Response of Two Annular Prostheses to Functional Mitral Regurgitation Main Determinants: An In Vitro Evaluation

Functional mitral regurgitation (FMR) is usually treated through annuloplasty, i.e., the restriction of the mitral annulus by implanting an undersized prosthetic ring. We conceived a steady-state fluid-dynamic mock simulator that allows for controlling the main mechanic determinants of FMR: transmitral pressure and papillary muscle (PM) apical and lateral dislocation. We used our system to compare the FMR-specific Geoform ring with the general purpose Physio ring in the treatment of FMR. Each ring was implanted on 10 excised fresh porcine valves. Different transmitral pressures (40, 80, 120, 140, and 160 mm Hg) and symmetrical PM apical displacements (2.5-15 mm, step 2.5 mm) were imposed with submillimetric precision. In each configuration, the regurgitant flow through the valve was measured. For PM apical displacement ≥7.5 mm, the regurgitant flow was lower (p < 0.05) with the Geoform ring than with the Physio ring. Differences and their statistical significance increased as PM displacement or transmitral pressure increased. Regression analysis showed that this outcome did not depend on the morphology of the valves. The adopted approach proved itself simple and reliable and allowed to highlight the differences between the two examined annuloplasty devices in countering the two main determinants of FMR: high apical PM dislocation and transvalvular pressure.