Method and apparatus for atrial fibrillation detection based on ventricular cycle lengths

1. A method for detecting atrial arrhythmias, comprising:

acquiring a cardiac signal, the cardiac signal including R-waves;

computing a plurality of RR interval differences between pairs of consecutive RR intervals of the cardiac signal occurring during a first time interval, the first time interval having a start time and an end time;

detecting an atrial arrhythmia subsequent to the end time of the first time interval in response to the computed differences; and

triggering storage of the cardiac signal for a second time interval in response to the atrial arrhythmia detection, the second time interval having a start time prior to the atrial arrhythmia detection.

2. The method of claim 1 wherein the second time interval corresponds to an onset time of the detected atrial arrhythmia.

3. The method of claim 1 wherein the second time interval includes a start time occurring prior to the start time of the first time interval.

4. The method of claim 1 wherein the second time interval includes an end time occurring concomitant with the start time of the first time interval.

5. The method of claim 1 wherein detecting an atrial arrhythmia subsequent to the end of the first time interval comprises:

computing a plurality of RR interval differences between pairs of consecutive RR intervals for a previous time interval having an end time preceding the end time of the first time interval;

determining atrial arrhythmia evidence during the previous time interval in response to the computed differences;

determining atrial arrhythmia evidence during the first time interval in response to the computed differences; and

detecting the atrial arrhythmia at the end of the first time interval in response to the atrial arrhythmia evidence determined during the previous time interval and the atrial arrhythmia evidence determined during the first time interval.

6. The method of claim 5 wherein the atrial arrhythmia is not detected at the end of the preceding time interval and the second time interval comprises the first time interval and the preceding time interval.

7. The method of claim 1 further comprising setting RR interval acceptance criteria, wherein computing the plurality of RR interval differences comprises rejecting RR intervals not meeting the RR interval acceptance criteria.

8. The method of claim 1 further comprising:

configuring a plurality of RR interval difference bins corresponding to R-R interval difference ranges;

assigning a computed RR interval difference to an RR interval difference bin corresponding to the computed RR interval difference; and

determining an occupied bin count at the first time interval end time, wherein detecting the atrial arrhythmia comprises comparing the occupied bin count to an onset threshold.

9. The method of claim 8 wherein detecting the atrial arrhythmia further comprises:

setting a detection threshold number;

determining an occupied bin count at the end of a plurality of time intervals preceding the first time interval; and

determining a number of the occupied bin counts exceeding the onset threshold, wherein detecting the atrial arrhythmia subsequent to the end time of the first time interval occurs in response to the determined number of the occupied bin counts exceeding the onset threshold exceeding the detection threshold number.

10. The method of claim 8 further comprising selecting one of a diagnostic mode and a monitoring mode wherein the onset threshold being set to a first value during the diagnostic mode and to a second value during the monitoring mode, wherein the second value being greater than the first value.

11. The method of claim 8 further comprising selecting one of a diagnostic mode and a monitoring mode wherein the triggered storage of the cardiac signal is suspended during the monitoring mode.

12. The method of claim 1 further comprising:

computing a plurality of differences between pairs of consecutive RR intervals occurring during a plurality of time intervals subsequent to the first time interval; and

detecting an atrial arrhythmia termination in response to the computed differences between pairs of consecutive RR intervals occurring during the plurality of time intervals subsequent to the first time interval

the second time interval having an end time subsequent to the end time of the first time interval.

13. The method of claim 12 wherein detecting the atrial arrhythmia termination comprises:

configuring a plurality of RR interval difference bins corresponding to RR interval difference ranges;

assigning a computed RR interval difference to an RR interval difference bin corresponding to the computed RR interval difference;

setting a termination threshold and a termination detection threshold number;

determining an occupied bin count at the end of each of the plurality of time intervals subsequent to the first time interval;

determining a number of the occupied bin counts being less than the termination threshold; and

detecting a termination of the atrial arrhythmia in response to the number of occupied bin counts being less than the termination threshold exceeding the termination detection threshold number.

14. The method of claim 12 further comprising:

defining a connect time;

detecting a next atrial arrhythmia;

computing a gap time between the detected termination of the atrial arrhythmia and the detected next atrial arrhythmia, and

detecting a continuous atrial arrhythmia episode in response to the gap time being less than the connect time.

15. A computer-readable medium for storing a set of instructions which when implemented in a system cause the system to:

acquire a cardiac signal, the cardiac signal including R-waves;

compute a plurality of RR interval differences between pairs of consecutive RR intervals occurring during a first time interval, the first time interval having a start time and an end time;

detect an atrial arrhythmia subsequent to the end time of the first time interval in response to the computed differences; and

trigger storage of the cardiac signal for a second time interval in response to the atrial arrhythmia detection, wherein the second time interval having a start time prior to the atrial arrhythmia detection and an end time subsequent to the end time of the first time interval.

16. A medical device system, comprising:

an electrode for acquiring a cardiac signal, the cardiac signal including R-waves;

a memory to store the cardiac signal; and

a control module, coupled to the electrode, to compute a plurality of RR interval differences between pairs of consecutive RR intervals occurring during a first time interval, the first time interval having a start time and an end time, detect an atrial arrhythmia subsequent to the end time of the first time interval in response to the computed differences, and trigger storage of the cardiac signal in the memory for a second time interval in response to the atrial arrhythmia detection, the second time interval having a start time prior to the atrial arrhythmia detection.

17. The system of claim 16 wherein the second time interval includes an onset time of the detected atrial arrhythmia.

18. The system of claim 16 wherein the second time interval is greater than the first interval of time.

19. The system of claim 16 wherein the second time interval includes a start time occurring prior to the start time of the first time interval.

20. The system of claim 16 wherein the second time interval includes an end time, the end time occurring concomitant with the start time of the first time interval.

21. The system of claim 16 wherein the control module computes a plurality of RR interval differences between pairs of consecutive RR intervals for a previous time interval having an end time preceding the first time interval end time; determines atrial arrhythmia evidence during the previous time interval in response to the computed differences, determines atrial arrhythmia evidence during the first time interval in response to the computed differences, and detects the atrial arrhythmia at the end of the first time interval in response to the atrial arrhythmia evidence determined during the previous time interval and the atrial arrhythmia evidence determined during the first time interval.

22. The system of claim 16 wherein the control module sets RR interval acceptance criteria and rejects RR intervals not meeting the RR interval acceptance criteria.

23. The system of claim 16 wherein the control module generates a plurality of RR interval difference bins corresponding to R-R interval difference ranges, assigns a computed RR interval difference to an RR interval difference bin corresponding to the computed RR interval differences, and determines an occupied bin count at the first time interval end time, and compares the occupied bin count to an onset threshold to detect the atrial arrhythmias.

24. The system of claim 23 wherein the control module sets a detection threshold number, determines an occupied bin count at the end of a plurality of time intervals preceding the first time interval, determines a number of the occupied bin counts exceeding the onset threshold, and detects the atrial arrhythmia subsequent to the end time of the first time interval in response to the number of the occupied bin counts exceeding the onset threshold exceeding the detection threshold number.

25. The system of claim 23 wherein the control module selects one of a diagnostic mode and a monitioring mode, and wherein the onset threshold is set to a first value during the diagnostic mode and to a second value, greater than the first value, during the monitoring mode.

26. The system of claim 16 wherein the control module determines a plurality of differences between pairs of consecutive RR intervals occurring during a plurality of time intervals subsequent to the first time interval, and

detects an atrial arrhythmia termination in response to the determined differences between pairs of consecutive RR intervals occurring during the plurality of time intervals subsequent to the first time interval, the second time interval having an end time subsequent to the end time of the first time interval.

27. The system of claim 26 wherein the control module determines RR interval difference bins corresponding to RR interval difference ranges, assigns an RR interval difference to an RR interval difference bin corresponding to the computed RR interval difference, sets a termination threshold and a termination detection threshold number, determines an occupied bin count at the end of each of the plurality of time intervals subsequent to the first time interval, determines a number of the occupied bin counts being less than the termination threshold, and detects a termination of the atrial arrhythmia in response to the number of occupied bin counts being less than the termination threshold exceeding the termination detection threshold number.

28. The system of claim 26 wherein the control module determines a connect time, computes a gap time between the detected termination of the atrial arrhythmia and the detected next atrial arrhythmia, and detects a continuous atrial arrhythmia episode in response to the gap time being less than the connect time.