Left posterior hemiblock in acute myocardial infarction.

Fifteen cases of left posterior hemiblock associated with acute myocardial infaction were studied. In 5 cases the left posterior hemiblock was the only intraventricular conduction defect, while in the other 10 cases it was associated with complete right bundle-branch block. Left posterior hemiblock proved to be an early complication, appearing within a few hours from the onset of the acute episode, and an ominous sign, since hospital mortality rate was 87 per cent. Cause of death was mainly pump failure. In most of these cases ther was electrocardiographic evidence of infarction involving both anterior and inferior ventricular walls. Infarction of most or all of the ventricular septum was a common finding in the cases examined anatomically. Histologically, acute changes involving mainly the posterior septal and midseptal fibres were observed in 6 of the 8 cases studied. On the basis of these findings and of other published findings an alternative physiopathological mechanism for so-called left posterior hemiblock is proposed.