Repolarization Gradients in the Canine Left Ventricle Before and After Induction of Short-Term Cardiac Memory

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Abstract
Background— Questions remain about the contributions of transmural versus apicobasal repolarization gradients to the configuration of the T wave in control settings and after the induction of short-term cardiac memory. Methods and Results— Short-term cardiac memory is seen as T-wave changes induced by altered ventricular activation that persists after restoration of sinus rhythm. We studied cardiac memory in anesthetized, open-chest dogs paced from the ventricle for 2 hours. Unipolar electrograms were recorded from as many as 98 epicardial and 144 intramural sites, and activation times and activation-recovery intervals (ARIs) were measured. In separate experiments, epicardial monophasic action potentials were recorded. We found no appreciable left ventricular intramural gradients in repolarization times (activation time+ARI) in either control conditions or after the induction of memory. In controls, there was a left ventricular apicobasal gradient, with the shortest repolarization times in anterobasal reg...