The role of supraventricular extrasystoles in the initiation of ventricular arrhythmia was studied in 72 consecutive patients who developed primary ventricular fibrillation during the acute phase of myocardial infarction. In six patients (8%), a total of 12 episodes of ventricular fibrillation and 16 episodes of ventricular tachycardia were initiated by supraventricular extrasystoles. Ventricular fibrillation and tachycardia were initiated by single supraventricular extrasystoles in 16 and by salvos greater than or equal to two beats in 12 episodes. The RR coupling interval of the supraventricular impulse immediately preceding ventricular tachycardia ranged from 240 to 420 ms (mean 356 (62)) and was characteristic of R-on-T (prematurity index less than 1) in 63% of episodes. Average peak serum creatine kinase activity in the six patients in whom ventricular tachycardia was initiated by a supraventricular extrasystole was 1275 units compared with 720 units in the remaining 66 patients. Five of these six patients later showed evidence of pump failure. Lignocaine or procainamide or both suppressed the ventricular arrhythmia in five of the six patients. The initiation of ventricular fibrillation or tachycardia by supraventricular extrasystoles in acute myocardial infarction is not uncommon and may reflect the increased vulnerability of the heart after a large infarct. These arrhythmias may respond to drugs that suppress ventricular irritability.
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