Intraventricular conduction defects in acute myocardial infarction.

Of 325 consecutive cases with acute myocardial infarction admitted to a coronary care unit, II3 per cent developed one or more intraventricular conduction defects as an early, and often transient complication. The most common Lintraventricular conduction defect was block of the anterior fascicle, followed by complete right bundle-branch block, and by the association of right bundle-branch block with anterior fascicular block. Complete left bundle-branch block and the association of right bundle-branch block with block of the posterior fascicle were less frequent. The rarest intraventricular conduction defect was pure posterior fascicular block. The electrocardiographic localization of acute myocardial infarction was most commonly anterior in cases with anteriorfascicular block or right bundle-branch block with anteriorfascicular block; frequently anterior or anterior and inferior in cases with left bundle-branch block, right bundle-branch block with posterior fascicular block, or posteriorfascicular block alone. Anterior fascicular block did not modify the mortality rate which was increased, but not significantly, by left and by right bundle-branch block. The presence of more than one intraventricular conduction defect was associated with a mortality rate of 47 per cent, a significantly higher figure. The cause of death was mainly shock and/or left ventricular failure. The incidence of high grade or complete AV block was higher in patients with intraventricular conduction defect, but the difference was not statistically significant; the mortality rate in this group was 6o per cent when cases with block of the anterior fascicle were excluded. Cases with right bundle-branch block and block of the anterior fascicle, and cases with right bundle-branch block and block of the posterior fascicle showed severe twoor three-vessel atherosclerotic coronary artery disease. An infarction involving the anterior two-thirds of the ventricular septum was present in the first