First results in an animal model on stents sheathed with a polytetrafluoroethylene membrane.

Objectives: Mechanisms of restenosis after coronary stent implantation incl ude marked intimal proliferation as well as vascular tissue protrusion thro ugh the meshes. Thus, stent sheathed with membranes may be an alternative t o improve the long-term outcome. Methods: Seventeen cylindric serpentine sh aped 316L stainless steel stents (nominal diameter 3.0 mm, length 15 mm) li ned and covered by a polytetrafluoroethylene (PTFE) membrane and 10 unsheat hed devices were implanted into the iliac arteries of 14 New Zealand White Rabbits for an observation period of 1 - 10, 11 - 20, and 21 - 30 weeks. Af ter sacrificing the animals, specimens were harvested, fixed in formalin, p rocessed in paraffin, serially sliced into 5 mum thick preparations, and st ained (hematoxylin & eosin, elastica von Gieson). Results: The polytetraflu oroethylene membrane stents increased the vascular lumen significantly (p < 0.04) to 1185.3 - 1620.4 <mu>m compared with the native segments (655.6 +/ - 268.8 mum). In the stainless steel stents the lumen decreased from 1873.1 mum to 719.1 mum. None of the devices penetrated the internal elastic memb rane. There was no inflammatory vascular reaction. Compared to the native s egments, the amount of elastic fibres was slightly less (native: 8.9 %, PTF E: 2.3 - 3.5 %, without PTFE: 1.9 - 5.5 %) whereas the collagen fibres incr eased marginally (native: 5.1 %, PTFE: 6 - 6.9 %, without PTFE: 6.4 - 8.4 % ). Conclusions: In the rabbit iliac artery, stents sheathed with a micropor ous polytetrafluoroethylene membrane showed good tissue compatibility with no restenosis. These results warrant clinical trials.