Drug-Eluting versus Bare Metal Stents for the Treatment of Coronary Artery Stenosis
Two drug-eluting stents were approved by the FDA in 2003 for use in patients with coronary artery disease. Before drug-eluting stents were available, bare metal stents were used to correct for coronary artery stenosis. By the end of 2004, drug-eluting stents were used in nearly 80% of patients. Initial approval of the two drug-eluting stents was based on the results of randomized, controlled trials that showed superiority of drug-eluting stents over bare metal stents up to 1 year after implantation. Shortly after drug-eluting stents were approved, reports of late stent thrombosis began to appear. This complication can lead to restenosis, which may result in myocardial infarction or even death.
In 2006, the results of a large study suggested that between 7 and 18 months after implantation, the rates of nonfatal myocardial infarction, death from cardiac causes, and angiographically documented stent thrombosis were higher with drug-eluting stents than with bare metal stents. Over the next 6 months, the two manufacturers of the drug-eluting stents issued 19 press releases touting the effectiveness of their devices and never mentioned the potential risk of late thrombosis. Other studies presented conflicting results, some showing an increased risk of death or myocardial infarction with drug- eluting stents and others showing no difference in mortality between patients with drug-eluting stents and bare metal stents.
Upon further investigation into these studies, two important factors emerged as possible explanations for the conflicting results including differences in the characteristics of patients and coronary lesions. Drug-eluting stents were approved for use in patients with newly diagnosed coronary lesions and without additional serious medical conditions, like those studied in the clinical trials that led to FDA approval. However, since FDA approval was granted, more than 60% of drug-eluting stents have been implanted in patients with complex conditions (such as multi-vessel disease or acute myocardial infarction) or with complex lesions. These should be considered as off-label use.
On-label use of drug-eluting stents is associated with a persistent, long-term (>3year) reduction in the need for repeated revascularization (another stent, angioplasty, or clot dissolving therapy), without increasing the rates of mortality or myocardial infarction. Therefore, the risk of thrombosis associated with drug-eluting stents does not outweigh their advantages over bear metal stents in reducing the rate of repeated revascularization procedures.
On the other hand, off-label use of drug-eluting stents is associated with increased risk of both early and late stent thrombosis, as well as death and myocardial infarction. For this reason, patients who receive drug-eluting stents should be placed on extended (at least 12 months) antiplatelet therapy as an added measure of protection against stent thrombosis. More studies are needed to determine if extended antiplatelet therapy will improve the overall outcome of drug-eluting stents in patients with multi-vessel disease or concomitant serious medical conditions.
(* Adapted from two articles that appeared in the New England Journal of Medicine, March 2007, pages 981-987)
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