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Home > Vascular Annual Meeting > zhao_long_term_histological

Long-Term Histological Effects of Oversizing Self Expanding Nitinol Stents Implanted in the Peripheral Arteries of a Porcine Model

H. Zhao¹, A. Nikanorov¹, R. Virmani², R. Jones², E. Pacheco², L.B. Schwartz.^1
1Abbott Vascular, Santa Clara, Calif.;²CVPath, Gaithersburg, Md.

OBJECTIVES: Self-expanding stent implantation has been championed as a means of improving the results of peripheral endovascular intervention. Similar to balloon expandable stents, self-expanding stents are commonly oversized in relation to target arteries in order to assure optimal wall apposition and prevent migration. The histological consequences of oversizing have not been well studied, however, nor has the kinetics of continued stent expansion following deployment. The purpose of this experimental study was to examine the effects of self-expanding stent oversizing with respect to, 1) the kinetics of continued stent expansion post-deployment, and 2) the long-term histologic effects of oversizing.

METHODS: Pairs of overlapped 8x28 mm Nitinol self-expanding stents were implanted into the iliofemoral arteries of 14 Yucatan Swine. Due to variations in target artery size, the nominal-stent-diameter-to-artery ratio ranged from 1.2:1 to 1.9:1 (20-90% oversizing). Expanded stent diameter was assessed by quantitative angiography at the time of implantation and after six months. Following angiography at six months, stented arteries were perfusion-fixed, sectioned and stained for histologic analysis.

RESULTS: Immediately following implantation, the 8 mm nominal diameter stents were found to be expanded to a range of 4.7-7.1 mm, largely conforming to the diameter of the recipient target artery. The stents continued to expand over time, however, and all stents had enlarged to near their 8 mm nominal diameter by six months (mean 7.7±0.5 mm). The histologic effects of oversizing were profound with marked increases in injury and luminal area stenosis, including a statistically significant linear correlation between nominal-stent-diameter-to-artery ratio and area stenosis (Figure 1; p=0.0001).

CONCLUSIONS: In this experimental model of peripheral endovascular intervention, oversized self-expanding Nitinol stents are constrained by their target artery diameter upon implantation, but expand to their nominal diameter within six months. Severe oversizing (nominal-stent-diameter-to-artery ratio >1.4:1) results in a profound long-term histologic response including exuberant neointimal proliferation and luminal stenosis.

AUTHOR DISCLOSURES: H. Zhao, Abbott; A. Nikanorov, Abbott; R. Virmani, Abbott; R. Jones, Abbott; E. Pacheco, Abbott; L.B. Schwartz, Abbott.