Macro-porosity is necessary for the reduction of neointimal and medial thickening by external stenting of porcine saphenous vein bypass grafts

Background: placing external non-restrictive macro-porous stents around por cine vein grafts prevents neointima formation and medial thickening in both the short and long term. Whether the porosity of the stent material influe nces this effect, however, has not been determined. Therefore, the effect o n neointimal and medial thickening of external macro-porous (polyester) and micro-porous (polytetrafluorethylene) stents of equal diameter were compar ed. The effect on expression of platelet-derived growth factor (PDGF), a po tent mediator of vascular smooth muscle cell migration and proliferation an d its. receptors was also investigated. Methods and results: saphenous vein -carotid artery interposition grafting was performed in Landrace pigs with external placement of 8 mm diameter macro- and micro-porous stents contrala terally. One month after surgery, graft wall dimensions, PDGF and PDGF rece ptor expression and cell proliferation using proliferating cell nuclear ant igen (PCNA) were measured on histological sections. Macro-porous stents sig nificantly reduced neointimal and medial thickening compared with micro-por ous stents (0.1 +/- 0.02 vs. 0.25 +/- 0.03 mm, P < 0.002, and 0.10 <plus/mi nus> 0.02 vs. 0.17 +/- 0.02 mm, P < 0.014, respectively). Macro-porous sten ts significantly reduced the percentage of cells: expressing PDGF and PCNA, compared with micro-porous stents (36 <plus/minus> 9 vs. 80 +/- 7, P < 0.0 02. and 11 <plus/minus> 3 vs. 21 +/- 2, P < 0.02, respectively). The percen tage of cells expressing PDGF receptors was similar with both the stent typ es. Adventitial microvessel formation occurred across macro-porous stents b ut was markedly suppressed by micro-porous stents. Conclusions: porosity is crucial to the efficacy of external stents in reducing neointima formation in porcine vein grafts. Decreases in PDGF expression and cell proliferatio n accompany the reduction in neointima formation. In addition, macro-porous stents allow adventitial microvessels to connect with the vasculature outs ide the stent, thereby potentially improving oxygenation. Although external stenting is highly effective in reducing neointima formation after vein gr afting, the properties of the stent material necessary for this effect have not been defined. This study establishes that macro-porosity is one essent ial feature required to reduce PDGF expression cell proliferation and neoin tima formation. <(c)> 2001 Elsevier Science Ireland Ltd. All rights reserve d.