Like all invasive medical procedures, implanting stents in the coronary arteries carries risk. For the newer drug-eluting stents, very-long-term results are not yet available; however, five-years after implantation sirolimus-eluting stents remained superior to bare-metal stents.
Risks associated with cardiac catheterization procedures include bleeding, allergic reaction to the X-ray contrast agents used to visualize the coronary arteries, and myocardial infarction. With PCI, the requirement for emergency CABG has markedly decreased since the days of balloon angioplasty, such that in some communities, coronary stenting is permitted in hospitals without on-site cardiac surgery facilities, though this remains highly controversial in the United States, including because of the rare but largely unpredictable risk of coronary artery perforation
Stent thrombosis
Although drug-eluting stents were regarded as a major medical advance when they first appeared, new evidence suggests that they also put patients at risk for stent thrombosis, or the formation of a clot in the stent. A stent is a foreign object in the body, and the body responds to the stent’s presence in a variety of ways. Macrophages accumulate around the stent, and nearby smooth muscle cells proliferate. These physiological changes, which can cause restenosis, are limited by the drugs released by the stent, but these drugs also limit re-endothelialization. This lack of healing can make the stent an exposed surface on which a life-threatening clot can form.
Though less frequent with drug-eluting stents, neointimal proliferation can still occur in DES and cause restenosis. Stent occlusion because of thrombosis may occur during the procedure, in the following days, or later. The presence of thrombus around the stent may in turn affect the drug-eluting performance of the stent. Treatment with the antiplatelet drugs aspirin and clopidogrel appears to be the most important factor reducing this risk of thrombosis, and early cessation of one or both of these drugs after drug-eluting stenting markedly increases the risk of stent thrombosis and myocardial infarction.
Whether drug-eluting stents are at higher risk than bare-metal stents for late thrombosis is intensely debated. In meta-analyses of the sirolimus and paclitaxel-eluting stent trials, there was a small but statistically higher risk of thrombosis after the first year, compared to bare metal stents. Late stent thrombosis often causes myocardial infarction and sometimes death. In other analyses, the late thrombosis risk is offset by drug-eluting stents' markedly reduced risk of restenosis and its complications including myocardial infarction. A meta-analysis concluded that the mortality risk associated with drug-eluting and bare-metal stents is similar.
Comparing different drug-eluting stents
Whether sirolimus or paclitaxel-eluting stents are measurably different in their outcomes is a topic of great interest, including to the marketing departments of the manufacturers themselves. Analyses favoring one or the other stent have been advanced. The differences, if any, between the two devices are small.
The SPIRIT II study showed the Xience V DES was better than the Taxus.
Drug-eluting stents with a biodegradable coating
In order to address the risk of late stent thrombosis, drug-eluting stents with a biodegradable coating have been developed. One such stent is the BioMatrix stent of Biosensors International, which has been approved by European authorities in January 2008. Two year results of a large all-comers trial suggest a reduced risk of late stent thrombosis, especially after discontinuation of dual antiplatelet therapy. The Nevo stent of Cordis/J&J, also uses a biodegradable coating and is currently undergoing trials.
Further Reading
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