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

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Abstract
To characterize the electrophysiologic properties of the ventricular arrhythmias occurring during reperfusion after acute coronary artery ligation, a study was undertaken to correlate the time course of appearance of such arrhythmias with specific electrophysiologic mechanisms. Dogs [37] survived 30 min ligations of the left descending coronary artery. All had either instantaneous (onset at 0-1 min) or delayed (onset at 2-7 min) ventricular arrhythmias on reperfusion. Local electrograms recorded from ischemic myocardium were markedly abnormal after 30 min of coronary ligation, but rapidly returned to approximately normal within 1-2 min after reperfusion. Instantaneous reperfusion ventricular arrhythmias occurred in the midst of the recovery process when fragmented activity was recorded on electrograms from the long duration (i.e., spanning diastole) and was associated with the occurrence of ventricular fibrillation in 24 of 37 dogs. By 3 min after reperfusion, all electrical activity was again synchronous and inscribed completely within the QRS complex. In 8 of 19 dogs that survived the initial reperfusion period, including 6 resuscitated from ventricular fibrillation, there was a 2nd 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 min after reperfusion) were associated with electrophysiologic properties characteristic of enhanced automaticity and only infrequently (1 of 8 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 ventricular 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.