Sensing and atrial-synchronized ventricular pacing in an intracardiac pacemaker

1. A method for use in an implanted medical device, the method comprising:

producing a filtered cardiac electrical signal using an adjustable filter within a sensing module by filtering a raw cardiac electrical signal received from implanted electrodes operably connected to the sensing module, the raw cardiac electrical signal comprising R-waves, T-waves and P-waves via electrodes coupled to the sensing module;

determining if the T-waves are distinct from the P-waves in the filtered cardiac electrical signal;

adjusting the filter to increase a difference between a feature of the P-waves and a feature of the T-waves in the filtered cardiac signal when the T-waves are not distinct from the P-waves;

determining P-wave sensing criteria based on the difference;

sensing a P-wave from the filtered cardiac electrical signal when the P-wave sensing criteria are met; and

setting a ventricular pacing escape interval in response to sensing the P-wave.

2. The method of claim 1 , wherein adjusting the filter to increase the difference comprises adjusting the filter to increase a difference between a peak P-wave amplitude and a peak T-wave amplitude in the filtered cardiac electrical signal.

3. The method of claim 2 , wherein adjusting the filter comprises adjusting the filter to increase the peak T-wave amplitude in the filtered cardiac signal.

4. The method of claim 3 , wherein determining the P-wave sensing criteria comprises determining a first threshold less than the maximum P-wave amplitude and a second threshold greater than the first threshold but less than the maximum T-wave amplitude,

wherein sensing the P-wave from the filtered cardiac signal comprises sensing a crossing of the first sensing threshold by the filtered cardiac signal, setting a time limit, and not sensing a crossing of the second sensing threshold during the time limit.

5. The method of claim 1 , wherein adjusting the filter comprises adjusting at least one of a center frequency and a bandpass width.

6. The method of claim 1 , further comprising:

determining a plurality of T-P intervals between consecutive pairs of T-waves and P-waves in the filtered cardiac electrical signal;

detecting a decreasing trend in the plurality of T-P intervals; and

adjusting at least one of the filter and a T-wave sensing window in response to detecting the decreasing trend; and

sensing P-waves from the filtered cardiac signal when the P-wave sensing criteria are met outside the T-wave sensing window.

7. The method of claim 1 , further comprising:

detecting a decrease in a difference between a P-wave feature and T-wave feature in the filtered cardiac electrical signal; and

adjusting the filter in response to detecting the decrease.

8. The method of claim 1 , further comprising:

repeating the adjusting of the filter and the determining if the T-waves are distinct from the P-waves in the filtered cardiac electrical signal;

determining if the P-waves and the T-waves of the filtered cardiac electrical signal are distinct based on at least one of time, peak amplitude and morphology within a maximum number of filter adjustments; and

disabling setting the ventricular pacing escape interval when the P-waves and the T-waves of the filtered cardiac electrical signal are not distinct based on at least one of time, peak amplitude and morphology within the maximum number of filter adjustments.

9. The method of claim 8 , further comprising:

periodically adjusting at least one of the filter and a T-wave sensing window;

re-determining if the P-waves and the T-waves are distinct based on at least one of time, peak amplitude and morphology; and

re-determining the P-wave sensing criteria when the P-waves and the T-waves in the filtered cardiac electrical signal are distinct after a periodic adjustment of at least one of the filter and the T-wave sensing window; and

re-enabling setting the ventricular pacing escape interval in response to P-waves sensed by the sensing module when the P-waves and the T-waves are distinct after a periodic adjustment of at least one of the filter and the T-wave sensing window.

10. The method of claim 1 , further comprising:

determining if oversensing of the T-waves by the sensing module is suspected;

lowering a P-wave sensing control parameter to increase a sensitivity of the sensing module for sensing P-waves when T-wave oversensing is suspected;

determining if T-waves can be identified from the filtered cardiac electrical signal after lowering the P-wave sensing control parameter; and

withholding the adjusting of the filter in response to determining that T-waves cannot be identified from the filtered cardiac electrical signal after lowering the P-wave sensing control parameter.

11. An implantable medical device, comprising:

a sensing module comprising an adjustable filter and configured to:

receive a raw cardiac electrical signal comprising R-waves, T-waves and P-waves via electrodes coupled to the sensing module;

filter the raw cardiac electrical signal by the adjustable filter to produce a filtered cardiac electrical signal;

determine if the T-waves are distinct from the P-waves in the filtered cardiac electrical signal;

adjust the filter to increase a difference between a feature of the P-waves and a feature of the T-waves in the filtered cardiac signal when the T-waves are not distinct from the P-waves;

determine P-wave sensing criteria based on the difference; and

sense a P-wave from the filtered cardiac electrical signal when the P-wave sensing criteria are met;

a pulse generator configured to generate and deliver a ventricular pacing pulse via electrodes coupled to the pulse generator; and

a control module coupled to the sensing module and the pulse generator and configured to set a ventricular pacing escape interval in response to the sensing module sensing the P-wave to control the pulse generator to deliver a ventricular pacing pulse when the ventricular pacing escape interval expires.

12. The device of claim 11 , wherein the sensing module is configured to adjust the filter to increase the difference by adjusting the filter to increase a difference between a peak P-wave amplitude and a peak T-wave amplitude in the filtered cardiac electrical signal.

13. The device of claim 12 , wherein the sensing module is configured to adjust the filter to increase the difference by adjusting the filter to increase the peak T-wave amplitude in the filtered cardiac signal.

14. The device of claim 13 , wherein the sensing module is configured to:

determine the P-wave sensing criteria by at least determining a first threshold less than the maximum P-wave amplitude and a second threshold greater than the first threshold but less than the maximum T-wave amplitude, and

sense the P-wave from the filtered cardiac signal by at least sensing a crossing of the first sensing threshold by the filtered cardiac signal, setting a time limit, and not sensing a crossing of the second sensing threshold during the time limit.

15. The device of claim 11 , wherein the sensing module is configured to adjust the filter by adjusting at least one of a center frequency and a bandpass width.

16. The device of claim 11 , wherein:

the control module is further configured to:

determine a plurality of T-P intervals between consecutive pairs of T-waves and P-waves in the filtered cardiac electrical signal; and

detect a decreasing trend in the plurality of T-P intervals;

the sensing module is further configured to

adjust at least one of the filter and a T-wave sensing window when the control module detects the decreasing trend; and

sense P-waves from the filtered cardiac signal when the P-wave sensing criteria are met outside the T-wave sensing window.

17. The device of claim 11 , wherein:

the control module is further configured to detect a decrease in a difference between a P-wave feature and T-wave feature in the filtered cardiac electrical signal; and

the sensing module is further configured to adjust the filter when the control module detects the decrease.

18. The device of claim 11 , wherein the sensing module is further configured to:

repeat the adjusting of the filter and the determining if the T-waves are distinct from the P-waves in the filtered cardiac electrical signal;

determine if the P-waves and the T-waves of the filtered cardiac electrical signal are distinct based on at least one of time, peak amplitude and morphology within a maximum number of filter adjustments; and

the control module is configured to disable setting the ventricular pacing escape interval when the sensing module determines that the P-waves and the T-waves of the filtered cardiac electrical signal are not distinct based on at least one of time, peak amplitude and morphology within the maximum number of filter adjustments.

19. The device of claim 18 , wherein:

the sensing module is further configured to:

periodically adjust at least one of the filter and a T-wave sensing window;

re-determine if the P-waves and the T-waves are distinct based on at least one of time, peak amplitude and morphology; and

re-determine the P-wave sensing criteria when the P-waves and the T-waves in the filtered cardiac electrical signal are distinct after a periodic adjustment of at least one of the filter and the T-wave sensing window; and

the control module is further configured to re-enable setting the ventricular pacing escape interval in response to P-waves sensed by the sensing module when the sensing module determines that the P-waves and the T-waves are distinct after a periodic adjustment of at least one of the filter and the T-wave sensing window.

20. The device of claim 11 , wherein:

the control module is further configured to determine if oversensing of the T-waves by the sensing module is suspected; and

the sensing module is further configured to:

lower a P-wave sensing control parameter to increase a sensitivity of the sensing module for sensing P-waves when the control module determines that T-wave oversensing is suspected;

determine if T-waves can be identified from the filtered cardiac electrical signal after lowering the P-wave sensing control parameter; and

withhold the adjusting of the filter in response to determining that T-waves cannot be identified from the filtered cardiac electrical signal after lowering the P-wave sensing control parameter.

21. The device of claim 11 , further comprising:

a housing enclosing the sensing module, the pulse generator and the control module;

at least one electrode carried by the housing and coupled to the sensing module for receiving the raw cardiac electrical signal and coupled to the pulse generator for delivering the ventricular pacing pulse.

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

produce a filtered cardiac electrical signal by filtering a raw cardiac electrical signal by an adjustable filter of a sensing module of the medical device configured to receive the raw cardiac electrical signal, the raw cardiac electrical signal comprising R-waves, T-waves and P-waves via electrodes coupled to the sensing module;

determine if the T-waves are distinct from the P-waves in the filtered cardiac electrical signal;

adjust the filter to increase a difference between a feature of the P-waves and a feature of the T-waves in the filtered cardiac signal when the T-waves are not distinct from the P-waves;

determine P-wave sensing criteria based on the difference;

sense a P-wave from the filtered cardiac electrical signal when the P-wave sensing criteria are met; and

set a ventricular pacing escape interval in response to sensing the P-wave.