Effects of activation sequence on ventricular refractory periods of ischemic canine myocardium.

Refractory periods were measured in pentobarbital-anesthetized dogs during control periods and one to one and a half hours after distal left anterior descending coronary artery occlusion. The refractory period test site was on the anterior surface of the left ventricle in the distribution of the artery to be occluded. Measurements were made during drive of the refractory period test site, drive of a distant site on the pulmonary conus and during fusion drive in which drive of the test site was delayed with respect to drive of the pulmonary conus. Refractory periods were longer during test site drive than during pulmonary conus or fusion drives in both the control periods and following coronary occlusion. However, the effects of driving mode on refractory periods were greater following coronary occlusion than in the control periods. The findings are likely secondary to different magnitudes of change in electrotonic interactions associated with changes in activation sequence in ischemic and nonischemic myocardium. The greater dependence of repolarization properties in ischemic than nonischemic tissue suggests that inhomogeneity of these properties could be modified considerably by the site of origin of ectopic ventricular complexes.