Incidence ? Combined antiplatelet therapy (aspirin plus clopidogrel) is recommended with drug-eluting as well as bare metal stents. (See "Prevention with combined antiplatelet therapy" above).
The risk of stent thrombosis appears to be similar with drug-eluting and bare metal stents [7,28,29]. This was illustrated in a 2006 meta-analysis of 19 randomized trials with 7060 patients [28]. There was no significant difference between drug-eluting and bare metal stents in the risk of stent thrombosis (0.7 versus 0.8 percent, odds ratio 0.71, 95% CI 0.41-1.25). In another meta-analysis, the rate of stent thrombosis was similar with sirolimus and paclitaxel stents (0.9 versus 1.1 percent, odds ratio 0.85, 95% CI 0.50-1.46) [30].
The same findings have been noted in studies of patients not involved in clinical trials. In an analysis of over 15,000 patients who underwent sirolimus stent implantation at 279 medical centers in 41 countries, the 12 month rate of stent thrombosis was 0.87 percent (0.13 percent acute, 0.56 percent subacute, and 0.19 percent late) [31].
Risk factors ? The following risk factors have been identified for stent thrombosis with drug-eluting stents:
Cessation of antiplatelet therapy ? Premature cessation of antiplatelet therapy appears to be the most important risk factor. In the above review in which stent thrombosis occurred in 29 of 2229 patients, premature cessation of antiplatelet therapy was associated with stent thrombosis in 5 of 17 patients (29 percent, adjusted hazard ratio 161 for subacute stent thrombosis and 57 for late stent thrombosis) [32]. The risk of late (in some cases more than one year) cessation of aspirin is discussed below. (See "Late stent thrombosis and cessation of antiplatelet therapy" below).
Similar findings were noted in a series of 38 cases of stent thrombosis occurring after drug-eluting stent implantation in 2974 consecutive patients [33]. The patients with stent thrombosis were significantly more likely to have discontinued clopidogrel (37 versus 11 percent in those without stent thrombosis). The mean duration between cessation of clopidogrel and stent thrombosis was nine days in patients with subacute stent thrombosis and 56 days with late stent thrombosis.
A possible explanation for at least some episodes of thrombosis in drug-eluting stents after cessation of antiplatelet therapy is incomplete neointimal coverage. As mention above, clopidogrel is given without interruption for at least three months for sirolimus stents and six months for paclitaxel stents. However, an angioscopy study of 37 consecutive stented lesions (15 sirolimus stents and 22 bare metal stents) suggested that neointimal coverage is often not complete at three to six months with sirolimus stents [34]: The following findings were noted on angioscopy:
Neointimal coverage was complete in all 22 bare metal stents. In contrast, neointimal coverage was complete in only 2 of the 15 sirolimus stents and three had essentially no coverage.
Thrombi were present in eight stented segments, none of which was seen on angiography. Thrombi were more common with incomplete neointimal coverage (5 of 13 versus 3 of 24 stents with complete neointimal coverage).
Other ? A variety of additional risk factors for coronary artery stent thrombosis have been identified. These include:
Failure of optimal stent placement with full stent expansion [35,36]. In a review of 652 patients, the seven patients with stent thrombosis had a smaller final balloon diameter (2.75 versus 3.00 mm) [35]. (See "General principles of the use of intracoronary stents", section on Optimal stenting).
Residual reference segment stenosis. In a series in which 15 patients with stent thrombosis were compared to 45 matched controls without stent thrombosis, significant residual reference segment stenosis was present much more often in the patients with stent thrombosis (10 of 15 versus 4 of 45 [67 versus 9 percent]) [36].
Greater stent length [7,37]. In one of the above meta-analyses, the mean stented length in patients treated with a drug-eluting stent was significantly longer in those who developed stent thrombosis (23.4 versus 21.3 mm) [7].
Multivessel stenting [31,38]. In a series of 225 such patients, stent thrombosis occurred in seven {3.1 percent) [38]. Only one event occurred while the patient was on dual antiplatelet therapy. Five of the seven thrombotic events occurred within one week and another within 45 days of stopping clopidogrel; four of these patients also stopped taking aspirin, one for a gastrointestinal bleed. Two of these events occurred within the first week after implantation and all but one occurred within the first eight months. As noted above, we recommend aspirin indefinitely and clopidogrel therapy for at least 9 to 12 months in patients who are not at high risk for bleeding. (See "Recommendations" above).
Bifurcation stenting [27,32,33,39,40], particularly with use of the crush technique [39,40]. (See "Use of intracoronary stents for specific coronary lesions", section on Bifurcation lesions).
Diabetes mellitus [31-33].
Postprocedure TIMI flow grade <3 [31].
Renal failure [32,33].
In-stent restenosis [33]
In rare cases, a hypersensitivity reaction to the stent [41]. (See "Drug-eluting intracoronary stents to prevent restenosis", section on Hypersensitivity reactions).
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