity; and deliver left ventricular pacing therapy in response to determining that the patient’s heart rhythm has not been regularized in response to the AV node stimulation.

2. A method comprising: monitoring cardiac electrical activity of a patient using a plurality of electrodes; determining an irregular cardiac rhythm or a regular cardiac rhythm based on the monitored cardiac electrical activity; delivering atrioventricular (AV) node stimulation using a neural electrode to regularize the patient’s heart rhythm and decrease the patient’s heart rate in response to determining the irregular cardiac rhythm; determining that the patient’s heart rhythm has not been regularized in response to the AV node stimulation based on the monitored cardiac electrical activity; and delivering left ventricular pacing therapy in response to determining that the patient’s heart rhythm has not been regularized in response to the AV node stimulation.

3. The system as in claim 1 or method as in claim 2, wherein the left ventricular pacing therapy comprises one or more of left bunch branching pacing therapy and adaptative left ventricular pacing therapy, wherein the adaptative left ventricular pacing therapy comprises periodically adjusting atrioventricular delay based on the patient’s intrinsic atrioventricular delay.

4. The system as in claim 1 or the method as in claim 2, wherein the computing apparatus is further configured to execute or the method further comprises: determining that the patient’s heart rate is less than or equal to a heart rate threshold in response to determination of the irregular cardiac rhythm; and delivering adaptive left ventricular pacing therapy in response to determining that the patient’s heart rate is less than or equal to the heart rate threshold, wherein the adaptative left ventricular pacing therapy comprises periodically adjusting atrioventricular delay based at least on the patient’s intrinsic atrioventricular delay.

5. The system or method as in claim 4, wherein the computing apparatus is further configured to execute or the method further comprises delivering adaptative biventricular pacing therapy in response to determining that the patient’s heart rate is greater than the heart rate threshold, wherein the adaptative biventricular pacing therapy comprises periodically adjusting atrioventricular delay and interventricular delay based at least on the patient’s activity level and intrinsic atrioventricular delay.

6. The system or method as in any one of claims 4-5, wherein the heart rate threshold is greater than or equal to 100 beats per minute (bpm).

7. The system or method as in any one of claims 1-6, wherein the computing apparatus is further configured to execute or the method further comprises adjusting the AV node stimulation to decrease heart rate while maintaining intrinsic atrioventricular activation and without exceeding an intrinsic atrioventricular delay threshold.

8. The system or method as in claim 7, wherein the intrinsic atrioventricular delay threshold is 150 milliseconds.

9. The system or method as in any one of claims 1-8, wherein delivering left ventricular pacing therapy in response to determining that the patient’s heart rhythm has not been regularized in response to the AV node stimulation comprises: delivering left ventricular pacing based on right ventricle activation; and estimating right ventricle activation when intrinsic right ventricle activation is not sensed.

10. The system or method as in any one of claims 1-9, wherein the computing apparatus is further configured to execute or the method further comprises determining atrial fibrillation based on the monitored cardiac electrical activity, wherein determining an irregular cardiac rhythm or a regular cardiac rhythm based on the monitored cardiac electrical activity is in response to determining atrial fibrillation.

11. The system or method as in any one of claims 1-10, wherein determining the irregular cardiac rhythm based on the monitored cardiac electrical activity comprises determining ventricular tachyarrhythmia or fibrillation.

12. The system as in any one of claims 1 and 3-11, wherein the system further comprises a plurality of electrodes operably coupled to the sensing circuit and the therapy delivery circuit, wherein the plurality of electrodes comprises: a neural electrode implantable in right atrium of a patient’s heart to deliver therapy of one or both of the atrioventricular (AV) node or nerves innervating the AV node of the patient’s heart; a right ventricular electrode configured to deliver pacing therapy to the right ventricle of the patient’s heart; and a left ventricular electrode configured to deliver pacing therapy to the left ventricle of the patient’s heart.

13. The system as in any one of claims 1 and 3-12, wherein system further comprises AV node pacing lead comprising: a lead body; anda fixation helix coupled to the lead body and extending from an insulated proximal end region to a distal end region, wherein the fixation helix comprises a neural electrode positioned at the distal end region of the fixation helix, wherein the fixation helix defines a length of greater than or equal to 2 millimeters.

14. The system or method as in any one of claims 1-13, wherein the AV node stimulation is delivered to a vagal nerve branch from the right atrium between 5 millimeters and 30 millimeters from the coronary sinus ostium in the posterior septum.

15. The system or method as in any one of claims 1-14, wherein the AV node stimulation comprises 40 hertz to 60 hertz pulses delivered during refractory periods of one or both of the atria and ventricles.

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