Bundle branch block in acute myocardial infarction

The incidence and natural history of bundle branch block in 565 patients admitted to a coronary care unit were examined. Right bundle branch block (RBBB) was present in 7 per cent of patients with mortality rate of 61 per cent, and left bundle branch block (LBBB) in 4 per cent of patients (mortality rate 48 per cent). The majority of patients with RBBB developed it during the course of their acute infarction compared to those with LBBB in whom the lesion was more chronic. RBBB was associated with a significantly higher incidence of asystole than LBBB. This usually occurred during the course of complete heart block and was not a terminal manifestation of shock or cardiac failure. The presence of left axis deviation did not adversely effect the prognosis of patients with RBBB, either for survival or for the development of asystole. RBBB nearly always developed during the course of anterior transmural infarction, and autopsy in fatal cases showed proximal occlusion of the left anterior descending coronary artery as an almost constant finding. The site of infarction could seldom be determined from the cardiogram in patients with LBBB, and autopsies showed more generalized coronary atheroma. These results suggest that the use of a transvenous electrode catheter attached to a demand pacemaker should be considered in patients with anterior transmural infarction who develop RBBB.