Pressure Gradients without Obstruction

OBSTRUCTION to left ventricular outflow has been considered a characteristic and functionally important feature of "hypertrophic subaortic stenosis." The presence of obstruction has been inferred from the finding of a pressure gradient within the left ventricle during catheterization of the left heart in certain patients with idiopathic left ventricular hypertrophy. Indeed, the disease was not recognized as a clinical entity until after the advent of left heart catheterization technics. Infrequent descriptions of massive hypertrophy with virtual obliteration of the left ventricular cavity in autopsy reports dating back to 1907,1 lend some support to the concept of muscular obstruction. A number of observations render the functional importance of obstruction less clear in "hypertrophic subaortic stenosis" than in discrete forms of aortic stenosis. 1. There is no correlation between the size of the left ventricular gradient ("severity of the obstruction") and the functional status of the patient.2 2. The pressure gradient is quite variable and often absent during the course of a left heart catheterization study or on repeated studies. 3. No obstruction is found at operation or at autopsy in some patients with large pressure gradients.