Electrical stimulation rate modulation for communicating data values in a medical device system

Abstract

An implantable medical device is configured to determine a value of a monitored variable by the implantable medical device and convert the value to a data sequence of modulated electrical stimulation rate intervals. The implantable medical device delivers electrical stimulation pulses according to the data sequence of modulated stimulation rate intervals to produce a modulated activation rate of excitable tissue of a patient corresponding to the modulated stimulation rate intervals. The modulated activation rate is detectable by a rate monitor to demodulate the value of the monitored variable data. In some examples, the implantable medical device is a pacemaker that delivers cardiac pacing pulses according to modulated pacing rate intervals to produce a modulated heart rate of the patient that is detectable by a heart rate monitor to demodulate the value of the monitored variable.

Description

Technical Field

[0001] This disclosure relates to a medical device system including an implantable medical device (IMD) and a method for modulating the rate of electrical stimulation pulses delivered through the IMD to transmit values ​​of monitored variables to another medical device. Background Technology

[0002] A variety of implantable medical devices (IMDs) for delivering therapeutic electrical stimulation pulses to treat medical conditions are in clinical use or recommended for clinical use in patients. Examples include IMDs that deliver electrical stimulation therapy to the heart, muscles, nerves, brain, stomach, or other tissues. Such IMDs employ electrodes to deliver therapeutic electrical signals to such organs or tissues. IMDs may include electrodes for sensing physiological electrical signals inherent in the patient's body, said electrodes may be propagated from such organs or tissues, and / or other sensors for sensing the patient's physiological signals. The electrodes for delivering electrical stimulation pulses may be carried by medical electrical leads extending from the IMD or carried on the IMD housing of an electronic circuitry surrounding the IMD.

[0003] For example, leadless intracardiac pacemakers with housing-based electrodes can be implanted within the heart chambers to sense cardiac electrical signals and deliver pacing pulses to detect and treat cardiac arrhythmias. Leadless intracardiac pacemakers can be miniaturized to facilitate integral implantation within a single ventricle. Other intracardiac devices (IMDs), such as neurostimulators for treating pain, urinary or fecal incontinence, paralysis, tremor, or other neurological disorders or symptoms, can be miniaturized to reduce the complexity, invasiveness, or complications of the implantation procedure, alleviate patient discomfort, or enable implantation within limited anatomical spaces.

[0004] An IMD capable of delivering electrical stimulation therapy can be a programmable device that can wirelessly communicate with an external programming device, for example, using radio frequency (RF) telemetry. The IMD can transmit data about the delivered therapy, signals sensed from the patient, or diagnostic data from the device to the external programming or monitoring device via RF telemetry. In this way, clinicians can adjust the therapy as needed or obtain additional information about the patient's condition or the IMD itself. Summary of the Invention

[0005] The technology disclosed herein generally relates to transmitting values ​​of monitored variables by modulating the rate of delivered electrical stimulation pulses using an IMD (Inductively Coupled Device). An IMD operating according to the technology disclosed herein determines the value of the monitored variable and conceals the value within a sequence of modulated stimulation rate intervals representing that value. A rate monitor detects the modulated activation rate of excitable tissue generated by the modulated stimulation rate intervals and demodulates the detected rate to determine the value of the monitored variable without directly detecting the stimulation pulses via a rate monitor or radio frequency or other wireless transmission signals to transmit the value. In some instances, the IMD is a pacemaker that delivers cardiac pacing pulses at modulated pacing rate intervals, and the rate monitor is a heart rate monitor.

[0006] In one example, this disclosure provides a medical device system comprising an IMD with control circuitry configured to determine the value of a variable monitored by the IMD according to a monitoring scheme and to convert the value into a data sequence of modulated stimulation rate intervals. The IMD includes a pulse generator configured to deliver electrical stimulation pulses according to the data sequence of modulated stimulation rate intervals to generate a modulated activation rate of the patient's excitable tissue corresponding to the modulated stimulation rate intervals. The modulated activation rate can be detected by a rate monitor to demodulate the modulated activation rate into the value of the monitored variable.

[0007] In another example, this disclosure provides a method comprising determining, via an IMD (Inductively Coupled Device), a numerical value of a variable monitored by the IMD according to a monitoring protocol, and converting the numerical value into a data sequence comprising a plurality of modulated stimulation rate intervals. The method further comprises delivering electrical stimulation pulses via the IMD according to the data sequence of modulated stimulation rate intervals to generate a modulated activation rate corresponding to the modulated stimulation rate intervals through excitable tissues of a patient. The modulated activation rate can be detected by a rate monitor to demodulate the modulated activation rate back to the numerical value of the monitored variable.

[0008] In yet another example, this disclosure provides a non-transitory computer-readable storage medium comprising a set of instructions, when executed by control circuitry of an IMD, causing the device to determine a value of a variable monitored by the IMD according to a monitoring scheme, and to convert the value into a data sequence of modulated stimulation rate intervals. The instructions further cause the IMD to deliver electrical stimulation pulses according to the data sequence of modulated stimulation rate intervals to generate a modulated activation rate of the patient's excitable tissue corresponding to the modulated stimulation rate intervals. The modulated activation rate can be detected by a rate monitor to demodulate the modulated activation rate back to the value of the monitored variable.

[0009] Details of one or more aspects of this disclosure are set forth in the accompanying drawings and the following description. Other features, objects, and advantages described in this disclosure will become apparent from the description and drawings and from the claims. Attached Figure Description

[0010] Figure 1 This is a conceptual diagram of an IMD system that can be used to deliver therapeutic electrical stimulation pulses and modulate the rate of the stimulation pulses to transmit data to another device.

[0011] Figure 2 yes Figure 1 The diagram shown is a conceptual illustration of an intracardiac pacemaker.

[0012] Figure 3 yes Figure 2 A schematic diagram of an example configuration of a pacemaker is shown.

[0013] Figure 4 yes Figure 1 A conceptual diagram of a heart rate monitor (HRM).

[0014] Figure 5 It is based on an instance. Figure 1 The flowchart shows the method of pacemaker execution.

[0015] Figure 6 It is a timing diagram that shows the delivery of ventricular pacing pulses at modulated pacing pulse intervals to transmit numerical data values ​​to the HRM.

[0016] Figure 7 It is a timing diagram showing a pacing rate sequence for transmitting numerical data values, based on another example.

[0017] Figure 8 It is a timing diagram of a modulated pacing rate data sequence based on another example.

[0018] Figure 9 It is a timing diagram modulated based on the pacing rate of another example.

[0019] Figure 10 It is a flowchart of a method that can be performed by a heart rate monitor to detect heart rate and demodulate the detected heart rate to determine data values, based on an instance.

[0020] Figure 11 It is based on another instance. Figure 1 The flowchart of the system execution method. Detailed Implementation

[0021] Generally, this disclosure describes an IMD system configured to monitor device and / or patient-related variables to determine the values ​​of the monitored variables, and to transmit the values ​​of the monitored variables by modulating the rate intervals of electrical stimulation pulses delivered via the IMD. Each electrical stimulation pulse delivered at modulated rate intervals is intended to generate capture or activation of stimulated excitable tissue. As used herein, the term "excitable tissue" refers to body tissue comprising cells that can generate action potentials at their membranes in response to depolarization and can transmit pulses along the membranes. The term "activation" refers to electrical depolarization caused by the electrical stimulation pulses delivered by the IMD or the subsequent mechanical contraction caused by electrical depolarization. Examples of excitable tissue include skeletal muscle, smooth muscle, cardiac muscle, nerves, spinal cord, and the brain. The rate monitor detects the rate of depolarization or contraction of the excitable tissue generated by the modulated rate of the stimulation pulses by detecting physiological signals comprising waveforms appearing at the rate of depolarization or contraction of the excitable tissue. The rate monitor thereby detects the modulated activation rate of the excitable tissue from the physiological signals and demodulates the detected rate to determine the value of the monitored variable.

[0022] In some instances of the techniques disclosed herein, the IMD is a pacemaker, cardioverter-defibrillator, or other IMD capable of generating and delivering electrical stimulation pulses as cardiac pacing pulses designed to capture the heart muscle or nerves. The cardiac pacing pulses are delivered at modulated cardiac pacing rate intervals to produce depolarization and subsequent mechanical contraction at modulated rate intervals. A heart rate monitor can detect the resulting modulated heart rate and demodulated detected heart rate to determine the values ​​of patient-related or device-related variables monitored by the IMD.

[0023] This data communication technology, which includes modulating the rate of electrical stimulation pulses delivered via the IMD, does not require the IMD to use a radio frequency (RF) transceiver or other dedicated circuitry for transmitting wireless communication signals to transmit values. Furthermore, no rate monitor is needed to detect the electrical stimulation pulses delivered via the IMD. The rate monitor detects the activation rate of the stimulated tissue, such as electrical depolarization or resulting mechanical contraction, without detecting the actual stimulation pulse or any specific characteristic of the stimulation pulse itself. For example, a rate monitor can detect heart rate from physiological sensor signals to demodulate the rate of modulation of cardiac pacing pulses without detecting the cardiac pacing pulses themselves.

[0024] As used herein, a “monitoring variable” is a patient- or device-related variable monitored or measured by the IMD, rather than a control parameter set or directly controlled by the IMD, rate monitor, or any other device, as a control parameter for controlling the function of the IMD or rate monitor. For example, a monitoring variable might include the remaining battery voltage of the IMD, the cardiac pacing capture threshold, the impedance of the cardiac pacing vector, or, as an example, the cardiac pacing frequency derived from the total number of sensed cardiac and pacing cardiac events over a specified time period. Unlike control parameters programmed or automatically set by the IMD to control its function, a monitoring variable is not directly set or controlled by the IMD.

[0025] As used herein, “control parameters” are parameters programmed, set, or adjusted by the IMD to control its sensing and therapy delivery functions. Sensing control parameters, for example, are used to control the sensing of physiological signals, such as cardiac electrical signals like R waves or P waves. Examples of sensing control parameters may include, but are not intended to be limited to, sensing thresholds, sensitivity, blanking periods, and refractory periods. While these control parameters are used to control how the IMD senses events from physiological signals, the number of events sensed (e.g., the number of sensed R waves) may be a monitoring or measurement variable not directly set by the IMD. Examples of therapy delivery or electrical stimulation control parameters may include, but are not intended to be limited to, pacing rate, pacing pulse amplitude, and pacing pulse width. These parameters can be directly programmed, set, or adjusted by the IMD. However, the capture threshold used to set the pacing pulse amplitude is an example of a monitoring variable that has a numerical value and is not set or controlled by the IMD. The pacing rate modulation techniques disclosed herein are used to transmit the numerical value of the monitoring variable.

[0026] As used herein, a “physiological signal” is a signal generated by a sensor (e.g., an electrical, chemical, mechanical, or optical sensor of an IMD or rate monitor) in response to physiological changes in body tissue. As used herein, a physiological signal does not refer to a signal generated by a device and detected by another device, such as an electrical stimulation pulse. One example of a physiological signal is a cardiac electrical signal generated by a cardiac electrical sensing circuit receiving signals from sensing electrodes, and includes a depolarization signal accompanying electrical depolarization of myocardial tissue. Other examples of physiological signals include, but are not intended to be limited to, pulsatile signals that can be sensed by mechanical or optical sensors, and include pulsatile signals generated by periodic changes in blood volume corresponding to periodic changes in the cardiac cycle or the movement of the heart chambers or blood vessel walls. In the communication techniques disclosed herein, the rate monitor senses the physiological signal and determines the activation rate corresponding to the modulated rate interval of the electrical stimulation pulse delivered via the IMD. In the examples presented herein, the rate monitor does not directly detect the electrical stimulation pulse delivered via the IMD or demodulate the characteristics or features of the actual stimulation pulse delivered via the IMD. Rate monitors detect activation rates, such as electropolarization or mechanical contraction, represented by pulsating or periodic waveforms of physiological signals sensed by the rate monitor's sensors.

[0027] Figure 1 This is a conceptual diagram illustrating an IMD system 10, which can be used to deliver therapeutic electrical stimulation pulses and modulate the rate of the stimulation pulses to transmit data to another device. Figure 1 In an illustrative example, system 10 includes an intracardiac pacemaker (IMD) 14 and an external wearable heart rate monitor (HRM) 40. The pacemaker 14 is configured to deliver therapeutic pacing pulses to the heart 8 to treat or prevent arrhythmias. The pacemaker 14 is configured to modulate pacing rate intervals to deliver pacing pulses at different rates according to a coding scheme. As described herein, the coding scheme may be based on binary, ternary, quaternary, or other base systems or other coding schemes, containing predetermined pacing rate intervals for causing the heart to beat at a modulated heart rate. The HRM 40 detects the modulated heart rate and demodulates the heart rate into numerical values ​​of variables monitored by the pacemaker 14.

[0028] As used herein, a “therapeutic” pacing pulse comprises a pacing pulse designed to capture the heart 8 to generate pacing-induced myocardial depolarization to produce a pacing pulse that causes the heart to contract or “beat” at a desired rate. As an example, in the absence of an inherent R wave sensed at or above a programmed lower pacing rate, pacemaker 14 may deliver bradycardia pacing therapy by delivering a therapeutic pacing pulse at a programmed lower pacing rate. Rate-responsive pacing therapy may comprise a therapeutic pacing pulse delivered at a temporary pacing rate above a programmed lower pacing rate to increase heart rate during physical activity. Each pacing pulse delivered at modulated pacing rate intervals, as disclosed herein, can be considered a “therapeutic” pacing pulse because it delivers pacing pulse energy outside the physiological refractory period of myocardial tissue, designed to capture the heart and induce a heartbeat above a programmed lower pacing rate, thereby preventing cardiac arrest or bradycardia.

[0029] For example, pacing pulses delivered at modulated pacing rate intervals (also referred to herein as “modulated pacing intervals”) can be delivered without pausing bradycardia pacing in pacing-dependent patients because the pacing pulses delivered at modulated pulse intervals capture the heart at rate intervals within an acceptable range of the programmed lower pacing rate or other targeted therapeutic pacing rate or the sensed intrinsic heart rate. For example, if the programmed lower rate for bradycardia pacing is 40 to 60 pulses per minute (corresponding to a pulse rate interval of 1.5 to 1.0 seconds), the modulated pacing rate interval used to deliver the values ​​of the monitored variables can be in the range of about 1000 milliseconds to about 660 milliseconds (corresponding to an overspeed pacing rate of about 60 to about 90 pulses per minute), as an example and not intended to limit. Since the number of modulated pacing rate intervals required to deliver one or more values ​​of one or more monitored variables can typically be delivered over several minutes or even a minute or less, modulated pacing rates can be delivered without impairing the intended therapeutic benefits of pacing therapies such as bradycardia pacing. For example, the modulated pacing rate may account for about 1% or even 0.1% or less of the total number of pacing pulses delivered by the pacemaker 14 in 24 hours.

[0030] exist Figure 1 In this example, pacemaker 14 is shown in the right ventricle (RV) of a patient's heart 8, used to sense cardiac electrical signals and deliver cardiac pacing pulses. Pacemaker 14 may be a transcatheter intracardiac pacemaker suitable for implantation entirely within the heart chambers (e.g., entirely within RV 4, entirely within the left ventricle (LV) 6, or entirely within the right atrium (RA) 2). Compared to subcutaneously implanted pacemakers, pacemaker 14 can be smaller in size and its shape can be generally cylindrical to allow for transvenous implantation into the heart chambers via a delivery catheter.

[0031] The technologies disclosed in this article are not limited to Figure 1 The pacemaker location shown in the examples is possible, as are other locations within the heart 8. For example, a pacemaker 14 performing the techniques disclosed herein can be positioned in or on the heart 8 to deliver electrical stimulation pulses that capture and modulate the heart at the rate of electrical stimulation pulses. The pacemaker 14 can deliver cardiac pacing pulses via electrodes on the pacemaker housing, referred to herein as “housing-based electrodes.” The pacemaker 14 can be configured to use the housing-based electrodes to sense cardiac electrical signals from RV 4 to detect ventricular R waves to generate an electrocardiogram (EGM) signal. The cardiac electrical signals can be sensed using housing-based electrodes that are also used to deliver pacing pulses to the heart 8.

[0032] HRM 40 can be a wearable device capable of detecting a patient's heart rate and demodulating the heart rate to extract information from pacemaker 14. HRM 40 can be a dedicated heart rate tracking device provided to a patient receiving pacemaker 14 for detecting and demodulating the modulated heart rate to obtain values ​​of variables monitored by pacemaker 14. In other instances, HRM 40 can be a commercially available smartwatch, activity tracker, or other wearable accessory capable of detecting a patient's heart rate and storing and executing an application for demodulating the detected heart rate to extract data encoded by the modulated heart rate. In yet another instance, HRM 40 can be an implantable device, such as an implantable device for sensing subcutaneous ECG signals, such as Reveal, available from Medtronic, Inc., Minneapolis, MN. It can be inserted into a cardiac monitoring system. As described below, the HRM 40 can detect and demodulate the modulated heart rate to determine the values ​​of one or more patient-related and / or device-related variables monitored by the pacemaker 14. The HRM 40 can provide various responses to the values ​​of the monitored variables, such as generating patient notifications that the data can be viewed, generating alarms for values ​​that are outside the normal range, generating displays that may include historical values ​​of the monitored variables, generating notifications of the status of the monitored variables based on the values, and / or transmitting the values ​​to another device.

[0033] HRM 40 is capable of bidirectional wireless communication with external device 50 to transmit demodulated data from the detected heart rate to external device 50. External device 50 may be a home medical monitor, smartphone or other handheld device, personal computer, or other device, which can be used by a non-bedridden patient or at a fixed location or other location in the patient's home to wirelessly retrieve data from HRM 40. External device 50 is shown having a wireless communication link 42 established with HRM 40. Communication link 42 can use, for example... The connection is established via Wi-Fi, Medical Implantable Communication Services (MICS), or other radio frequency (RF) links. In some instances, HRM 40 and external device 50 are... Enable the device to allow data extracted from the detected heart rate via HRM 40. The connection can be used to transfer data to external device 50 or cloud-based storage at any time. In one instance, external device 50 may be MYCARELINK, commercially available from Medtronic Inc., Minneapolis, Minnesota, USA. TM Patient monitor.

[0034] The HRM 40 and / or external device 50 can display numerical values ​​or status indicators of values ​​demodulated from the detected heart rate to the patient or other user for viewing, enabling the patient or other user to take any corrective action as needed. Notifications or alarms can be initiated by the HRM 40 to be displayed directly to the patient or via the external device 50. Access to patient-related or device-related variables monitored or measured by the pacemaker 14 is provided without the pacemaker 14 performing wireless radio frequency transmission. The operation of the pacemaker 14 transmitting data to the patient or clinician via an external device is improved by making the communication process energy-efficient (no power supply to the RF transmitter is required). While the HRM 40 is monitoring the patient's heart rate, values ​​of the monitored parameters can be obtained from the pacemaker 14 multiple times over an hour, day, week, etc. The HRM can initiate patient alarms or notifications without time limits or waiting for queries from other devices. Data can be obtained from the pacemaker 14 at a high compliance rate when transmitting data without relying on patient or user interaction with the system 10, such as by manually initiating a communication session.

[0035] It is conceivable that the HRM and / or external device 50 can be connected to a communication network, either wired or wirelessly, via telemetry circuitry including a transceiver and antenna, or via hardwired communication lines for transmitting data to a centralized database or computer, to allow for remote patient management. A remote patient management system containing a remote patient database can be configured to receive data and information determined by the HRM 40, enabling clinicians to view data transmitted via heart rate modulation by the pacemaker 14.

[0036] Although a pacemaker 14 and a wearable HRM 40 are shown in System 10, it is conceivable that other types of implantable electrical stimulation devices could deliver therapeutic single pulses or sequences of single pulses, such as high-frequency pulse sequences separated by rate intervals, for muscle stimulation or pain control. The implantable electrical stimulation device can be configured to determine data values ​​of monitoring variables related to patient or device status and convert numerical data values ​​into sequences of modulated rate intervals (between single stimulation pulses or between high-frequency pulse sequences). A rate monitor, which may be a wearable or implantable monitor, can be configured to detect signals containing a resulting evoked response or activation of stimulated muscle or nerve tissue occurring at a modulated rate. The rate detection device can determine the rate of the evoked response or activation, for example, based on neural signals, electromyographic signals, or mechanosensor signals, and demodulate the rate to determine values ​​of device-related or patient-related variables. In some instances, the HRM 40 monitor may be configured solely for monitoring, but in others, it may include therapy delivery functionality. For example, an HRM configured to demodulate the detected heart rate can be a pacemaker, an implantable cardioverter defibrillator, a neurostimulator, or other medical device capable of detecting the activation rate generated by the stimulation rate modulated by the IMD and delivering a therapy (such as electrical stimulation therapy, drug delivery, or other therapies).

[0037] Figure 2 yes Figure 1 The diagram shows a conceptual representation of an intracardiac pacemaker 14. The pacemaker 14 includes leadless electrodes 20 and 22 spaced apart on a housing 15 for sensing cardiac electrical signals and delivering pacing pulses. Electrode 22 is shown as a tip electrode extending from the distal end 24 of the pacemaker 14, and electrode 20 is shown as a ring electrode along a middle portion of the sidewall of the housing 15 (e.g., adjacent to the proximal end 26). Electrode 20 may be externally attached to a portion of the sidewall of the housing 15 extending from the distal end 24 to the proximal end 26. The distal end 24 is referred to as “distal” because it is intended to be the tip when the pacemaker 14 is advanced through a delivery tool (such as a catheter) and placed close to the target pacing site.

[0038] Electrodes 20 and 22 form an anode and cathode pair for bipolar cardiac pacing and sensing of cardiac electrical signals. In alternative embodiments, pacemaker 14 may include two or more annular electrodes, two tip electrodes, and / or other types of electrodes exposed along pacemaker housing 15 for delivering electrical stimulation to the heart 8 and sensing cardiac electrical signals. Electrodes 20 and 22 may be positioned along pacemaker 14 at locations other than those shown. Electrodes 20 and 22 may be, but are not limited to, titanium, platinum, iridium, or alloys thereof, and may contain low-polarity coatings such as titanium nitride, iridium oxide, ruthenium oxide, platinum black, etc.

[0039] The housing 15 is formed of a biocompatible material, such as stainless steel or titanium alloy. In some instances, the housing 15 may include an insulating coating. Examples of insulating coatings include parylene, urethane, PEEK, or polyimide. The housing 15 may be entirely insulating, except for electrodes 20 and 22, which are not insulating. Electrode 22 may act as a cathode electrode and be coupled via an electrical feedthrough across the housing 15 to an internal circuitry system enclosed by the housing 15, such as a pacemaker pulse generator and a cardiac electrical signal sensing circuitry system. Electrode 20 may be formed as a definition of the housing 15, such as... Figure 2 The conductive portion of the annular electrode, generally shown, is electrically isolated from the rest of the housing 150. In other embodiments, instead of providing a partial annular electrode such as the anode electrode 20, the entire periphery of the housing 15 can be used as an electrode electrically isolated from the tip electrode 22. The electrode 20, defined by the conductive portion of the housing 15, serves as a return anode during pacing and sensing.

[0040] The housing 15 includes a cavity for housing as described below. Figure 3 The described control electronics subassembly 18 is for sensing cardiac signals, generating pacing pulses, and controlling the therapy delivery and other functions of the pacemaker 14. The housing 15 further includes a battery subassembly 16 that supplies power to the control electronics subassembly 18.

[0041] The pacemaker 14 may include a set of fixation teeth 28 to secure the pacemaker 14 to patient tissue, for example, by active engagement with the ventricular endocardium and / or interaction with ventricular trabeculae. The fixation teeth 28 are configured to anchor the pacemaker 14 to position the electrode 22 in a location operatively close to the target tissue for the delivery of therapeutic electrical stimulation pulses. Various types of active and / or passive fixation members can be employed to anchor or stabilize the pacemaker 14 in the implantation location. The pacemaker 14 may include a set of fixation teeth as disclosed in commonly assigned U.S. Patent No. 9,775,982 (Grubac et al.).

[0042] The pacemaker 14 may optionally include a delivery tool interface 30. The delivery tool interface 30 may be located at the proximal end 26 of the pacemaker 14 and is configured to connect to a delivery device (such as a catheter) for positioning the pacemaker 14 at the implantation site, for example, within the LV, during the implantation procedure.

[0043] Figure 3 yes Figure 1 The diagram shows an example configuration of pacemaker 14. Pacemaker 14 includes a pulse generator 202, cardiac electrical signal sensing circuitry 204 (also referred to herein as "sensing circuitry 204"), control circuitry 206, memory 210, telemetry circuitry 208, and power supply 214. Figure 3The circuits represented herein may be combined on one or more integrated circuit boards, which include: application-specific integrated circuits (ASICs), electronic circuits, processors (shared, dedicated, or grouped) and memories that execute one or more software or firmware programs, combinational logic circuits, state machines, or other suitable components that provide the described functions.

[0044] Cardiac electrical signal sensing circuit 204 is configured to receive cardiac electrical signals via electrodes 20 and 22 through pre-filter and amplifier circuitry 220. The pre-filter and amplifier circuitry may include a high-pass filter for removing DC offset, such as a 2.5 to 5 Hz high-pass filter, or a broadband filter with a passband of 2.5 Hz to 100 Hz to remove DC offset and high-frequency noise. Pre-filter and amplifier circuitry 220 may further include an amplifier to amplify the “raw” cardiac electrical signal passed to analog-to-digital converter (ADC) 226. ADC 226 may pass a multi-bit digital electrogram (EGM) signal to control circuitry 206 for detecting cardiac events and determining a patient’s heart rhythm. The digital signal from ADC 226 may be passed to rectifier and amplifier circuitry 222, which may include a rectifier, a bandpass filter, and an amplifier for passing the filtered and rectified cardiac electrical signal to cardiac event detector 224.

[0045] The cardiac event detector 224 may include a sensing amplifier or other detection circuitry that compares the input rectified cardiac electrical signal with an R-wave detection threshold amplitude, which may be automatically adjusted. When the input signal crosses the R-wave detection threshold, the cardiac event detector 224 generates an R-wave sensing event signal that is passed to the control circuitry 206. The R-wave sensing event signal passed from the cardiac event detector 224 to the control circuitry 206 can be used to schedule ventricular pacing pulses via the pacing timing circuitry 242 to determine the ventricular rate interval, or RR interval (between two consecutively received R-wave sensing event signals). The control circuitry 206 can determine the intrinsic heart rate from the RR interval.

[0046] Control circuit 206 includes pacing timing circuit 242 and processor 244. Control circuit 206 can receive R-wave sensing event signals and / or digital cardiac electrical signals from sensing circuit 204 for detecting and confirming cardiac events and controlling ventricular pacing. For example, the R-wave sensing event signal can be passed to pacing timing circuit 242 to suppress scheduled ventricular pacing pulses. Pacing timing circuit 242 (or processor 244) can receive R-wave sensing event signals from cardiac event detector 224 to control the timing of pacing pulses delivered by pulse generator 202 and to determine the intrinsic heart rate when pacemaker 14 is not delivering pacing pulses.

[0047] Control circuit 206 can retrieve programmable pacing control parameters, such as pacing pulse amplitude and pacing pulse width, which are passed to pulse generator 202 for controlling the delivery of pacing pulses from memory 210. In addition to providing control signals to pacing timing circuit 242 and pulse generator 202 to control pacing pulse delivery, control circuit 206 can also provide sensing control signals to sensing circuit 204 (e.g., R-wave sensing threshold, sensitivity, and / or various blanking and refractory intervals applied to the cardiac electrical signal).

[0048] Pulse generator 202 generates an electrical pacing pulse (RV) delivered to the patient's heart via cathode electrode 22 and return anode electrode 20. Pulse generator 202 may include a charging circuit 230, a switching circuit 232, and an output circuit 234. Charging circuit 230 may include a holding capacitor that can be charged to the pacing pulse amplitude at a multiple of the battery voltage signal of power supply 214 under the control of a voltage regulator. The pacing pulse amplitude can be set based on a control signal from control circuit 206. Switching circuit 232 can control when the holding capacitor of charging circuit 230 is coupled to output circuit 234 for delivering the pacing pulse. For example, switching circuit 232 may include a switch activated by a timing signal received from pacing timing circuit 242 when the pacing interval expires and remaining closed for a programmed pacing pulse width to allow the holding capacitor of charging circuit 230 to discharge. During the programmed pacing pulse duration, the holding capacitor, pre-charged to the pacing pulse voltage amplitude, discharges between electrodes 20 and 22 via the output capacitor of output circuit 234. Examples of pacing circuitry systems generally disclosed in U.S. Patent No. 5,507,782 (Kieval et al.) and in commonly assigned U.S. Patent No. 8,532,785 can be implemented in pacemaker 14 to charge pacing capacitors to a predetermined pacing pulse amplitude under the control of control circuitry 206, thereby generating and delivering pacing pulses.

[0049] The pacemaker 14 may include sensors 212 for generating physiological signals, which are used by control circuitry 206 to monitor patient-related variables. For example, sensor 212 may include a motion sensor such as an accelerometer for detecting cardiac motion and / or motion caused by the patient's physical activity. Alternatively, sensor 212 may include pressure sensors, optical sensors, acoustic sensors, temperature sensors, pH sensors, or any combination thereof. Control circuitry 206 can derive numerical values ​​of the patient's condition from the signals received from sensor 212 according to a monitoring protocol.

[0050] Control circuitry 206 is configured to monitor one or more patient-related and / or device-related variables. As examples, variables that may be monitored by control circuitry 206 include the battery voltage of power supply 214, pacing electrode impedance, pacing capture threshold determined by performing a pacing capture threshold test, the percentage of pacing pulses delivered from all pacing and sensing events, the number of detected premature ventricular contractions (PVCs) or the number of PVC runs, the number of atrial arrhythmia episodes or atrial arrhythmia loads, the percentage of time pacing at the rate-response rate, the percentage of time pacing at a programmed lower rate, the percentage of time at resting physical activity level, blood oxygen saturation, or blood pressure. Control circuitry 206 can monitor variables by detecting or determining their values ​​according to a predetermined schedule or pattern stored in memory 210. The values ​​of the monitored device-related variables may be determined by circuitry included in pacemaker 14, for example, for measuring the voltage of the battery included in power supply 214. The values ​​of monitored patient-related variables can be determined using signals from sensor 212 or cardiac electrical signal sensing circuitry 204, such as those used to determine blood oxygen saturation, blood pressure, cardiac impedance, pacing capture threshold, or other patient-related variables. It is understood that pacemaker 14 can monitor multiple types of variables on a weekly, daily, hourly, or higher or lower frequency basis, or on a trigger-based basis. The methods disclosed herein for transmitting values ​​of monitored variables via pacing rate interval modulation are not limited to any particular type of monitored variable.

[0051] Control circuit 206 is configured to convert the numerical value of a monitored variable into a data sequence of modulated pacing rate intervals. In some instances, the modulated pacing rate intervals may correspond to a binary sequence of zeros and ones. For example, the binary representation of the monitored variable's numerical value can be converted into a modulated pacing rate interval data sequence by converting all zeros in the binary representation of the numerical variable's value to a first pacing interval and all ones in the sequence to a second distinct pacing interval. For example, for each zero in the sequence, the pacing pulse interval can be set to 700 milliseconds. For each one in the sequence, the pacing pulse interval can be set to 800 milliseconds. When using a ternary encoding scheme, three pulse intervals, such as 700, 750, and 800 milliseconds, can be used. Four pulse intervals (e.g., 700, 750, 800, and 800 millisecond intervals) can be used to convert the numerical value of the monitored variable into a sequence of pacing intervals representing quaternary values, etc. When using a higher radix system to convert variable numerical values ​​into modulated pacing intervals, fewer modulated pacing intervals may be needed to encode the numerical values ​​in the sequence of modulated pacing intervals. For example, compared to binary encoding schemes, quaternary encoding schemes may require half the number of modulation pacing intervals to encode the values ​​of monitored variables.

[0052] In other instances, control circuitry 206 converts the value of a monitored variable into a modulated pacing rate interval by setting the modulated pacing rate interval to a fixed pacing interval (the number of intervals equals the digit of the numerical value). For example, if the numerical value is 6, the pacing rate interval is set to a fixed rate interval for 6 pacing cycles to transmit the value "6". Multiple sets of pacing rate intervals can be delivered for transmitting multi-digit numerical values, where the number of pacing rate intervals in each set equals the value of one digit of the multi-digit numerical value.

[0053] Control circuit 206 establishes a sequence of modulated pacing rate intervals representing the values ​​of monitored variables by controlling pacing timing circuit 242 to set a timer or control signal according to the modulated pacing rate intervals. Based on the modulated pacing rate interval sequence, pulse generator 206 responds to the signal received from pacing timing circuit 242 by generating and delivering therapeutic pacing pulses, for example, pacing pulse amplitude and pulse width that capture myocardial tissue to generate pacing-induced depolarization. In various instances, the modulated pacing rate interval sequence may include a header containing one or more pacing pulses delivered at one or more intervals, indicating that subsequent pulses are being delivered at modulated pulse intervals to transmit one or more monitored data values. The modulated pacing rate interval sequence may be repeated once or multiple times to increase the likelihood that the HRM40 will successfully detect and demodulate the modulated heart rate. Other examples of the modulated pacing rate interval sequence and related techniques are described below.

[0054] Memory 210 may contain computer-readable instructions that, when executed by processor 244 of control circuitry 206, cause control circuitry 206 to perform various functions belonging to pacemaker 14 throughout this disclosure. The computer-readable instructions may be encoded within memory 210. Memory 210 may contain any non-transitory computer-readable storage medium, including any volatile, non-volatile, magnetic, optical, or electrical medium, such as random access memory (RAM), read-only memory (ROM), non-volatile RAM (NVRAM), electrically erasable programmable ROM (EEPROM), flash memory, or other digital media. According to the technology disclosed herein, memory 210 may store timing periods and other data used by control circuitry 206 to control the delivery of pacing pulses via pulse generator 202.

[0055] Power supply 214 can be with Figure 2 The battery subassembly 16 shown corresponds to and provides power to each of the other circuits and components of the pacemaker 14 as needed. The power source 214 may include one or more energy storage devices, such as one or more rechargeable or non-rechargeable batteries. For clarity, the connections between the power source 214 and other pacemaker circuits and components are not shown in the diagram. Figure 3 As shown in the text, but should be obtained from... Figure 3 The overall block diagram is understood as follows. For example, power supply 214 can provide power to charging circuit 230 to charge the holding capacitor to the pacing voltage amplitude as needed, and to supply current to switch 232 and other circuitry included in pulse generator 202 to generate and deliver pacing pulses. Power supply 214 also provides power to telemetry circuit 208, sensing circuit 204 and sensor 212, and memory 210 as needed.

[0056] The pacemaker 14 may optionally include telemetry circuitry 208, which includes a transceiver 209 and an antenna 211 for transmitting and receiving data, for example, via a radio frequency (RF) communication link with an external programmer or home monitor. For example, telemetry circuitry 208 may be used to transmit large amounts of data and to receive programming commands for setting programmable pacing and heart sensing parameters. For example, when the external device 50 is a programmer or home monitor for transmitting programming commands to and retrieving data from the pacemaker 14, telemetry circuitry 208 may be able to communicate with the external device 50 (…). Figure 1 Two-way communication is enabled. Cardiac electrical signals, marker channel data depicting the timing of cardiac event sensing and pacing, currently programmed parameters, or other data can be transmitted from the telemetry circuit 208 to the external device 50. Programmable control parameters and programming commands used to control cardiac electrical signal sensing and cardiac pacing can be received by the telemetry circuit 208 and stored in the memory 210 for access by the control circuit 206.

[0057] The functions attributed to pacemaker 14 herein may be embodied in one or more processors, controllers, hardware, firmware, software, or any combination thereof. Describing different features as specific circuit systems is intended to highlight different functional aspects and does not necessarily imply that such functions must be implemented through separate hardware, firmware, or software components or through any particular circuit architecture. Rather, the functions associated with one or more circuits described herein may be performed by separate hardware, firmware, or software components, or integrated within general-purpose hardware, firmware, or software components. For example, pacing rate modulation operations performed by pacemaker 14 may be implemented in control circuitry 206, which executes instructions stored in memory 210 to control pulse generator 202.

[0058] As disclosed herein, the operation of the circuitry contained in pacemaker 14 should not be construed as reflecting a specific form of hardware, firmware, and software necessary to reflect the technology described in practice. It is believed that the specific form of the software, hardware, and / or firmware will be determined primarily by the specific system architecture employed in pacemaker 14 and the specific sensing and therapy delivery circuitry employed in pacemaker 14. Given the disclosure herein, providing software, hardware, and / or firmware to perform the described functions in the context of any modem IMD is within the capabilities of those skilled in the art. Figure 3 The functions and components described for performing cardiac pacing rate modulation to transmit values ​​of monitored variables can generally be included in any IMD or wearable medical device configured to provide electrical stimulation therapy, thereby generating depolarization or activation of excitable tissue at a modulated rate.

[0059] Figure 4 It is based on an instance. Figure 1 A conceptual diagram of the HRM 40. The HRM 40 can take various forms, but is typically an implantable or wearable device equipped with a sensor for generating a pulsatile signal with a frequency related to heart rate, and a processor for detecting heart rate from the signal and demodulating the detected heart rate into values ​​of variables monitored by pacemaker 14. Figure 1 In one example, the HRM 40 is shown as a smartwatch but can be configured as a wearable strap, belt, or patch, such as a chest band, armband, wristband, headband, or other wearable device like an earpiece. The HRM 40 may include a heart rate sensor 102, a processor 104, a memory 106, communication circuitry 108, an alarm circuitry 110, a power supply 112, a display 114, and a user interface 116. In other examples, the HRM 40 may not include a display 114 and a user interface 116 but may be capable of monitoring heart rate and communicating via communication circuitry 108. Or other RF wireless communication transmission of data values ​​demodulated from heart rate data. An example of an implantable HRM that can be included in the disclosed system, as previously indicated, is Reveal, available from Medtronic Ltd., Minneapolis, Minnesota. An insertable cardiac monitor. In other instances, the HRM can be an implantable or wearable medical device that, in addition to having the ability to detect the depolarization or contraction rate generated by electrical stimulation pulses produced and delivered by another medical device, also has therapeutic delivery capabilities. Such devices can include pacemakers, implantable cardioverter defibrillators, neurostimulators, drug delivery pumps, etc. Although in Figure 4 Therapeutic delivery circuitry or modules are not shown, but it should be understood that the functions attributed to HRM 40 can be included in circuits other than those described above. Figure 4In medical devices with additional components besides those shown, these components may include circuitry systems and components for generating or delivering therapy.

[0060] Power supply 112 supplies power to processor 104, heart rate sensor 102, and other circuitry of HRM 40 as needed. Power supply 112 may include one or more rechargeable or non-rechargeable batteries. Heart rate sensor 102 may include electrodes for receiving electrical signals generated by the patient's heart, and circuitry for sensing R waves accompanying ventricular depolarization to detect a heartbeat. In other examples, heart rate sensor 102 may include optical sensors and circuitry for determining heart rate using photoplethysmography (PPG), a bioimpedance sensor for detecting heart rate from periodic changes in tissue impedance, or another sensor capable of generating a pulsatile signal associated with the patient's heart rate.

[0061] Processor 104 determines the patient's heart rate based on signals received from heart rate sensor 102. Processor 104 can determine the heart rate by: detecting and counting individual pulses of a pulsation signal within a predetermined or variable time interval; timing the intervals between consecutive pulses of the pulsation signal; performing a Fast Fourier Transform (FFT) within a predetermined time interval to determine the frequency of the pulsation signal; or other techniques for detecting the patient's heart rate from the heart rate sensor signal. Processor 104 can execute instructions stored in memory 106 for determining the heart rate and for demodulating the heart rate intervals to determine the numerical values ​​of the monitored variable data transmitted from pacemaker 14 via heart rate modulation. HRM 40 can be configured to monitor the user's heart rate continuously, at specified times of day, at regularly scheduled time intervals, or according to a predetermined monitoring scheme that can be customized for a given patient. An application program can be stored in memory 106 for execution by processor 104 each time a heart rate is determined to detect one or more heart rate intervals, the one or more heart rate intervals being known to be contained in an encoding scheme for establishing a sequence of modulated pacing rate intervals.

[0062] Processor 104 can determine one or more values ​​corresponding to a corresponding number of monitored variables by demodulating the heart rate intervals, and can display a notification to the user on display 114 to inform the user that new data is available for viewing. In some instances, processor 104 can transmit the determined values ​​to another device, such as external device 50 or another implantable or wearable medical device, via communication circuitry 108. Communication circuitry 108 includes a wireless transceiver for transmitting and receiving radio frequency signals. For example, communication circuitry 108 may be for transmitting and receiving data from external device 50. Enable the device. In this way, pacemaker 14 can transmit values ​​of device-related and / or patient-related variables to HRM 40 using only modulated pacing rate intervals, without pacemaker 14 performing wireless radio frequency communication transmission and associated power consumption, and without interrupting cardiac pacing.

[0063] In some instances, processor 104 may compare a determined numerical data value with a threshold or range and generate an alarm or notification via alarm circuitry 110 to inform the user of the corresponding status of the monitored variable, such as whether it is within or outside the normal range. When the monitored variable value is outside the normal range, the user may be alerted and advised to contact their physician or seek medical attention. Alarm circuitry 110 may generate a vibration or audible sound to alert the user, and / or may generate a visual display via display 114 to notify the user that the numerical data value determined based on the modulated heart rate interval is outside the normal range. In other instances, an alarm generated based on a numerical data value may be an indication that pacemaker 14 (or other IMD performing electrical stimulation rate modulation) is changing its therapy delivery mode, stopping therapy delivery, performing a temporary operation, or other status indicator. The alarm may be transmitted to another medical device, which may respond to the alarm by notifying a clinician or altering its own therapy delivery and / or monitoring functions within the medical device system 10.

[0064] HRM 40 may include a user interface 116, which may include a touchscreen, buttons, voice response, or other interfaces or combinations thereof, to enable a user to set user-selectable settings to control notifications and alarms or other functions of HRM 40. User interface 116 and display 114 may be configured to allow the user to select monitored variables and display current and / or historical values ​​of the monitored variables in tabular or graphical format. For example, the user may choose to be notified by HRM 40 whenever new data is available, once a day, or at other selected frequencies. In other instances, the user may choose to be notified by HRM 40 only when the value is outside the normal range. At other times, the user may choose to disable patient notifications related to data values ​​derived from modulated heart rate and only allow the transmission of monitored variable values ​​to another medical device, such as external device 50, another implantable or wearable therapy delivery device, a clinician's computer, telephone or other device, or a central patient management database, etc.

[0065] Figure 5This is a flowchart 300 of a method performed by pacemaker 14 according to one example. Initially, pacemaker 14 may operate in normal pacing mode at block 301, delivering pacing therapy according to programmed therapy control parameters without modulating the pacing rate interval. At block 302, control circuitry 206 determines the value of a monitored variable to be transmitted via heart rate modulation. This value may be determined according to a monitoring protocol, such as once per hour, once per day, once per week, or at longer, shorter, or variable intervals. As described above, the value that may be determined at block 302 may be related to device diagnostic and / or patient-related variables. Various examples of values ​​that pacemaker 14 may transmit via heart rate modulation include, but are not intended to be limited to, pacemaker battery voltage; the percentage of pacing events among all pacing and sensing events within a given time period; impedance measurements; and pacing capture thresholds. The numerical values ​​transmitted via heart rate modulation can typically contain any value, which can be converted to units or multi-bit words in binary, ternary, quaternary, or other base-10 systems, or represented according to the number of pacing intervals (equal to the numerical value in a base-10 number system). In some cases, if the data value cannot be transmitted as a single multi-bit word, it can be converted to multiple bytes. In other instances, the data value can be converted to a set of multiple pacing intervals, each representing a numerical value between a defined range (e.g., 0-9).

[0066] At block 304, control circuitry 206 converts each value into a sequence of modulated pacing intervals. In some instances, the values ​​are determined in a binary number system, where one predetermined pacing interval represents the binary digit "0" and another predetermined pacing interval represents the binary digit "1". The second pacing rate interval representing the binary digit "1" is different from the first pacing rate interval representing the binary digit "0" and can be distinguished from the first pacing rate interval by the resolution of the heart rate monitoring technology and HRM 40. This is achieved by an IMD system (e.g., Figure 1The pacing rate intervals established by system 10 to represent binary "0" and "1" can be selected to be different from pacing rate intervals corresponding to available programmable pacing rates, or at least different from one or more pacing intervals corresponding to normally programmed pacing rates. For example, a normally programmed lower pacing rate of 60 pulses per minute corresponds to a pacing interval of 1000 milliseconds. A pacing interval established for use in rate modulation of data communication using a binary encoding scheme can avoid a 1000-millisecond interval. In one instance, a pacing interval of 700 milliseconds (corresponding to a pacing rate of approximately 86 pulses per minute) can be specified as binary "1" and an 800-millisecond pacing interval (corresponding to a pacing rate of 75 pulses per minute) can be specified as binary "0". In some instances, the selected pacing intervals representing binary "0" and binary "1" can be reserved intervals not programmed in pacemaker 14 for the intended therapeutic pacing rate.

[0067] In other instances, a ternary encoding scheme can be used, where the value of the monitored variable is converted from a first base system (e.g., binary or base-10) to a ternary number system, and then to a sequence of pacing rate intervals representing the values ​​in the ternary number system, where each of the three different pacing rate intervals represents a corresponding "0", "1", or "2" for each digit in the ternary value of the monitored variable. Therefore, in some instances, control circuitry 206 can be configured to convert the value of the monitored variable determined in one number system (e.g., binary or base-10) to a different base system (e.g., ternary or quaternary), and then convert each digit or bit of the converted value to a corresponding predetermined pacing rate interval.

[0068] Each possible value of the numerical value can be selected as a pacing interval, and these intervals can be spaced apart from each other, such that, according to the therapeutic pacing protocol, the beat-by-beat variation between two pacing intervals is clearly identified by the HRM as a communication interval, which is the opposite of the physiological variation of heart rate or the normal variation of pacing rate. For example, in contrast to a series of heartbeats containing only two specified rates (in the case of binary values), where rate variation occurs only between these two specified rates, the expected normal pacing rate variation will gradually increase, gradually decrease, or remain stable.

[0069] In one illustrative example, the value to be transmitted by pacemaker 14 is the pacemaker battery voltage. In one example, the normal range of the battery voltage of power supply 214 can be 2.56V to 3.2V, with 64 possible voltage values ​​reaching the percentile. Each possible voltage value can be identified as a unique six-bit binary value, as listed in Table I below.

[0070]

[0071] Table I. Normal battery voltage values ​​and corresponding six-bit binary values ​​for pacing pulse interval sequences with transitions.

[0072] After determining the battery voltage value as a six-bit binary value, the binary value is converted into a pacing rate interval sequence, as shown in Table I, where each interval represents the digit "0" or the digit "1". Thus, at block 304, after determining the value of the monitored variable in the selected cardinality system, the value is converted into a sequence of modulated pacing intervals, where each interval in the sequence corresponds to a possible value of the digit in the selected cardinality system. Control circuitry 206 can establish a modulated pacing rate sequence at block 306, which includes pacing rate intervals representing numerical values ​​and may include other information. As described below, in addition to modulated pacing intervals representing each numerical value of one or more monitored variables to be transmitted, the modulated pacing rate sequence may also include modulated pacing rate intervals representing headers, footers, and error detection codes. In other instances, the modulated pacing rate intervals may include a sequence of modulated pacing rate intervals indicating the operating state of pacemaker 14, such as therapy mode state, patient state, or other categorical data that can be represented by a predetermined sequence of modulated pacing rate intervals. At block 308, control circuitry 206 waits for a period of time to transmit the modulated pacing sequence. In some instances, the modulated pacing sequence can be delivered without delay as long as the inherent heart rate or the currently delivered therapy rate is less than the minimum pacing rate contained in the modulated pacing sequence. The modulated pacing sequence overspeeds to pace the heart to control the heart rate detected by HRM 40.

[0073] In some cases, control circuit 206 can compare the inherent heart rate determined based on sensing event signals received from sensing circuit 204 with the lowest heart rate associated with the modulated pacing sequence. If the inherent heart rate is faster than the lowest heart rate associated with the modulated pacing sequence, control circuit 206 waits at block 308 until the inherent heart rate drops below the rate of the lowest modulated pacing rate contained in the modulated pacing sequence. For example, the RR interval (RRI) can be determined based on R-wave sensing event signals received from sensing circuit 204. The RRI is the time interval between two consecutively received R waves sensed by sensing circuit 204. Before initiating the modulated pacing rate sequence at block 310, control circuit 206 can wait for the detection of a predetermined safety interval or percentage threshold number of consecutive RRIs greater than the longest modulated pacing rate interval.

[0074] In other instances, control circuitry 206 may wait for a predetermined time of day to initiate a modulated pacing rate sequence. The HRM 40 can be programmed or configured to detect a patient's heart rate at a specified time of day. The pacemaker 14 and HRM 40 can be synchronized for data communication by programming the pacemaker 14 to deliver the modulated pacing rate sequence at a specified time of day or at a specified time interval when the HRM 40 is scheduled to detect heart rate. The pacemaker 14 can be programmed to initiate the modulated pacing rate sequence at a short time delay to ensure that the HRM 40 operates to detect heart rate while the modulated pacing rate sequence is being delivered.

[0075] In some cases, the scheduled time of day may be at night or when the patient is expected to fall asleep. In this way, the expected intrinsic heart rate will be lower than the minimum modulated pacing rate, and due to the overspeed pacing required to deliver the modulated pacing rate sequence, the patient may be unlikely to perceive heart rate fluctuations or any symptoms. When the pacemaker 14 includes an accelerometer or other type of patient physical activity sensor, the control circuitry 80 can detect the time of day and / or detect low patient activity levels, corresponding to inactivity or rest. The modulated pacing rate sequence can be delivered at any time when the patient is expected to rest.

[0076] In some instances, control circuitry 206 can be configured to receive signals from a patient's body movement sensor (e.g., Figure 3 Sensor 212 in the circuit determines the pacing rate indicated by the sensor to provide rate-responsive pacing that automatically adjusts the pacing rate according to the patient's level of physical activity. At block 308, control circuitry 206 can verify that the pacing rate indicated by the sensor is at a programmed lower rate (corresponding to rest) or at least less than the minimum pacing rate included in the modulated pacing sequence. If the pacing rate indicated by the sensor is greater than the minimum pacing rate included in the modulated pacing rate sequence, control circuitry 206 waits for the pacing rate indicated by the sensor to decrease before delivering the modulated pacing rate sequence at block 310.

[0077] In some cases, pacemaker 14 can be configured to detect tachyarrhythmias, such as tachycardia or fibrillation, and can deliver anti-tachyarrhythmic pacing therapy (ATP). If a tachyarrhythmia is being detected and / or ATP or other therapy is being delivered to terminate the tachyarrhythmia, control circuitry 206 waits at block 308 for the heart rhythm to return to a normal sinus rhythm or pacing rhythm at a rate less than the lowest pacing rate contained in the modulated pacing rate sequence. Therefore, control circuitry 206 can be configured to apply one or more requirements at block 308, such as time of day, patient activity level, sensor-indicated pacing rate, intrinsic heart rate, heart rhythm, or any combination thereof, to determine the appropriate time to generate a modulated pacing sequence to transmit one or more monitored variable values ​​via a modulated pacing heart rate.

[0078] When it is time to deliver the modulated pacing rate sequence, at block 310, control circuitry 206 controls pulse generator 202 to schedule and deliver cardiac pacing pulses according to the sequence of modulated pacing rate intervals. After completing the delivery of the modulated pacing rate sequence for transmitting one or more values ​​of one or more monitored variables, pulse generator 202 returns to unmodulated pacing at block 312. The first unmodulated pacing interval after the delivery of the modulated pacing rate interval sequence may be equal to the last unmodulated pacing interval before the modulated pacing sequence. In other instances, the unmodulated pacing interval returning to block 312 may be adjusted due to the last unmodulated pacing interval before the modulated pacing sequence. For example, pacemaker 14 may have already updated the pacing rate indicated by the sensor to provide rate-responsive pacing, and deliver the first pacing pulse after the modulated pacing sequence according to the unmodulated interval set to provide rate-responsive pacing. Typically, by delivering the first unmodulated pacing interval at a rate-smoothed interval, within a threshold difference from the pacing interval at the end of the sequence, abrupt changes in heart rate can be avoided. It is recognized that in some cases, reverting to unmodulated pacing at box 312 may result in a cardiac sensing event without pacing delivery based on programmed pacing therapy control parameters.

[0079] At block 314, control circuitry 206 can determine the pacing rate sequence that should be repeatedly modulated. In some instances, the modulated pacing rate sequence is repeated multiple times, for example, distributed over a 24-hour period, to increase the likelihood that the HRM 40 will detect and correctly demodulate the modulated heart rate. In other instances, the modulated pacing rate sequence can be repeated if an inherent sensing event occurs during the delivery of the first delivery sequence. The inherent heart rate may increase spontaneously, premature contractions may occur, or non-cardiac noise may be over-sensed by sensing circuitry 204 (and by the HRM 40, depending on the heart rate sensor used by the HRM 40). When control circuitry 206 receives one or more sensing event signals from sensing circuitry 204, control circuitry 206 can determine the pacing rate sequence that should be repeatedly modulated.

[0080] When control circuit 206 determines that the modulated pacing rate sequence should be repeated, control circuit 206 returns to block 308 to wait for an appropriate time to repeat the modulated pacing rate sequence, which may be repeated once or multiple times. When further repetition of the modulated pacing rate sequence is no longer needed, control circuit 206 returns to block 302 to continue monitoring one or more variables and determine the next one or more values ​​to be transmitted via pacing rate modulation.

[0081] It is conceivable that when numerical data values ​​are above or below a given threshold or outside a given range, certain device-related and / or patient-related variables monitored by pacemaker 14 may be transmitted only to HRM 40. For example, the battery voltage of power supply 214 may be monitored by control circuitry 206. An optional replacement battery voltage may be established. Based on therapy delivery needs, the optional replacement battery voltage may be a voltage level associated with the limited remaining functional lifespan of power supply 214, such as three months. The battery voltage value may only be transmitted via pacing rate modulation if the value is within a predetermined range (equal to or less than the optional replacement battery voltage). In this example, the battery voltage may be determined periodically, such as once daily, but the indication of the numerical battery voltage value may not be included in the modulated pacing rate sequence unless it has reached or fallen below a threshold relative to the optional replacement battery voltage. In other examples, a modulated pacing rate sequence may be established indicating that the battery voltage is equal to or less than the optional replacement battery voltage and is, in effect, a data flag or warning detected by HRM 40.

[0082] Thus, pacemaker 14 can be configured to monitor multiple device-related and / or patient-related variables, and control circuitry 206 can be configured to determine which data values ​​should be transmitted to HRM 40. Some data values ​​(e.g., those falling within the normal or expected range) may not be transmitted each time they are determined. In some instances, digital data values ​​for a specific monitored variable may be transmitted via pacing heart rate modulation only when they are outside the normal range or represent a change from a threshold indicating a previous data value. In other instances, numerical data values ​​may be transmitted relatively infrequently when within the normal range, such as once a week, and transmitted at an increased frequency, such as once a day, when the numerical data values ​​are close to or outside the normal range. As an example, data values ​​determined at block 302 that do not need to be transmitted to HRM 40 may be stored in pacemaker memory 210 for later transmission, comparison with future measurements to detect trends, or for radio frequency transmission during interrogation sessions with external device 50.

[0083] Figure 6 This is a timing diagram 400 illustrating the delivery of ventricular pacing pulses 402 via pacemaker 14 using modulated pacing pulse intervals 404 and 406 to transmit numerical data values ​​to the HRM. In the example shown, the pacing pulses 402 are delivered according to a sequence of modulated pacing pulse intervals, which include a relatively short pacing pulse interval 404 corresponding to the digit "0" and a relatively long pacing pulse interval 406 corresponding to the digit "1" in a binary encoding scheme. In this example, the HRM is configured to detect a series of heartbeats occurring at modulated rate intervals and demodulate the rate intervals to generate a binary value 000110. The HRM can convert the binary value into a corresponding numerical base value of 10. In the example of the battery voltage in Table I, the digital signal 000110 can be converted into a battery voltage value of 2.62V. The HRM can generate a numerical display and / or transmit the value to another device, such as... Figure 1 The external device 50 is shown. In other instances, the HRM 40 may compare a numerical value to an alarm threshold. As long as the value is within the normal range, the HRM 40 may not take any action. However, if the data value is within the alarm range, the HRM 40 may generate a notification by producing a visual and / or audible alarm. In instances where the HRM 40 includes therapy delivery capabilities such as a pacemaker, ICD, or neurostimulator, the HRM may respond to the numerical value by starting, stopping, or adjusting therapy in response to any changes in therapy delivered by the pacemaker 14. For example, if the battery voltage indicates the service termination voltage of the pacemaker power supply, the HRM detecting the modulated rate interval may activate pacing or other therapy delivery functions to replace therapy no longer delivered by the pacemaker 14.

[0084] Otherwise, the pacing pulses 402 delivered at modulated pacing rate intervals 404 and 406 are the same as those delivered according to pacing therapy. For example, the pacing pulse voltage amplitude, pulse width, polarity, pulse shape, and other characteristics of each ventricular pacing pulse 402 can be kept constant between normal pacing therapy delivery and pacing rate modulation to transmit numerical data values. In some instances, depending on the modulation scheme, the only pacing control parameter that changes during data transmission is the pacing pulse interval, and therefore the pacing rate. Figure 6 Each pacing pulse 402 shown includes the first, leftmost pacing pulse that is delivered as the last pacing pulse delivered before the modulation intervals 404 and 406, and can be delivered according to the same pacing pulse amplitude, pulse width, polarity, and pulse shape or waveform control parameters.

[0085] Figure 7 This is a timing diagram illustrating a modulated pacing rate sequence 410 for transmitting data according to another example. In the pacing rate sequence 410, a header 412 containing one or more pacing pulses transmitted at one or more predefined pacing intervals 414 may be delivered before a modulated pacing cycle representing a numerical data value. The header 412 is a predefined sequence of one or more pacing rate intervals identified by the HRM 40 as an indication that subsequent heart rate intervals contain coded data. The header 412 may be two or more cycles at a single predefined pacing interval, two or more cycles at two or more predefined pacing intervals in a specified pattern, or a single overdrive pacing cycle at a predefined pacing interval. In the example shown, three ventricular pacing pulses are delivered at a fixed header pacing interval 414, which may be the same as or different from pacing intervals 404 and 406, which respectively specify the numbers "0" and "1". Although header 412 is shown with a fixed pacing interval 414, two alternating intervals or other patterns can be used as header sequences that can be recognized by HRM 40. Starting with a modulated pacing rate sequence 410 with header 412 may increase the likelihood that HRM 40 will successfully detect a subsequently modulated heart rate, the header containing one or more pacing pulses delivered according to a predefined header sequence.

[0086] The modulated pacing rate sequence 410 comprises a data sequence 415 of six modulated pacing intervals, wherein the modulated pacing intervals represent digital zeros and ones, as combined with... Figure 6As described. Data sequence 415 may contain one or more pacing cycles, which represent one or more values ​​of one or more monitored variables encoded as pacing intervals according to a rate modulation scheme. Modulated pacing rate sequence 410 may be terminated by a footer 416 that is the same as or different from header 412. Footer 416 follows data sequence 415 to indicate that the modulated pacing rate for data transmission has been completed. Footer 416 may contain one or more pacing cycles at one or more predefined pacing intervals 418 to generate a heart rate over one or more cycles, which can be recognized by HRM 40 as the end of footer 416 and heart rate modulation for data transmission.

[0087] exist Figure 7 In the illustrative modulated pacing sequence 410 shown, header 412, data sequence 415, and footer 416 are shown to be consecutively delivered one after another within the modulated pacing sequence 410. In other instances, one or more pacing cycles with one or more “normal” pacing pulse intervals may be delivered between header 412 and data sequence 415 and / or between data sequence 415 and footer 416. A “normal” pacing pulse interval is a pacing pulse interval applied according to a pacing therapy protocol, as opposed to a pacing pulse interval modulated according to a rate modulation protocol used for delivery. As an example, the normal pacing pulse interval may be a programmed lower rate interval. For example, if the programmed lower rate is 60 pulses per minute, corresponding to 1000 milliseconds, then header and footer pulse intervals 414 and 418 may be delivered at intervals of 850 milliseconds. Modulated pacing data sequence intervals 404 and 406 may be delivered at intervals of 700 and 800 milliseconds. The header 412 and footer 416 can be separated from the data sequence 415 at a lower rate of 60 pulses per minute, with one or more “normal” intervals of 1000 milliseconds.

[0088] When the header precedes the data sequence of modulated pacing rate intervals and / or the footer follows the data sequence of modulated pacing rate intervals, the intervals and / or the number of intervals included in the header or footer may contain information demodulated by HRM 40. For example, header 412 may be delivered based on a unique pattern or number of header pacing intervals 414 that identifies the monitored variable transmitted by data sequence 415. In one instance, three header intervals 414 may indicate that the subsequent data sequence 415 is a battery voltage value. In another instance, five header intervals 414 may indicate that the subsequent data sequence 415 is a pacing capture threshold value. In other instances, two or more distinct pacing intervals may be included in header 412 based on a predefined sequence or pattern identified by HRM 40 as indicating an associated monitored variable.

[0089] Footer 416 can be common to all data sequences, independent of the specific monitored variable being transmitted, and only indicates that the data sequence is complete. In other instances, footer 416 may duplicate header 412 and indicate the monitored variable being transmitted and the completion of the data sequence. In other instances, footer 416 is optional. Following data sequence 415 may be another header, which differs from header 412 in the number of pacing intervals, the duration of the pacing intervals, and / or the pattern of two or more different pacing intervals. This next header is delivered according to a predefined pacing rate interval modulation to indicate what the next monitored variable is, and its value to be transmitted by subsequent data sequences.

[0090] In other instances, a single header 412 may be a sequence of modulated pacing intervals indicating the number and / or type of monitored variables to be transmitted with a corresponding number of subsequent data sequences. For example, the number of pacing intervals 414 included in header 412 may indicate a corresponding number of monitored variables to be transmitted in a similar number of subsequent consecutive data sequences, which may or may not be separated by footer 416 or by one or more separate heartbeats delivered according to a predefined pacing interval or a “normal” pacing interval. For example, three pacing intervals 414 may indicate three monitored variable data values ​​to be transmitted. Three subsequent data sequences may follow, which may or may not be separated by footer 416 or other separate heartbeats. The three subsequent data sequences may be delivered according to a predefined order (e.g., battery voltage, electrode impedance, and pacing capture threshold) and according to a pacing rate modulation scheme.

[0091] In some instances, data sequence 415 may include pacing intervals set according to Cyclic Redundancy Check (CRC), Hamming, or other error detection codes. Therefore, data sequence 415 may include additional pacing cycles modulated into digital "0" or "1" pacing intervals, continuous with the modulation intervals representing numerical data values, to provide error detection bits in the pacing interval stream detected and demodulated by HRM 40. Including error detection codes along with data sequence 415, header 414, and / or footer 416 may increase the likelihood that HRM 40 correctly detects the modulated heart rate and reduce the likelihood that random pacing or inherent heart rate fluctuations appear as modulated heart rates corresponding to the true data.

[0092] Figure 8This is a timing diagram of a modulated pacing rate data sequence 450 according to another example. In this example, the data sequence 450 contains one or more sets of modulated pacing intervals, where each set represents the numerical value of a digit of the transmitted numerical data value. The number of pacing cycles delivered in each set at modulated rate intervals is equal to the numerical value of the given digit. For example, to transmit the value 8, a set of 8 pacing cycles is delivered at a predefined modulated pacing rate interval. To transmit multiple digit values, two or more sets of pacing intervals can be delivered sequentially in order from lowest to highest bit value or from highest to lowest bit value, one set per digit. Each set can be separated from subsequent sets to separate the "digits" by one or more separate heartbeats, which can be "normal" pacing intervals or predefined separate heartbeat pacing intervals, specifically when each set is delivered at the same pacing interval, such as... Figure 8 As shown. When using different pacing interval indicator values ​​for each set, it may not be necessary to separate the heartbeats.

[0093] exist Figure 8 In the illustrative example shown, the value 2.62 is transmitted via data sequence 450. The value 2.62 may represent 2.62 volts, indicating the battery voltage of power supply 214. A first set 420 of two modulated pacing intervals 454 is delivered to indicate the digital value 2 in the highest bit. The pacing intervals 454 are predefined intervals, such as 700 milliseconds, 750 milliseconds, or 800 milliseconds, which may be reserved pacing intervals not used in pacing therapy protocols.

[0094] The first set 420 can be separated from the second set 422 by an interval 456. The separation interval 456 can be a "normal" pacing cycle according to the pacing therapy, for example, a lower rate interval programmed as described above. Alternatively, the separation interval 456 can be a predefined modulated interval, different from the modulated pacing interval 454 used within a given set 420, 422, or 424 of modulated pacing intervals. One or more predefined separation intervals 456 can separate sets 420, 422, and 424 in the data sequence 450.

[0095] The second set 422 of modulation pacing intervals 454 contains six intervals representing the value 6 of the second bit value. The third set 424, separated from the second set 422 by one or more separation intervals 456, contains two modulation pacing intervals 454 representing the median value 2 of the third bit value. From the largest to the smallest bit value, the HRM 40 demodulates the value 2.62 from the data sequence 450.

[0096] As is usually the case above Figure 7As described, the data sequence 450 may begin with a header and / or end with a footer to indicate the start and / or end of the data sequence 450. In this example, the header and / or footer may contain modulation information indicating, for example, the number of data sets represented by the data sequence 450 (i.e., the number of bit values) and / or the order of the bit values ​​from highest to lowest or from lowest to highest.

[0097] Based on the possible range of values ​​for a given monitored variable, the value of a digit in a given location can be inferred by HRM 40 without necessarily being represented by a set of pacing intervals within data sequence 450. For example, since the normal range for battery voltage is 2.56 to 3.20, the set of intervals representing the modulated values ​​of the decimal places and the set representing the values ​​of the percentile places can be included in data sequence 450. The set of intervals representing the modulated values ​​of the quartile places can be omitted. Since any decimal place value of 0.5 or higher must start with a value of 2 in the quartile places, and any decimal place value of 0.2 or lower must start with a value of 3 in the quartile places to span the normal battery voltage range of 2.56 to 3.20, HRM 40 can infer the quartile values ​​based on the decimal place values. Therefore, in some cases, all battery voltages can be transmitted via a data sequence containing two sets of modulated pacing intervals, where each set contains the number of modulated pacing intervals equal to the numerical value of the corresponding decimal or percentile place value. Furthermore, in this example of battery voltage, for instance, when transmitting a set of values ​​from highest to lowest, HRM 40 can interpret a set of individual pacing intervals at modulated pacing rate intervals 454 as decimal digits representing decimal digits, where the decimal digit is the value zero. In other multi-bit data values, a specified number of separation intervals 456 can indicate that a bit value located between two other non-zero bit values ​​is zero. When two consecutive bit values ​​are zero, such as battery voltage 3.00, and the decimal digit to be inferred by HRM 40 is omitted, the values ​​of two consecutive zeros in the decimal and hundredths can be represented by a predefined series of separation intervals 456 delivered with modulated pacing intervals different from those used in sets of pacing intervals such as sets 420, 422, and 424.

[0098] Although they have already combined Figure 6 , 7 Sections 8 and 9 describe two examples of pacing rate modulation used to generate data sequences detected by the HRM 40 as modulated heart rates that can be demodulated into numerical data values. However, it is recognized that many schemes can be envisioned to modulate the pacing rate to represent the numerical value of the monitored variable. Specific modulation schemes can be defined based on the heart rate detection method employed by the HRM 40. For example, in… Figure 6 , 7In the example of 8, it is assumed that the HRM 40 is capable of detecting heart rate beat by beat to distinguish heart rate intervals from one cardiac cycle to the next, thereby detecting the length of each modulated cardiac cycle and distinguishing it from different modulated cardiac cycle lengths and cycle lengths (or heart rates) corresponding to the “normal” pacing intervals of a programmed pacing therapy, or even the inherent heartbeat.

[0099] In other instances, the HRM 40 can detect heart rate by counting PPG pulses, bioimpedance pulses, R waves, or other heart rate sensor signal features that indicate heartbeats within a given time interval, converting the number of counted heartbeats within that time interval into a heart rate. Conversely, the HRM 40 can be configured to determine the time interval in which a predetermined number of sensor signal pulses or R waves occur, and convert said time interval into a heart rate. In still other instances, the HRM 40 can use FFT or other techniques to derive the frequency of the heart rate sensor signal and convert said frequency into a heart rate. In these instances of detecting heart rate within fixed or variable time intervals by counting heartbeats or performing a Fourier transform or other techniques for deriving heart rate from sensor signals, the pacing rate modulation delivery scheme may involve delivering a fixed, modulated pacing rate over a sufficiently long time interval to be detected by the HRM 40 as a modulated heart rate, in conjunction with the above. Figure 6-8 The described heart rate detection is the opposite of a single heartbeat.

[0100] Figure 9 This is a timing diagram 460 based on the pacing rate modulation of another example. Instead of delivering modulated pacing rate intervals for a single pacing cycle to be detected as a modulated heart rate by the HRM 40, modulated pacing rate intervals can be delivered for multiple cycles so that the HRM can detect the corresponding heart rate. In this case, pacing pulses are delivered at modulated pacing rate intervals for a predetermined number of pacing cycles or a predetermined time interval, allowing the HRM 40 to detect the heart rate corresponding to the modulated pacing rate by counting pulses or performing FFT or other frequency analyses within fixed or variable time intervals as described above. For example, during a first data time period 470, a fixed pacing rate at a first modulated pacing rate interval 471 can be delivered by the HRM 40 and detected as the digit "0" (or "1"). The fixed heart rate detected within data time period 470 can be demodulated to a value of a monitored variable or one of its digits. A second modulated pacing rate can be delivered during a second data time period 474 so that it can be detected by the HRM 40 as a different heart rate. The pacing rate interval 475 of the data time period 474 can represent the number "1" (or "0") in a binary encoding scheme or a value assigned to another number system, such as 0, 1, 2, or 3 in a base-4 system.

[0101] Two modulated data time periods 470 and 474 are shown separated by a separation time period 472, which may contain pacing according to a programmed pacing therapy, such as pacing according to a programmed lower rate interval. In other instances, separation time period 472 may contain pacing at a uniquely defined overspeed pacing rate interval 473, different from the modulated pacing rate intervals 471 and 475 of data time periods 470 and 474. The second data time period 474 is followed by another separation time period 472, and the pacing modulation sequence 460 may continue as needed with additional modulated pacing rate time intervals delivered within predetermined time periods to complete the transmission of one or more numerical data values ​​for a corresponding number of monitored variables. In some cases, separation time period 472 may contain an inherent heartbeat, for example, occurring at a rate faster than the programmed lower rate but slower than the modulated pacing rate intervals 471 and 475.

[0102] use Figure 9 The total time required to transmit the value of a single monitored variable using this technology, and the number of modulation pacing cycles, can be greater than... Figure 6 , 7 The instances of 8 are longer; however, depending on the heart rate detection method employed by HRM 40, longer time periods with fixed modulation intervals may be required. Time periods 470, 472, and 474 can be set long enough to cover the entire sampling interval used by HRM 40 to detect a heart rate. For example, if HRM 40 samples the heart rate sensor signal every 2 seconds to determine a heart rate value, the length of each data time period 470 and 474 can be 4 seconds or longer to facilitate reliable detection of the corresponding heart rate by HRM 40 sampling once every 2 seconds. Control circuitry 206 can extend data time periods 470 or 474 in response to an inherent increase in heart rate during said time periods. For example, if control circuitry 206 receives one or more R-wave sensing event signals from sensing circuitry 204 during time period 470, time period 470 can be increased to three times the sampling interval, such as 6 seconds, to cause HRM 40 to discard a rate in an unexpectedly varying sampling interval. Figure 6-9 Any of the presented pacing rate modulation examples, or combinations or variations thereof, can be used in accordance with the modulated pacing rate delivery scheme. Figure 5 It is executed during the process.

[0103] Figure 10This is a flowchart 500 of a method, performed by HRM 40, for detecting heart rate and demodulating the detected heart rate to determine numerical data values, according to one example. At block 502, HRM 40 uses heart rate detection technology implemented in HRM 40 to determine the heart rate according to a heart rate monitoring scheme. For example, HRM 40 can be configured to detect the heart at a scheduled time of day, at predetermined time intervals, or on a continuous basis. To detect the modulated heart rate resulting from the modulated pacing rate sequence delivered by pacemaker 14, HRM 40 can determine the time interval between consecutive pulses or heartbeats detected by the heart rate sensor implemented in HRM 40, i.e., the cardiac cycle length. For example, when HRM 40 includes electrodes for sensing ECG signals, RRI can be determined by HRM 40, or when HRM 40 includes an optical sensor for PPT, the cardiac cycle length between pulse peaks can be determined. In other examples, HRM 40 can use FFT or other techniques to detect heart rate within a sampling interval.

[0104] At box 454, HRM 40 determines whether a heart rate corresponding to a modulation used for data transmission is detected. The processor 104 of HRM 40 can compare the individual heart rate intervals or detected heart rates with the pacing rate of the modulation established for data transmission. The modulated pacing rate corresponding to the pacing rate interval used by pacemaker 14 can be stored in the memory 106 of HRM 40 for comparison with the detected heart rate to identify the modulated heart rate. For example, a heart rate corresponding to a modulated pacing rate interval established as a digit "0" or a digit "1" or a known header interval can be detected within one or more cardiac cycles or heart rate sampling intervals. If no heart rate corresponding to a modulated pacing rate interval is detected at box 504, HRM 40 does not search for another modulated heart rate and returns to box 502 to monitor the heart rate according to the heart rate monitoring scheme.

[0105] In some instances, at box 503, when no heart rate corresponding to the modulated pacing rate is detected, HRM 40 can compare the detected heart rate to a threshold rate. If the heart rate detected at box 503 is less than a low threshold rate or greater than a high threshold rate, HRM 40 can maintain enabled heart rate detection while waiting for the modulated heart rate by returning to box 504 to continue heart rate detection per beat or per sampling interval. In some cases, very low or very high heart rates, such as less than 40 beats per minute or greater than 140 beats per minute, or other established thresholds applicable to the patient, may indicate a worrying condition. Pacemaker 14 can be configured to transmit one or more patient-related and / or device-related monitoring variables that can be used to detect or diagnose serious patient conditions associated with low or high heart rates that warrant medical care. It is intended to transmit important patient-related or device-related monitoring variables so that HRM 40 can maintain the ability to detect the modulated heart rate when an abnormal heart rate is detected.

[0106] If a heart rate corresponding to a modulated pacing rate interval is detected at box 504, processor 104 determines the heart rate for subsequent consecutive cardiac cycles, beat-by-beat, or subsequent heart rate sampling intervals based on the implemented heart rate detection technique. Continuous heart rates can be determined until a threshold number of detected heart rates does not correspond to a modulated pacing rate interval. For example, a heart rate may be detected once or multiple times (over one or more cardiac cycles or sampling intervals) corresponding to a lower pacing rate or otherwise mismatching a modulated pacing rate interval defined by the modulation scheme. When performing non-modulated heart rate detection for a threshold number, HRM 40 may or may discontinuously continue determining the heart rate, for example, over consecutive cardiac cycles or consecutive sampling intervals, depending on the normal heart rate monitoring scheme performed by the HRM. In some instances, HRM 40 detects modulated heart rates at box 504 by detecting a header containing one or more modulated rate intervals, such as in conjunction with... Figure 7 As described, a continuous heart rate (per heartbeat or within a continuous sampling interval) can be determined until a threshold number of unmodulated heart rates are detected, until a predetermined number of expected modulated heart rates are detected based on information contained in the header, or until the footer is detected.

[0107] When a modulated heart rate is detected at box 504 or after a complete modulated heart rate sequence is detected, processor 104 demodulates the heart rate sequence by converting each heart rate into a corresponding value according to an encoding scheme. For example, the length of each individual cardiac cycle (e.g., corresponding to...) Figure 6 The data sequence in the data can be converted into binary "0" or "1" to determine the binary word of the number (based on 10) value of the monitored variable. In other instances, HRM detects a set of cardiac cycle lengths (e.g., corresponding to...). Figure 8The HRM 40 converts the number of cardiac cycles into a numerical value for the monitored variable (data sequence). In other instances, the HRM 40 converts the heart rate detected within one or more sampling intervals into a corresponding binary value (or other base system). It converts consecutive cardiac cycles, sets of cardiac cycles, or sampling intervals into corresponding numerical values.

[0108] At box 508, HRM processor 104 can be configured to acknowledge received data, which may include error detection codes as previously described. Header and / or footer detection can be used to verify that the demodulated data sequence is valid. For example, if the header indicates that a specific monitored variable data value is being transmitted, but a subsequently detected and demodulated heart rate does not correspond to a valid value for the monitored variable (e.g., outside the specified range of possible values), HRM processor 104 can determine that the value is invalid. In other instances, HRM 40 can be configured to detect outliers for monitored variables. For example, if a demodulated value of a monitored variable is within the range of possible values ​​but exceeds a threshold change from a previous value, HRM 40 can mark the data value as a possible outlier. If the next value of the monitored variable received after the marked value is within a threshold change from the first previous value, the intermediate marked data value can be considered an outlier and treated as a false or invalid data value.

[0109] HRM 40 can provide various responses to demodulated data values. In some instances, at box 510, the numerical data value is compared to alarm criteria. The numerical data value can be compared to an alarm range that indicates a recommendation for medical follow-up. If the alarm criteria are met, as determined at box 512, HRM 40 can generate a display of the data and / or generate an audible, visual, or other sensory alarm, such as vibration, at box 514 to notify the patient to follow up with their clinician.

[0110] In some instances, HRM 40 can be configured to adjust the settings of the IMD system (e.g., Figure 1The system 10 shown delivers the therapy. The HRM 40 can be configured to adjust the therapy directly or via transmission to another medical device included in the IMD system. For example, when the HRM is implemented as an ICD, the ICD can enable pacing to replace the pacing provided by pacemaker 14 when the monitored battery voltage value meets an alarm criterion or other therapy adjustment criterion. When the battery voltage reaches a threshold level (e.g., an optional replacement voltage or service termination voltage), the HRM can determine that the pacing therapy delivered by pacemaker 14 can be stopped or adjusted to an energy-efficient pacing mode. The HRM can adjust its own pacing mode or other therapies based on the demodulated values ​​of the monitored variables. In other instances, at block 515, the HRM can, for example, transmit therapy adjustment commands to another medical device via external device 50 to generate therapy delivery adjustments.

[0111] In another example, at box 515, when the value of a monitored parameter is demodulated to indicate that pacemaker 14 may be performing a temporary operation, the HRM can respond to the demodulated value by adjusting therapy delivery. For example, the transmitted value of the pacing capture threshold could be an indication that pacemaker 14 will perform a pacing capture threshold test. The HRM can adjust pacing therapy, heart rhythm monitoring, or other functions of the HMD system to avoid interfering with capture tests or obfuscating heart rhythm monitoring results. Thus, the HRM can adjust its own operation or generate commands or notifications that require adjustment by another medical device included in the HMD system in response to the demodulated value of the monitored variable.

[0112] In other instances, the need for adjustments to system operation can be based on any categorized data transmitted according to a predefined sequence of modulated pacing rate intervals. For example, the current pacing mode of pacemaker 14 can be demodulated by the HRM based on the modulated heart rate, and at block 515, the pacing mode of the HRM or another medical device can be adjusted based on the current pacing mode. For example, when the HRM is an extravascular ICD, when the pacing mode of pacemaker 14 changes, for example due to a low battery voltage, the ICD can activate antitachycardia therapy, backup pacing therapy, or other pacing therapies previously delivered by pacemaker 14.

[0113] At box 516, each time data is received, regardless of whether alarm criteria are met and / or whether system operation adjustments are required, the HRM 40 can generate a notification that new data is available. Users can view the data using an application programmed into the HRM 40. The application can allow users to open a window displaying the new data value, such as a graph or table, which may include historical data and / or indicators of the normal range for the displayed numerical data values.

[0114] At box 518, HRM 40 can, for example, be accessed via... The connection transmits data values ​​to a patient monitor or external device, such as external device 50, or to a centralized patient monitoring database. The transmitted data values ​​can exclude data values ​​identified as out of range or spurious values ​​identified at box 508. In some instances, HRM 40 can transmit detected modulated heart rate or heart rate intervals without demodulating the heart rate or heart rate intervals prior to transmission. Demodulation can be performed by a receiving device, such as external device 50 or another pacemaker, implantable cardioverter defibrillator, or other medical device or centralized database. In this way, HRM 40's... The function can be used to transmit data from pacemaker 14 without pacemaker 14 having or utilizing it. Or other RF transmission functions, thereby saving space and / or power consumption of pacemaker 14.

[0115] Figure 11 It is based on another instance. Figure 1 The flowchart 600 shows the method executed by system 10. In some instances, pacemaker 14 may determine that a query session is needed (block 602) and, at block 604, modulate the pacing rate according to the query command code. For example, pacemaker 14 may determine that a query session is needed based on a regular schedule stored in memory 210, such as once a day, once a week, etc. The query session is scheduled to retrieve data from pacemaker 14 using wireless RF transmission via an external device (e.g., HRM 40 or external device 50). Control circuitry 206 may determine at block 602 that a query session is needed at the scheduled time and, at block 604, modulate the pacing rate according to the query command code. In other instances, control circuitry 206 may determine at block 602 that a query session is needed because the scheduled query session has expired or the expected query session has not yet occurred. Control circuit 206 may transmit an interrogation command code to HRM 40 without modulating the pacing rate at block 604, unless the expected interrogation session has not occurred or has expired for at least a threshold time interval, such as 8 hours, 24 hours or other threshold time intervals.

[0116] In other instances, pacemaker 14 may determine at block 602 the need for an interrogation session in response to the detection of a patient-related event or a device-related event. For example, pacemaker 14 may detect an arrhythmia, a change in pacing impedance or capture threshold, out-of-range monitoring parameters, or other events that warrant medical care. As described in the various examples given above, in response to an event that warrants data transmission via wireless RF transmission (as opposed to pacing rate modulation only), at block 604, control circuitry 206 may modulate the pacing rate according to an interrogation command code to initiate the interrogation process. The modulated pacing rate used to transmit the interrogation command code at block 604 may be repeated multiple times until telemetry circuitry 208 receives an RF interrogation command transmitted from another device.

[0117] At box 610, HRM 40 detects the patient's heart rate. HRM 40 determines whether the detected heart rate corresponds to a modulated heart rate. At box 612, a modulated heart rate is detected based on the detection of a heart rate or heart rate interval, which corresponds to a specified, reserved heart rate or interval of a header or specified pattern used for transmitting or detecting the heart rate or rate interval. When a modulated heart rate is detected at box 612, at box 618, HRM 40 determines the modulated heart rate and compares the modulated heart rate or pattern with an interrogation command code. A predefined reserved heart rate for a predefined number of heartbeats or time intervals, such as 70 heartbeats per minute, may correspond to an interrogation command code. An interrogation command code may be defined based on a specified number of heartbeats or a specified number of heart rate time intervals containing one or more specified heart rates appearing in a specified pattern.

[0118] When no query command code is detected at box 618, the HRM 40 can demodulate the detected modulated heart rate to determine the values ​​of the monitored parameters, as described above. Figure 5-10 As described. When an inquiry command code is detected at box 618, the HRM 40 generates an inquiry alarm at box 620. The inquiry alarm can be a visual display or audible sound generated by the HRM 40 to alert the patient that an inquiry session is needed. The patient can be instructed to respond to the alarm by taking any necessary steps to initiate an inquiry session. For example, the patient may need to open an application on the HRM 40 or external device 50 and / or hold the HRM 40 or external device 50 within a specific proximity to the pacemaker 14 (e.g., within one foot).

[0119] In other instances, the interrogation alerts generated by HRM 40 can be transmitted from HRM 40 to another external device (e.g., Figure 1The signal from the external device 50 shown. The external device 50 can respond to the receipt of an inquiry alarm by automatically initiating an inquiry session at block 620, by transmitting a wake-up command or other signal to the pacemaker 14 to establish a bidirectional communication link with the pacemaker 14. Alternatively, the external device 50 can respond to the receipt of an inquiry alarm transmitted from the HRM 40 by generating a patient alarm, such as a notification on the external device 50's display, a text message, an audible alarm, or other patient notification method. In this case, the patient can be instructed to respond to the alarm from the external device 50 by taking the necessary steps to enable the inquiry session to occur.

[0120] At block 622, external device 50 initiates an interrogation session by establishing a two-way communication link and transmitting an interrogation command to pacemaker 14. In response to receiving the interrogation command at block 606, pacemaker 14 transmits data via wireless RF transmission through telemetry circuitry 208. The data that can be transmitted during the interrogation session may include data that cannot be transmitted solely through pacing rate modulation. Such data can typically include a larger volume of data, such as recorded cardiac electrical signal episodes and labeled channel data, detected rhythms, therapy delivery and sensing control parameters, sensing and pacing data, or other data stored by pacemaker 14 in memory 210, or real-time transmitted cardiac electrical signals.

[0121] When pacemaker 14 is configured to determine the need for an inquiry session and transmit an inquiry command code via pacing rate modulation for HRM 40 detection, the operation of system 10 is improved because power is saved by avoiding frequent wake-ups of pacemaker 14's telemetry circuitry to listen for pings or communication requests from another device. The power required for pacemaker 14 to initiate a communication session by modulating the pacing rate used to transmit the inquiry command is minimal, as it is the same or similar to the power used to deliver pacing therapy. The entire system 10 is further improved because patient compliance is enhanced when retrieving data from pacemaker 14 for clinician review. Increased patient compliance allows clinicians to confirm appropriate pacemaker operation and identify any changes required for sensing and / or therapy operation of pacemaker 14 to best meet the patient's needs. Intracardiac pacemakers such as Figure 1 The reduced size of the pacemaker 14 shown may limit the power available for wireless data transmission, such as through... Furthermore, the implantation depth of the pacemaker within the heart may limit the transmission range of RF signals. The ability of pacemaker 14 to transmit large amounts of data to external devices is improved by first transmitting interrogation commands via pacing rate modulation to subsequently facilitate successful and efficient RF data transmission to external devices placed within the transmission range of pacemaker 14.

[0122] The techniques of this disclosure are described in the following examples.

[0123] Example 1. A method comprising: determining, via an implantable medical device, a value of a monitoring variable monitored by the implantable medical device based on a monitoring protocol; converting the value of the monitoring variable into a data sequence comprising a plurality of modulated stimulation rate intervals via a control circuit of the implantable medical device; and delivering a plurality of electrical stimulation pulses via a pulse generator of the implantable medical device according to the modulated stimulation rate intervals of the data sequence to generate a modulated activation rate of an excitable tissue of a patient corresponding to the modulated stimulation rate intervals, the modulated activation rate being detectable by a rate monitor to demodulate the modulated activation rate to the value of the monitoring variable.

[0124] Example 2. The method according to Example 1, wherein: converting the numerical value into the data sequence includes converting the numerical value into a plurality of modulated cardiac pacing rate intervals; and delivering the plurality of electrical stimulation pulses includes delivering the plurality of electrical stimulation pulses according to the plurality of modulated cardiac pacing rate intervals to generate a modulated heart rate of the patient, the modulated heart rate being detectable by a heart rate monitor.

[0125] Example 3. According to the method of Example 2, converting the value into the data sequence includes: converting the value from a first base system to a second base system, the second base system including a plurality of numbers in the second base system; and converting each number in the second base system into a corresponding modulated pacing interval.

[0126] Example 4. The method according to Example 2 or 3, wherein converting the numerical value into the data sequence of modulated pacing rate intervals comprises: determining a binary value of the numerical value having a predetermined number of digits; and converting the binary value into the sequence of modulated pacing rate intervals by setting at least one pacing interval representing one of the predetermined number of digits, the at least one pacing interval being set to one of a first pacing rate interval representing a binary digit of zero in the binary value and a second pacing rate interval representing a binary digit of one, the first pacing rate interval being different from the second pacing rate interval.

[0127] Example 5. The method according to any one of Examples 2 to 4, wherein converting the numerical value into the data sequence comprising the plurality of modulated pacing rate intervals comprises: setting a number of the plurality of modulated pacing rate intervals to a fixed pacing rate interval, wherein the number is equal to the numerical value of the monitored variable.

[0128] Example 6. The method according to any one of Examples 2 to 5, wherein the value is a multi-digit value and converting the value into the data sequence comprising: converting a first value of a first digit of the multi-digit value into at least one corresponding modulated pacing rate interval; and removing a second value of a second digit of the multi-digit value from the data sequence, wherein the removed second value of the second digit can be inferred from the first value of the first digit of the multi-digit value.

[0129] Example 7. The method according to any one of Examples 2 to 6, wherein delivering the plurality of pacing pulses according to the data sequence comprises: delivering pacing pulses at fixed pacing rate intervals within a time interval to generate a heart rate for the time interval, the heart rate representing a numerical value of the value.

[0130] Example 8. The method according to any one of Examples 2 to 7, wherein converting the numerical value into a data sequence comprises: scheduling a set of consecutive modulated pacing rate intervals, wherein each set of modulated pacing rate intervals includes at least one modulated pacing rate interval representing a single digit of the numerical value; and including at least one separate pacing interval between the consecutive sets, the separate interval being different from the modulated pacing rate intervals in the set of consecutive modulated pacing rate intervals.

[0131] Example 9. The method according to any one of Examples 2 to 8, further comprising: sensing a cardiac event signal by a cardiac electrical signal sensing circuit of the pacemaker; and repeatedly delivering at least a portion of the plurality of pacing pulses according to the data sequence in response to the cardiac event signal being sensed by the cardiac electrical signal sensing circuit during the data sequence.

[0132] Example 10. The method according to any one of Examples 2 to 9, further comprising: detecting a modulated heart rate via a heart rate monitor; determining the value of the monitored variable by demodulating the detected modulated heart rate; and generating a response to the determined value by at least one of: wirelessly transmitting the value to a patient monitoring device, generating a display of the value, generating an alarm, and adjusting the therapy delivery mode of the medical device.

[0133] Example 11. The method according to any one of Examples 2 to 10, further comprising delivering a modulated stimulation rate sequence, the modulated stimulation rate sequence comprising a header containing at least one modulated stimulation rate interval and a data sequence following the header.

[0134] Example 12. The method according to Example 11, further comprising setting the stimulation rate interval of the at least one modulated terminator of the header to indicate information about the data sequence.

[0135] Example 13. The method according to any one of Examples 1 to 12, further comprising delivering at least one error detection stimulus rate interval in the data sequence of the plurality of modulated stimulus rate intervals.

[0136] Example 14. The method according to any one of Examples 1 to 13, further comprising: modulating a plurality of electrical stimulation rate intervals according to an interrogation command code sequence; delivering the modulated plurality of electrical stimulation rate intervals according to the interrogation command code sequence via the pulse generator for detection by the rate monitor; and after delivering the modulated plurality of electrical stimulation rate intervals according to the interrogation command code sequence, receiving an interrogation command from an external device via a telemetry circuit of the implantable medical device, the telemetry circuit being configured to perform bidirectional wireless communication with the external device.

[0137] Example 15. A non-transitory computer-readable storage medium comprising a set of instructions, which, when executed by control circuitry of an implantable medical device, cause the device to: determine a value of a variable monitored by the implantable medical device according to a monitoring scheme; convert the value into a data sequence comprising a plurality of modulated stimulation rate intervals; and deliver a plurality of electrical stimulation pulses according to the data sequence of the modulated stimulation rate intervals to generate a modulated activation rate of a patient’s excitable tissue corresponding to the modulated stimulation rate intervals, the modulated activation rate being detectable by a rate monitor to demodulate the modulated activation rate to the value of the monitored variable.

[0138] It should be understood that, depending on the instance, certain actions or events of any method described herein may be performed in a different order, may be added, combined, or may be excluded entirely (e.g., not all described actions or events are necessary for the practice of the method). Furthermore, in some instances, actions or events may be performed simultaneously rather than sequentially, for example, through multithreaded processing, interrupt handling, or multiple processors. Additionally, for clarity, although some aspects of this disclosure are described as being performed by a single circuit or unit, it should be understood that the techniques of this disclosure can be performed by a combination of units or circuits associated with, for example, a medical device.

[0139] In one or more instances, the described functionality may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functionality may be stored on a computer-readable medium in the form of one or more instructions or code and may be executed by a hardware-based processing unit. The computer-readable medium may include a computer-readable storage medium, which corresponds to a tangible medium, such as a data storage medium (e.g., RAM, ROM, EEPROM, flash memory, or any other medium that may be used to store the required program code in the form of instructions or data structures and that may be accessible by a computer).

[0140] Instructions can 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 arrays (FPGAs), or other equivalent integrated or discrete logic circuit systems. Therefore, the term "processor" as used herein can refer to any of the foregoing structures or any other structure suitable for implementing the techniques described herein. Furthermore, the techniques can be fully implemented in one or more circuit or logic elements.

[0141] Therefore, the IMD system has been presented in the foregoing description with reference to specific examples. It should be understood that the various aspects disclosed herein can be combined in different combinations than those presented in the accompanying drawings. It should be understood that various modifications can be made to the reference examples without departing from the scope of this disclosure and the appended claims.

Claims

1. A medical device system comprising: An implantable medical device, the implantable medical device comprising: Control circuit, the control circuit being configured to: Determine the values ​​of the monitoring variables monitored by the implantable medical device based on the monitoring protocol; and The values ​​of the monitored variables are converted into a data sequence comprising multiple modulated stimulation rate intervals; and A pulse generator configured to deliver a plurality of electrical stimulation pulses according to a header comprising at least one modulated stimulation rate interval and the plurality of modulated stimulation rate intervals of the data sequence, to generate a modulated activation rate of the patient’s excitable tissue corresponding to the at least one modulated stimulation rate interval of the header and the plurality of modulated stimulation rate intervals of the data sequence, the modulated activation rate being detectable by a rate monitor to demodulate the modulated activation rate to the value of the monitored variable.

2. The system according to claim 1, wherein: The implantable medical device is configured to deliver cardiac pacing pulses; The control circuit is configured to convert the numerical value into the data sequence by converting the numerical value into a plurality of modulated cardiac pacing rate intervals; and The pulse generator is configured to deliver the plurality of electrical stimulation pulses as cardiac pacing pulses according to the plurality of modulated cardiac pacing rate intervals to generate the patient's modulated heart rate, which can be detected by a heart rate monitor.

3. The system of claim 2, wherein the control circuitry is configured to convert the numerical value into the data sequence by: Convert the value from a first radix system to a second radix system, the second radix system comprising a plurality of digits in the second radix system; and Each number in the second base system is converted into the corresponding modulated pacing rate interval.

4. The system of claim 2 or 3, wherein the control circuitry is configured to convert the numerical value into the data sequence of modulated pacing rate intervals by: Determine the binary value of the numerical value, the binary value having a predetermined number of digits; and The binary value is converted into the sequence of modulated pacing rate intervals by setting at least one pacing interval representing one of the predetermined number of numbers, the at least one pacing interval being set to one of a first pacing rate interval representing a binary digit of zero in the binary value and a second pacing rate interval representing a binary digit of one, the first pacing rate interval being different from the second pacing rate interval.

5. The system of claim 2 or 3, wherein the control circuitry is configured to convert the numerical value into the data sequence comprising the plurality of modulated pacing rate intervals by: The number of the plurality of modulated pacing rate intervals is set to a fixed pacing interval, wherein the number is equal to the numerical value of the monitored variable.

6. The system of claim 2 or 3, wherein the numerical value is a multi-digit value, and the control circuitry is configured to convert the numerical value into the data sequence comprising the plurality of modulated pacing rate intervals by: The first value of the first digit of the multi-digit value is converted into at least one corresponding modulated pacing rate interval; and The second value of the second number is obtained by removing the second number of the multi-digit value from the data sequence, and the removed second value of the second number can be inferred from the first value of the first number of the multi-digit value.

7. The system of claim 2 or 3, wherein the pulse generator is configured to deliver the plurality of electrical stimulation pulses according to the data sequence: Pacing pulses are delivered at fixed pacing rate intervals within a certain time interval to generate a heart rate for the time interval, the heart rate being a numerical value representing the value.

8. The system of claim 2 or 3, wherein the control circuitry is configured to convert the numerical value into a data sequence by: A set of continuously modulated pacing rate intervals is scheduled, wherein each set of modulated pacing rate intervals includes at least one modulated pacing rate interval representing a single digit of the stated value; and At least one separate pacing interval among the set of continuous modulated pacing rate intervals, the separate pacing interval being different from the modulated pacing rate interval in the set of continuous modulated pacing rate intervals.

9. The system according to claim 2 or 3, wherein The implantable medical device further includes a cardiac electrical signal sensing circuit configured to sense cardiac event signals; and The pulse generator is configured to repeatedly deliver at least a portion of the plurality of electrical stimulation pulses according to the data sequence in response to the cardiac electrical signal sensing circuit sensing cardiac event signals during the data sequence.

10. The system according to claim 2 or 3, further comprising: Heart rate monitor, the heart rate monitor being configured to: Detect the modulated heart rate; The value of the monitored variable is determined by demodulating the detected modulated heart rate; and A response to the determined value is generated by at least one of the following: wirelessly transmitting the value to a patient monitoring device, generating a display of the value, generating an alarm, and adjusting the therapy delivery mode of the system.

11. The system according to any one of claims 1 to 3, wherein the pulse generator is configured to deliver a modulated stimulation rate sequence, the modulated stimulation rate sequence comprising: The header; and The data sequence following the header.

12. The system according to any one of claims 1 to 3, wherein the control circuit is configured to set the stimulation rate interval of the at least one modulated header to indicate information about the data sequence.

13. The system according to any one of claims 1 to 3, wherein the control circuit is further configured to set at least one error detection stimulus rate interval in the data sequence of the plurality of modulated stimulus rate intervals.

14. The system according to any one of claims 1 to 3, wherein: The control circuit is further configured to modulate multiple electrical stimulation rate intervals according to an interrogation command code sequence; The pulse generator is further configured to deliver the modulated multiple electrical stimulation rate intervals according to the interrogation command code sequence for detection by the rate monitor; and The implantable medical device further includes a telemetry circuit configured to communicate wirelessly with an external device in both directions, the telemetry circuit being configured to receive an interrogation command from the external device after delivering the modulated plurality of electrical stimulation rate intervals according to the interrogation command code sequence.

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