Electrophysiologic and anatomic correlates of sustained ventricular tachyarrhythmias in a model of chronic myocardial infarction

Abstract

Ten healthy adult mongrel dogs were subjected to two stage occlusions of the mid or distal left anterior descending coronary artery modified by a reperfusion stage. In 9 of 10 animals studied at 3 or more days after coronary occlusion, sustained reentrant ventricular tachyarrhythmias could be reproducibly initiated or terminated, or both, using routine methods of programmed electric stimulation. Plunge electrodes were inserted at multiple subepicardial, intramyocardial and subendocardial sites from areas of normal and infarcted myocardium to evaluate electrophysiologic properties of excitability and refractoriness. With use of constant current unipolar cathodal stimulation, strength-interval curves were measured at these sites and correlated with regional histopathologic findings. In this model, infarcts were mottled, with close interspersing of normal and abnormal myocardium. Although excitability thresholds and refractoriness tended to increase within areas of infarction, marked disparities in excitability thresholds, effective and relative refractory periods and duration of relative refractory periods (relative minus effective refractory period) were observed within areas of infarction at sites only 1 to 2 mm apart anatomically. This milieu of anatomic and electrophysiologic heterogeneity is apparently sufficient to predispose to the initiation of sustained reentrant ventricular tachyarrhythmias.