DynaRing: A Patient-Specific Mitral Annuloplasty Ring With Selective Stiffness Segments

Annuloplasty ring choice and design are critical to the long-term efficacy of mitral valve (MV) repair. DynaRing is a selectively compliant annuloplasty ring composed of varying stiffness elastomer segments, a shape-set nitinol core, and a cross diameter filament. The ring provides sufficient stiffness to stabilize a diseased annulus while allowing physiological annular dynamics. Moreover, adjusting elastomer properties provides a mechanism for effectively tuning key MV metrics to specific patients. We evaluate the ring embedded in porcine valves with an ex-vivo left heart simulator and perform a 150 million cycle fatigue test via a custom oscillatory system. We present a patient-specific design approach for determining ring parameters using a finite element model optimization and patient MRI data. Ex-vivo experiment results demonstrate that motion of DynaRing closely matches literature values for healthy annuli. Findings from the patient-specific optimization establish DynaRing's ability to adjust the anterior-posterior and intercommissural diameters and saddle height by up to 8.8%, 5.6%, 19.8%, respectively, and match a wide range of patient data.

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

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.

Annular and subvalvular dynamics after extracellular matrix mitral tube graft implantation in pigs

OBJECTIVES

Entire mitral valve reconstruction with an extracellular matrix tube graft is a potential candidate to overcome the current limitations of mechanical and bioprosthetic valves. However, clinical data have raised concern with respect to patch failure. The aim of our study was to evaluate the impact of extracellular matrix mitral tube graft implantation on mitral annular and subvalvular regional dynamics in pigs.

METHODS

A modified tube graft design made of 2-ply extracellular matrix was used (CorMatrix®; Cardiovascular Inc., Alpharetta, GA, USA). The reconstructions were performed in an acute 80-kg porcine model (N = 8), where each pig acted as its own control. Haemodynamics were assessed with Mikro-Tip pressure catheters and mitral annular and subvalvular geometry and dynamics with sonomicrometry.

RESULTS

Catheter-based peak left atrial pressure and pressure difference across the mitral and aortic valves in the reconstructions were comparable to the values seen in the native mitral valves. Also comparable were maximum mitral annular area (755 ± 100 mm2), maximum septal-lateral distance (29.7 ± 1.7 mm), maximum commissure-commissure distance (35.0 ± 3.4 mm), end-systolic annular height-to-commissural width ratio (10.2 ± 1.0%) and end-diastolic interpapillary muscle distance (27.7 ± 3.3 mm). Systolic expansion of the mitral annulus was, however, observed after reconstruction.

CONCLUSIONS

The reconstructed mitral valves were fully functional without regurgitation, obstruction or stenosis. The reconstructed mitral annular and subvalvular geometry and subvalvular dynamics were found in the same range to those in the native mitral valve. A regional annular ballooning effect occurred that might predispose to patch failure. However, the greatest risk was found at the papillary muscle attachments.

Mitral Valve Posterior Leaflet Reconstruction Using Extracellular Matrix: In Vitro Evaluation

PURPOSE

To investigate the anatomical and functional effects of complete surgical reconstruction of the posterior mitral leaflet and associated chordae tendineae with a patch made of 2-ply small intestinal submucosal extracellular matrix in vitro.

METHODS

Seven explanted mitral valves with intact subvalvular apparatus from 80-kg pigs were evaluated in a left heart simulator and served as their own controls. After testing the native valve, the mitral posterior leaflet and associated chordae tendineae were excised and reconstructed by using the 2-ply small intestinal submucosa extracellular matrix patch. The characterization of the reconstruction was based on geometric data from digital images, papillary muscle force, annular tethering force and leaflet pressure force.

RESULTS

The reconstructed valves were fully functional without regurgitation, tearing or rupture during incrementally increased pressure from 0 to 120 mmHg. The leaflet areas were preserved after reconstruction, with a normal configuration of the coaptation line. However, the coaptation midpoint moved posteriorly after reconstruction (A2: 15.8 ± 1.4 vs. 18.9 ± 1.5 mm, p = 0.002, diff = 3.1 mm, 95% CI 1.3 to 4.8 mm). The anterior papillary muscle force increased significantly (3.9 vs. 4.6 N, p = 0.029, diff = 0.7 N, 95% CI 0.1 to 1.4 N at 120mmHg) after reconstruction. The posterior papillary muscle force, leaflet pressure force and annular pressure force did not change significantly.

CONCLUSIONS

In this in vitro model, mitral valve anatomy and function were comparable between the native mitral valve and our new surgical technique for complete reconstruction of the posterior mitral leaflet and associated chordae tendineae. These promising results warrant further in vivo evaluation.