Recordings of the local pacing-induced myocardial activation and repolarization.

We have studied the endocardial ventricular evoked response which follows delivery of a unipolar stimulus down the sensing electrode. The system uses the same lead for both pacing and sensing and permits recordings of the evoked T wave representing a dominantly local repolarization which follows a pacing-induced depolarization at the same site. In 12 animal experiments and in the course of electrophysiological investigations in 19 patients, we evaluated changes in the morphology and duration of the paced evoked response following drug interventions which alter myocardial refractoriness and repolarization time. These changes paralleled results obtained by simultaneous, paced monophasic action potential recordings, and suggest that myocardial repolarization can be accurately assessed by this new technique, which could overcome some of the difficulties in comparing 'in vivo' experiments with the clinical effects of drugs in man.