Granulomatous 'foreign body reactions' contribute to exaggerated in-stent restenosis

Background Results of previous studies with stents coated with 'biocompatib le' polymers showed that severe inflammatory reaction and subsequent in-ste nt restenosis may occur, Objective To evaluate the contribution of granulomatous reaction from uncoa ted stents to formation of in-stent neointimal hyperplasia. Methods Uncoated stainless-steel stents were implanted into 21 porcine coro nary arteries without oversizing and harvested after 2 months (n = 6) or 6 months (n = 7). We compared the stents with granulomatous reaction with tho se without foreign-body reaction, Results Granulomatous reactions occurred in five of 21 stents and resulted in there being significantly greater in-stent neointimal hyperplasia than t here was with stents without foreign-body reaction (angiographic diameter s tenosis 45 +/- 36 versus 16 +/- 16%, area of neointimal 3.30 +/- 1.4 versus 1.22 +/- 0.4 mm(2), thickness of neointima 0.46 +/- 0.29 versus 0.11 +/- 0 .09 mm, stenosed area 56 +/- 24 versus 20 +/- 7%, P<0.01 for each compariso n), This increase in amount of neointima was accompanied by significantly g reater proliferating cell nuclear antibody staining (15+/-5 versus 3 +/- 2% , P< 0.05) in the presence of a granuloma near the stent struts. Conclusions A localized granulomatous reaction is associated With a signifi cant increase in amount of stent neointima and proliferation of cells, Thus , permanent stent implants may provoke granulomatous vascular reactions tha t may affect late-healing responses and clinical outcomes. Coronary Artery Dis 10:9-14 (C) 1999 Lippincott Williams & Wilkins.