MODULATION OF HEALTHY PIG CORONARY-ARTERIES BY SELF-EXPANDING STENTS

Objectives: To evaluate the expansion ratio of a self-expanding stent over time, and the chronic effect of stent pressure on the vessel wall . Methods: Self-expanding stents, developed by Medtronic Inc. (Minneap olis, MN, USA) and the Rouen group (Letac, Cribier, France), were impl anted in 21 normal pig coronary arteries. Animals were sacrificed afte r recatheterization at I 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 front 73 % to 93% after 8 weeks, which implicates that radial force decreased c oncomitantly from 0.10 N to 0.03 N. Media compression under the rods r anged from 41%-66% immediately after stent implantation. The mean comp ression was unrelated to stent expansion and remained nearly the same (40%-50%) during follow-up. Individual media rod compression ranged fr om 5%-95%. The neointimal layer on top of the rods increased until the third week after stent implant (neointimal thickness 211 +/- 108 mu m ). The layer significantly decreased at 8 weeks (neointimal thickness 65 +/- 9 mu m). The cross-sectional neointimal al-ea increased gradual ly only at the end of the stent during the 8-week follow-up. Conclusio ns: 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 co mpression, which was only positively related to the thickness of the n eointimal layer at 3 weeks after implant.