Papillary muscle approximation reduces systolic tethering forces and improves mitral valve closure in the repair of functional mitral regurgitation

Abstract Background Undersizing mitral annuloplasty (UMA) to repair functional mitral regurgitation (FMR) lacks durability, as it forces leaflet coaptation without relieving the subleaflet tethering forces. In this biomechanical study, we demonstrate that papillary muscle approximation (PMA) before UMA can drastically relieve tethering forces and improve valve function, without the need for significant annular downsizing. Methods An ex vivo model of FMR was used, in which pig mitral valves were geometrically perturbed to induce FMR, and the repairs were performed. Nine pig mitral valves were studied as follows: normal (baseline), FMR, true-sized annuloplasty to 30 mm (true-sized ring [TSR]), and undersized annuloplasty to 26 mm (down-sized ring [DSR]), along with concomitant PMA at both ring sizes. Mitral regurgitation, valve kinematics, and chordal forces were measured and compared among the groups. Results FMR geometry induced a mean regurgitant fraction of 16.31 ± 7.33% compared with 0% at baseline. The 30-mm TSR reduced the regurgitant fraction to 6.05 ± 5.63%, whereas the 26-mm DSR reduced it to 5.06 ± 6.76%. The addition of PMA before the use of these rings reduced the mean regurgitant fraction to 3.87 ± 6.79% with the TSR (TSR + PMA) and 3.71 ± 6.25% with the DSR (DSR + PMA). Mean peak anterior and posterior marginal chordal forces were elevated to 0.09 ± 0.1 N and 0.12 ± 0.1 N, respectively, with FMR and were not reduced by annuloplasty of either sizes. The addition of PMA significantly reduced these forces to 0.23 ± 0.02 N and 0.51 ± 0.04 N. Conclusions This biomechanical study demonstrates that PMA relieves tethering forces and when added to annuloplasty and mobilizes the leaflets to achieve a good valve closure. Such a result could be achieved without the need for extensive annular downsizing.