THE CORONARY-ARTERY RESPONSE TO IMPLANTATION OF A BALLOON-EXPANDABLE FLEXIBLE STENT IN THE ASPIRIN-TREATED AND NON-ASPIRIN-TREATED SWINE MODEL

Intracoronary stents may potentially alleviate some of the problems associated with coronary angioplasty. Since the anatomy and physiology of swine coronary arteries closely resemble those of humans, the response to implantation of the Gianturco-Roubin, balloon-expandable, flexible stent was studied in this model. Additionally, the effect of aspirin, 1 mg/kg/day orally, on this response was evaluated. Eighteen Hanford miniature swine underwent stenting of the left anterior descending coronary artery. Two died within 24 hours of stent implantation. The 16 survivors were put to death at 4 (n = 4), 11 (n = 4), 28 (n = 4), 56 (n = 3), and 180 (n = 1) days. Angiographically, reduction of stent lumen diameter of 0.1 to 1.3 mm was observed and was maximum at 11 days, with gradual improvement at subsequent time periods. Scanning electron microscopy, transmission electron microscopy, and light microscopy showed early disruption of subjacent endothelium, and adherence of platelets to exposed subendothelium and stent wires. Microthrombi were readily apparent. At 11 days, initimal thickening, made up predominantly of smooth muscle cells with abundant extracellular matrix, was observed and covered the stent wires. At 28 days, regression of intimal thickening was apparent and a confluent endothelium with flow-directed orientation was seen. At 56 and 180 days, the luminal surface was smooth; intimal thickening averaged 525-mu-m over the stent wires and 55-mu-m away from the wires. Findings in aspirin-treated animals were similar to results in those that did not receive aspirin. Thus in this swine model, stent implantation results in a time-dependent and self-limited vascular response.