Non-invasive determination of the aortic valve area in stenosis: hydraulic orifice formula for application to echocardiography and correlation with catheterization.

We have investigated the validity of a hydraulic orifice formula which specifically excludes explicit dependence on the aortic valve pressure gradient in aortic stenosis. The new equation requires knowledge of stroke volume and systolic ejection periods (s/min) and is expressed as, A = 7 V/T2, where A is the effective aortic valve area in cm2, V is the stroke volume in cm3, T is the systolic ejection period in s/min and 7 is a clinically derived orifice coefficient. The data base consisted of 33 pediatric patients undergoing cardiac catheterization for the quantification of aortic stenosis. Additionally 12 of these patients had a conventional M-mode echographic investigation offering sufficient information to test the orifice formula in a non-invasive context. Using potentially non-invasive portions of the catheterization data, the new formula correlated with the classical Gorlin formula at a level of r = 0.85, s.e. = 0.22 cm2. In the M-mode echographic context with stroke volume computed from left ventricular dimensions by the Teichholz equation, the new formula yielded an area correlation with classical methods given by r = 0.87 and s.e. = 0.21 cm2. Additionally five cases each of subvalvular and supravalvular aortic stenosis were studied revealing significant differences in the flow parameters in these two cases. These initial results suggest that non-invasive methods may be of value in quantification, screening and follow-up of patients with stenotic aortic valve disease.