Changes in myocardial refractory periods following ischemia in the porcine heart

Abstract

Summary The purpose of this study was to utilize computer technique to analyze the time course of changes in myocardial refractory periods following coronary ligation in the porcine model in order to: o 1) compare these changes with those in the canine heart, a model with extensive coronary collateral circulation; 2) correlate alterations in refractory periods with spontaneous ventricular arrhythmias; and 3) correlate changes in refractory periods with the ability to initiate a repetitive ventricular rhythm by a premature stimulus applied near the effective refractory period. An on-line microprocessor with a real-time clock was interfaced with a sensing-stimulating unit to provide continuous determination of refractory period changes in 14 pigs in which the heart was exposed via a thoracotomy. The results were compared with the number of premature ventricular contractions (PVCs) and the ability to precipitate ventricular fibrillation by a premature ventricular stimulus. The results showed that: o 1) refractory periods in ischemic tissue were significantly reduced (p 2) both the number of PVCs per minute and changes in refractory periods increased to minute 3–4, however, the frequency of PVCs had declined significantly by minute 8–9 (20.4±16.55 vs. 1.60±2.51; p 3) the ability to initiate ventricular fibrillation was proportional to the reduction in refractory periods in ischemic tissue with fibrillation in only two of 14 animals stimulated at 0–20% vs. four of six at refractory period reductions of 20–40% (p These studies establish the distinctive time course of changes in refractory periods following ischemia in an animal without significant pre-existing coronary collateral circulation, and correlate these changes with spontaneous and induced ventricular arrhythmias.