New Mitral Valve Annuloplasty Concept: Optimizing Annular Dynamics and Force Distribution.

BACKGROUND: Temporal three-dimensional (3D) analysis of the mitral valve biomechanics has prompted a re-evaluation of surgical approaches and repair device designs to accommodate the natural dynamics of the valve. Such new designs strive to obtain lower annulus restraining forces, resulting in more natural leaflet and chordal stresses. A new annuloplasty system was evaluated using 3D motion and out-of-plane force analysis. It was hypothesized that this system would not impact the valve with adverse motion restrictions or high systolic annular forces compared to conventional flat rigid ring designs. METHODS: In an acute porcine set-up, six 80 kg pigs were monitored before and after implantation of the new annuloplasty system consisting of two half-rings with a saddle-shaped outline. Valvular 3D dynamic geometry was obtained using sonomicrometry before and after annuloplasty system implantation. Strain gauges mounted on the commissural segments provided the annular restraining force distribution perpendicular to the annular plane. RESULTS: The change in annular height to commissural width ratio from diastole to systole did not alter following implantation (p >0.05). Out-of-plane systolic restraining forces were 0.2 ± 0.1 N and 0.8 ± 0.3 N (mean ± SEM) in the posterior and anterior commissural segments, respectively, without any difference in-between (p >0.1). Forces in both commissural segments were significantly lowered compared to previous measurements with a flat and stiff mitral annuloplasty ring (p <0.01). Mitral annular septal-lateral distance, area, and circumference in the commissural segments were decreased after implantation (p <0.05). The cross-annular distance between the commissural segments and the lengths of the anterior and posterior annular segments did not change following implantation (p >0.05). CONCLUSIONS: The new annuloplasty system design maintained annular 3D dynamics and provided a minimized out-of-plane restraining force distribution compared to earlier studies on flat rigid rings. This may have important implications in the selection of annuloplasty devices in order to increase repair durability.

Remodeling Mitral Annuloplasty Ring Concept with Preserved Dynamics of Annular Height.

BACKGROUND AND AIM OF THE STUDY: The configuration of the native annulus changes from nearly flat in the diastolic phase to saddle-shaped in the systolic phase. The present study was conducted to test a novel remodeling annuloplasty ring with built-in septal-lateral fixation and commissural axial flexibility so as to maintain the change in annular saddle shape. The study aim was to evaluate the in-vivo biomechanical performance of the novel annuloplasty ring, compared with the native valve and a semi-rigid and rigid annuloplasty ring. METHODS: All measurements were performed in vivo using a porcine model. A total of 28 pigs (bodyweight ca. 80 kg) were randomized to four groups: (i) with no ring; (ii) with a novel remodeling ring; (iii) with a semi-rigid ring (Physio I Ring, Edwards Lifesciences); and (iv) with a rigid ring (Classic Annuloplasty Ring, Edwards Lifesciences). Force measurements were performed using a dedicated transducer to determine remodeling capacity of the annuloplasty rings. Geometric parameters were measured by implanting sonomicrometry crystals along the mitral annulus. RESULTS: All ring groups significantly restricted the cyclic change of the mitral annulus compared with the 'no-ring' group. The change and maximum value of the annular height were maintained for the novel ring but were significantly decreased for the rigid and semi-rigid rings compared with the 'no-ring' group. Mitral annular force measurements confirmed that the overall remodeling capacity of the novel ring was comparable with the conventional ring groups, and significantly higher in the septal-lateral direction compared to the semi-rigid ring. CONCLUSIONS: In-vivo geometry and force measurements indicated that the intended design features of the new device were successfully provided. The novel ring concept with remodeling properties, combined with the advantages of a flexible annuloplasty ring, is unique. The maintenance of annular saddle shape and cyclic change in annular height may be an important step towards improved mitral valve repair.