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

Results of previous studies with stents coated with 'biocompatible' polymers showed that severe inflammatory reaction and subsequent in-stent restenosis may occur.

To evaluate the contribution of granulomatous reaction from uncoated stents to formation of in-stent neointimal hyperplasia.

Uncoated stainless-steel stents were implanted into 21 porcine coronary arteries without oversizing and harvested after 2 months (n = 6) or 6 months (n = 7). We compared the stents with granulomatous reaction with those without foreign-body reaction.

Granulomatous reactions occurred in five 21 stents and resulted in there being significantly greater in-stent neointimal hyperplasia than there was with stents without foreign-body reaction (angiographic diameter stenosis 45 +/- 36 versus 16 +/- 16%, area of neointimal 3.30 +/- 1.4 versus 1.22 +/- 0.4 mm2, 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 comparison). This increase in amount of neointima was accompanied by significantly greater proliferating cell nuclear antibody staining (15 +/- 5 versus 3 +/- 2%, P < 0.05) in the presence of a granuloma near the stent struts.

A localized granulomatous reaction is associated with a significant increase in amount of stent neointima and proliferation of cells. Thus, permanent stent implants may provoke granulomatous vascular reactions that may affect late-healing responses and clinical outcomes.