Asymmetric septal hypertrophy. Echocardiographic identification of the pathognomonic anatomic abnormality of IHSS.

Idiopathic hypertrophic subaortic stenosis (IHSS) is characterized by subaortic obstruction to left ventricular (LV) outflow. However, the obstruction is variable and many patients have no resting gradient and no clinical evidence of IHSS. Although a characteristic systolic movement of the anterior mitral valve leaflet can be demonstrated echocardiographically in many patients with IHSS, this may be absent in patients without obstruction under baseline conditions. Several necropsy studies of patients with IHSS have demonstrated that the ventricular septum characteristically is asymmetrically hypertrophied in relation to the posterior left ventricular wall. Since echocardiography can measure the thickness of the ventricular septum and the posterior LV free wall during life, we have evaluated the sensitivity and specificity of asymmetric septal hypertrophy (ASH) in diagnosing IHSS. The ventricular septu-n and posterior LV free wall were measured in 15 patients with IHSS documented by catheterization, 11 patients with other forms of fixed LV outflow obstruction, 52 patients with miscellaneous forms of heart disease, and 16 normal subjects. The