Ventricular arrhythmias in first 12 hours of acute myocardial infarction. Natural history study.

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Abstract
The prevalence of ventricular arrhythmias in the first 12 h of acute myocardial infarction was compared in 17 patients selected on the basis of their developing primary ventricular fibrillation and 21 apparently similar patients without primary ventricular fibrillation. None received or was receiving antiarrhythmic therapy, digoxin or diuretics before inclusion in the study. Continuously recorded ECG tapes were analyzed by 3 independent observers and a specially developed computer system. The frequency of primary ventricular fibrillation and R-on-T ventricular ectopic complexes was highest in the first 3 h after infarction and was lower thereafter. Other ventricular arrhythmias including ventricular tachycardia increased in frequency in the 4th-12th h. Primary ventricular fibrillation in 16 of the 17 patients was initiated by an R-on-T ventricular ectopic complex (QR''/QT .ltoreq. 0.85), while 4 of 265 spisodes of ventricular tachycardia were so initiated. In the 22 patients (11 with primary ventricular fibrillation, 11 without it) who demonstrated R-on-T ventricular ectopic complexes, the average rate of occurrence of this event was higher in those with primary ventricular fibrillation. In the 10 min before primary ventricular fibrillation, there was a striking increase in the incidence of R-on-T ventricular ectopic complexes. Different ventricular arrhythmias have a different and changing rate of occurrence in acute myocardial infarction. A close relation was observed between R-on-T ventricular ectopic complexes and primary ventricular fibrillation. Though presently this appears not to be of value in predicting primary ventricular fibrilla, it may illuminate the genesis of arrhythmias in infarction and have implications for their prevention.