Stents

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A stent in a coronary artery. Stocktrek Images/Getty Images

Over the past few decades, stents have revolutionized the treatment of coronary artery disease. Stents are metal wire-mesh struts that are positioned into an artery to “prop open” the artery after an angioplasty. Virtually all angioplasty procedures today include the insertion of a stent.

The Purpose of Stents

Stents are designed to diminish the problem of restenosis, which occurs frequently after angioplasty alone.

Restenosis is caused by new tissue growth at the site of angioplasty, possibly provoked by the trauma which angioplasty invariably induces when it compresses an atherosclerotic plaque.

The earliest stents were made of uncoated metal (bare metal stents, or BMS). Most modern stents are coated with drugs that inhibit tissue growth, and thus inhibit restenosis. These are called drug eluting stents, or DES. Stents - especially DES - have substantially minimized the problem of restenosis.

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 is removed, leaving the stent in place. Usually, the balloon inflation which is used to expand the stent is also be used to perform the actual angioplasty, so that angioplasty/stenting is 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.

Complications With Stents

Problems 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.

A more significant complication seen with stents is stent thrombosis.

Stent Thrombosis

While stents have been successful at reducing the chief problem associated with angioplasty - restenosis - they have introduced a new problem - stent thrombosis. Stent thrombosis is the sudden occlusion of a coronary artery at the site of stent placement, caused by the sudden formation of a blood clot. This sudden event is often catastrophic, leading to myocardial infarction (heart attack) or death. Fortunately, the incidence of stent thrombosis is quite small - as long as anti-platelet drugs are used to inhibit blood clotting.

All patients receiving stents need to be placed on “dual anti-platelet therapy” (DAPT) with two anti-platelet drugs to inhibit blood clotting: aspirin, and one of the P2Y12 receptor blockers.

The P2Y12 blockers that are used to prevent stent thrombosis are clopidogrel (Plavix), prasugrel (Effient), and ticagrelor (Brilinta).

DAPT carries its own risks, and there is a lot of controversy about how long patients should remain on these drugs after receiving a stent. Because of the possibility of late stent thrombosis (that is, thrombosis occurring a year or more after stent placement), some authorities are urging doctors to keep their stent patients on DAPT for at least several years, or perhaps forever.

The Bottom Line

The bottom line is that stents have greatly reduced the risk of restenosis, and have made the (relatively) noninvasive treatment of coronary artery blockages feasible and routine. However, receiving a stent always introduces a new issue -the risk of stent thrombosis - and optimally managing this risk is not a trivial problem.

Anyone whose doctor recommends a stent needs to carefully consider both the risks and benefits of this therapy, as well as all the alternative therapies that are available for coronary artery disease.

Sources:

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.

Mauri L, Kereiakes DJ, Yeh RW, et al. Twelve or 30 months of dual antiplatelet therapy after drug-eluting stents. N Engl J Med 2014; DOI:10.1056NEJMoa1409312.

Columbo A and Chieffo A. Dual antiplatelet therapy after drug-eluting stents—How long to treat? N Engl J Med 2014; DOI:10.1056/NEJMe1413297.

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