Restenosis and Asymmentric Expansion of Stents in the Aorta of Hypercholesterolemic Rabbits

pp 174-179

Abstract

Assymetric expansion (AE) of stents is a heterogenerous distribution of the stent within the circumference of the arterial wall caused by distortions in the normal architecture of the expanded stent. This could relate to an increased aggression of the vessel wall in the location where greater metal concentration is found with a consequent increase of endothelial proliferation. Previous experimental studies seem to support this mechanism. The objective of this study was to explore the effect of AE on neointimal hyperplasia in the  aorta of hypercholesterolemic rabbits and to assess to which extent the degree of overexpansion of the stent due to high pressure would influence its configuration. 

Twenty tubular 316L stainless steel stents were implanted in the abdominal aorta of hypercholesterolemic New Zealand rabbits. Intravascular ultrasound (IVUS) was performed during the procedure and after 8 weeks previous to sacrifice. IVUS analysis was employed to measure the degree of elastic retraction of the stents and to classify the stents in symmetric and asymmetric. For the latter, all the cuts obtained were integrated in a planar drawing during the mechanical withdrawal of the IVUS at 1 mm/sec (stereomorphometry). The histological analysis of neointimal growth was performed comparing the asymmetric stents (A) with the symmetric (S) ones, and the quadrants with increased metal concentration (M+) were compared to those where the wall was more metal free (M-). Seventeen animals completed the follow-up period and an early mortality rate of 15% was recorded. 

Increased stent neointimal hyperplasia was observed in the stents defined as asymmetric (264.65 vs. 185.00 microns) (p=0.025) and in zones with more metal concentration (279.90 vs. 205.34 microns) (p=0.022).

No significant differences were observed regarding symmetry and amount of neointimal hyperplasia when comparing both implant techniques. The mechanical retraction was significantly higher in the overexpanded 3.0 stents, (0.28±0.18 vs. 0.10± 0.11mm) (p<0.001).

Conclusion

In accordance with previous evidence  and as suggested by the involved physiopathological mechanisms, the assymetric expansion of stents in the abdominal aorta of hypercholesterolemic rabbits causes a significant increase of neointimal hyperplasia due to an increased hyperplasia in areas with increased metal concentration.