Impact of wall constraint on velocity distribution in proximal flow convergence zone: Implications for color Doppler quantification of mitral regurgitation

Objectives. This study sought to evaluate the effect of proximal flow constraint induced by the left ventricular wall on the accuracy of calculated flow rates and to assess a possible correction factor to adjust the proximal convergence angle. We further defined under which hydrodynamic and geometric conditions it is necessary to apply the corrected convergence angle. Background. The proximal flow convergence method has been proposed as a new approach to quantify valvular regurgitation. However, significant overestimation of the calculated regurgitant flow rate has been reported, particularly in patients with mitral valve prolapse and severe mitral regurgitation. Methods. We used an in vitro flow model and induced various degrees of proximal flow constraint. The accuracy of the proposed convergence angle formula, α = π + 2 tan^-1 d/r (d = wall distance; r = isovelocity radius) was tested in vitro and in a three-dimensional numerical simulation. Results. With a constraining wall near the orifice, overestimation of regurgitant flow rates was noted and was most significant with the constraining wall positioned closest to the orifice (calculated flow rate [Q_c]/true flow rate [Q_o] = 1.85 ± 0.55 [mean ± SD]). These findings were similar to the results of the numerical simulation. Applying the correction factor nearly completely eliminated the overestimation of the calculated flow rates (cQ_c), with cQ_c/Q_o = 1.13 ± 0.25. Conclusions. In the presence of a constraining wall, significant overestimation of calculated flow rates is observed when hemispheric symmetry of the flow field is assumed. In this situation, it is necessary to apply the corrected convergence angle formula to improve the accuracy of the proximal flow convergence method.