Why is this study important? 

• Achieving early restoration of blood flow in infarct-related artery (IRA) is critical to attenuate myocardial injury and improve prognosis in ST-segment elevation myocardial infarction (STEMI) patients. 
• Unfractionated heparin (UFH) is frequently administered before primary PCI procedure in patients with STEMI and observational studies indicated that pretreatment with UFH may improve early restoration of myocardial blood flow. However, high-quality evidence is lacking. 

What question was this study supposed to answer? 

• The study evaluated the effect of administration of UFH at first medical contact (FMC) versus in the Cathlab in STEMI patients.  
• The primary endpoint of the study was Thrombolysis in Myocardial Ischemia (TIMI) 3 flow of infarct-related artery at diagnostic angiography before Primary PCI. Patients were randomized (n=999) to receive 100U/Kg of UFH at FMC vs. Cath lab if symptom onset within 12 hours. 

What did the study show? 

• Pretreatment with loading-dose UFH at FMC was associated with improved spontaneous reperfusion of IRA (23.6% in FMC vs. 17.6% in Cath lab; RR 1.34, 95% CI 1.04-1.71, p value - 0.02) without increasing the risk of major bleeding (BARC≥2). There was no significant difference in epicardial or myocardial reperfusion post-PCI procedure.  
• Additionally, there was no significant difference in MACCE (death, cardiac death, admission for heart failure, myocardial infarction, stent thrombosis, unplanned revascularization, and stroke) at 1 year after randomization. However, at 30 days MACCE was lower in the FMC group (2.2% vs. 4.7%, HR 0.47; 0.24-0.91, p value – 0.03) with reduction in heart failure hospitalization (0% vs. 1%, p value – 0.02). 
• Of note, patients on anticoagulation, history of coronary artery bypass grafting (CABG), CPR prior to randomization and mechanical complications, were excluded from the study.