Physiologic Mitral Annuloplasty Ring Sizing: Surgical Technique and Animal Model Validation

OBJECTIVE: The current method for mitral annuloplasty ring sizing has remained essentially unchanged for a half century and offers surgeons limited actionable information. A novel technique is illustrated and validated in a cadaver swine heart model. METHODS: Twenty cadaver swine hearts were used to validate the novel sizing device and method. We hypothesized that the paired-ring sizer would force annuloplasty sutures to conform to its exact shape and therefore accurately predict changes in coaptation length when used to "downsize" the mitral annulus. Anterior leaflet coaptation length was measured under conditions of left ventricular saline distention: (1) at baseline, (2) with the sizer in place temporarily holding the sutures in position, and (3) after final implantation of a (corresponding size) Physio II ring (Edwards Lifesciences, Irivne, CA, USA). The "predicted" (sizer) and "actual" (implanted Physio II ring) coaptation lengths were compared using Bland-Altman analysis to assess accuracy. RESULTS: A moderate (2.0 to 5.5 mm) increase in coaptation length was achieved in 19 hearts and no change (0.0 mm) in 1 heart. The initial predicted (sizer) coaptation lengths corresponded well (≤0.5 mm difference) with the final, actual (implanted ring) coaptation lengths across all 20 hearts. Bland-Altman plots are provided for (derived) coaptation length increases. The mean difference (95% confidence interval) indicated that predicted were slightly greater than actual (0.08 [-0.06, 0.21]) but not different than zero. Limits of agreement were from -0.50 to 0.65. There did not appear to be significant heteroscedasticity. CONCLUSIONS: The accuracy of a novel mitral annuloplasty ring-sizing device was validated using a cadaveric swine heart model. Coaptation lengths initially predicted by the sizer corresponded accurately with coaptation lengths observed upon implantation of a corresponding commercially available ring. Continued development of this technology should provide surgeons with precise control over the final coaptation length by previewing several different rings prior to committing to a final implant.