Method and apparatus for atrial arrhythmia detection

1. A method for detecting atrial arrhythmias, comprising:

sensing a signal including ventricular cycle length information in a patient;

determining a ventricular cycle length occurring during a predetermined time period;

determining a difference between successive ventricular cycle lengths occurring during the predetermined time period;

storing the difference as a data point in a histogram;

determining a metric of variability of at least two data points of the histogram;

determining a number of ventricular cycle lengths occurring during the predetermined time period;

determining a first threshold in response to the determined number of ventricular cycle lengths; and

detecting an atrial arrhythmia in response to the metric crossing the first threshold.

2. A method according to claim 1 wherein storing each succeeding difference includes normalizing the difference by a selected difference.

3. A method according to claim 2 wherein the selected difference is a maximum one of each ventricular cycle length difference and a preceding ventricular cycle length difference.

4. A method according to claim 1 wherein determining the threshold includes computing a proportion of a maximum threshold, wherein the proportion corresponds to the number of ventricular cycle lengths occurring during the predetermined period of time.

5. A method according to claim 1 further comprising detecting no atrial arrhythmia in response to the metric crossing a second threshold after crossing the first threshold.

6. A method according to claim 5 wherein the second threshold being less than the first threshold.

7. A method according to claim 6 wherein the second threshold being a percentage of the first threshold.

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

sense a signal including ventricular cycle length information in a patient;

determine each ventricular cycle length occurring during a predetermined time period;

determine each difference between successive ventricular cycle lengths occurring during the predetermined time period;

store each succeeding difference as a data point in a histogram;

determine a metric of variability of the data points of the histogram;

determine a number of ventricular cycle lengths occurring during the predetermined period of time;

determine a first threshold in response to the determined number of ventricular cycle lengths; and

detect an atrial arrhythmia in response to the metric crossing the first threshold.

9. A computer-readable medium according to claim 8 wherein instructions for storing each succeeding difference include instructions for normalizing the difference by a selected difference.

10. A computer-readable medium according to claim 9 wherein the selected difference is a maximum one of each ventricular cycle length difference and a preceding ventricular cycle length difference.

11. A computer-readable medium according to claim 8 wherein instructions for determining the threshold include instructions for computing a proportion of a maximum threshold, wherein the proportion corresponds to the number of ventricular cycle lengths occurring during the predetermined period of time.

12. A computer-readable medium according to claim 8 further comprising instructions for causing the system to detect no atrial arrhythmia in response to the metric crossing a second threshold after crossing the first threshold.

13. A computer-readable medium according to claim 12 wherein the second threshold being less than the first threshold.

14. A computer-readable medium according to claim 13 wherein the second threshold being a percentage of the first threshold.

15. A medical device for detecting atrial arrhythmias, comprising:

a sensor for sensing a signal including ventricular cycle length information in a patient;

memory allocated for storing ventricular cycle length data in a histogram; and

a control module coupled to the sensor and the memory, the control module configured to determine from the signal each difference between successive ventricular cycle lengths occurring during a predetermined time period, store each succeeding difference as a data point in the histogram, determining a metric of variability of the data points of the histogram, and detect an atrial arrhythmia in response to the metric crossing a first threshold,

wherein the first threshold being determined by the control module in response to the number of ventricular cycle lengths occurring during the predetermined time period.

16. A medical device according to claim 15 wherein storing each succeeding difference includes normalizing the difference by a selected difference.

17. A medical device according to claim 16 wherein the selected difference is a maximum one of each ventricular cycle length difference and a preceding ventricular cycle length difference.

18. A medical device according to claim 15 wherein determining the threshold includes computing a proportion of a maximum threshold, wherein the proportion corresponds to the number of ventricular cycle lengths occurring during the predetermined period of time.

19. A medical device according to claim 15 wherein the control module being further configured to detect no atrial arrhythmia in response to the metric crossing a second threshold after crossing the first threshold.

20. A medical device according to claim 19 wherein the second threshold being less than the first threshold.

21. A medical device according to claim 19 wherein the second threshold being a percentage of the first threshold.