STENT-INDUCED INTIMAL HYPERPLASIA - ARE THERE FUNDAMENTAL DIFFERENCESBETWEEN FLEXIBLE AND RIGID STENT DESIGNS

PURPOSE: To evaluate possible differences in neointimal development re sulting from overdilation of rigid versus flexible vascular stents. MA TERIALS AND METHODS: Twelve vascular sheaths were placed bilaterally t hrough femoral arteries in six swine. After angiographic measurement, 12 stents (six flexible and six rigid) were balloon expanded to 8-mm d iameters in 12 6-mm iliac arteries (approximately 30% overdilation). A ll stents were similar in surface area, gauge, and type of wire (tanta lum). The primary difference was longitudinal flexibility (low hoop st rength) versus rigidity (high hoop strength). Stents were studied with angiography and intravascular ultrasound 5 weeks after implantation. The animals were killed, and the stented segments were removed and exa mined histologically. RESULTS: Rigid stents maintained larger diameter s than flexible stents: mean, 6.52 mm versus 5.82 mm (mean difference, 0.70; standard deviation [SD], 0.47; confidence interval [CI], +/- 0. 49; P < .05). In addition, rigid stents developed a thicker, eccentric neointimal reaction relative to flexible stents: mean 1.08 mm versus 0.74 mm (mean difference, 0.338; SD, 0.315; CI, +/- 0.331; P < .05). C ONCLUSION: Rigid stents maintain larger diameters over the long term r elative to flexible stents when overdilated in normal swine arteries. However, a thicker neointima develops within the lumen of rigid stents at follow-up (greater late loss).