[Acute phase of ventricular fibrillation in myocardial infarct. Importance of studying electrical systole by determining the QTc].

Recent reports have drawn attention to the association between long QT intervals and sudden death in myocardial infarction and certain congenital syndromes. This study was undertaken to determine the relationship between lengthening of the QT interval and primary ventricular fibrillation in acute myocardial infarction. Thirteen cases were chosen out of a total of 21 cases of primary ventricular fibrillation (5.09% of 412 cases of myocardial infarction hospitalised during this period). Ten other cases of myocardial infarction with the same features apart from the arrhythmia were used as controls. Three series of electrocardiogrammes recorded under the same technical and chronological conditions (2 before and 1 after ventricular fibrillation) were analysed. The average QT interval was corrected for heart rate (RR) with Bazett's formula. The average QTc in acute myocardial infarction was longer than the theoretical QTc (p less than 0.05). The graph showing this increase reached a peak at the 48th hour. The average QTc in patients with primary ventricular fibrillation was longer than in the control patients (p less than 0.05) and significantly longer than the theoretical value (p less than 0.001). The average QTc in survivors of ventricular fibrillation was not significantly longer than that of the control group but was longer than the theoretical value (p less than 0.01). These results justify the strict surveillance of the length of electrical systole in the first hours of the acute phase of myocardial infarction. In this series, values greater than 440 ms were associated with a high risk of ventricular fibrillation in the first week after myocardial infarction.