Unusual evolution of acquired infundibular stenosis in patients with ventricular septal defect. Clinical and morphologic observations.

Hemodynamic and cardiac morphologic observations were made on two patients with ventricular septal defect who showed unusual evolution of obstruction to right ventricular outflow. Both patients developed progressive infundibular stenosis, one in the presence of a spontaneously closing ventricular septal defect and the other after operative closure of the defect. Light and electron microscopic examination of resected infundibular muscle revealed hypertrophy and abnormal shapes and arrangements of cardiac muscle cells. These abnormalities resembled those found in left ventricular outflow tract muscle of patients with idiopathic hypertrophic subaortic stenosis. It is suggested that the pattems of distribution and growth of these abnormal cells in the right ventricular outflow tract may lead to localized hypertrophy and to development of progressive infundibular obstruction in some patients with ventricular septal defect.