Drug eluting stents and late thrombosis

Unlike restenosis, which is fairly common, stent thrombosis is a rare but much more dangerous complication after coronary stent placement. It usually occurs before endothelialisation has been completed. For bare-metal stents, this process takes a few weeks; the newer, drug-eluting stents inhibit restenosis by inhibiting fibroblast proliferation, but they also tend to delay the endothelialisation process. For this reason, patients who have had drug-eluting stents are prescribed aspirin and clopidogrel therapy for at least 6 months.

In this week’s Lancet is a Research Letter describing four cases of late stent thrombosis, occurring over a year after stent implantation and shortly after anti-platelet therapy was discontinued for various reasons. Two patients had had both drug-eluting and bare stents implanted; the thrombosis occurred only on the drug-eluting stents. Two of the patients had Cypher sirolimus-eluting stents and two had Taxus paclitaxel-eluting stents.

These numbers are, of course, minute compared to the large number of drug-eluting stents that have been placed, but they presumably represent only some of the actual cases that have occurred. Late stent thrombosis is thus a rare but potentially dangerous complication of drug-eluting stents, when anti-platelet therapy is discontinued.

Since drug-eluting stents reduce the incidence of restenosis significantly, they will continue to be used. Nevertheless, as the accompanying editorial points out, the issue of late stent thrombosis should make us wary of these stents in patients in whom discontinuation of antiplatelet therapy is likely to occur; more data from registries are needed; the duration of antiplatelet therapy may need to be prolonged; and shorter interruption for surgical procedures may need to be considered.

Interestingly, a press release from the Canadian Cardiovascular Congress 2004 that was referred to by EchoJournal indicates work being done on a stent coated with antibodies that attract endothelial cells from the bloodstream. This could conceivably speed up endothelialisation, a very attractive although not-yet-ready-for-prime-time approach.

Many new devices are sure to appear. Given the large sums of money being spent on drug-eluting stents, I find it very interesting that the authors report stent thrombosis in two each of the two main players in the market. A serendipitous coincidence, I assume.

Of course, lowering cardiovascular risk remains the best approach. You don’t need to worry about what kind of stent you’ll be getting if you don’t need a stent.

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