Frequency and significance of conduction defects in acute myocardial infarction.

The frequency of intraventricular conduction defects was determined in 556 consecutive patients with proven acute myocardial infarction. Complete left bundle branch block was present in 23 patients and carried a high mortality rate (61 per cent). Complete right buldle branch block was the rarest defect to be seen in isolation (8 patients) and carried a lower mortality rate (38%). Lone left anterior hemiblock was present in 72 patients and was associated with a low mortality rate (13 per cent); left posterior hemiblock occurred in 32 patients (mortality rate 19 per cent). In a further 59 patients right bundle branch block with left anterior or posterior hemiblock in addition was present and these patients had a high mortality rate which was greater than isolated right bundle branch block or hemiblock alone. Complete atrioventricular block developed in 51 patients, 26 of whom had prior evidence of intraventricular conduction defect. Despite the use of temporary transvenous pacing, mortality in patients who developed complete heart block was significantly increased whether or not an intraventricular conduction defect was already present. The significance of these findings for the management of patients with myocardial infarction is discussed.