Pacemaker and method of operating the same

Abstract

The present invention is directed to a pacemaker 10 for a patient's heart 20 providing activity based pacing and reducing current consumption, the pacemaker comprising a processing unit 120, a detector 126, and a pacing signal generator 124, the processing unit, the detector, and the pacing signal generator being electrically interconnected, the detector being configured to determine a patient activity signal and provide the activity signal to the processing unit, the processing unit being configured to determine a pacing rate based on a currently received activity signal of the detector and a gain value in an adaptive or stabilizing mode, the processing unit being configured to calculate a pacing rate based on the determined pacing rate. and generating a pace control signal based on the most recently adapted gain value and providing the pace control signal to the pacing signal generator; in an adaptive mode, the processing unit is configured to adapt the gain value to a particular patient; the processing unit is configured to remain in the adaptive mode unless at least one stability criterion is met, and to transition to a stabilization mode if the processing unit identifies that the at least one stability criterion has been met; and in the stabilization mode, the processing unit is configured to use a locked gain value determined based on a most recently adapted gain value to determine a pacing rate.

Description

[Technical field]

[0001] The present invention is generally directed to a pacemaker for a patient's heart and a method of operating such a pacemaker, respective computer program products, and computer readable data carriers. [Background technology]

[0002] A pacemaker (or artificial pacemaker) for a patient's heart is a medical device that generates electrical pulses delivered by electrodes connected to or affixed to the pacemaker to cause the patient's myocardial chambers (i.e., atria and / or ventricles) to contract and thus pump blood. By doing so, the device replaces and / or regulates the function of the heart's electrical conduction system. One purpose of a pacemaker is to maintain an appropriate heart rate, either because the heart's natural pacemaker is not fast enough or because the heart's electrical conduction system is impaired. Additionally or alternatively, a pacemaker may stimulate different locations within the ventricles to improve their synchronization or provide defibrillation capabilities to treat life-threatening arrhythmias. Most modern pacemakers are externally programmable, allowing the healthcare professional (HCP) to select the pacing mode that is best suited for an individual patient.

[0003] A conventional pacemaker comprises a control and generator device with a processing unit and power source external to the patient's heart and electrodes implanted within the heart muscle. The electrodes are connected to the device via leads and a header that is placed on the device. In most cases, the device is implanted through the skin on the front of the chest in the area of ​​the left or right shoulder. An implantable intracardiac pacemaker (also called an implantable leadless pacemaker - ILP) is a well-known miniature pacemaker that is fully implanted in the ventricle (V) or atrium (A) of the patient's heart. ILPs are considered to be the future of cardiac pacing. Alternative or additional functions of conventional or intracardiac pacemakers include providing other electrical or electromagnetic signals to the heart or its surrounding tissues and sensing electrical or electromagnetic signals (e.g., signals from an electrical depolarization field) or other physiological parameters of the heart and / or its surrounding tissues, such as intrinsic (i.e., the heart's natural) atrial contractions or intrinsic (i.e., the heart's natural) ventricular contractions. Due to its very limited size, the ILP has a small battery capacity. As a self-contained implantable device, the size of the ILP is less than 1 cm. 3 The battery volume and capacity of a leadless pacemaker are significantly smaller (less than 1 / 10) than that of a conventional pacemaker. To ensure that the lifespan of an ILP is comparable to that of a conventional pacemaker (approximately 10 years or more), it is important to keep the current consumption of all modules / units of the ILP to a minimum.

[0004] In VDD mode, which may be used in conventional pacemakers or in ILPs, the pacemaker synchronizes ventricular pacing with the intrinsic ventricular or atrial timing by sensing when ventricular or atrial contractions occur. Ventricular pacing is then calculated based on the pacing rate, if necessary, and in activity-based rate-responsive pacing algorithms, the actual pacing rate takes into account the patient's current activity. Such algorithms realize the discovery that when a pacemaker-dependent patient is active, the pacing rate must be increased to meet the associated higher metabolic requirements. Thus, when the patient is inactive, the pacing rate must be decreased.

[0005] In a conventional pacemaker with a motion sensor, the activity-based rate-response algorithm uses a scale factor, or gain value, to convert the physical exertion signal derived from the motion signal of the motion sensor (which senses the patient's activity) to a target exertion-modulated pacing rate. The gain value is patient-specific and is automatically adjusted slowly over a period of days to ensure that the generated target rate meets the metabolic requirements of each individual patient. In a conventional pacemaker, if the automatic gain feature is enabled, the rate adaptation algorithm runs continuously, even when pacing of the device is inhibited, and the scale factor of the rate adaptation algorithm is adjusted to meet the unique needs of the patient. Even when the pacemaker is not working in the physical exertion-based rate adaptation mode, the motion sensor and part of the algorithm still run to support updates of the gain value.

[0006] The above methods cause wasteful current consumption. In particular, ILPs, which have very stringent size and power consumption requirements, are challenged by the continuous execution of the rate adaptation algorithm. The current consumption of the motion sensor and the rate adaptation algorithm has a large impact on the lifetime. Furthermore, the known methods are susceptible to random noise in the activity level. If there are unexpected or abnormal days with extremely low or high activity, i.e., days when random noise occurs, the automatic gain value will be adjusted accordingly. And the next day, the gain value corresponding to the abnormal noise will be applied to the rate adaptation algorithm until the gain value is readjusted. Summary of the Invention [Problem to be solved by the invention]

[0007] Thus, a need exists for a pacemaker that provides activity-based pacing but operates with low power consumption. [Means for solving the problem]

[0008] The above problem is solved by a pacemaker comprising the features of claim 1 and an operating method comprising the features of claim 8 as well as a computer program product comprising the features of claim 14 and a computer readable data carrier comprising the features of claim 15.

[0009] Specifically, a pacemaker for a patient's heart is disclosed, comprising a processing unit, a detector, and a pacing signal generator, the processing unit, the detector, and the pacing signal generator being electrically interconnected. The detector is configured to determine a patient activity signal and transmit or provide the activity signal to the processing unit. The processing unit is configured to determine a pacing rate based on a currently received detector activity signal and a gain value in an adaptive mode or a stabilization mode, the processing unit is configured to generate a pace control signal based on the determined pacing rate, and transmit or provide the pace control signal to the pacing signal generator. In the adaptive mode, the processing unit is configured to continuously or incrementally adapt the gain value to a particular patient, the processing unit is configured to remain in the adaptive mode unless at least one stability criterion is met, and to transition to the stabilization mode if the processing unit identifies that at least one stability criterion is met. In the stabilization mode, the processing unit is configured to use a locked gain value determined based on a most recently adapted gain value to determine a pacing rate.

[0010] The processing unit processes signal data received from the detector, e.g., activity signals detected over time, from which the processing unit can determine movement signals, which are described in detail below.

[0011] The pacemaker may be a conventional cardiac pacemaker or an ILP having the general structure shown above.

[0012] An ILP or a conventional pacemaker may operate in VDD pacing mode (i.e., a pacing mode in which the ventricles are stimulated according to atrial activity and AV conduction monitoring). In VDD mode, the pacemaker synchronizes ventricular pacing with the intrinsic atrial timing by sensing when an atrial contraction occurs. An ILP implanted in the right ventricle can detect atrial contraction information as a far-field signal, but this is less reliable and accurate than a dual chamber pacemaker that has a lead in the right atrium as well as the right ventricle. In VDD mode, since there is no atrial pace, the pacemaker relies entirely on synchronizing with the heart's condition, rather than being able to control timing in both chambers as can be done in DDD pacing mode (atrium, ventricle are paced). The processing unit may be configured to detect atrial sensed events (i.e., detected spontaneous atrial contractions) and / or ventricular sensed events (i.e., detected spontaneous ventricular contractions), e.g., by a detector, which may be configured to detect electrical and / or electromagnetic signals, e.g., signals from an electrical depolarization field.

[0013] In the context of the present invention, the processing unit is generally considered to be a functional unit of the pacemaker that interprets and executes instructions, including an instruction control unit and an arithmetic and logic unit. The processing unit may comprise a microprocessor, a controller, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), a discrete logic circuit, or any combination thereof. Additionally, the processing unit may comprise a counter and a clock. The counter may be used to count clock signals of the clock. The counter may be started each time an atrial or ventricular event is sensed and count the number of clock signals until a ventricular sensed event is determined or a ventricular pace signal is provided by the pacing signal generator. The actual pacing rate determined by the processing unit is used to provide a pacing control signal (e.g., a ventricular pace control signal) to the pacing signal generator. The pacing rate may be calculated using the last sensed atrial or ventricular event or the last atrial or ventricular pacing control signal, using the clock signals counted by the counter.

[0014] Based on the pacing control signal, the pacing signal generator generates an electrical pacing signal for delivery to the electrode, which applies the signal to cardiac tissue adjacent the electrode.

[0015] The pacemaker may be equipped with a data memory, which may include any volatile, nonvolatile, magnetic, or electrical medium, such as random access memory (RAM), read only memory (ROM), nonvolatile RAM (NVRAM), electrically erasable programmable ROM (EEPROM), flash memory, or any other memory device.

[0016] The detector comprises an accelerometer, a vibration sensor, an acoustic sensor (including ultrasound), and / or any other mechanical, electrical, and / or magnetic sensor (i.e., a motion sensor) that can detect time-dependent patient activity, such as whether the patient is moving or not moving, e.g. lying, sleeping, sitting, moving fast or moving slowly (including exertion). The detector collects patient activity signals and converts these activity signals into electrical signals. Furthermore, the detector may digitize or smooth analog signals. Some pre-processing steps may be provided by the detector as well. The time-dependent activity signals generated by the detector may be transmitted to a processing unit directly or after a predefined time delay. Furthermore, the detector may comprise means for detecting ECG signals, as indicated above.

[0017] The pacing signal generator generates a pacing signal that is applied to the cardiac tissue via the electrodes. The pacing signal is a pulse that begins at a desired time and has a desired strength and length. Furthermore, the shape of the pulse may be varied. The information about the pacing signal required to generate the correct pacing signal is provided by a pace control signal from the processing unit.

[0018] The pacemaker may comprise further modules such as a communication unit for communicating with a remote computer and a power source such as a battery. The communication unit may exchange messages with an external (at least partially outside the body) remote computer, e.g., unidirectionally or bidirectionally. The communication may be provided wirelessly through the patient's body and / or through the air, e.g., in the radio frequency domain, using Bluetooth, WLAN, ZigBee, NFC, Wibree, or WiMAX, or in the infrared or optical frequency domain, using IrDA or free space optical communication (FSO), or by wires (electrical and / or optical). The remote computer may be a functional unit capable of performing substantial calculations without human intervention, including many arithmetic and logical operations, e.g., a personal mobile device (PMD), a desktop computer, a server computer, a cluster / warehouse scale computer, or an embedded system. The pacemaker units and components may be housed in a hermetically sealed housing.

[0019] In one embodiment, the pacemaker comprises electrodes for applying electrical pacing signals provided by a pacing signal generator. The electrodes are electrically connected to the pacing signal generator via a header of the pacemaker. In one embodiment (i.e., when the pacemaker is a conventional pacemaker), the electrodes may comprise leads that may be removably connected to respective connectors at the header. With respect to the ILP, one electrode may be located at the distal end of the ILP near a fixation member where the ILP is fixed in the tissue of the patient's heart, e.g., in the internal tissue of the ventricle. A second electrode may be located at the proximal end of the ILP or in a part of the ILP housing, and may function, for example, as a counter electrode. Furthermore, the electrodes may be adapted to detect native ventricular or native atrial signals by picking up electrical potentials. Thus, the electrodes may be part of the detector of the pacemaker.

[0020] According to the invention, for example, the processing unit of a pacemaker operating in VDD mode is configured to determine a pacing rate based on a currently received time-dependent activity signal of a detector, for example, a raw accelerometer signal provided by the detector as shown above, and a gain value. The gain value is a scale factor used as a slope to convert a motion signal derived from the detector activity signal into a pacing rate, whereby the pacing rate is adapted to suit the currently sensed patient activity. The amplitude of the activity signal over time is first compared by the processing unit to an activity threshold. Only activity above the motion threshold is used to calculate the pacing rate. If the activity is below the motion threshold, the pacing rate is not updated and the gain value is not affected. In a next step, the integral of the activity signals above the threshold over a pre-determined time period (next integration time period), for example, one second or one minute, is calculated, and the integral value becomes the motion signal mentioned above. If the activity is below the motion threshold, those signals are not integrated and the pacing rate is not updated. A scaled activity value is then derived from the motion signal, where the motion signal is multiplied with a first component (slope) of a gain value, and this product may be added to a second component (offset) of the gain value, if applicable. The scaled activity value so calculated is added to a predetermined base pacing rate to obtain a patient activity-based pacing rate. As indicated above, the gain value may include two components, namely a slope value and an offset value. Alternatively, the gain value may include only a slope value and / or one value for each activity direction in the three-dimensional space, thereby calculating a scaled activity separately for each direction in space. As a further alternative, gain values ​​may be determined for different time period types, e.g., rest days, exertion days, sleep time periods, or activity time periods. The final value of the scaled activity is an absolute value across the three dimensions. If the time period types are different, the scaled activity is calculated separately for each type of time period. The determined scaled activity is then used to determine an activity-based pacing rate, as indicated above.Thus, the gain values ​​may be one-dimensional or multi-dimensional values. Furthermore, the gain values ​​may have one component (slope only) or two components (slope and offset) for each gain value dimension.

[0021] During the adaptive mode, the gain values ​​are continuously or stepwise adapted to the particular patient by the processing unit using the calculations above and based on the description below.

[0022] In one embodiment, the stability criterion is met if the absolute value of the difference between a first average value of the adapted gain values ​​determined within a first time period (hereinafter also referred to as the first window) and a second average value of the adapted gain values ​​determined within a second or following time period (hereinafter also referred to as the second window) is smaller than a pre-determined stability threshold. This means that the stability criterion evaluates the delta between the first average value of the gain values ​​and the second average value of the gain values ​​between two adjacent windows. Here, in one embodiment, the first time period and the second time period are directly adjacent, most recently evaluated time periods. The first time period and the second time period may be several hours, a day or several days and may cover a number of integral time periods as mentioned above. The length of the first time period and the second time period may be identical. The average value may be the arithmetic mean, the geometric mean or the harmonic mean or the median of the gain values ​​determined within the first window or within the second window, respectively. Alternatively or additionally, the stability criterion may be met when the pacing rate is updated in the adaptive mode over a predefined adaptation time period, e.g., 60 days. The preprogrammed or user adaptable (e.g., by a programmer) adaptation time period may be long enough to allow complete adaptation of the gain values ​​and may cover multiple integral time periods. In one example, both stability criteria may be checked continuously and a transition to the stabilization mode is provided by the processing unit if one of both criteria is satisfied.

[0023] In detail, in the adaptive mode, which is the initial mode after a conventional pacemaker is implanted, the gain value is set to a predefined initial value. For safety reasons, the initial gain value is close to the lowest setting to avoid pacing at an excessively high rate. When the rate adaptation algorithm is running in the adaptive mode, the pacing rate is calculated using the activity signal and the actual gain value as shown above. Thus, in the adaptive mode, the target pacing rate and the gain value are adapted simultaneously. Statistics of the pacing rate are calculated and used to automatically adjust the gain value every predefined time period, e.g., daily. Here, in one embodiment, a duration counter is used to record the duration when the activity rate is above a predefined maximum rate threshold. This means that the patient's pacing rate is high and can meet the increased metabolic requirements for the duration of the duration counter. In a balanced scenario, the duration counter should fall within a predefined range, e.g., within 30 to 60 minutes daily. If the duration counter is below the predefined balance (the pacing rate is above the maximum rate threshold for too short a time), the gain is too low and needs to be incremented by one or more set steps. On the other hand, if the duration counter is above the predefined balance (the pacing rate is above the maximum rate threshold for too long), the gain is too high and needs to be decremented by one or more set steps. The purpose of the adjustment is to ensure that the distribution of pacing rates over a period of time meets a defined balance, i.e. the predefined rate balance of the duration counter.

[0024] If the stability criteria described above is reached, i.e., if the processing unit indicates that the average gain value has stabilized, e.g., as described above, the processing unit enters a stabilization mode in which a locked gain value is used to determine a pacing rate from the activity signal provided by the detector. In the stabilization mode, the locked gain value may be the most recently determined average gain value (calculated in the adaptive mode). In the stability mode, the gain value does not change.

[0025] In one embodiment, in the stabilization mode, the processing unit is configured to discontinue or reduce detection of the activity signal by the detector, and the processing unit is configured to determine the motion signal from the reduced activity signal. For example, the activity signal is determined by the detector less frequently, for example only every minute of every second. Furthermore, if an activity-based algorithm is not currently being used in the pacemaker, detection of the activity signal by the detector is discontinued. This can be set by the programmer.

[0026] In one embodiment, the processing unit transitions from the stabilizing mode to the adaptive mode, for example, when the processing unit receives a respective request by the programmer and / or when a predefined third time period, for example six months, has elapsed since transitioning to the stabilizing mode. The operation of the adaptive mode (after returning to this mode) is similar to the first use of the adaptive mode after implantation of the pacemaker, except that in this case the locked gain values ​​are used as the initial gain values ​​for the adaptive mode.

[0027] The above problems are further solved by a method of operating a cardiac pacemaker, the pacemaker comprising a processing unit, a detector, and a pacing signal generator, the processing unit, the detector, and the pacing signal generator being electrically interconnected, a patient activity signal is determined by the detector and sent to the processing unit, a pacing rate is determined by the processing unit based on a current activity signal of the detector and based on a gain value in an adaptive mode or a stabilization mode, a pace control signal is generated by the processing unit based on the determined pacing rate and sent to the pacing signal generator, in the adaptive mode, the gain value is adapted continuously or stepwise to a particular patient, the processing unit remains in the adaptive mode unless at least one stability criterion is met, and transitions to the stabilization mode if the processing unit identifies that at least one stability criterion has been met, and in the stabilization mode, the processing unit uses a locked gain value determined based on a most recently adapted gain value to determine the pacing rate.

[0028] As indicated above, the gain value may be a one-dimensional or multi-dimensional value and may have one component or two components.

[0029] In one embodiment of the operating method, the stability criterion is met when an absolute value of a difference between a first average value of the adapted gain values ​​determined within a first time period and a second average value of the adapted gain values ​​determined within a second time period is smaller than a predetermined stability threshold, where the first time period and the second time period may be immediately adjacent, most recently evaluated time periods.

[0030] In one embodiment, in the stabilization mode, detection of activity signals by the detector is interrupted or reduced by the processing unit, which determines from the reduced activity signals the motion signals as indicated above.

[0031] In one embodiment, as described above, a transition from the stabilization mode to the adaptation mode is provided by the processing unit when the processing unit receives a respective request and / or when a predefined third time period, e.g. six months, has elapsed since the transition to the stabilization mode.

[0032] The above embodiment of the method of operation has the same advantages as the pacemaker described above. The above-described embodiment of the pacemaker can be realized with a similar method of operation. In this regard, reference is made to the above description of the pacemaker.

[0033] The above methods may, for example, be realized as a computer program comprising instructions (executed by the pacemaker, specifically in the processor) that, when executed, cause a processing unit (processor) to perform the steps of the above methods, the program being a combination of computer instructions and data definitions as specified above and below that enable computer hardware to perform a computational or control function, or the program being a syntactic unit that conforms to the rules of a particular programming language and is comprised of declarations and statements or instructions necessary to solve a function, task or problem as specified above and below.

[0034] Further disclosed is a computer program product comprising instructions which, when executed by a processing unit, cause the processing unit to perform the steps of the method defined above. Accordingly, disclosed is a computer readable data carrier storing such a computer program product.

[0035] In this disclosure, in order to meet the stringent current consumption requirements and still support automatic adaptation of the gain value, an automatic locking method of the gain value is proposed. Normally, in the adaptation mode, the gain value will be stabilized after the adaptation algorithm has been running for a long enough period of time. As long as there is no significant change in the activity level after this period, the gain value will remain stable with small fluctuations. A method is proposed to lock the adapted gain value to a stable value. This eliminates the need for the detector and the adaptation algorithm to run continuously in the background, which can extend the life of the pacemaker.

[0036] The invention will now be described in more detail with reference to the accompanying schematic drawings. [Brief description of the drawings]

[0037] [Figure 1] 1 shows a first embodiment of a pacemaker in a cross-section of a patient's heart. [Diagram 2] 2 illustrates a functional block diagram of the pacemaker shown in FIG. 1. [Diagram 3] 3 shows a flow chart of one embodiment of a method of operation of the present invention. [Figure 4] 13 depicts a diagram showing the variability of gain values ​​(in adaptive mode) before and after the stability criterion is reached. [Diagram 5] 13 depicts a diagram showing the variability of gain values ​​(in adaptive mode) before and after the stability criterion is reached. [Figure 6] 13 depicts a diagram showing the variability of gain values ​​(in adaptive mode) before and after the stability criterion is reached. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0038] In the following, embodiments of the invention refer to an ILP type pacemaker. However, the invention can be implemented in conventional pacemakers as well. FIGURE 1 shows an exemplary ventricular leadless pacemaker (ILP) 10 implanted in a heart 20 of a patient 30. The ILP 10 can be implanted in a right ventricle 21 of the heart 20 and configured to pace this ventricle in a VDD mode, sense intrinsic ventricular depolarizations and atrial (e.g., right atrium 22) depolarizations, and inhibit ventricular pacing in response to a detected ventricular depolarization. A programmer (not shown) can be used to program the ILP 10 and retrieve data from the ILP 10.

[0039] FIG. 2 shows a functional block diagram of the ILP 10 configured to be implanted in the ventricle 21 (FIG. 1). In the case of a conventional pacemaker, the units are housed in a control and generator device to which the electrodes are connected via leads. The ILP 10 comprises a processing unit 120 with a clock and at least one counter for the clock signal, a data memory 122, a pacing signal generator 124, a detector 126, a communication unit 128, and a power source 132. The power source 132 may include a battery, for example a rechargeable or non-rechargeable battery. The power source provides electrical energy to all units and components of the ILP 10, in particular to all units mentioned above, and is therefore electrically connected to these units and components. The units included in the ILP 10 are representative of their respective functions. Similar or identical units and functions may also be included in the ILP 10. The units of the present disclosure may include any discrete and / or integrated electronic circuit components implementing analog and / or digital circuits capable of generating the functions attributed to the units herein. For example, the units may include analog circuits, such as amplification circuits, filtering circuits, and / or other signal conditioning circuits. The units may include digital circuits, such as combinational or sequential logic circuits, memory devices, and the like. The data memory 122 may also include any volatile, non-volatile, magnetic, or electrical media described above. Additionally, the processing unit 120 may include instructions that, when executed by one or more processing circuits, cause the units to perform various functions attributed to those units herein. The functions attributed to the units herein may be realized as one or more processors, hardware, firmware, software, or any combination thereof. The depiction of different functions as units is intended to highlight aspects of the different functions and does not necessarily imply that such units must be realized by separate hardware or software components. Rather, functions associated with one or more units may be performed by separate hardware or software components or may be integrated within a common or separate hardware or software component.Data memory 122 may include computer readable instructions that, when executed by processing unit 120, cause processing unit 120 to perform various functions attributed to processing unit 120 herein. Additionally, data memory 122 may store parameters for these functions, such as pacing signal parameters. For example, data memory 122 may store predefined programmable AV delays. Pacing commands and pacing signal parameters may be updated by a programmer using communication unit 128. Communication unit 128 may comprise an antenna or a transceiver.

[0040] The processing unit 120 may communicate with, and transmit signals through, the pacing signal generator 124 and the detector 126. The pacing signal generator 124 and the detector 126 are electrically coupled to the electrodes 111, 112 of the ILP 10. The detector 126 is configured to monitor signals from the electrodes 111, 112 to monitor electrical activity of the heart 20. Additionally, the detector 126 comprises a motion sensor, which may include an accelerometer, an acoustic sensor, and / or a pressure sensor. The pacing signal generator 124 is configured to deliver an electrical stimulation signal to the ventricle 21 via the electrodes 111, 112.

[0041] The ILP 10 may include a housing, anchoring tines, and electrodes 111, 112. The housing may have a pill-shaped, cylindrical form factor in some instances. The anchoring tines are configured to connect (e.g., anchor) the ILP 10 to the heart 20. The anchoring tines may be fabricated from a shape memory material, such as Nitinol. In some instances, the anchoring tines may connect the ILP 10 to the heart 20 within one of the chambers of the heart 20. For example, as shown and described herein with respect to FIG. 1, the anchoring tines may be configured to anchor the ILP 10 to the heart 20 in the right ventricle 21. Although the ILP 10 includes a plurality of anchoring tines configured to anchor the ILP 10 to cardiac tissue in the right ventricle, it is contemplated that a pacemaker according to the present disclosure may be anchored to cardiac tissue in other chambers of the patient's heart 20 using other types of anchoring mechanisms.

[0042] The communication unit 128 may enable the ILP 10 to communicate with other electronic devices, such as a programmer or other external patient monitor. In some instances, the housing may house an antenna for wireless communication. The housing may also include a power source 132.

[0043] The ILP 10 may include two electrodes 111, 112, although in other instances a pacemaker may include more than two electrodes. The electrodes 111, 112 may be spaced apart a sufficient distance to be able to detect various electrical signals generated by the heart 20, such as P waves generated by the atria and QRS complexes generated by the ventricles. A housing houses the electronic components of the ILP 10. The electronic components may include any discrete and / or integrated electronic circuit components implementing analog and / or digital circuits capable of producing the functions attributed to the ILP 10 described above.

[0044] The processing unit 120 may control the pacing signal generator 124 to generate and deliver electrical stimuli to the ventricle 21 via the electrodes 111, 112. The electrical stimuli may include pacing pulses. The processing unit 120 may control the pacing signal generator 124 to deliver the electrical stimulation therapy according to one or more therapy programs including pacing parameters, which may be stored in the data memory 122.

[0045] Detector 126 may include circuitry to acquire electrical signals (e.g., electrical depolarization signals) from the heart, including intrinsic cardiac signals, such as intrinsic ventricular signals and / or intrinsic atrial signals. Additionally, detector 126 includes an accelerometer as a motion sensor to determine activity signals of patient 30 over time. Detector 126 may filter, amplify, and digitize the acquired electrical signals to generate raw digital data.

[0046] Processing unit 120 may receive the time-dependent digitized data generated by detector 126, specifically the digitized activity signal provided by detector 126. From the activity signal, processing unit 120 determines a pacing rate when ILP 10 is in an activity-based rate-responsive pacing mode, which may be set by a programmer. In the activity-based rate-responsive pacing mode, processing unit 120 may work in two different modes: an adaptive mode and a stabilization mode, which are described below with reference to the flow chart shown in FIG.

[0047] Processing unit 120 may evaluate the raw accelerometer signal (activity signal) received from detector 126 and is configured to set the gain value to a predefined initial value stored in data memory 122 close to the lowest setting after ILP 10 is implanted (see step 201 in FIG. 3). Processing unit 120 is initially in an adaptive mode. After implantation, an adaptive mode gain value adaptation algorithm is executed (see step 202 in FIG. 3), where the pacing rate is calculated and the gain value (with component slope and offset (if applicable)) is determined and adapted as indicated above.

[0048] In the proposed adaptation mode, when the pacing rate and gain value adaptation algorithm described above is executed, the average value of the gain value is calculated and tracked from a user-defined (or programmable) window size (see step 203 in FIG. 3), i.e. an average value (e.g. arithmetic mean value) is determined from the gain values ​​over a predefined time period, e.g. 10 days. Then, the delta between the averaged gain values ​​in adjacent windows is calculated for two adjacent time periods, e.g. 10 days (see step 204 in FIG. 3) and compared with a predefined stability threshold (stored in the data memory 122, see step 205 in FIG. 3). If the delta is smaller than the stability threshold, the determined gain value is approximately stabilized and changes only within small fluctuations. In this case, the gain value is locked to a stable value (see step 206 in FIG. 3), e.g. the average gain value determined within the most recent window, and the average gain value is considered to be approximately the appropriate gain value for the activity level of the patient 30. This locked gain value is stored in the data memory 122 and the rate / gain adaptation algorithm no longer needs to run in the background. A final step (step 207) is reached. If the pacemaker is programmed to work in a rate adaptive pacing mode, the locked gain value is used in the stabilization mode as a scale factor, and, if applicable, an offset value, for converting the motion signal determined as shown above to a pacing rate. In addition to using the delta between the average gain values ​​to determine the stabilization of the gain value, as further depicted in FIG. 3, the algorithm may also be run for a predefined adaptation time period (user defined and / or programmable) to ensure that the gain value reaches a stable phase (see step 208 of FIG. 3), after which the gain value is locked to the stabilized gain value (see step 206 of FIG. 3). The processing unit 120 then transitions to the stabilization mode.

[0049] If the delta is greater than or equal to the stability threshold (see step 205 in FIG. 3), then the average delta value for the next adjacent window is calculated, such as in step 204 in FIG.

[0050] Additionally, the stability of the locked gain values ​​may be checked and updated at regular intervals, e.g., every six months, or per patient request. Updating the locked gain values ​​is similar to the initial adaptation and locking of the gain values. The only difference is that in the update procedure, the initial gain values ​​are not the initial gain values ​​but the previously locked values. This means that the algorithm is restarted from step 202 of FIG. 3, where the initial gain values ​​are the previously locked gain values. Various triggers may trigger the unlocking of the gain values, including timers, manual setting by the clinician, expiration of a period of time that the pacing rate remains within the high or low heart rate range, detection of changes in metabolic, behavioral, or medication trends, and other clinically relevant signals.

[0051] Processing unit 120 continuously determines a pacing control signal, e.g., for ventricular pacing, in an activity-based rate-responsive pacing algorithm based on the activity signal received from detector 126 and the pacing rate calculated using the actual gain value (in adaptive mode) or using the locked gain value (in stabilization mode), as described above. The pacing control signal is transmitted to pacing signal generator 124, which generates corresponding electrical pacing pulses that are then applied by electrodes 111, 112 to the patient's heart 20, e.g., right ventricle 21.

[0052] The gain value is locked in the stabilization mode and the rate adaptation can be turned off to meet the current budget of ILP10. Figure 4 shows an example of the gain value (slope component) over time for a patient after implantation. Furthermore, Figure 5 shows the delta of the average gain value between two adjacent windows. From Figure 4, it can be derived that the gain value increases from an initial predefined value in the adaptation mode for a certain period of time and then remains stable with small fluctuations. This represents a typical trend of the adapted gain value of an implantable pacemaker. In this example, the gain setting has a step size of approximately 12.5%. From Figure 5, it can be derived that during the adaptation period of the gain value (i.e., during the adaptation mode), the average gain value changes by more than 25% (2 step sizes). On the other hand, when the gain value enters the stable period, the delta of the average gain value of adjacent windows is within approximately 12.5% ​​(1 step size). Therefore, the average gain value is a good parameter to determine the stabilization of the gain value. Then, after the gain values ​​are stabilized, they can be locked and stored in the device's registers (i.e., the processing unit 120 transitions to a stabilization mode), while the rate adaptation algorithm and the motion sensor do not need to run in the background to support the update of the gain values. The transition to the stabilization mode is not shown in Figures 4 and 5. In Figures 4 and 5, a time window is represented by a rectangle 210.

[0053] To ensure that the locked gain value represents the appropriate gain value corresponding to the patient's activity level, data from a VVIR conventional pacemaker was used to analyze the variability of the gain value after transition to the stabilization mode. An example is shown in Figure 6. The variability was calculated by the difference between the locked gain value and the expected gain value from the adaptive mode. The variability can be used to evaluate the locked gain and may represent the actual gain value if the adaptive mode continues to run. Thus, the locked gain is compared to the expected gain value from the adaptive mode. Figure 6 shows the number of cases and change intervals of the gain value change relative to the locked gain value. Note that in this example, the step size of the gain value setting is 12.5%. Thus, in most patients, after the lock point (i.e., the transition from the adaptive mode to the stabilization mode), the gain value obtained from the continuously running rate adaptation differs from the locked gain value by only one step. Thus, using the proposed method, the locked gain value can represent the appropriate gain value that truly corresponds to the patient's activity level.

[0054] The pacemaker and method of operation of the present invention described above may be further illustrated by the following general characteristics. Tracking the average gain in adaptive mode until it meets the stability criteria, i.e. until the delta is small enough and / or the algorithm has run for a certain period of time. The delta between the average gain values ​​of adjacent windows calculated in adaptive mode indicates the stabilization of the gain value. After the gain value is stabilized, the processing unit 120 goes into a stabilization mode, where the gain value is locked to the average gain value of the last window, also called the locked gain value. In the stabilization mode, when the pacemaker is not in a rate adaptive pacing mode, the motion sensor of detector 126 (e.g., accelerator) and the rate adaptation algorithm are turned off, reducing current consumption and improving the life of the ILP or conventional pacemaker. When the pacemaker is in a rate adaptive pacing mode, a locked gain value is used to calculate the pacing rate. Stabilized gain values ​​can be updated on demand or at scheduled follow-ups. · Clinical observations or timers or other clinically relevant events may also cause the pacer to return to adaptive mode, allowing further adaptation and determination of new stabilized gain values. It is also possible to lock multi-dimensional gain values, e.g. one gain value for a typical rest day and / or a typical exertion day, and / or a typical sleep period and a typical activity period. Depending on the patient's preference, different locked gain values ​​can be used to support the rate adaptation algorithm.

[0055] The above described pacemaker and method of operation provide the following advantages: Pacemaker current consumption reduces, meeting leadless pacer current budgets and extending life. The locked gain value has proven to be a robust gain value that is less susceptible to random noise in activity levels. By programming the time window for averaging the gain values, the locking strategy becomes flexible and can be locked to the most appropriate gain value for patients with different activity patterns. The above method is easily customizable. For example, multi-dimensional gain values ​​can be locked as shown above. Additionally, gain values ​​with two components (slope and offset) can also be locked. Depending on the patient's preference, different locked values ​​can be used to support the rate adaptation algorithm. The method of operation of the present invention is simple to implement.

Claims

1. A pacemaker (10) for a patient's heart (20), comprising a processing unit (120), a detector (126), and a pacing signal generator (124), wherein the processing unit, the detector, and the pacing signal generator are electrically interconnected, the detector configured to determine an activity signal of the patient and provide the activity signal to the processing unit, the processing unit configured to determine a pacing rate based on the activity signal currently received by the detector and a gain value in an adaptive mode or a stabilizing mode, the processing unit configured to generate a pace control signal based on the determined pacing rate, and a processing unit configured to provide the pace control signal to the pacing signal generator, wherein in the adaptive mode, the processing unit is configured to adapt the gain value to the particular patient, the processing unit is configured to remain in the adaptive mode unless at least one stability criterion is met, and to transition to the stabilization mode when the processing unit identifies that the at least one stability criterion has been met, and wherein in the stabilization mode, the processing unit is configured to use a locked gain value determined based on a most recently adapted gain value to determine the pacing rate.

2. 2. The pacemaker of claim 1, wherein the gain value is a one-dimensional value or a multi-dimensional value.

3. 3. The pacemaker of claim 1, wherein the stability criterion is met when an absolute value of a difference between a first average value of the adapted gain values ​​determined within a first time period and a second average value of the adapted gain values ​​determined within a second time period is less than a predetermined stability threshold, and / or when the pacing rate is determined in the adaptive mode for a predefined adaptation time period.

4. 3. A pacemaker according to claim 1, wherein the first and second time periods are immediately adjacent, most recently evaluated time periods.

5. 3. The pacemaker of claim 1, wherein in the stabilization mode, the processing unit is configured to discontinue or reduce detection of the activity signal by the detector, and the processing unit is configured to determine a motion signal from the reduced activity signal.

6. 3. The pacemaker of claim 1, wherein the processing unit (120) transitions from the stabilizing mode to the adaptive mode when the processing unit receives a respective request and / or when a predefined third time period has elapsed since the transition to the stabilizing mode.

7. 3. The pacemaker of claim 1, wherein the pacemaker (10) operates in the VDD mode.

8. A method of operating a pacemaker (10) for a patient's heart (20), the pacemaker comprising a processing unit (120), a detector (126), and a pacing signal generator (124), the processing unit, the detector, and the pacing signal generator being electrically interconnected, the patient's activity signal being determined by the detector and transmitted to the processing unit, a pacing rate being determined by the processing unit based on the current activity signal of the detector and based on a gain value in an adaptive mode or a stabilizing mode, and a pace control signal being generated by the processing unit. and generating and transmitting a locked gain value based on the determined pacing rate to the pacing signal generator, wherein in the adaptive mode the gain value is adapted to the particular patient, the processing unit remaining in the adaptive mode unless at least one stability criterion is met, and transitioning to the stabilization mode if the processing unit identifies that the at least one stability criterion has been met, wherein in the stabilization mode the processing unit uses a locked gain value determined based on a most recently adapted gain value to determine the pacing rate.

9. The method of claim 8 , wherein the gain value is a one-dimensional value or a multi-dimensional value.

10. 10. The method of claim 8 or 9, wherein the stability criterion is met if an absolute value of a difference between a first average value of the adapted gain values ​​determined within a first time period and a second average value of the adapted gain values ​​determined within a second time period is less than a predetermined stability threshold and / or if the pacing rate is determined in the adaptive mode for a predefined adaptation time period.

11. 10. The method of claim 8 or 9, wherein the first time period and the second time period are immediately adjacent, most recently evaluated time periods.

12. 10. The method of claim 8 or 9, wherein in the stabilization mode, detection of the activity signal by the detector (126) is interrupted or reduced by the processing unit, and the processing unit (120) determines a movement signal from the reduced activity signal.

13. 10. The method according to claim 8 or 9, wherein the transition from the stabilization mode to the adaptation mode is provided by the processing unit (120) when the processing unit receives a respective request and / or when a predefined third time period has elapsed since the transition to the stabilization mode.

14. A computer program product comprising instructions which, when executed by a processing unit, cause said processing unit (120) to perform the steps of the method according to claim 8 or 9.

15. 15. A computer readable data carrier storing a computer program product according to claim 14.

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