Objective: Undersizing mitral annuloplasty (UMA) has failed to yield durable functional mitral regurgitation (FMR) repair, as chordal tethering forces are not reduced, resulting in unphysiological leaflet coaptation. Our preliminary bench work demonstrated that papillary muscle approximation (PMA) relieves chordal tethering forces and increases leaflet mobility without annular downsizing. We report for the first time a patient‑specific PMA simulation performed using 3D computational mitral valve model.
Methods: FMR datasets were obtained in two pigs 3 months after they received myocardial infarction via left circumflex artery occlusion. 3D echo images were segmented to obtain the geometry of annulus, leaflets, and papillary muscles (PMs). Branched chordal network was developed according to ex-vivo findings since chordae are not visible on echo. FMR state was created by displacing the PMs and imposing pre‑strain on the chordae. To mimic PMA repair, the PMs were drawn together in diastole. Valve closure was simulated by applying transvalvular pressure gradient on the leaflets (Fig A).
Results: Peak systolic leaflet configurations of FMR and PMA models and stress distribution on the leaflets are shown in Fig B. After PMA, regurgitant gaps were largely eliminated with coaptation area increasing from 105.0 to 189.1 mm2 in model 1 and from 133.0 to 191.9 mm2 in model 2 (Fig C). Tenting height decreased from 10.4 to 5.0 mm and from 11.4 to 6.8 mm, showing increased leaflet mobility. Maximum chordal tension forces reduced from 2.82 to 1.96 N and from 6.62 to 1.80 N. Large stress distribution areas were eliminated with peak stress values decreasing from 2.04 to 1.07 MPa and from 5.32 to 1.31 MPa.
Conclusions: Computational model demonstrates that PMA reduces chordal tethering forces and leaflet stresses and increases coaptation of the valve without developing unphysiological leaflet mobility inherent to UMA. 