Vein graft-coated stents for endovascular occlusion of canine experimental arteriovenous fistulae

Estudo da resposta tissular à endoprótese recoberta de jugular bovina em veia cava inferior de suínos

OBJETIVO: Avaliar a resposta tissular a uma endoprótese, com cobertura biológica heteróloga, implantada em veia cava inferior de suínos. MÉTODO: Desenvolvemos uma endoprótese auto-expansível, revestida com um segmento de jugular bovina, conservada por processo L-hydro e suturada em um stent de aço inoxidável 316L. O dispositivo introdutor utilizado foi a bainha de liberação da endoprótese aórtica Taheri-Leonhardt (Flórida, EUA). Foram implantadas endopróteses em 10 suínos, todas na veia cava infra-renal. Os animais foram submetidos à flebografia peroperatória. À necropsia, após 2 meses, cada endoprótese foi retirada em bloco e analisada macroscopicamente, visando a avaliação da perviedade, aderência aos tecidos vizinhos e incorporação à parede venosa; e, histopatologicamente, visando a resposta histológica ao enxerto. RESULTADOS: Na análise macroscópica, todas as endopróteses encontravam-se pérvias e totalmente incorporadas à parede venosa, porém seis apresentavam trabeculações grosseiras no seu interior e quatro algum grau de fibrose perivascular. Três animais desenvolveram linfocele, uma retroperitoneal e as outras na parede abdominal. No estudo histopatológico, observamos reação inflamatória granulomatosa tipo corpo estranho em todos os casos, sendo predominante na camada média (80%). CONCLUSÃO: O modelo estudado apresentou baixa trombogenicidade, corroborando com a eficácia do meio de conservação e material escolhidos; porém, baixa biocompatibilidade, provavelmente pelo obstáculo imunológico dos xenoenxertos e resposta tissular exagerada do território venoso.

Finite element analysis of covered microstents

Currently available neuroendovascular devices are inadequate for effective treatment of many wide-necked or fusiform intracranial aneurysms and intracranial carotid-cavernous fistulae (CCF). Placing a covered microstent across the intracranial aneurysm neck and CCF rent could restore normal vessel morphology by preventing blood flow into the aneurysm lumen or CCF rent. To fabricate covered microstents, our research group has developed highly flexible ultra thin (approximately 150 microm) silicone coverings and elastomerically captured them onto commercially available metal stents without stitching. Preliminary in vivo studies were conducted by placing these covered microstents in the common carotid artery of rabbits. The feasibility of using covered stents was demonstrated. However, the cover affected the deployment pressure and the stents failed occasionally during deployment due to tearing of the cover. Appropriate modeling of covered stents will assist in designing suitable coverings, and help to reduce the failure rate of covered microstents. The purpose of this study is to use the finite element method to determine the mechanical properties of the covered microstent and investigate the effects of the covering on the mechanical behavior of the covered microstent. Variations in the mechanical properties of the covered microstent such as deployment pressure, elastic recoil and longitudinal shortening due to change in thickness and material properties of the cover have been investigated. This work is also important for custom design of covered microstents such as adding cutout holes to save adjacent perforating arteries.

Transjugular intrahepatic portosystemic shunt with an autologous vein-covered stent: results in a swine model

PURPOSE

To investigate the feasibility, safety, and efficacy of an autologous vein-covered stent (AVCS) to prevent shunt stenosis in a porcine transjugular intrahepatic portosystemic shunt (TIPS) model.

MATERIALS AND METHODS

TIPS were created with an AVCS in 12 healthy domestic swine and with a bare stent in 10 additional swine. Tissue response was compared with use of venography, histology, and computerized morphometry analysis 2 weeks after implantation. Differences between AVCS and noncovered stents (established by a t-test), as well as regional differences within a single stent (established by an f test), were considered significant at P <.05.

RESULTS

Twenty of 22 TIPS procedures were technically successful. Ten of 12 shunts with an AVCS (83%) and two of 10 with bare stents (20%) remained patent (<50% diameter narrowing) at euthanasia 2 weeks later (P <.01). Histologic evaluation of harvested bare stents showed marked intimal hyperplasia (IH), composed of smooth muscle cells, myofibroblasts, and fibroblasts. In contrast, the AVCS were remarkably free of IH and thromboses. In patent TIPS in both groups, endothelial coverage of the luminal surface was present histologically. IH accounted for 57% (26.27/45.79) of total stent cross-sectional lumen area in the control group and 21% (8.34/39.54) in the AVCS group (P <.01), with no intrashunt differences (P >.05).

CONCLUSION

Based on short-term follow-up, AVCS significantly improved TIPS patency by prevention of both IH and in-stent thrombosis. TIPS created with an AVCS was feasible and safe in our porcine model.