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

Abstract

The prevalence of ventricular arrhythmias in the first 12 hours of acute myocardial infarction has been 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 had been receiving antiarrhythmic therapy, digoxin, or diuretics before inclusion in the study. Continuously recorded electrocardiographic tapes were analysed by three 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 three hours after infarction and was lower thereafter. By contrast, other ventricular arrhythmias including ventricular tachycardia increased in frequency in the fourth to twelfth hours. Primary ventricular fibrillation in 16 of the 17 patients was inititated by an R-on-T ventricular ectopic complex (QR'/QT≤0.85), while only four of 265 episodes 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 minutes before primary ventricular fibrillation, there was a striking increase in the incidence of R-on-T ventricular ectopic complexes. This study shows that 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 at present this appears not to be of value in predicting primary ventricular fibrillation, it may shed light on the genesis of arrhythmias in infarction and have implications for their prevention.