Patent ID: 8473042

Claim:
An apparatus comprising: an implantable cardiac signal sensing circuit configured to produce a sensed cardiac signal representative of cardiac activity of a subject; a controller communicatively coupled to the cardiac signal sensing circuit, wherein the controller includes: a sensing module configured to detect a cardiac depolarization using the sensed cardiac signal; and an arrhythmia detection module configured to: detect a detection episode in which a depolarization rate or interval satisfies a first tachyarrhythmia detection rate zone threshold; adjust, for the same detection episode, a specified detection duration threshold for the tachyarrhythmia detection zone according to as a function of the detected depolarization rate or interval, wherein the detection duration threshold is adjustable to a plurality of values for depolarization rates or intervals within the same tachyarrhythmia detection rate zone, and wherein the detection duration threshold is adjustable according to a different function for a different tachyarrhythmia detection zone; generate an indication of detection of an episode of tachyarrhythmia when the detected depolarization rate is sustained for a period of time that meets or exceeds the adjusted detection duration threshold; and provide the indication of the detected episode of tachyarrhythmia to a user or process; and a therapy circuit communicatively coupled to the controller and configured to provide an anti-tachyarrhythmia therapy, wherein the arrhythmia detection module is configured to determine, following expiration of the adjusted detection duration threshold, whether the declared tachyarrhythmia episode is sustained during a specified sustained rate duration (SRD), and wherein the controller is configured to initiate a delivery of an anti-tachyarrhythmia therapy in response to an expiration of the SRD during which the declared tachyarrhythmia episode is sustained.