Electrophysiological and Anatomic Heterogeneity in Evolving Canine Myocardial Infarction

Although the heterogeneity of electrophysiological properties is increased after myocardial infarction, the degree of this heterogeneity has not been well quantitated and its relationship to the histological changes that occur after infarction has not been carefully examined. The purpose of the present study was to test the hypothesis that alterations in electrophysiological properties in healing canine infarction are related to particular histological changes. Experimental infarction was produced by left anterior descending coronary ligation. Six dogs were used as controls, six were studied 5 days following, and six were studied 8 weeks following infarction. Pacing thresholds, effective refractory periods, and activation-recovery times were determined at 112 sites on the anterior left ventricle using a multiple electrode plaque. Conduction velocity, conduction-heterogeneity index--a measure of conduction disturbance--and histology of the epimyocardium underlying the plaque were assessed. The effective refractory periods and activation-recovery times were greater in both infarction groups, most prominently in the subacute group. In subacute infarction, significant postrepolarization refractoriness was present. In healed infarction, conduction velocity was decreased and the conduction-heterogeneity index was increased compared to controls and subacute infarction. Dispersion of excitability and repolarization was associated with more extensive local scarring. Dispersion of myocardial fiber angles was associated with the conduction-heterogeneity index. Some but not all of the electrophysiological changes noted in the animals with infarction were also seen in sham operated animals. Thus, heterogeneity in repolarization and refractoriness is greatest in the subacute phase of myocardial infarction and is associated with the extent of local cell death. In contrast, disturbances in conduction are greatest in healed infarction and associated with disarray of myocardial fibers.