Intravascular stents. General principles and status of lower-extremity arterial applications.

The two major types of intravascular stents are balloon expandable and self-expanding. Many animal and, more recently, clinical studies have begun to delineate the real and potential roles of stents. Although the ideal intravascular stent does not exist, it is possible to identify characteristics of the hypothetical ideal stent. Iliac and femoropopliteal arterial applications of metallic stents are reviewed. Stents have proved useful in postangioplasty elastic recoil, in some cases of postangioplasty restenosis, and in angioplasty-induced dissection. Their role in primary angioplasty procedures is still uncertain, although in iliac angioplasty the immediate hemodynamic effects of angioplasty plus stenting are superior to those of angioplasty alone. It is clear that metallic stents have not solved the problem of postangioplasty restenosis, as restenosis still occurs in a significant number of cases. This problem is particularly evident in the femoropopliteal stent procedures, in which angiographic restenosis (more than 50% single diameter stenosis) at 6 months after treatment has occurred in approximately 30% of cases. The existence of poststenting restenosis, which often involves the stented segment, underscores the need for better drug regimens in angioplasty and for better understanding of the intimal fibrocellular proliferative response of the vessel wall to injury. Although potentially very useful, biodegradable stents are still a dream whose realization will demand the development of better materials.