Influence of stent design and material composition on procedure outcome

AbstractAlthough intravascular stents have received widespread application, significant limitations remain. In stent restenosis, the most pervasive problem affecting stents, is related in part to technical aspects of the device. Design features of the stent that influence outcome have been identified and optimized for improved performance. The influence of stent materials on critical aspects of healing, such as thrombotic, inflammatory, and hyperplastic responses, are less well understood. For this reason, significant progress in this area is lacking. Current stents have significant contamination with industrial impurities on the surface and in the bulk. This fact adds to the difficulties in interpreting the biologic reaction of the host to the device. Better understanding of the basic biologic interactions is the path to significant improvement. (J Vasc Surg 2002;36:1031-9.

Re-expansion of balloon-expandable stents after growth

AbstractObjectives. The purpose of this study was to evaluate the feasibility of re-expansion of balloon expandable intravascular stents and to examine the gross and histologic effects of re-expansion on vascular integrity.Background. Intravascular stents have been used successfully as an adjunct to balloon dilation of congenital pulmonary artery branch stenosis and postoperative stenosis of the pulmonary arteries in children. However, use of rigid stents in children could result in development of relative stenosis at the site of stent implantation with subsequent growth of the child.Methods. Stainless steel “iliac” stents were placed in the thoracic aorta of 10 normal juvenile swine by a transcatheter technique. Angiography and re-expansion were performed at a mean of 11 weeks (n = 9) and again at 18 weeks (n = 5). After euthanasia, the aortic specimens were removed for gross and histologic examination.Results. Stents were successfully implanted in 10 swine. Re-expansion was successfully performed in each animal at 11 weeks and at 18 weeks. Aortic growth produced a relative constriction of the aorta of 20% ± 10% (mean ± SD) at the site of stent implantation at both 11 and 18 weeks. Re-expansion produced a significant increase in mean stent diameter from 10.1 ± 1 mm to 12.3 ± 1.2 mm at 11 weeks and from 11.2 ± 0.7 to 13.5 ± 1.1 mm at 18 weeks after implantation (p < 0.001). Balloon dilation produced a relative increase in stent diameter of 21% ± 7% at 11 weeks and 18% ± 4% at 18 weeks. Stent re-expansion was accompanied by plastic deformation of the neointima without neointimal dissection. Where neointima was thick, there was no evidence of neointimal abrasion, but where neointima was thin, areas of localized neointimal abrasion were observed with focal fibrin and platelet adherence to the stent struts. There was no evidence of medial or adventitial hemorrhage or dissection produced by re-expansion.Conclusions. Re-expansion of intravascular stents is feasible after growth in juvenile swine without significant injury to neointima, media or adventitia. The results of this study support careful and selective use of intravascular stents as an adjunct to balloon dilation of congenital stenoses in children