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 cal culated how rates and to assess a possible correction factor to adjust the proximal convergence angle. We further defined under which hydrod ynamic and geometric conditions it is necessary to apply the corrected convergence angle. Background. The proximal flow convergence method h as been proposed as a new approach to quantify valvular regurgitation. However, significant overestimation of the calculated regurgitant Bow rate has been reported, particularly in patients with mitral valve pr olapse and severe mitral regurgitation. Methods. We used an in vitro h ow model and induced various degrees of proximal flow constraint. The accuracy of the proposed convergence angle formula, alpha = pi + 2 tan (-1) d/r (d = wall distance; r = isovelocity radius) was tested in vit ro and in a three-dimensional numerical simulation. Results. With a co nstraining mall near the orifice, overestimation of regurgitant flow r ates was noted and was most significant with the constraining mall pos itioned closest to the orifice (calculated flow rate [Q(c)]/true how r ate [Q(o)] = 1.85 +/- 0.55 [mean +/- SD]). These findings were similar to the results of the numerical simulation. Applying the correction f actor nearly completely eliminated the overestimation of the calculate d flow rates (cQ(c)), with cQ(c)/Q(o) = 1.13 +/- 0.25. Conclusions. In the presence of a constraining wall, significant overestimation of ca lculated flow rates is observed when hemispheric symmetry of the flow field is assumed, In this situation, it is necessary to apply the corr ected convergence angle formula to improve the accuracy of the proxima l how convergence method.