What is a stent?

A stent is a tubular mesh of metal (usually stainless steel) that is deployed in the coronary artery after an angioplasty. A stent is mounted on an angioplasty balloon in its collapsed state. The stent/balloon assembly is then advanced into the coronary artery and positioned over the site of the coronary lesion. When the balloon is inflated, the stent becomes fully expanded and apposed against the coronary artery wall, "tacking up" the atherosclerotic lesion and buttressing the artery wall. The balloon is then removed but the stent remains in the coronary artery (forever). Following stenting, the patient is treated with aspirin in addition to another blood thinner (clopidogrel or ticlopidine) in order to prevent blood clotting at the site of the bare metal stent. These drugs must be continued for 3 –4 weeks, until the stent becomes lined with a layer of tissue, making it less likely to induce blood clotting.

A balloon-mounted coronary stent being deployed

The use of stents has dramatically reduced the restenosis rate to 20%, or about half of that observed after angioplasty alone. This is because a fully expanded stent virtually abolishes the arterial recoil phenomenon seen after angioplasty. However, restenosis can occur within a stent. In this process, the stent does not collapse, but, rather, an aggressive scar tissue reaction occurs inside the stent, narrowing the channel. Some degree of scarring occurs after every stent, but differs in degree from patient to patient. Restenosis usually occurs within 6 to 12 months after a stent. Beyond that time period, the scarring process essentially stops. The restenosis rate seems to be more common in diabetics and in smaller sized coronary arteries. When restenosis occurs, it can usually be treated with repeat angioplasty. Recently, intracoronary radiation has been used to abate the scarring process. This is reserved for cases of recurrent and aggressive restenosis. Research and clinical trials are currently ongoing with drug-coated stents that have been reported to elicit virtually no scarring reaction. However, these drug-coated stents are still under investigation not yet available.