Ex vivo biomechanical analysis of flexible versus rigid annuloplasty rings in mitral valves using a novel annular dilation system

Abstract

Background Mitral annuloplasty rings restore annular dimensions to increase leaflet coaptation, serving a fundamental component in mitral valve repair. However, biomechanical evaluations of annuloplasty rings are lacking. We aim to biomechanically analyze flexible and rigid annuloplasty rings using an ex vivo mitral annular dilation model. Methods Juvenile porcine mitral valves (n = 4) with intercommissural distance of 28 mm were dilated to intercommissural distances of 40 mm using a 3D-printed dilator and were sewn to an elastic mount. Fiber bragg grating sensors were anchored to native chordae to measure chordal forces. The valves were repaired using size 28 rigid and flexible annuloplasty rings in a random order. Hemodynamic data, echocardiography, and chordal force measurements were collected. Results Mitral annular dilation resulted in decreased leaflet coaptation height and increased mitral regurgitation fraction. Both the flexible and rigid annuloplasty rings effectively increased leaflet coaptation height compared to that post dilation. Rigid ring annuloplasty repair significantly decreased the mitral regurgitation fraction. Flexible annuloplasty ring repair reduced the chordal rate of change of force (7.1 ± 4.4 N/s versus 8.6 ± 5.9 N/s, p = 0.02) and peak force (0.6 ± 0.5 N versus 0.7 ± 0.6 N, p = 0.01) compared to that from post dilation. Rigid annuloplasty ring repair was associated with higher chordal rate of change of force (9.8 ± 5.8 N/s, p = 0.0001) and peak force (0.7 ± 0.5 N, p = 0.01) compared to that after flexible ring annuloplasty repair. Conclusions Both rigid and flexible annuloplasty rings are effective in increasing mitral leaflet coaptation height. Although the rigid annuloplasty ring was associated with slightly higher chordal stress compared to that of the flexible annuloplasty ring, it was more effective in mitral regurgitation reduction. This study may help direct the design of an optimal annuloplasty ring to further improve patient outcomes.

Repairable ex vivo model of functional and degenerative mitral regurgitation

“…Previous ex vivo models of FMR are classified into (i) models using the whole heart or the left side of the heart [ 9 , 12–16 ] and (ii) models using only the excised mitral complex [ 10 , 11 , 17–20 ]. In the former type, the anatomical structure of the whole heart is preserved, which enables accurate simulation of the complex physiological characteristics of FMR.…”

“…However, this value was achieved when the annulus was dilated at maximum, which meant that this amount was the upper limit for the model. Another study on an excised mitral complex using a different dilator reported a regurgitant fraction of 23.2% [ 11 ].…”

Utilization of Engineering Advances for Detailed Biomechanical Characterization of the Mitral–Ventricular Relationship to Optimize Repair Strategies: A Comprehensive Review

“…Multiple formats of annuloplasty rings exist, including rigid, semi-rigid, and flexible types, as well as partial or complete ring or band formats, and flat or saddle-shaped geometries [166]. While rigid, semi-rigid, and flexible annuloplasty rings have been shown to improve mitral annular circumference and leaflet coaptation compared to no annuloplasty ring, only flexible annuloplasty rings were found to decrease both the chordal forces and maximum rate of change of forces compared to pre-procedural conditions [65,167]. In contrast, rigid annuloplasty rings were associated with a higher rate of change of force compared with pre-procedural conditions, which may reflect the rigidity of the implant [167].…”

“…While rigid, semi-rigid, and flexible annuloplasty rings have been shown to improve mitral annular circumference and leaflet coaptation compared to no annuloplasty ring, only flexible annuloplasty rings were found to decrease both the chordal forces and maximum rate of change of forces compared to pre-procedural conditions [65,167]. In contrast, rigid annuloplasty rings were associated with a higher rate of change of force compared with pre-procedural conditions, which may reflect the rigidity of the implant [167]. Saddle-shaped annuloplasty rings were shown to improve the distribution of forces across the annulus when compared with flat annuloplasty rings, indicating that reinforcement of the annulus in a more physiologic state improves how the forces are handled by the mitral valve [66].…”

“…Bhattacharya and He conducted a biomechanical analysis of annular tension after TEER in posterior and anterior leaflet prolapse in an ex vivo bioreactor and found that TEER does not restore annular tension to physiologic values, and therefore may leave patients at increased risk of progressive annular dilation and recurrent MR [173]. Using the Stanford ex vivo simulator [7,32,42,106,147,149,167], it was recently shown that, in contrast to surgical neochordal repair, application of a MitraClip does not normalize the forces exerted on the PMs, despite similar reductions in MR [174]. Computationally, Zhang and colleagues [2019] also demonstrated that this device induces abnormal strains in the ventricular wall.…”