Discordant S-T alternans contributes to formation of reentry: a possible mechanism of reperfusion arrhythmia.

Although a relationship between S-T alternans and life-threatening arrhythmia has been recognized, the mechanism is poorly understood. We examine the role of S-T alternans in the occurrence of ventricular fibrillation (VF) after reperfusion. The left anterior descending coronary artery was occluded for 20 min and then abruptly reperfused in 12 intravenously anesthetized open-chest dogs. Sixty unipolar epicardial electrograms were recorded during the control state, at the end of occlusion, and after reperfusion. The largest magnitude of S-T alternans among 60 leads was defined as the maximum S-T alternans. Isochronal maps of activation time in paced beat and spontaneous ventricular premature contractions (VPC) were analyzed. After reperfusion, VF ensued in six dogs. The maximum S-T alternans augmented progressively with time after reperfusion until VF occurred. In three dogs with VF, when activation of VPC resulted in conduction block and formed reentry, VF ensued. The conduction block was located between sites of discordant S-T alternans (S-T alternans at adjacent leads was out of phase). These data indicate that discordant S-T alternans relates to VF by facilitating the formation of a reentrant circuit.