Idiopathic Hypertrophic Subaortic Stenosis: Detection by Thallium 201 Myocardial Perfusion Imaging

To determine whether thallium 201 myocardial imaging could be used to detect hypertrophie cardiomyopathy, 10 patients with idiopathic hypertrophic subaortic stenosis were studied. Asymmetric septal hypertrophy, an anatomic marker for this disease, was evident on thallium scans in the patients with idiopathic hypertrophic subaortic stenosis, with a ratio of septum to left ventricular free wall of 1.7 cm compared to 1.0 cm in eight normal volunteers, and 1.0 cm in eight patients with concentric left ventricular hypertrophy. Patients with hypertrophic cardiomyopathy also demonstrated apical ventricular wall thickening, and athicker posterior ventricular free wall in the obstructive in contrast to the nonobstructive form of this disease. Thallium scans of three patients with pulmonary hypertension and secondary asymmetric septal hypertrophy were distinguished from idiopathic hypertrophic subaortic stenosis by marked right ventricular wall thickening. Thus, thallium 201 myocardial perfusion imaging provides a noninvasive method for detection and evaluation of idiopathic hypertrophie subaortic stenosis. (N Engl J Med 293:1113–1116, 1975). IDIOPATHIC hypertrophic subaortic stenosis (IHSS) is now recognized as a spectrum of primary myocardial disease.^{1 2 3 4}Regardless of the presence or absence of left ventricular outflow tract obstruction, most patients within this disease spectrum have the common anatomic abnormality of a disproportionate thickening of the interventricular septum relative to the left ventricular free wall, asymmetric septal hypertrophy (ASH).⁵Myocardial perfusion scanning after the intravenous administration of thallium 201⁶allows an estimate of regional myocardial perfusion, and permits measurement of the relative thickness of the left ventricular septum and free wall. This report presents our experience with thallium 201 myocardial imaging to.