Therapy optimization to improve device longevity

Abstract

A system includes a plurality of electrodes including one configured to sense cardiac electrical activity of a patient's heart and one configured to deliver defibrillation therapy to the patient's heart. The system includes a therapy delivery unit configured to detect a treatable cardiac event using a first detection criteria within a first detection period and initiate charging of one or more capacitors to deliver a defibrillation pulse based on the detection of the treatable cardiac event. The system includes a charge unit configured to estimate a charge time for the therapy delivery unit based on one or more battery parameters, determine the charge time exceeds a threshold value, and modify the therapy delivery unit to perform one or both of detecting a treatable cardiac event using a second detection criteria within a second detection period and initiating charging of the one or more capacitors during the first detection period.

Description

THERAPY OPTIMIZATION TO IMPROVE DEVICE LONGEVITY

[0001] This application claims the benefit of U.S. Provisional Patent Application Serial No. 63 / 712,028, filed October 25, 2024, the entire content of which is incorporated herein by reference.SUMMARY

[0002] According to various examples, the techniques described herein relate to a system including a plurality of electrodes including at least one electrode configured to sense cardiac electrical activity of a patient's heart and at least one electrode configured to deliver defibrillation therapy to the patient's heart. The system includes a therapy delivery unit configured to detect a treatable cardiac event using a first detection criteria within a first detection period and initiate charging of one or more capacitors to deliver a defibrillation pulse based on the detection of the treatable cardiac event. The system includes a charge unit configured to estimate a charge time for the therapy delivery unit based on one or more battery parameters, determine the charge time exceeds a threshold value, and modify the therapy delivery unit to perform one or both of detecting a treatable cardiac event using a second detection criteria within a second detection period and initiating charging of the one or more capacitors during the first detection period.

[0003] In some aspects, the techniques described herein relate to a method including: detecting a treatable cardiac event using a first detection criteria within a first detection period. The method includes charging one or more capacitors to deliver a defibrillation pulse based on the detection of the treatable cardiac event. The method further includes estimating a charge time for a therapy delivery unit based on one or more battery parameters, determining the charge time exceeds a threshold value, and modifying the therapy delivery unit to perform one or both of detecting a treatable cardiac event using a second detection criteria within a second detection period and initiating charging of the one or more capacitors during the first detection period.

[0004] In some aspects, the techniques described herein relate to a system including a plurality of electrodes including at least one electrode configured to sense cardiac electrical activity of a patient's heart and at least one electrode configured todeliver defibrillation therapy to the patient's heart. The system includes a therapy delivery unit configured to: detect a treatable cardiac event using a first detection criteria within a first detection period and initiate charging of one or more capacitors to deliver a defibrillation pulse based on the detection of the treatable cardiac event. The system includes a charge unit configured to estimate a time to therapy for the therapy delivery unit based on one or more battery parameters determine the time to therapy exceeds a threshold value, modify the therapy delivery unit to perform one or both of: detecting a treatable cardiac event using a second detection criteria within a second detection period and initiate charging of the one or more capacitors during the first detection period.

[0005] In some aspects, the techniques described herein relate to a method including: detecting a treatable cardiac event using a first detection criteria within a first detection period, initiating charging of one or more capacitors to deliver a defibrillation pulse based on the detection of the treatable cardiac event, estimating a time to therapy for a therapy delivery unit based on one or more battery parameters, determining the time to therapy exceeds a threshold value, and modifying the therapy delivery unit to perform one or both of: detecting a treatable cardiac event using a second detection criteria within a second detection period and initiating charging of the one or more capacitors during the first detection period.

[0006] 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

[0007] FIG. l is a schematic diagram of a heart of patient.

[0008] FIG. 2 is a conceptual diagram of an implantable medical device including a transvenous defibrillator in accordance with embodiments described herein.

[0009] FIGS. 3A and 3B are conceptual diagrams of an extra-cardiovascular ICD system according to various examples.

[0010] FIG. 4 is a functional block diagram illustrating an example of a configuration of an implantable medical device.

[0011] FIG. 5 is schematic block diagram of a pulse generator according to various examples.

[0012] FIGS. 6 A - 6C illustrate example timing diagrams for maintaining a time to therapy as a charge time increases in accordance with examples described herein..

[0013] FIG. 7 shows an illustrative method for maintaining a consistent time to therapy as battery charge time increases in accordance with examples described herein.DETAILED DESCRIPTION

[0014] In implantable cardioverter defibrillator (ICD) devices, as the battery capacity is used over time, the amount of time it takes to charge the capacitors to full energy for defibrillation is extended. In current devices, there are strict requirements on the charge time and this is often what limits the longevity of a device. In order to maintain effectiveness of defibrillation, it can be beneficial for the ICDs to deliver a defibrillation pulse to a patient within a set time period from the detected onset of a treatable event such as VT, also known as the time to therapy. An increase in time to therapy from the start of the episode may result in an increased risk of syncope or other complications. Historically this need translated into a goal within ICDs to set and maintain strict charge times. Once a device can no longer maintain the specified charge time, it may be signaled for replacement. At this replacement time there is still significant amount of battery capacity left.

[0015] Examples described herein maintain the time to therapy, as the battery capacity decreases beyond a level that may historically have signaled a need for device replacement. Examples described herein may extend the longevity of the device and allow more time between replacements for patients while still maintaining a comparable safety profile. This could significantly prolong the time to replacement by an estimated of 0.5 years to 1.5 years, for example. In some configurations, using the methods and devices described herein could drive a smaller battery or capacitor technology leading to a smaller device.

[0016] 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.

[0017] Illustrative systems, devices, and methods shall be described with reference to FIGS. 1-7. It will be apparent to one skilled in the art that elements or processes from one embodiment may be used in combination with elements or processes of the other embodiments, and that the possible embodiments of such systems, devices, and methods using combinations of features set forth herein is not limited to the specific embodiments shown in the Figures and / or described herein. Further, it will be recognized that the embodiments described herein may include many elements that are not necessarily shown to scale. Still further, it will be recognized that timing of the processes and the size and shape of various elements herein may be modified but still fall within the scope of the present disclosure, although certain timings, one or more shapes and / or sizes, or types of elements, may be advantageous over others.

[0018] FIG. 1 depicts a schematic diagram of a heart 12 and FIGS. 2-3B depict conceptual diagrams showing illustrative therapy systems that may be used to provide defibrillation therapy to the heart 12 of a patient. The patient ordinarily, but not necessarily, will be a human. As shown in FIGS. 2, the therapy system 11 may include an implantable medical device (IMD) 16 (e.g., a transvenous ICD, which is coupled to one or more leads 18, 20, 23, and a user interface device 24. The IMD 16 may provide electrical defibrillation pulses to the heart 12 via electrodes coupled to one or more of the leads 18, 20, 23. Further non-limiting examples of the IMD 16 be a pacemaker with a medical lead (e.g., CRT-D), an intracardiac device, and a non-vascular device such as a subcutaneous ICD (S-ICD) or substernal ICD.

[0019] The leads 18, 20, 23 may extend into the heart 12 of the patient to sense electrical activity of the heart 12 and / or deliver electrical stimulation to the heart 12. In the example shown in FIG. 2, 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 intothe 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.

[0020] One or more elongated conductors of any of the leads 18, 20, 23 may extend 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., coil electrode, 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.

[0021] 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 coupled to at least one of leads 18, 20, 23. The IMD 16 may provide defibrillation therapy and / or cardioversion therapy via electrodes located on at least one of the leads 18, 20, 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.

[0022] In some examples, the user interface device 24 diagrammatically shown in FIG. 2 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 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.

[0023] Additionally, various device settings may be adjusted, or configured, based on various sensed signals. For example, various near-field and far-field signals may be sensed by one or more of the electrodes of the IMD 16 and / or other devices operatively coupled thereto.

[0024] 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 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.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] The system 11 of FIG. 2 may be used for defibrillation. According to some examples, the system may provide one or both of cardiac rhythm therapy and cardioversion therapy (CRT-D). The leads 18, 20, 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, 23 may include electrical contacts that electrically couple to respective electrical contacts within the connectorblock 34. In addition, in some examples, the leads 18, 20, 23 may be mechanically coupled to the connector block 34 with the aid of set screws, connection pins, or another suitable mechanical coupling mechanism.

[0029] Each of the leads 18, 20, 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).

[0030] 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, may be electrically coupled to a respective one of the coiled conductors within the lead body of its associated lead 18, 20, 23, and thereby coupled to respective ones of the electrical contacts on the proximal end of the leads 18, 20, 23.

[0031] The electrodes 40, 42, 44, 46, 48, 50, 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, 23.. 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 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.

[0032] The leads 18, 20, 23 may also include elongated electrodes 62, 64, 66, respectively, which may take the form of a coil.. The IMD 16 may deliver defibrillationshocks 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.

[0033] The configuration of the therapy system 11, illustrated in FIGS. 2 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, 23, 25 illustrated in FIG. 2 or other configurations shown or described herein or incorporated by reference. Further, the IMD 16 may not be implanted within patient. For example, the IMD 16 may be an external device such as an external defibrillator. As such, it is to be understood that the illustrative therapy system 11 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.

[0034] FIGS. 3A and 3B are conceptual diagrams of an extra-cardiovascular ICD system 310 according to one example. FIG. 3 A is a front view of ICD system 310 implanted within patient 312. FIG. 3B is a side view of ICD system 310 implanted within patient 312. ICD system 310 includes an ICD 314 connected to an extra-cardiovascular electrical stimulation and sensing lead 316. FIGS. 1A and IB are described in the context of an ICD system 310 capable of providing defibrillation and / or cardioversion shocks and pacing pulses.

[0035] ICD 314 includes a housing 315 that forms a hermetic seal that protects internal components of ICD 314. The housing 315 of ICD 314 may be formed of a conductive material, such as titanium or titanium alloy. The housing 315 may function as a housing electrode (sometimes referred to as a can electrode). In examples described herein, housing 315 may be used as an active can electrode for use in delivering cardioversion / defibrillation (CV / DF) shocks or other high voltage pulses delivered using a high voltage therapy circuit. In other examples, housing 315 may be available for use in delivering unipolar, low voltage cardiac pacing pulses in conjunction with lead-based cathode electrodes. In other instances,the housing 315 of ICD 314 may include a plurality of electrodes on an outer portion of the housing. The outer portion(s) of the housing 315 functioning as an electrode(s) may be coated with a material, such as titanium nitride.

[0036] ICD 314 includes a connector assembly 317 (also referred to as a connector block or header) that includes electrical feedthroughs crossinghousing 315 to provide electrical connections between conductors extending within the lead body 318 of lead 316 and electronic components included within the housing 315 of ICD 314. As will be described in further detail herein, housing 315 may house one or more processors, memories, transceivers, sensors, electrical cardiac signal sensing circuitry, therapy delivery circuitry, power sources and other components for sensing cardiac electrical signals, detecting a heart rhythm, and controlling and delivering electrical stimulation pulses to treat an abnormal heart rhythm.

[0037] Lead 316 includes an elongated lead body 318 having a proximal end 327 that includes a lead connector (not shown) configured to be connected to ICD connector assembly 317 and a distal portion 325 that includes one or more electrodes. In the example illustrated in FIGS. 3A and 3B, the distal portion 325 of lead 316 includes defibrillation electrodes 324 and 326 and pace / sense electrodes 328, 330 and 331. In some cases, defibrillation electrodes 324 and 326 may together form a defibrillation electrode in that they may be configured to be activated concurrently. In some examples, defibrillation electrodes 324 and 326 may form separate defibrillation electrodes in which case each of the electrodes 324 and 326 may be activated independently. In some instances, defibrillation electrodes 324 and 326 are coupled to electrically isolated conductors, and ICD 314 may include switching mechanisms to allow electrodes 324 and 326 to be utilized as a single defibrillation electrode (e.g., activated concurrently to form a common cathode or anode) or as separate defibrillation electrodes, (e.g., activated individually, one as a cathode and one as an anode or activated one at a time, one as an anode or cathode and the other remaining inactive with housing 315 as an active electrode).

[0038] Electrodes 324 and 326 (and in some examples housing 315) are referred to herein as defibrillation electrodes because they are utilized, individually or collectively, for delivering high voltage stimulation therapy (e.g., cardioversion or defibrillation shocks). Electrodes 324 and 326 may be elongated coil electrodes andgenerally have a relatively high surface area for delivering high voltage electrical stimulation pulses compared to low voltage pacing and sensing electrodes 328, 330 and 331. However, electrodes 324 and 326 and housing 315 may also be utilized to provide pacing functionality, sensing functionality or both pacing and sensing functionality in addition to or instead of high voltage stimulation therapy. In this sense, the use of the term “defibrillation electrode” herein should not be considered as limitingthe electrodes 324 and 326 for use in only high voltage cardioversion / defibrillation shock therapy applications. Electrodes 324 and 326 may be used in a pacing electrode vector for delivering extra-cardiovascular pacing pulses such as anti-tachycardia pacing (ATP) pulses or bradycardia pacing pulses and / or in a sensing vector used to sense cardiac electrical signals and detect ventricular tachycardia (VT) and ventricular fibrillation (VF).

[0039] Electrodes 328, 330 and 331 are relatively smaller surface area electrodes for delivering low voltage pacing pulses and for sensing cardiac electrical signals. Electrodes 328, 330 and 331 are referred to as pace / sense electrodes because they are generally configured for use in low voltage applications, e.g., used as either a cathode or anode for delivery of pacing pulses and / or sensing of cardiac electrical signals. In some instances, electrodes 328, 330 and 331 may provide only pacing functionality, only sensing functionality, or both.

[0040] In the example illustrated in FIGS. 3A and 3B, electrode 328 is located proximal to defibrillation electrode 324, and electrode 330 is located between defibrillation electrodes 324 and 326. A third pace / sense electrode 331 may be located distal to defibrillation electrode 326. Electrodes 328 and 330 are illustrated as ring electrodes, and electrode 331 is illustrated as a hemispherical tip electrode in the example of FIGS. 1A and IB. However, electrodes 328, 330 and 331 may comprise any of a number of different types of electrodes, including ring electrodes, short coil electrodes, hemispherical electrodes, directional electrodes, segmented electrodes, or the like, and may be positioned at any position along the distal portion 325 of lead 316. Further, electrodes 328, 330 and 331 may be of similar type, shape, size, and material or may differ from each other.

[0041] Illustrated lead 316 extends subcutaneously or submuscularly over the ribcage 332 medially from the connector assembly 327 of ICD 314 toward a center ofthe torso of patient 312, e.g., toward xiphoid process 320 of patient 312. At a location near xiphoid process 320, lead 316 bends or turns and extends superior subcutaneously or submuscularly over the ribcage and / or sternum, substantially parallel to sternum 322. Although illustrated in FIGS. 3A and 3B as being offset laterally from and extending substantially parallel to sternum 322, lead 316 may be implanted at other locations, such as over sternum 322, offset to the right or left of sternum 322, angled laterally from sternum 322 toward the left or the right, or the like. Alternatively, lead 316 may be placed along other subcutaneous or submuscular paths, including but not limited to substernal placement, placement under the ribcage, epicardial placement, and the like. The path of lead 316 may depend on the location of ICD 314, the arrangement and position of electrodes carried by the lead distal portion 325, and / or other factors.

[0042] Electrical conductors (not illustrated) extend through one or more lumens of the elongated lead body 318 of lead 316 from the lead connector at the proximal lead end 327 to electrodes 324, 326, 328, 330 and 331 located along the distal portion 325 of the lead body 318. Lead body 318 may be tubular or cylindrical in shape. In other examples, the distal portion 325 (or all of) the elongated lead body 318 may have a flat, ribbon or paddle shape. The lead body 318 of lead 316 may be formed from a non-conductive material, including silicone, polyurethane, fluoropolymers, mixtures thereof, and other appropriate materials, and shaped to form one or more lumens within which the one or more conductors extend. However, the techniques disclosed herein are not limited to such constructions or to any particular lead body design.

[0043] The elongated electrical conductors contained within the lead body 318 are each electrically coupled with respective defibrillation electrodes 324 and 326 and pace / sense electrodes 328, 330 and 331. Each of pacing and sensing electrodes 328, 330 and 331 are coupled to respective electrical conductors, which may be separate respective conductors within the lead body. The respective conductors electrically couple the electrodes 324,326, 328, 330 and 331 to circuitry, such as a therapy circuit and / or a sensing circuit, of ICD 314 via connections in the connector assembly 317, including associated electrical feedthroughs crossing housing 315. The electrical conductors transmit therapy from a therapy circuit within ICD 314 to one or more of defibrillation electrodes 324 and 326 and / or pace / sense electrodes 328, 330and 331 and transmit sensed electrical signals from one or more of defibrillation electrodes 324 and 326 and / or pace / sense electrodes 328, 330 and 331 to the sensing circuit within ICD 314.

[0044] ICD 314 may obtain electrical signals corresponding to electrical activity of heart 308 via a combination of sensing vectors that include combinations of electrodes 328, 330, and / or 331. In some examples, housing 315 of ICD 314 is used in combination with one or more of electrodes 328, 330 and / or 331 in a sensing electrode vector. ICD 314 may even obtain cardiac electrical signals using a sensing vector that includes one or both defibrillation electrodes 324 and / or 326, e.g., between electrodes 324 and 326 or one of electrodes 324 or326 in combination with one or more of electrodes 328, 330, 331, and / or the housing 315.

[0045] ICD 314 analyzes the cardiac electrical signals received from one or more of the sensing vectors to monitor for abnormal rhythms, such as bradycardia, ventricular tachycardia (VT) or ventricular fibrillation (VF). ICD 314 may analyze the heart rate and / or morphology of the cardiac electrical signals to monitor for tachyarrhythmia in accordance with any of a number of tachyarrhythmia detection techniques.

[0046] ICD 314 generates and delivers electrical stimulation therapy in response to detecting a tachyarrhythmia (e.g., VT or VF). ICD 314 may deliver ATP in response to VT detection, and in some cases may deliver ATP prior to a CV / DF shock or during high voltage capacitor charging in an attempt to avert the need for delivering a CV / DF shock. ATP may be delivered using an extra-cardiovascular pacing electrode vector selected from any of electrodes 324, 326, 328, 330, 331 and / or housing 315. The pacing electrode vector may be different than the sensing electrode vector. In one example, cardiac electrical signals are sensed between pace / sense electrodes 328 and 330, and ATP pulses (or other cardiac pacing pulses) are delivered between pace / sense electrode330 used as a cathode electrode and defibrillation electrode 324 used as a return anode electrode. In other examples, cardiac pacing pulses may be delivered between pace / sense electrode 328 and either (or both) defibrillation electrode 324 or 326 or between defibrillation electrode 324 and defibrillation electrode 326. These examples are not intended to be limiting, and it is recognized that other sensingelectrode vectors and cardiac pacing electrode vectors may be selected according to individual patient need.

[0047] If ATP does not successfully terminate VT or when VF is detected, ICD 314 may deliver one or more cardioversion or defibrillation (CV / DF) shocks via one or both of defibrillation electrodes 324 and 326 and / or housing 315. ICD 314 may deliver the CV / DF shocks using electrodes 324 and 326 individually or together as a cathode (or anode) and with the housing 315 as an anode (or cathode). ICD 314 may generate and deliver other types of electrical stimulation pulses such as post-shock pacing pulses or bradycardia pacing pulses using a pacing electrode vector that includes one or more of the electrodes 324, 326, 328, 330 and 331 and the housing 315 of ICD 314.

[0048] FIGS. 3 A and 3B are illustrative in nature and should not be considered limiting of the practice of the techniques disclosed herein. In other examples, lead 316 may include less than three pace / sense electrodes or more than three pace / sense electrodes and / or a single defibrillation electrode or more than two electrically isolated or electrically coupled defibrillation electrodes or electrode segments. The pace / sense electrodes 328, 330 and / or 331 may be located elsewhere along the length of lead 316. For example, lead 316 may include a single pace / senseelectrode 30 between defibrillation electrodes 324 and 326 and no pace / sense electrode distal to defibrillation electrode 326 or proximal defibrillation electrode 324.

[0049] It is to be understood that the above systems are merely illustrations and one will understand that the below operational concepts can be implemented in other IMDs with different configurations.

[0050] FIG. 4 is a functional block diagram of an illustrative configuration of any IMD (e.g., ICD) described. As shown, the IMD 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, such as the control module 81, may be contained within a housing of the IMD (e.g., within a housing of an ICD). The control module, or apparatus, 81 may include a processing circuitry, or computing apparatus, 80, memory 82, and a telemetry module, or apparatus, 88. The memory 82 may include computer-readable instructions that, when executed, e.g., by the processing circuitry 80, cause the IMD and / or the control module 81 to perform various functions attributed to the IMD and / or the control module 81described 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.

[0051] 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 defibrillation therapy, 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.

[0052] The control module 81 may control the therapy delivery module, or apparatus, 84 to deliver therapy (e.g., electrical stimulation therapy 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) may control various parameters of the electrical stimulus delivered by the therapy delivery module 84 such as, e.g., AVdelays, 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, high voltage detection and therapy parameters, etc.). The therapy delivery module 84 is electrically coupled to electrodes 29, 40, 42, 44, 45, 46, 47, 48, 50, , 58, 62, 64, 66, 324, 326, 328, 330, 331, 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 or defibrillation therapy to the heart 12 using one or more of the electrodes 29, 40, 42, 44, 45, 46, 47, 48, 50, 58, 62, 64, 66, 324, 326, 328, 330, 331.

[0053] For example, the therapy delivery module 84 may deliver defibrillation shocks to the heart 12 via at least two of electrodes 58, 62, 64, 66, 324, 326. 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.

[0054] Therapy delivery module 84 includes a charging circuit 144 including one or more charge storage devices such as one or more holding capacitors, an output circuit 146, and switching circuitry 145. Switching circuitry 145 is controlled by control signals from control module 81 to control when the holding capacitor(s) of charging circuit 144 are charged and when the charged holding capacitor(s) are discharged through the output circuit 146 to deliver a therapeutic pulse via selected electrode vector(s) for providing therapy to the desired sites.

[0055] Output circuit 146 may include switching circuitry for selecting the electrode vector(s) and associated electrode polarities coupled to a holding capacitor of charging circuit 144 via switch 145. Charging of a holding capacitor to a programmed voltage amplitude and discharging of the capacitor for a programmed pulse width maybe performed by therapy delivery circuit 84 according to control signals received from control module 81.

[0056] The IMD 16 may further include a switch module, or apparatus, 85 and the control module 81 (e.g., the processing circuitry 80) may use the switch module 85 to select, e.g., via a data / address bus, which of the available electrodes are used to deliver therapy such as pacing pulses for pacing therapy, or which of the available electrodes are used for sensing. The switch module 85 may include a switch array, switch matrix, multiplexer, or any other type of switching device suitable to selectively couple the sensing module, or apparatus, 86 and / or the therapy delivery module 84 to one or more selected electrodes. More specifically, the therapy delivery module 84 may include one or more defibrillation output and / or pacing circuits 146. Each output circuit of the one or more defibrillation output circuits 146 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, 58, 62, 64, 66, 324, 326, 328, 330, 331 (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 defibrillation output circuits of the therapy delivery module using the switch module 85.

[0057] 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, 58, 62, 64, 66, 328, 330, 331 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, VT or VF. The ECGZEGM signals may be used to determine whether 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 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-Vintervals), 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.

[0058] 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, 58, 62, 64, 66, 328, 330, 331). Likewise, the switch module 85 may also be used with the sensing module 86 to select which of the available electrodes are not to be used (e.g., disabled) to, e.g., sense electrical activity of the patient's heart (e.g., one or more electrical vectors of the patient's heart using any combination of the electrodes 29, 40, 42, 44, 45, 46, 47, 48, 50, 58, 62, 64, 66, 328, 330, 331), 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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 charged from an external device, e.g., on a daily or weekly basis. The rechargeable battery may be charged in any suitable manner. For example, the rechargeable battery may be using an inductive process, using an energy harvester, and / or by using an optical recharge process. Power source 90 may be coupled to one or more charging circuits 144 included in therapy delivery module 84 for providing the power to charge holding capacitors included in therapy delivery circuit 84 that are discharged at appropriate times under the control of control module 81 for delivering therapeutic pulses such as defibrillation pulses. Power source 90 is also coupled to components of sensing module 86, such as sense amplifiers, analog-to-digital converters, switching circuitry, etc., telemetry module 88, activity sensor and memory 82 to provide power to the various components and circuits.

[0063] FIG. 5 illustrates an example in which the therapy delivery module 84 is a pulse generator configured to deliver defibrillation pulses. In general, the power source 90 may be a voltage source. The power source 90 may be configured to provide energy at a voltage of at least 0.25 volts to no greater than 2000 volts. Accordingly, the current provided by the power source 90 to the pulse generator 108 may vary based on a state of charge of the pulse generator. The power source 90 may include any suitable energy storage and / or power delivery apparatus. The power source 90 may include oneor more, for example, batteries, electrochemical cells, fuel cells, super capacitors, switches, controllers, battery management systems, or other energy storage and / or power delivery apparatus.

[0064] The pulse generator 108 may be configured to receive energy from the power source 90 within a nominal voltage range of the power source 90. The pulse generator 108 may be operatively coupled to or operatively couplable to the power source 90 via an input 112. The input 112 may include a switch to allow control of the receipt of energy from the power source 90. Alternatively, the input 112 may be operatively coupled to an external switch. The external switch may be part of the pulse generator 108 generally or included in the power source 90. The switch, whether internal or external to the pulse generator, may include any suitable device or devices. The switch may include, for example, one or more transistors, electromechanical switches, toggles, etc. The pulse generator 108 may include one or more capacitors 116.

[0065] The pulse generator 108 may include an output 118 operatively coupled to the one or more capacitors to deliver a therapeutic electrical pulse using energy stored in the one or more capacitors. The output 118 may include a switch to allow control delivery of the therapeutic electrical pulse from the one or more capacitors 116. The switch may include any suitable device or devices to control the delivery of the therapeutic electrical pulse. The switch may include, for example, one or more transistors, electromechanical switches, toggles, etc.

[0066] The pulse generator 108 may also include a step-up converter 114. The step-up converter 114 may be configured to increase the voltage of energy received from the power source 90. According to various examples, the output voltage of the power source 90 may be lower than a desired voltage for delivery of a therapeutic electrical pulse. In such embodiments, the step-up converter 114 may boost the voltage provided by the power source 90. In one or more embodiments, the step-up converter 114 may be adjustable to allow the pulse generator 108 to deliver therapeutic electrical pulses at various voltages. For example, the step-up converter 114 may be configured to adjust an output voltage based on commands or signals received from the processor 80. The step-up converter 114 may include any suitable device or devices to boost or increase the voltage provided by the power source 90. The step-up converter 114 mayinclude one or more of, for example, a direct current (DC)-DC converter, switches, transistors, transformers, inductors, etc.

[0067] Energy transfer from the power source 90 to the pulse generator 108 may be controlled by the processor 80. The processor 80 may be operatively coupled to the power source 90 and / or the pulse generator 108. The processor 80 may be configured to charge one or more capacitors 116 of the pulse generator 108 using the power source 90 and cause the pulse generator 108 to deliver a therapeutic electrical pulse using the charged one or more capacitors 116. Examples of types of capacitors used include tantalum electrolytic capacitors, aluminum electrolytic capacitors, ceramic capacitors, diamond capacitors, and other super capacitors. To charge the one or more capacitors 116, the processor 80 may be configured to close a switch associated with the input 112 and / or the power source 90 to allow current to flow from the power source 90 to the pulse generator 108. To deliver the therapeutic electrical pulse, the processor 80 may be configured to close a switch associated with the output 118 of the pulse generator 108. Additionally, the processor 80 may be configured to open the switch of the input 112 or the power source 90 before closing the switch of the output 118. When the switch of the output 118 is closed, energy stored in the capacitors 116 may flow through the output to one or more leads / electrodes and ultimately to therapy delivery sites of the patient.

[0068] The processor 80 may include any suitable analogue or digital circuitry to charge the one or more capacitors 116 and deliver therapeutic electrical pulses. The controller may include, for example, one or more processors, logic gates, operational amplifiers, transistors, analogue-to-digital converters, sensors, or other circuitry or devices to control the power source 90 and / or the pulse generator 108. The processor 80 may include data storage for data storage and access to processing programs or routines that may be employed to conduct the techniques, processes, and algorithms for charging the one or more capacitors 116 and delivering a therapeutic electrical pulse. For example, processing programs or routines may include programs or routines for pulse delivery timing, pulse delivery triggers, opening and closing switches, determining an output voltage, adjusting an output voltage, filtering background noise, computational mathematics, matrix mathematics, Fourier transforms, compression algorithms, calibration algorithms, inversion algorithms, signal processing algorithms,normalizing algorithms, deconvolution algorithms, averaging algorithms, standardization algorithms, comparison algorithms, vector mathematics, or any other processing required to implement one or more embodiments as described herein.

[0069] In examples described herein, a consistent time to therapy is maintained, independent of the charge times. Therefore, as the charge time gets longer, the event detection criteria, such as the number of intervals to detect (NID), is modified to account for the increased charge time. The NID may be defined as a number of abnormal (e.g., fast) beats out of a predefined number of beats.

[0070] The “time to therapy” may be defined as the time between the detected onset of a treatable event (e.g., VT, VF, or AF) until the delivery of a defibrillation pulse. The time to therapy is conventionally broken into two back-to-back segments, the “time to detection” which is the duration from the detected onset of a treatable event until the device has determined the that the event is treatable, and the “time to charge” which is the time needed for the IMD to charge the capacitors to deliver the defibrillation pulse, which typically is initiated after detection. IMD’s may also include a confirmation period that runs in parallel with the time to charge and / or following detection. The “time to detection” may include the time for the device to perform event detection criteria. This may include one or more of NID, set duration; VT, morphology mapping, algorithms to reject rhythms that are not VT or VF, Artificial Intelligence (Al) algorithms, a fast beat counter, and a noise counter, for example.

[0071] While some examples herein describe the event detection criteria as NID, it is to be understood that the devices and methods herein may use any of the event detection criteria. For example, the system may use a fast beat counter to count a number of fast beats. If the system determines that the number of fast beats goes beyond a predefined fast beat threshold, the system may initiate further action. For example, the system may initiate defibrillation therapy based on the number of fast beats being beyond the fast beat threshold. A noise counter may be used separately or in conjunction with the fast beat counter. For example, the system may use a noise counter to determine a number of beats that are within a predefined noise threshold. The system may only consider fast beats that are within the predefined noise threshold to count towards the fast beat threshold.

[0072] The system uses information from the battery voltage, battery technology, and capacitor technology to estimate the charge time as well as event detection criteria and the current rate to estimate the time to detection. These combine to calculate the time to therapy. As charge time gets longer, the event detection criteria may change to maintain the time to therapy. For example, the number of intervals to detect can be shortened to maintain the time to therapy.

[0073] In some examples, if the system determines that the charge time is beyond a predefined threshold the system may change the event detection criteria to maintain the time to therapy. For example, the number of intervals to detect may be shortened one time based on one charge time threshold or may be shortened multiple times as the time to charge increases beyond one or more additional predefined thresholds. According to various examples, a first detection time may be estimated. The first detection time may be based on one or both of a history for a particular patient or a population of patients, and programmable parameters. The programmable parameters may be adjusted to shorten the detection time.

[0074] FIGS. 6 A - 6C illustrate example timing diagrams in accordance with examples described herein. The concept will not bring about more frequent therapy. The system will start charging sooner within an episode when the charge times are longer towards end of battery life, but the detection algorithms and rejection rules still have just as much time to classify the rhythm. The system leverages confirmation during charging to accomplish this. While FIGS. 6A-6C generally describe determining whether a number of events occurs within a number of thresholds, it is to be understood that other types of metrics may be used to detect cardiac events as long as the initial detection time is reduced as described above.

[0075] The timing diagram shown in FIG. 6A shows a first example for a system having a detection time, Dtl. In this example, the charge time is less than or equal to the charge threshold. During the detection time, the system determines whether an initial event detection criteria, such as predefined threshold number of events, Nl, occurs within a predefined threshold number of intervals, Ml. Dtl may be in a range of 2 seconds to 80 seconds or in a range of 6 seconds to 10 seconds. In some examples, Dtl is 8 seconds. The intervals may include one or both of a time period and a number of beats. The events detected by the system may be irregular beats, forexample. If the system determines that a detected number of events N1 is greater than or equal to a threshold value within the predefined number of intervals, Ml, processing circuitry of the device may initiate charging of one or more capacitors to deliver a defibrillation pulse. Charging is anticipated to be completed within charge time, Chtl, which represents the anticipated charge time for the device based on the anticipated parameters for a new device. Chtl may be estimated in a range of 4 seconds to 12 seconds or in a range of 6 seconds to 10 seconds. In some examples, Chtl is estimated to be 8 seconds.

[0076] While the device is charging, the processor 80 may initiate a confirmation step that confirms an adverse cardiac event such as ventricular fibrillation, for example, for a confirmation time Ctl. Ctl may in a range of 2 seconds to 40 seconds or in a range of 6 seconds to 8 seconds. In some examples, Ctl is 7 seconds. If the processing circuitry confirms in the confirmation step the adverse cardiac event, the processing circuitry initiates delivery of therapy once the device is charged. According to various examples, N1 may be in a range of 12 to 100 irregular beats in consecutive intervals. In some examples, N1 is 30 irregular beats. Ml may be in a range of 12 to 100 beats. In some examples, Ml is 40 beats.

[0077] It may be difficult to maintain a consistent time to therapy as a battery ages and the charge time increases. According to various examples described herein, event detection criteria such as NID may be modified such that a consistent time to therapy is maintained as charge time increases above a charge time threshold. FIGS. 6B and 6C illustrate examples of timing diagrams that for a system that utilizes modified event detection criteria while maintaining a consistent time to therapy. These modified event detection criteria may enable a longer device life.

[0078] FIG. 6B illustrates another example of a timing diagram in accordance with examples described herein. In this example, the charge time, Cht2 is greater than a threshold. In response Cht2 being greater than the threshold, the system modifies the detection time, Dt2 to be shorter than Dtl. That is, Dt2 may be less discriminatory and the system may initiate charging at an earlier time or an earlier phase in the detection process than when compared to the example in FIG. 6A. Dt2 may be in a range of 2 seconds to 80 seconds or in a range of 3 seconds to 5 seconds. In some examples, Dt2 is 4.8 seconds. The number of threshold detection events, N2, and the number ofthreshold intervals to detect, M2, are both shorter than the respective thresholds, N1 and Ml, in FIG. 6A.

[0079] If the system determines that a detected number of events is greater than or equal to N2 within the predefined number of intervals, M2, the system initiates a charge and the device charges for a charge time, Cht2. Cht2 is in a range of 3 seconds to 32 seconds. In some examples, Cht2 is 12 seconds. It is to be understood that Cht2 may vary based on the capacitor technology and associated energy used (e.g., 10, 20, 25, 40, and / or 45 joules). While the device is charging, the system uses a confirmation step to confirm an adverse cardiac event for a confirmation time Ct2. The confirmation step in FIG. 6B may be longer or more rigorous when compared to the confirmation step in FIG. 6A. This longer confirmation time may be used to account for the shorter or less rigorous detection phase. In this example, Ct2 is greater than Ctl to compensate for the shorter detection time Dt2 when compared with Dtl . Ct2 may in a range of 2 seconds to 40 seconds or in a range of 7 seconds to 13 seconds. In some examples, Ct2 is estimated to be 10 seconds. If the system determines in the confirmation step that the adverse cardiac event is confirmed, the system delivers therapy once the device is charged. In the event that the system does not confirm the adverse cardiac event, the system may stop charging and therapy is not delivered. According to various examples, N2 may be in a range of 12 to 120 irregular beats. In some examples, N2 is 18 irregular beats. M2 may be in a range of 12 to 100 beats. In some examples, M2 is 24 beats.

[0080] According to various examples, the system initiates a charge during the detection phase as shown in FIG. 6C. That is, the system initiates at least a partial charge before the detection time, Dt3, has completed. The system may initiate the partial charge early to compensate for the longer charge time when compared to FIG.6A to maintain a consistent time to therapy. In this example, the system determines in the detection phase whether at least N3 out of M3 beats are irregular. The system may initiate the charge partially through the detection phase. In some examples, the system may initiate the charge halfway through the detection phase such that the charge is initiated at Dt3 / 2. For example, if at least N3 / 2 beats out of M3 / 2 beats are irregular, the system may initiate the charge. If at the completion of the detection phase the system determines that at least N3 out of M3 beats are not irregular, the system may stop the charge and continue to monitor cardiac activity. If at the completion of thedetection phase the system determines that at least N3 out of M3 beats are irregular, the system allows the charge to continue. In this example, N3 may be equal to Nl, M3 may be equal to Ml and the detection time, Dt3, may be equal to Dtl. The longer charge time is compensated for by the charge being initiated at an earlier time. Similarly, the confirmation time, Ct3 may be equal to Ctl because system initiates the charge time during the detection phase. In each of the scenarios detailed in FIGS.6A - 6C, the time to therapy is the same.

[0081] FIG. 7 shows an illustrative method for maintaining a consistent time to therapy utilizing the timing diagrams of 6A -6C as system charge time increases in accordance with examples described herein. The modified charge feature may be enabled 610 or disabled. If the feature is disabled, the system will not change a charge procedure based on charge times of the battery. If the modified charge feature is enabled, the system may change the charge procedure based on an estimated charge time of the battery. The charge procedure may not change until an estimated charge time goes beyond one or more predefined charge time thresholds. The one or more predefined time to charge thresholds may be set at manufacturing. In some examples, a user, for example a physician, may be able to set or change the one or more predefined time to charge thresholds. In some examples, the modified charge feature may be automatically disabled based on one or more triggers. For example, the process may be disabled if there is a recent history of multiple defibrillation events. A user may be able to manually disable the feature.

[0082] If the feature is enabled, one or more battery capacity metrics are measured 615. For example, a battery voltage may be measured. The one or more battery capacity metrics may be measured periodically. For example, the one or more battery capacity metrics may be measured once a week, once a day, or once an hour. In some examples, the one or more battery capacity metrics may be measured after a defibrillation event and / or after an internal test charge. The time interval and / or any trigger conditions for measuring the one or more battery capacity metrics may be set by a user.

[0083] A charge time for the battery may be estimated 620 based on the one or more battery capacity metrics including, but not limited to, battery voltage, battery impedance, type of capacitor technology used, battery chemistry, charge circuit, and aprevious charge time. In some examples, the system may determine whether at least one of the one or more battery metrics and / or a value based on a combination of at least two of the one or more battery metric go beyond a predefined battery metric threshold, the charge time of the battery may be determine and a number of intervals to detect may be changed automatically to maintain a time to therapy. In some examples, once the at least one of the one or more battery metrics go beyond a predefined battery metric threshold an alert is issued to a user. For example, the battery resistance changes with depth of discharge of a battery. The depth of discharge of the battery is in turn proportional to the time it will take to charge a capacitor. Measurements of battery resistance versus depth of discharge for a particular battery chemistry can be taken and used to build a model, equation or look up chart stored in the device that convert the measured battery resistance to depth of discharge. Since depth of discharge is proportional to charge time, the charge time can be estimated. The charge time is also dependent on the capacitance and the resistance of the circuit (time constant= circuit resistance x capacitance) so converting depth of discharge to charge time may involve knowledge of the specific circuit and capacitor technology.

[0084] The estimated charge time may be used to calculate 625 an estimated time to therapy using current settings. The estimated time to therapy is a function of a detection interval, for example a ventricular fibrillation detection interval, a number of intervals to detect, for example a number of intervals to detect ventricular fibrillation, and a charge time. If the estimated time to therapy is greater than a maximum time to therapy, detection setting may be modified to maintain a consistent time to therapy.

[0085] A user may be able to program one or both of the detection interval and the number of intervals to detect 627. While the number of intervals to detect an adverse cardiac event may be used to determine to provide therapy, it is to be understood that other rejection rules may prevent providing therapy even if the number of irregular beats within an interval meets the therapy threshold. For example, the wavelet rejection rule uses morphology to discriminate VT / VF from a fast normal conduction, or the T wave oversensing rule uses timing and amplitude patterns to discriminate VT / VF from t wave oversensing.

[0086] According to various implementations, a number of intervals to detect is an N of M number so one or both of an exact number of intervals and time to therapycould vary. The initial phase is a detection phase that operates under an event detection criteria before the device initiates charge. For example, the processing circuitry may determine N irregular events within a set time limit, N irregular events within the past M events, and an N irregular event counter exceeding a threshold, for example. All of these events may occur in the detection phase which starts at an initial event onset.

[0087] This calculation may assume the N number for the shortest time, or scale to get a typical or an average time to detect. In some examples, historic episode data may be used to determine a time to detect. This historic data may be particular to the patient or may be based on historic data for multiple patients.

[0088] The processing circuitry may use estimated charge time to determine 630 if a time to therapy is projected to be greater than a predefined time to therapy threshold. The time to therapy threshold may be fixed or may be user programmable. In some examples, the time to therapy threshold may be calculated based on other user programmable values. For example, the time to therapy threshold may be calculated based on one or both of the VFNID and the detection interval. The time to therapy threshold may be calculated periodically or may be calculated in response to a change in the user programmable values. If the system determines 630 that the time to therapy is not greater than the predefined time to therapy threshold, the system indicates that no changes are needed 635 and the system continues to periodically measure 615 the one or more battery capacity metrics.

[0089] If the system determines 630 that the time to therapy is greater than the predefined time to therapy threshold 632, the system determines 640 whether the number of intervals to detect may be adjusted such that the time to therapy is less than the predefined time to therapy threshold.

[0090] If the system determines 640 that the number of intervals to detect cannot be adjusted such that the time to therapy is less than the predefined time to therapy threshold, the system may recommend 645 replacement of the device within a specified time period and the number of intervals to detect is adjusted 650 to a lowest possible reasonable value. The lowest possible reasonable value may be predefined at manufacturing or may be programmed by a user of the device. The system may issue one or more alerts to a user of the device such as an audible or a visual alert. The lowest possible reasonable value may be defined by a user and / or may be based onhistoric episode data. In some examples, the lowest possible reasonable value may be based on the minimum programmable range for the VFNID (e.g., 12 / 16 for VF).

[0091] If the system determines 640 that the number of intervals to detect can be adjusted such that the time to therapy is less than the predefined time to therapy threshold, the number of intervals to detect may be adjusted 660 to maintain or substantially maintain a time to therapy. In some examples, the number of intervals to detect may be adjusted to a level that does not go below an effective detection threshold.

[0092] According to some examples, if the system determines 640 that the number of intervals to detect can be adjusted such that the time to therapy is less than or equal to the predefined time to therapy threshold, the system may maintain a number of intervals to detect but may start charging at an earlier time to maintain the time to therapy. It is to be understood that the system may use one or a combination of changing the number of intervals to detect and changing the start time of the charge. In some examples, a partial charge may be initiated early in the detection phase and may pause and finish after detection. If one or both of the number of intervals to detect and the start time have been changed, a user, for example a clinician, may be notified 665 of the change. According to some examples, a confirmation definition or criteria may be adjusted 662 when the number of intervals to detect is adjusted to account for spontaneous termination of an event. For example, the confirmation phase may be lengthened to more intervals. To overcome potential oversensing during the onset of charging, blanking may be used at least during the start of charging and end of charging.

[0093] Various examples have been described. These and other examples are within the scope of the following claims. For example, ICDs (e.g., CRT-D), EV-ICD, Sub Q ICDs, and wearable defibrillation devices can be used to implement the illustrative methods described herein.ILLUSTRATIVE EXAMPLES

[0094] 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.

[0095] Example Exl. A system comprising: a plurality of electrodes including at least one electrode configured to sense cardiac electrical activity of a patient's heart and at least one electrode configured to deliver defibrillation therapy to the patient's heart; a therapy delivery unit configured to: detect a treatable cardiac event using a first detection criteria within a first detection period; and initiate charging of one or more capacitors to deliver a defibrillation pulse based on the detection of the treatable cardiac event; and a charge unit configured to: estimate a charge time for the therapy delivery unit based on one or more battery parameters; determine the charge time exceeds a threshold value; and modify the therapy delivery unit to perform one or both of: detecting a treatable cardiac event using a second detection criteria within a second detection period and initiating charging of the one or more capacitors during the first detection period.

[0096] Example Ex2. A method comprising: detecting a treatable cardiac event using a first detection criteria within a first detection period; and initiating charging of one or more capacitors to deliver a defibrillation pulse based on the detection of the treatable cardiac event; estimating a charge time for a therapy delivery unit based on one or more battery parameters; determining the charge time exceeds a threshold value; and modifying the therapy delivery unit to perform one or both of: detecting a treatable cardiac event using a second detection criteria within a second detection period and initiating charging of the one or more capacitors during the first detection period.

[0097] Example Ex3. The system as in Exl or the method as in claim 2, wherein the first detection period is a first number of intervals and the second detection period is a second number of intervals.

[0098] Example Ex4. The system or method as in Ex3, further comprising determining whether the first number of intervals can be adjusted such that a time to therapy is less than or equal to a predefined time to therapy threshold.

[0099] Example Ex5. The system or method as in Ex4, further comprising issuing a device replacement alert based on the determination that the number of intervals cannot be adjusted such that the time to therapy is less than or equal to the predefined time to therapy threshold.

[0100] Example Ex6. The system or method as in any one of Exl-Ex5, further comprising: monitoring cardiac electrical activity; determining a number of irregular beats in the second detection period in a detection phase; and initiating a charge of the therapy delivery unit based on the number of irregular beats in the second detection period exceeding a predefined beat threshold.

[0101] Example Ex7. The system or method as in Ex6, further comprising performing confirmation of therapy during the charge of the therapy delivery unit.

[0102] Example Ex8. The system or method as in Ex7, further comprising adjusting one or more confirmation criteria based on an estimated time to therapy being less than a predefined time to therapy threshold.

[0103] Example Ex9. The system or method as in Ex6, further comprising an implantable cardioverter defibrillator (ICD) and wherein the therapy delivery unit is configured to initiate delivery of a therapeutic electrical defibrillation pulse to the patient's heart based on the number of irregular beats in the second time period exceeding the predefined beat threshold.

[0104] Example ExlO. The system or method as in Ex6, further comprising initiating at least a partial a charge of the therapy delivery unit during the detection phase.

[0105] Example Exl 1. The system or method as in any of Exl-ExlO wherein the therapy delivery unit is configured to estimate a charge time for the therapy delivery unit based on one or more battery capacity metrics, specific capacitor technology, charge circuit design, and charge voltage.

[0106] Example Exl2. The system or method as in Exl 1, wherein the one or more battery capacity metrics comprise a battery voltage and a battery impedance.

[0107] Example Exl3. The system or method as in any one of Exl-Exl2 wherein the plurality of electrodes comprises a defibrillation coil.

[0108] Example Exl4. The system or method as in any one of Exl-Exl3, wherein a time to therapy threshold may be set by a user.

[0109] Example Exl5. The system or method as in any one of Exl-Exl4, wherein one or both of the first detection criteria and the second detection criteria comprises one or both of an event counter and a noise counter.

[0110] Example Exl6. A system comprising: a plurality of electrodes including at least one electrode configured to sense cardiac electrical activity of a patient's heart and at least one electrode configured to deliver defibrillation therapy to the patient's heart; a therapy delivery unit configured to: detect a treatable cardiac event using a first detection criteria within a first detection period; initiate charging of one or more capacitors to deliver a defibrillation pulse based on the detection of the treatable cardiac event; and a charge unit configured to: estimate a time to therapy for the therapy delivery unit based on one or more battery parameters determine the time to therapy exceeds a threshold value; and modify the therapy delivery unit to perform one or both of: detecting a treatable cardiac event using a second detection criteria within a second detection period and initiating charging of the one or more capacitors during the first detection period.

[0111] Example Exl7. A method comprising: detecting a treatable cardiac event using a first detection criteria within a first detection period; initiating charging of one or more capacitors to deliver a defibrillation pulse based on the detection of the treatable cardiac event; estimating a time to therapy for a therapy delivery unit based on one or more battery parameters; determining the time to therapy exceeds a threshold value; and modifying the therapy delivery unit to perform one or both of: detecting a treatable cardiac event using a second detection criteria within a second detection period and initiating charging of the one or more capacitors during the first detection period.

[0112] Example Exl8. The system as in Exl6 or the method as in claim 17, wherein the first detection criteria is a first number of intervals and the second detection criteria is a second number of intervals.

[0113] Example Exl9. The system or method as in Exl8, further comprising determining whether the first number of intervals can be adjusted such that the time to therapy is less than or equal to a predefined time to therapy threshold.

[0114] Example Ex20. The system or method as in Exl9, further comprising issuing a device replacement alert based on the determination that the number of intervals cannot be adjusted such that the time to therapy is less than or equal to the predefined time to therapy threshold.

[0115] Example Ex21. The system or method as in any one of Exl6-Ex20, further comprising: monitoring cardiac electrical activity; determining a number of irregular beats in the second detection period in a detection phase; and initiating a charge of the therapy delivery unit based on the number of irregular beats in the second detection period exceeding a predefined beat threshold.

[0116] Example Ex22. The system or method as in Ex21, further comprising performing confirmation of therapy during the charge of the therapy delivery unit.

[0117] Example Ex23. The system or method as in Ex21, further comprising an implantable cardioverter defibrillator (ICD) and wherein the therapy delivery unit is configured to initiate delivery of a therapeutic electrical defibrillation pulse to the patient's heart based on the number of irregular beats in the second time period exceeding the predefined beat threshold.

[0118] Example Ex24. The system or method as in Ex21, further comprising initiating at least a partial a charge of the therapy delivery unit during the detection phase.

[0119] Example Ex25. The system or method as in any of Exl6-Ex24 wherein the therapy delivery unit is configured to estimate a charge time for the therapy delivery unit based on one or more battery capacity metrics, specific capacitor technology, charge circuit design, and charge voltage.

[0120] Example Ex26. The system or method as in Ex25, wherein the one or more battery capacity metrics comprise a battery voltage and a battery impedance.

[0121] Example Ex27. The system or method as in any one of Exl6-Ex26 wherein the plurality of electrodes comprises a defibrillation coil.

[0122] Example Ex28. The system or method as in any one of Exl6-Ex27, wherein the time to therapy threshold value may be set by a user.

[0123] 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 devices and methods described herein. Various modifications of the illustrative embodiments and examples will be apparent upon reference to this description.

[0124] 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).

[0125] 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.

[0126] 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.

[0127] 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.

[0128] 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.

[0129] 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) andany 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).

[0130] 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).

[0131] 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.

[0132] As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” encompass embodiments having plural referents, unless the content clearly 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.

[0133] 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.

[0134] The term “and / or” means one or all of the listed elements or a combination of at least two of the listed elements.

[0135] 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 plurality of electrodes including at least one electrode configured to sense cardiac electrical activity of a patient’s heart and at least one electrode configured to deliver defibrillation therapy to the patient’s heart;a therapy delivery unit configured to:detect a treatable cardiac event using a first detection criteria within a first detection period; and initiate charging of one or more capacitors to deliver a defibrillation pulse based on the detection of the treatable cardiac event; and a charge unit configured to:estimate a charge time for the therapy delivery unit based on one or more battery parameters;determine the charge time exceeds a threshold value; and modify the therapy delivery unit to perform one or both of: detecting a treatable cardiac event using a second detection criteria within a second detection period and initiating charging of the one or more capacitors during the first detection period.

2. The system as in claim 1, wherein the first detection period is a first number of intervals and the second detection period is a second number of intervals.

3. The system as in claim 2, further comprising determining whether the first number of intervals can be adjusted such that a time to therapy is less than or equal to a predefined time to therapy threshold.

4. The system as in claim 3, further comprising issuing a device replacement alert based on the determination that the number of intervals cannot be adjusted such that the time to therapy is less than or equal to the predefined time to therapy threshold.

5. The system as in any one of claims 1-4, further comprising:monitoring cardiac electrical activity;determining a number of irregular beats in the second detection period in a detection phase; andinitiating a charge of the therapy delivery unit based on the number of irregular beats in the second detection period exceeding a predefined beat threshold.

6. The system as in claim 5, further comprising performing confirmation of therapy during the charge of the therapy delivery unit.

7. The system as in claim 6, further comprising adjusting one or more confirmation criteria based on an estimated time to therapy being less than a predefined time to therapy threshold.

8. The system as in claim 5, further comprising an implantable cardioverter defibrillator (ICD) and wherein the therapy delivery unit is configured to initiate delivery of a therapeutic electrical defibrillation pulse to the patient’s heart based on the number of irregular beats in the second time period exceeding the predefined beat threshold.

9. The system as in claim 5, further comprising initiating at least a partial a charge of the therapy delivery unit during the detection phase.

10. The system as in any of claims 1-9 wherein the therapy delivery unit is configured to estimate a charge time for the therapy delivery unit based on one or more battery capacity metrics, specific capacitor technology, charge circuit design, and charge voltage.

11. The system as in claim 10, wherein the one or more battery capacity metrics comprise a battery voltage and a battery impedance.

12. The system as in any one of claims 1-11 wherein the plurality of electrodes comprises a defibrillation coil.

13. The system as in any one of claims 1-12, wherein a time to therapy threshold may be set by a user.

14. The system as in any one of claims 1-13, wherein one or both of the first detection criteria and the second detection criteria comprises one or both of an event counter and a noise counter.

15. A system comprising:a plurality of electrodes including at least one electrode configured to sense cardiac electrical activity of a patient’s heart and at least one electrode configured to deliver defibrillation therapy to the patient’s heart;a therapy delivery unit configured to:detect a treatable cardiac event using a first detection criteria within a first detection period;initiate charging of one or more capacitors to deliver a defibrillation pulse based on the detection of the treatable cardiac event; anda charge unit configured to:estimate a time to therapy for the therapy delivery unit based on one or more battery parametersdetermine the time to therapy exceeds a threshold value; and modify the therapy delivery unit to perform one or both of: detecting a treatable cardiac event using a second detection criteria within a second detection period and initiating charging of the one or more capacitors during the first detection period.

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