Patent ID: 7761154

Claim:
An implantable medical device, comprising: a sensing circuit configured to sense a cardiac signal; a pacing output circuit configured to deliver pacing pulses; a beat detector, coupled to the sensing circuits and configured to detect heart beats from the cardiac signal; a cycle length detector, coupled to the beat detector and configured to detect cardiac cycle lengths each being a time interval between two consecutively detected heart beats; a tachyarrhythmia detector, coupled to the cycle length detector and configured to detect a tachyarrhythmia episode using the cardiac cycle lengths and one or more tachyarrhythmia detection thresholds; a tachyarrhythmia classifier, coupled to the tachyarrhythmia detector and configured to classify the detected tachyarrhythmia episode as one of tachyarrhythmia types including ventricular tachyarrhythmia (VT) and supraventricular tachyarrhythmia (SVT); a primary duration timer, coupled to the tachyarrhythmia detector and configured to initiate a primary duration in response to the detection of the tachyarrhythmia episode; a cycle length stability analyzer, coupled to the sensing circuit and configured to analyze stability of the detected cardiac cycle lengths, wherein the cycle length stability analyzer comprises a stable VT cluster (SVTC) detector configured to detect SVTCs from the cardiac signal, the SVTCs each including at least a specified minimum number of consecutively detected heart beats over which the cardiac cycle lengths meet a specified stability criterion, the stable SVTC detector configured to declare an SVTC detection when the specified minimum number of consecutive heart beats have been detected during each of the SVTC; a secondary duration timer coupled to the primary duration timer and the cycle length stability analyzer, the secondary duration timer configured to control an initiation of a secondary duration using the stability of cardiac cycle lengths analyzed during the primary duration and the classification of the detected tachyarrhythmia episode, the secondary duration to be initiated in response to expiration of the primary duration; and an anti-tachyarrhythmia pacing (ATP) controller coupled to the primary duration timer, the cycle length stability analyzer, the secondary duration timer, and the pacing output circuit, the ATP controller configured to control the delivery of the pacing pulses according to an ATP mode using the stability of cardiac cycle lengths analyzed during the primary duration, the stability of cardiac cycle lengths analyzed during the secondary duration if the secondary duration is initiated, and the classification of the detected tachyarrhythmia episode.