Differences in Distribution of Myocardial Abnormalities in Patients with Obstructive and Nonobstructive Asymmetric Septal Hypertrophy (ASH)

Previous studies have shown that abnormal cellular morphology is present in the ventricular septum of patients with asymmetric septal hypertrophy (ASH). The present study was undertaken to determine whether these morphologic abnormalities are limited to the ventricular septum of patients with ASH or are more diffusely distributed throughout the heart, and whether different patterns of distribution of the cellular abnormalities exist in patients with and patients without left ventricular outflow obstruction. Myocardium was obtained at operation or necropsy from 22 patients, including 14 with obstructive and eight with non-obstructive ASH, and studied by both light and electron microscopy. Many hypertrophied, bizarrely shaped, and abnormally arranged cardiac muscle cells, presumably a morphologic manifestation of the genetically transmitted myocardial defect in ASH, were present in the ventricular septum of all patients. In patients with obstructive ASH, these abnormalities were either absent or rarely found in muscle from the left and right ventricular free walls. This observation suggests that functional limitation in these patients is due largely to left ventricular outflow obstruction. In contrast, numerous disorganized cells were extensively distributed in the left and right ventricular feee walls from seven of eight symptomatic patients with non-obstructive ASH, suggesting that these abnormalities probably contribute importantly to functional impairment in such patients.