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J Am Coll Cardiol, 2006; 48:2584-2591, doi:10.1016/j.jacc.2006.10.026
(Published online 1 November 2006). © 2006 by the American College of Cardiology Foundation |
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* Department of Cardiology, University Hospital, Basel, Switzerland
Department of Intensive Care Medicine, University Hospital, Basel, Switzerland
Department of Internal Medicine, University Hospital, Basel, Switzerland
Bruderholzspital, Basel, Switzerland
Manuscript received June 6, 2006; revised manuscript received August 24, 2006, accepted August 28, 2006.
* Reprint requests and correspondence: Dr. Matthias Pfisterer, Professor of Cardiology, Head Department of Cardiology, University Hospital, CH-4031 Basel, Switzerland. (Email: pfisterer{at}email.ch).
| Abstract |
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BACKGROUND: There is growing concern that delayed endothelialization after DES implantation may lead to late stent thrombosis and related myocardial infarction (MI) or death. However, event rates and outcomes after clopidogrel discontinuation versus BMS are unknown.
METHODS: A consecutive series of 746 nonselected patients with 1,133 stented lesions surviving 6 months without major events were followed for 1 year after the discontinuation of clopidogrel. Patients were assigned randomly 2:1 to DES versus BMS in BASKET (Basel Stent Kosten Effektivitäts Trial). The primary focus of this observation was cardiac death/MI.
RESULTS: Rates of 18-month cardiac death/MI were not different between DES and BMS patients. However, after the discontinuation of clopidogrel (between months 7 and 18), these events occurred in 4.9% after DES versus 1.3% after BMS implantation. Target vessel revascularization remained lower after DES, resulting in similar rates of all clinical events for this time period (DES 9.3%, BMS 7.9%). Documented late stent thrombosis and related death/target vessel MI were twice as frequent after DES versus BMS (2.6% vs. 1.3%). Thrombosis-related events occurred between 15 and 362 days after the discontinuation of clopidogrel, presenting as MI or death in 88%.
CONCLUSIONS: After the discontinuation of clopidogrel, the benefit of DES in reducing target vessel revascularization is maintained but has to be balanced against an increase in late cardiac death or nonfatal MI, possibly related to late stent thrombosis.
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To address these questions, we prospectively followed a consecutive series of 746 nonselected patients randomized to DES versus BMS who survived the first 6 months after stenting without major clinical events and who stopped taking clopidogrel at that point in time. They initially were enrolled in the Basel stent cost-effectiveness trial, BASKET (Basel Stent Kosten-Effektivitäts Trial) (19). The specific aims of this prospective follow-up evaluation were to define the incidence of late clinical events and late stent thrombosis in DES- versus BMS-treated patients after the discontinuation of clopidogrel and to define predictors, timing, and outcome of such thrombotic events in relation to stent type implanted.
| Methods |
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Angioplasty and antiplatelet therapy. Angioplasty was performed according to standard techniques with the final decision about the appropriate strategy in each patient left to the judgment of the physician in charge (19). All 157 patients presenting with ST-segment elevation MI were treated with primary angioplasty and all 273 patients with other acute coronary syndromes with urgent agioplasty within 24 h of presentation. All patients received a loading dose of 250 to 500 mg aspirin intravenously or orally and clopidogrel 300 mg orally. The use of glycoprotein IIb/IIIa inhibitors was left to the discretion of the physician in charge, mainly given in patients with acute coronary syndromes, complex lesions, or suboptimal angioplasty results. All patients received a maintenance dual antiplatelet therapy with aspirin 100 mg and clopidogrel 75 mg daily for 6 months, irrespective of stent type used. In addition, in all patients long-term statin therapy was prescribed. Patients were advised to stop clopidogrel after 6 months but to continue 100 mg of aspirin daily long-term. Medication was recorded at follow-up and at the time of any event.
Definition of late events. For this study, "late" was defined as occurring between 7 and 18 months after stenting. Late clinical events, the focus of this observation, were any cardiac death and documented nonfatal MI. Of these events, all sudden cardiac deaths and all MIs attributable to the target vessel were considered to be "thrombosis-related" (previously called "possible" thromboses) (11). Angiographically documented "definite" late stent thrombosis was defined as ischemic clinical event with angiographically proven stent thrombosis (i.e., Thrombosis In Myocardial Infarction [TIMI] flow 0 or 1 or the presence of flow-limiting thrombus [TIMI flow 1 or 2]). Target vessel revascularizations not related to thrombosis-related events were assumed to be "restenosis-related." Thus, major cardiac events were a composite of cardiac death, nonfatal MI, and TVR. All deaths not clearly due to other causes like cancer or suicide were considered to be cardiac. Nonfatal MI was diagnosed according to current guidelines (20). All these events were adjudicated by an independent clinical event committee blinded to the stent types used.
Statistics.
All analyses were performed with the primary aim to compare patients with DES and BMS and to perform additional secondary exploratory analyses between the 2 DES used. Because this study was planned as follow-up investigation of BASKET, sample size calculations were performed for that purpose (19). Therefore, patients were followed in an "observational" manner, which did not allow formal statistical comparisons for the time period of month 7 to 18. Quantitative variables are presented as mean ± standard deviation or median ± interquartile ranges as appropriate. Categorical variables are described by their distribution. Two-group comparisons were performed using the Fisher exact test for categorical variables and unpaired t test or Mann-Whitney U test for quantitative variables. Kaplan-Meier curves were used for calculating time-dependent occurrences of events and the log rank test to compare DES and BMS. Predictors with a p value
0.1 were entered in a multivariate Cox-regression analysis adjusted to differences in baseline characteristics to test independence of these predictors. All calculations were performed with the use of a commercially available statistical package (version 13.0, SPSS Inc., Chicago, Illinois).
| Results |
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2.5 mm (Table 1). This was true despite the fact that fewer patients treated with DES had such events during the first 6 months compared with patients treated with BMS (7.2% vs. 12.1%, p = 0.02) (19). Baseline characteristics reflect a relatively high-risk patient population presenting often with acute coronary syndromes and an extensive, complex coronary anatomy as seen in contemporary high-volume centers.
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Late thrombosis-related events. After the discontinuation of clopidogrel, 16 of 65 events (25%) were related to stent thrombosis: 3 cardiac deaths, 11 nonfatal MIs, and 2 angiographically proven subtotal thrombotic obstructions with increasing angina but no infarction. Late stent thrombosis was documented in one patient who died (the other 2 patients died suddenly without autopsy) and in 8 of 11 patients with MI. Figure 4 shows the incidence of these late thrombosis-related events in relation to the stent type implanted. Although differences were not significant in view of the relatively low overall frequencies, there was a 2- to 3-fold increased rate of such late events in DES- compared with BMS-treated patients. Importantly, however, these findings between DES versus BMS were consistent and congruent with the primary focus of this study.
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Outcome of late thrombosis-related events.
Comparing presentation and outcome of the 16 thrombosis-related with the 49 other events during months 7 to 18 showed that in thrombosis-related events, cardiac mortality was somewhat higher (19% vs. 6%, p = 0.13) and the rate of nonfatal MIs significantly higher (75% vs. 22%, p
0.0001). Thus, thrombosis-related events carried a substantially increased risk of cardiac death or nonfatal MI compared with non-thrombosisrelated events (88% vs. 27%, OR 19.4, p < 0.0001).
| Discussion |
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Late thrombotic stent occlusion. Late and sudden thrombotic coronary occlusion after percutaneous coronary interventions was first noted as a significant problem 2 to 15 months after brachytherapy (22). In contrast, meta-analyses of initial long-term outcomes after sirolimus-eluting (10,23) or paclitaxel-eluting stent implantation (12) pointed to the overall benefit of DES compared with BMS in selected patient groups and suggested no increased hazard of stent thrombosis compared with BMS use. However, there were case reports (8,16) demonstrating the occurrence of late stent thrombosis after DES implantation associated with a high risk of death or nonfatal MI. Reasons for thrombotic events were described in experimental (24) and autopsy studies (25): DES may delay endothelialization and impair intimal healing, partly in association with hypersensitivity and inflammatory reactions, and thereby extend the time window during which stents are prone to thrombosis (8). This has been confirmed recently by angioscopic findings (26). Two large cohort-studies on >2,000 patients each analyzed their data for late angiographic stent thrombosis after DES implantation and reported an incidence of up to 0.7% during a follow-up duration of 9 and 18 months, respectively (13,15). Events occurred between 2 and 26 months, with case fatality rates of 29% and 45%. In the present report, rates of late angiographically documented stent thrombosis and thrombosis-related clinical events were even greater (1.6% and 2.6%, respectively). However, BASKET-LATE differs from previous such trials: late follow-up data were collected prospectively, more complex lesions were treated, almost 60% patients had acute coronary syndromes (one-third of them with ST-segment elevation myocardial infarction, 26% treated acutely with glycoprotein IIb/IIIa inhibitors), and clopidogrel was discontinued in all patients after 6 months with no protocol-driven control angiograms allowed and therefore no angiogram-driven repeat TVRs performed. In fact, several of these high-risk characteristics of the BASKET population turned out to be predictors of late thrombosis-related events, among them stenting of bifurcation or bypass-graft lesions. In contrast, the rate of clinically driven late restenosis-related TVRs remained lower after DES versus BMS. Of clinical relevance for the patient, however, is the "price" to pay (i.e., the high rate of cardiac deaths or nonfatal MI associated with late thrombosis-related events).
Implications of BASKET-LATE findings. The findings of BASKET-LATE may have major clinical implications. First, when using an antiplatelet regime as currently recommended and applied in BASKET/BASKET-LATE, one has to balance the benefit of the lower rate of reinterventions after DES implantation with the cost of an increased rate of late, presumably thrombosis-related, death or nonfatal MI compared with BMS use. In nonselected patients, implantation of DES may avoid 5 major cardiac events at 6 months in 100 patients treated (19) but lead to 3 patients suffering cardiac death or nonfatal MI during months 7 to 18. Second, one may speculate whether prolonged dual antiplatelet therapy may be beneficial as suggested after brachytherapy (27) and BMS implantation (28). However, the wide time window in which these thrombotic events occur, as noted in this study and in registry data by Ong et al. (15), may question a direct relation of clopidogrel discontinuation with these events, although clopidogrel withdrawal may even be associated with proinflammatory and prothrombotic effects in diabetic patients (29). In addition, the bleeding risk of prolonged dual antiplatelet therapy of up to 2% per year (30,31) and the increased cost would have to be taken into account. Therefore, such a prolonged dual antiplatelet therapy may only be justified in patients at increased risk for such events (13,15,32). Third, new strategies to reduce late thrombosis-related events have to be searched for; they may consist of other antiplatelet regimes, other stent types (e.g., bioabsorbable or endothelialization promoting stents) (33) or other drugs/drug dosages or drug release kinetics of DES. It may also be important to identify individual patient factors such as aspirin (34) or clopidogrel resistance (35), or drug-drug interactions (36) and to treat affected patients specifically.
Study limitations. A major limitation of this study lies in the fact that power calculations were not based on the hypothesis of this study. Therefore, the data remain observational. In view of previous observations (14,15) and a meta-analysis of 4 randomized sirolimus-eluting stent trials with up to 3 years follow-up (37), the expected incidence of late stent thrombosis was up to 0.3% for BMS and up to 0.9% for DES after the first year resulting in an estimated sample size of >6,000 patients needed to reach statistical significance. Although the present observational data suggest a somewhat-greater rate of these events, such a large study of nonselected patients randomized to DES versus BMS will hardly be performed to address this question, today.
Conclusions. This study highlights the clinical relevance of a relatively new phenomenon, late clinical events possibly related to late stent thrombosis, which seems to be of particular importance after DES implantation. It could not prove that thrombosis-related events were significantly more frequent after DES compared with BMS; however, the consistency of the findings within BASKET-LATE and with the marked difference in "hard" events, late death or MI, together with similar directional observations in previous randomized studies of selected patient groups underline the potential relevance of this observation. Although findings suggest a relation to discontinuation of dual antiplatelet therapy, this study gave no proof for a direct cause-effect relationship nor that thrombosis-related events could be prevented by such a therapy. Still, such a strategy may be chosen empirically, at least for patients at increased risk for such events, until better strategies to prevent late thrombosis-related events have been found and shown to be effective. In any case, physicians and patients should be alerted to this potential late harm of DES use.
| Appendix |
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Principal Investigator: M. Pfisterer, Basel.
University Hospital Basel: F. Bader, A. Bernheim, P. Bonetti, H. P. Brunner-La Rocca, P. Buser, T. Faeh, P. Hunziker, R. Jeger, C. Kaiser, C. Mueller, S. Osswald, M. Zellweger, A. Zutter.
University Hospital Bruderholz: P. Rickenbacher.
University Hospital Liestal: W. Estlinbaum.
Regional Hospital Delemont: J.-L. Crevoisier.
St. Claraspital Basel: B. Hornig.
Critical Events Committee: P. Rickenbacher (chair), P. Hunziker, C. Mueller.
Secretarial assistance: E. Stalder, U. Vogt.
| Footnotes |
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This study was supported by the Basel Cardiac Research Foundation, Basel, Switzerland, and the University Hospital, Basel, Switzerland. They had no role in the design and conduct of the study, collection, management, analysis, or interpretation of the data. There was no industry sponsor for this study.
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