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Posterior Papillary Muscle Relocation affects Stress and Pump Function: Finite Element Based Surgery
Joe L. Pantoja1, Liang Ge1, Zhihong Zhang2, William G. Morrel1, Sarthak Gulati3, Eugene A. Grossi4, Mark B. Ratcliffe1.
1University of California San Francisco, San Francisco, CA, USA, 2Veterans Affairs Medical Center, San Francisco, CA, USA, 3University of California Los Angeles, Los Angeles, CA, USA, 4New York University, New York City, NY, USA.

OBJECTIVE: The role of posterior papillary muscle relocation (PPM:PPMR) concomitant to mitral annuloplasty (MA) in the management of chronic ischemic functional mitral regurgitation (CIMR) is controversial. Traction suture placement and PPM displacement vary between procedures. The goal of this study was to determine the effects of PPM displacement and various anchor points on left ventricular (LV) regional myofiber stress and pump function.
METHODS: Previously described finite element (FE) models of the ovine LV, 16 weeks after postero-lateral myocardial infarction (MI) were used. PPMR + true-sized MA was simulated using the virtual suture technique (figure 1). PPMR anchor points tested included the mitral commissures and mid-anterior annulus. The anchor point to PPM distance (APD) was reduced between 10% - 40% of baseline distance. In each case, myofiber stress in the MI, border zone (BZ), and remote zone, ventricular short axes, coaptation depth, and stroke volume were calculated. Outcomes were analyzed using mixed-model linear regression.
RESULTS: PPMR reduced end-diastolic and end-systolic myofiber stress proportionally to the reduction in APD in all LV regions (all regions: p<0.01). Stress reduction was greatest in the MI (8.67±1.31 kPa) and least in the remote zone (1.03±0.12 kPa). When considering ventricular shape, reductions in septal-lateral short axis had a strong effect on stress reductions in all regions (all regions: p<0.01) while the effect of APD reduction become insignificant (MI: p=0.82, BZ: p=0.99, Remote: p=0.37). Despite decreases in stroke volume at 40% APD reductions, forward stroke volume increased in all PPMR cases. Finally, coaptation depth decreased with higher APD reductions.
CONCLUSIONS: These findings support the addition of ventricular reshaping, subvalvular procedures to MA in the management of CIMR. When selecting an anchor point and post-surgical PPM position, surgeons should consider post-surgical ventricular shape as it mediates stress reduction. In the future, FE optimized surgical procedures implemented on patient specific LV models may elucidate the impact of myofiber stress reduction on ventricular remodeling.

Figure 1: LV with PPMR+MR prior to(A) and after tightening sutures(B)

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