Patent Description:
Heart failure (HF) is a complex disease state broadly defined by an inability of the heart to pump sufficiently to cope with its venous return and/or to deliver sufficient output to meet the metabolic demands of the body. Heart failure is an increasingly common, life-threatening cardiovascular disorder, characterized by marked disability, frequent hospitalization and high mortality. HF is increasingly prevalent in older individuals (up to <NUM>% of the population) and it has become the most common cause for hospitalization in people ><NUM> yrs. HF is a leading cause or contributor to hospitalization and therefore is emerging as a substantial contributor to healthcare spending. The particular clinical manifestations of HF are determined by the underlying cause of the heart failure.

The term heart failure (HF) refers broadly to a pathophysiologic disorder in which cardiac performance is incapable of delivering sufficient blood to meet metabolic demand (e.g. during physical activity or in severe cases at rest), or to accommodate venous return. A range of further sub-classifications and/or structure of the heart, can then be applied, based on the symptoms exhibited by the patient. Exemplary classifications of heart failure by symptoms or objective assessments are provided by the New York Heart Association (classes I-IV, classes A-D)) Heart failure can also be defined by ejection fraction. Generally, patients exhibiting an ejection fraction of less than or equal to <NUM> are classified as having heart failure with reduced ejection fraction (HFrEF) while an ejection fraction above <NUM> is considered to be heart failure with preserved ejection fraction (HFpEF).

Congestive heart failure symptoms are indicative of congestive heart failure. Exemplary congestive heart failure symptoms include reduced cardiac output leading to easy fatigue and organ dysfunction (e.g. renal), and to symptoms related to congestion either in the lungs (causing breathlessness) or peripherally (leading to swelling of the lower limbs and abdomen).

A possible correlation has been identified between sedentary lifestyle and risk of ventricular arrhythmias based on a comparison of occurrences of ventricular arrhythmias in healthy active vs. sedentary men, and men with previous myocardial infarction. One result of a sedentary lifestyle is that the size of the chambers of the heart may decrease, which often occurs as a result of increased muscle thickness. Accordingly, the greatest number and highest grades of ventricular arrhythmias during exercise were found in healthy sedentary men.

Nearly half of all patients with heart failure have a normal ejection fraction (EF), commonly referred to as heart failure with preserved ejection fraction (HFpEF). In congestive heart failure patients with HFpEF the amount of blood pumped from the heart's left ventricle with each beat (ejection fraction) is greater than <NUM>%. HFpEF is also commonly known as diastolic heart failure or diastolic dysfunction, as the deficit in function frequently relates to changes occurring during diastole and filling of the ventricles. Approximately half of people with heart failure have HFpEF, while the remainder display a reduction in ejection fraction, or heart failure with reduced ejection fraction (HFrEF).

The prevalence of HFpEF continues to increase, likely because of the increasing prevalence of common risk factors, including older age, hypertension, metabolic syndrome, renal dysfunction and obesity. HFpEF is characterized by abnormal diastolic function, which manifests as an increase in the stiffness of the heart's left ventricle, a decrease in left ventricular relaxation when filling with blood before the next beat, and decreased chamber volume, which often occurs as a result of increased muscle thickness. There is an increased risk for atrial fibrillation and pulmonary hypertension for patient's experiencing HFpEF. Cardiac remodeling pacing is described in <CIT>.

The present disclosure is directed to a method and device for delivering a pacing therapy capable of remodeling a patient's heart over a period of time. According to one example of the present disclosure, a method comprises method for delivering a cardiac remodeling pacing therapy to a patient, comprises delivering remodeling pacing during a first interval, the first interval comprising a first rate and a first duration; determining whether to adjust one or both of the first rate and the first duration during delivery of remodeling pacing during a next interval subsequent to the first interval; and delivering remodeling pacing during the next interval in response to the determining, wherein the next interval comprises one of the first rate and the first duration of the first interval and the adjusted one or both of the first rate and the first duration.

It will be apparent to a skilled artisan 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 methods, devices, and systems 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.

<FIG> is a schematic diagram of an exemplary cardiac therapy delivery system that may be used to deliver a pacing therapy according to the present disclosure. The therapy delivery system <NUM> may include an implantable medical device <NUM> (IMD), which may be coupled to leads <NUM>, <NUM>, <NUM> and a programmer <NUM>. The IMD <NUM> may be, e.g., an implantable pacemaker, cardioverter, and/or defibrillator, that provides electrical signals to the heart <NUM> of a patient <NUM> via electrodes coupled to one or more of the leads <NUM>, <NUM>, <NUM>. Patient <NUM> may, but not necessarily, be a human.

The leads <NUM>, <NUM>, <NUM> extend into the heart <NUM> of the patient <NUM> to sense electrical activity of the heart <NUM> and/or to deliver electrical stimulation to the heart <NUM>. In the example shown in <FIG>, the right ventricular (RV) lead <NUM> extends through one or more veins (not shown), the superior vena cava (not shown), and the right atrium <NUM>, and into the right ventricle <NUM>. The left ventricular (LV) coronary sinus lead <NUM> extends through one or more veins, the vena cava, the right atrium <NUM>, and into the coronary sinus <NUM> to a region adjacent to the free wall of the left ventricle <NUM> of the heart <NUM>. The right atrial (RA) lead <NUM> extends through one or more veins and the vena cava, and into the right atrium <NUM> of the heart <NUM>. In one example, the atrial lead <NUM> can be positioned near the AV nodal/septal area for delivery of His bundle pacing and at least one the ventricular lead <NUM> is positioned in the right ventricle or the ventricular lead <NUM> is positioned in the left ventricle, as described below.

The IMD <NUM> may sense, among other things, electrical signals attendant to the depolarization and repolarization of the heart <NUM> via electrodes coupled to at least one of the leads <NUM>, <NUM>, <NUM>. In some examples, the IMD <NUM> provides pacing therapy (e.g., pacing pulses) to the heart <NUM> based on the electrical signals sensed within the heart <NUM>. The IMD <NUM> may be operable to adjust one or more parameters associated with the pacing therapy such as, e.g., pulse duration, voltage amplitude, burst length, etc. Further, the IMD <NUM> may be operable to use various electrode configurations to deliver pacing therapy, which may be unipolar or bipolar. The IMD <NUM> may also provide defibrillation therapy and/or cardioversion therapy via electrodes located on at least one of the leads <NUM>, <NUM>, <NUM>. Further, the IMD <NUM> may detect arrhythmia of the heart <NUM>, such as fibrillation of the ventricles <NUM>, <NUM>, and deliver defibrillation therapy to the heart <NUM> in the form of electrical pulses. I n some examples, IMD <NUM> may be programmed to deliver a progression of therapies, e.g., pulses with increasing energy levels, until a fibrillation of heart <NUM> is stopped.

In some examples, a programmer <NUM>, which may be a handheld computing device or a computer workstation, may be used by a user, such as a physician, technician, another clinician, and/or patient, to communicate with the IMD <NUM> (e.g., to program the IMD <NUM>). For example, the user may interact with the programmer <NUM> to retrieve information concerning one or more detected or indicated faults associated within the IMD <NUM> and/or the pacing therapy delivered therewith. The IMD <NUM> and the programmer <NUM> may communicate via wireless communication using any techniques known in the art. Examples of communication techniques may include, e.g., low frequency or radiofrequency (RF) telemetry, but other techniques are also contemplated.

<FIG> is a schematic diagram illustrating the exemplary cardiac therapy delivery system of <FIG> in more detail. The leads <NUM>, <NUM>, <NUM> may be electrically coupled to a therapy delivery module (e.g., for delivery of pacing therapy), a sensing module (e.g., one or more electrodes to sense or monitor electrical activity of the heart <NUM> for use in determining effectiveness of pacing therapy), and/or any other modules of the IMD <NUM> via a connector block <NUM>. In some examples, the proximal ends of the leads <NUM>, <NUM>, <NUM> may include electrical contacts that electrically couple to respective electrical contacts within the connector block <NUM> of the IMD <NUM>. In addition, in some examples, the leads <NUM>, <NUM>, <NUM> may be mechanically coupled to the connector block <NUM> with the aid of set screws, connection pins, or another suitable mechanical coupling mechanism.

Each of the leads <NUM>, <NUM>, <NUM> includes an elongated insulative lead body, which may carry a number of conductors (e.g., concentric coiled conductors, straight conductors, etc.) separated from one another by insulation (e.g., tubular insulative sheaths). In the illustrated example, bipolar electrodes <NUM>, <NUM> are located proximate to a distal end of the lead <NUM>. In addition, the bipolar electrodes <NUM>, <NUM> are located proximate to a distal end of the lead <NUM> and the bipolar electrodes <NUM>, <NUM> are located proximate to a distal end of the lead <NUM>.

The electrodes <NUM>, <NUM>, <NUM> may take the form of ring electrodes, and the electrodes <NUM>, <NUM>, <NUM> may take the form of extendable helix tip electrodes mounted retractably within the insulative electrode heads <NUM>, <NUM>, <NUM>, respectively. Each of the electrodes <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> may be electrically coupled to a respective one of the conductors (e.g., coiled and/or straight) within the lead body of its associated lead <NUM>, <NUM>, <NUM>, and thereby coupled to respective ones of the electrical contacts on the proximal end of the leads <NUM>, <NUM>, <NUM>. The electrodes <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> may further be used to sense electrical signals (e.g., morphological waveforms within electrograms (EGM)) attendant to the depolarization and repolarization of the heart <NUM>. The sensed electrical signals are conducted to the IMD <NUM> via the respective leads <NUM>, <NUM>, <NUM>. In some examples, the IMD <NUM> may also deliver pacing pulses via the electrodes <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> to cause depolarization of cardiac tissue of the patient's heart <NUM>. In some examples, as illustrated in <FIG>, the IMD <NUM> includes one or more housing electrodes, such as housing electrode <NUM>, which may be formed integrally with an outer surface of a housing <NUM> (e.g., hermetically-sealed housing) of the IMD <NUM> or otherwise coupled to the housing <NUM>. Any of the electrodes <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> may be used for unipolar sensing or pacing in combination with housing electrode <NUM>. In other words, any of electrodes <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> may be used in combination to form a sensing vector, e.g., a sensing vector that may be used to evaluate and/or analysis the effectiveness of pacing therapy. An example of a configuration sensing and pacing may be seen with respect to <CIT>, and assigned to the assignee of the present invention, as modified by preferably using a LVtip (i.e. electrode <NUM>)-RVcoil (i.e. electrode <NUM>) for the pacing vector and the sensing vector. The LVtip to RVcoil vector may be better for performing impedance measurements. This impedance may be inversely correlated to LV chamber size, and may drop as the LV chamber dilates with remodeling pacing. It is generally understood by those skilled in the art that other electrodes can also be selected as pacing and sensing vectors.

As described in further detail with reference to <FIG> and <FIG>, the housing <NUM> may enclose a therapy delivery module that may include a stimulation generator for generating cardiac pacing pulses and defibrillation or cardioversion shocks, as well as a sensing module for monitoring the patient's heart rhythm. The leads <NUM>, <NUM>, <NUM> may also include elongated electrodes <NUM>, <NUM>, <NUM>, respectively, which may take the form of a coil. The IMD <NUM> may deliver defibrillation shocks to the heart <NUM> via any combination of the elongated electrodes <NUM>, <NUM>, <NUM> and the housing electrode <NUM>. The electrodes <NUM>, <NUM>, <NUM>, <NUM> may also be used to deliver cardioversion pulses to the heart <NUM>. Further, the electrodes <NUM>, <NUM>, <NUM> may be fabricated from any suitable electrically conductive material, such as, but not limited to, platinum, platinum alloy, and/or other materials known to be usable in implantable defibrillation electrodes. Since electrodes <NUM>, <NUM>, <NUM> are not generally configured to deliver pacing therapy, any of electrodes <NUM>, <NUM>, <NUM> may be used to sense electrical activity during pacing therapy (e.g., for use in analyzing pacing therapy effectiveness) and may be used in combination with any of electrodes <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>. In at least one embodiment, the RV elongated electrode <NUM> may be used to sense electrical activity of a patient's heart during the delivery of pacing therapy (e.g., in combination with the housing electrode <NUM> forming a RV elongated, coil, or defibrillation electrode-to-housing electrode vector).

The configuration of the exemplary therapy delivery system <NUM> illustrated in <FIG> is merely one example. In one example, the atrial lead <NUM> is positioned near the AV nodal/septal area for delivery of His bundle pacing and either the ventricle lead <NUM> is positioned in the right ventricle or the ventricle lead <NUM> positioned in the left ventricle, or both ventricle leads <NUM> and <NUM> may be included, as described below. In addition, the electrode <NUM> of lead <NUM> may take the form of a helical tip electrode to enable the lead to be fixedly engaged near the AV nodal/septal area for delivery of His bundle pacing, described below.

<FIG> is a functional block diagram of an exemplary configuration of an implantable medical device according to an example of the present disclosure. As illustrated in <FIG>, the IMD <NUM> may include a control module <NUM>, a therapy delivery module <NUM> (e.g., which may include a stimulation generator), a sensing module <NUM>, and a power source <NUM>. The control module <NUM> may include a processor <NUM>, memory <NUM>, and a telemetry module <NUM>. The memory <NUM> may include computer-readable instructions that, when executed, e.g., by the processor <NUM>, cause the IMD <NUM> and/or the control module <NUM> to perform various functions attributed to the IMD <NUM> and/or the control module <NUM> described herein. Further, the memory <NUM> 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. Memory <NUM> includes computer instructions related to capture management, including the method of capture management according to the present disclosure, described in detail below. Furthermore, memory <NUM> includes computer instructions for one or more pacing regimen(s) (e.g. one or more pacing algorithm(s) etc.). For example, one or more pacing algorithms pace the heart at an elevated heart rate for a specified duration followed by pacing the heart at a second heart rate level for another pre-specified duration of time. One or more other embodiments involve pacing the patient's heart at a first elevated rate and a first duration. In one or more pacing regimens, the pacemaker delivers a first elevated pacing rate (e.g. up to <NUM> heart beats per minute above resting heart rate for up to <NUM> minutes or up to <NUM> minutes. Thereafter, the pacing rate is elevated to a second elevated pacing rate (e.g. up to <NUM> HBM above the first elevated heart rate for up to <NUM> or <NUM> minutes. Thereafter a third pacing rate is delivered to allow the heart to beat more slowly than the second elevated pacing rate. A fourth pacing rate, lower than the third pacing rate, is delivered to the heart through a pacemaker. Thereafter, the heart rate is allowed to gradually return to a resting heart rate level (with or without pacing). Multiple other pacing regimens are disclosed herein that may be employed by a pacemaker in order to remodel the heart.

The processor <NUM> (also referred to as processor circuit) of the control module <NUM> may include any 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 processor <NUM> 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 processor <NUM> herein may be embodied as software, firmware, hardware, or any combination thereof.

The control module <NUM> may control the therapy delivery module <NUM> to deliver therapy (e.g., electrical stimulation therapy such as pacing) to the heart <NUM> according to a selected one or more therapy programs, which may be stored in the memory <NUM>. More, specifically, the control module <NUM> (e.g., the processor <NUM>) may control the therapy delivery module <NUM> to deliver electrical stimulus such as, e.g., pacing pulses with the amplitudes, pulse widths, frequency, or electrode polarities specified by the selected one or more therapy programs (e.g., pacing therapy programs, pacing recovery programs, capture management programs, etc.). As shown, the therapy delivery module <NUM> is electrically coupled to electrodes <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, e.g., via conductors of the respective lead <NUM>, <NUM>, <NUM>, or, in the case of housing electrode <NUM>, via an electrical conductor disposed within housing <NUM> of IMD <NUM>. Therapy delivery module <NUM> may be configured to generate and deliver electrical stimulation therapy such as pacing therapy to the heart <NUM> using one or more of the electrodes <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>.

For example, therapy delivery module <NUM> may deliver pacing stimulus (e.g., pacing pulses) via ring electrodes <NUM>, <NUM>, <NUM> coupled to leads <NUM>, <NUM>, and <NUM>, respectively, and/or helical tip electrodes <NUM>, <NUM>, and <NUM> of leads <NUM>, <NUM>, and <NUM>, respectively. Further, for example, therapy delivery module <NUM> may deliver defibrillation shocks to heart <NUM> via at least two of electrodes <NUM>, <NUM>, <NUM>, <NUM>. In some examples, therapy delivery module <NUM> may be configured to deliver pacing, cardioversion, or defibrillation stimulation in the form of electrical pulses. In other examples, therapy delivery module <NUM> 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.

The IMD <NUM> may further include a switch module <NUM> and the control module <NUM> (e.g., the processor <NUM>) may use the switch module <NUM> 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 <NUM> may include a switch array, switch matrix, multiplexer, or any other type of switching device suitable to selectively couple the sensing module <NUM> and/or the therapy delivery module <NUM> to one or more selected electrodes. More specifically, the therapy delivery module <NUM> may include a plurality of pacing output circuits. Each pacing output circuit of the plurality of pacing output circuits may be selectively coupled, e.g., using the switch module <NUM>, to one or more of the electrodes <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> (e.g., a pair of electrodes for delivery of therapy to a pacing vector). In other words, each electrode can be selectively coupled to one of the pacing output circuits of the therapy delivery module using the switching module <NUM>.

The sensing module <NUM> is coupled (e.g., electrically coupled) to sensing apparatus, which may include, among additional sensing apparatus, the electrodes <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> to monitor electrical activity of the heart <NUM>, e.g., electrocardiogram (ECG)/electrogram (EGM) signals, etc. The ECG/EGM signals may be used to analyze a plurality of paced events. More specifically, one or more morphological features of each paced event within the ECG/EGM signals may be used to determine whether each paced event has a predetermined level of effectiveness. The ECG/EGM signals may be further used to monitor heart rate (HR), heart rate variability (HRV), heart rate turbulence (HRT), deceleration/acceleration capacity, deceleration sequence incidence, T-wave alternans (TWA), P-wave to P-wave intervals (also referred to as the P-P intervals or A-A intervals), R-wave to R-wave intervals (also referred to as the R-R intervals or V-V intervals), P-wave to QRS complex intervals (also referred to as the P-R intervals, A-V intervals, or P-Q intervals), QRS-complex morphology, ST segment (i.e., the segment that connects the QRS complex and the T-wave), T-wave changes, QT intervals, electrical vectors, etc..

The switch module <NUM> may be also be used with the sensing module <NUM> to select which of the available electrodes are used 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 <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>). In some examples, the control module <NUM> may select the electrodes that function as sensing electrodes via the switch module within the sensing module <NUM>, e.g., by providing signals via a data/address bus. In some examples, the sensing module <NUM> may include one or more sensing channels, each of which may include an amplifier.

In some examples, sensing module <NUM> 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 that are selected for coupling to this wide-band amplifier may be provided to a multiplexer, and thereafter converted to multi-bit digital signals by an analog-to-digital converter for storage in memory <NUM> as an EGM. In some examples, the storage of such EGMs in memory <NUM> may be under the control of a direct memory access circuit. The control module <NUM> (e.g., using the processor <NUM>) may employ digital signal analysis techniques to characterize the digitized signals stored in memory <NUM> to analyze and/or classify one or more morphological waveforms of the EGM signals to determine pacing therapy effectiveness. For example, the processor <NUM> may be configured to determine, or obtain, one or more features of one or more sensed morphological waveforms within one or more electrical vectors of the patient's heart and store the one or more features within the memory <NUM> for use in determining effectiveness of pacing therapy at a later time.

If IMD <NUM> is configured to generate and deliver pacing pulses to the heart <NUM>, the control module <NUM> may include a pacer timing and control module, which may be embodied as hardware, firmware, software, or any combination thereof. The pacer timing and control module may include one or more dedicated hardware circuits, such as an ASIC, separate from the processor <NUM>, such as a microprocessor, and/or a software module executed by a component of processor <NUM>, which may be a microprocessor or ASIC. The pacer timing and control module may include programmable counters which control the basic time intervals associated with DDD, VVI, DVI, VDD, AAI, DDI, DDDR, VVIR, DVIR, VDDR, AAIR, DDIR and other modes of single and dual chamber pacing. In the aforementioned pacing modes, "D" may indicate dual chamber, "V" may indicate a ventricle, "I" may indicate inhibited pacing (e.g., no pacing), "A" may indicate an atrium, and "R" may indicate rate responsive. The first letter in the pacing mode may indicate the chamber that is paced, the second letter may indicate the chamber in which an electrical signal is sensed, and the third letter may indicate the chamber in which the response to sensing is provided.

Intervals defined by the pacer timing and control module within control module <NUM> may include atrial and ventricular pacing escape intervals, refractory periods during which sensed P-waves and R-waves are ineffective to restart timing of the escape intervals, and/or the pulse widths of the pacing pulses. As another example, the pacer timing and control module may define a blanking period and provide signals from sensing module <NUM> to blank one or more channels, e.g., amplifiers, for a period during and after delivery of electrical stimulation to the heart <NUM>. The durations of these intervals may be determined in response to stored data in memory <NUM>. The pacer timing and control module of the control module <NUM> may also determine the amplitude of the cardiac pacing pulses.

During pacing, escape interval counters within the pacer timing/control module may be reset upon sensing of R-waves and P-waves. Therapy delivery module <NUM> (e.g., including a stimulation generator) may include one or more pacing output circuits that are coupled, e.g., selectively by the switch module <NUM>, to any combination of electrodes <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or <NUM> appropriate for delivery of a bipolar or unipolar pacing pulse to one of the chambers of heart <NUM>. The control module <NUM> may reset the escape interval counters upon the generation of pacing pulses by therapy delivery module <NUM>, and thereby control the basic timing of cardiac pacing functions, including anti-tachyarrhythmia pacing.

In some examples, the control module <NUM> 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 necessary mathematical calculations may be performed by the processor <NUM> and any updating of the values or intervals controlled by the pacer timing and control module may take place following such interrupts. A portion of memory <NUM> may be configured as a plurality of recirculating buffers, capable of holding series of measured intervals, which may be analyzed by, e.g., the processor <NUM> in response to the occurrence of a pace or sense interrupt to determine whether the patient's heart <NUM> is presently exhibiting atrial or ventricular tachyarrhythmia.

The telemetry module <NUM> of the control module <NUM> may include any suitable hardware, firmware, software, or any combination thereof for communicating with another device, such as the programmer <NUM> as described herein with respect to <FIG>. For example, under the control of the processor <NUM>, the telemetry module <NUM> may receive downlink telemetry from and send uplink telemetry to the programmer <NUM> with the aid of an antenna, which may be internal and/or external. The processor <NUM> may provide the data to be uplinked to the programmer <NUM> and the control signals for the telemetry circuit within the telemetry module <NUM>, e.g., via an address/data bus. In some examples, the telemetry module <NUM> may provide received data to the processor <NUM> via a multiplexer. In at least one embodiment, the telemetry module <NUM> may be configured to transmit an alarm, or alert, if the pacing therapy becomes ineffective or less effective (e.g., does not have a predetermined level of effectiveness).

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

<FIG> is an exemplary functional block diagram of circuitry of an implantable medical device according to the present disclosure. <FIG> depicts bipolar RA lead <NUM>, bipolar RV lead <NUM>, and bipolar LV CS lead <NUM> without the LA CS pace/sense electrodes <NUM> and <NUM> coupled with an implantable pulse generator (IPG) circuit <NUM> having programmable modes and parameters of a bi-ventricular DDD/R type known in the pacing art. In turn, the sensor signal processing circuit <NUM> indirectly couples to the timing circuit <NUM> and via data and control bus to microcomputer circuitry <NUM>. The IPG circuit <NUM> is illustrated in a functional block diagram divided generally into a microcomputer circuit <NUM> and a pacing circuit. The pacing circuit includes the digital controller/timer circuit, the output amplifiers circuit <NUM>, the sense amplifiers circuit <NUM>, the RF telemetry transceiver <NUM>, the activity sensor circuit <NUM> as well as a number of other circuits and components described below.

Crystal oscillator circuit <NUM> provides the basic timing clock for the pacing circuit while battery <NUM> provides power. Power-on-reset circuit <NUM> responds to initial connection of the circuit to the battery for defining an initial operating condition and similarly, resets the operative state of the device in response to detection of a low battery condition. Reference mode circuit <NUM> generates stable voltage reference and currents for the analog circuits within the pacing circuit, while analog to digital converter ADC and multiplexer circuit <NUM> digitizes analog signals and voltage to provide real time telemetry of cardiac signals from sense amplifiers <NUM>, for uplink transmission via RF transmitter and receiver circuit <NUM>. Voltage reference and bias circuit <NUM>, ADC and multiplexer <NUM>, power-on-reset circuit <NUM> and crystal oscillator circuit <NUM> may correspond to any of those presently used in current marketed implantable cardiac pacemakers.

The IPG generates pacing pulses to cardiac tissue. Typically, pacing pulses can be timed to a target heart rate for each patient. To adjust a patient's heart rate, the interval between pacing pulses is adjusted by the pacemaker. For example, to increase a patient's heart rate, the interval between pulses generated from the pacemaker is decreased. In contrast, to decrease a patient's heart rate, the interval between pulses is increased. In one or more embodiments, an exercise regimen may be configured to include exercise intervals (i.e. higher target heart rate that is higher than a patient's resting heart rate level) interleaved with recovery intervals (i.e. lower target heart rate that are lower than an immediately preceding exercise interval). One target heart rate zone for exercising the heart may be <NUM>-<NUM>% of a patient's maximum heart rate. In one or more embodiments, the target heart rate zone can be set to <NUM>-<NUM>% of the patient's maximum heart rate zone. In one or more other embodiments, the target heart rate zone can be set up to <NUM>% of the patient's maximum heart rate zone for a short period of time (e.g. up to <NUM> minutes, or up to <NUM> minutes etc.).

The exercise regimens, comprising a set of increased rate intervals interleaved with recovery rate intervals (also referred to as reduced rate intervals), can be implemented by using a base rate that is adjusted by modifying the pacing pulses for each interval. For example, if the resting heart rate is the base rate from which the intervals are measured, then the first increased rate can be determined by taking the average resting heart rate for that patient (e.g. 60HBM) adding a pre-specified number of HBMs (e.g. 20HBMs etc.) for that particular interval to obtain 80HBM (i.e. 60HBM + 20HBM) over a first time period (e.g. <NUM> minutes). Since the target heart rate level is now 80HBM, the interval between pulses generated from the pacemaker is decreased.

The pacemaker can be configured to use the maximum heart rate level as a base rate and a target rate would be adjusted down from the maximum heart rate to a target heart rate zone (e.g. <NUM>%-<NUM>% of the maximum heart rate zone). The patient's maximum heart rate can be determined by using the patient's tracked daily activities or using known equations (i.e. <NUM> HBPM minus the patient's age). Maximum heart rate can depend on a variety of factors including the patient's age, physical activity, and heart condition.

If the IPG is programmed to a rate responsive mode, the signals output by one or more physiologic sensor are employed as a rate control parameter (RCP) to derive a physiologic escape interval. For example, the escape interval is adjusted proportionally the patient's activity level developed in the patient activity sensor (PAS) circuit <NUM> in the depicted, exemplary IPG circuit <NUM>. The patient activity sensor <NUM> is coupled to the IPG housing and may take the form of a piezoelectric crystal transducer as is well known in the art and its output signal is processed and used as the RCP. Sensor <NUM> generates electrical signals in response to sensed physical activity that are processed by activity circuit <NUM> and provided to digital controller/timer circuit <NUM>. Activity circuit <NUM> and associated sensor <NUM> may correspond to the circuitry disclosed in <CIT> and <CIT>.

Conventional pacemakers are presently configured to automatically track a person's heart rate for a certain period of time (e.g. <NUM> day) and customize the pacing pulse intervals in response to the patient's activity. The activity sensor senses the person's activities throughout the day and the processor adjusts the pacing rate of the pacemaker to the patient's activities. After a person's heart rate has been tracked for a day, a rate profile optimization is automatically performed, as fully described in Medtronic Manual CLARIA MRI™/CLARIA MRI™ QUAD CRT-Ds reference manual M963432A001, freely available from Medtronic, Inc. located at <NUM> Medtronic Parkway, Minneapolis, MN <NUM> and www. The goal of the rate profile optimization is to ensure that the rate response of the pacemaker remains appropriate for the full range of patient activities. Each day, the pacemaker collects and stores daily and long-term averages of the percentage of time that the patient sensor-indicated rate is at different pacing rates. The pacemaker then uses the ADL Response and exertion response parameters to define the percentage of time that the pacing rate stays in the ADL rate range and exertion rate range, respectively. Based on daily comparisons, the pacemaker automatically adjusts the ADL Setpoint, the UR Setpoint, or both setpoints. During implementation of the exercise regimen, the rate profile optimization recognizes that the heart is being intentionally exercised and does not reduce the pacing.

Similarly, the present disclosure may be practiced in conjunction with alternate types of sensors such as oxygenation sensors, pressure sensors, pH sensors and respiration sensors, all well known for use in providing rate responsive pacing capabilities. Alternately, QT time may be used as the rate indicating parameter, in which case no extra sensor is required. Similarly, the present disclosure may also be practiced in non-rate responsive pacemakers.

Data transmission to and from the external programmer is accomplished by means of the telemetry antenna <NUM> and an associated RF transceiver <NUM>, which serves both to demodulate received downlink telemetry and to transmit uplink telemetry. Uplink telemetry capabilities will typically include the ability to transmit stored digital information, e.g. operating modes and parameters, EGM histograms, and other events, as well as real time EGMs of atrial and/or ventricular electrical activity and Marker Channel pulses indicating the occurrence of sensed and paced depolarizations in the atrium and ventricle, as are well known in the pacing art.

Microcomputer <NUM> contains a microprocessor <NUM> and associated system clock and on-processor RAM and ROM chips 82A and 82B, respectively. In addition, microcomputer circuit <NUM> includes a separate RAM/ROM chip 82C to provide additional memory capacity. Microprocessor <NUM> normally operates in a reduced power consumption mode and is interrupt driven. Microprocessor <NUM> is awakened in response to defined interrupt events, which may include A-TRIG, RV-TRIG, LV-TRIG signals generated by timers in digital timer/controller circuit <NUM> and A-EVENT, RV-EVENT, and LV-EVENT signals generated by sense amplifiers circuit <NUM>, among others. The specific values of the intervals and delays timed out by digital controller/timer circuit <NUM> are controlled by the microcomputer circuit <NUM> by means of data and control bus <NUM> from programmed-in parameter values and operating modes. In addition, if programmed to operate as a rate responsive pacemaker, a timed interrupt, e.g., every cycle or every two seconds, may be provided in order to allow the microprocessor to analyze the activity sensor data and update the basic A-A, V-A, or V-V escape interval, as applicable. In addition, the microprocessor <NUM> may also serve to define variable, operative AV delay intervals and the energy delivered to each ventricle.

In one embodiment, microprocessor <NUM> is a custom microprocessor adapted to fetch and execute instructions stored in RAM/ROM unit 82C in a conventional manner. It is contemplated, however, that other implementations may be suitable to practice the present disclosure. For example, an off-the-shelf, commercially available microprocessor or microcontroller, or custom application-specific, hardwired logic, or state-machine type circuit may perform the functions of microprocessor <NUM>.

Digital controller/timer circuit <NUM> operates under the general control of the microcomputer <NUM> to control timing and other functions within the pacing circuit and includes a set of timing and associated logic circuits of which certain ones pertinent to the present disclosure are depicted. The depicted timing circuits include URI/LRI timers 83A, V-V delay timer 83B, intrinsic interval timers 83C for timing elapsed V-EVENT to V-EVENT intervals or V-EVENT to A-EVENT intervals or the V-V conduction interval, escape interval timers 83D for timing A-A, V-A, and/or V-V pacing escape intervals, an AV delay interval timer 83E for timing the A-LVp delay (or A-RVp delay) from a preceding A-EVENT or A-TRIG, a post-ventricular timer 83F for timing post-ventricular time periods, and a date/time clock <NUM>.

The AV delay interval timer 83E is loaded with an appropriate delay interval for one ventricular chamber (i.e., either an A-RVp delay or an A-LVp delay as determined using known methods) to time-out starting from a preceding A-PACE or A-EVENT. The interval timer 83E triggers pacing stimulus delivery, and can be based on one or more prior cardiac cycles (or from a data set empirically derived for a given patient).

The post-event timers 83F time out the post-ventricular time periods following an RV-EVENT or LV-EVENT or a RV-TRIG or LV-TRIG and post-atrial time periods following an A-EVENT or A-TRIG. The durations of the post-event time periods may also be selected as programmable parameters stored in the microcomputer <NUM>. The post-ventricular time periods include the PVARP, a post-atrial ventricular blanking period (PAVBP), a ventricular blanking period (VBP), a post-ventricular atrial blanking period (PVARP) and a ventricular refractory period (VRP) although other periods can be suitably defined depending, at least in part, on the operative circuitry employed in the pacing engine. The post-atrial time periods include an atrial refractory period (ARP) during which an A-EVENT is ignored for the purpose of resetting any AV delay, and an atrial blanking period (ABP) during which atrial sensing is disabled. It should be noted that the starting of the post-atrial time periods and the AV delays can be commenced substantially simultaneously with the start or end of each A-EVENT or A-TRIG or, in the latter case, upon the end of the A-PACE which may follow the A-TRIG. Similarly, the starting of the post-ventricular time periods and the V-A escape interval can be commenced substantially simultaneously with the start or end of the V-EVENT or V-TRIG or, in the latter case, upon the end of the V-PACE which may follow the V-TRIG. The microprocessor <NUM> also optionally calculates AV delays, post-ventricular time periods, and post-atrial time periods that vary with the sensor based escape interval established in response to the RCP(s) and/or with the intrinsic atrial rate.

The output amplifiers circuit <NUM> contains a RA pace pulse generator (and a LA pace pulse generator if LA pacing is provided), a RV pace pulse generator, and a LV pace pulse generator or corresponding to any of those presently employed in commercially marketed cardiac pacemakers providing atrial and ventricular pacing. In order to trigger generation of an RV-PACE or LV-PACE pulse, digital controller/timer circuit <NUM> generates the RV-TRIG signal at the time-out of the A-RVp delay (in the case of RV pre-excitation) or the LV-TRIG at the time-out of the A-LVp delay (in the case of LV pre-excitation) provided by AV delay interval timer 83E (or the V-V delay timer 83B). Similarly, digital controller/timer circuit <NUM> generates an RA-TRIG signal that triggers output of an RA-PACE pulse (or an LA-TRIG signal that triggers output of an LA-PACE pulse, if provided) at the end of the V-A escape interval timed by escape interval timers 83D.

The output amplifiers circuit <NUM> includes switching circuits for coupling selected pace electrode pairs from among the lead conductors and the indifference can (IND_CAN) electrode <NUM> to the RA pace pulse generator (and LA pace pulse generator if provided), RV pace pulse generator and LV pace pulse generator. Pace/sense electrode pair selection and control circuit <NUM> selects lead conductors and associated pace electrode pairs to be coupled with the atrial and ventricular output amplifiers within output amplifiers circuit <NUM> for accomplishing RA, LA, RV and LV pacing.

The sense amplifiers circuit <NUM> contains sense amplifiers corresponding to any of those presently employed in contemporary cardiac pacemakers for atrial and ventricular pacing and sensing. It has been common in the prior art to use very high impedance P-wave and R-wave sense amplifiers to amplify the voltage difference signal which is generated across the sense electrode pairs by the passage of cardiac depolarization wavefronts. The high impedance sense amplifiers use high gain to amplify the low amplitude signals and rely on pass band filters, time domain filtering and amplitude threshold comparison to discriminate a P-wave or R-wave from background electrical noise. Digital controller/timer circuit <NUM> controls sensitivity settings of the atrial and ventricular sense amplifiers <NUM>.

The sense amplifiers are typically uncoupled from the sense electrodes during the blanking periods before, during, and after delivery of a pace pulse to any of the pace electrodes of the pacing system to avoid saturation of the sense amplifiers. The sense amplifiers circuit <NUM> includes blanking circuits for uncoupling the selected pairs of the lead conductors and the IND_CAN electrode <NUM> from the inputs of the RA sense amplifier (and LA sense amplifier if provided), RV sense amplifier and LV sense amplifier during the ABP, PVABP and VBP. The sense amplifiers circuit <NUM> also includes switching circuits for coupling selected sense electrode lead conductors and the IND_CAN electrode <NUM> to the RA sense amplifier (and LA sense amplifier if provided), RV sense amplifier and LV sense amplifier. Again, sense electrode selection and control circuit <NUM> selects conductors and associated sense electrode pairs to be coupled with the atrial and ventricular sense amplifiers within the output amplifiers circuit <NUM> and sense amplifiers circuit <NUM> for accomplishing RA, LA, RV and LV sensing along desired unipolar and bipolar sensing vectors.

Right atrial depolarizations or P-waves in the RA-SENSE signal that are sensed by the RA sense amplifier result in a RA-EVENT signal that is communicated to the digital controller/timer circuit <NUM>. Similarly, left atrial depolarizations or P-waves in the LA-SENSE signal that are sensed by the LA sense amplifier, if provided, result in a LA-EVENT signal that is communicated to the digital controller/timer circuit <NUM>. Ventricular depolarizations or R-waves in the RV-SENSE signal are sensed by a ventricular sense amplifier result in an RV-EVENT signal that is communicated to the digital controller/timer circuit <NUM>. Similarly, ventricular depolarizations or R-waves in the LV-SENSE signal are sensed by a ventricular sense amplifier result in an LV-EVENT signal that is communicated to the digital controller/timer circuit <NUM>. The RV-EVENT, LV-EVENT, and RA-EVENT, LA-SENSE signals may be refractory or non-refractory and can inadvertently be triggered by electrical noise signals or aberrantly conducted depolarization waves rather than true R-waves or P-waves.

<FIG> is a flowchart of a method of using a pacemaker to deliver a pacing therapy capable of remodeling the heart over a period of time according to an example of the present disclosure. In one or more embodiments, the pacing therapy may result in cardiac remodeling. According to one example, pacing therapy for cardiac remodeling may be delivered using the atrial lead <NUM> positioned near the AV nodal/high septal area for delivery of pacing via the tip electrode <NUM> and ring electrode <NUM>. Skilled artisans appreciate that other pacing vectors may be used to pace the heart (e.g. His bundle therapy as described in <CIT> and <CIT>. According to one example of the present disclosure, remodeling pacing therapy may be delivered at a predetermined time of the day. For example, pacing therapy can be delivered when the patient is most likely to be inactive (e.g. patient is asleep or in a supine position). Inactivity can be determined in a variety of ways (e.g. detection monitoring, historical data gathered from wearable devices having sensors (e.g. watch such as Garmin™ etc.), or user-inputted information. A patient can be determined to be inactive when a resting heart rate is detected, such as when the patient is asleep or in a supine position. Alternatively, the pacing therapy can be automatically delivered manually or without sensing any data (e.g. at a certain time of day (e.g. night time)). Therefore, as illustrated in <FIG>, in a method of delivering a pacing therapy via a pacemaker device for cardiac remodeling <NUM> according to an example of the present disclosure, the processor <NUM> may determine whether to initiate delivery of remodeling pacing therapy, Block <NUM>. For example, processor <NUM> may determine that it is a predetermined time of day when the patient is most likely to inactive, such as between the hours of 12am-5am, for example, or by determining that activity of the patient sensed via an activity sensor is less than a predetermined threshold indicative of the patient being asleep and/or in a supine position.

Upon determining that delivery of the remodeling pacing is scheduled, Yes in Block <NUM>, the processor <NUM> may deliver the remodeling pacing therapy, Block <NUM>, at a predetermined rate and/or duration. For example, the processor <NUM> may cause the remodeling pacing to be delivered at an elevated rate (e.g., <NUM> bpm for a <NUM>-minute duration), or in another example at an elevated rate (e.g., <NUM> bpm, etc., for a certain period of time, e.g., <NUM> hours per day). In another example, the processor <NUM> may cause the remodeling pacing to be delivered at an initial lower rate, such as <NUM> bpm, and gradually increase the patient's heart rate to a predetermined heart rate threshold, such as <NUM> bpm, for example. Exemplary patterns for delivering the remodeling pacing at variable rates and/or durations are described in detail below. Additionally, exercising the heart may continue for a period of time, with an adjusted pacing parameter (e.g. amplitude etc.) to increase heart rate, and/or until detection of a termination condition.

Once delivery of the remodeling pacing is initiated, Block <NUM>, the processor <NUM> may begin monitoring symptoms of the patient resulting from the delivered remodeling pacing, Block <NUM>. In addition, the processor <NUM> may monitor whether a patient activation signal has been received from the patient. Examples of the patient activation signal may be either a signal initiated by the patient indicating that the patient is experiencing discomfort as a result of the delivered remodeling pacing, or a signal received from the activity sensor <NUM> indicating the patient is no longer asleep or in a supine position, Block <NUM>. If the processor <NUM> determines that a patient activation signal has been received, Yes in Block <NUM>, the processor <NUM> suspends delivery of the remodeling pacing therapy, Block <NUM>, and waits for the next scheduled session for delivery of remodeling pacing, Block <NUM>.

Based on the monitored symptoms, Block <NUM>, and if a patient activation signal has not been received, No in Block <NUM>, the processor <NUM> determines whether the delivered remodeling pacing results in there being a measurable effect that would indicate that the delivery of the remodeling pacing is effective in causing some level of normalization of the condition of patient's heart, Block <NUM>. For example, the processor <NUM> may monitor changes in one or more parameters, such as tissue perfusion, atrial perfusion, estimated pulmonary artery diastolic pressure (ePad), right ventricular pressure, left ventricular pressure, and a pressure surrogate, such as impedance, as indicators that the remodeling pacing is affecting the overall condition of the patient's heart in a way that is indicative of there being some level of cardiac normalization. In one or more other embodiments, therapy is automatically delivered and/or suspended after a period of time (e.g. suspend therapy after ½ hour after delivering pacing, <NUM> hour etc.) without detection of a parameter such as tissue perfusion, atrial perfusion, estimated pulmonary artery pressure (ePad), right ventricular pressure, left ventricular pressure, and a pressure surrogate, such as impedance.

In one example, in order to determine whether there is a measurable normalization effect, Block <NUM>, the processor <NUM> may determine whether there is a change in perfusion associated with the patient. For example, change in tissue perfusion may be determined by measuring tissue perfusion during delivery of the remodeling pacing therapy and comparing the measured tissue perfusion with a non-paced baseline tissue perfusion level determined prior to the remodeling pacing being delivered to the patient, such as at implant of the device, for example. While the description below uses tissue perfusion as a target parameter to adjust therapy, other parameters mentioned above can be used as well.

If the current measured level of tissue perfusion has not increased relative to the baseline tissue perfusion level, the processor <NUM> determines that the delivered remodeling pacing has not resulted in there being a measurable effect indicative of cardiac normalization, No in Block <NUM>. A determination is then made as to whether to adjust delivery of the remodeling pacing, Block <NUM>, in order to increase the likelihood that subsequently delivered remodeling pacing will result in a measurable effect indicative of cardiac normalization.

<FIG> is a graphical representation illustrating the effect of remodeling pacing on cardiac output of a patient. Cardiac output (CO) refers to the amount of blood pumped by the heart per minute, and is the product of the heart rate (HR) or number of beats per minute and the stroke volume (SV), which is the amount of blood pumped per beat, so that CO = HR x SV. As illustrated in <FIG>, cardiac output typically increases as the heart rate increases until a maximum increase in cardiac output <NUM> is achieved. This maximum output <NUM> tends to vary from patient to patient and may vary for a single patient, depending upon a current condition of the patient's heart. Once the maximum cardiac output <NUM> is achieved, any further increase in the paced heart rate results in a reduction of the patient's cardiac output <NUM> and may likely indicate detrimental effects to the patient's cardiac condition.

Therefore, in order to determine whether to adjust the pacing therapy, Block <NUM> of <FIG>, when a measurable effect indicative of cardiac normalization is not being detected, No in Block <NUM>, the processor <NUM> may determine to adjust the pacing therapy, Yes in Block <NUM>, if a slope of the cardiac output of the patient is determined to be increasing. The processor <NUM> may then adjust the remodeling pacing by increasing the rate and/or the duration of the remodeling pacing, Block <NUM>. The typical intervention adjustments favor increasing the maximum pacing rate, with increasing duration as a secondary adjustment should rate effects become symptomatic. However, if the slope of the cardiac output of the patient is not determined to be increasing, the processor <NUM> determines not to adjust the pacing therapy, No in Block <NUM>.

Once the processor <NUM> either determines to adjust the therapy, Yes in Block <NUM>, and therefore the remodeling pacing is adjusted, Block <NUM>, or the processor <NUM> determines not to adjust the therapy, No in Block <NUM>, a determination is made as to whether the session time has ended, Block <NUM>. For example, the processor <NUM> may determine whether the remodeling pacing therapy has been delivered at a rate of least <NUM> bpm for a certain period of time (e.g., <NUM> minutes, etc.), or in another example whether the remodeling pacing therapy has been delivered at a rate of at least <NUM> bpm for <NUM> hours per day.

If the session time has not ended, No in Block <NUM>, the processor <NUM> continues delivering the remodeling pacing therapy, Block <NUM>, using either the same or the adjusted rate and/or duration. On the other hand, if the session time has ended, Yes in Block <NUM>, the processor <NUM> suspends delivery of the remodeling pacing therapy, Block <NUM>, and waits for the next scheduled session for delivery of remodeling pacing, Block <NUM>.

If the current measured level of tissue perfusion has increased relative to the baseline tissue perfusion level, the processor <NUM> determines that the delivered remodeling pacing has resulted in there being a measurable effect indicative of cardiac normalization, Yes in Block <NUM>. A determination is then made as to whether the effect is greater than a predetermined symptom avoidance threshold, Block <NUM>, indicative of the remodeling pacing being too aggressive for the patient. If the effect is determined to be greater than the predetermined symptom avoidance threshold, Yes in Block <NUM>, the processor <NUM> determines whether to adjust and continue delivery of the adjusted remodeling pacing therapy or to suspend delivery of the remodeling therapy to address the indication of the remodeling pacing being too aggressive for the patient, Block <NUM>.

For example, the processor <NUM> may determine the effect to be greater than the predetermined symptom avoidance threshold, Yes in Block <NUM>, and therefore that the remodeling therapy is too aggressive, if there has been an increase in the number of premature ventricular contractions (PVCs) that have occurred during delivery of the remodeling pacing. When increased PVCs is the indication used in Block <NUM> to determine that the remodeling pacing is too aggressive, the processor <NUM> determines not to suspend delivery of the remodeling pacing, No in Block <NUM>, and therefore adjusts the pacing therapy, Yes in Block <NUM>, by reducing the rate of delivery of pacing by a predetermined increment. For example, the delivery rate may be reduced by <NUM> beats per minute. In another example, the processor <NUM> may track an original baseline slope and suspend therapy when the slope deviates from the baseline slope by a predetermined amount or percentage.

In another example, the processor <NUM> may determine the effect to be greater than the predetermined symptom avoidance threshold, Yes in Block <NUM>, and therefore that the remodeling therapy is too aggressive, if a measure of contractility threshold is determined to be satisfied. For example, determining whether a measure of contractility is satisfied may include determining whether there is a decrease in amplitudes of S1 and S2 heart sounds sensed via a heart sounds sensor, or whether an S3 heart sound is sensed via the heart sensor during the delivered remodeling pacing. Many pacemakers are configured to detect heart sounds. Exemplary pacemakers AMPLIA™ or CLARIA™, available from Medtronic, Inc. located in Minneapolis, MN, are configured to detect heart sounds. When a measure of contractility threshold is the indication used in Block <NUM> to determine that the remodeling therapy is too aggressive, the processor <NUM> determines to suspend delivery of the remodeling pacing, Yes in Block <NUM>, as a result of the indication, and therefore suspends delivery of the remodeling pacing therapy, Block <NUM>, and waits for the next scheduled session for delivery of remodeling pacing, Block <NUM>.

In yet another example, the processor <NUM> may determine the effect to be greater than the predetermined symptom avoidance threshold, Yes in Block <NUM>, and therefore that the remodeling therapy is too aggressive, if a biomarker indicator exceeds a biomarker indicator threshold. For example, determining whether a biomarker indicator exceeds a biomarker indicator threshold may include determining whether a biomarker indicator for diagnosing congestive heart failure (CHF), such as brain natriuretic peptide (BNP), also referred to as B-type natriuretic peptide increases beyond a predetermined threshold indictive of CHF. When a biomarker indicator is the indication that was used to determine that the remodeling therapy is too aggressive, the processor <NUM> determines to suspend delivery of remodeling pacing , Yes in Block <NUM>, as a result of the indication, and therefore suspends delivery of the remodeling pacing therapy, Block <NUM>, and waits for the next scheduled session for delivery of remodeling pacing, Block <NUM>.

In another example, the processor <NUM> may determine the effect to be greater than the predetermined symptom avoidance threshold, Yes in Block <NUM>, and therefore that the remodeling therapy is too aggressive, if ST segment measurements are determined to satisfy an ST segment threshold. For example, ST segment measurements may be determined during the delivered remodeling pacing based on ECG signals sensed by the IMD <NUM> or based on EGM cardiac signals sensed by another internal or external monitoring device sensed from an alternate location. In one or more embodiments, data is stored (such as in a table) into memory for a patient in which the data associates ST segments with an acceptable pacing therapy result so pacing can continue and/or the ST segment is associated with a too aggressive pacing therapy in order to suspend therapy. The ST segment measurements determined during the delivered pacing are compare to an ST threshold, which may be determined during non-paced cardiac activity, and if an increase in the ST segment measurements is determined to occur, the ST segment threshold is determined to be satisfied. When changes in ST segment measurements is the indication used in Block <NUM> to determine that the remodeling therapy is too aggressive,
the processor <NUM> determines not to suspend delivery of the remodeling pacing, No in Block <NUM>, and therefore adjusts the pacing therapy, Yes in Block <NUM>, by reducing the rate of delivery of pacing by a predetermined increment.

Once the processor <NUM> adjusts delivery of the remodeling pacing, Block <NUM>, either to address instances of the remodeling pacing therapy being too aggressive, Yes in Block <NUM>, or to address instances of the remodeling pacing therapy not resulting in there being a measurable normalization effect, No in Block <NUM>, a determination is then made as to whether the session time has ended, Block <NUM>. For example, the processor <NUM> may determine whether the remodeling pacing therapy has been delivered at a rate of at least <NUM> bpm for <NUM> minutes. In another example, the processor <NUM> may determine whether the remodeling pacing therapy has been delivered at a rate of at least <NUM> bpm for <NUM> hours per day for a two-week period of time. If the session time has not ended, No in Block <NUM>, the processor <NUM> continues delivering the remodeling pacing therapy, Block <NUM>, and the therapy continues. On the other hand, if the session time has ended, Yes in Block <NUM>, the processor <NUM> suspends delivery of the remodeling pacing therapy, Block <NUM>, and waits for the next scheduled delivered remodeling pacing session, Block <NUM>.

In this way, a method for delivering a cardiac remodeling pacing therapy according to an example of the present disclosure may include the processor <NUM> sensing a cardiac signal <NUM> via the tip electrode <NUM> and the ring electrode <NUM> of the atrial lead <NUM> and monitoring cardiac symptoms to determine whether undesirable symptoms are induced as a result of the delivered remodeling pacing. For example, the processor <NUM> may deliver cardiac remodeling pacing to stimulate normalization of a condition of the patient's heart, monitor one or more parameters in response to the delivered remodeling pacing, determine an effect on cardiac normalization in response to the monitoring, and adjust the remodeling pacing in response to the determined effect on cardiac normalization.

<FIG> is a flowchart of a method of delivering a pacing therapy for cardiac remodeling according to an example of the present disclosure. According to another example, during real-time delivery of the remodeling pacing therapy, the processor <NUM> may determine whether undesirable symptoms are induced as a result of the delivered remodeling pacing based on short-term symptom avoidance factors, and adjust or suspend the delivered therapy accordingly, as described above. In addition, the processor <NUM> may also monitor long-term efficacy improvement factors to determine whether there is long-term improvement in the cardiac condition as a result of the delivered remodeling pacing therapy over an extended period of time. In particular, once the remodeling pacing therapy has been delivered for a predetermined long-term period of time, such as being delivered at a rate of at least <NUM> bpm for <NUM> hours per day for a two-week period of time, for example, the processor <NUM> may begin performing long-term monitoring of the effects of the remodeling pacing to determine whether there has been a desired level of improvement towards cardiac normalization.

For example, as illustrated in the example of <FIG>, during the continuous real-time monitoring of the delivered remodeling pacing <NUM>, described above, the processor <NUM> evaluates long-term effects of the delivered remodeling pacing to determine whether the remodeling pacing has resulted in there being successful normalization of the patient's heart. For example, once the processor <NUM> determines that it is time to perform long-term monitoring of the remodeling pacing, Yes in Block <NUM>, i.e., when it is determined that the remodeling pacing has been delivered at a rate of at least <NUM> bpm for <NUM> hours per day for a two-week period of time, for example, the processor <NUM> begins monitoring one or more long-term parameters associated with long-term delivery of the remodeling pacing, Block <NUM>, and evaluates long-term effects of the delivered remodeling pacing to determine whether the remodeling pacing has resulted in there being successful normalization of the patient's heart. A determination is then made, based on the long-term parameter, as to whether to adjust the remodeling pacing, Block <NUM>. If the processor <NUM> determines that the long-term parameter indicates that the remodeling pacing should be adjusted, Yes in Block <NUM>, the processor <NUM> adjusts the remodeling pacing, Block <NUM>, and waits for the next scheduled time to perform long-term monitoring of the remodeling pacing, Yes in Block <NUM>. On the other hand, if the processor <NUM> determines that the long-term parameter indicates that the remodeling pacing should not be adjusted, No in Block <NUM>, the processor <NUM> may determine whether to monitor an additional long-term parameter, Block <NUM>, to determine whether the additional long-term parameter indicates that the remodeling pacing has resulted in there being successful normalization of the patient's heart.

If an additional long-term parameter is not to be determined, No in Block <NUM>, the processor <NUM> waits for the next scheduled time to perform long-term monitoring of the remodeling pacing, Yes in Block <NUM>. If an additional long-term parameter is to be determined, Yes in Block <NUM>, the processor <NUM> monitors the additional long-term parameter, Block <NUM>, to determine whether the additional long-term parameter indicates that the remodeling pacing has resulted in there being successful normalization of the patient's heart. A determination is then made, based on the additional long-term parameter, as to whether to adjust the remodeling pacing, Block <NUM>. If the processor <NUM> determines that the additional long-term parameter indicates that the remodeling pacing should be adjusted, Yes in Block <NUM>, the processor <NUM> adjusts the remodeling pacing, Block <NUM>, and waits for the next scheduled time to perform long-term monitoring of the remodeling pacing, Yes in Block <NUM>. On the other hand, if the processor <NUM> determines that the additional long-term parameter indicates that the remodeling pacing should not be adjusted, No in Block <NUM>, the processor <NUM> may determine whether to monitor an additional long-term parameter, Block <NUM>.

In this way, in one example, the processor <NUM> may monitor a single long-term parameter to determine whether the long-term parameter indicates that the remodeling pacing should be adjusted. In another example, the processor <NUM> may monitor multiple long-term parameters to determine whether at least one of the long-term parameters indicates that the remodeling pacing should be adjusted.

According to one example, the processor <NUM> may monitor a QRS duration of the patient, Block <NUM>, to determine whether the QRS duration is increasing over time as a result of the delivered remodeling pacing. If the QRS duration is determined to be increasing, the processor <NUM> determines the remodeling pacing should be adjusted, Yes in Block <NUM>, and therefore makes the adjustment, Block <NUM>, by reducing the rate and or duration of the delivered remodeling pacing and waits for the next scheduled time to perform long-term monitoring of the remodeling pacing, Yes in Block <NUM>. On the other hand, if the QRS duration is not determined to be increasing the processor <NUM> determines that the remodeling pacing should not be adjusted, No in Block <NUM>.

In another example, the processor <NUM> may monitor one or more circadian parameters, Block <NUM>, to determine whether to adjust the period of time during which the remodeling pacing is to be delivered. For example, assuming the processor <NUM> delivers the remodeling pacing during a predetermined time of day when the patient is most likely to inactive, such as between the hours of 12am-5am, as described above, the processor <NUM> may divide the period of time during which the remodeling pacing is to be delivered into predetermined time segments, such as <NUM> minute time segments for example, and determine for each of the <NUM> minute time segments, or for a predetermined number of beats during the segment, whether there is a lack of conduction from the atria to the ventricles indicative of AV-block occurring for that <NUM> minute time segment. The processor <NUM> then adjusts the time period for delivery of the remodeling pacing, Block <NUM>, by not delivering the remodeling pacing during those <NUM>-minute time segments of the initial delivery period, i.e., between the hours of 12am-5am, for which AV-block is determined to likely occur.

In addition to the previously described pacing algorithms, a pacemaker can use one or more pacing regimens to remodel the heart. In another example, the processor <NUM> may merely characterize the patient circadian rhythms throughout the day, deliver rapid pacing during those rhythms and determine when the patient's heart is likely to conduct in a more normal manner based on the delivered rapid pacing, indicating that AV-block is less likely. The processor <NUM> then adjusts the time period for delivery of the remodeling pacing, Block <NUM>, by delivering the remodeling pacing during those periods when AV-block is less likely. In this way, the processor utilizes circadian parameters to learn or determine when to deliver the remodeling pacing rather than merely delivering the remodeling pacing during a fixed time period.

In another example, the processor <NUM> may monitor one or more long-term parameters, Block <NUM>, to identify whether there is a threshold level of long-term improvement in cardiac normalization. For example, the processor <NUM> may determine there is a threshold level of long-term improvement if a slope of the cardiac output of the patient is increasing. If there is a threshold level of long-term improvement, the processor <NUM> may adjust the rate and/or duration of the remodeling pacing. In another example, the processor <NUM> may determine there is a threshold level of long-term improvement if there is a desired change in pulmonary artery pressure, or a desired changed in impedance, such as a shift in impedance indicative of dilation of chambers of the heart. If there is a threshold level of long-term improvement as a result of the delivered remodeling pacing, the processor <NUM> may increase the rate and/or duration of the delivered remodeling pacing, Block <NUM>.

In another example, the processor <NUM> may be programmed to utilize a predetermined duty cycle range for delivery of the remodeling pacing, such as a range between a minimum time period of <NUM> hours per day and a maximum time period of <NUM> hours per day. In this way, if there is a threshold level of long-term improvement as a result of the delivered remodeling pacing, the processor <NUM> may increase the duration of the delivered remodeling pacing, Block <NUM>, unless the maximum duty cycle has been reached. Once the maximum duty cycle has been reached, the processor <NUM> may maintain delivery of the remodeling pacing at the maximum duty cycle.

<FIG> is a flowchart of a method of delivering a pacing therapy for cardiac remodeling according to an example of the present disclosure. According to another example, once the processor <NUM> determines that it is time to perform long-term monitoring of the remodeling pacing, Yes in Block <NUM>, the processor <NUM> begins monitoring one or more long-term parameters associated with long-term delivery of the remodeling pacing, Block <NUM>, and evaluates long-term effects of the delivered remodeling pacing to determine whether the remodeling pacing should be suspended.

As illustrated in <FIG>, the monitoring of a long-term parameter, Block <NUM>, may include the processor <NUM> monitoring a parameter to determine whether to either suspend delivery of the remodeling pacing, Yes in Block <NUM>, or to maintain delivery of the remodeling pacing at the current set rate and/or duration, No in Block <NUM>. For example, the monitoring of a long-term parameter, Block <NUM>, may include monitoring a return to resting heart rate of the patient over an extended period of time to determine whether there is a change in the patient's long-term resting heart rate.

For example, the processor <NUM> may determine a recovery rate associated with the amount of time for the heart rate to return to a resting heart rate after delivery of the remodeling pacing at an elevated heart rate resulting during the delivered remodeling pacing. The determined recovery rate is compared to a baseline recovery rate, determined at implant for example. If there is not a reduction in the amount of time associated with the determined recovery rate over a long-term period of time, such as one week for example, the processor <NUM> determines that the long-term parameter indicates that the remodeling pacing should not be suspended, No in Block <NUM>, and therefore delivery of the remodeling pacing is continued or maintained at the current rate and/or duration. If there is a reduction in the amount of time associated with the determined recovery rate, the processor <NUM> determines that the remodeling pacing has resulted in a desired level of normalization of the condition of patient's heart, and therefore delivery of the remodeling pacing should be suspended, Yes in Block <NUM>, and therefore suspends delivery of the remodeling pacing, Block <NUM>.

In another example, if the processor <NUM> determines that the long-term parameter indicates that the remodeling pacing should not be suspended, No in Block <NUM>, based on the determined recovery rate and therefore delivery of the remodeling pacing is continued or maintained at the current rate and/or duration, the processor <NUM> may determine whether to monitor an additional long-term parameter, Block <NUM>, to determine whether the additional long-term parameter indicates that the remodeling pacing should be suspended.

In another example, the monitoring of a long-term parameter, Block <NUM>, may include monitoring a systolic time interval (STI) over an extended period of time to determine whether there is a change in the patient's long-term STI. The current long-term STI is compared to a baseline STI, determined at implant for example. If there is not a predetermined reduction in the STI, such as a <NUM> percent reduction for example, the processor <NUM> determines that the long-term parameter indicates that the remodeling pacing should not be suspended, No in Block <NUM>, and therefore delivery of the remodeling pacing is continued or maintained at the current rate and/or duration. If there is a predetermined reduction in the current determined STI, the processor <NUM> determines that the remodeling pacing has resulted in a desired level of normalization of the condition of patient's heart, and therefore delivery of the remodeling pacing should be suspended, Yes in Block <NUM>, and therefore suspends delivery of the remodeling pacing, Block <NUM>.

In another example, if the processor <NUM> determines that the long-term parameter indicates that the remodeling pacing should not be suspended, No in Block <NUM>, based on the determined reduction in the STI and therefore delivery of the remodeling pacing is continued or maintained at the current rate and/or duration, the processor <NUM> may determine whether to monitor an additional long-term parameter, Block <NUM>, to determine whether the additional long-term parameter indicates that the remodeling pacing should be suspended.

In another example, the monitoring of a long-term parameter, Block <NUM>, may include monitoring a biomarker indicator for diagnosing congestive heart failure (CHF), such as brain natriuretic peptide (BNP) for example, over an extended period of time to determine whether there is a change in the biomarker that would indicate the delivered remodeling pacing has resulted in a desired level of normalization of the condition of the patient's heart. The biomarker measured over a long period of time is compared to a baseline measure, determined at implant for example. If there is not a predetermined long-term change in the biomarker, the processor <NUM> determines that the long-term parameter indicates that the remodeling pacing should not be suspended, No in Block <NUM>, and therefore delivery of the remodeling pacing is continued or maintained at the current rate and/or duration. If there is a predetermined long-term change in the biomarker, the processor <NUM> determines that the remodeling pacing has resulted in a desired level of normalization of the condition of patient's heart, and therefore delivery of the remodeling pacing should be suspended, Yes in Block <NUM>, and thus suspends delivery of the remodeling pacing, Block <NUM>.

<FIG> is a flowchart of a method of delivering a remodeling pacing therapy according to an example of the present disclosure. As illustrated in <FIG>, in order to increase the likelihood that the delivery of the remodeling pacing will be effective in causing a desired level of normalization of the condition of patient's heart, the processor <NUM> may deliver the remodeling pacing during multiple intervals, with the multiple intervals having variations in the rate and/or duration of the remodeling pacing in such a way as to increase muscular endurance of the heart. For example, the processor <NUM> may deliver the remodeling pacing at the current set rate, Block <NUM>, for a predetermined duration, and once the remodeling pacing has been delivered at the current rate for the current duration, Yes in Block <NUM>, determine whether to adjust the rate from the current rate to a next rate, Block <NUM>, and/or determine whether to adjust the duration from the current duration to a next duration, Block <NUM>.

In this way, once the remodeling pacing has been delivered at the current rate for the current duration, Yes in Block <NUM>, the processor <NUM> either adjusts only the rate, Block <NUM>, and delivers the next remodeling pacing interval, Block <NUM>, with the adjusted rate for the current duration, adjusts only the duration, Block <NUM>, and delivers the next remodeling pacing interval, Block <NUM>, at the current rate with the adjusted next duration, adjusts both the current rate, Block <NUM>, and the current duration, Block <NUM>, and delivers the next remodeling pacing interval, Block <NUM>, at the adjusted rate for the adjusted duration, or makes no adjustment to the rate or the duration and continues delivering the next remodeling pacing interval, Block <NUM>, at the current rate for the current duration. Once the duration has expired during delivery of the next remodeling pacing, Yes in Block <NUM>, the process is repeated to generate a next remodeling pacing delivery interval until the current remodeling pacing delivery session has ended.

In this way, the processor <NUM> may deliver remodeling pacing during a first interval having a first rate and a first duration, determine whether to adjust one or both of the first rate and the first duration during delivery of remodeling pacing during a next interval subsequent to the first interval, and deliver remodeling pacing during the next interval in response to the determining, so that the next interval may include the remodeling pacing being delivered having one of both the first rate and the first duration, the adjusted rate and the first duration, the first rate and the adjusted duration, and both the adjusted rate and the adjusted duration.

In particular, in one example delivery of the remodeling pacing may include a warm-up interval during which the remodeling pacing is delivered for an initial duration at a rate slightly above a resting heart rate associated with the patient, followed by a build-up interval during which the remodeling pacing is delivered at an increased rate for a shorter duration relative to the initial duration. Once delivery of the remodeling pacing during the build-up interval is completed, the remodeling pacing may be delivered using the rate and duration of the initial interval to generate an up/down delivery of the remodeling pacing, or may be delivered at an increased rate, increased duration, or an increased rate and duration, etc. In this way, the remodeling pacing may be delivered in repeatedly ascending and/or descending patterns to increase muscular endurance and thereby increase the likelihood that the delivery of the remodeling pacing will be effective in causing a desired level of normalization of the condition of patient's heart.

In one example, delivery of the remodeling pacing may include a <NUM>-minute warm-up interval (first time period) during which the remodeling pacing is delivered at a low rate just above the patient's resting rate (a first rate to increase the heart rate up to <NUM> heart beats per minute (HBM) above resting heart rate), followed by a <NUM> minute first build-up interval during which the remodeling pacing is delivered at a maximum rate (such as up to <NUM> HBM above the first heart rate), followed by a second interval (e.g., <NUM> minute interval) during which the remodeling pacing is delivered at a rate less than the maximum rate, followed by a third build-up interval (e.g., <NUM> minute interval) during which the remodeling pacing is delivered at the maximum rate, followed by a one minute time interval during which the remodeling pacing is delivered at the rate less than the maximum rate, followed by a one minute interval during which the remodeling pacing is delivered at the maximum rate, followed by a <NUM> minute time interval during which the remodeling pacing is delivered at the rate less than the maximum rate. The process may then be repeated. For example, this algorithm may be repeatedly implemented up to <NUM> hour per day.

In another example, delivery of the remodeling pacing may include delivery at the same rate but at varying duration. For example, delivery of the remodeling pacing may include delivering the remodeling pacing during a two minute interval (first interval) at a given rate (first rate), followed by delivering the remodeling pacing during a four minute interval (second interval) at the same rate, followed by delivering the remodeling pacing during a six minute interval (third interval) at the same rate, followed by delivering the remodeling pacing during another six minute interval (fourth interval) at the same rate, followed by delivering the remodeling pacing during a four minute interval (fifth interval) at the same rate, and followed by delivering the remodeling pacing during a two minute interval (sixth interval) at the same rate. In another example, the delivery may include a recovery interval (seventh interval) between each of the varying intervals during which the remodeling pacing is delivered at a reduced rate and reduced duration. This algorithm may be repeatedly implemented up to <NUM> hour per day.

In another example, the remodeling pacing may be delivered in a stepped pattern that includes a warm-up interval (first interval that allows the heart rate to gradually build up to <NUM> HBM) during which the remodeling pacing is delivered at a minimum rate (e.g. raises heart rate by up to <NUM> HBM), followed by a build-up interval during which the remodeling pacing is delivered at a first rate greater than the minimum rate delivered during the warm-up interval, followed by another build-up interval during which the remodeling pacing is delivered a second rate greater than the minimum rate (e.g. increases heart rate up to 30HBM above the first rate) and either equal to or greater than the first rate utilized during the previous build-up interval. This algorithm may be repeatedly implemented up to <NUM> hour per day.

In another example, delivery of the remodeling pacing may include an initial interval (up to <NUM> to <NUM> minutes) during which the remodeling pacing is delivered at a high rate (causing the heart rate to increase up to 50HBM), followed by a next interval during which the remodeling pacing is delivered at a reduced rate (decrease HBM by 20HBM from first interval), or an initial interval during which the remodeling pacing is delivered at a reduced rate, followed by a next interval during which the remodeling pacing is delivered at a high rate, may include alternating between the two.

In this way, delivery of the remodeling pacing may include multiple combinations of different rate and/or duration patterns being delivered over long or short periods of time, such as days or one or more weeks. In addition, recovery intervals may also be included during which delivery of the remodeling pacing is either withheld for a period of time or is delivered at a reduced rate and/or duration to allow variable patterns for delivery of the remodeling pacing, which may also include a combination of one or more a warm-up intervals and one or more build-up intervals, resulting in a desired level of normalization of the condition of patient's heart.

The techniques described in this disclosure, including those attributed to the IMD <NUM>, the programmer <NUM>, the processor <NUM> or various constituent components, may be implemented, at least in part, in hardware, software, firmware, or any combination thereof. For example, various aspects of the techniques may be implemented within one or more processors, including one or more microprocessors, DSPs, ASICs, FPGAs, or any other equivalent integrated or discrete logic circuitry, as well as any combinations of such components, embodied in programmers, such as physician or patient programmers, stimulators, image processing devices, or other devices. The term "module," "processor," or "processing circuitry" may generally refer to any of the foregoing logic circuitry, alone or in combination with other logic circuitry, or any other equivalent circuitry.

Such hardware, software, and/or firmware may be implemented within the same device or within separate devices to support the various operations and functions described in this disclosure. In addition, any of the described units, modules, or components may be implemented together or separately as discrete but interoperable logic devices. Rather, functionality associated with one or more modules or units may be performed by separate hardware or software components or integrated within common or separate hardware or software components.

When implemented in software, the functionality ascribed to the systems, devices and techniques described in this disclosure may be embodied as instructions on a computer-readable medium such as RAM, ROM, NVRAM, EEPROM, FLASH memory, magnetic data storage media, optical data storage media, or the like. The instructions may be executed by one or more processors to support one or more aspects of the functionality described in this disclosure.

Claim 1:
A cardiac device for delivering a cardiac remodeling pacing to a patient, comprising:
a housing (<NUM>);
a plurality of electrodes (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) electrically connected to the housing to deliver the cardiac remodeling pacing to stimulate normalization of a condition of the patient's heart; and
a processor (<NUM>) positioned within the housing and configured to:
deliver cardiac remodeling pacing during a first interval at a first rate for a first duration;
determine whether to adjust one or both of the first rate and the first duration during delivery of cardiac remodeling pacing during a next interval subsequent to the first interval;
adjust one or both of the first rate and the first duration during delivery of remodeling pacing during a next interval subsequent to the first interval in response to the determining to adjust one or both of the first rate and the first duration; and
deliver cardiac remodeling pacing during the next interval at the first rate for the first duration; and characterized in that.
the processor is further configured to deliver cardiac remodeling pacing at a second rate for a second duration, wherein the second rate is greater than the first rate and the second duration is less than the first duration.