Pathologic Features of Atrioventricular and Intraventricular Conduction Disturbances

T HE AVAILABILITY of continuous electrocardiographic monitoring techniques has resulted in recognition that conduction disturbances occur more frequently in patients with acute myocardial infarction than was previously thought to be the case. Complete atrioventricular (A-V) block has been reported in up to 9% of patients who have had acute infarcts,1 and bundle-branch block has been recorded in 13% of cases.2 Complete A-V block is an especially important complication of acute infarction since it is associated with a higher mortality rate. For example, in a recent report by Kostuk and Beanlands, the mortality in 378 patients with acute myocardial infarction was 20%, whereas in those patients who also developed complete A-V block the mortality was 50%.1 Important differences have been described between A-V block occurring during the course of acute posterior as contrasted with acute anterior infarction (table 1). A-V block occurs more frequently in patients with acute posterior wall infarction, but it is associated with a lower mortality rate than A-V block with acute anterior infarction. For example, Norris reported that out of 34 cases of second and third degree A-V block occurring in 276 patients with acute infarctions, 26 had a posterior and eight an anterior infarct.3 The