Mitral valve annular downsizing forces: implications for annuloplasty device development.

Objective: Mitral valve repair with annulus downsizing is a popular surgical procedure for functional mitral regurgitation. We investigated the effects of externally applied downsizing on the observed in-plane forces and valvular dimensions. Methods: Five animals were included in an acute porcine study. Three traction sutures were anchored at the right fibrous trigone (T) and suspended across the annulus for externalization at the P1, P2, and P3 annular segments. The annulus was downsized with the sutures in controlled increments while measuring the tension force in the sutures. Downsizing percentages ranged from a 2% to 32% reduction of the T-P distances. Sonomicrometry was used to measure the resulting valvular dimensions. Results: No difference in force was found between the P1, P2, and P3 segments across all levels of downsizing. The peak forces at 32% downsizing were 1.2 +/- 0.9 N, 1.5 +/- 1.0 N, and 0.8 +/- 0.2 N for the T-P1, T-P2, and T-P3 segments, respectively. The maximum total suture forces in the mitral plane during downsizing increased from 0.12 +/- 0.03 N to 3.5 +/- 1.3 N (P<.005). Sonomicrometry showed a decrease in the systolic thickening of the posterior myocardial wall at the annular level with annular downsizing (0%-32%) from 5 +/- 3 mm to 1 +/- 1 mm (P<.05). Conclusions: Segmental mitral valve annulus downsizing increased in-plane traction suture forces and has a significant influence on the in-plane biomechanics. These results have implications for device design in terms of mechanical strength requirements and can be used to supplement boundary conditions for computational left heart models.