Comparison of the novel Medtentia double helix mitral annuloplasty system with the Carpentier-Edwards Physio annuloplasty ring: morphological and functional long-term outcome in a mitral valve insufficiency sheep model

Abstract

Background: The prevalence of mitral regurgitation in cardiac diseases requires annuloplasty systems that can be implanted without excessive patient burden. This study was designed to examine the morphological and functional outcome of a new double helix mitral annuloplasty ring in an ovine model in comparison to the classical Carpentier-Edwards (CE) annuloplasty ring as measured by reduction of mitral regurgitation and tissue integration. The Medtentia annuloplasty ring (MAR) is a helical device that is rotated into the annulus self-restoring the valve geometry, enabling a faster fixation without the need of elaborate repair of the valve geometry. The ventricular part of the helical ring encircles the valve chords.

Methods: Twenty adult sheep were overpaced until 2+ level mitral valve regurgitation was achieved. Seven animals per group received either the MAR or the CE ring. Implantation was performed on-pump in a beating heart through the left atrial appendix. The animals were sacrificed 3.6 ± 0.3 months after surgery following an echocardiography for assessing mitral regurgitation as primary endpoint. The annuloplasty rings with surrounding tissue were harvested for histological analyses as secondary endpoints. The remaining six sheep received the MAR system and were sampled seven, nine or 12 months after surgery.

Results: Implantation time (p < 0.01) and perfusion time (p < 0.001) as clinical secondary endpoints were significantly shorter in the MAR group. Echocardiography follow-ups showed sufficient valve function repair in nearly all animals with a normalization of the ventricle diameters in both groups (group difference: p = 0.147). The weights of the hearts did not differ significantly. Histology revealed adequately covered atrial annuloplasty rings with functional endothelium and lack of excessive granulation tissue or fibrosis in all specimens. The ventricular projections of the MAR systems encircling the chordae tendineae were not completely covered with neointimal tissue, although in no case were microthrombi detected and no thromboembolic events were recorded.

Conclusions: The new MAR system is an easy to use annuloplasty system with a functional outcome comparable to that of the well-proven CE ring. Mitral valve regurgitation is effectively stopped both by restricting the pathological expansion of the annulus and by gathering the chords without thrombus formation.

Figures

Figure 1

The Medtentia annuloplasty ring. The atrial helix arm is covered by a cuff, the ventricular part is uncovered. The carbonated titanium surface effectively prevents cell adhesion and clotting.

Figure 2

Clinical parameters: Left ventricle diameters assessed by echocardiography before annuloplasty (a) and at the time of sacrifice (b). c, perfusion time, and d, ring implantation time. Boxplots with 25, 50 and 75th percentiles. Red line = mean.

Figure 3

Annuloplasty rings after sacrifice. a: Edwards-Carpentier annuloplasty ring seen from the atrial side 16 weeks after implantation. b: shows an example 14 weeks after implantation. Note the macroscopically complete coverage of the device with connective tissue and the absence of thrombi. c and d show the Medtentia annuloplasty ring 16 weeks after implantation. Note that the ventricular aspect is only partially covered with endocardial tissue. e and f: Medtentia annuloplasty ring nine months after harvesting from the atrial (e) and ventricular aspect. Note the partially missing coverage from the ventricular aspect.

Figure 4

Microscopic findings in reference annuloplasty rings (left panel, a, c, e; and Medtentia annuloplasty ring (right panel, b, d, f). a & b: H&E histology of the newly formed endocardial tissue. Note the significantly thicker layer in the reference sample (bar = 500 μm) than in the Medtentia annuloplasty ring (bar = 200 μm). c &d: anti-Factor VIII staining reveals a functional endothelium on the surface (arrowheads) and some subendocardial vessels (arrows). e &f: anti PCNA stains show the fraction of mitotic and postmitotic cells with brownish nuclei. Bars in b-f = 200 μm.

Figure 5

Implant integration as seen in polished MMA microsections and scanning electron microscopy. Left panel from reference CE animal 16 weeks after implantation, right images from MAR animal. The coating meshes of both annuloplasty rings are fully penetrated by cells and connective tissue. The thicknesses of the layer seem to be larger in the reference. In b, the atrial ring is to the right, the ventricular part is not completely covered with newly formed tissue. d shows details of the sleeve integration. The insets in e and f show the complete endothelial coverage. Bars in a-d = 500 μm.