The Mechanism of the Intraventricular Pressure Gradient in Idiopathic Hypertrophic Subaortic Stenosis

T HE INTRAVENTRICULAR pressure gradients that are recorded in patients with idiopathic hypertrophic subaortic stenosis (IHSS) differ in many respects from those observed in patients with the various discrete forms of obstruction to left ventricular outflow. Thus, it is now generally recognized that the magnitude of the pressure gradient measured in the resting state may bear little relation to the severity of the patient's symptoms, and that in some patients, variations in the magnitude of the pressure gradient occur in the course of a single hemodynamic study, or at sequential cardiac catheterizations. The finding that in patients with IHSS approximately 80% of the stroke volume is ejected during the first half of left ventricular systole led Hernandez and co-workers' to consider the possibility that no obstruction to left ventricular outflow occurs in this disease. These investigators suggested that little or no orthograde flow might emanate from the area of high pressure and that the elevated systolic pres-