Periodic beat detection to detect artifacts in a cardiac electrogram

1. A method comprising:

determining, using a processor, a derivative of a cardiac electrogram of a patient;

detecting, using the processor, beats within the derivative;

determining, using the processor, whether the beats are periodic; and

determining, using the processor, whether artifacts are present in the cardiac electrogram based on the determination of whether the beats are periodic, wherein determining whether artifacts are present comprises determining whether a tachyarrhythmia is present in the patient based on the determination of whether the beats are periodic, and further comprising classifying the cardiac electrogram as treatable using a tachyarrhythmia detection technique, wherein determining whether a tachyarrhythmia is present comprises reclassifying the treatable cardiac electrogram as nontreatable when the beats are periodic.

2. The method of claim 1 , wherein determining a derivative comprises determining a second order derivative.

3. A method comprising:

determining, using a processor, a derivative of a cardiac electrogram of a patient;

detecting, using the processor, beats within the derivative;

determining, using the processor, whether the beats are periodic; and

determining, using the processor, whether artifacts are present in the cardiac electrogram based on the determination of whether the beats are periodic, wherein detecting beats comprises:

comparing the derivative to a first threshold to detect small beats; and

comparing the derivative to a second threshold to detect large beats,

wherein the first threshold is smaller than the second threshold.

4. The method of claim 3 , further comprising:

rectifying the derivative;

identifying a maximum of the derivative; and

determining the first threshold and the second threshold based on the maximum,

wherein comparing the derivative to the first and second thresholds comprises comparing the rectified derivative to the first and second thresholds.

5. The method of claim 3 , wherein determining whether the beats are periodic comprises:

determining whether the large beats are periodic;

determining whether the small beats are periodic if the large beats are not periodic; and

determining that the beats are periodic if either the large or small beats are periodic.

6. The method of claim 1 , wherein determining whether the beats are periodic comprises determining beat to beat intervals between successive beats.

7. The method of claim 6 , wherein determining whether the beats are periodic comprises:

comparing the beat to beat intervals to a minimum beat to beat interval threshold; and

determining that beats are not periodic if any of the beat to beat intervals is less than the threshold.

8. A method comprising:

determining, using a processor, a derivative of a cardiac electrogram of a patient;

detecting, using the processor, beats within the derivative;

determining, using the processor, whether the beats are periodic; and

determining, using the processor, whether artifacts are present in the cardiac electrogram based on the determination of whether the beats are periodic, wherein determining whether the beats are periodic comprises determining beat to beat intervals between successive beats, and wherein determining whether the beats are periodic comprises:

determining differences between successive beat to beat intervals;

determining means of successive beat to beat intervals;

comparing the differences to the means; and

determining whether the beats are periodic based on the comparison.

9. A method comprising:

determining, using a processor, a derivative of a cardiac electrogram of a patient;

detecting, using the processor, beats within the derivative;

determining, using the processor, whether the beats are periodic; and

determining, using the processor, whether artifacts are present in the cardiac electrogram based on the determination of whether the beats are periodic, wherein determining whether the beats are periodic comprises determining beat to beat intervals between successive beats, and wherein the cardiac electrogram comprises a sample of a predetermined length of time, the method further comprising:

determining a time before a first one of the beats;

determining a time after a last one of the beats;

determining a mean of the beat to beat intervals;

comparing the time before a first one of the beats and the time after a last one of the beats to the mean; and

determining whether the beats are periodic based on the comparisons.

10. A method comprising:

determining, using a processor, a derivative of a cardiac electrogram of a patient;

detecting, using the processor, beats within the derivative;

determining, using the processor, whether the beats are periodic; and

determining, using the processor, whether artifacts are present in the cardiac electrogram based on the determination of whether the beats are periodic, wherein determining whether the beats are periodic comprises:

determining a number of the beats;

comparing the number to a threshold; and

determining whether the beats are periodic based on the comparison.

11. The method of claim 1 , further comprising determining whether to analyze a cardiac rhythm using the electrogram based on the determination of whether artifacts are present.

12. The method of claim 1 , further comprising determining whether to store the electrogram within a memory based on the determination of whether artifacts are present.

13. A system comprising:

a plurality of electrodes;

a medical device coupled to the electrodes that senses a cardiac electrogram via the electrodes; and

a processor that:

determines a derivative of a cardiac electrogram of a patient,

detects beats within the derivative,

determines whether the beats are periodic, and

determines whether artifacts are present in the cardiac electrogram based on the determination of whether the beats are periodic, wherein the processor compares the derivative to a first threshold to detect small beats, and compares the derivative to a second threshold to detect large beats, and

wherein the first threshold is smaller than the second threshold.

14. The system of claim 13 , wherein the processor determines whether a tachyarrhythmia is present in the patient based on the determination of whether the beats are periodic.

15. The system of claim 14 , wherein the processor classifies the cardiac electrogram as treatable using a tachyarrhythmia detection technique, and wherein the processor reclassifies the treatable cardiac electrogram as nontreatable when the beats are periodic.

16. The system of claim 13 , the derivative comprises a second order derivative.

17. The system of claim 13 , wherein the processor:

rectifies the derivative,

identifies a maximum of the derivative,

determines the first threshold and the second threshold based on the maximum, and

compares the rectified derivative to the first and second thresholds.

18. The system of claim 13 , wherein the processor:

determines whether the large beats are periodic,

determines whether the small beats are periodic if the large beats are not periodic, and

determines that the beats are periodic if either the large or small beats are periodic.

19. The system of claim 13 , wherein the processor determines beat to beat intervals between successive beats and determines whether the beats are periodic based on the beat to beat intervals.

20. The system of claim 19 , wherein the processor compares the beat to beat intervals to a minimum beat to beat interval threshold, and determines that beats are not periodic if any of the beat to beat intervals is less than the threshold.

21. A system comprising:

a plurality of electrodes;

a medical device coupled to the electrodes that senses a cardiac electrogram via the electrodes; and

a processor that:

determines a derivative of a cardiac electrogram of a patient,

detects beats within the derivative,

determines whether the beats are periodic, and

determines whether artifacts are present in the cardiac electrogram based on the determination of whether the beats are periodic, wherein the processor determines beat to beat intervals between successive beats and determines whether the beats are periodic based on the beat to beat intervals, and wherein the processor:

determines differences between successive beat to beat intervals,

determines means of successive beat to beat intervals,

compares the differences to the means, and

determines whether the beats are periodic based on the comparison.

22. A system comprising:

a plurality of electrodes;

a medical device coupled to the electrodes that senses a cardiac electrogram via the electrodes; and

a processor that:

determines a derivative of a cardiac electrogram of a patient,

detects beats within the derivative,

determines whether the beats are periodic, and

determines whether artifacts are present in the cardiac electrogram based on the determination of whether the beats are periodic, wherein the processor determines beat to beat intervals between successive beats and determines whether the beats are periodic based on the beat to beat intervals, and wherein the cardiac electrogram comprises a sample of a predetermined length of time, and the processor:

determines a time before a first one of the beats,

determines a time after a last one of the beats,

determines a mean of the beat to beat intervals,

compares the time before a first one of the beats and the time after a last one of the beats to the mean, and

determines whether the beats are periodic based on the comparisons.

23. A system comprising:

a plurality of electrodes;

a medical device coupled to the electrodes that senses a cardiac electrogram via the electrodes; and

a processor that:

determines a derivative of a cardiac electrogram of a patient,

detects beats within the derivative,

determines whether the beats are periodic, and

determines whether artifacts are present in the cardiac electrogram based on the determination of whether the beats are periodic, wherein the processor:

determines a number of the beats,

compares the number to a threshold, and

determines whether the beats are periodic based on the comparison.

24. The system of claim 13 , wherein the processor comprises a processor of the medical device.

25. A system comprising:

a plurality of electrodes;

a medical device coupled to the electrodes that senses a cardiac electrogram via the electrodes; and

a processor that:

determines a derivative of a cardiac electrogram of a patient,

detects beats within the derivative,

determines whether the beats are periodic, and

determines whether artifacts are present in the cardiac electrogram based on the determination of whether the beats are periodic, wherein the electrodes comprise implantable electrodes and the medical device comprises an implantable medical device.

26. The system of claim 25 , wherein the implantable medical device comprises a subcutaneously implantable medical device comprising a housing, and the electrodes comprise electrodes on or integral with the housing.

27. The system of claim 13 , wherein the processor determines whether to analyze a cardiac rhythm using the electrogram based on the determination of whether artifacts are present.

28. The system of claim 13 , further comprising a memory, wherein the processor determines whether to store the electrogram within the memory based on the determination of whether artifacts are present.

29. A system comprising:

means for determining a derivative of a cardiac electrogram of a patient;

means for detecting beats within the derivative;

means for determining whether the beats are periodic; and

means for determining whether artifacts are present in the cardiac electrogram based on the determination of whether the beats are periodic, wherein means for determining whether artifacts are present comprises means for determining whether a tachyarrhythmia is present in the patient based on the determination of whether the beats are periodic, and further comprising means for classifying the cardiac electrogram as treatable using a tachyarrhythmia detection technique, wherein means for determining whether a tachyarrhythmia is present comprises means for reclassifying the treatable cardiac electrogram as nontreatable when the beats are periodic.

30. A computer-readable storage medium comprising instructions that cause a programmable processor to:

determine a derivative of a cardiac electrogram of a patient;

detect beats within the derivative;

determine whether the beats are periodic; and

determine whether artifacts are present in the cardiac electrogram based on the determination of whether the beats are periodic, wherein determining whether artifacts are present comprises determining whether a tachyarrhythmia is present in the patient based on the determination of whether the beats are periodic, and further comprising classifying the cardiac electrogram as treatable using a tachyarrhythmia detection technique, wherein determining whether a tachyarrhythmia is present comprises reclassifying the treatable cardiac electrogram as nontreatable when the beats are periodic.