Utilization of shape memory in external vein-graft meshes allows extreme diameter constriction for suppressing intimal hyperplasia: A non-human primate study

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Abstract

Objective

Constrictive external Nitinol meshes have been shown to suppress neointimal tissue formation and preserve endothelial integrity in vein grafts. As this mitigating effect increased with the degree of constriction, we investigated whether extreme constriction was possible without leading to detrimental luminal encroachment.

Methods

A senescent non-human primate model (Chacma baboons/bilateral femoral interposition grafts) mimicking the clinical size-mismatch between vein grafts and run-off arteries was used. Control grafts were either untreated (group 1) or spray-coated with fibrin glue (group 2). Nitinol meshes constricting the lumen by ≤80% (group 3) were compared with longitudinally pleated meshes of identical circumference that constricted the lumen by >90% (group 4). Anastomotic size mismatch at implantation was expressed as quotient of cross-sectional area of run-off artery to vein graft (Q C).

Results

At 6 months, all vein grafts without mesh support showed thick eccentric layers of neointimal tissue (group 1: 348 ± 130 μm [QC median at implant 0.19]; group 2: 318 ± 142 μm [QC median at implant 0.17]). Fibrin glue-spraying had no effect. In contrast, neointimal tissue was absent in all mesh-supported grafts (P< .007 in all cases) both at 6 weeks/6 months (group 3: 7.5 ± 8.8 μm and 2.5 ± 4.4 μm [QC median at implant 1.47]; group 4: 1.3 ± 0.6 μm and 3.8 ± 5.6 μm [QC median at implant 3.09]). Except for mild tissue buckling (fold height <356 μm) in one group 3 graft, none of the mesh-constricted grafts showed wall folds. Endothelial coverage was only complete in the mesh-supported groups (100% in group 3 and 4 vs 85 ± 14%;P< .023 in group 1). Fibrin glue alone (52 ± 48%) did not preserve endothelialization of control grafts (P< .38).

Conclusion

Extreme vein graft constriction using external Nitinol meshes is possible without detrimental tissue buckling. Although moderate constriction was found to be sufficient for mitigating diffuse intimal hyperplasia and endothelial detachment, extremer constriction may occasionally be required to eliminate luminal irregularities.

Clinical Relevance

Neointimal proliferation holds a key to vein graft failure. Among the many factors contributing to the development of flow-limiting intimal hyperplasia, low shear stress and high circumferential wall stress play a key role. Constricting vein grafts with external meshes counters these forces through higher flow velocity and smaller diameters. Eliminating luminal irregularities additionally alleviates turbulences, a main trigger of focal stenoses. Being able to distinctly constrict vein grafts without creating folds protruding into the lumen will offer a clinical tool expected to distinctly improve the performance of vein grafts.

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