The incidence and mortality of intraventricular conduction defects in acute myocardial infarction

Abstract

The incidence of intraventricular conduction defects during sinus mechanism was 24 percent in 212 consecutive cases of acute myocardial infarction observed in a coronary care unit. Patients with intraventricular conduction defects had a higher mean age than that for the entire series (P < 0.01), and death occurred at a younger age than in patients without such defects (P < 0.1). The most common isolated defect was left anterior hemiblock (incidence of 9.4 percent). The next most common conduction defect was incomplete bilateral bundle branch block (incidence 7.5 percent); more than half of these patients had right bundle branch block with left anterior hemiblock. Far less frequent were isolated complete right bundle branch block and complete left bundle branch block. Left posterior hemiblock was rare and was not seen in patients without other intraventricular conduction defects either transient or permanent. The hospital mortality rate of the entire series was 21.2 percent. The mortality rate among patients with intraventricular conduction defects was 47 percent which is significantly different from that for the entire series (P < 0.01) and from a series matched by sex and age (P < 0.01). The most innocuous intraventricular conduction defect was left anterior hemiblock (in-hospital mortality rate 25 percent). This was statistically not different from the mortality rate in the total series. Higher mortality rates were associated with other conduction defects which produced QRS prolongation and bifascicular block.