Impact of chronic outward force on arterial responses of proximal and distal of long superficial femoral artery stent

Background Self-expanding nitinol stent (SENS) implantation is commonly oversized in the superficial femoral artery (SFA), and leads to chronic outward force (COF) and in-stent restenosis (ISR). This study aimed to investigate the impact of COF of oversizing SENS on ISR of SFA. Methods In patients with implanted SENS in SFA, intimal hyperplasia especially between proximal segment and distal segment was evaluated by quantitative angiography, and the impact of COF on mid-term angiographic outcomes was investigated. In addition, porcine model with implanted SENS was used to evaluate the impact of COF on angiographic and histopathologic outcomes at 1 month. Excised stented arteries were evaluated by histopathologic analysis. Results We analyzed 65 SENS in 61 patients with follow-up angiography at 6 months to 1 year. The baseline diameter was 6.8 [+ or -] 0.71 mm and length were 97.0 [+ or -] 33.8 mm for the SENS. The ratio of the diameter of the stent to the reference vessel was 1.3 [+ or -] 0.24 at the proximal portion and 1.53 [+ or -] 0.27 at the distal portion (P < 0.001). In the long SFA stent, stent-to-vessel ratio was significantly higher in the distal stent than in the proximal stent (1.3 [+ or -] 0.2 vs. 1.55 [+ or -] 0.25, P = 0.001). ISR incidence was higher at the distal stent (37.3% vs 52.6%, P = 0.029). All 11 pigs survived for 4 weeks after SENS implantation. The vessel diameter was 4.04 [+ or -] 0.40 mm (control group) vs 4.45 [+ or -] 0.63 mm (oversized group), and the implanted stent diameter was 5.27 [+ or -] 0.46 mm vs. 7.18 [+ or -] 0.4 mm (P = 0.001). The stent-to-vessel diameter ratio was 1.31 [+ or -] 0.12 versus 1.63 [+ or -] 0.20 (P < 0.001). After 4 weeks, restenosis % was 29.5 [+ or -] 12.9% versus 46.8 [+ or -] 21.5% (P = 0.016). The neointimal area was 5.37 [+ or -] 1.15 mm.sup.2 vs. 8.53 [+ or -] 5.18 mm.sup.2 (P = 0.05). The restenosis % was 39.34 [+ or -] 8.53% versus 63.97 [+ or -] 17.1% (P = 0.001). Conclusions COF is an important cause of restenosis in the distal portion of the SFA stent. Optimal sizing of the SFA stent is important to reduce the incidence of restenosis. Therefore, COF was an important factor of restenosis following distal SFA stenting. Keywords: Chronic outward force, Superficial femoral artery, Self-expanding nitinol stents, Stent oversizing, Histomorphometry