The clinical features and significance of bifascicular block complicating acute myocardial infarction.

Two series of patients with anterior myocardial infarction complicated by right bundle branch block with either left anterior hemiblock (RBBB+LAH) or left posterior hemiblock (RBBB+LPH), have been studied. The first was a retrospective analysis taken from a time when prophylactic pacing wires were not inserted, and the second was a prospective series in whom pacing wires were inserted as soon as the condition defect was seen. The overall prevalence of RBBB+LAH was 3.3% compared to 1.6% for RBBB+LPH, and complete atrioventricular block was seen in 36% of the former and 66% of the latter. From the retrospective data it was apparent that hospital death was usually associated with massive myocardial infarction, although 3 of the 25 patients in this series died in hospital from sudden development of complete atrioventricular block. If the defect was transitory (1-3 days) then the prognosis was that of acute anterior infarction uncomplicated by fascicular block. The policy of prophylactic pacing failed to show any overall change in hospital mortality, and only 3 patients survived long enough to have permanent pacemakers inserted. This procedure has been of benefit to only one of these cases.