SELF-EXPANDABLE AND HIGHLY FLEXIBLE NITINOL STENT - IMMEDIATE AND LONG-TERM RESULTS IN DOGS

We sought to investigate the acute and long-term patency rates and the histologic response of coronary arteries to a self-expandable nitinol coil stent. Twenty-two stents were implanted. Angiographic patency wa s demonstrated acutely in all but one dog, in which the stent was rele ased in a small branch (1 mm); mismatch in stent-to-artery diameters r esulted in vessel closure. Two dogs died from anesthesia overdose and two from bleeding within 24 hours. All dogs were treated with aspirin (80 mg/day) and warfarin (2.5 mg/day) for up to 1 month. Sixteen dogs were monitored for 1 to 2 weeks, 1 month, 3 months, 6 months, and 1 ye ar and underwent subsequent angiography and histopathologic examinatio n. Angiographic artery dimensions measured immediately after stent imp lantation (2.72 +/- 0.4 mm) did not differ from those noted at follow- up (2.68 +/- 0.44 mm, p not significant). Histologic examination showe d outward stent pressure compressing the internal elastic membrane and media in most cases. Intimal hyperplasia started at 2 weeks and was m ost apparent at 3 and 6 months. Mean intimal thickness was 30.7 +/- 10 .9 mu, 141.8 +/- 105.4 mu, 227.1 +/- 104.1 mu, 211.8 +/- 99.1 mu, and 170.1 +/- 42.7 mu at 1 to 2 weeks and 1, 3, 6 and 12 months, respectiv ely. Therefore the nitinol self-expandable stent provokes a moderate c ellular proliferative response that reaches its maximum in 3 to 6 mont hs without further progression.