Quantitative assessment of lumen area stenosis by Doppler echocardiography and application of continuity equation

Assessment of luminal stenosis plays a central role in the clinical decision makings for patients with heart diseases. To examine the role of Doppler echocardiography in the measurement of stenotic areas, we attempted to determine the mitral valve area and coronary artery stenosis by Doppler technique with a continuity equation. Mitral valve area was determined as a product of aortic or pulmonic annular cross-sectional area and the ratio of time velocity integral of aortic or pulmonic flow to that of the mitral stenotic jet. Mitral valve area determined at catheterization by Gorlin's formula was used as a gold standard. In the determination of coronary artery stenosis, flow velocity at the site prior to the stenotic lesion and that of stenosis was measured by catheter-tipped Doppler flowmeter (3-Fr, 20 MHz). The severity of the stenosis was calculated from the ratio of time-velocity integrals from prestenotic and stenotic segments. In 41 patients with mitral valve stenosis, valve area determined by continuity equation method correlated well with catheterization measurements irrespective the presence of aortic regurgitation (r = 0.91, y = 0.84x + 0.15, P less than 0.01). Of 20 patients with coronary artery disease, flow velocity both at the stenosis and prior to the stenosis could be determined in 13 patients examined. Under these conditions, coronary artery stenosis determined by continuity equation varied from 21%-76%. When these values were compared with those determined by biplane cineangiography, there was good correlation between them (r = 0.83, y = 0.92x - 0.45, P less than 0.01). These results demonstrate that Doppler-derived luminal area stenosis is applicable to assess the severity of the stenotic lesions, providing further information which cannot be obtained by the conventional methods, although several limitations should further be resolved.