Neointimal vascularization and intimal thickening in response to self-expanding stents: A swine model

BACKGROUND: Neovascularization has been suggested as a biological response to vessel injury and associated with restenosis. Self-expanding (SE) stents generate a lasting force on the arterial wall and may lead to an increased arterial response with time. OBJECTIVES: To characterize the process of neovascularization with SE stents, and to correlate it with vascular injury, inflammation and intimal proliferation. METHODS: Sixty-nine SE stents were implanted in 37 non-atherosclerotic pigs. Detailed, multisection histological examination was performed at 15 days, 1, 3 and 6 months post-deployment. Neovascularization in addition to other histologic parameters where determined and scored. RESULTS: Intravascular-ultrasound-based average vessel diameter was 3.3 ± 0.04 mm; stent size was 3.75 ± 0.35 mm leading to an oversizing ratio of 1.14 ± 0.15. Intimal thickness (IT), inflammatory score (IFS) and vascularization score (VAS) reached peak values at three months (IT = 344 ± 202 μm, IFS = 0.91 ± 0.5, and VAS = 1.56 ± 0.8). In contrast, the injury score (INS) continued to increase at all time-points, with maximum value at six months (INS = 1.6 ± 0.7). Both vascularization and inflammation indices increased with an increase in the injury score (p <0.01). When vessels were divided according to vascularization score (VAS