Patent ID: 7103405
Filing Date: 2006-09-05
Classification: A61B,A61N

Abstract:
1. In an implantable medical device that provisionally detects a polymorphic tachyarrhythmia of the heart of a patient as a function of measured time intervals between sensed events in a cardiac signal, a method of improving the specificity of discriminating between a monomorphic tachyarrhythmia and a polymorphic tachyarrhythmia comprising the steps of: a) provisionally declaring a polymorphic tachyarrhythmia when at least a first number of the measured time intervals satisfy the polymorphic tachyarrhythmia detection criteria; b) successively sampling, processing, and temporarily storing the cardiac signal to provide sampled signal amplitudes; c) determining a baseline window between sensed events and a sensed event window encompassing the sensed event; d) determining baseline zero crossing points from the sampled signal amplitudes in the baseline window and event zero crossing points from the sampled signal amplitudes in the sensed event window; e) determining the absolute signal slope at each zero crossing point; f) weighting each zero crossing point by the determined absolute signal slope; g) summing the weighted zero crossing points in the baseline window to provide a baseline weighted zero crossing sum; h) summing the weighted zero crossing points in the sensed event window to provide a sensed event weighted zero crossing sum; i) subtracting the baseline weighted zero crossing sum from the sensed event weighted zero crossing sum to provide a weighted zero crossing sum metric related to the morphology of the cardiac signal; j) comparing the weighted zero crossing sum metric to a weighted zero crossing sum threshold; k) accumulating a match count x of weighted zero crossing sum metrics that meet the weighted zero crossing threshold over y repetitions of steps b) through j) as long as a polymorphic tachyarrhythmia is provisionally declared in step a); l) withholding the final declaration of a polymorphic tachyarrhythmia if the count x indicates that the corresponding cardiac signals exhibit frequency content suggestive of a monomorphic tachyarrhythmia; and m) making the final declaration of a polymorphic tachyarrhythmia if the count x indicates that the corresponding cardiac signals exhibit frequency content suggestive of a polymorphic tachyarrhythmia and the polymorphic tachyarrhythmia is provisionally declared in step a).