Doppler evaluation of aortic valve area in children with aortic stenosis

Abstract

To evaluate the usefulness of the Doppler-derived aortic valve area calculated from the continuity equation in assessing the hemodynamic severity of aortic valve stenosis in infants and children, two-dimensional and Doppler echocardiographic examinations were performed on 42 patients (aged 1 day to 24 years) a median of 1 day before or after cardiac catheterization. The left ventricular outflow tract diameter was measured from the parasternal long-axis view at the base of the aortic cusps from inner edge to inner edge in early systole. The flow velocities proximal to the aortic valve were measured from the apical view with use of pulsed Doppler echocardiography; the jet velocities were recorded from the apical, right parasternal and suprasternal views by using continuous wave Doppler echocardiography. The velocity-time integral, mean velocity and peak velocity were measured by tracing the Doppler waveforms along their outermost margins.Seventeen patients (all ≤6 years old) had a very small left ventricular outflow tract diameter (≤1.4 cm) and cross-sectional area (≤1.5 cm2). The Doppler aortic valve area calculated with use of velocity-time integrals in the continuity equation (0.57 ± 0.25 cm2/m2, mean value ± SD) correlated well with the Doppler aortic valve area calculated by using mean (0.55 ± 0.25 cm2/m2) and peak (0.54 ± 0.24 cm2/m2) velocities, with correlations of r = 0.97 and 0.95, respectively.Thirty-four patients had sufficient catheterization data to calculate aortic valve area from the Gorlin formula. In these patients, the Doppler-derived aortic valve area correlated well with aortic valve area measured at catheterization (r = 0.73, SEE = 0.15 cm2/m2). When data for patients with hemodynamic findings that affect the calculation of valve area from the Gorlin formula were excluded from the analysis, then the correlation improved (r = 0.81, SEE = 0.16 cm2/m2). In addition, when altered transvalvular flow was taken into consideration, estimates of the severity of the aortic stenosis obtained from the Doppler aortic valve area were in agreement with those obtained from the Doppler mean gradient in 38 (90.5%) of the 42 study patients.Thus, aortic valve area measured with Doppler echocardiography by using the continuity equation correlates with that measured at cardiac catheterization. The usefulness of the Doppler technique does not appear to be significantly limited by a small proximal flow diameter or a small stenotic valve orifice. Together with the Doppler mean gradient, Doppler aortic valve area provides important information for estimating the severity of aortic valve stenosis in children.