Sensing and atrial-synchronized ventricular pacing in an intracardiac pacemaker

1. A medical device system, comprising:

an intracardiac pacemaker, the pacemaker comprising:

a sensing module configured to receive a cardiac electrical signal and detect a crossing of a first sensing threshold by the cardiac electrical signal;

a pulse generator configured to generate and deliver a pacing pulse to the patient's heart via a pair of electrodes, and

a control module coupled to the sensing module and the pulse generator and configured to:

set a pacing escape interval timer to a first pacing escape interval in response to the cardiac electrical signal crossing the first sensing threshold,

set a time limit in response to the cardiac electrical signal crossing the first sensing threshold, the time limit shorter than the first pacing escape interval;

adjust the pacing escape interval timer in response to the cardiac electrical signal crossing a second sensing threshold higher than the first sensing threshold within the time limit; and

control the pulse generator to deliver the pacing pulse if the first pacing escape interval expires.

2. The system of claim 1 , wherein the control module is configured to establish the time limit based on a cardiac event signal width.

3. The system of claim 1 , wherein the control module is configured to adjust the pacing escape interval timer by cancelling the first pacing escape interval in response to the cardiac electrical signal crossing the second sensing threshold within the time limit.

4. The system of claim 1 , wherein the control module is configured to adjust the pacing escape interval timer by setting the pacing escape interval timer to a second pacing escape interval that is longer than the first pacing escape interval in response to the cardiac electrical signal crossing the second sensing threshold within the time limit.

5. The system of claim 1 , wherein the control module is further configured to adjust the pacing escape interval timer by:

adjusting the pacing escape interval timer from the first pacing escape interval to a second pacing escape interval that is longer than the first pacing escape interval in response to the cardiac electrical signal crossing the second sensing threshold within the time limit, and

cancelling the first pacing escape interval without setting a new pacing escape interval if the cardiac electrical signal crosses a third sensing threshold within the time limit, the third sensing threshold different than the first sensing threshold and the second sensing threshold.

6. The system of claim 1 , wherein the cardiac electrical signal comprises at least an R-wave and a P-wave, wherein the sensing module is configured to set the first sensing threshold less than a peak amplitude of the P-wave.

7. The system of claim 1 , wherein the control module is further configured to:

confirm during the first pacing escape interval that the crossing of the first sensing threshold by the cardiac electrical signal is a first cardiac event by comparing first cardiac event sensing criteria to at least one of a waveform of the cardiac electrical signal during an analysis window, a differential signal of the cardiac electrical signal and an integrated signal of the cardiac electrical signal;

confirm the far-field cardiac event when the first cardiac event sensing criteria are met, the first cardiac event sensing criteria discriminating the first cardiac event from a second cardiac event; and

cancel the first pacing escape interval before it expires in response to the crossing of the first sensing threshold not being confirmed as the first cardiac event.

8. The system of claim 1 , wherein:

the sensing module is configured to set a cardiac event sensing window in response to the cardiac electrical signal crossing the second sensing threshold; and

the control module is configured to ignore the first sensing threshold crossing by not setting the pacing escape interval timer to the first pacing escape interval if the cardiac electrical signal crosses the first sensing threshold within the cardiac event sensing window.

9. The system of claim 1 , further comprising an external device configured to receive data from the pacemaker via a wireless communication link,

wherein the sensing module is further configured to confirm sensing a cardiac event at a delay time interval after the cardiac electrical signal crossed the first sensing threshold if the cardiac electrical signal did not cross the second sensing threshold during the time limit, and

wherein the control module is configured to:

produce a sense event signal in response to the sensing module confirming sensing the cardiac event,

transmit the cardiac electrical signal to the external device, and

transmit the sense event signal,

the external device further comprising a user display configured to generate a display of a marker of the transmitted sense event signal and the transmitted cardiac electrical signal, the display of the transmitted cardiac electrical signal delayed in time by at least the delay time interval so that the marker is aligned with the crossing of the first sensing threshold of the displayed cardiac electrical signal.

10. The system of claim 9 , wherein

the control module is configured to transmit a marker channel pacing pulse signal aligned in time with the delivered pacing pulse; and

the external device user display is configured to generate the display comprising a marker of the delivered pacing pulse delayed in time from the marker channel pacing pulse signal by at least the delay time interval.

11. The system of claim 1 , wherein the control module is configured to set the first pacing escape interval up to a maximum interval limit.

12. A method, comprising:

receiving a cardiac electrical signal by a sensing module of an intracardiac pacemaker;

detecting a crossing of a first sensing threshold by the cardiac electrical signal;

setting a pacing escape interval timer to a first pacing escape interval in response to the cardiac electrical signal crossing the first sensing threshold,

setting a time limit in response to the cardiac electrical signal crossing the first sensing threshold, the time limit shorter than the first pacing escape interval;

adjusting the pacing escape interval timer in response to the cardiac electrical signal crossing a second sensing threshold higher than the first sensing threshold within the time limit; and

delivering a pacing pulse to the patient's heart if the first pacing escape interval expires.

13. The method of claim 12 , further comprising establishing the time limit based on a cardiac event signal width.

14. The method of claim 12 , further comprising adjusting the pacing escape interval timer by cancelling the first pacing escape interval in response to the cardiac electrical signal crossing the second sensing threshold within the time limit.

15. The method of claim 12 , further comprising adjusting the pacing escape interval timer by setting the pacing escape interval timer to a second pacing escape interval that is longer than the first pacing escape interval in response to the cardiac electrical signal crossing the second sensing threshold within the time limit.

16. The method of claim 12 , further comprising adjusting the pacing escape interval timer by:

adjusting the pacing escape interval timer from the first pacing escape interval to a second pacing escape interval that is longer than the first pacing escape interval in response to the cardiac electrical signal crossing the second sensing threshold within the time limit, and

cancelling the first pacing escape interval without setting a new pacing escape interval if the cardiac electrical signal crosses a third sensing threshold within the time limit, wherein the third sensing threshold is different than the first sensing threshold and the second sensing threshold.

17. The method of claim 12 , further comprising setting the first sensing threshold less than a peak amplitude of a P-wave, wherein the cardiac electrical signal comprises at least an R-wave and the P-wave.

18. The method of claim 12 , further comprising:

confirming during the first pacing escape interval that the crossing of the first sensing threshold by the cardiac electrical signal is a first cardiac event by comparing first cardiac event sensing criteria to at least one of a waveform of the cardiac electrical signal during an analysis window, a differential signal of the cardiac electrical signal and an integrated signal of the cardiac electrical signal;

confirm the far-field cardiac event when the first cardiac event sensing criteria are met, the first cardiac event sensing criteria discriminating the first cardiac event from a second cardiac event; and

cancelling the first pacing escape interval before it expires in response to the crossing of the first sensing threshold not being confirmed as the first cardiac event.

19. The method of claim 12 , further comprising:

setting a cardiac event sensing window in response to the cardiac electrical signal crossing the second sensing threshold; and

ignoring the first sensing threshold crossing by not setting the pacing escape interval timer to the first pacing escape interval if the cardiac electrical signal crosses the first sensing threshold within the cardiac event sensing window.

20. The method of claim 12 , further comprising:

confirming a sensed cardiac event at a delay time interval after the cardiac electrical signal crossed the first sensing threshold if the cardiac electrical signal did not cross the second sensing threshold during the time limit;

producing a sense event signal in response to confirming the sensed cardiac event;

transmitting the cardiac electrical signal and the sense event signal from the pacemaker to an external device via a wireless communication link; and

generating by a user display of the external device a display of a marker of the transmitted sense event signal and the transmitted cardiac electrical signal, the display of the transmitted cardiac electrical signal delayed in time by at least the delay time interval so that the marker is aligned with the crossing of the first sensing threshold of the displayed cardiac electrical signal.

21. The method of claim 20 , further comprising:

transmitting a marker channel pacing pulse signal upon delivering the pacing pulse; and

generating in the display a marker of the delivered pacing pulse delayed in time by at least the delay time interval from the marker channel pacing pulse signal.

22. The method of claim 12 , further comprising setting the pacing escape interval timer up to a maximum interval limit.

23. A non-transitory computer-readable medium storing a set of instructions which when executed by an intracardiac pacemaker, cause the pacemaker to:

receive a cardiac electrical signal via electrodes coupled to the pacemaker;

detect a crossing of a first sensing threshold by the cardiac electrical signal;

set a pacing escape interval timer to a first pacing escape interval in response to the cardiac electrical signal crossing the first sensing threshold,

set a time limit in response to the cardiac electrical signal crossing the first sensing threshold, the time limit shorter than the first pacing escape interval;

adjust the pacing escape interval timer in response to the cardiac electrical signal crossing a second sensing threshold higher than the first sensing threshold within the time limit, wherein adjusting the pacing escape interval comprises one of cancelling the first pacing escape interval and extending the first pacing escape interval; and

deliver a pacing pulse to the patient's heart if the first pacing escape interval expires.