[Conduction disorders at multiple levels during the acute phase of a myocardial infarct: an electrophysiological study]

Abstract

Forty patients with a diagnosis of acute myocardial infarction (anterior 24, and inferior 16) were studied. Of these patients, 37.5% manifested second and third degree atrioventricular (AV) block as a complication; another 30% showed complete right bundle branch and left anterior hemiblock. Right bundle branch and left posterior hemiblock were evidenced in 12.5% of the subjects. There was 20% with complete left bundle branch block. Electrophysiologic studies were performed in all patients to assess the site of block. A direct relation was found between the surface ECG and the His bundle electrogram studies in patients with an inferior myocardial infarction and AV block, both procedures located the conduction disturbances at the AV node (suprahisian block), in contrast to patients with anteroseptal myocardial infarction whose surface ECG only showed bundle branch block or fascicular block. The His bundle electrogram registered multiple levels of AV block, 70% with troncular and infrahisian block that gave way to sudden AV block. The mechanism responsible for this block was considered to be a functional longitudinal dissociation of conduction system due to an acute ischemic injury of the His bundle, more than a sudden and simultaneous failure of all the bundle branch of His. We conclude that electrophysiologic studies are a useful procedure for identification of a group of patients with multiple AV conduction disturbances that have a less favorable prognosis than those with only suprahisian level of block.