An implantable cardiac device that delivers electrical therapy to a
patient's heart determines if a T wave alternan pattern of the patient's
heart exists. The device includes a sensing circuit that generates an
electrical signal including T waves representing paced electrical
activity of the heart and a morphology detector that measures a metric of
each T wave in the electrical signal. A T wave alternan pattern detector
determines, responsive to the measured T wave metrics, if a paced
activity T wave alternan pattern is present. The T wave alternan pattern
detector may also detect for intrinsic T wave alternan patterns. A
therapy control initiates suitable different responses for a paced T wave
alternan pattern detection and an intrinsic T wave alternan pattern
detection.