Relationship between infarct size and incidence of severe ventricular arrhythmias in a double-blind trial with metoprolol in acute myocardial infarction.

In 585 patients having an acute myocardial infarction for the first time the relationship was investigated between estimated infarct size and the incidence of ventricular fibrillation and treated ventricular tachycardia during hospitalization. The size of the infarct was estimated from analyses of heat stable lactate dehydrogenase (LD) (EC 1.1.1.27.) in serum collected every 12 hr for 48-108 hr. All patients participated in a double-blind comparison of the beta 1-selective blocker metoprolol with placebo in suspected acute myocardial infarction. A correlation was observed between the enzymatically estimated infarct size and the incidence of ventricular fibrillation and treated ventricular tachycardia in patients on placebo (P less than 0.001), while this could not be demonstrated in patients on the beta-blocker (P greater than 0.2). In placebo treated patients there was a correlation between the maximum heat stable LD activity and early ventricular fibrillation (P = 0.034), late ventricular fibrillation (P less than 0.001), primary ventricular fibrillation (P = 0.002) as well as secondary ventricular fibrillation (P = 0.034). It is concluded that there seems to be a relatively strong correlation between the final size of the infarction and the occurrence of severe ventricular arrhythmias. Treatment with beta-blockade appeared to disturb this correlation.