Strength comparison of mitral annuloplasty ring and suturing combinations: An in-vitro study

Background and aim of the study: While mattress sutures are commonly used to secure annuloplasty rings during mitral valve repair, the use of a flexible ring secured with a running polypropylene suture has recently been advocated. The study aim was to assess the separation tensions of semi-rigid and flexible rings using mattress and running suture techniques in an in-vitro static load model. Methods: Semi-rigid and flexible annuloplasty rings were sutured with either mattress or running sutures (RM, RR, FM, FR) in four groups, of eight hearts each. Twelve additional sutures were passed through the surfaces of each ring to fix the preparation to a testing machine. In a fifth (control) group the mattress sutures securing a flexible ring (FMS) were connected directly to the machine. Each preparation was subjected to progressive axially directed (base-apex) tension until ring-tissue separation occurred. Results: The first major decrease in tension (defined as ≥10 N in ≤1.5 s) typically occurred with the separation of at least three adjacent sutures. These starting tensions (N) were: FMS 117 ± 32.6, RR 131.7 ± 30.5, RM 137.4 ± 35.3, FM 152.1 ± 32.3, and FR 213.2 ± 30.5. The magnitudes of tension decrease with separation (and percentage of starting tensions) were: FMS 25.4 (21.2%), RR 26.8 (17.6%), RM 28.9 (21.6%), FM 24.6 (17.6%), and FR 22.5 (10.8%). The FR group required more tension to separate than the other groups (p <0.001), but had a lower magnitude of force drop at dehiscence. Conclusion: Flexible rings secured with a running suture required more force to separate than other ring-suture combinations. The lower magnitude of force drop in this group indicated a better tension distribution than in the other groups. Semi-rigid rings separated with a lower force, and had larger drops in tension, regardless of the suture technique used.