In the setting of primary Percutaneous Coronary Intervention (PCI), the investigators hypothesize that a 24-48 hour delay strategy of stenting after successful thrombus aspiration and establishment of Thrombolysis In Myocardial Infarction (TIMI)-3 flow with optimal antithrombotic therapy may decrease the risk of MicroVascular Obstruction (MVO) as assessed by Cardiac Magnetic Resonance Imaging (CMRI).

Primary PCI is the reperfusion therapy of choice in patients with acute ST-elevation myocardial infarction (STEMI) [Van de Werf et al. 2008; Kushner et al. 2009]. The first objective in primary PCI is to restore TIMI-3 flow. However, despite restoration of TIMI-3 flow, myocardial reperfusion remains suboptimal in a significant proportion of patients, predominantly as a consequence of the so called "myocardial non-reperfusion phenomenon", "low/no-reflow phenomenon" or MVO. This, in turn, is associated with significant morbidity and mortality [Brodie et al. 2005; Bruder et al. 2008; Hombach et al. 2005; Nijveldt et al. 2008; Thiele et al. 2008; Wu et al. 1998]. Although TIMI flow is well assessed by angiography, contrast-enhanced CMRI remains the gold standard in the assessment of MVO. Indeed, the presence and extent of hypoenhanced areas have been shown to be associated with a poor outcome [Bruder et al. 2008; Hombach et al. 2005; Nijveldt et al. 2008; Wu et al. 1998].

There is now a large body of evidence to suggest that even in patients with TIMI-3 flow on angiography, as many as 60% of these patients will subsequently exhibit MVO with CMRI [Brodie et al. 2005; Bruder et al. 2008; Hombach et al. 2005; Nijveldt et al. 2008; Thiele et al. 2008; Wu et al. 1998]. Our knowledge of the mechanisms of MVO occurrence as well as measures to reduce MVO has been considerably enhanced by recent publications. For instance, Sianos et al. [2007] demonstrated that the thrombus burden at the time of angiography is an independent predictor of MVO extension and 2-year mortality. Furthermore, Isaaz et al. [2006] recommended a two-step strategy as a means of minimising the risk of MVO, with the first step consisting of TIMI-3 flow restoration, followed 2-6 days later by further angiography to determine the therapeutic strategy of choice (PCI, cardiac surgery, or medical treatment: 67%, 25%, and 8% respectively). Meneveau et al. [2009] also adopted a two-step strategy in a small cohort of STEMI patients with TIMI-3 flow and ST-segment regression at the time of the procedure. They demonstrated that a 24-hour delay in stent implantation led to a higher rate of procedural success than immediate stenting. Isaaz et al. [2006] and Meneveau et al. [2009] also reported a decreased thrombus burden and no culprit-artery re-occlusion between the first and the second procedure.

Both the Thrombus Aspiration during Percutaneous coronary intervention in Acute myocardial infarction Study (TAPAS) [Svilaas et al. 2008] and the thrombectomy with EXPort catheter in Infarct-Related Artery during primary percutaneous coronary intervention (EXPIRA) [Sardella et al. 2009] studies demonstrated the benefits of thrombus aspiration as the first step in primary PCI prior to either ballooning or direct stenting. However, as the effects of stenting upon MVO in the setting of acute STEMI remain poorly understood, we propose a randomized study to evaluate the benefits of a 24-48-hour delay in stent implantation compared to immediate stenting in patients presenting with acute STEMI who will undergo primary PCI.

Inclusion Criteria:

• Patients with acute STEMI presenting within 12 hours of symptom onset, requiring a primary percutaneous coronary intervention; and written informed consent.
• Patients will be randomized during the angiography if the initial TIMI flow is 0 or 1 in a major artery and if TIMI-3 flow can be restored after thrombus aspiration and sustained for 10 minutes.
• Acute STEMI is defined as typical chest pain with 30 minutes of sustained ST-segment elevation >1 mm in two or more consecutive limb leads or >2 mm in two or more precordial leads in the ECG. Major artery is defined as the proximal or mid segment of the left descending artery, the proximal segment of the circumflex artery (before the first marginal), or the right coronary artery before the posterior descendant artery.

Exclusion Criteria:

• Patients less than 18 years' old
• Pregnant and breast feeding women
• Patients with a pacemaker, automated implantable cardioverter-defibrillator (AICD), or left bundle branch block
• Contraindication to abciximab, prasugrel, or clopidogrel
• Cardiac arrest as initial presentation
• Current medical condition with a life expectancy of < 6 months
• Patients not living in France
• Patients in cardiogenic shock
• Culprit artery <2.5 mm
• Absence of informed consent
• Patients with initial TIMI 2 or 3 flow or no TIMI-3 flow restored after thrombus aspiration
• Rescue PCI after fibrinolysis
• Known creatinine clearance < 30 ml/min.