Reentrant Ventricular Arrhythmias in the Late Myocardial Infarction Period 9. Electrophysiologic-Anatomic Correlation of Reentrant Circuits

We studied isochronal maps of ventricular activation during ventricular arrhythmias induced by programmed premature stimulation in dogs 3–5 days after ligation of the left anterior descending coronary artery. The entire epicardial surface and selective intramural sites were recorded using a computerized multiplexing technique. The electrophysiologic data were correlated with the anatomic characteristics of the infarction. In nine of 17 dogs (55%), the induced ventricular rhythm was due to reentrant activation in the surviving epicardial layer overlying the infarction. The irregular epicardial layer (up to 4 mm thick) had grossly intact myocardial fibers on microscopic examination but showed abnormal electrophysiologic characteristics. The stimulated premature beat that initiated reentry produced a continuous arc offunctional conduction block within the surviving epicardial layer. The activation wave front circulated slowly around both ends of the arc of block, rejoined on the distal side of the arc before breaking through the arc to reactivate an area proximal to the block. This resulted in splitting of the initial single arc of block into two arcs. Reentrant activation continued as two synchronous circuits that traveled clockwise around one arc and counterwise around the other. Reentry spontaneously terminated when the leading edge of both reentrant circuits encountered refractory tissue, resulting in the coalescence of the two arcs of block into one. The present study may increase the understanding of the electrophysiologic mechanism of some ventricular repetitive responses and tachyarrhythmias induced by programmed premature stimulation in the clinical laboratory.