Potentiating effects of a ventricular premature beat on the alternation of the ST-T complex of epicardial electrograms and the incidence of ventricular arrhythmias during acute coronary occlusion in dogs.

A relation between ST-T alternans (STTA) and incidence of ventricular arrhythmias (VA) was examined, and the effects of a premature beat on these were tested during acute coronary occlusion in dogs. Epicardial unipolar electrograms, epicardial and endocardial bipolar electrograms and monophasic action potentials were recorded during coronary occlusion. During the period of STTA, a remarkably late conduction and its alternation were also observed in ischemic areas. The more serious delay appeared during the negative deflection of the ST-T complex. VA followed mainly the negative deflection of the ST-T complex. The first premature activation appeared in either ischemic areas or the border areas. A ventricular premature beat (VPB) which occurred spontaneously or was produced by an electrical stimulation potentiated STTA, and additional VA frequently followed the negative deflection of the ST-T complex of the second sinus beat after the VPB. A VPB pronounced the conduction delay during the second sinus beat. The discordant STTA became concordant after the VPB. The duration of a monophasic action potential of the second sinus beat after the VPB in mildly ischemic areas decreased. These changes and enhanced STTA may contribute to the occurrence of the additional VA.