Differences in distribution of myocardial abnormalities in patients with obstructive and nonobstructive asymmetric septal hypertrophy (ASH). Light and electron microscopic findings.

was obtained at operation or necropsy from 22 patients, including 14 with obstructive and eight with nonobstructive 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 nonobstructive ASH, suggesting that these abnormalities probably contribute importantly to functional impairment in such patients.