Modulation of Healthy Pig Coronary Arteries by Self-Expanding Stents

Objectives: To evaluate the expansion ratio of a self-expanding stem over time, and the chronic effect of stent pressure on the vessel wall . Methods: Self-expanding stents, developed by Medtronic Inc. (Minneapolis, MN, USA) and the Rouen group (Letac, Cribier, France), were implanted in 21 normal pig coronary arteries. Animals were sacrificed after recatheterization at 1 day (group I, n = 4), I week (group 2, n = 3), 3 weeks (group 3, n = 5), or 8 weeks (group 4, n = 4). Histological morphometry of the vessel medial and neointimal layers was performed. Changes were related to the, stent diameter and. its force on the vessel wall . Results: The stent expansion ratio gradually increased from 73% to 93% after 8 weeks, which implicates that radial force decreased concomitantly from 0.10 N to 0.03 N. Media compression under the rods ranged from 4l%-66% immediately after stent implantation. The mean compression was unrelated to stent expansion and remained nearly the same (40%-50%) during follow-up. Individual media rod compression ranged from 5%-95%. The neointimal layer on top of the rods increased until the third week after stent implant (neointimal thickness 211 ± 108 μm). The layer significantly decreased at 8 weeks (neointimal thickness 65 ± 9 μm). The cross-sectional neointimal area increased gradually only at the end of the stent during the 8-week follow-up . Conclusions: The self-expanding stent implanted in normal pig coronary arteries reached a gradual relaxation state 8 weeks after implantation due to the persistent radial force. This radial force induces medial wall compression, which was only positively related to the thickness of the neointimal layer at 3 weeks after implant . (J Interven Cardiol 1996;9:45–52)