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Stent oversizing has been suggested as a cause of restenosis in superficial femoral artery (SFA) in previous animal studies with stents lacking reported clinical performance. In this study, we investigated whether oversizing of a clinically available stent also promotes restenosis in a porcine model, and explored alternative predictors.
A total of 12 self-expanding bare metal stents (Misago, Terumo) were implanted in porcine femoral arteries. In each animal, two stents were deployed bilaterally in different stent-to-artery ratios: >1.4 in oversized arms and ≤1.4 in normal-sized arms. After implantation for 3 weeks (n=3) and 3 months (n=3), quantitative vessel angiography, histopathology and histomorphometry were performed. Ki67-immuno reactive cells were quantified in the neointima to assess proliferation activity.
No significant differences were found between oversized and normal-sized arms in percent diameter/area stenosis, neointimal area, and vessel wall injury score at 3 weeks and 3 months, in spite of more stent expansion in oversized arm at 3 months (1.3±0.4 mm vs. 0.4±0.2 mm, P<0.001). On the other hand, neointimal thickness was positively correlated at 3 weeks with scores for histopathological changes indicative of repetitive intra-neointima trauma (i.e. peri-strut hemorrhage, angiogenesis and fibrin deposition) independently of oversizing. Neointimal area was enlarged in arterial segments apparently bended during hip flexion compared with non-bended segments at both 3 weeks (12.4±3.6 mm2 vs. 8.3±2.1 mm2, P<0.001) and 3 months (24.5±4.0 mm2 vs. 14.5±5.0 mm2, P<0.05). Proliferation activity in outer (i.e. peri-strut) neointima in bended segments tended to be higher than that in non-bended segments at 3 weeks, and was very low and equivalent in both areas at 3 months.
This study showed that oversizing of a clinically available stent in porcine femoral artery did not promote neointimal formation without severe vessel wall injury. Instead, intra-neointima injury, which was topographically attributable to repetitive physical friction between stent and neointima due to pelvic-limb motion, may be a better predictor of neointimal enlargement.
ENDOVASCULAR: Peripheral Vascular Disease and Intervention