Some interventional cardiologists are beginning to talk among themselves about a problem some of them think they have seen with drug coated stents. The problem is late, sudden occlusion of some of these stents, apparently soon after the patient stops taking anti-platelet medications.
While it is difficult to find references to this phenomenon in the medical literature, and while it has not yet been systematically studied, some cardiologists describe seeing drug coated stents suddenly clot off and occlude, as late as a year or longer after the stent has been placed. When this happens the patient is likely to experience an acute myocardial infarction, or even sudden death. So far, each of these late occlusions has apparently occurred soon after anti-platelet medications (such as aspirin or clopidrogel) were discontinued.
This phenomenon was first reported in a research letter appearing in the journal Lancet in October, 2004. The letter described 4 patients whose stents occluded due to clotting within days or weeks after anti-platelet drugs were stopped. Since then, a few other case reports have been described of the same kind of event.
Speculation has been that the drug-coated stents not only inhibits abnormal cell growth within the stent (thus reducing the risk of stent occlusion,) but also inhibits the growth of a layer of normal cells (called endothelial cells) that would prevent the bare metal of the stent from being exposed to the blood. So, when anti-platelet drugs are stopped, platelets in the bloodstream are more likely to "stick" to the stent, and to begin forming a clot that could block blood flow within a matter of several minutes.
At this point, late occlusion of drug coated stents has not been carefully studied, so its actual incidence is not known. Even with this "new" phenomenon, however, the overall risk of stent restenosis is substantially lower with drug coated stents than with bare metal stents. ( Read about restenosis here.)
What does this mean?
Just how frequently this phenomenon may occur won't be known for some time. In the meantime, however, it does appear to be limited to patients no longer taking anti-platelet medication. Until the issue of late stenosis of drug coated stents is fully characterized, patients with these stents would be justified in interrogating their doctors carefully if they suggest stopping anti-platelet medications.
