Reducing False Messages and Their Impact in Multi-Chamber Leadless Pacemaker Systems and Other IMD Systems

Abstract

The implantable medical devices (IMDs) described herein and methods for their use described herein reduce the frequency of false messages received by the IMD and / or reduce the adverse effects of false messages received by the IMD. Such IMDs may be, but are not limited to, leadless pacemakers (LPs) or implantable cardiac defibrillators (ICDs). Such embodiments may be used to help multiple IMDs (e.g., multiple LPs) implanted in the same patient maintain synchronized operation, such as synchronized multi-chamber pacing.

Description

Technical Field

[0001] The embodiments described herein generally relate to methods and systems for providing and improving communication between implantable medical devices, one or more of which may be leadless cardiac pacemakers.

[0002] Priority claim

[0003] This application claims priority to U.S. Provisional Patent Application No. 62 / 907,396, filed on September 27, 2019, and U.S. Non-Provisional Patent Application Nos. 17 / 022,774 and 17 / 022,994, filed on September 16, 2020, which are incorporated herein by reference in their entirety. Background Art

[0004] Implantable medical devices and systems often rely on proper communication to operate correctly. For example, in a dual-chamber leadless pacemaker system, implant-to-implant (i2i) communication is crucial for proper synchronization and operation of the system. However, noise can cause one or more devices in such a system to erroneously detect i2i messages and respond inappropriately to them. To give a more specific example, noise can cause a ventricular leadless pacemaker (LP) to erroneously detect information from the atrial LP, which can then trigger the ventricular LP to pace at an inappropriately high rate and, more generally, at inappropriate times. In another example, the atrial LP can erroneously detect a message that causes the atrial LP to pace the right atrium at a rate much higher than the ventricular LP is pacing the right ventricle, resulting in asynchronous pacing. To reduce the probability of an implantable medical device erroneously detecting an i2i message, such i2i messages can include redundant data for error detection and correction. However, due to the desire to maintain low power consumption, the i2i messaging and / or error correction and detection scheme can be simple, and spurious messages can still pass through. Summary of the Invention

[0005] Certain embodiments of the present technology relate to a method for use by a leadless pacemaker (LP) implanted within or upon a first cardiac chamber of a patient, the first cardiac chamber of the patient also having an implantable medical device (IMD) remotely located relative to the LP, wherein the LP is configured to pace the first cardiac chamber and adjust a pacing rate of the first cardiac chamber based on a pacing rate indicator included in an implant-to-implant (i2i) message received from the IMD. According to certain embodiments, the method includes the LP monitoring the i2i messages, and in response to the LP receiving the i2i message including the pacing rate indicator that would cause the adjustment to the pacing rate to exceed a rate adjustment threshold, the LP limiting an adjustment to the pacing rate to a specified amount. According to certain embodiments, the specified amount to which the LP limits an adjustment to the pacing rate in response to receiving the i2i message including the pacing rate indicator that would cause the adjustment to the pacing rate to exceed the rate adjustment threshold includes the rate adjustment threshold. In accordance with certain embodiments, the specified amount to which the LP limits adjustment of the pacing rate in response to receiving an i2i message including a pacing rate indicator that will cause the adjustment of the pacing rate to exceed a rate adjustment threshold comprises a predetermined value or a predetermined function of the current pacing rate. In accordance with certain embodiments, the LP comprises a first LP (LP1) and the IMD comprises a second LP (LP2) implanted in or on a second cardiac chamber. For example, the first cardiac chamber comprises a right atrium (RA) chamber and the second cardiac chamber comprises a right ventricle (RV) chamber. In accordance with certain embodiments, the LP is implanted in or on the RV chamber and the IMD comprises a subcutaneously implantable cardioverter-defibrillator (S-ICD). In certain such embodiments, the i2i messages are transmitted and received via conducted communication.

[0006] Certain embodiments of the present technology relate to an implantable pacing device (LP) configured to be implanted within or on a first cardiac chamber of a patient and configured to pace the first cardiac chamber and adjust the pacing rate of the first cardiac chamber based on a pacing rate indicator included in an i2i message received from an IMD remotely located relative to the LP. The LP may include at least one receiver configured to receive the i2i message and a controller configured to limit adjustments to the pacing rate to a specified amount in response to the LP receiving a message including a pacing rate indicator that would cause the adjustment to the pacing rate to exceed a rate adjustment threshold. According to certain embodiments, the specified amount to which the controller limits adjustments to the pacing rate in response to receiving the i2i message including a pacing rate indicator that would cause the adjustment to the pacing rate to exceed the rate adjustment threshold includes the rate adjustment threshold. According to certain embodiments, the specified amount to which the controller limits adjustments to the pacing rate in response to receiving the i2i message including a pacing rate indicator that would cause the adjustment to the pacing rate to exceed the rate adjustment threshold includes a predetermined value or a predetermined function of the current pacing rate. According to certain embodiments, the LP includes a first LP (LP1), and the IMD includes a second LP (LP2) implanted in or on a second heart chamber. For example, the first heart chamber includes the RA chamber, and the second heart chamber includes the RV chamber. According to certain embodiments, the LP is implanted in or on the RV chamber, and the IMD includes an S-ICD. In certain such embodiments, i2i messages are transmitted and received via conducted communication.

[0007] According to certain embodiments in which the LP monitors for i2i messages, the LP expects to receive an i2i message from an IMD remotely located relative to the LP within an expected period. In response to the LP not receiving the i2i message within the expected period, the LP reduces the pacing rate of the LP-paced first cardiac chamber. According to certain embodiments, the expected period includes a predetermined time period, or a predetermined number (N) of cardiac cycles, where N is an integer equal to or greater than 1. According to certain embodiments, in response to the LP not receiving the i2i message within the expected period, the amount by which the LP reduces the pacing rate of the LP-paced first cardiac chamber includes a predetermined value or a predetermined function of the current pacing rate. In certain such embodiments, in response to the LP not receiving the i2i message within the expected period, the LP limits the amount by which the pacing rate is reduced such that the pacing rate does not fall below a predetermined minimum rate. According to certain embodiments, the LP includes a first LP (LP1), the IMD includes a second LP (LP2) implanted within or on a second cardiac chamber, the first cardiac chamber includes the RA chamber, and the second cardiac chamber includes the RV chamber. According to certain embodiments, the i2i messages are transmitted and received via conducted communication, the LP is implanted in or on the RV chamber, and the IMD comprises an S-ICD. In certain such embodiments, the i2i messages are transmitted and received via conducted communication.

[0008] According to certain embodiments, a life cycle controller (LP) includes at least one receiver configured to receive an i2i message, and a controller configured to reduce a pacing rate of a first cardiac chamber paced by the LP in response to the LP not receiving the i2i message within an expected period of time. According to certain embodiments, the expected period of time includes a predetermined time period, or a predetermined number (N) of cardiac cycles, where N is an integer equal to or greater than 1. According to certain embodiments, the amount by which the controller reduces the pacing rate of the first cardiac chamber paced by the LP in response to the LP not receiving the i2i message within the expected period of time includes a predetermined value or a predetermined function of a current pacing rate. In certain such embodiments, the controller limits the amount by which the pacing rate is reduced in response to the LP not receiving the i2i message within the expected period of time such that the pacing rate does not fall below a predetermined minimum rate.

[0009] Certain embodiments of the present technology are directed to a method involving a LP monitoring i2i messages, and in response to the LP receiving at least a specified plurality of i2i messages including the same pacing rate indicator, the LP adjusting a pacing rate of a first cardiac chamber based on the pacing rate indicator included in the specified plurality of i2i messages received by the LP. The method also includes, in response to the LP not receiving at least a specified plurality of i2i messages including the same pacing rate indicator, the LP not adjusting the pacing rate of the first cardiac chamber based on the pacing rate indicator included in the i2i messages received by the LP. According to certain embodiments, the specified plurality of i2i messages includes at least N consecutive i2i messages including the same pacing rate indicator, where N is a predetermined integer equal to or greater than 2, and the IMD is configured to send the at least N consecutive i2i messages including the same pacing rate indicator to the LP each time the IMD changes the rate at which the LP paces the first cardiac chamber. According to other embodiments, the designated plurality of i2i messages includes at least M of the N i2i messages including the same pacing rate indicator, where M is a predetermined integer equal to or greater than 2, and where N is a predetermined integer greater than M, and the IMD is configured to send the at least N i2i messages including the same pacing rate indicator to the LP each time the IMD changes the rate at which the LP paces a first cardiac chamber. In some embodiments, the LP includes a first LP (LP1), and the IMD includes a second LP (LP2) implanted within or on a second cardiac chamber. For example, the first cardiac chamber includes the RA chamber, and the second cardiac chamber includes the RV chamber. In other embodiments, the LP is implanted in or on the RV chamber, and the IMD includes an S-ICD. In some such embodiments, the i2i messages are transmitted and received via conducted communication.

[0010] Certain embodiments of the present technology relate to a system including a LP and an IMD, wherein the LP is configured to be implanted within or on a first cardiac chamber of a patient and configured to pace the first cardiac chamber, and the IMD is remotely located relative to the LP. Additionally, the LP includes a controller configured to adjust a pacing rate of the first cardiac chamber based on a pacing rate indicator included in an i2i message received from the IMD. In response to the LP receiving at least a specified plurality of i2i messages including the same pacing rate indicator, the controller of the LP is configured to adjust the pacing rate of the first cardiac chamber based on the pacing rate indicator included in the specified plurality of i2i messages received by the LP. In response to the LP not receiving at least a specified plurality of i2i messages including the same pacing rate indicator, the controller of the LP is configured to adjust the pacing rate of the first cardiac chamber based on the pacing rate indicator included in the i2i message received by the LP. In certain such embodiments, the designated plurality of i2i messages includes at least N consecutive i2i messages including the same pacing rate indicator, where N is a predetermined integer equal to or greater than 2, and the IMD is configured to send the at least N consecutive i2i messages including the same pacing rate indicator to the LP at least whenever the IMD changes the rate at which the LP paces a first cardiac chamber. According to other embodiments, the designated plurality of i2i messages includes at least M of the N i2i messages including the same pacing rate indicator, where M is a predetermined integer equal to or greater than 2, and where N is a predetermined integer greater than M, and the IMD is configured to send the at least N i2i messages including the same pacing rate indicator to the LP whenever the IMD changes the rate at which the LP paces the first cardiac chamber. In certain embodiments, the LP includes a first LP (LP1), and the IMD includes a second LP (LP2) implanted in or on a second cardiac chamber. For example, the first cardiac chamber includes the RA chamber, and the second cardiac chamber includes the RV chamber. In other embodiments, the LP is implanted in or on the RV chamber, and the IMD includes an S-ICD. In certain such embodiments, i2i messages are transmitted and received via conducted communications.

[0011] In a method according to certain embodiments of the present technology, an IMD transmits i2i messages to a LP, wherein a subset of the i2i messages transmitted by the IMD to the LP include a pacing rate indicator. In certain such embodiments, the LP monitors the i2i messages and adjusts the pacing rate of a first cardiac chamber based on the pacing rate indicators included in at least some of the i2i messages received by the LP from the IMD. In certain such embodiments, the i2i messages transmitted from the IMD to the LP that include the pacing rate indicator include longer error detection and correction codes than the error detection and correction codes included in at least some of the i2i messages transmitted from the IMD to the LP that do not include the pacing rate indicator. In certain such embodiments, the error detection and correction code includes a cyclic redundancy check (CRC) code. In certain such embodiments, the LP includes a first LP (LP1), and the IMD includes a second LP (LP2) implanted within or on a second cardiac chamber. For example, the first cardiac chamber includes the RA chamber, and the second cardiac chamber includes the RV chamber. In other embodiments, the LP is implanted in or on the RV chamber, and the IMD includes an S-ICD. In certain such embodiments, i2i messages are transmitted and received via conducted communications.

[0012] According to certain embodiments, a system includes a laparoscopic implantable cardioverter-stimulator (LP) configured to be implanted in or on a first cardiac chamber of a patient and configured to pace the first cardiac chamber, and an intravenous device (IMD) remotely located relative to the LP. The LP is configured to adjust the pacing rate of the first cardiac chamber based on a pacing rate indicator included in an i2i message received from the IMD. In certain such embodiments, the IMD is configured to include a longer error detection and correction code in i2i messages transmitted from the IMD to the LP that include a pacing rate indicator, compared to the error detection and correction code included in at least some i2i messages transmitted from the IMD to the LP that do not include the pacing rate indicator. In certain such embodiments, the error detection and correction code includes a CRC code. In certain such embodiments, the LP includes a first LP (LP1), and the IMD includes a second LP (LP2) implanted in or on a second cardiac chamber. For example, the first cardiac chamber includes the RA chamber, and the second cardiac chamber includes the RV chamber. In other embodiments, the LP is implanted in or on the RV chamber, and the IMD includes an S-ICD. In certain such embodiments, the i2i messages are transmitted and received via conducted communication.

[0013] This summary is not intended to be a complete description of embodiments of the present technology. Other features and advantages of embodiments of the present technology will become apparent from the following description, in which preferred embodiments have been described in detail in conjunction with the accompanying drawings and claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Embodiments of the present technology, both as to structure and method of operation, may be best understood by reference to the following description and drawings in which like reference numerals refer to like elements throughout the several views:

[0015] Figure 1 A system configured for implantation in a heart according to some embodiments herein is illustrated.

[0016] Figure 2 is a block diagram of a single LP according to some embodiments herein.

[0017] Figure 3 An LP according to some embodiments herein is illustrated.

[0018] Figure 4 is a timing diagram illustrating one embodiment of implant-to-implant (i2i) communication for pacing events.

[0019] Figure 5 is a timing diagram illustrating one embodiment of i2i communication for sensing events.

[0020] Figure 6A is a high-level flow chart summarizing a method for providing slew rate protection according to certain embodiments of the present technology.

[0021] Figure 6B is a high-level flow chart summarizing a method for providing selective reduction in pacing rate in accordance with certain embodiments of the present technology.

[0022] Figure 6C is a high-level flow chart summarizing a method for sending and receiving multiple i2i messages to and by a LP before the LP adjusts its pacing rate in response to receiving an i2i message including a pacing rate indicator, in accordance with certain embodiments of the present technology.

[0023] Figure 6D is a high-level flow chart summarizing a method in which an i2i message including a pacing rate indicator includes longer error detection and correction codes than certain other types of messages, in accordance with certain embodiments of the present technology.

[0024] Figure 7 A block diagram is shown of one embodiment of an IMD (eg, an LP or in an ICD) implanted in a patient as part of an implantable cardiac system, according to some embodiments herein. DETAILED DESCRIPTION

[0025] Certain embodiments of the present technology relate to implantable medical devices (IMDs) and methods of use thereof that reduce the frequency of receiving false messages and / or reduce the impact of false messages received by the IMD. Such embodiments are particularly useful for, but not limited to, use with, systems that include one or more leadless cardiac pacemakers. Before providing additional details of the specific embodiments of the present technology mentioned above, reference will first be made to Figure 1-Figure 5 Describes an exemplary system in which embodiments of the present technology can be used. More specifically, Figure 1-Figure 5 An exemplary cardiac pacing system will be described in which pacing and sensing operations can be performed by multiple medical devices, which can include one or more leadless cardiac pacemakers, ICDs (such as subcutaneous ICDs (S-ICDs)), and / or programmers to reliably and safely coordinate pacing and / or sensing operations. Leadless cardiac pacemakers may also be more succinctly referred to herein as leadless pacemakers (LPs). Where the cardiac pacing system includes an S-ICD, the S-ICD can perform certain sensing operations and can communicate with one or more LPs by sending and / or receiving messages to one or more LPs, as can be appreciated from the discussion below. Where the cardiac pacing system includes a programmer, the programmer can be used to program one or more IMDs, download information to one or more IMDs, and / or upload information from one or more IMDs, as can be appreciated from the description below.

[0026] Figure 1 A system 100 is illustrated that is configured to be implanted in a heart 101. The system 100 includes two or more leadless pacemakers (LPs) 102a and 102b located in different chambers of the heart. LP 102a is located in the right atrium, while LP 102b is located in the right ventricle. LPs 102a and 102b communicate with each other to inform each other of various local physiological activities, such as local intrinsic events, local pacing events, etc. LPs 102a and 102b can be constructed in a similar manner but operate differently based on which chamber LP 102a or 102b is located. LPs 102a and 102b may sometimes be collectively referred to herein as LP 102, or individually as LP 102.

[0027] In certain embodiments, LPs 102a and 102b communicate with each other, and / or with ICD 106, by conducting conducted communication via the same electrodes used to sense and / or deliver pacing therapy. LPs 102a and 102b may also be able to communicate with an external device (e.g., programmer 109) using conducted communication, with electrodes placed on the skin of the patient in whom LPs 102a and 102b are implanted. Although not shown (and not preferred as it would increase the size and power consumption of LPs 102a and 102b), LPs 102a and 102b may potentially include antennas and / or telemetry coils that enable them to communicate with each other, ICD 106, and / or external devices using radio frequency or inductive communication. Although Figure 1 Only two LPs are shown, but it is possible to implant more than two LPs in a patient. For example, in order to provide biventricular pacing and / or cardiac resynchronization therapy (CRT), in addition to LPs implanted in the right atrial (RA) chamber and the right ventricular (RV) chamber, another LP can be implanted in the left ventricular (LV) chamber.

[0028] In some embodiments, one or more LPs 102a may be co-implanted with an ICD 106. Each LP 102a uses two or more electrodes located within, on, or within a few centimeters of the pacemaker housing for pacing and sensing in cardiac chambers and for bidirectional communication with a programmer 109, the ICD 106, and each other.

[0029] While the methods, devices, and systems described herein include examples primarily in the context of LPs, it should be understood that the methods, devices, and systems described herein can be used with various other types of IMDs. For example, the methods, devices, and systems can dynamically control communications between various IMDs implanted in the human body, not just LPs. Certain embodiments enable a first IMD to receive communication messages from at least a second IMD via conducted communication on at least a first channel. It should also be understood that the embodiments described herein can be used for communications between more than two IMDs and are not limited to communications between only a first and a second IMD. The methods, devices, and systems can also be used for communications between two or more IMDs implanted in the same chamber, which IMDs can be the same type of IMD or can be different types of IMDs. The methods, devices, and systems can also be used for communications between two or more IMDs in a system that includes at least one IMD that is not implanted within a cardiac chamber but is implanted epicardially, transmurally, intravascularly (e.g., in the coronary sinus), or subcutaneously (e.g., an S-ICD), etc.

[0030] refer to Figure 2, a block diagram illustrates an embodiment of a portion of the electronics within LPs 102a, 102b configured to provide conducted communication via sensing / pacing electrodes. One or more of LPs 102a and 102b include at least two leadless electrodes configured for delivering cardiac pacing pulses, sensing induced and / or natural cardiac electrical signals, and unidirectional or bidirectional communication. Figure 2 (and Figure 3 ), wherein the two electrodes shown are labeled 108a and 108b. Such electrodes may be collectively referred to as electrodes 108, or individually as electrodes 108. LP 102 or other types of IMDs may include more than two electrodes 108, depending on the implementation.

[0031] exist Figure 2 , each of the LPs 102a, 102b is shown as including first and second receivers 120 and 122 that together define separate first and second communication channels 105 and 107 between the LPs 102a and 102b ( Figure 1 ) (among other things). Although first and second receivers 120 and 122 are depicted, in other embodiments, each LP 102a, 102b may include only the first receiver 120, or may include additional receivers in addition to the first and second receivers 120 and 122. As will be described in more detail below, the pulse generator 116 may be used as a transmitter for transmitting i2i communication signals using the electrodes 108. In some embodiments, the LPs 102a and 102b may communicate via more than just the first and second communication channels 105 and 107. In some embodiments, the LPs 102a and 102b may communicate via a common communication channel 105. More specifically, the LPs 102a and 102b may communicate over a common physical channel via the same electrodes 108 that are also used to deliver pacing pulses. Using the electrodes 108 for communication enables one or more LPs 102a and 102b to perform antenna-less and telemetry coil-less communication.

[0032] Receivers 120 and 122 may also be referred to as low-frequency (LF) receiver 120 and high-frequency (HF) receiver 122, respectively, because receiver 120 is configured to monitor one or more signals within a relatively low frequency range (e.g., below 100 kHz), and receiver 122 is configured to monitor one or more signals within a relatively high frequency range (e.g., above 100 kHz). In some embodiments, receiver 120 (and more specifically, at least a portion thereof) is always enabled and monitors for wake-up notifications, which may simply be wake-up pulses, within a specific low frequency range (e.g., between 1 kHz and 100 kHz); and receiver 122 is selectively enabled by receiver 120. Receiver 120 is configured to consume less power than receiver 122 when both the first and second receivers are enabled. Consequently, receiver 120 may also be referred to as a low-power receiver 120, and receiver 122 may also be referred to as a high-power receiver 122. Low-power receiver 120 cannot receive signals within a relatively high frequency range (e.g., above 100 kHz), but consumes significantly less power than high-power receiver 122. In this way, the low-power receiver 120 is able to always monitor for wake-up notifications without significantly draining the battery of the LP (e.g., 114). According to certain embodiments, in response to the low-power receiver 120 receiving the wake-up notification, the high-power receiver 122 is selectively enabled by the low-power receiver 120 so that the high-power receiver 122 can receive higher frequency signals, thereby handling the higher data throughput required for effective i2i communication, without unnecessarily and quickly draining the battery of the LP (which the high-power receiver 122 would do if it were always enabled).

[0033] According to certain embodiments, when one of the LPs 102a and 102b senses an intrinsic event or delivers a pacing event, the corresponding LP 102a, 102b transmits an implant event message to the other LP 102a, 102b. For example, when the atrial LP 102a senses / paces an atrial event, the atrial LP 102a transmits an implant event message including an event tag indicating the nature of the event (e.g., intrinsic / sensed atrial event, paced atrial event). When the ventricular LP 102b senses / paces a ventricular event, the ventricular LP 102b transmits an implant event message including an event tag indicating the nature of the event (e.g., intrinsic / sensed ventricular event, paced ventricular event). In certain embodiments, each LP 102a, 102b transmits the implant event message to the other LP 102a, 102b prior to the actual pacing pulse, so that the remote LP can blank its sensing input in anticipation of that remote pacing pulse (to prevent inappropriate crosstalk sensing).

[0034] The implant event message can be formatted in various ways. As an example, each event message can include a leading trigger pulse (also known as an LP wake-up notification, a wake-up pulse, or a wake-up signal) followed by an event marker. The notification trigger pulse (also known as a wake-up notification, a wake-up pulse, or a wake-up signal) is transmitted on a first channel (e.g., a pulse duration of about 10 μs to about 1 ms and / or a base frequency in the range of about 1 kHz to about 100 kHz). The notification trigger pulse indicates that the event marker is to be transmitted via a second channel (e.g., in a higher frequency range). The event marker can then be transmitted via the second channel.

[0035] Event markers can include data indicating one or more events (e.g., intrinsic atrial activation of a sensed LP located in the atrium, intrinsic ventricular activation of a sensed LP located in the ventricle). Event markers can include different markers for intrinsic and paced events. Event markers can also indicate the start or end time of a timer (e.g., AV interval, blanking interval, etc.). Optionally, the implant event message can include a message segment containing additional / secondary information.

[0036] Alternatively, an LP (or other IMD) receiving any i2i communication signal from another LP (or another IMD) or from an external device may transmit a receipt confirmation indicating that the receiving LP (or other IMD) received the i2i communication signal. In some embodiments, when an IMD expects to receive an i2i communication signal within a window and fails to receive the i2i communication signal within the window, the IMD may transmit a confirmation indicating that the receiving IMD failed to receive the i2i communication signal. Other variations are possible and within the scope of the embodiments described herein.

[0037] Event messages enable LPs 102a, 102b to deliver synchronized therapy and additional supporting features (e.g., measurements, etc.). To maintain synchronized therapy, each of LPs 102a, 102b is made aware (via event messages) when an event occurs in a chamber containing the other LP 102a, 102b. Some embodiments described herein provide an efficient and reliable process for maintaining synchronization between LPs 102a, 102b without maintaining continuous communication between LPs 102a, 102b. According to certain embodiments herein, low-power event messaging / signaling can be maintained between LPs 102a, 102b either synchronously or asynchronously.

[0038] With synchronous event signaling, LPs 102a and 102b can maintain synchronization and communicate periodically at specific intervals. Synchronous event signaling allows the transmitter and receiver in each LP 102a, 102b to use limited (or minimal) power, as each LP 102a, 102b is powered only for a small fraction of the time associated with transmission and reception. For example, LPs 102a, 102b can transmit / receive (Tx / Rx) communication messages in time slots having a duration of 10-20 μs, where the Tx / Rx time slots occur periodically (e.g., every 10-20 ms).

[0039] LPs 102a and 102b can lose synchronization, even within a synchronization event signaling scheme. As explained herein, features can be included in LPs 102a and 102b to maintain device synchronization, and when synchronization is lost, LPs 102a and 102b undergo operations to restore synchronization. Furthermore, synchronization event messages / signaling can introduce delays between transmissions, which can cause a reaction lag at the receiving LPs 102a and 102b. Thus, features can be implemented to address this reaction lag.

[0040] During asynchronous event signaling, LPs 102a and 102b do not maintain communication synchronization. During asynchronous event signaling, one or more of the receivers 120 and 122 of LPs 102a and 102b can be "always on" (always awake) to search for incoming transmissions. However, maintaining LP receivers 120 and 122 in an "always on" (always awake) state can present challenges, as received signal levels are often low due to high channel attenuation caused by the patient's anatomy. Additionally, maintaining the receivers awake can drain battery 114 more quickly than might be desired.

[0041] The asynchronous event signaling method avoids the risks associated with loss of synchronization between devices. However, the asynchronous event signaling method uses additional receiver current between transmissions. For illustrative purposes only, a non-limiting example is described below. For example, the channel attenuation can be estimated to have a gain of 1 / 500 to 1 / 10000. The gain factor can be 1 / 1000. The transmission current is a design factor in addition to the receiver current. As an example, the system can allocate half of the implant communication current budget to the transmitter (e.g., 0.5 μA per transmitter). When LP 102a, 102b maintains the transmitter in a continuous conduction state and the electrode load is 500 ohms, the transmitted voltage can be 2.5V. When the event signal is transmitted at 2.5V, the event signal is attenuated during propagation and will appear at the LP 102a, 102b receiver with an amplitude of approximately 0.25mV.

[0042] To overcome the aforementioned receive power limitations, a pulsed transmission scheme may be used, wherein communication transmissions occur in association with events. For example, a pulsed transmission scheme may be simplified such that each transmission constitutes a single pulse of selected amplitude and width.

[0043] According to certain embodiments herein, LPs 102a and 102b may utilize a multi-stage receiver that implements a hierarchical receiver wakeup scheme to improve reliability while maintaining power efficiency. Each of LPs 102a and 102b may include first and second receivers 120 and 122 operating with different first and second activation protocols and different first and second receive channels. For example, the first receiver 120 may be assigned a first activation protocol that is "always on" (also known as always awake) and listens on a first receive channel having a lower fundamental frequency range / pulse duration (e.g., 1 kHz to 100 kHz / 10 μs to approximately 1 ms) than the fundamental frequency range assigned to the second receive channel (e.g., greater than 100 kHz / less than 10 μs per pulse).

[0044] According to certain embodiments, the first receiver 120 may always maintain the first channel active (awake) (including when the second channel is inactive (dormant)) in order to listen for messages from the remote LP. The second receiver 122 may be designated as a second activation protocol for the trigger protocol, where the second receiver 122 becomes active (awake) in response to detecting a trigger event on the first receive channel (e.g., when an incoming signal corresponds to an LP wake-up notification, activating the second channel of the local LP). The terms active, awake, and enabled are used interchangeably herein.

[0045] Still refer to Figure 2Each LP 102a, 102b is shown as including a controller 112 and a pulse generator 116. The controller 112 may include, for example, but not limited to, a microprocessor (or equivalent control circuitry), RAM and / or ROM memory, logic and timing circuitry, state machine circuitry, and I / O circuitry. The controller 112 may also include, for example, timing control circuitry to control the timing of stimulation pulses (e.g., pacing rate, atrioventricular (AV) delay, atrial conduction (AA) delay, or interventricular conduction (VV) delay, etc.). Such timing control circuitry may also be used for timing of refractory periods, blanking intervals, noise detection windows, evoked response windows, alarm intervals, marker channel timing, etc. The controller 112 may also include other specialized circuitry and / or firmware / software components that facilitate monitoring various conditions of the patient's heart and managing pacing therapy. The controller 112 and pulse generator 116 may be configured to transmit event messages via the electrodes 108 in a manner that does not inadvertently capture the heart in the chamber where the LP 102a, 102b is located, such as when the associated chamber is not in a refractory state. Furthermore, LPs 102a and 102b receiving an event message may enter an "event not expected" state (or event blanking state) after receiving the event message. The event not expected / blanking state may be set to extend for a predetermined period of time after receiving the event message to prevent the receiving LP 102a and 102b from inadvertently sensing another signal as an event message that could potentially cause a re-triggering. For example, the receiving LP 102a and 102b may detect a measurement pulse from another LP 102a and 102b or the programmer 109.

[0046] According to certain embodiments herein, programmer 109 can communicate with LPs 102a, 102b over a programmer-to-LP channel using the same communication scheme. The external programmer can listen for event messages transmitted between LPs 102a, 102b and synchronize programmer-to-implant communications such that programmer 109 does not transmit communication signals 113 until the implant-to-implant messaging sequence is complete.

[0047] According to certain embodiments, LPs 102a, 102b can combine transmission operations with therapy. Transmission event markers can be configured to have amplitude and pulse width characteristics similar to pacing pulses, and LPs 102a, 102b can use the energy in the event message to help capture the heart. For example, pacing pulses can typically be delivered with pacing parameters of 2.5V amplitude, 500 ohm impedance, 60 bpm pacing rate, and 0.4 ms pulse width. These pacing parameters correspond to a current draw of approximately 1.9 μA. The same LPs 102a, 102b can implement event messages using event signaling parameters for amplitude, pulse width, pulse rate, etc., which correspond to a current draw of approximately 0.5 μA for transmission.

[0048] LP 102a, 102b can combine event message transmission with pacing pulses. For example, LP 102a, 102b can use a 50μs wake-up transmission pulse with an amplitude of 2.5V, which will draw 250nC (nanocoulombs) for a 500 ohm electrode load. The pulse transmitting the event message can be followed by the event message encoded in a series of short duration pulses (e.g., 16, 2μs on / off bits), which will draw an additional 80nC. The event message pulse is then followed by the remaining pulse width required to achieve the equivalent charge of a nominal 0.4ms pacing pulse. In this case, the current required to transmit the marker is essentially free because it is used to achieve the necessary pacing capture. Using this approach, the savings in transmission current can be budgeted for the receiver, or the service life can be extended.

[0049] When either LP 102a, 102b senses an intrinsic event, it can transmit an event pulse train of similar quality (but indicative of the sensed event) without adding a pacing pulse remainder. Because the LP 102a, 102b lifetime calculation is designed based on the assumption that the LP 102a, 102b will deliver pacing therapy 100% of the time, transmitting the intrinsic event marker to the other LP 102a, 102b does not affect the nominal calculated LP lifetime.

[0050] In some embodiments, LPs 102a, 102b can deliver pacing pulses at relatively low amplitudes. When low-amplitude pacing pulses are used, the power budget for event messages can be modified to account for a larger portion of the overall device energy budget. As the pacing pulse amplitude is reduced to closer to the amplitude of the event message, LPs 102a, 102b increase the use of event messages by LPs 102a, 102b as part of pacing therapy (also known as sharing "capture charge" and "transmit charge"). As an example, if the nominal pacing voltage can be reduced to <1.25V, then the "half-power" pacing charge circuit can reduce the battery current draw by approximately 50%. A 1.25V pacing pulse will save 1.5μA of the pacing current budget. For lower pulse amplitudes, LPs 102a, 102b can use larger pulse widths.

[0051] By combining event messaging and low-power pacing, LPs 102a, 102b can achieve additional lifespan. Today's lifespan standards specify that lifespan is based on therapy using 2.5V amplitude, 0.4ms pulses at 100% pacing. Alternatively, new standards can be established based on delivering lower amplitude pacing pulses and / or shorter pacing pulses.

[0052] Although not shown, communication capacitors may be provided in LPs 102a, 102b. Communication capacitors may be used to transmit event signals with a higher voltage than event message pulses to improve communication, such as when LPs 102a, 102b have difficulty sensing event messages. High-voltage event signaling may be used for implants with high signal attenuation or in the context of a retry ARQ (Automatic Repeat Request) handshake scheme.

[0053] In some embodiments, an individual LP 102a can include a sealed housing 110 configured for placement or attachment inside or outside a cardiac chamber, and at least two leadless electrodes 108 proximate to the housing 110 and configured for bidirectional communication with at least one other device 106 inside or outside the body.

[0054] Figure 2 A single LP 102a (or 102b) is depicted, showing the functional elements of the LP substantially enclosed within a sealed housing 110. The LP 102a (or 102b) has at least two electrodes 108 located within, on, or near the housing 110 for delivering pacing pulses to and sensing electrical activity from the cardiac chamber muscle, as well as for bidirectional communication with at least one other device within or outside the body. Sealed feedthroughs 130, 131 conduct electrode signals through the housing 110. The housing 110 contains a primary battery 114 to power pacing, sensing, and communication. The housing 110 also contains circuitry 132 for sensing cardiac activity from the electrodes 108, receivers 120, 122 for receiving information from at least one other device via the electrodes 108, and a pulse generator 116 for generating pacing pulses for delivery via the electrodes 108 and for transmitting information to the at least one other device via the electrodes 108. Housing 110 may also contain circuitry for monitoring device health, such as battery current monitor 136 and battery voltage monitor 138, and may contain circuitry for controlling operation in a predetermined manner.

[0055] The electrodes 108 can be configured to communicate bidirectionally between multiple leadless cardiac pacemakers and / or implanted ICDs 106 to coordinate pacing pulse delivery and optional other therapeutic or diagnostic features using messages that identify an event at the individual pacemaker that initiated the message and the pacemaker receiving the message reacts as directed by the message based on the source of the message. The LP 102a, 102b receiving the event message reacts as directed by the event message based on the source or location of the message. In some embodiments or conditions, two or more leadless cardiac pacemakers 108 can be configured to communicate bidirectionally between one or more leadless cardiac pacemakers 102a and / or ICDs 106 and transmit data including a designated code for an event detected or created by an individual pacemaker. Each pacemaker can be configured to emit a unique code corresponding to the type of event and the location of the sending pacemaker.

[0056] In some embodiments, an individual LP 102a, 102b can be configured to deliver pacing pulses with an event message encoded therein, with a code assigned based on the pacemaker location, and configured to transmit the message to one or more other leadless cardiac pacemakers via the event message-encoded pacing pulses. The one or more pacemakers receiving the message are adapted to respond to the message in a predetermined manner based on the type and location of the event.

[0057] Furthermore, information transmitted on the incoming channel can also include an event message from another leadless cardiac pacemaker indicating that the other leadless cardiac pacemaker has sensed a heartbeat or has delivered a pacing pulse, and identifying the location of the other pacemaker. For example, LP 102b can receive an event message from LP 102a and relay it to the programmer. Similarly, information transmitted on the outgoing channel can also include a message sent to another leadless cardiac pacemaker or pacemakers or to the ICD indicating that the sending leadless cardiac pacemaker has sensed a heartbeat or has delivered a pacing pulse at the location of the sending pacemaker.

[0058] Reference again Figure 1 and 2 In addition to one or more LPs 102 a, 102 b, the cardiac pacing system 100 may also include an ICD 106 configured for implantation in electrical contact with a cardiac chamber and for performing cardiac rhythm management functions in combination with the implantable ICD 106. The implantable ICD 106 and the one or more LPs 102 a, 102 b are configured for leadless intercommunication according to conduction of information through body tissue and / or wireless transmission between a transmitter and a receiver as discussed herein.

[0059] In further embodiments, a cardiac pacing system 100 includes at least one LP 102 a, 102 b configured for implantation in electrical contact with a cardiac chamber and configured to perform cardiac pacing functions in combination with a co-implanted ICD 106. The leadless cardiac pacemaker or pacemakers 102 a include at least two leadless electrodes 108 configured for delivering cardiac pacing pulses, sensing induced and / or natural cardiac electrical signals, and transmitting information to the co-implanted ICD 106.

[0060] As shown in the illustrative embodiment, the leadless cardiac pacemakers 102a, 102b can include two or more leadless electrodes 108 configured for delivering cardiac pacing pulses, sensing induced and / or natural cardiac electrical signals, and bidirectionally communicating with a co-implanted ICD 106.

[0061] The LPs 102a, 102b can be configured to operate in a specific location and with a specific function at the time of manufacture and / or when programmed by an external programmer. Bidirectional communication between multiple leadless cardiac pacemakers can be arranged to transmit notification of a sensed heartbeat or delivered pacing pulse event, along with the coded type and location of the event, to one or more implanted pacemakers. The LPs 102a, 102b receiving the communication decode the information and respond based on the receiving pacemaker's location and the predetermined system function.

[0062] In some embodiments, LPs 102a and 102b are configured to be implantable in any chamber of the heart, i.e., either atrium (RA, LA) or either ventricle (RV, LV). Additionally, for a dual-chamber configuration, multiple LPs may be co-implanted (e.g., one in the RA, one in the RV, one in the RV, and one in the coronary sinus proximal to the LV). Certain pacemaker parameters and functions depend on (or assume) knowledge of the chamber in which the pacemaker is implanted (and therefore the chamber with which the LP interacts; e.g., pacing and / or sensing). Some non-limiting examples include sensing sensitivity, induced response algorithms, use of AF suppression in local chambers, blanking & refractory periods, etc. Thus, each LP needs to know the identity of the chamber in which the LP is implanted, and a process may be implemented to automatically identify the local chamber associated with each LP.

[0063] The process for chamber identification can also be applied to subcutaneous pacemakers, ICDs, with leads, etc. For devices with one or more implanted leads, identifying and / or confirming the chamber of the implanted lead can be useful in several related scenarios. For example, for a DR or CRT device, automatic identification and confirmation can reduce the likelihood of a clinician inadvertently placing a V-type lead into the A port of the implantable medical device, or vice versa. As another example, for an SR device, automatic identification of the implanted chamber can enable the device and / or programmer to select and present the correct subset of pacing modes (e.g., AAI or VVI), and the IPG can utilize the correct set of settings and algorithms (e.g., V-AutoCapture versus ACap-Confirm, sensing sensitivity, etc.).

[0064] Likewise Figure 2 , the primary battery 114 has a positive terminal 140 and a negative terminal 142. Current from the positive terminal 140 of the primary battery 114 flows through a shunt 144 to a regulator circuit 146 to create a positive voltage supply 148 suitable for powering the remaining circuits of the pacemaker 102. The shunt 144 enables the battery current monitor 136 to provide an indication of battery current drain and an indirect indication of device health to the processor 112. An illustrative power source may be the primary battery 114.

[0065] refer to Figure 2 The LP is shown as including a temperature sensor 152. The temperature sensor can be any of a variety of well-known temperature sensors, or it can be a temperature sensor developed in the future. For example, temperature sensor 152 can be, but is not limited to, a thermistor, a thermocouple, a resistance thermometer, or a silicon bandgap temperature sensor. Regardless of how temperature sensor 152 is implemented, the temperature sensed by the sensor is preferably provided to controller 112 as a digital signal indicating the blood temperature of the patient implanted with the LP. Temperature sensor 152 can be hermetically sealed within housing 110, but this is not required. Temperature sensor 152 can be used in various ways. For example, temperature sensor 152 can be used to detect the patient's activity level to adjust the pacing rate, i.e., for rate-responsive pacing. When a person begins exercising, their core body temperature initially drops, and then, after extended periods of exercise, their core body temperature eventually increases. Thereafter, when the person stops exercising, their core body temperature will return to baseline. Thus, controller 112 can be configured to detect the patient's activity level based on core blood temperature measurements obtained using temperature sensor 152.

[0066] refer to Figure 2LP is also shown as including an accelerometer 154, which can be sealed within housing 110. Accelerometer 154 can be any of a variety of well-known accelerometer types, or can be an accelerometer developed in the future. For example, accelerometer 154 can be or include a MEMS (micro-electromechanical system) multi-axis accelerometer, such as a type utilizing capacitive or optical cantilever technology, or a piezoelectric accelerometer that exploits the piezoelectric effect of certain materials to measure dynamic changes in mechanical variables. For example, accelerometer 154 can be used to detect the patient's activity level to adjust the pacing rate, i.e., for rate-responsive pacing. It is also possible to use the output of both accelerometer 154 and temperature sensor 152 to monitor the patient's activity level. Alternatively or additionally, the patient's activity level can be monitored based on the patient's heart rate, as detected from the IEGM sensed using electrodes 108, and / or the patient's activity level sensed using a plethysmographic signal obtained using a plethysmographic sensor (not shown) or a heart sound sensor (not shown), but is not limited thereto. The one or more signals generated and output by the accelerometer 154 can be analyzed for frequency content, energy, duration, amplitude, and / or other characteristics. Such signals may or may not be amplified and / or filtered before being analyzed. For example, filtering can be performed using low-pass, high-pass, and / or band-pass filters. The signals output by the accelerometer 154 can be analog signals, which can be analyzed in the analog domain, or can be converted to digital signals (via an analog-to-digital converter) and analyzed in the digital domain. Alternatively, the signals output by the accelerometer 154 can already be in the digital domain. The one or more signals output by the accelerometer 154 can be analyzed by the controller 112 and / or other circuitry. In some embodiments, the accelerometer 154 is packaged with an integrated circuit (IC) designed to analyze the signal(s) it generates. In such embodiments, one or more outputs of the packaged sensor / IC can be an indication of acceleration along one or more axes. In other embodiments, the accelerometer 154 can be packaged with an IC that performs signal conditioning (e.g., amplification and / or filtering), performs analog-to-digital conversion, and stores digital data (indicative of the sensor output) in a memory (e.g., RAM, which may or may not be in the same package). In such embodiments, the controller 112 or other circuitry can read the digital data from the memory and analyze the digital data. Other variations are possible and within the scope of embodiments of the present technology. According to certain embodiments of the present technology described in more detail below, the sensor signal generated by the accelerometer 154 implanted in or on a cardiac chamber can be used to detect mechanical cardiac activity associated with another cardiac chamber.

[0067] In various embodiments, LPs 102a, 102b can manage power consumption to draw limited power from the battery, thereby reducing device size. Each circuit in the system can be designed to avoid large peak currents. For example, cardiac pacing can be achieved by discharging a storage capacitor (not shown) across pacing electrodes. Recharging the storage capacitor is typically controlled by a charge pump circuit. In certain embodiments, the charge pump circuit is throttled so that the storage capacitor is recharged with a constant power from the battery.

[0068] In some embodiments, the controller 112 in one leadless cardiac pacemaker 102a can access the signals on the electrodes 108 and can examine the output pulse duration from the other pacemaker for use as a signature for determining the validity of the triggering information and, for signature limits within predetermined limits, activate the delivery of a pacing pulse after a predetermined delay of zero or more milliseconds. The predetermined delay can be preset at the time of manufacture, programmed via an external programmer, or determined by adaptive monitoring to facilitate identification of the trigger signal and to distinguish the trigger signal from noise. In some embodiments or under some conditions, the controller 112 can examine the output pulse waveform from the other leadless cardiac pacemaker for use as a signature for determining the validity of the triggering information and, for signature limits within predetermined limits, activate the delivery of a pacing pulse after a predetermined delay of zero or more milliseconds.

[0069] Figure 2 LPs 102a, 102b are shown. The LP can include a sealed housing 202 with electrodes 108a and 108b disposed thereon. As shown, electrode 108a can be separate from but partially surrounded by a fixation mechanism 205, and electrode 108b can be disposed on housing 202. The fixation mechanism 205 can be a fixation helix, a plurality of hooks, barbs, or other attachment features configured to attach the pacemaker to tissue, such as cardiac tissue. Electrodes 108a and 108b are reference Figure 2 Examples of electrodes 108 are shown and discussed above.

[0070] The housing may also include an electronics compartment 210 within the housing that contains the electronic components necessary for pacemaker operation, including, for example, a pulse generator, a receiver, a battery, and a processor for operation. For example, the sealed housing 202 may be suitable for implantation on or within a human heart and may be cylindrical, rectangular, spherical, or any other suitable shape.

[0071] The housing may comprise a conductive, biocompatible, inert, and anodically safe material such as titanium, 316L stainless steel, or other similar material. The housing may also comprise an insulator disposed over the conductive material to separate the electrodes 108a and 108b. The insulator may be an insulating coating on a portion of the housing between the electrodes and may comprise a material such as silicone, polyurethane, parylene, or other biocompatible electrical insulators commonly used in implantable medical devices. Figure 2 In some embodiments, a single insulator 208 is disposed along the portion of the housing between electrodes 108a and 108b. In some embodiments, the housing itself may comprise an insulator rather than a conductor, such as alumina ceramic or other similar material, and the electrodes may be disposed on the housing.

[0072] like Figure 2 As shown in FIG, the pacemaker may also include a header assembly 212 for isolating 108a and 108b. The header assembly 212 may be made of PEEK, tecothane, or another biocompatible plastic and may include a ceramic-to-metal feedthrough, a glass-to-metal feedthrough, or other suitable feedthrough insulators known in the art.

[0073] Electrodes 108a and 108b may comprise pacing / sensing electrodes or return electrodes. For example, a low polarization coating may be applied to the electrodes, such as sintered platinum, platinum-iridium, iridium, iridium oxide, titanium nitride, carbon, or other materials commonly used to reduce polarization effects. Figure 2 In the embodiment of the present invention, electrode 108a can be a pace / sense electrode and electrode 108b can be a return electrode. Electrode 108b can be a portion of conductive housing 202 that does not include insulator 208.

[0074] Several techniques and structures can be used to attach the housing 202 to the inner or outer wall of the heart. The helical fixation mechanism 205 can enable the device to be inserted through a guide catheter toward the endocardium or epicardium. A twistable catheter can be used to rotate the housing and force the fixation device into the heart tissue, thereby attaching the fixation device (and Figure 2 Electrode 108a) in the device is fixed in contact with the stimulable tissue. Electrode 108b can be used as an indifferent electrode for detection and pacing. The fixation mechanism can be partially or fully coated to achieve electrical insulation and can include a steroid-eluting matrix on or near the device to minimize fibrotic reactions, as is known in conventional pacing electrode leads.

[0075] Implant-to-implant event messaging

[0076] LPs 102a and 102b can coordinate operations with each other in various ways using implant-to-implant (i2i) communication via event messages. The terms i2i communication, i2i event message, and i2i event marker are used interchangeably herein to refer to event-related messages and IMD / IMD operation-related messages transmitted from an implanted device and directed to another implanted device (although an external device, such as a programmer, can also receive i2i event messages). In certain embodiments, LPs 102a and 102b operate as two independent leadless pacemakers to maintain beat-to-beat dual-chamber functionality via a "master / slave" operational configuration. For descriptive purposes, the ventricular LP 102b shall be referred to as the "vLP" and the atrial LP 102a shall be referred to as the "aLP." The LP 102 designated as the master device (e.g., the vLP) may implement all or most dual-chamber diagnostic and therapy determination algorithms. For the purposes of the following description, it is assumed that the vLP is the "master" device and the aLP is the "slave" device. Alternatively, the aLP may be designated as the master device and the vLP may be designated as the slave device.The master device orchestrates most or all decision making and timing determinations (including, for example, rate-response changes).

[0077] In accordance with certain embodiments, a method for coordinating operation between first and second leadless pacemakers (LPs) configured to be fully implanted within first and second chambers of a heart is provided. A method transmits an event marker via conductive communication through electrodes positioned along a housing of a first LP, the event marker indicating one of a local pacing or sensing event. The method detects the event marker at a second LP via a sensing channel. The method identifies the event marker at the second LP based on a predetermined pattern configured to indicate that an event of interest has occurred in a remote chamber. In response to identifying the event marker, the method initiates a related action in the second LP.

[0078] Figure 4 FIG. 4 is a timing diagram 400 illustrating an example of i2i communication for a pacing event. For example, an i2i communication may be transmitted from LP 102a to LP 102b. Figure 4 As shown in FIG, in this embodiment, an i2i transmission 402 is sent prior to delivery of a pacing pulse 404 by a transmitting LP (e.g., LP 102). This enables a receiving LP (e.g., LP 102b) to prepare for remote delivery of the pacing pulse. The i2i transmission 402 includes an envelope 406, which may include one or more individual pulses. For example, in this embodiment, the envelope 406 includes a low-frequency pulse 408 followed by a high-frequency pulse train 410. The low-frequency pulse 408 lasts for a period of time T. i2iLF , and the high frequency pulse train 410 lasts for a period of time T i2iHF The end of the low frequency pulse 408 and the beginning of the high frequency pulse train 410 are separated by a gap period T i2iGap separate.

[0079] like Figure 4 As shown in FIG, an i2i transmission 402 lasts for a period Ti2iP, and a pacing pulse 404 lasts for a period Tpace. The end of the i2i transmission 402 and the start of the pacing pulse 404 are separated by a delay means TdelayP. The delay period can be, for example, between approximately 0.0 and 10.0 milliseconds (ms), particularly between approximately 0.1 ms and 2.0 ms, and more particularly, between approximately 1.0 ms. As used herein, the term "approximately" refers to + / - 10% of a specified value.

[0080] Figure 5 FIG. 5 is a timing diagram 500 illustrating an example of i2i communication for sensing an event. For example, an i2i communication may be transmitted from LP 102a to LP 102b. Figure 5 As shown in FIG, in this embodiment, the LP is transmitted (eg, the LP 102a detects a sensing event when the sensed intrinsic activation 502 crosses the sensing threshold 504). A predetermined delay period T follows the detection. delayS , the transmission LP transmission lasts for a predetermined period of time T i2iS i2i transmission 506. The delay period may be, for example, between approximately 0.0 and 10.0 milliseconds (ms), particularly between approximately 0.1 ms and 2.0 ms, and more particularly approximately 1.0 ms.

[0081] As with i2i transmission 402, i2i transmission 506 may include an envelope that may include one or more individual pulses. For example, similar to envelope 406, the envelope of i2i transmission 506 may include a low-frequency pulse followed by a high-frequency pulse train.

[0082] Optionally, where the first LP is located in the atrium and the second LP is located in the ventricle, the first LP generates an AS / AP event marker to indicate that an atrial sensing (AS) event or an atrial pacing (AP) event has occurred or will occur in the near future. For example, the AS and AP event markers can be transmitted after the corresponding AS or AP event. Alternatively, the first LP can transmit the AP event marker slightly before delivering the atrial pacing pulse. Alternatively, where the first LP is located in the atrium and the second LP is located in the ventricle, the second LP initiates an atrioventricular (AV) interval after receiving the AS or AP event marker from the first LP; and initiates a post-atrial ventricular blanking (PAVB) interval after receiving the AP event marker from the first LP.

[0083] Alternatively, the first and second LPs can operate in a "pure" master / slave relationship, where the master LP delivers a "command" marker in addition to or instead of an "event" marker. The command marker instructs the slave LP to perform an action, such as delivering a pacing pulse. For example, when the slave LP is located in the atrium and the master LP is located in the ventricle, in a pure master / slave relationship, upon receiving an AP command marker from the master LP, the slave LP will immediately deliver a pacing pulse to the atrium.

[0084] According to some embodiments, communication and synchronization between the aLP and vLP is achieved via conducted communication (according to the i2i communication protocol) of tags / commands in event messages. As explained above, conducted communication refers to event messages transmitted from the sensing / pacing electrodes at frequencies outside the RF or Wi-Fi frequency range. Alternatively, event messages can be conveyed via a communication channel operating within the RF or Wi-Fi frequency range. The following figures and corresponding descriptions illustrate non-limiting examples of tags that can be transmitted in event messages. The following figures and corresponding descriptions also include descriptions of the tags and examples of the consequences that occur in the LP receiving the event message. Table 1 shows exemplary event tags sent from the aLP to the vLP, while Table 2 shows exemplary event tags sent from the vLP to the aLP. In a master / slave configuration, an AS event tag is sent from the aLP each time an atrial event is sensed outside the post-ventricular atrial blanking (PVAB) interval or some other alternatively defined atrial blanking period. An AP event tag is sent from the aLP each time the aLP delivers a pacing pulse in the atrium. The aLP may restrict the transmission of the AS marker, such that the aLP transmits the AS event marker when an atrial event is sensed outside the PVAB interval and outside the post-ventricular atrial refractory period (PVARP) or some other alternatively defined atrial refractory period. Alternatively, the aLP may not restrict the transmission of the AS event marker based on the PVARP, but rather transmit the AS event marker every time an atrial event is sensed.

[0085] Table 1

[0086]

[0087] As shown in Table 1, when the aLP transmits an event message including an AS event marker (indicating that the aLP sensed an intrinsic atrial event), the vLP initiates the AV interval timer. If the aLP transmits an AS event marker for all sensed events, the vLP will preferably first determine if the PVAB or PVARP interval is inactive before initiating the AV interval timer. However, if the aLP transmits an AS event marker only when it senses an intrinsic signal outside of the PVAB or PVARP interval, the vLP can initiate the AV interval timer after receiving the AS event marker without first checking the PVAB or PVARP status. When the aLP transmits an AP event marker (indicating that the aLP has delivered or is about to deliver a pacing pulse to the atria), if the PVARP interval is inactive, the vLP initiates the PVAB timer and the AV interval timer. The vLP can also blank its sense amplifier to prevent possible crosstalk sensing of remote pacing pulses delivered by the aLP.

[0088] Table 2

[0089]

[0090] As shown in Table 2, when the vLP senses a ventricular event, the vLP transmits an event message including a VS event marker, in response to which the aLP can initiate a PVARP interval timer. When the vLP delivers or is about to deliver a pacing pulse in the ventricle, the vLP transmits a VP event marker. When the aLP receives a VP event marker, the aLP initiates the PVAB interval timer and the PVARP interval timer. The aLP can also blank its sense amplifier to prevent possible crosstalk sensing of remote pacing pulses delivered by the vLP. The vLP can also transmit an event message including an AP command marker to command the aLP to deliver a pacing pulse in the atrium immediately upon receiving the command, without delay.

[0091] The aforementioned event markers are examples of a subset of markers that can be used to enable the aLP and vLP to maintain full dual chamber functionality. In one embodiment, the vLP can execute all dual chamber algorithms, while the aLP can execute atrial-based hardware-related functions, such as PVAB implemented locally within the aLP. In this embodiment, the aLP is effectively considered a remote "wireless" atrial pacing / sensing electrode. In another embodiment, the vLP can execute most but not all dual chamber algorithms, while the aLP can execute a subset of diagnostic and therapeutic algorithms. In alternative embodiments, the vLP and aLP can execute diagnostic and therapeutic algorithms equally. In some embodiments, decision-making responsibility can be divided solely into one of the aLP or vLP. In other embodiments, decision-making responsibility can involve joint inputs and responsibilities.

[0092] In one embodiment, ventricular-based pacing and sensing functions do not rely on any i2i communication to provide safer therapy. For example, in the event of a loss (prolonged or transient) of LP-to-LP (i2i) communication, the system 100 can automatically revert to safe ventricular-based pacing / sensing functions because the vLP device is running all necessary algorithms to independently implement these functions. For example, the vLP can revert to VVI mode because the vLP does not rely on i2i communication to perform ventricular pacing / sensing activities. Once i2i communication is restored, the system 100 can automatically restore dual-chamber function.

[0093] Messages transmitted between LPs (e.g., aLP and vLP) are generally referred to herein as i2i messages because they are implant-to-implant messages. As described above, such messages can include event markers that enable one LP to notify the other LP of a pacing event or a sensed event. For example, in certain embodiments, whenever the aLP senses an atrial event or paces the right atrium, the aLP will transmit an i2i message to the vLP to notify the vLP of the sensed or paced event in the atrium. In response to receiving such an i2i message, the vLP can start one or more timers that enable the vLP to sense or pace the right ventricle. Similarly, whenever the vLP senses a ventricular event or paces the right ventricle, the vLP can transmit an i2i message to the aLP.

[0094] The i2i messages sent between LPs can be relatively short messages that only allow a first LP to notify a second LP of an event sensed by or caused (paced) by the first LP, and vice versa. Such i2i messages may be referred to herein as event marker i2i messages, or more concisely, event i2i messages. In some cases, the i2i messages sent between LPs may be extended i2i messages that include (in addition to the event marker) an extension. In some embodiments, the extended i2i message includes an event marker (e.g., 9 bits), followed by an extension indicator (e.g., 2 bits), followed by an extended message payload portion (e.g., 17 bits), followed by a cyclic redundancy check (CRC) code (e.g., 6 bits) or some other type of error detection and correction code.

[0095] In certain embodiments, whenever an i2i message is sent by an LP (or other type of IMD, such as an S-ICD), the i2i message will include an extension indicator so that the receiving LP knows whether the i2i message it received includes an extension portion. In such embodiments, even relatively short event i2i messages will include an extension indicator. The extension indicator (e.g., two bits) is used by the LP (or other IMD) transmitting the i2i message to indicate to the receiving LP whether the i2i message is an extended i2i message. In certain embodiments, if the receiving LP determines that the received i2i message is not an extended i2i message based on the extension indicator bit, the receiving LP may ignore any bits after the extension bit. In this case, the receiving LP only decodes the event flag. On the other hand, if the LP receiving the i2i message determines that the received i2i message is an extended i2i message based on the extension indicator bit, the LP receiving the i2i message also decodes the bits following the extension bit and determines whether the i2i message is a valid message based on a CRC code (or other type of error detection and correction code). If the extended i2i message is a valid i2i message, the LP receiving the extended i2i message will appropriately modify its operations, update parameters, etc. based on the information included in the extended i2i message. In some embodiments, event i2i messages that are not extended i2i messages do not include any error detection and correction code.

[0096] In an extended i2i message, the event marker bit and the extension indicator bit are located in the event marker field and the extension indicator field, respectively, of the i2i message packet. In some embodiments, the extended portion (following the event marker bit and the extension indicator bit) includes a message bit (in the message field) and a rate indicator bit (in the rate indicator field), which are part of the payload. The payload may alternatively or additionally include other types of fields, such as an acknowledgment field, which is used in some cases by one LP to acknowledge receipt of an i2i message from another LP for certain (e.g., critical) types of messages.

[0097] More generally, various types of information can be included within the payload of an extended i2i message. For example, the payload can include a pacing rate indicator that enables one LP to notify another LP of the pacing rate. For example, assume an LP system provides rate-responsive pacing, in which the pacing rate is adjusted based on detected patient physical activity, e.g., using an accelerometer, a temperature sensor, and / or other type of LP sensor. In such an LP system, the vLP can notify the aLP of the rate at which the patient's heart should be paced so that the aLP and vLP can perform synchronized pacing. To accomplish this, the vLP can send a pacing rate indicator to the aLP in the payload of an extended i2i message. For example, the pacing rate indicator can be a value indicating a pacing rate value (e.g., 80 bpm), a code that the aLP can look up (e.g., in a stored lookup table) and that corresponds to the paced rate value, or an equation fed to the aLP to determine the pacing rate value, but is not limited thereto. Alternatively, the pacing rate indicator can be a beat-to-beat interval value (e.g., 0.75 seconds), and the aLP can look up a code corresponding to the beat-to-beat interval value, or the aLP feeds an equation to determine the beat-to-beat interval value, but is not limited thereto. Other variations are possible and are within the scope of the embodiments described herein.

[0098] Fake news

[0099] As described above, implantable medical devices and systems often rely on proper communication to operate correctly. For example, in dual leadless cardiac pacemaker systems, such as those described above with reference to Figure 1-5 In the described system, i2i communication is critical for proper synchronization of the system. However, noise can cause one or more devices in such a system to falsely detect i2i messages and respond inappropriately thereto. For example, the atrial LP may falsely detect a message from the ventricular LP, where the false message includes a portion that the atrial LP incorrectly decodes as a pacing rate indicator, causing the atrial LP to pace the right atrium at an inappropriately high rate. As also described above, to reduce the chance of false messages, such messages can include redundant data for error detection and correction. However, due to the desire to maintain low power consumption, the message delivery and / or error correction and detection schemes can be simple, and false messages may still slip through.

[0100] Certain embodiments of the technology described herein can be used to reduce the frequency with which an IMD, such as a vLP (e.g., 102b) or an aLP (e.g., 102a), receives false messages. Additionally or alternatively, certain embodiments of the technology can be used to mitigate the adverse effects of an IMD receiving one or more false messages.

[0101] When the message is accepted by the IMD, the IMD may trigger a timer, trigger an event, and / or otherwise respond to the message to control or provide instructions to the IMD that received the message. Conversely, when the message is rejected, this means that the message is prevented (e.g., blocked) from being used to trigger a timer, trigger an event, and / or otherwise be used to control or provide instructions to the IMD that received the message.

[0102] As used herein, the term "message" may refer to an actual transmitted message that is received and capable of being decoded by an IMD, an actual transmitted message that is received but is too noisy to be decoded by the IMD, an actual transmitted message that is received but is incorrectly decoded as a different message due to noise, and noise that is received but initially mistaken for an actual message but cannot be decoded by the IMD because it is sufficiently different from the actual message. As used herein, the term "false message" refers to noise that is received and decoded by an IMD and is mistaken for an actual message because it is sufficiently similar to the actual message. As used herein, the term "false message" may also refer to an actual transmitted message that is received but is incorrectly decoded as a different message due to noise. As used herein, the term "real message" refers to an actual transmitted message that is received by an IMD and correctly decoded by the IMD. The actual transmitted message may have been sent by another IMD, or alternatively, by a non-implanted device, such as a programmer (e.g., 109). In the case where the message actually sent includes multiple parts, it is possible that the first part of the received message is decoded correctly, while the second part of the received message is decoded incorrectly. In this case, it can be said that the first part of the received message is the "true sub-message" and the second part of the received message is the "wrong sub-message".

[0103] In systems that include an aLP (e.g., 102a) and a vLP (e.g., 102b) designed to provide coordinated (also called synchronized) pacing of the atrial and ventricular heart chambers, false messages can potentially cause the aLP and vLP to become desynchronized, such that the aLP and vLP take a long time to resynchronize, or they may not resynchronize at all. For example, if the aLP receives a false message indicating that the aLP is pacing at a high rate (e.g., 110 bpm), then when the vLP is actually pacing at a low rate (e.g., 60 bpm), the aLP will pace the right atrium at a much higher rate than the vLP is pacing the right ventricle. While pacing at the high rate, the aLP will search for messages from the vLP at the high rate, but the vLP will still send messages at the low rate. If the rate difference is large enough, the aLP and vLP may never have a chance to resynchronize, and the desynchronization of the aLP and vLP can continue indefinitely. In this case, the vLP device can no longer correct the incorrect high rate used by the aLP. In certain embodiments, the system will enter a "safe mode" during this time, and the aLP will cease pacing indefinitely.The problem of the aLP and vLP not being able to synchronize back up with each other may be referred to herein as a "lock-up" problem.

[0104] The "locking" problem described above can occur, for example, if the aLP receives an erroneous i2i message indicating that the aLP is pacing at a much higher rate than the vLP is currently pacing, or if the vLP receives an erroneous i2i message indicating that the vLP is pacing at a much higher rate than the aLP. The so-called "locking" problem can also occur for a variety of other reasons discussed below, some of which are related to the LP receiving false messages and others of which are related to the LP failing to receive a sent message. For example, if the vLP sends an i2i message to the aLP notifying the aLP that it should pace at a higher rate than before (and assuming that the vLP itself increases its rate to the higher rate), if the aLP fails to receive that i2i message and therefore does not increase its pacing rate, then the aLP may pace at a rate much lower than the vLP, potentially preventing the aLP and vLP from being able to synchronize back up with each other again.

[0105] Examples of other types of i2i messages that, if missed, could potentially cause the "lockout" issue described above are i2i messages that include, for example, a Recommended Change Time (RRT) indicator or an Automatic Mode Switch (AMS) in indicator, an AMS out indicator, a magnet in indicator, or a magnet out indicator. Each of these indicators will be discussed below, along with an explanation of how failure to receive an i2i message that includes such an indicator could potentially cause the "lockout" issue described above.

[0106] According to certain embodiments, when the aLP detects atrial flutter (AF1) or atrial fibrillation (AF), the aLP triggers automatic mode switching (AMS). Automatic mode switching (AMS) is a standard dual-chamber pacemaker feature that provides an automatic transition from AV synchronized pacing mode to a non-atrial tracking mode when a high atrial rate is detected (e.g., during atrial fibrillation or flutter) to avoid nonphysiologically high ventricular rates that would otherwise lead to poor / symptomatic hemodynamic cardiac performance. Conversely, when the high atrial rate returns to a higher physiological rate, the AMS function terminates and the pacemaker system transitions back to AV synchronized pacing mode. In addition, the pacemaker system can use these AMS entry and exit events as triggers to initiate other actions, such as collecting diagnostic data, storing intracardiac electrograms, etc.

[0107] By using two independent LPs (e.g., a vLP and an aLP) operating in dual-chamber mode, it can be expected that the LPs will respond to AMS entry and exit events in a consistent and synchronized manner (assuming the AMS functionality is available and selected). One means of accomplishing this response synchronization is to send a special message from the first LP (e.g., the aLP) to the second LP (e.g., the vLP) indicating that the threshold for AMS entry or exit has been met. Since the AMS entry / exit thresholds are related to the atrial rate, a preferred embodiment is to have the aLP directly responsible for determining AMS transitions, which the aLP then communicates to the vLP via a special message. Alternatively, the vLP can be responsible for determining AMS transitions by monitoring the rate at which it receives atrial sensing (AS) atrial to ventricular (A2V) i2i markers.

[0108] Because the underlying high atrial rate can persist for a relatively long and undetermined duration, an exemplary embodiment includes sending an AMS special message (e.g., an "AMS Enter" special message) from the first LP to the second LP upon arrival of an AMS Enter trigger, and then sending a separate "AMS Exit" special message upon arrival of an AMS Exit trigger. In other words, each time the aLP enters AMS mode, the aLP can send an i2i message including an AMS Enter indicator to the vLP, and each time the aLP exits AMS mode, the aLP can send an i2i message to the vLP. If the vLP receives an erroneous i2i message including a message that the vLP decodes as an AMS Enter indicator, the vLP and the aLP can become out of sync with each other, potentially leading to the locking issue described above, where the aLP and vLP cannot synchronize back up with each other.

[0109] Separate and independent LPs will likely reach their respective recommended replacement times (RRTs) at different points in their lifecycles (e.g., due to different initial battery capacities, different pacing output levels or burdens, etc.). However, it may be desirable or important for the dual-chamber system to synchronize the response of either LP to the RRT. For example, it may be desirable to disable the rate-response after reaching the RRT. As another example, it may be desirable to reduce the basal rate after reaching the RRT. Modifying other features is also contemplated. One means of achieving this synchronization of RRT responses is to send a special message from the first LP to the second LP indicating that the RRT threshold has been reached in the first LP. In other words, when the first LP reaches its RRT, the first LP can send an i2i message to the second LP including an RRT arrival indicator. In response to receiving the RRT arrival indicator from the first LP, the second LP can shut down certain types of circuits and / or functions. If the first LP receives an erroneous i2i message including content that the first LP decodes as an RRT arrival indicator sent by the second LP, this can cause the first and second LPs (e.g., the vLP and the aLP) to become unsynchronized with each other, potentially leading to the locking issue described above.

[0110] An externally applied magnet to a patient with an implanted IMD (e.g., pacemaker, ICD, etc.) is used to (a) immediately initiate uninhibited fixed-rate pacing (e.g., DOO, VOO, or AOO modes, as appropriate) and / or (b) provide a rapid means of assessing the IMD's battery status (via a standardized pattern of induced pacing rates). By using two independent LPs operating in dual-chamber mode, it is desirable for these LPs to respond to the applied magnet in a consistent and synchronized manner (assuming the magnet mode functionality is available and selected). One means of achieving this synchronization of responses is to send a special message from the first LP to the second LP indicating that a magnet has been (or is being) actively detected by the first LP. In other words, the first LP that detects a magnet can send an i2i message including a magnet detection indicator to the second LP to indicate the first LP's initial detection of the magnet, and can then send a separate i2i message to indicate the loss of detection of that magnet by the first LP. After the first LP detects the applied magnet and the second LP receives the i2i message including the magnet detection indicator, the LPs can immediately and synchronously initiate the appropriate predefined or programmed magnet mode protocol. For example, the LP can immediately transition from its programmed dual chamber functional mode (e.g., DDDR) to a defined uninhibited fixed rate magnet mode (e.g., DOO or VOO). In addition, the mode and / or rate of the pacing output can conform to a defined magnet mode protocol (e.g., according to AAMI PC88). The magnet mode setting can be maintained by both LPs until a magnet is no longer detected, at which point the LPs will synchronize and return to their normal mode and function. If the first LP receives an erroneous i2i message that includes content that the first LP decodes as a magnet detection indicator that it believes was sent by the second LP, then this can cause the first and second LPs (e.g., vLP and aLP) to become out of sync with each other, potentially leading to the locking issue described above.

[0111] The various embodiments of the present technology described herein can be used to prevent or reduce the probability of the above-mentioned "lock-in" problem. Additionally or alternatively, the various embodiments of the present technology described herein can be used to mitigate the adverse effects of false messages, if they occur. The various embodiments described herein can be used alone or in combination with each other. For example, one, two, or more of the embodiments described below can be implemented.

[0112] Slew rate protection

[0113] In accordance with certain embodiments of the present technology for a system including two or more LPs, whenever a first LP receives an i2i message from a second LP that instructs the second LP to increase its pacing rate by more than a threshold amount, the second LP limits its increase to the threshold amount, which is set at some level that prevents the LPs from becoming excessively out of sync with each other. For such embodiments, if an increase in pacing rate by more than the threshold amount is indeed required, then that increase will need to occur gradually, rather than all at once, to avoid the "lock-up" problem described above. Such embodiments may be referred to as slew rate protection embodiments because they limit the rate at which one LP can increase its pacing rate in response to a message that may (or may not) be a false message. Such embodiments may also be used in situations where one or more LPs are configured to adjust their pacing rate in response to an i2i message that includes a pacing rate indicator transmitted by another type of IMD, such as an S-ICD, but is not limited thereto. More generally, the following references Figure 6A Such embodiments, described in more detail by a high-level flowchart, are for use with a leadless pacemaker (LP) implanted within or on a first cardiac chamber of a patient, the patient's first cardiac chamber also having an implantable medical device (IMD) remotely located relative to the LP, wherein the LP is configured to pace the first cardiac chamber (e.g., the right atrium or right ventricle) and adjust the pacing rate of the first cardiac chamber based on a pacing rate indicator included in an i2i message received from the IMD (e.g., another LP or an S-ICD).

[0114] refer to Figure 6A Step 602 involves the LP monitoring i2i messages. The LP performing step 602 may be, for example, an aLP 102a implanted in (or on) the right atrium, but is not limited thereto. The i2i messages monitored at step 602 may be, but are not limited to, i2i messages transmitted by another LP (e.g., a vLP 102b implanted in or on the right ventricle) or by an S-ICD (e.g., 106). Such monitored i2i messages may include extended i2i messages that include a pacing rate indicator within their payload. One or more receivers (e.g., 120 and / or 122) of the LP may be used to perform step 602. Such receiver(s) may be connected to electrodes (e.g., 108) if the i2i messages are conducted communication type messages, or may be connected to antennas (e.g., 128) if the i2i messages are RF communication type messages.

[0115] Still refer to Figure 6AAt step 604, it is determined whether an i2i message has been received. If it is determined that no i2i message has been received, the process returns to step 602 and the LP continues to monitor i2i messages. If it is determined that an i2i message has been received, the process proceeds to step 606. The message received at step 604 may not actually be a genuine message, but may be a false message.

[0116] The types of messages that may be received include relatively simple event marker i2i messages that do not include a pacing rate indicator, or extended i2i messages that may include a pacing rate indicator. As described above, such extended i2i messages may include error detection and correction codes, such as CRC codes. Thus, steps 602 and / or 604 may involve performing error detection and correction.

[0117] At step 606, a determination is made as to whether the received i2i message includes a pacing rate indicator. As described above, the pacing rate indicator can be, for example, a value indicating a pacing rate value (e.g., 80 bpm), a code that the LP can look up (e.g., in a stored lookup table) and corresponds to the paced rate value, or an equation fed to the LP to determine the pacing rate value, but is not limited thereto. Alternatively, the pacing rate indicator can be a beat-to-beat interval value (e.g., 0.75 seconds), a code that the LP can look up and correspond to the beat-to-beat interval value, or an equation fed to the LP to determine the beat-to-beat interval value, but is not limited thereto. Other variations are possible and are within the scope of the embodiments described herein. For another example, the pacing rate indicator can be a signed adjustment value or code that specifies by how much the LP should increase its pacing rate (if the signed adjustment value or code has a positive sign) or decrease its pacing rate (if the signed adjustment value or code has a negative sign). In situations where the LP is to adjust its pacing rate to equal a new rate indicated by another LP or other type of IMD, rather than jumping directly to the new rate, the LP may adjust its pacing rate gradually, eg, linearly, exponentially, or otherwise.

[0118] If the answer to the determination at step 606 is "no" (meaning that the received i2i message does not include a pacing rate indicator), then the process proceeds to step 610 and there is no adjustment to the pacing rate. If the answer to the determination at step 606 is "yes" (meaning that the received i2i message does include a pacing rate indicator), then the process proceeds to step 608 and a determination is made whether adjusting the pacing rate to match the value set by the pacing rate indicator will result in an adjustment of the pacing rate exceeding a rate adjustment threshold. The rate adjustment threshold may be a predetermined value (e.g., 15 bpm or 20 bpm). Alternatively, the rate adjustment threshold may be a predetermined function of the current pacing rate. For example, the rate adjustment threshold may be a predetermined percentage of the current pacing rate (e.g., 15% or 20%). For another example, the rate adjustment threshold may be a predetermined percentage (e.g., 25%) of the difference between the current pacing rate (e.g., 80 bpm) and the base pacing rate (e.g., 60 bpm). For further examples, the rate adjustment threshold can be limited to the greater (or lesser) of a predetermined value, a predetermined percentage of the current pacing rate, or a predetermined percentage of the difference between the current pacing rate and the basal pacing rate. Other variations are possible and within the scope of the embodiments described herein. Additionally, it should be noted that the rate adjustment threshold used when the pacing rate is increased can be different from the rate adjustment threshold used when the pacing rate is decreased. In other words, there can be a rate increase threshold and a rate decrease threshold that can be different from each other.

[0119] If the answer to the determination at step 608 is "no" (meaning that adjusting the pacing rate to match the rate specified by the pacing rate indicator would not cause the adjustment to the pacing rate to exceed the rate adjustment threshold), then flow proceeds to step 612. At step 612, the pacing rate is adjusted to match the rate specified by the pacing rate indicator.

[0120] If the answer to the determination at step 608 is "yes" (meaning that adjusting the pacing rate to match the frequency specified by the pacing rate indicator will result in an adjustment to the pacing rate that exceeds the frequency adjustment threshold), then the process proceeds to step 614. The pacing rate is adjusted at step 614, but the amount by which the pacing rate is adjusted is limited to a specified amount. The specified amount (the amount to which the pacing rate adjustment is limited) can be a predetermined value (e.g., 15 bpm or 20 bpm), or a predetermined function of the current pacing rate, but is not limited thereto. For example, the predetermined amount can be a predetermined percentage of the current pacing rate (e.g., 15% or 20%). For another example, the predetermined amount can be a predetermined percentage (e.g., 25%) of the difference between the current pacing rate (e.g., 80 bpm) and the basal pacing rate (e.g., 60 bpm). Other variations are possible and within the scope of the embodiments described herein.

[0121] Periodic decreases in pacing rate

[0122] Assume that in a master / slave leadless pacemaker system configuration, the vLP acts as the "master" and the aLP acts as the "slave." As described above, "locking" can occur, for example, if the aLP receives a false message indicating that the aLP is pacing at a high rate, when the vLP is actually pacing at a low rate, thereby causing the aLP to pace the atria at a rate much higher than the rate at which the vLP is pacing the ventricles. To prevent the aLP and vLP from remaining out of sync indefinitely, the aLP will periodically (e.g., once every specified length of time, or once every specified number of cardiac cycles) reduce its pacing rate by a specified amount (e.g., a value or percentage) whenever the aLP does not receive an i2i message from the vLP for at least a specified period of time, thereby eventually bringing the pacing rate aLP close enough to the pacing rate of the vLP so that the aLP can receive the i2i message from the vLP and the aLP and vLP can regain synchronization with each other. Such embodiments may also be used where one or more LPs are configured to adjust their pacing rates in response to an i2i message including a pacing rate indicator transmitted by another type of IMD, such as an S-ICD, but are not limited thereto. More generally, the following references Figure 6B Such embodiments, described in more detail by a high-level flowchart, are for use with a leadless pacemaker (LP) implanted within or on a first cardiac chamber of a patient, the patient's first cardiac chamber also having an implantable medical device (IMD) remotely located relative to the LP, wherein the LP is configured to pace the first cardiac chamber (e.g., the right atrium or right ventricle) and adjust the pacing rate of the first cardiac chamber based on a pacing rate indicator included in an i2i message received from the IMD (e.g., another LP or an S-ICD).

[0123] refer to Figure 6B , step 602 involves the LP monitoring i2i messages. Figure 6B Step 602 in the above reference Figure 6A The steps 602 described above are the same and therefore do not need to be described again. At step 603, a determination is made as to whether a specified time period (a time period during which an i2i message including a pacing rate indicator is expected to be received, or a specified number of i2i messages including a pacing rate indicator are expected to be received, has expired. The specified time period, which may also be referred to as an expected time period, may be a predetermined time period, such as, but not limited to, 1 second, 1.5 seconds, 2 seconds, 5 seconds, or 10 seconds. The expected time period (also referred to as the specified time period) may alternatively be a specified number (N) of cardiac cycles, where N is a predetermined integer equal to or greater than 1. For example, N may be 1, 2, 3, 5, 10, or 15, but not limited to this.

[0124] If the answer to the determination at step 603 is "no," the flow proceeds to step 604. At step 604, it is determined whether an i2i message has been received. If it is determined that an i2i message has not been received, the flow returns to step 602 and the LP continues to monitor for i2i messages. If it is determined that an i2i message has been received, the flow proceeds to step 606. Steps 604 and 606 are identical to those described above with reference to FIG. Figure 6A Steps 604 and 606 are identical and therefore need not be described again. Figure 6B Steps 606, 608, 610, 612, and 614 in FIG. 6A are identical to those commonly numbered steps described above with reference to FIG. 6A and therefore require further description. In an alternative embodiment, the order of steps 603 and 604 is reversed, and if the answer to the determination at step 604 is "no," then the flow will proceed from step 604 to step 603, if the answer to step 603 is "no," then the flow will return from step 603 to step 602, if the answer to step 603 is "yes," then the flow will still proceed to step 605, and if the answer to step 604 is "yes," then the flow will still proceed to step 606. Figure 6B If the answer to the determination at step 606 is "yes", then the process can also go directly to Figure 6B Step 606 in the flow jumps to 612. Other variations are also possible.

[0125] Return to Figure 6B If the answer to the determination at step 603 is "yes" (meaning that the specified time period for which the i2i message was expected to have been received has expired), then the process proceeds to step 605. At step 605, in response to the LP not receiving the i2i message within the expected time period, the LP reduces its pacing rate at which it paces the cardiac chamber it is responsible for pacing (e.g., the first cardiac chamber). At step 605, in response to the LP not receiving the i2i message within the expected time period, the amount by which the LP reduces the pacing rate of the first cardiac chamber paced by the LP may be a predetermined value, such as, but not limited to, 5 bpm, 10 bpm, or 15 bpm. Alternatively, at step 605, the amount by which the LP reduces the pacing rate may be a predetermined function of the current pacing rate. For example, the amount may be a predetermined percentage of the current pacing rate (e.g., 15% or 20%). For another example, the amount may be a predetermined percentage (e.g., 25%) of the difference between the current pacing rate (e.g., 80 bpm) and the basal pacing rate (e.g., 60 bpm). Other variations are possible and within the scope of the embodiments described herein.

[0126] Multiple messages

[0127] According to certain embodiments of the present technology, when a second LP (or other type of IMD, such as an S-ICD) sends certain types of extended i2i messages to a first LP, the second LP (or other type of IMD) must send the extended i2i message at least M times (where M is an integer greater than or equal to 2) within a specified time or cardiac cycle, and the first LP must receive the extended i2i message at least N times (where N is an integer greater than or equal to 2 and may be equal to or less than M) within the specified amount of time or cardiac cycle in order for the first LP to comply with the instructions included in the extended i2i message. Exemplary extended i2i message types that the sending LP (or other type of IMD) must send at least M times and the receiving LP must receive at least N times may include, but are not limited to, extended i2i messages that include a pacing rate indicator, a recommended replacement time (RRT) indicator, or at least one of an automatic mode switch (AMS) entry indicator, an AMS exit indicator, a magnet entry indicator, or a magnet exit indicator.

[0128] Figure 6C A high-level flow chart of will now be used to summarize a method by which multiple i2i messages including a pacing rate indicator must be sent to and received by a LP before the LP adjusts its pacing rate in response to receiving an i2i message including the pacing rate indicator. Such a method is for use with a LP implanted in or on a first cardiac chamber of a patient, the LP also having an IMD remotely located relative to the LP, wherein the LP is configured to pace the first cardiac chamber and adjust the pacing rate at which the first cardiac chamber is paced based on the pacing rate indicator included in the i2i message received from the IMD. The IMD may be, but is not limited to, another LP implanted in or on a second cardiac chamber, or an S-ICD. Although Figure 6C This is described from the perspective of an LP receiving an i2i message (including a pacing rate indicator) from another IMD (e.g., another LP), but it should be understood that the IMD (e.g., another LP) transmitting the i2i message (including the pacing rate indicator) should be configured to transmit at least M consecutive i2i messages including the pacing rate indicator whenever the IMD wants the LP (to which the i2i message is being sent) to change its pacing rate.

[0129] refer to Figure 6C , step 602 involves the LP monitoring i2i messages, step 604 involves determining whether an i2i message is received, and step 606 involves determining whether the received i2i message includes a pacing rate indicator. Steps 602, 604, and 606 are the same as those described above with reference to Figure 6A The steps described that are numbered in common are the same and therefore do not need to be described again.

[0130] If the answer to the determination at step 606 is "no" (meaning that the received i2i message does not include a pacing rate indicator), then the process proceeds to step 610 and no adjustment is made to the pacing rate. If the answer to the determination at step 606 is "yes" (meaning that the received i2i message does include a pacing rate indicator), then the process proceeds to step 618. At step 618, a determination is made as to whether the previously received N-1 i2i messages also include the same pacing rate indicator. More generally, a determination is made at steps 602, 604, 606, and 618 as to whether N consecutive received i2i messages include the same pacing rate indicator, where N is an integer equal to or greater than 2. If the answer to the determination at step 618 is "no," then the process proceeds to step 610 and no adjustment is made to the pacing rate. If the answer to the determination at step 618 is "yes" (meaning that N consecutive received i2i messages include the same pacing rate indicator), then the process proceeds to step 622. At step 622, the pacing rate is adjusted based on the pacing rate indicator included in N consecutively received i2i messages.

[0131] As described above, the pacing rate indicator can be, for example, but not limited to, a value indicating a pacing rate value (e.g., 80 bpm), a code that the LP can look up (e.g., in a stored lookup table) and that corresponds to the pacing rate value, or an equation that the LP feeds to determine the pacing rate value. Alternatively, the pacing rate indicator can be a beat-to-beat interval value (e.g., 0.75 seconds), a code that the LP can look up and that corresponds to the beat-to-beat interval value, or an equation that the LP feeds to determine the beat-to-beat interval value. Other variations are possible and within the scope of the embodiments described herein.

[0132] About Reference Figure 6C The described embodiments significantly reduce the probability that the LP will adjust its pacing rate in response to a false message by requiring the LP to receive N consecutive i2i messages including the same pacing rate indicator in order for the LP to change its pacing rate based on the pacing rate indicator. This also has the effect of significantly reducing the probability that one or more false messages will cause the lock-up issue described above. In other words, such embodiments take advantage of the very low probability that the LP will receive multiple consecutive false i2i messages including the same pacing rate indicator. In certain alternative embodiments, rather than requiring N consecutive i2i messages to include the same pacing rate indicator in order for the LP to change its pacing rate based on the pacing rate indicator, the LP may change its pacing rate as long as M of the N received i2i messages include the same pacing rate indicator, where M is a first specified integer greater than or equal to 2 and N is a second specified integer greater than M (e.g., M=3 and N=5).

[0133] Optional increased error detection and correction code length

[0134] The LP can use a cyclic redundancy check (CRC) or some other type of error detection and correction scheme to determine whether a message received by the LP is valid or invalid. The shorter the message, the higher the probability that the LP will receive a "false message." Conversely, the longer the message, the lower the probability that the LP will receive a "false message." However, using longer messages consumes more power than shorter messages. Therefore, from a device lifespan perspective, it is impractical to ensure that every message sent between LPs and / or other types of IMDs is a long message.

[0135] In error detection and correction schemes, error detection generally refers to detecting errors caused by noise or other impairments during transmission from a transmitter on one device to a receiver on another device. Error correction generally refers to detecting errors and, if possible, reconstructing the original error-free data. Typically, to enable error detection and correction, some redundancy (i.e., some additional data) is added to the message. This allows the recipient to check the consistency of the received message and recover data that has been determined to be corrupted. Error detection is often implemented using an appropriate hash function (or checksum algorithm) that adds a fixed-length tag to the message. This allows the recipient to verify the delivered message by recalculating the tag and comparing it with the provided tag. For example, a repetition code can be used, which is a coding scheme that repeats bits across the channel in an attempt to achieve error-free communication. Such repetition codes are often inefficient and prone to problems if errors occur in exactly the same location in each group. However, an advantage of repetition codes is that they are very simple and, therefore, are generally power-efficient compared to more complex schemes. Instead of or in addition to the repetition code, a parity bit may be used, where a parity bit is added to a set of source bits to ensure that the number of bits set in the result (e.g., bits with a value of 1) is even or odd. Alternatively or additionally, a checksum and / or a cyclic redundancy check may be used. The checksum of a message is the modular arithmetic sum of message code words (e.g., byte values) of a fixed word length. The sum may be negated by means of a one's complement operation before transmission to detect errors that result in an all-zero message. A checksum scheme may include a parity bit, a check bit, and a longitudinal redundancy check. A cyclic redundancy check (CRC) is a non-secure hash function designed to detect accidental changes to digital data.

[0136] When errors are detected in a received message, it is often possible to correct them. This error correction can involve, but is not limited to, the use of automatic repeat requests, error correction codes, or a hybrid scheme. Automatic repeat request (ARQ) is an error control technique for data transmission that utilizes error detection codes, acknowledgment and / or negative acknowledgment messages, and timeouts to achieve reliable data transmission. An acknowledgment is a message sent by the receiver indicating that it has correctly received a data frame. Typically, when the sender does not receive an acknowledgment before a timeout occurs (e.g., within a reasonable amount of time after sending the data frame), it retransmits the frame until it is either received correctly or the error persists for more than a predetermined number of retransmissions. Error correction coding (ECC) or forward error correction (FEC) is the process of adding redundant data or parity data to a message, allowing the receiver to recover even if multiple errors (up to the capabilities of the code used) are introduced either during transmission or in storage. Because the receiver does not have to ask the sender to retransmit the data, forward error correction does not require a reverse channel and is therefore suitable for simplex communications such as broadcast. Hybrid ARQ is a combination of ARQ and forward error correction. The above description is included to provide a high level of possible error correction and detection schemes and is not intended to be limiting and / or all-inclusive, as embodiments of the present technology can be used with virtually any error correction and detection scheme already developed or developed in the future.

[0137] While other types of error detection and correction schemes exist besides CRC schemes, for most of the discussion herein, a CRC scheme will be assumed. However, it should be understood that embodiments of the present technology can be used with other types of error detection and correction schemes besides CRC. When a CRC scheme is used, the CRC is calculated from the received message. The received message plus the CRC must match in order for the combined message to be considered valid. The more bits used for the CRC, the less likely it is that random noise will create a pattern that is exactly the message with a matching CRC. This is like adding more numbers to a combination lock. By increasing the message length of certain types of messages, the probability of the LP receiving a "false message" that is one of these specific message types (e.g., a message including a pacing rate indicator, or a message including a critical message, but not limited to such) is significantly reduced. By limiting the use of longer messages to only certain types of messages, the increase in power consumption associated with using longer messages is limited. Example message types that can use this solution include messages including a pacing rate indicator, a recommended change time (RRT) indicator, an automatic mode switch (AMS) entry or exit indicator, or a magnet entry or exit indicator.

[0138] Now we will use Figure 6DA high-level flow chart is provided to summarize certain methods used by an implantable system including a LP implanted within or on a first cardiac chamber of a patient and an IMD remotely located relative to the LP, wherein the LP is configured to pace the first cardiac chamber and adjust the pacing rate of the first cardiac chamber based on a pacing rate indicator included in an i2i message received from the IMD. The IMD can be another LP or an ICD, such as, but not limited to, an S-ICD. Such embodiments are particularly useful for the LP acting as a slave device, where the LP or S-ICD acts as a master device. Figure 6D The flowchart of FIG. 5 is described from the perspective of an IMD transmitting an i2i message to an LP that receives the i2i message and may adjust its pacing rate if the received i2i message includes a pacing rate indicator.

[0139] refer to Figure 6D At step 632, the IMD determines whether an event (e.g., a sensing or pacing event) or trigger exists in response to which the IMD should send a message to the remotely located LP. For example, if the IMD is a vLP, then the vLP can send an i2i message to the remotely located aLP each time the vLP paces the right ventricle or detects an intrinsic ventricular event. For another example, if the IMD is an S-ICD, then in response to detecting tachycardia or some other event or condition, the S-ICD can send an i2i message to the vLP instructing the vLP to deliver anti-tachycardia pacing (ATP). If the answer to step 632 is "no," then step 632 is repeated until the answer to step 632 is "yes," at which point the process proceeds to step 634.

[0140] At step 634, the IMD (or more specifically, its controller) determines whether there is information to be included in the message such that an extended i2i message should be sent. If the answer to the determination at step 634 is "no," then the flow proceeds to step 638. At step 638, an event marker i2i message (which is not an extended message) is generated and transmitted.

[0141] If the answer to the determination at step 634 is "yes," the process proceeds to step 636. At step 636, a determination is made as to whether the extended i2i message should include a rate adjustment indicator and / or any other type of indicator for which a longer CRC code should be used (e.g., an RRT indicator, a magnet entry indicator, a magnet exit indicator, an AMS entry indicator, an AMS exit indicator, an ATP trigger, or a stored EGM data trigger). The IMD may have a list or table of such messages for which a longer CRC code should be used. If the answer to the determination at step 636 is "no," the process proceeds to step 642, where an extended i2i message including a shorter CRC code (e.g., a 4-bit CRC code) is generated and transmitted. If the answer to the determination at step 636 is "yes," the process proceeds to step 640, where an extended i2i message including a longer CRC code (e.g., a 6-bit CRC code) is generated and transmitted. Other types of error correction and detection codes may alternatively be used in place of the CRC code.

[0142] The i2i messages transmitted at the instances of steps 638, 640, and 642, or at least a subset of those instances, are received by the LP to which the i2i messages are sent. The LP monitors the i2i messages and, in response to receiving an i2i message including a pacing rate indicator, can adjust the rate at which the LP paces the cardiac chamber in which (or on which) it is located. In such embodiments, the i2i messages transmitted from the IMD to the LP that include the pacing rate indicator include longer error detection and correction codes compared to at least some of the i2i messages that do not include the pacing rate indicator transmitted from the IMD to the LP. Using longer error detection and correction codes (e.g., longer CRC codes) for certain types of messages reduces the probability that false messages of such messages will be received, which also has the effect of significantly reducing the probability that one or more false messages will cause the lockout problem described above.

[0143] The above reference Figure 6A 、 6B , 6C and 6C described embodiments can be used alone or in combination with each other. For example, referring to Figure 6A The described embodiments can be used alone or in combination with the reference Figure 6B 、 6C and / or one or more of the embodiments described in 6D. For another example, refer to Figure 6B The described embodiments can be used alone or in combination with the reference Figure 6A 、 6C and / or one or more of the embodiments described in 6D. For further examples, see Figure 6C The described embodiments can be used alone or in combination with the reference Figure 6A 、 6Band / or one or more of the embodiments described in 6D are used in combination. For another example, refer to Figure 6D The described embodiments can be used alone or in combination with the reference Figure 6A 、 6B and / or one or more of the embodiments described in 6C may be used in combination.

[0144] Figure 7 A block diagram of one embodiment of an IMD (e.g., LP or ICD) 701 implanted in a patient as part of an implantable cardiac system according to certain embodiments herein is shown. IMD 701 can be implemented as a fully functional biventricular pacemaker, equipped with atrial and ventricular sensing and pacing circuitry for four-chamber sensing and stimulation therapy (including pacing and shock therapy). Optionally, IMD 701 can provide fully functional cardiac resynchronization therapy. Alternatively, IMD 701 can be implemented with a reduced set of functions and components. For example, the IMD can be implemented without ventricular sensing and pacing.

[0145] IMD 701 has a housing 700 to hold the electronic / computing components. Housing 700 (which is often referred to as a "can," "housing," "encapsulation," or "housing electrode") can be programmably selected to serve as a return electrode for certain stimulation modes. Housing 700 can also include a connector (not shown) having a plurality of terminals 702, 704, 706, 708, and 710. The terminals can be connected to electrodes located at various locations on housing 700 or elsewhere in and around the heart. IMD 701 includes a programmable microcontroller 720 that controls various operations of IMD 701, including cardiac monitoring and stimulation therapy. Microcontroller 720 includes a microprocessor (or equivalent control circuitry), RAM and / or ROM memory, logic and timing circuitry, state machine circuitry, and I / O circuitry.

[0146] IMD 701 also includes a first pulse generator 722 that generates stimulation pulses for delivery to one or more electrodes coupled thereto. Pulse generator 722 is controlled by microcontroller 720 via control signal 724. Pulse generator 722 can be coupled to (one or more) selected electrodes via electrode configuration switch 726, which includes multiple switches for connecting the desired electrodes to appropriate I / O circuits, thereby facilitating electrode programmability. Switch 726 is controlled by control signal 728 from microcontroller 720.

[0147] exist Figure 7In the embodiment of FIG, a single pulse generator 722 is illustrated. Alternatively, the IMD may include multiple pulse generators, similar to pulse generator 722, wherein each pulse generator is coupled to one or more electrodes and controlled by microcontroller 720 to deliver selected stimulation pulse(s) to the corresponding electrode(s).

[0148] The microcontroller 720 is shown as including a timing control circuit 732 to control the timing of stimulation pulses (e.g., pacing rate, atrioventricular (AV) delay, atrial conduction (AA) delay, or interventricular conduction (VV) delay, etc.). The timing control circuit 732 can also be used for timing of the refractory period, blanking interval, noise detection window, evoked response window, alarm interval, marker channel timing, etc. The microcontroller 720 also has an arrhythmia detector 734 and a morphology detector 736 for detecting arrhythmia conditions. Although not shown, the microcontroller 720 may also include other specialized circuits and / or firmware / software components that assist in monitoring various conditions of the patient's heart and managing pacing therapy.

[0149] The IMD 701 is also equipped with a communication modem (modulator / demodulator) 740 to enable wireless communication with a remote slave pacing unit. The modem 740 may include one or more transmitters and two or more receivers, as described herein. Figure 2 As discussed above. In one embodiment, the modem 740 can use low-frequency or high-frequency modulation. As an example, the modem 740 can transmit i2i messages and other signals via conductive communication between a pair of electrodes. The modem 740 can be implemented in hardware as part of the microcontroller 720, or as software / firmware instructions programmed into and executed by the microcontroller 720. Alternatively, the modem 740 can reside as a separate component from the microcontroller.

[0150] IMD 701 includes sensing circuitry 744 selectively coupled to one or more electrodes that perform sensing operations via switch 726 to detect the presence of cardiac activity in the right ventricle of the heart. Sensing circuitry 744 may include dedicated sense amplifiers, multiplexed amplifiers, or shared amplifiers. It may also employ one or more low-power precision amplifiers with programmable gain and / or automatic gain control, bandpass filtering, and threshold detection circuitry to selectively sense cardiac signals of interest. Automatic gain control enables the unit to sense low-amplitude signals characteristic of atrial fibrillation. Switch 726 determines the sensing polarity of the cardiac signal by selectively closing the appropriate switch. In this manner, the clinician can program the sensing polarity independently of the stimulation polarity.

[0151] The output of the sensing circuit 744 is connected to the microcontroller 720, which in turn triggers or inhibits the pulse generator 722 in response to the presence or absence of cardiac activity. The sensing circuit 744 receives control signals 746 from the microcontroller 720 for controlling the gain, threshold, polarization charge removal circuitry (not shown), and the timing of any blocking circuitry (not shown) coupled to the input of the sensing circuit.

[0152] exist Figure 7 In the embodiment of FIG, a single sensing circuit 744 is illustrated. Alternatively, the IMD may include multiple sensing circuits, similar to sensing circuit 744, wherein each sensing circuit is coupled to one or more electrodes and controlled by microcontroller 720 to sense electrical activity detected at the corresponding one or more electrodes. Sensing circuit 744 can operate in a unipolar sensing configuration or a bipolar sensing configuration.

[0153] IMD 701 also includes an analog-to-digital (A / D) data acquisition system (DAS) 750 coupled to one or more electrodes via switch 726 to sample cardiac signals across any desired pair of electrodes. Data acquisition system 750 is configured to acquire intracardiac electrogram signals, convert the raw analog data into digital data, and store the digital data for later processing and / or telemetry transmission to an external device 754 (e.g., a programmer, a local transceiver, or a diagnostic system analyzer). Data acquisition system 750 is controlled by control signals 756 from microcontroller 720.

[0154] Microcontroller 720 is coupled to memory 760 via a suitable data / address bus. Programmable operating parameters used by microcontroller 720 are stored in memory 760 and are used to customize the operation of IMD 701 to suit the needs of a particular patient. Such operating parameters define, for example, pacing pulse amplitude, pulse duration, electrode polarity, rate, sensitivity, automatic features, arrhythmia detection criteria, and the amplitude, waveform, and vector of each shock pulse to be delivered to the patient's heart within each corresponding layer of therapy.

[0155] The operating parameters of IMD 701 can be non-invasively programmed into memory 760 by telemetry circuitry 764, which is in telemetric communication with external device 754 via communication link 766. Telemetry circuitry 764 allows intracardiac electrograms and status information related to the operation of IMD 701 (contained in microcontroller 720 or memory 760) to be sent to external device 754 via communication link 766.

[0156] IMD 701 may also include a magnet detection circuit (not shown) coupled to microcontroller 720 to detect when a magnet is placed on the unit. A clinician can use the magnet to perform various test functions of IMD 701 and / or signal microcontroller 720 that external device 754 is in place to receive or transmit data to microcontroller 720 via telemetry circuit 764.

[0157] The IMD 701 may also include one or more physiological sensors 770. Such sensors are often referred to as "rate-responsive" sensors because they are typically used to adjust the pacing stimulus rate based on the patient's exercise state. However, the physiological sensors 770 may also be used to detect changes in cardiac output, changes in cardiac physiology, or diurnal changes in activity (e.g., detecting sleep and wake states). The signals generated by the physiological sensors 770 are transmitted to the microcontroller 720 for analysis. The microcontroller 720 responds by adjusting various pacing parameters (such as rate, AV delay, VV delay, etc.) of the atrial and ventricular pacing pulses. Although shown as being included within the IMD 701, the physiological sensor(s) 770 may be external to the IMD 701 but still implanted in the patient or carried by the patient. Examples of physiological sensors may include, for example, sensors that sense respiratory rate, blood pH, ventricular gradient, activity, position / posture, minute ventilation (MV), etc.

[0158] Battery 772 provides operating power for all components in IMD 701. Battery 772 is capable of operating for extended periods at low current draw and is capable of providing high current pulses (for capacitor charging) when the patient requires a shock pulse (e.g., exceeding 2A at a voltage greater than 2V for 10 seconds or longer). Battery 772 also desirably has predictable discharge characteristics so that selective replacement time can be detected. As an example, IMD 701 employs a lithium / silver vanadium oxide battery.

[0159] IMD 701 also includes impedance measurement circuitry 774, which can be used for a number of things, including: monitoring lead impedance during the acute and chronic phases to properly position or dislodge the lead; detecting the operable electrode and automatically switching to the operable electrode pair if dislodgement occurs; measuring respiration or minute ventilation; measuring thoracic impedance to determine shock thresholds; detecting when the device is implanted; measuring beat-to-beat volume; and detecting the opening of heart valves, among other things. Impedance measurement circuitry 774 is coupled to switch 726 so that any desired electrode can be used. In this embodiment, IMD 701 also includes shock circuitry 780, which is coupled to microcontroller 720 via data / address bus 782.

[0160] In some embodiments, LPs 102a and 102b are configured to be implantable in any chamber of the heart, i.e., either atrium (RA, LA) or either ventricle (RV, LV). Additionally, for a dual-chamber configuration, multiple LPs may be co-implanted (e.g., one in the RA, one in the RV, one in the RV, and one in the coronary sinus proximal to the LV). Certain pacemaker parameters and functions depend on (or assume) knowledge of the chamber in which the pacemaker is implanted (and therefore interacts with the LP; e.g., pacing and / or sensing). Some non-limiting examples include sensing sensitivity, induced response algorithms, use of AF suppression in local chambers, blanking periods and refractory periods, etc. Thus, each LP needs to know the identity of the chamber in which the LP is implanted, and a process may be implemented to automatically identify the local chamber associated with each LP.

[0161] The process for chamber identification can also be applied to subcutaneous pacemakers, ICDs, lead bands, etc. Devices with one or more implanted leads, identification and / or confirmation of the chamber in which the leads are implanted can be useful in several related scenarios. For example, for DR or CRT devices, automatic identification and confirmation can reduce the likelihood of a clinician inadvertently placing a V-lead into the A-port of an implantable medical device, or vice versa. As another example, for SR devices, automatic identification of the implanted chamber can enable the device and / or programmer to select and present the correct subset of pacing modes (e.g., AAI or VVI), and the IPG can utilize the correct set of settings and algorithms (e.g., V-AutoCapture versus ACap-Confirm, sensing sensitivity, etc.).

[0162] While many of the above embodiments of the present technology have been described as being used with LP-type IMDs, embodiments of the present technology for reducing the frequency with which an IMD's first receiver wakes up its second receiver to reduce power consumption can also be used with IMDs of other types besides LP. Therefore, unless specifically limited to use with LP, the claims should not be limited to use with LP-type IMDs.

[0163] It should be understood that the subject matter described herein is not limited in its application to the construction details and arrangements of parts set forth in the description herein or shown in the accompanying drawings. The subject matter described herein is capable of other embodiments and can be practiced or implemented in various ways. Moreover, it should be understood that the wording and terminology used herein are for descriptive purposes and should not be considered restrictive. The use of "including," "comprising," or "having" and their variations herein is intended to cover the items listed thereafter and their equivalents as well as additional items. In addition, it should be noted that, unless otherwise stated, the term "based on" used herein should be interpreted as being at least partially based on, meaning that there may be one or more additional factors on which a decision is made, etc. For example, if a decision is based on the results of a comparison, then the decision may also be based on one or more other factors in addition to the results of the comparison.

[0164] It should be understood that the above description is intended to be illustrative and not restrictive. For example, the above-described embodiments (and / or aspects thereof) may be used in combination with one another. Furthermore, many modifications may be made to adapt a particular situation or material to the teachings of the embodiments of the present technology without departing from the scope of the present technology. While the dimensions and types of materials and coatings described herein are intended to define parameters of the embodiments of the present technology, they are by no means limiting, but rather exemplary embodiments. Many other embodiments will be apparent to those skilled in the art upon reviewing the above description. Therefore, the scope of the embodiments of the present technology should be determined with reference to the appended claims and the full scope of equivalents to which such claims are entitled. In the appended claims, the terms "including" and "wherein" are used as the plain-English equivalents of the respective terms "comprising" and "wherein." Furthermore, in the following claims, the terms "first," "second," and "third," etc. are used merely as labels and are not intended to impose numerical requirements on their objects. In addition, the following claim limitations are not written in means-plus-function format and are not intended to be interpreted under 35 USC §112(f) unless such claim limitations expressly use the phrase "means for..." followed by a functional statement without further structure.

Claims

1. An implantable leadless pacemaker (LP) configured to be implanted in or on a first cardiac chamber of a patient and configured to pace the first cardiac chamber and adjust a pacing rate of the first cardiac chamber based on a pacing rate indicator included in an implant-to-implant i2i message received from an implantable medical device (IMD) remotely located relative to the LP, the LP comprising: at least one receiver configured to receive the i2i message; as well as controller, configured as determining whether the received i2i message includes a pacing rate indicator specifying a new pacing rate at which the LP should pace the first cardiac chamber, determining whether an adjustment to the pacing rate of the first cardiac chamber to match the new pacing rate specified by a pacing rate indicator would cause the adjustment to the pacing rate to exceed a rate adjustment threshold, wherein the adjustment is equal to a difference between the pacing rate and the new pacing rate, and wherein the rate adjustment threshold limits the magnitude of the adjustment in response to the LP receiving the i2i message; as well as In response to determining that the adjustment to the pacing rate of the first cardiac chamber to match the new pacing rate specified by the pacing rate indicator will cause the adjustment to the pacing rate to exceed the rate adjustment threshold, the pacing rate is adjusted to another new pacing rate by limiting the adjustment to the pacing rate to a specified amount.

2. The implantable LP of claim 1, wherein: The specified amount to which the controller limits the adjustment to the pacing rate comprises the rate adjustment threshold in response to the LP receiving the i2i message including a pacing rate indicator that would cause the adjustment to the pacing rate to exceed the rate adjustment threshold.

3. The implantable LP of claim 1, wherein: The specified amount to which the controller limits the adjustment of the pacing rate in response to the LP receiving the i2i message including the pacing rate indicator that would cause the adjustment of the pacing rate to exceed the rate adjustment threshold comprises one of: a predetermined value; or A predetermined function of the current pacing rate.

4. An implantable LP according to any one of claims 1 to 3, wherein: i2i messages are transmitted and received via conducted communication; LP includes first LP; as well as The IMD includes a second LP implanted in or on a second cardiac chamber.

5. The implantable LP according to any one of claims 1 to 3, wherein: i2i messages are transmitted and received via conducted communications; and IMDs include subcutaneous implantable cardioverter-defibrillators (S-ICDs).

6. A system comprising: The implantable leadless pacemaker LP according to any one of claims 1 to 5; as well as The implantable medical device (IMD) is remotely located relative to the LP.

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