ASYSTOLE DETECTION AND RESPONSE IN AN IMPLANTABLE CARDIOVERTER DEFIBRILLATOR

1 . A medical device comprising:

a sensing circuit configured to:

receive a cardiac electrical signal;

sense cardiac event signals from the cardiac electrical signal;

a therapy delivery circuit configured to deliver cardiac pacing pulses; and

a control circuit coupled to the sensing circuit and the therapy delivery circuit and configured to:

detect asystole based on the cardiac electrical signal;

in response to detecting the asystole:

start a termination timer; and

start a first pacing escape interval to schedule a first cardiac pacing pulse;

a therapy delivery circuit configured to deliver the first pacing pulse when the first pacing escape interval expires without the sensing circuit sensing a cardiac event signal during the first pacing escape interval; and

the control circuit is further configured to, prior to the termination timer expiring, schedule subsequent cardiac pacing pulses for delivery by the therapy delivery circuit at pacing escape intervals from cardiac event signals sensed by the sensing circuit and/or pacing pulses delivered by the therapy delivery circuit that occur prior to the termination timer expiring.

2 . The medical device of claim 1 wherein the control circuit is further configured to:

determine that the termination timer is expired; and

terminate scheduling cardiac pacing pulses at the pacing escape intervals in response to the termination timer expiring.

3 . The medical device of claim 1 wherein the control circuit is further configured to:

start the first pacing escape interval as a hysteresis interval; and

schedule at least a portion of the subsequent cardiac pacing pulses prior to the termination timer expiring at pacing escape intervals that are shorter than the hysteresis interval.

4 . The medical device of claim 1 further comprising a sensor sensing a physiological signal; and

wherein the control circuit is further configured to:

determine one of a patient rest state or a patient non-rest state from the physiological signal;

in response to determining the patient rest state, schedule the subsequent cardiac pacing pulses at the pacing escape interval prior to the termination timer expiring according to a resting state pacing rate interval; or

in response to determining the patient non-rest state, schedule the subsequent cardiac pacing pulses at the pacing escape interval prior to the termination timer expiring according to a non-resting state pacing rate interval that is shorter than the resting state pacing rate interval.

5 . The medical device of claim 1 wherein the control circuit is further configured to:

determine that a threshold number of cardiac event signals are sensed by the sensing circuit prior to the termination timer expiring; and

terminate scheduling the subsequent pacing pulses in response to determining that the threshold number of cardiac event signals are sensed prior to the termination timer expiring.

6 . The medical device of claim 1 wherein the control circuit is further configured to:

detect a tachyarrhythmia from at least the cardiac electrical signal sensed by the sensing circuit; and

terminate scheduling the subsequent pacing pulses in response to detecting the tachyarrhythmia.

7 . The medical device of claim 1 wherein the control circuit is further configured to:

detect a patient rest state; and

withhold delivering the first pacing pulse in response to detecting the patient rest state.

8 . The medical device of claim 1 wherein the control circuit is further configured to detect the asystole by:

starting an asystole timer; and

determining that the asystole timer is expired without a cardiac event signal being sensed by the sensing circuit.

9 . The medical device of claim 8 further comprising a sensor sensing a physiological signal; and

wherein the control circuit is further configured to:

determine one of a patient rest state or a patient non-rest state from the physiological signal;

set the asystole detection timer to a first time interval when the patient rest state is detected; or

set the asystole timer to a second time interval when the patient non-rest state is detected, the first time interval being longer than the second time interval.

10 . The medical device of claim 1 wherein the control circuit is further configured to schedule the subsequent cardiac pacing pulses at pacing escape intervals by:

in response to a cardiac event signal sensed by the sensing circuit prior to the termination timer expiring, start a hysteresis pacing escape interval; and

in response to a pacing pulse delivered by the therapy delivery circuit prior to the termination timer expiring, start an asystole backup pacing interval that is shorter than the hysteresis pacing escape interval.

11 . A method comprising:

receiving a cardiac electrical signal;

sensing cardiac event signals from the cardiac electrical signal;

detecting asystole based on the cardiac electrical signal;

in response to detecting the asystole:

starting a termination timer; and

starting a first pacing escape interval to schedule a first cardiac pacing pulse;

delivering the first pacing pulse when the first pacing escape interval expires without a cardiac event signal being sensed during the first pacing escape interval; and

prior to the termination timer expiring, scheduling subsequent cardiac pacing pulses for delivery at pacing escape intervals from sensed cardiac event signals and/or delivered pacing pulses that occur prior to the termination timer expiring.

12 . The method of claim 11 further comprising:

determining that the termination timer is expired; and

terminating scheduling cardiac pacing pulses at the pacing escape intervals in response to the termination timer expiring.

13 . The method of claim 11 further comprising:

starting the first pacing escape interval as a hysteresis interval; and

scheduling at least a portion of the subsequent cardiac pacing pulses prior to the termination timer expiring at pacing escape intervals that are shorter than the hysteresis interval.

14 . The method of claim 11 further comprising:

sensing a physiological signal;

determining one of a patient rest state or a patient non-rest state from the physiological signal;

in response to determining the patient rest state, scheduling the subsequent cardiac pacing pulses at the pacing escape interval prior to the termination timer expiring according to a resting state pacing rate interval; or

in response to determining the patient non-rest state, scheduling the subsequent cardiac pacing pulses at the pacing escape interval prior to the termination timer expiring according to a non-resting state pacing rate interval that is shorter than the resting state pacing rate interval.

15 . The method of claim 11 further comprising:

determining that a threshold number of cardiac event signals are sensed prior to the termination timer expiring; and

terminating scheduling the subsequent pacing pulses in response to determining that the threshold number of cardiac event signals are sensed prior to the termination timer expiring.

16 . The method of claim 11 further comprising:

detecting a tachyarrhythmia from at least the cardiac electrical signal; and

terminating scheduling the subsequent pacing pulses in response to detecting the tachyarrhythmia.

17 . The method of claim 11 further comprising:

detecting a patient rest state; and

withholding delivering the first pacing pulse in response to detecting the patient rest state.

18 . The method of claim 11 wherein detecting the asystole comprises:

starting an asystole timer; and

determining that the asystole timer is expired without a cardiac event signal being sensed.

19 . The method of claim 18 further comprising:

sensing a physiological signal;

determining one of a patient rest state or a patient non-rest state from the physiological signal;

setting the asystole detection timer to a first time interval when the patient rest state is detected; or

setting the asystole timer to a second time interval when the patient non-rest state is detected, the first time interval being longer than the second time interval.

20 . The method of claim 11 wherein scheduling the subsequent cardiac pacing pulses at pacing escape intervals comprises:

in response to a cardiac event signal being sensed prior to the termination timer expiring, starting a hysteresis pacing escape interval; and

in response to a pacing pulse delivered prior to the termination timer expiring, starting an asystole backup pacing interval that is shorter than the hysteresis pacing escape interval.

21 . A non-transitory computer readable medium storing instructions that, when executed by a control circuit of a medical device, cause the medical device to:

receive a cardiac electrical signal;

sense cardiac event signals from the cardiac electrical signal;

detect asystole based on the cardiac electrical signal;

in response to detecting the asystole:

start a termination timer; and

start a first pacing escape interval to schedule a first cardiac pacing pulse;

deliver the first pacing pulse when the first pacing escape interval expires without a cardiac event signal being sensed during the first pacing escape interval; and

prior to the termination timer expiring, schedule subsequent cardiac pacing pulses for delivery at pacing escape intervals from sensed cardiac event signals and/or delivered pacing pulses that occur prior to the termination timer expiring.