Atrial arrhythmia episode detection in a cardiac medical device

1. A method of detecting an atrial tachyarrhythmia in a medical device, comprising:

sensing a first cardiac electrical signal from a first sensing electrode vector;

identifying R-waves in the first cardiac electrical signal attendant ventricular depolarizations;

determining RR intervals between successive R-waves in the first cardiac electrical signal;

determining classification factors from the R-waves identified over a first predetermined time period by determining at least a first classification factor correlated to variability of the RR intervals and a second classification factor indicating a presence of a ventricular tachyarrhythmia;

classifying the first predetermined time period as one of unclassified, atrial tachyarrhythmia and non-atrial tachyarrhythmia by comparing the determined classification factors to classification criteria, wherein the first predetermined time period is classified as unclassified in response to the second classification factor indicating the presence of a ventricular tachyarrhythmia;

detecting an atrial tachyarrhythmia episode in response to the first time period being classified as unclassified and at least one preceding time period and at least one subsequent time period being classified as atrial tachyarrhythmia; and

in response to detecting the atrial tachyarrhythmia episode, storing episode data determined from at least the first cardiac electrical signal in a memory of the medical device for transmission to an external device.

2. The method of claim 1 , further comprising:

determining a third classification factor by detecting ventricular pacing pulses during the first predetermined time period;

determining a count of the detected ventricular pacing pulses during the first predetermined time period; and

classifying the first predetermined time period as unclassified in response to the count exceeding a threshold.

3. The method of claim 1 , wherein determining the second classification factor comprises detecting a ventricular tachyarrhythmia based on an analysis of the identified R-waves.

4. The method of claim 1 , wherein detecting the atrial tachyarrhythmia comprises:

classifying a plurality of successive predetermined time periods comprising the first time period, the at least one preceding time period and the at least one subsequent time period;

increasing an atrial tachyarrhythmia counter in response to each of the plurality of successive predetermined time periods that is classified as atrial tachyarrhythmia; and

detecting the atrial tachyarrhythmia in response to the atrial tachyarrhythmia counter reaching an atrial tachyarrhythmia detection threshold.

5. The method of claim 4 , further comprising:

increasing an unclassified counter in response to each of the plurality of successive predetermined time periods that is classified as unclassified;

comparing the unclassified counter to an unclassified threshold; and

resetting both of the atrial tachyarrhythmia counter and the unclassified counter to zero in response to the unclassified counter reaching the unclassified threshold prior to the atrial tachyarrhythmia counter reaching the atrial tachyarrhythmia detection threshold.

6. The method of claim 1 , further comprising:

classifying subsequent time periods after detecting the atrial tachyarrhythmia;

increasing an unclassified counter in response to each one of the subsequent time periods that is classified as unclassified;

resetting the unclassified counter to zero in response to classifying one of the subsequent time periods as atrial fibrillation;

comparing the unclassified counter to an unclassified threshold upon classifying each of the subsequent time periods; and

detecting termination of the atrial tachyarrhythmia episode in response to the unclassified counter reaching the unclassified threshold.

7. The method of claim 6 , further comprising determining an episode duration of the detected atrial tachyarrhythmia episode in response to detecting termination, wherein determining the episode duration comprises excluding from the determined episode duration the subsequent time periods classified as unclassified after the last one of the subsequent time periods classified as atrial tachyarrhythmia.

8. The method of claim 1 , further comprising:

detecting termination of the atrial tachyarrhythmia episode;

wherein storing the episode data comprises determining a time duration of the detected atrial tachyarrhythmia episode, wherein the time duration includes the first time period.

9. The method of claim 1 , further comprising:

sensing a second cardiac electrical signal from a second sensing electrode vector different than the first sensing electrode vector;

responsive to detecting the atrial tachyarrhythmia, storing a first episode of the first cardiac electrical signal in the memory at a first gain;

storing a second episode of the second cardiac electrical signal in the memory at a second gain that is higher than the first gain.

10. The method of claim 8 , further comprising:

receiving an interrogation command from the external device;

transmitting the first cardiac electrical signal having the first gain and the second cardiac signal having the second gain to the external device;

generating by the external device a display of the first cardiac electrical signal at the first gain and the second cardiac electrical signal at the second gain.

11. A medical device system for detecting an atrial tachyarrhythmia, comprising:

sensing circuitry configured to sense a first cardiac electrical signal from a first sensing electrode vector;

a processor; and

memory accessible by the processor,

the processor configured to:

identify R-waves in the first cardiac electrical signal attendant ventricular depolarizations;

determine RR intervals between successive R-waves in the first cardiac electrical signal;

determine classification factors from the R-waves identified over a first predetermined time period by determining at least a first classification factor correlated to variability of the RR intervals and a second classification factor indicating a presence of a ventricular tachyarrhythmia;

classify the first predetermined time period as one of unclassified, atrial tachyarrhythmia and non-atrial tachyarrhythmia by comparing the determined classification factors to classification criteria, wherein the first predetermined time period is classified as unclassified in response to the second classification factor indicating the presence of a ventricular tachyarrhythmia;

detect an atrial tachyarrhythmia episode in response to the first time period being classified as unclassified and at least one preceding time period and at least one subsequent time period being classified as atrial tachyarrhythmia; and

in response to detecting the atrial tachyarrhythmia episode, storing episode data determined from at least the first cardiac electrical signal in the memory for transmission to an external device.

12. The medical device system of claim 11 , wherein the processor is configured to:

determine a third classification factor by detecting ventricular pacing pulses during the first predetermined time period;

determine a count of the detected ventricular pacing pulses during the first predetermined time period; and

classify the first predetermined time period as unclassified in response to the count exceeding a threshold.

13. The medical device system of claim 11 , wherein the processor is configured to determine the second classification factor by detecting a ventricular tachyarrhythmia based on an analysis of the identified R-waves.

14. The medical device system of claim 11 , wherein the processor is configured to detect the atrial tachyarrhythmia by:

classifying a plurality of successive predetermined time periods comprising the first time period, the at least one preceding time period and the at least one subsequent time period;

increasing an atrial tachyarrhythmia counter in response to each of the plurality of successive predetermined time periods that is classified as atrial tachyarrhythmia; and

detecting the atrial tachyarrhythmia in response to the atrial tachyarrhythmia counter reaching an atrial tachyarrhythmia detection threshold.

15. The medical device system of claim 14 , wherein the processor is further configured to:

increase an unclassified counter in response to each of the plurality of successive predetermined time periods that is classified as unclassified;

compare the unclassified counter to an unclassified threshold; and

reset both of the atrial tachyarrhythmia counter and the unclassified counter to zero in response to the unclassified counter reaching the unclassified threshold prior to the atrial tachyarrhythmia counter reaching the atrial tachyarrhythmia detection threshold.

16. The medical device system of claim 1 , wherein the processor is further configured to:

classify subsequent time periods after detecting the atrial tachyarrhythmia;

increase an unclassified counter in response to each one of the subsequent time periods that is classified as unclassified;

reset the unclassified counter to zero in response to classifying one of the subsequent time periods as atrial fibrillation;

compare the unclassified counter to an unclassified threshold upon classifying each of the subsequent time periods; and

detect termination of the atrial tachyarrhythmia episode in response to the unclassified counter reaching the unclassified threshold.

17. The medical device system of claim 16 , wherein the processor is further configured to determine an episode duration of the detected atrial tachyarrhythmia episode in response to detecting termination, wherein determining the episode duration comprises excluding from the episode duration the subsequent time periods classified as unclassified after the last one of the subsequent time periods classified as atrial tachyarrhythmia.

18. The medical device system of claim 11 , wherein the processor is further configured to:

detect termination of the atrial tachyarrhythmia episode;

wherein the processor is configured to store the episode data by determining a time duration of the detected atrial tachyarrhythmia episode, wherein the time duration includes the first time period.

19. The medical device system of claim 11 , wherein:

the sensing circuitry is further configured to sense a second cardiac electrical signal from a second sensing electrode vector different than the first sensing electrode vector;

responsive to detecting the atrial tachyarrhythmia, the processor is further configured to:

store a first episode of the first cardiac electrical signal in the memory at a first gain; and

store a second episode of the second cardiac electrical signal in the memory at a second gain that is higher than the first gain.

20. The medical device system of claim 19 , further comprising:

an external device comprising an external telemetry circuit and a display;

an implantable telemetry circuit coupled to the processor and configured to:

receive an interrogation command from the external device; and

transmit the first cardiac electrical signal having the first gain and the second cardiac signal having the second gain to the external device;

the external device configured to display the first cardiac electrical signal at the first gain and the second cardiac electrical signal at the second gain.

21. The medical device system of claim 11 , further comprising an extracardiovascular lead coupled to the sensing circuitry and carrying the electrodes of the first sensing vector.

22. The medical device system of claim 11 , further comprising:

an electrical stimulation lead carrying at least one of the electrodes of the first sensing vector; and

an implantable cardioverter-defibrillator (ICD) coupled to the electrical stimulation lead, the ICD comprising a housing the encloses the sensing circuitry, processor, and memory.

23. The medical device system of claim 22 , wherein the ICD further comprises therapy circuitry configured to generate an electrical stimulation therapy in response to detecting the ventricular tachyarrhythmia being one of ventricular tachycardia (VT) or ventricular fibrillation (VF).

24. A non-transitory, computer-readable storage medium storing instructions for causing a processor, upon executing the instructions, to:

sense a first cardiac electrical signal from a first sensing electrode vector;

identify R-waves in the first cardiac electrical signal attendant ventricular depolarizations;

determine RR intervals between successive R-waves in the first cardiac electrical signal;

determine classification factors from the R-waves identified over a first predetermined time period by determining at least a first classification factor correlated to variability of the RR intervals and a second classification factor indicating a presence of a ventricular tachyarrhythmia;

classify the first predetermined time period as one of unclassified, atrial tachyarrhythmia and non-atrial tachyarrhythmia by comparing the determined classification factors to classification criteria, wherein the first predetermined time period is classified as unclassified in response to the second classification factor indicating the presence of a ventricular tachyarrhythmia;

detect an atrial tachyarrhythmia episode in response to the first time period being classified as unclassified and at least one preceding time period and at least one subsequent time period being classified as atrial tachyarrhythmia; and

in response to detecting the atrial tachyarrhythmia episode, store episode data determined from at least the first cardiac electrical signal in a memory of the medical device for transmission to an external device.