A model of myocardial ischemia for the simultaneous assessment of electrophysiological changes and arrhythmias in intact rabbits.

A method of recording epicardial monophasic action potentials (MAPs) and ischemia-induced arrhythmias following coronary artery ligation in intact rabbits is described. It is expected that this model will have utility in analyzing drug effects and mechanisms of ischemic arrhythmogenesis. Rabbits were found to have two arrhythmic phases following coronary artery occlusion which correspond to phase Ia and Ib arrhythmias in other species. Epicardial MAPs recorded from ischemic tissue allowed electrophysiological effects to be correlated with these phases. Phase Ia arrhythmias occurred within the first 2 min of coronary artery occlusion and were associated with a reduction in the maximum upstroke velocity of MAPs and changes in MAP duration, including the occurrence of alternans in duration. Phase Ib arrhythmias occurred between 8 and 15 min after coronary artery occlusion. These arrhythmias were associated with a decrease in MAP duration and amplitude, alternans in MAP duration as well as conduction block. Coronary artery occlusion reliably induced arrhythmias in rabbits if the left branch of the coronary artery and the left anterior descending artery were occluded. There was a 95% incidence of premature ventricular contractions, 38% of ventricular tachycardia, and 48% of ventricular fibrillation (n = 21). The results of this study show that epicardial MAPs can be used to aid in the characterization of the electrophysiological mechanisms of ischemia-induced arrhythmias in vivo.