Systems and methods for detecting arrhythmias

A system for detecting atrial tachyarrhythmia (AT), comprising:

• a ventricular beat analyzer circuit configured to receive physiologic information of a patient and to detect ventricular beats using the received physiologic information;
• an arrhythmia detector circuit configured to detect respective AT indications in distinct time periods using portions of the received physiologic information during the distinct time periods;
• and
• a control circuit configured to:
• monitor the ventricular beats on a beat-by-beat basis;
• in response to the ventricular beats satisfying an instability criterion indicative of unstable ventricular rate, trigger the arrhythmia detector circuit to detect the respective AT indications in distinct time periods using a stability of ventricular beats in the distinct time periods, and determine an AT characteristic using the detected respective AT indications;
• and
• in response to an AT indication indicating an absence of AT in one of the distinct time periods, control the arrhythmia detector circuit to withhold detecting AT indication in a time period subsequent to the one of the distinct time periods, and trigger the ventricular beat analyzer to monitor and analyze additional ventricular beats.