Asystole detection and response in an implantable cardioverter defibrillator

1. A medical device, comprising:

a sensing circuit configured to receive a cardiac electrical signal and sense cardiac events 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 operate in a sensing mode and a pacing mode, wherein the control circuit is configured to:

during the sensing mode, detect asystole based on the cardiac electrical signal without setting a pacing escape interval for scheduling a cardiac pacing pulse;

switch from the sensing mode to the pacing mode in response to detecting the asystole by switching to a temporary pacing mode;

start the pacing escape interval to schedule a cardiac pacing pulse upon switching to the pacing mode; and

during the pacing mode, determine that the pacing escape interval expires without a cardiac event sensed by the sensing circuit during the pacing escape interval; and

the therapy delivery circuit is further configured to deliver the scheduled pacing pulse in response to the pacing escape interval expiring.

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

switch to the pacing mode by switching to a temporary pacing mode;

set a termination timer;

determine that the termination timer expires; and

switch from the temporary pacing mode back to the sensing mode in response to the termination timer expiring.

3. The medical device of claim 2 , wherein the control circuit is further configured to set the termination timer to at least thirty seconds.

4. The medical device of claim 1 , wherein:

the therapy delivery circuit is further configured to deliver a cardiac pacing pulse in response to the control circuit switching to the pacing mode; and

the control circuit is further configured to start the pacing escape interval in response to the delivered cardiac pacing pulse.

5. The medical device of claim 1 , wherein the control circuit is further configured to detect the asystole during the sensing mode by:

starting an asystole detection time interval in response to a cardiac event sensed by the sensing circuit;

determining that the asystole detection time interval expires without a cardiac event sensed by the sensing circuit; and

detecting the asystole in response to the asystole detection time interval expiring.

6. The medical device of claim 5 , wherein the control circuit is further configured to set the asystole detection time interval to at least two seconds.

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

detect a tachyarrhythmia episode during the pacing mode; and

switch from the pacing mode back to the sensing mode in response to detecting the tachyarrhythmia episode.

8. The medical device of claim 1 , further comprising:

a memory coupled to the control circuit; and

a telemetry circuit coupled to the control circuit;

wherein:

the control circuit is further configured to store asystole episode data in the memory in response to detecting the asystole; and

the telemetry circuit is configured to transmit the asystole episode data.

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

switch to the pacing mode by switching to a permanent pacing mode; and

set the pacing escape interval to a bradycardia pacing lower rate interval.

10. A method, comprising:

receiving a cardiac electrical signal;

sensing cardiac events from the cardiac electrical signal;

operating in a sensing mode by detecting asystole based on the cardiac electrical signal without setting a pacing escape interval for scheduling a cardiac pacing pulse;

switching from operating in the sensing mode to operating in a pacing mode in response to detecting the asystole;

starting the pacing escape interval to schedule a cardiac pacing pulse upon switching to the pacing mode; and

during the pacing mode, determining that the pacing escape interval expires without a cardiac event sensed during the pacing escape interval; and

delivering the scheduled pacing pulse in response to the pacing escape interval expiring.

11. The method of claim 10 , further comprising:

switching to the pacing mode by switching to a temporary pacing mode;

setting a termination timer;

determining that the termination timer expires; and

switching from the temporary pacing mode back to the sensing mode in response to the termination timer expiring.

12. The method of claim 11 , further comprising setting the termination timer to at least thirty seconds.

13. The method of claim 10 , further comprising:

delivering a cardiac pacing pulse in response to switching to the pacing mode; and

starting the pacing escape interval in response to the delivered cardiac pacing pulse.

14. The method of claim 10 , further comprising

during the sensing mode, starting an asystole detection time interval in response to sensing a cardiac event from the cardiac electrical signal;

determining that the asystole detection time interval expires without sensing a cardiac event from the cardiac electrical signal; and

detecting the asystole in response to the asystole detection time interval expiring.

15. The method of claim 14 , further comprising setting the asystole detection time interval to at least two seconds.

16. The method of claim 10 , further comprising:

detecting a tachyarrhythmia episode during the pacing mode; and

switching from the pacing mode back to the sensing mode in response to detecting the tachyarrhythmia episode.

17. The method of claim 10 , further comprising:

storing an asystole episode data in a memory in response to detecting the asystole; and

transmitting the asystole episode data.

18. The method of claim 10 , further comprising:

switching to the pacing mode by switching to a permanent pacing mode; and

setting the pacing escape interval to a bradycardia pacing lower rate interval.

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

receive a cardiac electrical signal;

sense cardiac events from the cardiac electrical signal;

operate in a sensing mode by detecting asystole based on the cardiac electrical signal without setting a pacing escape interval for scheduling a cardiac pacing pulse;

switch from operating in the sensing mode to operating in a pacing mode in response to detecting the asystole;

start the pacing escape interval to schedule a cardiac pacing pulse upon switching to the pacing mode;

during the pacing mode, determine that the pacing escape interval expires without a cardiac event sensed during the pacing escape interval; and

deliver the scheduled pacing pulse in response to the pacing escape interval expiring.