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A leadless pacing device (LPD) includes a motion sensor configured to generate a motion signal as a function of heart movement. The LPD is configured to analyze the motion signal within an atrial contraction detection window that begins an atrial contraction detection delay period after activation o

A leadless pacing device (LPD) includes a motion sensor configured to generate a motion signal as a function of heart movement. The LPD is configured to analyze the motion signal within an atrial contraction detection window that begins an atrial contraction detection delay period after activation of the ventricle, and detect a contraction of an atrium of the heart based on the analysis of the motion signal within the atrial contraction detection window. If the LPD does not detect a ventricular depolarization subsequent to the atrial contraction, e.g., with an atrio-ventricular (AV) interval beginning when the atrial contraction was detected, the LPD delivers a ventricular pacing pulse.

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1. A leadless pacing device configured to deliver atrio-synchronous ventricular pacing, the leadless pacing device comprising: a plurality of electrodes;a motion sensor configured to generate a motion signal as a function of movement of a heart of a patient;a stimulation module coupled to the plural

1. A leadless pacing device configured to deliver atrio-synchronous ventricular pacing, the leadless pacing device comprising: a plurality of electrodes;a motion sensor configured to generate a motion signal as a function of movement of a heart of a patient;a stimulation module coupled to the plurality of electrodes, wherein the stimulation module is configured to generate pacing pulses and deliver the pacing pulses to a ventricle of the heart via the plurality of electrodes;an electrical sensing module coupled to the plurality of electrodes, wherein the electrical sensing module is configured to detect depolarizations of the ventricle within a cardiac electrogram sensed via the plurality of electrodes;a mechanical sensing module coupled to the motion sensor and configured to: receive the motion signal from the motion sensor;identify an activation of the ventricle;upon identification of the activation of the ventricle, initiate an atrial contraction detection delay period;analyze the motion signal within an atrial contraction detection window that begins upon completion of the atrial contraction detection delay period; anddetect a contraction of an atrium of the heart based on the analysis of the motion signal within the atrial contraction detection window;a processing module configured to control the stimulation module to generate a pacing pulse and deliver the pacing pulse to the ventricle via the plurality of electrodes in response to the detection of the contraction of the atrium by the mechanical sensing module; anda housing configured to be implanted within the ventricle, wherein the housing encloses the motion sensor, the stimulation module, the electrical sensing module, the mechanical sensing module, and the processing module;wherein the processing module is configured to:determine that the electrical sensing module did not detect a depolarization of the ventricle within an atrioventricular (AV) interval beginning when the mechanical sensing module detected the contraction of the atrium; andcontrol the stimulation module to generate the pacing pulse and deliver the pacing pulse to the ventricle via the plurality of electrodes in response to the determination; and,wherein the mechanical sensing module is configured to detect a contraction of the ventricle based on the motion signal after delivery of the pacing pulse to the ventricle, and the processing module is configured to:determine whether the delivery of the pacing pulse to the ventricle was effective based on the detection of the contraction of the ventricle; andadjust the AV interval based on the determination of whether the delivery of the pacing pulse to the ventricle was effective. 2. The leadless pacing device of claim 1, wherein the processing module is configured to: determine that an interval from the delivery of the pacing pulse to the detection of the contraction of the ventricle is less than a threshold; anddecrease the AV interval in response to the determination that the interval from the delivery of the pacing pulse to the detection of the contraction of the ventricle is less than the threshold. 3. The leadless pacing device of claim 1, wherein the mechanical sensing module is configured to: detect a peak of the ventricular contraction based on the motion signal; anddetermine an amplitude of the motion signal at the peak, andwherein the processing module is configured to: determine that the amplitude is greater than the threshold; andincrease the AV interval in response to the determination that the amplitude is greater than the threshold. 4. A leadless pacing device configured to deliver atrio-synchronous ventricular pacing, the leadless pacing device comprising: a plurality of electrodes;a motion sensor configured to generate a motion signal as a function of movement of a heart of a patient;a stimulation module coupled to the plurality of electrodes, wherein the stimulation module is configured to generate pacing pulses and deliver the pacing pulses to a ventricle of the heart via the plurality of electrodes;an electrical sensing module coupled to the plurality of electrodes, wherein the electrical sensing module is configured to detect depolarizations of the ventricle within a cardiac electrogram sensed via the plurality of electrodes;a mechanical sensing module coupled to the motion sensor and configured to: receive the motion signal from the motion sensor;identify an activation of the ventricle;upon identification of the activation of the ventricle, initiate an atrial contraction detection delay period;analyze the motion signal within an atrial contraction detection window that begins upon completion of the atrial contraction detection delay period; anddetect a contraction of an atrium of the heart based on the analysis of the motion signal within the atrial contraction detection window;a processing module configured to control the stimulation module to generate a pacing pulse and deliver the pacing pulse to the ventricle via the plurality of electrodes in response to the detection of the contraction of the atrium by the mechanical sensing module; anda housing configured to be implanted within the ventricle, wherein the housing encloses the motion sensor, the stimulation module, the electrical sensing module, the mechanical sensing module, and the processing module;wherein the processing module is configured to:determine that the electrical sensing module did not detect a depolarization of the ventricle within an atrioventricular (AV) interval beginning when the mechanical sensing module detected the contraction of the atrium; andcontrol the stimulation module to generate the pacing pulse and deliver the pacing pulse to the ventricle via the plurality of electrodes in response to the determination; and,wherein the AV interval comprises a mechanical AV interval,wherein the electrical sensing module is configured to detect depolarizations of the atrium within the cardiac electrogram sensed via the plurality of electrodes,wherein, in response to the electrical sensing module detecting a depolarization of the atrium, the processing module is configured to: determine that the electrical sensing module did not detect a depolarization of the ventricle within an electrical AV interval beginning when the electrical sensing module detected the depolarization of the atrium; andcontrol the stimulation module to generate a pacing pulse and deliver the pacing pulse to the ventricle via the plurality of electrodes in response to the determination that the electrical sensing module did not detect a depolarization of the ventricle,wherein the processing module is further configured to determine that the electrical sensing module did not detect a depolarization of the atrium during a predetermined number of one or more cardiac cycles and, in response to the determination: control the mechanical sensing module to detect a contraction of the atrium based on the motion signal;determine that the electrical sensing module did not detect a depolarization of the ventricle within the mechanical AV interval beginning when the mechanical sensing module detected the contraction of the atrium; andcontrol the stimulation module to generate a pacing pulse and deliver the pacing pulse to the ventricle via the plurality of electrodes in response to the determination that the mechanical sensing module did not detect a depolarization of the ventricle, andwherein the electrical AV interval is greater than the mechanical AV interval. 5. A leadless pacing device configured to deliver atrio-synchronous ventricular pacing, the leadless pacing device comprising: a plurality of electrodes;a motion sensor configured to generate a motion signal as a function of movement of a heart of a patient;a stimulation module coupled to the plurality of electrodes, wherein the stimulation module is configured to generate pacing pulses and deliver the pacing pulses to a ventricle of the heart via the plurality of electrodes;an electrical sensing module coupled to the plurality of electrodes, wherein the electrical sensing module is configured to detect depolarizations of the ventricle within a cardiac electrogram sensed via the plurality of electrodes;a mechanical sensing module coupled to the motion sensor and configured to: receive the motion signal from the motion sensor;identify an activation of the ventricle;upon identification of the activation of the ventricle, initiate an atrial contraction detection delay period;analyze the motion signal within an atrial contraction detection window that begins upon completion of the atrial contraction detection delay period; anddetect a contraction of an atrium of the heart based on the analysis of the motion signal within the atrial contraction detection window;a processing module configured to control the stimulation module to generate a pacing pulse and deliver the pacing pulse to the ventricle via the plurality of electrodes in response to the detection of the contraction of the atrium by the mechanical sensing module; anda housing configured to be implanted within the ventricle, wherein the housing encloses the motion sensor, the stimulation module, the electrical sensing module, the mechanical sensing module, and the processing module;wherein the processing module is configured to:determine a heart rate of the patient based on depolarizations detected by the electrical sensing module;determine that the heart rate exceeds a threshold; andcontrol the stimulation module to generate pacing pulses and deliver the pacing pulses to the ventricle according to an asynchronous ventricular pacing mode in response to the determination that the heart rate exceeds the threshold. 6. A leadless pacing device configured to deliver atrio-synchronous ventricular pacing, the leadless pacing device comprising: a plurality of electrodes;a motion sensor configured to generate a motion signal as a function of movement of a heart of a patient;a stimulation module coupled to the plurality of electrodes, wherein the stimulation module is configured to generate pacing pulses and deliver the pacing pulses to a ventricle of the heart via the plurality of electrodes;an electrical sensing module coupled to the plurality of electrodes, wherein the electrical sensing module is configured to detect depolarizations of the ventricle within a cardiac electrogram sensed via the plurality of electrodes;a mechanical sensing module coupled to the motion sensor and configured to: receive the motion signal from the motion sensor;identify an activation of the ventricle;upon identification of the activation of the ventricle, initiate an atrial contraction detection delay period;analyze the motion signal within an atrial contraction detection window that begins upon completion of the atrial contraction detection delay period; anddetect a contraction of an atrium of the heart based on the analysis of the motion signal within the atrial contraction detection window;a processing module configured to control the stimulation module to generate a pacing pulse and deliver the pacing pulse to the ventricle via the plurality of electrodes in response to the detection of the contraction of the atrium by the mechanical sensing module; anda housing configured to be implanted within the ventricle, wherein the housing encloses the motion sensor, the stimulation module, the electrical sensing module, the mechanical sensing module, and the processing module;wherein the motion sensor comprises a plurality of accelerometers, each of the plurality of accelerometers oriented along a respective axis and configured to generate a respective accelerometer signal,wherein mechanical sensing module derives the motion signal based on a first one or more of the accelerometer signals according to a first sensing vector, andwherein the processing module is configured to: determine that the mechanical sensing module did not detect a contraction of the atrium during a predetermined number of one or more cardiac cycles; andcontrol the mechanical sensing module to derive the motion signal based on a second one or more of the accelerometer signals according to a second sensing vector in response to the determination. 7. A method for delivering atrio-synchronous ventricular pacing by a leadless pacing device implanted within a ventricle of a heart of a patient, the method comprising: identifying an activation of the ventricle;upon identification of the activation of the ventricle, initiating an atrial contraction detection delay period;analyzing a motion signal within an atrial contraction detection window that begins upon completion of the atrial contraction detection delay period, wherein the motion signal is generated by a motion sensor of the leadless pacing device as a function of movement of the heart;detecting a contraction of an atrium of the heart based on the analysis of the motion signal within the atrial contraction detection window; anddelivering a pacing pulse to the ventricle in response to the detection of the atrial contraction;determining that a depolarization of the ventricle resulting from the depolarization of the atrium that caused the contraction of the atrium was not detected within an atrioventricular (AV) interval beginning when the contraction of the atrium was detected;delivering the pacing pulse to the ventricle in response to the determination;determining that a depolarization of the ventricle resulting from the depolarization of the atrium that caused the contraction of the atrium was not detected within an atrioventricular (AV) interval beginning when the contraction of the atrium was detected; anddelivering the pacing pulse to the ventricle in response to the determination;detecting a contraction of the ventricle based on the motion signal after delivery of the pacing pulse to the ventricle;determining whether the delivery of the pacing pulse to the ventricle was effective based on the detection of the contraction of the ventricle; andadjusting the AV interval based on the determination of whether the delivery of the pacing pulse to the ventricle was effective. 8. The method of claim 7, further comprising: determining that an interval from the delivery of the pacing pulse to the detection of the contraction of the ventricle is less than a threshold; anddecreasing the AV interval in response to the determination that the interval from the delivery of the pacing pulse to the detection of the contraction of the ventricle is less than the threshold. 9. The method of claim 7, further comprising: detecting a peak of the ventricular contraction based on the motion signal;determining an amplitude of the motion signal at the peak;determining that the amplitude is greater than the threshold; andincreasing the AV interval in response to the determination that the amplitude is greater than the threshold. 10. A method for delivering atrio-synchronous ventricular pacing by a leadless pacing device implanted within a ventricle of a heart of a patient, the method comprising: identifying an activation of the ventricle;upon identification of the activation of the ventricle, initiating an atrial contraction detection delay period;analyzing a motion signal within an atrial contraction detection window that begins upon completion of the atrial contraction detection delay period, wherein the motion signal is generated by a motion sensor of the leadless pacing device as a function of movement of the heart;detecting a contraction of an atrium of the heart based on the analysis of the motion signal within the atrial contraction detection window; anddelivering a pacing pulse to the ventricle in response to the detection of the atrial contraction;determining that a depolarization of the ventricle resulting from the depolarization of the atrium that caused the contraction of the atrium was not detected within an atrioventricular (AV) interval beginning when the contraction of the atrium was detected;delivering the pacing pulse to the ventricle in response to the determination;determining that a depolarization of the ventricle resulting from the depolarization of the atrium that caused the contraction of the atrium was not detected within an atrioventricular (AV) interval beginning when the contraction of the atrium was detected; anddelivering the pacing pulse to the ventricle in response to the determination;wherein the leadless pacing device is configured to detect depolarizations of the atrium, and the AV interval comprises a mechanical AV interval, the method further comprising:in response to detecting a depolarization of the atrium: determining that a depolarization of the ventricle was not detected within an electrical AV interval beginning when the electrical sensing module detected the depolarization of the atrium; anddelivering a pacing pulse to the ventricle in response to the determination that a depolarization of the ventricle was not detected, andin response to determining that a depolarization of the atrium was not detected during a predetermined number of one or more cardiac cycles: detecting a contraction of the atrium based on the motion signal;determining that a depolarization of the ventricle was not detected within the mechanical AV interval beginning when the contraction of the atrium was detected; anddelivering a pacing pulse to the ventricle in response to the determination that a depolarization of the ventricle was not detected, andwherein the electrical AV interval is greater than the mechanical AV interval. 11. A method for delivering atrio-synchronous ventricular pacing by a leadless pacing device implanted within a ventricle of a heart of a patient, the method comprising: identifying an activation of the ventricle;upon identification of the activation of the ventricle, initiating an atrial contraction detection delay period;analyzing a motion signal within an atrial contraction detection window that begins upon completion of the atrial contraction detection delay period, wherein the motion signal is generated by a motion sensor of the leadless pacing device as a function of movement of the heart;detecting a contraction of an atrium of the heart based on the analysis of the motion signal within the atrial contraction detection window; anddelivering a pacing pulse to the ventricle in response to the detection of the atrial contraction;determining an amount of motion of the patient based on the motion signal; anddelivering the pacing pulses to the ventricle according to an asynchronous ventricular pacing mode in response to the amount of motion of the patient exceeding a threshold. 12. A method for delivering atrio-synchronous ventricular pacing by a leadless pacing device implanted within a ventricle of a heart of a patient, the method comprising: identifying an activation of the ventricle;upon identification of the activation of the ventricle, initiating an atrial contraction detection delay period;analyzing a motion signal within an atrial contraction detection window that begins upon completion of the atrial contraction detection delay period, wherein the motion signal is generated by a motion sensor of the leadless pacing device as a function of movement of the heart;detecting a contraction of an atrium of the heart based on the analysis of the motion signal within the atrial contraction detection window; anddelivering a pacing pulse to the ventricle in response to the detection of the atrial contraction;determining a contraction of the atrium was not detected during a predetermined number of one or more cardiac cycles; anddelivering pacing pulses to the ventricle according to an asynchronous ventricular pacing mode in response to the determination. 13. A method for delivering atrio-synchronous ventricular pacing by a leadless pacing device implanted within a ventricle of a heart of a patient, the method comprising: identifying an activation of the ventricle;upon identification of the activation of the ventricle, initiating an atrial contraction detection delay period;analyzing a motion signal within an atrial contraction detection window that begins upon completion of the atrial contraction detection delay period, wherein the motion signal is generated by a motion sensor of the leadless pacing device as a function of movement of the heart;detecting a contraction of an atrium of the heart based on the analysis of the motion signal within the atrial contraction detection window; anddelivering a pacing pulse to the ventricle in response to the detection of the atrial contraction;determining that a heart rate exceeds a threshold; anddelivering the pacing pulses to the ventricle according to an asynchronous ventricular pacing mode in response to the determination that the heart rate exceeds the threshold.