Cardiac event sensing in an implantable medical device

1. An implantable medical device comprising:

a therapy delivery circuit configured to generate cardiac pacing pulses;

a sensing circuit configured to receive a first cardiac signal from a patient's heart via sensing electrodes and sense intrinsic cardiac electrical events from the first cardiac signal; and

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

start a pacing interval;

detect an event interval that is greater than a P-wave oversensing threshold interval, the event interval extending from an intrinsic cardiac electrical event sensed from the first cardiac signal by the sensing circuit to a most recent preceding cardiac event;

determine a first amplitude of the first cardiac signal in response to detecting the event interval greater than the P-wave oversensing threshold interval;

determine that the first amplitude satisfies P-wave oversensing criteria;

withhold restarting of the pacing interval in response to at least the first amplitude satisfying the P-wave oversensing criteria;

detect the pacing interval expiring; and

control the therapy delivery circuit to generate a pacing pulse in response to the pacing interval expiring.

2. The device of claim 1 , wherein

the sensing circuit is configured to receive a second cardiac signal from the patient's heart; and

the control circuit is configured to:

determine a second amplitude of the second cardiac signal in response to detecting the event interval greater than the P-wave oversensing threshold interval; and

determine that the P-wave oversensing criteria are met based on the first amplitude and the second amplitude.

3. The device of claim 2 , wherein the control circuit is configured to determine the second amplitude by:

setting a post-sense blanking interval in response to the intrinsic cardiac electrical event sensed by the sensing circuit from the first cardiac signal; and

determining a maximum peak amplitude of the second cardiac signal occurring within the post-sense blanking interval.

4. The device of claim 2 , wherein the control circuit is configured to determine that the P-wave oversensing criteria are met by:

establishing a first reference amplitude from the first cardiac signal;

establishing a second reference amplitude from the second cardiac signal;

determining that the first amplitude is within a threshold difference of the first reference amplitude and that the second amplitude is within a threshold difference of the second reference amplitude.

5. The device of claim 2 , wherein the control circuit is configured to determine that the P-wave oversensing criteria are met by determining that the first amplitude is less than the second amplitude.

6. The device of claim 2 , further comprising a housing enclosing the therapy delivery circuit, the sensing circuit and the control circuit and having a connector block for receiving an extra-cardiovascular lead carrying a first sensing electrode pair for receiving the first cardiac signal, the sensing circuit configured to receive the second cardiac signal via a second sensing electrode pair comprising a sensing electrode carried by the extra-cardiovascular lead and the housing.

7. The device of claim 1 , wherein the control circuit is configured to set the P-wave oversensing threshold interval based on the pacing interval.

8. The device of claim 1 , wherein the control circuit is configured to set the P-wave oversensing threshold interval greater than a tachyarrhythmia detection interval and less than the pacing interval.

9. The device of claim 1 , further comprising a housing enclosing the therapy delivery circuit, the sensing circuit and the control circuit and having a connector block for receiving an extra-cardiovascular lead carrying at least one sensing electrode for receiving the first cardiac signal.

10. The device of claim 1 , wherein the control circuit is configured to determine that the P-wave oversensing criteria are met by:

establishing a reference amplitude from the first cardiac signal;

determining that the first amplitude is within a threshold difference of the reference amplitude.

11. A method comprising:

sensing intrinsic cardiac electrical events from a first cardiac signal received by a sensing circuit of an implantable medical device via sensing electrodes from a patient's heart;

starting a pacing interval by a control circuit of the implantable medical device;

detecting by the control circuit an event interval that is greater than a P-wave oversensing threshold interval, the event interval extending from an intrinsic cardiac electrical event sensed from the first cardiac signal by the sensing circuit to a most recent preceding cardiac event;

determining a first amplitude of the first cardiac signal in response to detecting the event interval greater than the P-wave oversensing threshold interval;

determining that the first amplitude satisfies P-wave oversensing criteria;

withholding restarting of the pacing interval in response to at least the first amplitude satisfying the P-wave oversensing criteria;

detecting the pacing interval expiring; and

generating a pacing pulse by a therapy delivery circuit of the implantable medical device in response to the pacing interval expiring.

12. The method of claim 11 , further comprising:

receiving a second cardiac signal from the patient's heart by the sensing circuit;

determining a second amplitude of the second cardiac signal in response to detecting the event interval greater than the P-wave oversensing threshold interval; and

determining that the P-wave oversensing criteria are met based on the first amplitude and the second amplitude.

13. The method of claim 12 , wherein determining the second amplitude comprises:

setting a post-sense blanking interval in response to the intrinsic cardiac electrical event sensed from the first cardiac signal; and

determining a maximum peak amplitude of the second cardiac signal occurring within the post-sense blanking interval.

14. The method of claim 12 , wherein determining that the P-wave oversensing criteria are met comprises:

establishing a first reference amplitude from the first cardiac signal;

establishing a second reference amplitude from the second cardiac signal;

determining that the first amplitude is within a threshold difference of the first reference amplitude and that the second amplitude is within a threshold difference of the second reference amplitude.

15. The method of claim 12 , wherein determining that the P-wave oversensing criteria are met comprises determining that the first amplitude is less than the second amplitude.

16. The method of claim 12 , further comprising receiving the first cardiac signal via a first sensing electrode pair carried by an extra-cardiovascular lead and receiving the second cardiac signal via a second sensing electrode pair comprising a sensing electrode carried by the extra-cardiovascular lead and a housing that encloses the sensing circuit, the therapy delivery circuit and the control circuit.

17. The method of claim 11 , further comprising setting the P-wave oversensing threshold interval based on the pacing interval.

18. The method of claim 11 , further comprising setting the P-wave oversensing threshold interval greater than a tachyarrhythmia detection interval and less than the pacing interval.

19. The method of claim 11 , further comprising receiving the first cardiac signal via at least one sensing electrode carried by an extra-cardiovascular lead.

20. The method of claim 11 , wherein determining that the P-wave oversensing criteria are met comprises:

establishing a reference amplitude from the first cardiac signal;

determining that the first amplitude is within a threshold difference of the reference amplitude.