Reducing false alarms in cardiac monitoring devices

1. An apparatus of an ambulatory medical device, the apparatus comprising:

an arrhythmia detection circuit including signal processing circuitry configured to:

receive a cardiac signal representative of cardiac activity;

apply an atrial arrhythmia detection criteria to the received cardiac signal;

apply, in response to the applied atrial arrhythmia detection criteria producing a positive indication of a type of arrhythmia, an atrial arrhythmia confirmation criteria to the received cardiac signal, wherein the atrial arrhythmia confirmation criteria is different from the atrial arrhythmia detection criteria and is more specific to detection of the type of arrhythmia detected than the atrial arrhythmia detection criteria;

detect a sensing event that causes false indications of detection of arrhythmia by one or both of the atrial arrhythmia detection criteria and the atrial arrhythmia confirmation criteria; and

adjust the sensitivity or specificity of the atrial arrhythmia detection criteria and the atrial arrhythmia confirmation criteria in response to detecting one or more of a number of pauses in cardiac depolarization in the received cardiac signal that exceeds a specified threshold number of pauses, a heart rate that is non-physiologically slow, and a number of changes in amplitude of the received cardiac signal that exceed a specified amplitude change threshold within a specified period of time.

2. The apparatus of claim 1 , wherein the arrhythmia detection circuit is configured to adjust the sensitivity or specificity of the atrial arrhythmia detection criteria and the atrial arrhythmia confirmation criteria in response to detection of one or both of a heart rate that is non-physiologically fast, and a specified number of noise hits in sensing of the cardiac signal that occur within a specified time duration.

3. The apparatus of claim 1 , wherein the arrhythmia detection circuit is configured to adjust the sensitivity or specificity of the atrial arrhythmia detection criteria and the atrial arrhythmia confirmation criteria in response to detection of a cardiac rhythm for which one or both of the atrial arrhythmia detection criteria and the atrial arrhythmia confirmation criteria are susceptible to false alarms.

4. The apparatus of claim 1 , wherein the arrhythmia detection circuit is configured to detect atrial tachyarrhythmia using the atrial arrhythmia detection criteria and the atrial arrhythmia confirmation criteria; adjust a detection threshold of the arrhythmia detection criteria and the atrial arrhythmia confirmation criteria to change sensitivity or specificity to atrial tachyarrhythmia detection in response to detection of the sensing event, and restore the detection threshold to an original sensitivity or specificity when the detected sensing event ceases to be detected for a specified period of time.

5. The apparatus of claim 4 , wherein the arrhythmia detection circuit is configured to detect atrial flutter (AF) using the atrial arrhythmia detection criteria and the atrial arrhythmia confirmation criteria, wherein the arrhythmia detection criteria and the atrial arrhythmia confirmation criteria include one or more of: detection that sensed ventricular depolarization intervals (V-V intervals) satisfy a specified V-V interval scatter AF detection threshold, detection that sensed V-V intervals satisfy a specified V-V interval double decrement AF detection threshold, and detection that sensed V-V intervals satisfy a specified Wenckebach AF detection threshold.

6. The apparatus of claim 1 , wherein the arrhythmia detection circuit is configured to: detect ventricular tachyarrhythmia using the atrial arrhythmia detection criteria and the atrial arrhythmia confirmation criteria;

adjust a detection threshold of one or both of the and atrial arrhythmia detection criteria to change sensitivity or specificity to ventricular tachyarrhythmia detection in response to detection of the sensing event; and restore the detection threshold to an original sensitivity or specificity when the detected sensing event ceases to be detected for a specified period of time.

7. The apparatus of claim 6 , including:

a therapy circuit configured to provide defibrillation shock therapy to the subject; and

a control circuit configured to initiate delivery of the defibrillation shock therapy in response to the detection of the ventricular tachyarrhythmia.

8. The apparatus of claim 1 , wherein the arrhythmia detection circuit is configured to: detect bradycardia using the atrial arrhythmia detection criteria and the atrial arrhythmia confirmation criteria; adjust a detection threshold of one or both of the and atrial arrhythmia detection criteria to change sensitivity or specificity to bradycardia detection in response to detection of the sensing event; and restore the detection thresholds to an original specificity when the detected sensing event ceases to be detected for a specified period of time.

9. The apparatus of claim 8 , including:

a therapy circuit configured to provide electrical pacing therapy to the subject; and

a control circuit configured to initiate delivery of the electrical pacing therapy according to a first pacing therapy mode; and change the pacing therapy mode according to the detected cardiac arrhythmia.

10. The apparatus of claim 1 , wherein the arrhythmia detection circuit is configured to continue to adjust the sensitivity or specificity of the atrial arrhythmia detection criteria and the atrial arrhythmia confirmation criteria when continuing to detect the sensing event, and restore original sensitivity or specificity to the atrial arrhythmia detection criteria and the atrial arrhythmia confirmation criteria when the detected sensing event ceases to be detected for a specified period of time.

11. A method of controlling operation of an arrhythmia detection circuit, the method comprising:

receiving a cardiac signal representative of electrical cardiac activity at the arrhythmia detection circuit;

applying an arrhythmia detection criteria to the received cardiac signal using the arrhythmia detection circuit;

applying, in response to the applied atrial arrhythmia detection criteria producing a positive indication of a type of arrhythmia, an atrial arrhythmia confirmation criteria to the received cardiac signal using the arrhythmia detection circuit, wherein the atrial arrhythmia confirmation criteria is different from the atrial arrhythmia detection criteria and is more specific to detection of the type of arrhythmia detected than the atrial arrhythmia detection criteria;

detecting, using the arrhythmia detection circuit, a sensing event that causes false indications of detection of arrhythmia by one or both of the atrial arrhythmia detection criteria and the second atrial arrhythmia confirmation criteria, wherein the detecting the sensing event includes one or more of detecting a number of pauses in cardiac depolarization in the sensed cardiac signal, detecting a heart rate that is non-physiologically slow, and sensing a specified number of changes in amplitude of the sensed cardiac signal that exceed a specified amplitude change threshold within a specified period of time; and

adjusting, in response to the detected sensing event, sensitivity or specificity of the atrial arrhythmia detection criteria and the atrial arrhythmia confirmation criteria using the arrhythmia detection circuit.

12. The method of claim 11 , wherein the detecting the sensing event includes one or both of:

detecting a specified number of noise hits in the sensing of the cardiac signal within a specified time duration, and

detecting a heart rate that is non-physiologically fast.

13. The method of claim 11 , wherein the detecting the sensing event includes detecting a cardiac rhythm for which one or both of the atrial arrhythmia detection criteria and the atrial arrhythmia confirmation criteria are susceptible to false alarms.

14. The method of claim 11 , wherein the atrial arrhythmia detection criteria and the atrial arrhythmia confirmation criteria detect atrial tachyarrhythmia, wherein the adjusting sensitivity or specificity includes adjusting an atrial tachyarrhythmia detection threshold of one or both of the atrial arrhythmia detection criteria and the atrial arrhythmia confirmation criteria, and wherein the method further includes restoring the atrial tachyarrhythmia detection threshold to an original sensitivity or specificity when the detected sensing event ceases to be detected for a specified period of time.

15. A system comprising:

a sensing circuit configured to provide a sensed ventricular cardiac signal of a subject when operatively coupled to electrodes that contact a subject; and

an arrhythmia detection circuit operatively coupled to the sensing circuit and configured to:

apply a atrial arrhythmia detection criteria to the sensed ventricular cardiac signal;

apply, in response to the applied atrial arrhythmia detection criteria producing a positive indication of atrial arrhythmia, a atrial arrhythmia confirmation criteria to the sensed ventricular cardiac signal, wherein the arrhythmia confirmation criteria is different from the criteria and is more specific to detection of atrial arrhythmia than the atrial arrhythmia detection criteria;

detect a sensing event that causes false indications of detection of arrhythmia by one or both of the and atrial arrhythmia detection criteria, wherein the sensing event includes one or more of detecting a number of pauses in cardiac depolarization in the sensed cardiac signal, detecting a heart rate that is non-physiologically slow, and sensing a specified number of changes in amplitude of the sensed cardiac signal that exceed a specified amplitude change threshold within a specified period of time; and

adjust, in response to the detected sensing event, sensitivity or specificity of the atrial arrhythmia detection criteria and the atrial arrhythmia confirmation criteria.

16. The system of claim 15 , wherein the arrhythmia detection circuit is configured to detect atrial flutter (AF) using the atrial arrhythmia detection criteria and the atrial arrhythmia confirmation criteria, adjust a detection threshold of one or both of the detection criteria and the atrial arrhythmia confirmation criteria to change sensitivity or specificity to AF in response to detection of the sensing event, and restore the detection threshold to an original sensitivity or specificity when the detected sensing event ceases to be detected for a specified period of time.

17. The system of claim 16 , wherein the arrhythmia detection circuit is configured to:

confirm AF using the atrial arrhythmia confirmation criteria when sensed ventricular depolarization intervals (V-V intervals) satisfy one or more of a specified V-V interval scatter AF detection threshold, a specified V-V interval double decrement AF detection threshold, and a specified Wenckebach AF detection threshold; and

change the sensitivity or specificity of the one or more of the V-V interval scatter AF detection threshold, the V-V interval double decrement AF detection threshold, and the Wenckebach AF detection threshold in response to detection of the sensing event.

18. The system of claim 15 , wherein the arrhythmia detection circuit is configured to includes restoring the atrial arrhythmia detection threshold to an original sensitivity or specificity when the detected sensing event ceases to be detected for a specified period of time.

19. The system of claim 15 , including:

a therapy circuit configured to provide electrical pacing therapy to the subject; and

a control circuit configured to initiate delivery of the electrical pacing therapy according to a pacing therapy mode; and change the pacing therapy to a different pacing therapy mode according to the detected cardiac arrhythmia.

20. The method of claim 11 , including:

delivering electrical pacing therapy according to a pacing therapy mode; and

changing the pacing therapy mode according to the detected cardiac arrhythmia.