Assessment of a polyester-covered nitinol stent in an atherosclerotic swine model

To evaluate the short-term patency and healing characteristics of the Cragg EndoPro covered stent in an atherosclerotic model as one of the Food and Drug Administration requirements before possible approval of the device for human use in the United States.

Seventeen self-expanding stent-grafts were placed in the aorta and right and left iliac arteries of six Yucatan microswine exposed to a regimen of accelerated atherosclerosis. The stent-grafts were constructed from nitinol wire formed into a tubular zigzag configuration. The stent frame was covered by a thin woven polyester fabric tube, with medium permeability, available in multiple diameters and lengths. The animals were killed at 24 hours, 3 months, and 6 months. Assessment was done by angiography and histology.

All stents were patent immediately after deployment. Two stents were occluded at follow-up, indicating an 88% patency rate. Minor lumen narrowing was found at the follow-up intervals. Histologic examination revealed a mixture of mature and immature endothelial cells lining both the native and stented regions in all vessels examined. The new endoluminal surface was composed primarily of fibrocollagen and elastic fibers and smooth muscle cells. Intimal thickness was inversely correlated to medial thickness. Medial compression with atrophy was observed routinely with rare necrosis. Complete tissue ingrowth was seen by 3 months. The degree of vascular inflammation increased over time, as well as the foreign body giant cell reaction to the polyester fabric.

The patency rate does not appear to be better than that with angioplasty or noncovered stent placement in the studied time frame. The progressive vascular inflammatory changes noted should be further investigated in longer-term animal trials to ensure its safety in humans because this device is meant to be permanent.