Instantaneous and delayed ventricular arrhythmias after reperfusion of acutely ischemic myocardium: evidence for multiple mechanisms.

To characterize the electrophysiologic properties of the ventricular arrhythmias occurring dur- ing reperfusion after acute coronary artery ligation, a study was undertaken to correlate the time course of appearance of such arrhythmias with specific electrophysiologic mechanisms.Thirty-seven dogs survived 30- minute ligations of the left descending coronary artery, and all had either instantaneous (onset at 0-1 minute) or delayed (onset at 2-7 minutes) ventricular arrhythmias on reperfusion.Local electrograms recorded from ischemic myocardium were markedly abnormal after 30 minutes of coronary artery ligation, but rapidly returned to approximately normal within 1-2 minutes after reperfusion.Instantaneous reperfusion ventricular arrhythmias occurred in the midst of the recovery process when fragmented activity was recorded on elec- trograms from the ischemic area.This activity increased in amplitude, was of long duration (i.e., spanning diastole) and was associated with the occurrence of ventricular fibrillation in 24 of 37 dogs.By 3 minutes after reperfusion, all electrical activity was again synchronous and inscribed completely within the QRS complex.However, in eight of 19 dogs that survived the initial reperfusion period, including six resuscitated from ventricular fibrillation, there was a second surge of ventricular arrhythmias that was independent of diastolic or asynchronous electrical activity.In contrast to the instantaneous reperfusion ventricular arrhythmias, the delayed arrhythmias (2-7 minutes after reperfusion) were associated with electrophysiologic properties characteristic of enhanced automaticity and only infrequently (one of eight dogs) degenerated to ventricular fibrillation.Although the incidence of ventricular arrhythmias during the antecedent period of coronary artery ligation and the occurrence of instantaneous reperfusion arrhythmias were closely correlated, the delayed ven- tricular arrhythmias of reperfusion and those occurring during the antecedent coronary artery ligation period were not correlated.Distinct electrophysiologic mechanisms are apparently associated with a specific time course of appearance and with the severity of ventricular arrhythmias that occur when blood flow is suddenly restored to acutely ischemic myocardium.