Stents are small, wire-mesh struts that are placed into arteries after an angioplasty procedure. The purpose of a stent is to help "prop open" the portion of the artery that has been treated with angioplasty.
Stents have helped to substantially reduce restenosis (that is, reclosing of the artery), which is the main complication of angioplasty. There are two general types of restenosis: early restenosis, which is usually caused by blood clots resulting from the angioplasty procedure itself; and late restenosis, caused by too much local tissue growth as the angioplasty site heals. Stents help prevent both types.
Bare Metal Stents Vs. Erug-Eluting StentsThere are two broad types of stents -- bare metal stents (the original kind), and drug-eluting stents (DES). DES are coated with drugs aimed at limiting the tissue growth that causes late restenosis after an angioplasty procedure.
The use of stents of either type, along with strong anti-clotting drugs (usually a combination of aspirin, Plavix and heparin), has substantially reduced the risk of early restenosis, from 5% to 10% to less than 1%. The use of bare metal stents has also reduced the risk of late restenosis from roughly 30% to 15%, and the use of DES reduces that risk further to about 10%.
How are Stents Inserted?Stents are inserted by placing a collapsed stent over a deflated balloon at the end of a catheter. The catheter is advanced to the portion of the artery that has just undergone angioplasty, and the balloon is inflated, thus expanding the stent against the wall of the artery. The balloon is then deflated and the catheter removed, leaving the stent in place. In recent years, the balloon inflation which is used to expand the stent can also be used to perform the actual angioplasty, so that angioplasty/stenting can be performed in one step.
Stents come in numerous sizes and shapes to allow the cardiologist to choose a device which will best fit the patient's artery.
What Are the Complications With Stents?Even though stents were developed to reduce the risk of restenosis after angioplasty, and even though stents have successfully reduced that risk, restenosis remains the most common complication after angioplasty and stenting. Early restenois is seen in less than 1%, and late restenosis in up to 10%, of patients receiving modern stents.
Stents have even introduced two new "kinds" of restenosis. First, obtruction of the artery can occur if a stent is positioned improperly within the artery, or if a stent of the wrong size or shape is used. Once a stent is placed in an artery, it cannot be removed, so problems related to such "poor deployment" are difficult to treat, and may require bypass surgery. This complication was much more frequent in the early days of stent usage, when only a few varieties of stents were available to choose from. Fortunately, the risk of complications from poor deployment is far less than 1% today.
The second "new" type of restenosis appears to be particularly related to the use of DES, and can be thought of as "very late" restenosis. This problem can occur up to several years after DES placement. It is related to the sudden formation of blood clots within a DES, which can cause sudden blockage of the artery. Because this clot forms suddenly, and often completely blocks the artery, this late restenosis frequently leads to myocardial infarction or death. The risk of "very late" restenosis with DES appears to be low (1% to 2% according to most experts). But because of this risk, patients who receive DES are now being asked to take Plavix for at least a year, and perhaps for the rest of their lives.
The need for long-term Plavix creates its own significant problems in some patients, and has made the question of using DES (as opposed to bare metal stents) much less straightforward and much more controversial than it was just a few years ago.
Fischman, DL, Leon, MB, Baim, DS, et al. A randomized comparison of coronary– stent placement and balloon angioplasty in the treatment of coronary artery disease. N Engl J Med 1994; 331:496.
Colombo, A, Stankovic, G, Moses, JW. Selection of coronary stents. J Am Coll Cardiol 2002; 40:1021.
Pfisterrer M, Brunner-La Rocca HP, Buser PT, Rickenbacher P, Hunziker P, Mueller C, Jeger R, Bader F, Osswald S, Kaiser C. Late clinical events after clopidogrel discontinuation may limit the benefits of drug-eluting stents. J Am Coll Cardiol 2006;48:2584.