A new expandable intracoronary tantalum (Strecker) stent: early experimental results and follow-up to twelve months.

A new radiopaque balloon expandable tantalum stent was tested in the coronary arteries of sheep. A total of 28 stents with a diameter of 2.0 to 3.8 mm were successfully deployed. The stent to coronary artery diameter ratio was 1.1-1.2:1. The animals were heparinized with 100 U/kg of heparin but did not receive antiplatelet drugs. Coronary angiography that was performed 10 minutes after stent implantation showed 100% patency with no side-branch occlusion. Four sheep died within 2 hours of stent implantation, and pathologic studies showed thrombosis of the smaller sized stents: 2 mm (n = 2), 2.8 mm (n = 1), and 3.2 mm (n = 1); three fourths of the sheep had two stents implanted. An oversized stent caused coronary rupture and cardiac tamponade in one other sheep. Follow-up study protocol included coronary angiography before animal sacrifice and pathologic studies within 48 hours (n = 11), 2 weeks (n = 1), 3 months (n = 2), 5 months (n = 1), 10 months (n = 7), and 12 months (n = 1). At 3 to 12 months of follow-up the coronary stent was completely covered with a layer of neointima, and there was no angiographic evidence of coronary stenosis and patent side branches. According to histologic examination, the neointima had nonuniform thickness (20 to 330 microns) and consisted of smooth muscle cells and some collagen. At 7 months of follow-up one of seven stents had angiographic (20%) and pathologic evidence of stenosis, which was secondary to thrombus. The tantalum device is easily deployed technically and notable for its excellent fluoroscopic visibility and flexibility. Thrombosis with a tantalum stent remains a problem, and therefore the larger diameter stents > or = 3.2 mm, antiplatelet drugs, and anticoagulation therapy are indicated for human studies. Implantation of multiple coronary stents increases the risk of stent thrombosis. The long-term, mild neointimal thickness and the patency of the stent and side branches are encouraging.