Our first hypothesis is that dose adjustment of aspirin and clopidogrel based on biological monitoring reduces the rate of severe cardiovascular complications compared to a conventional strategy in patients scheduled for drug eluting stent implantation and followed up for one year. Our second hypothesis is that interruption of clopidogrel / Prasugrel after one year of a combined therapy of clopidogrel/Prasugrel and aspirin is associated with a higher rate of severe cardiovascular complications as compared with patients in whom aspirin and clopidogrel / Prasugrel is maintained during the subsequent 6 months of follow-up.

Participating Centers : 38 french high PCI volume (>700) centers Rationale: Clopidogrel / Prasugrel (75 mg/day), in combination with aspirin (75 mg/day), is currently the antiplatelet treatment of choice for prevention of stent thrombosis, and clinical trials have shown that, in high-risk patients, prolonged dual antiplatelet treatment is more effective than aspirin alone in preventing major cardiovascular events. However, despite the use of clopidogrel, a considerable number of patients continue to have cardiovascular events. Numerous in VITRO studies have shown that individual responsiveness to clopidogrel but also to aspirin is not uniform in all patients and is subject to inter- and intraindividual variability. The recent possibility of bedside monitoring of oral antiplatelet therapy offers the unique opportunity of tailoring antiplatelet therapy. However, the relevance of such strategy has never been evaluated in a randomized prospective adequately powered study having long term follow-up (rationale 1). Late state stent thrombosis, especially in the era of drug eluting stent and after interruption of OAT, is another important safety issue raising the questions of the modalities of interruption of dual OAT after one year according to the most recent updated recommendations. Can we switch from dual to single OAT after one year? If so, what is the ischemic hazard? (Rational 2) Our first hypothesis is that a strategy of dose adjustment of OAT based on biological monitoring reduces the rate of the combined ischemic endpoints of death, urgent revascularization, stent thrombosis and stroke as compared to a conventional strategy (local practice without monitoring) in patients scheduled for DES implantation and followed up for one year. Our second hypothesis is that interruption of clopidogrel after one year of dual OAT is associated with a higher rate of the same combined ischemic endpoints as compared with patients in whom dual OAT is maintained during the subsequent 6 months of follow-up. Objectives: 1) To demonstrate the superiority of the strategy of monitoring with dose adjustment in suboptimal responders (Monitoring Arm) as compared to a more conventional strategy (Conventional Arm) with fixed dose regimen of both oral antiplatelet agents in all patients as defined by the international guidelines to reduce the primary endpoint evaluated one year after DES implantation. 2) to demonstrate the superiority of a strategy of pursuit of a dual OAT beyond one year (Pursuit Arm) as compared to a strategy of interruption (Interruption Arm).

Duration of the participation : from 18 up to 30 months according to the time delay from study start to randomization. No participants will be excluded from the study at the exception of consent withdrawal. However, participants who have not been randomized for interruption or continuation of DAPT at the 12 month follow up visit will terminate the study

Number of patients: 2500 patients. This number was obtained for the demonstration of the superiority of the strategy of monitoring (Monitoring Arm) over the conventional strategy (Conventional Arm) to reduce the primary endpoint by 33% (relative risk reduction).

Expected results: The ARCTIC study will provide answers to two major clinical challenges. It will also give a unique opportunity to assess the prevalence and the associated risk factors of suboptimal answers to OAT, but also to improve a suboptimal biological response. Finally, the economic impact of both strategies of monitoring and of interruption will be evaluated.

Inclusion Criteria:

• Patients (≥18 years) in whom elective DES stent placement is scheduled after diagnostic angiography
• Patients not treated by GPIIb/IIIa inhibitors prior to randomization.
• Provided written consent for participation in the trial prior to any study-specific procedures or requirements.

Exclusion Criteria:

• Oral anticoagulation (Vitamin K Antagonists).
• Contraindication for aspirin and/or clopidogrel/Prasugrel or GPIIb/IIIa inhibitors or to increasing dose of clopidogrel or aspirin
• Ongoing or recent bleeding and/or recent major surgery (<3 weeks)
• Severe liver dysfunction
• Thrombocytopenia (Platelet count <80000/µl).
• IIb/IIIa inhibitors within a week prior to randomization
• STEMI presentation
• Patient at risk of poor compliance to the study
• Patient not affiliated to social security
• Pregnant women, no signed inform consent
• Any invasive or surgical planned intervention during the year after stent placement