The purpose of this research project is to improve how we treat heart attacks. The study will assess whether it might not be better to wait a few hours before implanting the coronary stent into the coronary artery rather than implanting it immediately, in order to allow the drugs to completely dissolve the clot. This might help to reduce the risks of the clot migrating and damaging the heart. By delaying coronary stent implantation, we hope to be able to reduce the size of the infarction and reduce the risk of suffering from heart failure following a heart attack.

The PRIMACY trial seeks to assess whether a strategy of delayed stent implantation combined with adjunctive anticoagulation is superior to immediate stent implantation at improving cardiovascular outcomes in patients with mechanically reperfused ST-elevation Myocardial Infarction (STEMI). The investigators hypothesize that delayed stent implantation combined with systemic anticoagulation and maximal antiplatelet therapy will reduce the combined occurrence of cardiac death, non-fatal myocardial infarction, congestive heart failure, or unplanned target vessel revascularization over a 9-month period.

Inclusion Criteria:

1. Age between 18 and 80 years;
2. STEMI, presenting within 12 hours of symptoms onset, and persisting for more than 20 minutes;
3. ECG that fulfills any of the following criteria: ≥ 2 mm ST elevation in two anterior or lateral leads; or ≥ 1 mm ST elevation in two inferior leads; or new left bundle branch block (LBBB) with at least 1 mm concordant ST elevation;
4. Infarct-related artery with TIMI flow 0 or 1 at baseline angiogram;
5. Successful reperfusion (TIMI 2-3 flow), either spontaneously or after wire passage, thrombectomy, small size (≤ 2.0mm) angioplasty catheter, and persisting for more than 10 minutes;
6. Infarct related artery with a diameter above 2.5 mm.

Exclusion Criteria:

1. Prior STEMI in the qualifying coronary artery;
2. Coronary dissection following reperfusion;
3. STEMI caused by acute stent thrombosis or a venous or arterial bypass graft occlusion;
4. Significant left main disease, as determined by angiography (≥ 50%) or other imaging technologies;
5. Cardiac condition requiring emergent or urgent surgical repair;
6. Failed thrombolysis and rescue PCI;
7. High risk of bleeding;
8. Contraindication to either ticagrelor or GpIIb/IIIa inhibitors;
9. STEMI with Killip III-IV or cardiogenic shock or presenting as sudden death, ventricular fibrillation, or sustained ventricular tachycardia;
10. Women who are pregnant or breastfeeding;
11. Creatinine clearance < 20 ml/min;
12. Other contraindication to PCI;
13. Participation with another investigational drug or investigational device study within 30 days prior to randomization (participation to registries is allowed);
14. Any condition that in the opinion of the investigator would preclude compliance with the study protocol.