Risks and benefits

After PCI, cells grow rapidly in an attempt to heal the vessel lining and envelop the stent, which the body considers a foreign object. In about 15 to 40 percent of the cases, depending on the complexity of the original obstruction, that reaction will narrow the artery again and cause another blockage of blood flow, usually within six to 12 months after the procedure. The renewed blockage, called restenosis, might cause the gradual onset of chest pain or acute coronary syndrome—sudden, severe chest pain that can result in a heart attack. A second PCI or even open-heart surgery could be needed.

The medication gradually released by a drug-eluting stent—such as sirolimus (Rapamycin) or paclitaxel (Taxol)—suppresses the inflammatory reaction that triggers rapid cell growth, thus reducing the chance of restenosis and repeat procedures.

In a study published in June 2009, researchers at the University of Minnesota and other institutions analyzed the combined results of 28 clinical trials. They found that second procedures on blocked vessels were needed in 21 percent of the patients who had bare-metal stents vs. 8 percent with drug-eluting ones—a relative reduction of 62 percent and an absolute reduction of 13 percent.

But by blocking cell proliferation, which leads to covering the stent with scar tissue, it may leave the stent exposed and thus more likely to develop a dangerous blood clot, called stent thrombosis. Such clots can occur long after PCI, particularly after the required preventive treatment with anticlotting medication—such as aspirin plus either clopidogrel (Plavix) or prasugrel (Effient) plus aspirin—is discontinued. Current guidelines recommend such treatment for a year.

The risk of stent thrombosis is almost identical during the first year for both types of stents. But a slightly greater risk persists after that with the drug-eluting stents, while it almost disappears with bare-metal ones, the Minnesota analysis found.

Reassuring Results

The key question is whether the benefit of reduced restenosis with drug-eluting stents outweighs the slightly higher risk of thrombosis. While there's still no definitive answer, much of the research now indicates that it does for most patients.

One of the studies that raised the initial alarm about stent thrombosis came from Sweden, where researchers tracked all patients who received coronary stents there for one year. However, in May 2009 The New England Journal of Medicine published results from a second, expanded study involving some 48,000 patients followed for up to five years. It found that those given a drug-eluting stent had lower restenosis rates than those who received the bare-metal type, with comparable rates of both heart attack and death for both devices.

In the most comprehensive analysis yet, published in June 2009, researchers at the Columbia University Medical Center evaluated evidence from 22 randomized and controlled trials involving nearly 9,470 patients. They calculated no increase in deaths or heart attacks between the two categories of stents. But according to Greg W. Stone, M.D., the study's author, roughly two of 10 patients given a bare-metal stent required a second procedure, while only one of 10 with a drug-eluting stent needed another procedure. That's an overall reduction in relative risk of about 50 percent and an absolute risk of 10 percent. So while drug-eluting stents don't seem to help patients live longer, they apparently can help at least some of them live better by decreasing the chance of renewed heart problems and procedures.

The study also addressed another major concern: the use of drug-eluting stents for unapproved, or off-label use, including the treatment of more-complicated blockages and for higher-risk patients than those enrolled in the trials originally submitted to the FDA. Such use accounts for well over half of all cases in real-world practice. The analysis suggested that off-label uses were generally as safe and effective as using the stents for the approved treatments, though further study is needed to confirm.