Biodegradable External Stents Inhibit Saphenous Vein Graft Thickening in the Pig

Abstract

Aim: External, non-restrictive, macro-porous stents prevent neointima formation in porcine vein grafts and have been proposed as a therapeutic approach to the prevention of late vein graft failure. Since these stents are non-biodegradable and therefore may elicit deleterious long-term, inflammatory, infective and mechanical complications the effect of external macro-porous biodegradable (polyglactin) stents on neointimal and medial thickening in porcine vein grafts was investigated. Methods: Bilateral vein saphenous vein-carotid artery interposition grafting was performed in Large White pigs (22–36 kg, n = 6) with external placement of 8 mm diameter polyglactin stents on one side, the contralateral side acting as a control. One month after surgery, graft wall dimensions were measured on histological sections using computer-aided planimetry and immunocytochemistry undertaken for selected parameters. Results: Polyglactin stents significantly reduced medial thickening compared to the All grafts were patent at explantation. Intimal thickness was significantly lower (p < 0.05) in the stented grafts (0.11 ± 0.01 mm) compared to the unstented controls (0.18 ± 0.01 mm). Similarly, medial thickness was significantly lower (p < 0.05) in the stented grafts (0.24 ± 0.03 mm) compared to the unstented controls (0.43 ± 0.04 mm) mm. Grafts externally supported with polyglactin had a pronounced increase in inflammatory cells (in particular, giant cells) around the biodegradable stent compared to both unstented controls and previously studied Dacron stented grafts. The space between graft and stent had become organised into a neo-adventitia with abundant microvessels which stained positively for VEGF and lectin (markers of micorvessels and endothelial cells). Conclusions: An over-size biodegradable stent reduces medial thickening, a component of late vein graft failure in experimental grafts. If subsequent studies confirm the preservation of this beneficial effect when the stent biodegrades completely, this form of stent may have an advantage over permanent stent material in the clinical use of external stenting to prevent vein graft thickening and failure.