Variability of mitral valve area by Gorlin formula after replacement by a caged-ball prosthesis☆

Abstract The hemodynamically effective orifice size for valve prostheses is calculated using the modified Gorlin formula 1,2 in the same way as for native valves. The comparison of hemodynamic performance of different types of biological and mechanical prostheses has relied on the values obtained in this way, 3,4 although there are obvious anatomic and flow pattern differences with the native valves. Caged-ball prostheses have a fixed, nondistensible, maximal anatomic orifice area and therefore are generally thought to have also a constant Gorlin mitral area. Considerable variability of the Gorlin mitral area in patients with these prostheses is difficult to explain in the absence of obstruction by tissue or thrombus and provokes questions in regard to the use of this calculation for assessment of the performance of the mechanical valves. It is conceivable that the mitral area calculated by the Gorlin formula is variable and dependent on flow in mechanical ball prostheses. We tested this hypothesis by determining the Gorlin mitral area of mechanical mitral prostheses at rest and after an increase in transvalvular flow.