Neointimal hyperplasia in low-profile Nitinol stents, Palmaz stents, and Wallstents: a comparative experimental study.

PURPOSE: To compare neointima formation following insertion of low-profile Nitinol stents, Palmaz stents, and Wallstents. METHODS: Nitinol stents, Palmaz stents, and Wallstents similar in size were transfemorally inserted into the iliac arteries of 12 sheep. Four stents per sheep were deployed; the position of the stents was varied so that each type of stent was placed in each position (right or left, proximal or distal) with equal frequency. Stent patency was followed by angiography. Six sheep were euthanized after 1 month, and the remaining six after 6 months. Iliac arteries were removed en bloc and prepared for histological examination. Neointimal and medial thickness were measured by light microscopy, and measurements were analyzed statistically. RESULTS: Mean neointimal thickness both over (NO) and between (NB) the stent struts was greater in Wallstents (NO = 0.341 mm, NB = 0.368 mm) than in the Nitinol (NO = 0.260 mm, NB = 0.220 mm) and Palmaz stents (NO = 0.199 mm, NB = 0. 204 mm), but differences were not significant (p > 0.05). Medial atrophy in the area between the stent struts was greater in Wallstents compared with Nitinol and Palmaz stents (p < 0.007 and p < 0.02, respectively); in the area under the stent struts there was a significant difference only between Palmaz stents and Wallstents (p < 0.02). CONCLUSION: Under defined experimental conditions, none of the three types of stent appears to be preferable to the others regarding neointima formation in the short- to mid-term follow-up period.

Experimental arterial stent placement. Comparison of a new Nitinol stent and Wallstent.

RATIONALE AND OBJECTIVES: To compare technical aspects and neointima formation of a new Nitinol stent and a Wallstent. METHODS: A Nitinol sten and a Wallstent were placed into the iliac arteries of 14 sheep (total of 28 stents) and followed angiographically. Seven sheep were killed after 1 month and 7 after 4.5 months. Examination of histologic specimen by light microscopy was performed to determine neointimal and medial thickness inside the stents. Measurements were analyzed statistically. RESULTS: Neointima was thicker in Nitinol stents (N) than in Wallstents (W) (P < 0.004), both adjacent to (W = 0.265 mm, N = 0.596 mm) and between the stent wires (W = 0.177 mm, N = 0.361 mm). Because of poor radiopacity and the Crochê releasing technique, delivery was more difficult with Nitinol stents. High-grade stenosis was found in two Nitinol stents at 1 and 4.5 months of follow-up, respectively. One Wallstent was insufficiently incorporated into the vessel wall. CONCLUSIONS: The observed difference in neointima formation that may be caused by differences in design, mechanical properties or the metal alloy of the stents probably is too insignificant to be relevant to patency of large arteries. However, it may be relevant in small vessels such as coronary arteries.