Three-dimensional surface geometry correction is required for calculating flow by the proximal isovelocity surface area technique.

This study addressed the hypothesis that surface geometry must be taken into account in proximal convergence calculations of regurgitant flow rate. In vitro models allowed flow to converge within models designed to test derived angle correction equations. Flow was overestimated by the uncorrected equation for surfaces allowing flow to converge over less than a hemisphere and underestimated if flow converged over more than a hemisphere. The extent of deviation depended on the two-dimensional versus three-dimensional nature of the surface (angled flat surfaces versus conical surfaces). Correcting these estimates according to the derived equation produced good agreement for all geometries.