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 occu r after infarction has not been carefully examined. The purpose of the pres ent study was to test the hypothesis that alterations in electrophysiologic al properties in healing canine infarction are related to particular histol ogical changes. Experimental infarction was produced by left anterior desce nding 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 wer e determined at 112 sites on the anterior left ventricle using a multiple e lectrode plaque. Conduction velocity, conduction-heterogeneity index - a me asure of conduction disturbance - and histology of the epimyocardium underl ying the plaque were assessed. The effective refractory periods and activat ion-recovery times were greater in both infarction groups, most prominently in the subacute group, in subacute infarction, significant postrepolarizat ion refractoriness was present. in healed infarction, conduction velocity w as decreased and the conduction-heterogeneity index was increased compared to controls and subacute infarction. Dispersion of excitability and repolar ization was associated with more extensive local scarring. Dispersion of my ocardial fiber angles was associated with the conduction-heterogeneity inde x. Some but not all of the electrophysiological changes noted in the animal s with infarction were also seen in sham operated animals. Thus, heterogene ity in repolarization and refractoriness is greatest in the subacute phase of myocardial infarction and is associated with the extent of local cell de ath. In contrast, disturbances in conduction are greatest in healed infarct ion and associated with disarray of myocardial fibers.