Detecting ventricular lead dislodgement during atrial fibrillation

A medical device system and method for detecting dislodgement of a ventricular lead determines one or more characteristics of a cardiac signal received via the ventricular lead that are associated with dislodgement of the ventricular lead during atrial fibrillation, and detects dislodgement of the ventricular lead based on the determined characteristics. The medical device and system provides a lead dislodgment alert in response to detecting dislodgement. In some examples, an implantable medical device withholds delivery of a ventricular defibrillation therapy based on detecting dislodgement of the ventricular lead.

TECHNICAL FIELD

The disclosure relates generally to medical devices and, more particularly, to a medical device, medical device system and method for detecting dislodgment of a ventricular lead during the occurrence of an atrial fibrillation episode.

BACKGROUND

Implantable medical devices (IMDs), including pacemakers and implantable cardioverter-defibrillators (ICDs), record cardiac electrogram (EGM) signals for sensing cardiac events, e.g., P-waves and R-waves. Episodes of bradycardia, tachycardia and/or fibrillation are detected from the sensed cardiac events and responded to as needed with pacing therapy or high-voltage cardioversion/defibrillation therapy. Reliable detection and treatment of potentially life-threatening ventricular tachycardia (VT) and ventricular fibrillation (VF) requires reliable sensing of cardiac signals.

Dislodgement or dislocation of a cardiac lead carrying electrodes for sensing EGM signals reduces reliable sensing and could result in erroneous sensing of cardiac signals, leading to improper detection of the cardiac rhythm and inappropriate delivery or withholding of pacing or shock therapy. While an occurrence of ventricular lead dislodgement is rare, such dislodgement could potentially cause inappropriate shock therapy to be delivered. For example, in some rare instances of a ventricular lead dislodging or being dislodged during an episode of atrial fibrillation, cardiac signals associated with the atrial fibrillation episode may be inappropriately sensed as ventricular signals, causing inappropriate detection of a ventricular fibrillation episode and the resultant delivery of therapy. In other instances, improper detection of the cardiac rhythm may cause a necessary or optimal therapy to not be delivered, such as bradycardia pacing or anti-tachycardia pacing. Accordingly, it is desirable to provide an implantable medical device and associated medical device system that is capable of detecting ventricular lead dislodgement during episodes of atrial fibrillation.

SUMMARY

Devices, systems, and techniques for identifying dislodgment of a ventricular lead during atrial fibrillation are described in this disclosure. When a ventricular lead is dislodged during atrial fibrillation, a cardiac signal sensed via the ventricular lead may demonstrate one or more characteristics associated with the dislodgement of the ventricular lead during atrial fibrillation and sensing a combination of atrial and ventricular depolarizations, such as reduced amplitude and increased variability of detected RR intervals due to sensing a combination of atrial and ventricular depolarizations. The techniques of this disclosure may include detecting dislodgement of the ventricular lead based on such characteristics.

In one example, a method of detecting dislodgement of a ventricular lead coupled to an implantable medical device comprises sensing, by sensing circuitry of the implantable medical device, a cardiac signal via the ventricular lead, determining, by processing circuitry, at least one characteristic of the cardiac signal associated with dislodgement of the ventricular lead during atrial fibrillation, detecting, by the processing circuitry, dislodgement of the ventricular lead based on the determined at least one characteristic, and providing, by the processing circuitry, a lead dislodgement alert in response to detecting the dislodgement of the ventricular lead.

In another example, a medical device system comprises a ventricular lead comprising a plurality of electrodes, and sensing circuitry configured to sense a cardiac signal via at least one of the plurality of electrodes of the ventricular lead. The system further comprises processing circuitry configured to determine at least one characteristic of the cardiac signal associated with dislodgement of the ventricular lead during atrial fibrillation, detect dislodgement of the ventricular lead based on the determined at least one characteristic, and provide a lead dislodgement alert in response to detecting the dislodgement of the ventricular lead.

In another example, a non-transitory computer-readable medium comprises instructions that, when executed by processing circuitry, cause the processing circuitry to determine at least one characteristic of the cardiac signal a cardiac signal sensed via a ventricular lead, the at least one characteristic associated with dislodgement of a ventricular lead during atrial fibrillation, detect dislodgement of the ventricular lead based on the determined at least one characteristic, and provide a lead dislodgement alert in response to detecting the dislodgement of the ventricular lead.

In another example, a medical device system comprises a ventricular lead comprising a plurality of electrodes, and an implantable medical device coupled to the ventricular lead. The implantable medical device comprises sensing circuitry configured to sense a near-field cardiac signal via at least one of the plurality of electrodes, therapy delivery circuitry configured to deliver a ventricular defibrillation therapy, and processing circuitry. The processing circuitry is configured to detect a ventricular fibrillation episode based on the sensed near-field cardiac signal, determine a variability of RR intervals of the near-field cardiac signal and an amplitude of the near-field cardiac signal in response to the ventricular fibrillation episode being detected, detect dislodgement of the ventricular lead based on the variability satisfying a variability threshold and the amplitude satisfying an amplitude threshold, and withhold delivery of a ventricular defibrillation therapy by the therapy delivery circuitry to treat the detected ventricular fibrillation episode based on the detection of dislodgement of the ventricular lead.

This summary is intended to provide an overview of the subject matter described in this disclosure. It is not intended to provide an exclusive or exhaustive explanation of the apparatus and methods described in detail within the accompanying drawings and description below. The details of one or more aspects of the disclosure are set forth in the accompanying drawings and the description below.

DETAILED DESCRIPTION

As described above, methods, devices, and systems for identifying dislodgment of a ventricular lead during atrial fibrillation are described in this disclosure. In the following description, references are made to illustrative examples. It is understood that other examples may be utilized without departing from the scope of the disclosure.

FIG. 1is an example schematic diagram of an implantable medical device system configured to detect dislodgement of a ventricular lead during atrial fibrillation. As illustrated inFIG. 1, a medical device system8for sensing cardiac events (e.g. P-waves and R-waves) and detecting tachyarrhythmia episodes, as well as detecting dislodgement of a ventricular lead during atrial fibrillation, may include an implantable medical device (IMD)10, a ventricular lead20and an atrial lead21. In one example, IMD10may be an implantable cardioverter-defibrillator (ICD) capable of delivering pacing, cardioversion and defibrillation therapy to the heart16of a patient14.

Ventricular lead20and atrial lead21are electrically coupled to IMD10and extend into the patient's heart16. Ventricular lead20includes electrodes22and24shown positioned on the lead in the patient's right ventricle (RV) for sensing ventricular EGM signals and pacing in the RV. Atrial lead21includes electrodes26and28positioned on the lead in the patient's right atrium (RA) for sensing atrial EGM signals and pacing in the RA. Such a medical device and medical device system is described, for example, in commonly assigned U.S. Patent Publication No. 2014/0018873, which is incorporated herein by reference in its entirety.

Ventricular lead20additionally carries a high voltage coil electrode42, and atrial lead21carries a high voltage coil electrode44, used to deliver cardioversion and defibrillation shock pulses. In other examples, ventricular lead20may carry both of high voltage coil electrodes42and44, or may carry a high voltage coil electrode in addition to those illustrated in the example ofFIG. 1. Both the ventricular lead20and the atrial lead21may be used to acquire cardiac EGM signals from the patient14and to deliver therapy in response to the acquired data. Medical device system8is shown as a dual chamber ICD, but in some embodiments, system8may be a multi-chamber system including a coronary sinus lead extending into the right atrium, through the coronary sinus and into a cardiac vein to position electrodes along the left ventricle (LV) for sensing LV EGM signals and delivering pacing pulses to the LV. In other examples, system8may be a single chamber system, or otherwise not include atrial lead21.

In some examples, ventricular lead20is anchored along the right ventricular apex or the intraventricular septum by a fixation member (not shown), such as tines positioned at the distal end of lead20in the vicinity of electrode22or a helical screw, which may also serve as electrode22. Use of a fixation member generally anchors the position of ventricular lead20in the RV. However, on rare occasions, ventricular lead20may become dislodged from the ventricular myocardium and shift or migrate within the ventricle or toward or within the right atrium. When this occurs, the EGM signal received by IMD10from electrodes22and24will change due to the altered location of electrodes22and24, which may result in electrical activity of the atria of heart being inadvertently sensed via ventricular lead20as ventricular activity. Such a situation of sensing both atrial and ventricular depolarizations as ventricular signals can be especially problematic during the occurrence of atrial fibrillation, since the result could be inappropriate detection of a ventricular fibrillation episode and unnecessary delivery of ventricular defibrillation therapy. Techniques for detecting cardiac lead dislodgement, particularly dislodgement of a ventricular lead during the occurrence of atrial fibrillation, will be described herein.

Implantable medical device circuitry configured for performing the methods described herein and an associated battery or batteries are housed within a sealed housing12. Housing12may be conductive so as to serve as an electrode for use as an indifferent electrode during pacing or sensing or as an active electrode during defibrillation. As such, housing12is also referred to herein as “housing electrode”12.

EGM signal data, cardiac rhythm episode data, and lead dislodgement data acquired by IMD10can be transmitted to an external device30. External device30may be a computing device, e.g. used in a home, ambulatory, clinic, or hospital setting, to communicate with IMD10via wireless telemetry. External device30may be coupled to a remote patient monitoring system, such as Carelink®, available from Medtronic plc, of Dublin, Ireland. External device30may be, as examples, a programmer, external monitor, or consumer device, e.g., smart phone.

External device30may be used to program commands or operating parameters into IMD10for controlling IMD function, e.g., when configured as a programmer for IMD10. External device30may be used to interrogate IMD10to retrieve data, including device operational data as well as physiological data accumulated in IMD memory. The interrogation may be automatic, e.g., according to a schedule, or in response to a remote or local user command. Programmers, external monitors, and consumer devices are examples of external devices10that may be used to interrogate IMD10. Examples of communication techniques used by IMD10and external device30include radiofrequency (RF) telemetry, which may be an RF link established via Bluetooth, WiFi, or medical implant communication service (MICS).

One or more components of system8may identify dislodgment of ventricular lead20during atrial fibrillation using the techniques described in this disclosure. For example, IMD10may sense a ventricular EGM via ventricular lead20, e.g., a near-field EGM sensed via tip electrode22and ring electrode24of ventricular lead20, and one or more of IMD10and external device30may determine whether ventricular lead20is dislodged based on the ventricular EGM. External device30may receive the ventricular EGM and/or data representative of the ventricular EGM from IMD10via RF telemetry.

For example, IMD10or external device30may identify one or more characteristics of the ventricular EGM that are associated with the dislodgement of ventricular lead20during atrial fibrillation, such as reduced signal amplitude and/or increased variability of detected RR intervals, which may be due to sensing both atrial and ventricular depolarizations in the near-field EGM sensed via ventricular lead20. IMD10or external device30may detect dislodgement of ventricular lead20based on such characteristics meeting one or more respective thresholds. IMD10and/or external device30may provide a lead dislodgement alert in response to detecting dislodgement of ventricular lead20. In some examples, IMD10may alter its sensing or therapy delivery, such as withholding a ventricular defibrillation therapy, in response to detecting dislodgement of ventricular lead20.

FIG. 2is a functional block diagram of an example configuration of IMD10that detects dislodgement of a ventricular lead (e.g., ventricular lead20ofFIG. 1) during atrial fibrillation. In the example illustrated byFIG. 2, IMD10includes sensing circuitry102, therapy delivery circuitry104, processing circuitry106and associated memory108, and telemetry circuitry118.

Processing circuitry106may include any combination of integrated circuitry, discrete logic circuitry, analog circuitry, such as one or more microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASICs), or field-programmable gate arrays (FPGAs). In some examples, processing circuitry106may include multiple components, such as any combination of one or more microprocessors, one or more DSPs, one or more ASICs, or one or more FPGAs, as well as other discrete or integrated logic circuitry, and/or analog circuitry.

Memory108may store program instructions, which may include one or more program modules, which are executable by processing circuitry106. When executed by processing circuitry106, such program instructions may cause processing circuitry106and IMD10to provide the functionality ascribed to them herein. The program instructions may be embodied in software, firmware and/or RAMware. Memory108may include any volatile, non-volatile, magnetic, optical, or electrical media, such as a random access memory (RAM), read-only memory (ROM), non-volatile RAM (NVRAM), electrically-erasable programmable ROM (EEPROM), flash memory, or any other digital media.

Sensing circuitry102is configured to receive cardiac electrical signals from selected combinations of two or more of electrodes22,24,26,28,42and44carried by the ventricular lead20and atrial lead21, along with housing electrode12. Sensing circuitry102is configured to sense cardiac events attendant to the depolarization of myocardial tissue, e.g. P-waves and R-waves. Sensing circuitry102may include a switching circuitry for selectively coupling electrodes12,22,24,26,28,42,44to sensing circuitry102in order to monitor electrical activity of heart16. The switching circuitry may include a switch array, switch matrix, multiplexer, or any other type of switching device suitable to selectively couple one or more of the electrodes to sensing circuitry102. In some examples, processing circuitry106selects the electrodes to function as sense electrodes, or the sensing vector, via the switching circuitry within sensing circuitry102.

Sensing circuitry102may include multiple sensing channels, each of which may be selectively coupled to respective combinations of electrodes12,22,24,26,28,42,44to detect electrical activity of a particular chamber of heart16, e.g., an atrial sensing channel and a ventricular sensing channel. Each sensing channel may be configured to amplify, filter and rectify the cardiac electrical signal received from selected electrodes coupled to the respective sensing channel to detect cardiac events, e.g., P-waves and/or R-waves. For example, each sensing channel may include one or more filters and amplifiers for filtering and amplifying a signal received from a selected pair of electrodes. The resulting cardiac electrical signal may be passed to cardiac event detection circuitry that detects a cardiac event when the cardiac electrical signal crosses a sensing threshold. The cardiac event detection circuitry may include a rectifier, filter and/or amplifier, a sense amplifier, comparator, and/or analog-to-digital converter.

Sensing circuitry102outputs an indication to processing circuitry106in response to sensing of a cardiac event, in the respective chamber of heart16(e.g., detected P-waves or R-waves). In this manner, processing circuitry106may receive detected cardiac event signals corresponding to the occurrence of detected R-waves and P-waves in the respective chambers of heart16. Indications of detected R-waves and P-waves may be used for detecting ventricular and/or atrial tachyarrhythmia episodes, e.g., ventricular or atrial fibrillation episodes. Sensing circuitry102may also pass one or more digitized EGM signals to processing circuitry106for analysis, e.g., for use in cardiac rhythm discrimination. Processing circuitry106may use the indications of R-waves and/or the digitized ventricular EGM signals to detect dislodgement of ventricular lead20during atrial fibrillation. Indications of R-wave and P-wave timing, as well as digitized EGMs, may be stored in memory108as EGM data110.

Memory108may also store a lead analysis module112. Lead analysis module112may be a software, firmware, or RAMware module executable by processing circuitry106to cause processing circuitry106to provide functionality related to identifying dislodgement of ventricular lead20during atrial fibrillation as described herein. Such functionality may include identifying characteristics of a ventricular EGM signal, detecting dislodgment based on the characteristics, providing an alert, and/or modifying sensing or therapy provided by IMD10, as described herein. Processing circuitry106may load lead analysis module112from memory108(shown by the dotted lead analysis module112within processing circuitry106) and execute the loaded lead analysis module112in response to an event, such as detection of atrial fibrillation via an atrial EGM, detection of ventricular fibrillation via a ventricular EGM, or a command from external device30received via telemetry circuitry118. In other examples, processing circuitry106may execute lead analysis module112periodically, e.g., according to a schedule, or substantially continuously, throughout the operation of IMD10.

Processing circuitry106may control therapy delivery circuitry104to deliver electrical therapy, e.g., cardiac pacing, anti-tachyarrhythmia therapy, or shock pulses, to heart16according to therapy parameters stored in memory108. Therapy delivery circuitry104is electrically coupled to electrodes12,22,24,26,28,42,44, and is configured to generate and deliver electrical therapy to heart16via selected combinations of electrodes12,22,24,26,28,42,44. Therapy delivery circuit104may include charging circuitry, one or more charge storage devices, such as one or more high voltage capacitors and/or one or more low voltage capacitors, and switching circuitry that controls when the capacitor(s) are discharged to selected combinations of electrodes12,22,24,26,28,42,44. Charging of capacitors to a programmed pulse amplitude and discharging of the capacitors for a programmed pulse width may be performed by therapy delivery circuit104according to control signals received from processing circuitry106.

Memory108stores intervals, counters, or other data used by processing circuitry106to control the delivery of pacing pulses by therapy delivery circuitry104. Such data may include intervals and counters used by processing circuitry106to control the delivery of pacing pulses to heart16. The intervals and/or counters are, in some examples, used by processing circuitry106to control the timing of delivery of pacing pulses relative to an intrinsic or paced event in another chamber. Memory108also stores intervals for controlling cardiac sensing functions such as blanking intervals and refractory sensing intervals and counters for counting sensed events for detecting cardiac rhythm episodes. Events sensed by sense amplifiers included in sensing circuitry102are identified in part based on their occurrence outside a blanking interval and inside or outside of a refractory sensing interval. Events that occur within predetermined interval ranges are counted for detecting cardiac rhythms. According to embodiments described herein, sensing circuitry102, therapy circuitry104, memory108, and processing circuitry106are configured to use timers and counters for measuring sensed event intervals and determining event patterns for use in detecting possible ventricular lead dislodgement.

Processing circuitry106may receive analog and/or digitized EGM signals and sensed event signals corresponding to detected R-waves and P-waves from sensing circuitry102for use in identifying possible dislodgement or dislocation of ventricular lead20, e.g., when executing lead analysis module112. As will be described herein, processing circuitry106may detect dislodgement of ventricular lead20during atrial fibrillation based on an amplitude of the ventricular EGM signal, e.g., an amplitude of R-waves in the digitized ventricular EGM, and/or variability of RR intervals indicated by the sensing of R-waves by sensing circuitry102.

Processing circuitry106may respond to a lead dislodgement by generating a patient or clinician alert, which may be transmitted by telemetry circuitry118, by withholding delivery of therapy, or both, as will be described below. Processing circuitry106may additionally respond to a possible lead dislodgement by adjusting cardiac rhythm episode detection criteria and/or adjusting the control of therapy delivery module104to avoid inappropriate delivery or withholding of a therapy.

Telemetry circuitry118is used to communicate with external device30, for transmitting data accumulated by IMD10and for receiving interrogation and programming commands from external device30. Under the control of processing circuitry106, telemetry circuitry118may transmit an alert to notify a clinician and/or the patient that IMD10has detected a possible ventricular lead dislodgement. This alert enables the clinician to perform additional testing to confirm the dislodgement and to intervene if necessary to reposition or replace the lead, or to prevent unnecessary defibrillation therapy from being delivered to the patient. In other embodiments, IMD10may be equipped with alert circuitry configured to emit a sensory alert perceptible by the patient, e.g. a vibration or an audible tone, under the control of processing circuitry106to alert the patient to the possibility of a ventricular lead displacement.

As described above, in instances of a ventricular lead dislodging or being dislodged during an episode of atrial fibrillation, the ventricular lead may migrate from the ventricle towards the atrium, increasing the likelihood that cardiac signals associated with the atrial fibrillation episode (e.g., atrial cardiac events) may be inappropriately sensed as ventricular events, causing inappropriate sensing of a ventricular tachyarrhythmia episode, such as ventricular fibrillation, and resulting in an inappropriate delivery of ventricular fibrillation therapy. Accordingly, in some examples, processing circuitry106controls therapy delivery circuitry104to withhold the delivery of a therapy for treating ventricular arrhythmias, e.g., a ventricular defibrillation shock for treating a detected ventricular fibrillation episode, based on detecting dislodgement of ventricular lead20. In some examples, processing circuitry106determines characteristics of the ventricular EGM associated with lead dislodgement in response to detection of a ventricular fibrillation episode and, if dislodgement of ventricular lead20is detected, controls therapy delivery circuitry104to withhold delivery of a defibrillation shock to treat the detected ventricular fibrillation based on the detection of lead dislodgement.

In some examples, processing circuitry106initiates the analysis to identify characteristics of the ventricular EGM indicative of dislodgment of ventricular lead at the time of implant of ventricular lead20in the patient14, either in response to a command from external device30, or automatically. Since the likelihood of lead dislodgement occurring is greatest within the first few months after implant, processing circuitry106may initiate the lead dislodgement surveillance techniques described herein at the time of implant of ventricular lead20in the patient14, and then turn of the lead dislodgment surveillance after a predetermined time period subsequent to implant, e.g., after three, four, or six months, as examples, either in response to commands from external device30and/or automatically.

In some examples, to further increase the likelihood that dislodgment of ventricular lead may be detected during the occurrence of atrial fibrillation, processing circuitry106initiates the lead dislodgement surveillance techniques described herein based on an atrial fibrillation episode having previously been detected in patient14, e.g., by processing circuitry106based on an atrial EGM, or by some other device or clinician and indicated to processing circuitry106via telemetry circuitry118. In some examples in which processing circuitry106initiates the lead dislodgement surveillance techniques based on an atrial fibrillation episode having previously been detected in patient14, processing circuitry106may still end the lead dislodgment surveillance after the predetermined period of time, e.g., after three, four, or six months, from implant of ventricular lead20. In such examples, processing circuitry106may initiate the lead dislodgement surveillance techniques based on both an atrial fibrillation episode having previously been detected in patient14and the ventricular lead having been implanted for less than the predetermined time period.

In some examples, processing circuitry106may enable or disable a withholding feature, e.g., based on whether ventricular lead20has been implanted for less than the predetermined time period and/or whether an atrial fibrillation episode has previously been detected in patient14in the manner described above. In some examples, processing circuitry106performs the lead dislodgement surveillance techniques described herein when the withholding feature is enabled, and does not perform the lead dislodgement surveillance techniques described herein when the withholding feature is disabled. In other examples, processing circuitry106may perform lead surveillance and provide alerts in response to detecting lead dislodgment whether or not the withholding feature is enabled, but will only withhold therapy, e.g., a defibrillation shock, in response to detecting lead dislodgement, if the withholding feature is enabled.

FIG. 3is a functional block diagram of an example configuration of external device30. In the example ofFIG. 3, external device30includes processing circuitry140, memory142, user interface (UI)144, and telemetry circuitry146. External device30may be a dedicated hardware device with dedicated software for the programming and/or interrogation of IMD10. Alternatively, external device30may be an off-the-shelf computing device, e.g., running an application that enables external device30to program and/or interrogate IMD10.

In some examples, a user uses external device30to select or program values for operational parameters of IMD10, e.g., for cardiac sensing, therapy delivery, and lead dislodgment detection. In some examples, a user uses external device30to receive data collected by IMD10, such as cardiac EGM data110or other operational and performance data of IMD10. The user may also receive lead dislodgment alerts provided by IMD10, or data regarding modifications to sensing or therapy made by IMD10in response to detecting lead dislodgement, e.g., indications of when IMD10withheld defibrillation therapy, via external device30. The user may interact with external device30via UI144, which may include a display to present a graphical user interface to a user, and a keypad or another mechanism for receiving input from a user. External device30may communicate wirelessly with IMD10using telemetry circuitry146, which may be configured for RF communication with telemetry circuitry118of IMD10.

Processing circuitry140may include any combination of integrated circuitry, discrete logic circuitry, analog circuitry, such as one or more microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASICs), or field-programmable gate arrays (FPGAs). In some examples, processing circuitry106may include multiple components, such as any combination of one or more microprocessors, one or more DSPs, one or more ASICs, or one or more FPGAs, as well as other discrete or integrated logic circuitry, and/or analog circuitry.

Memory142may store program instructions, which may include one or more program modules, which are executable by processing circuitry140. When executed by processing circuitry140, such program instructions may cause processing circuitry140and external device30to provide the functionality ascribed to them herein. The program instructions may be embodied in software, firmware and/or RAMware. Memory142may include any volatile, non-volatile, magnetic, optical, or electrical media, such as a random access memory (RAM), read-only memory (ROM), non-volatile RAM (NVRAM), electrically-erasable programmable ROM (EEPROM), flash memory, or any other digital media.

In some examples, processing circuitry140of external device30may be configured to provide some or all of the functionality ascribed to processing circuitry106of IMD10herein. For example, processing circuitry140may receive EGM data110of a ventricular EGM signal sensed via ventricular lead20from IMD10via telemetry circuitry144, and may store the EGM data110in memory142. EGM data110may be current EGM data, or data previously collected and stored by IMD10. Using EGM data110, processing circuitry140of external device30may identify characteristics of the ventricular EGM indicative of dislodgment of a ventricular lead during atrial fibrillation, and detect dislodgment of ventricular lead20based on such characteristics. Based on the detection of dislodgment, processing circuitry140may provide an alert to a user, e.g., via UI144. In some examples, the lead dislodgment detection functionality may be provided by lead analysis module112, which may a software module stored in memory142, and loaded and executed by processing circuitry140(as illustrated by the dotted outline lead analysis module112within processing circuitry140), e.g., in response to a command from the user.

FIG. 4is a functional block diagram illustrating an example system that includes external computing devices, such as a server164and one or more other computing devices170A-170N, that are coupled to IMD10and external device30via a network162. In this example, IMD10may use its telemetry module118to, e.g., at different times and/or in different locations or settings, communicate with external device30via a first wireless connection, and to communication with an access point160via a second wireless connection. In the example ofFIG. 4, access point160, external device30, server164, and computing devices170A-170N are interconnected, and able to communicate with each other, through network162.

Access point160may comprise a device that connects to network162via any of a variety of connections, such as telephone dial-up, digital subscriber line (DSL), or cable modem connections. In other examples, access point160may be coupled to network162through different forms of connections, including wired or wireless connections. In some examples, access point160may be co-located with patient14. Access point160may interrogate IMD10, e.g., periodically or in response to a command from patient14or network162, to retrieve EGM data110or other operational data from IMD10. Access point160may provide the retrieved data to server164via network162.

In some cases, server164may be configured to provide a secure storage site for data that has been collected from IMD10and/or external device30, such as the Internet. In some cases, server164may assemble data in web pages or other documents for viewing by trained professionals, such as clinicians, via computing devices170A-170N. The illustrated system ofFIG. 4may be implemented, in some aspects, with general network technology and functionality similar to that provided by the Medtronic CareLink® Network developed by Medtronic plc, of Dublin, Ireland.

In some examples, one or more of access point160, server164, or computing devices170may be configured to perform, e.g., may include processing circuitry configured to perform, some or all of the techniques described herein relating to detecting dislodgment of a ventricular lead. In the example ofFIG. 4, server164includes a memory166to store EGM data received from IMD10, and processing circuitry168, which may be configured to provide some or all of the functionality ascribed to processing circuitry106of IMD16herein. For example, processing circuitry168may identify characteristics of the ventricular EGM indicating dislodgment of a ventricular lead during atrial fibrillation based on the EGM data received from IMD10. Processing circuitry168may identify dislodgment of ventricular lead20based on the identified characteristics, and may provide a lead dislodgment alert to a user, e.g., via external device30or one of computing devices170.

FIG. 5is a timing diagram illustrating an example cardiac signal190, e.g., ventricular EGM, sensed via a ventricular lead, e.g., ventricular lead20, when dislodged and during an atrial fibrillation episode.FIG. 5also illustrates instances at which therapy delivery circuitry104of IMD10delivered pacing pulses192A and192B (collectively “pacing pulses192”) via ventricular lead20, and instances at which sensing circuitry102of IMD10detected R-waves194A-194L (collectively “R-waves194”) in cardiac signal190.FIG. 5also illustrates RR intervals196, only one of which is labeled inFIG. 5for ease of illustration, determined by processing circuitry described herein, such as processing circuitry106of IMD10. An RR interval is the interval between consecutive ventricular events whether those events are a result of pacing or of intrinsic conduction. In other words, an RR interval may be an interval between consecutive R-waves194, between consecutive pacing pulses192, or between a consecutive R-wave194and pacing pulse192, in either order.

Although an atrial EGM is not illustrated inFIG. 5, an atrial fibrillation episode of heart16was ongoing during the acquisition of the illustrated ventricular cardiac signal190. Furthermore, the ventricular lead, e.g., ventricular lead20, used to acquire ventricular cardiac signal190was dislodged during acquisition of cardiac signal190. Consequently, as illustrated inFIG. 5, cardiac signal190demonstrates characteristics associated with dislodgement of ventricular lead20during atrial fibrillation.

For example, cardiac signal190may be a near-field EGM, and the amplitudes of the features of cardiac signal190detected by sensing circuitry102as R-waves194may be relatively lower and more variable when ventricular lead20is dislodged then R-waves detected by sensing circuitry102prior to the dislodgment of ventricular lead20. The features of cardiac signal190detected by sensing circuitry102as R-waves194when ventricular lead20is dislodged during atrial fibrillation may include actual ventricular depolarizations, and atrial fibrillation signals incorrectly detected as R-waves. The amplitudes of these features may be relatively low due to the electrodes of ventricular lead20, e.g., tip electrode22, being in contact with neither of the ventricular or atrial myocardium, and may be variable due to variable proximity of dislodged ventricular lead20to ventricular or atrial myocardium during the cardiac cycle. Additionally, the atrial fibrillation signals may generally have lower amplitudes than atrial depolarizations during sinus rhythm.

Processing circuitry106(or any other processing circuitry described herein that receives a digitized version of cardiac signal190from IMD10) may determine amplitudes of R-waves194detected by sensing circuitry102via ventricular lead20as a characteristic associated with dislodgement of ventricular lead20during atrial fibrillation. For example, the processing circuitry may determine the R-wave amplitude to be an absolute value of cardiac signal190, e.g., near-field ventricular EGM, relative to a baseline at the point of detection of an R-wave194or a peak, mean or other amplitude value within a window of cardiac signal190around the point of detection of the R-wave.

Processing circuitry106may detect dislodgement of ventricular lead20based on determined amplitudes of R-waves194, e.g., detected by sensing circuitry102in near-field ventricular EGM via ventricular lead20, such as based on whether the amplitudes of R-waves194are less than an amplitude threshold. The amplitude threshold may be a fixed, predetermined value, or may be a variable value, e.g., determined based on amplitudes of R-waves194, or cardiac signal190generally, when ventricular lead20was not dislodged. In some examples, processing circuitry, e.g., processing circuitry106, determines the amplitude threshold based on the amplitudes of R-waves detected during one or more prior induced or spontaneous ventricular fibrillation episodes of patient14. For example, the amplitude threshold may be a percentage, e.g., 50%, of the amplitudes of R-waves detected during one or more prior induced or spontaneous ventricular fibrillation episodes of patient14. In one example, the amplitude threshold is 1 mV.

In some examples, processing circuitry106detects dislodgement of ventricular lead20based on the amplitudes of a threshold percentage or fraction of a group of R-waves194that are part of an episode, e.g., a group of R-waves194leading up to detection of ventricular fibrillation, being less than the threshold amplitude. In some examples, the group of R-waves194includes the R-waves194in a detected ventricular fibrillation episode that were associated with R-R intervals less than the ventricular fibrillation interval threshold. In one example, the number of R-waves194whose amplitude is considered is 18, e.g., the R-waves194associated with the 18 RR intervals of 24 consecutive RR intervals below the ventricular fibrillation interval threshold that led to detection of a ventricular fibrillation episode. In one example, processing circuitry106detects dislodgement of ventricular lead20based on at least 25% of the amplitudes of the group of R-waves194being less than the amplitude threshold.

As another example, the variability of RR intervals196detected via ventricular lead20when the ventricular lead is dislodged may be greater than the variability of RR intervals196before dislodgement of ventricular lead20, e.g., greater than the variability of RR intervals196detected via ventricular lead20during ventricular fibrillation episodes before dislodgment of ventricular lead20. Processing circuitry106(or any other processing circuitry described herein that receives indications of the timing of pacing pulses192and R-waves194from IMD10) may determine one or more parameters indicative of the variability of RR intervals196as a characteristic associated with dislodgement of ventricular lead20during atrial fibrillation. For example, processing circuitry106may determine at least one of a modesum of the RR intervals196or a ratio of a maximum and a minimum of the RR intervals196within a group of RR intervals196as parameters indicative of the variability of RR intervals196. The group of RR intervals may be consecutive RR intervals196, which may have preceded detection of ventricular fibrillation, as described above.

To determine the modesum, in one example, processing circuitry106groups interval values into bins, each bin associated with a range of interval values, and determines the percentage of the values of RR intervals196that are within the two most populated interval value bins. In one example, processing circuitry106detects dislodgment of ventricular lead20based on the modesum of RR intervals196being less than the modesum threshold, e.g., 50%. In some examples, the ratio between the maximum and minimum of the RR intervals196is a ratio of the maximum to the minimum, and processing circuitry106detects dislodgment of ventricular lead20based on the ratio exceeding a ratio threshold, e.g., 2.0. In other examples, the ratio between the maximum and minimum of the RR intervals196is a ratio of the minimum to the maximum, and processing circuitry106detects dislodgment of ventricular lead20based on the ratio being less than a ratio threshold.

In some examples, processing circuitry106may determine differences between consecutive RR intervals196of the group of RR intervals196, and may determine a number or percentage of the determined differences that exceed a threshold difference as a parameter indicative of the variability of RR intervals196. In such examples, processing circuitry106detects dislodgment of ventricular lead20based on the number or percentage of supra-threshold differences exceeding a threshold number or percentage. In general, processing circuitry106may detect dislodgement of ventricular lead20based on the variability of RR intervals196satisfying a variability threshold.

In some examples, in response to a group of RR intervals196satisfying a programmable number of intervals to detect (NID) criterion for detecting ventricular fibrillation (e.g., 18 RR intervals196out of 24 consecutive RR intervals196being shorter than the ventricular fibrillation threshold), processing circuitry106determines the amplitude of R-waves194and variability of RR-intervals196leading to the satisfaction of the NID criterion, such as consecutive R-waves or RR intervals prior to detection, or the specific RR intervals196(e.g., the 18 RR intervals196) that were shorter than the ventricular fibrillation threshold and R-wave amplitudes associated with those RR intervals.

FIG. 6is a flowchart of an example technique for identifying dislodgment of a ventricular lead during atrial fibrillation. The flowchart ofFIGS. 6-10are intended to illustrate the functional operation of IMD10, medical system8, and other devices and systems described herein, and should not be construed as reflective of a specific form of software or hardware necessary to practice the methods described. Methods described in conjunction with flow charts presented herein may be implemented in a non-transitory computer-readable medium that includes instructions for causing a programmable processor to carry out the methods described. A non-transitory computer-readable medium includes but is not limited to any volatile or non-volatile media, such as a RAM, ROM, CD-ROM, NVRAM, EEPROM, flash memory, or other computer-readable media, with the sole exception being a transitory, propagating signal. The instructions may be implemented as one or more software modules, which may be executed by themselves or in combination with other software.

The example methods illustrated byFIGS. 6-10may be performed, by any one or more devices described herein, and may be performed, in part, by processing circuitry of any one or more devices described herein, such as by processing circuitry106of IMD10, processing circuitry140of external device30, processing circuitry168of server164, or processing circuitry of access point160and/or computing devices170. For ease of description, the methods ofFIGS. 6-10will be described hereafter as being performed by processing circuitry106of IMD10.

According to the example method ofFIG. 6, sensing circuitry102of IMD10senses a cardiac signal190via ventricular lead20, e.g., a ventricular EGM signal (200). Processing circuitry106determines one or more characteristics of ventricular lead dislodgment during atrial fibrillation, such as an amplitude of R-waves194and/or variability of RR intervals (202). Processing circuitry106detects whether ventricular lead20is dislodged based on the one or more determined characteristics, e.g., based on the amplitude and/or variability satisfying respective thresholds (204). If processing circuitry106does not detect lead dislodgment (NO of204), the processing circuitry continues to analyze the sensed cardiac signal (200,202). If processing circuitry106detects lead dislodgment (YES of204), processing circuitry106may provide an alert to a user, e.g., to external device30or another device via telemetry circuitry118(206).

FIG. 7is a flowchart of an example technique for determining characteristics of a cardiac signal sensed via a dislodged ventricular lead during atrial fibrillation. The technique described inFIG. 7may be used, for example, in blocks202and/or204ofFIG. 6,FIG. 8and/orFIG. 10. According to the example ofFIG. 7, processing circuitry106determines an amplitude of cardiac signal190, e.g., determines an amplitude of one or more of R-waves194, as described with respect toFIG. 5(210). Cardiac signal190may be a near-field ventricular EGM signal. Processing circuitry106also determines a variability of cardiac signal190, e.g., determines one or more parameters indicating the variability of RR intervals196, as described with respect toFIG. 5(212).

Processing circuitry106determines whether the amplitude and variability satisfy respective thresholds (214). For example, processing circuitry106may determine whether an amplitude of a threshold percentage (e.g., 25%) of a group of R-waves194is less than an amplitude threshold (e.g., 1 mV). As another example, processing circuitry106may determine whether a modesum of consecutive RR intervals196is less than a modesum threshold (e.g., 50%) and/or a ratio of the maximum to the minimum of the consecutive RR intervals is greater than the ratio threshold (e.g., 2.0). Processing circuitry106detects dislodgement of ventricular lead20(216) based on the amplitude and variability meeting their respective thresholds (YES of214), and does not detect dislodgement of ventricular lead20(218) based on the amplitude and/or variability not meeting their respective thresholds (NO of214).

FIG. 8is a flowchart of another example technique for identifying dislodgment of a ventricular lead during atrial fibrillation. The like-numbered blocks inFIG. 8are described above in further detail with reference toFIG. 6.

According to the example ofFIG. 8, sensing circuitry102of IMD10senses a cardiac signal190via ventricular lead20, e.g., a ventricular EGM signal (200). Processing circuitry106determines whether ventricular fibrillation of heart16is detected based on cardiac signal190(230). Processing circuitry106may employ any technique for detecting ventricular fibrillation, e.g., based on the length of a number of RR intervals in an episode being less than a threshold length and/or other parameters, including signal morphology.

In response to detecting ventricular fibrillation, processing circuitry106determines whether a withholding feature is enabled (232). If the withholding feature is not enabled (NO of232), processing circuitry106may control therapy delivery circuitry104to deliver a ventricular defibrillation therapy to treat the detected ventricular fibrillation (234). However, in some examples, processing circuitry106may perform other analyses not described in this disclosure to determine whether or not the defibrillation therapy should be withheld or delivered, whether or not the withholding feature described herein is enabled. Therefore, processing circuitry106does not necessarily control therapy delivery circuitry104to deliver the ventricular defibrillation therapy in response to the withholding feature not being enabled. Furthermore, in some examples, the withholding feature, and the determination as to whether the withholding feature is enabled (232), is optional, and may be excluded from the example technique ofFIG. 8

If the withholding feature is enabled (YES of232), or the withholding feature is omitted from the example technique and block232does not exist, processing circuitry106determines one or more characteristics of ventricular lead dislodgment during atrial fibrillation, such as an amplitude of R-waves194and/or variability of RR intervals (202). Processing circuitry106detects whether ventricular lead20is dislodged based on the one or more determined characteristics, e.g., based on the amplitude and/or variability satisfying respective thresholds (204). If processing circuitry106does not detect lead dislodgment (NO of204), the processing circuitry may, but does not necessarily, control therapy delivery circuitry104to deliver the defibrillation therapy (234). If processing circuitry106detects lead dislodgment (YES of204), the processing circuitry may control therapy delivery circuitry104to withhold the defibrillation therapy (236), and provide an alert to a user, e.g., to external device30or another device via telemetry circuitry118(206).

FIG. 9is a flowchart of an example technique for determining whether a withholding feature is enabled or disabled. The technique described inFIG. 9may be used, for example, in block232ofFIG. 8and/orFIG. 10. According to the example technique ofFIG. 9, processing circuitry106determines that the withholding feature is disabled (240) until an atrial fibrillation episode of heart16of patient14is detected (YES of242) when ventricular lead20has been implanted for less than a predetermined time, e.g., 6 months (YES of244). When these conditions are satisfied, processing circuitry106enables the withholding feature (246). However, when ventricular lead20has been implanted for at least the threshold period of time (NO of244), processing circuitry106disables the withholding feature (240). In other examples, processing circuitry106may enable or disable the withholding feature based on only one of the conditions identified inFIG. 9, e.g., based either on whether lead20has been implanted less than a threshold period of time, or whether atrial fibrillation has previously been detected or has been detected within a threshold period of time in patient14. In some examples, processing circuitry106may additionally or alternatively determine whether the withholding feature is enabled or not enabled in response to a user command, e.g., received from external device30. Processing circuitry106may detect atrial fibrillation of heart16based on an atrial EGM from atrial lead22, based on the ventricular EGM from ventricular lead20, or may receive an indication of atrial fibrillation from another device, such as from a user via external device30. Detection of atrial fibrillation of heart16based on the ventricular EGM from ventricular lead20may be, for example, according to algorithms that analyze characteristics of RR intervals196that reflect conduction of atrial fibrillation to the ventricles through the atrioventricular node, such as those employed by the Visia AF™ single chamber ICD available from Medtronic plc, of Dublin Ireland.

FIG. 10is a flowchart of another example technique for identifying dislodgment of a ventricular lead during atrial fibrillation. The like-numbered blocks inFIG. 10are described above in further detail with reference toFIG. 6and/orFIG. 8.

According to the example technique ofFIG. 10, sensing circuitry102of IMD10senses a cardiac signal190via ventricular lead20, e.g., a ventricular EGM signal (200). Processing circuitry106determines whether ventricular fibrillation of heart16is detected based on cardiac signal190(230). In response to detecting ventricular fibrillation, processing circuitry106determines one or more characteristics of ventricular lead dislodgment during atrial fibrillation, such as an amplitude of R-waves194and/or variability of RR intervals (202). Processing circuitry106detects whether ventricular lead20is dislodged based on the one or more determined characteristics, e.g., based on the amplitude and/or variability satisfying respective thresholds (204).

If processing circuitry106does not detect lead dislodgment (NO of204), the processing circuitry may, but does not necessarily, control therapy delivery circuitry104to deliver the defibrillation therapy (234). If processing circuitry106detects lead dislodgment (YES of204), the processing circuitry may provide an alert to a user, e.g., to external device30or another device via telemetry circuitry118(206). Processing circuitry106also determines whether a withholding feature is enabled (232). If the withholding feature is not enabled (NO of232), processing circuitry106may control therapy delivery circuitry104to deliver a ventricular defibrillation therapy to treat the detected ventricular fibrillation (234) despite having detecting detected dislodgement of ventricular lead20, e.g., to avoid inappropriately withholding a needed therapy. If the withholding feature is enabled (YES of232), processing circuitry may control therapy delivery circuitry104to withhold the defibrillation therapy (236).

In some examples, the withholding feature, and the determination as to whether the withholding feature is enabled (232), is optional, and may be excluded from the example technique ofFIG. 10. In such examples, processing circuitry106may deliver the alert (206) and withhold the defibrillation therapy (236) in response to detecting ventricular lead dislodgment (YES of204).

In one or more examples, the functions described in this disclosure may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on, as one or more instructions or code, a computer-readable medium and executed by a hardware-based processing unit. Computer-readable media may include computer-readable storage media forming a tangible, non-transitory medium. Instructions may be executed by one or more processors, such as one or more DSPs, ASICs, FPGAs, general purpose microprocessors, or other equivalent integrated or discrete logic circuitry. Accordingly, the term “processor,” as used herein may refer to one or more of any of the foregoing structure or any other structure suitable for implementation of the techniques described herein.

In addition, in some aspects, the functionality described herein may be provided within dedicated hardware and/or software modules. Depiction of different features as modules or units is intended to highlight different functional aspects and does not necessarily imply that such modules or units must be realized by separate hardware or software components. Rather, functionality associated with one or more modules or units may be performed by separate hardware or software components, or integrated within common or separate hardware or software components. Also, the techniques could be fully implemented in one or more circuits or logic elements. The techniques of this disclosure may be implemented in a wide variety of devices or apparatuses, including an IMD, an external programmer, a combination of an IMD and external programmer, an integrated circuit (IC) or a set of ICs, and/or discrete electrical circuitry, residing in an IMD and/or external programmer.