Ticagrelor vs. Prasugrel Effects on Infarct Size

This study has been designed as a randomized, double-blind trial to provide definitive evidence on the effects of ticagrelor and prasugrel on myocardial salvage in patients with anterior ST Segment Elevation Myocardial Infarction (STEMI) undergoing primary Percutaneous Coronary Intervention (PCI). This study will also measure the effects of ticagrelor vs. prasugrel on secondary endpoints listed above. This study design aims to test the hypothesis that ticagrelor will reduce myocardial infarct size as a proportion of the ischemic area at risk when compared to prasugrel.

Subjects and research staff (including the Magnetic Resonance Imaging (MRI) readers and interventional cardiologists) will not know what active treatment study drug the subjects are receiving. Study Arm 1: Ticagrelor (180 mg loading dose, followed by 90 mg twice a day) PO plus matching placebo Study Arm 2: Prasugrel (60 mg loading dose followed by 5 or 10 mg once per day based on weight) PO plus matching placebo Additional study drug: Aspirin (81mg per day) Participation in this study will be about 90 days and includes 4 study visits (other than your hospital stay) and 3 telephone calls. ENROLLMENT PROCEDURES: The following procedures are to be completed after informed consent has been obtained: * Informed Consent Form signed * Medical history * Vital signs (eg, blood pressure, heart rate, respiration rate, temperature) * Review for Adverse Events (AEs) and Serious Adverse Events (SAEs) (only AEs possibly related to study procedures and SAEs are collected) * Documentation of concomitant medications * Physical exam * Body height * Body weight * 12-lead Electrocardiogram (ECG) * Angiographic and Percutaneous Coronary Intervention (PCI) data * Randomization of treatment assignment * Investigational product dispensing (on Day 0 and during hospital stay) - Loading dose on Day 0 - 3 day investigational product dosing while in the hospital - 30 day supply dispensing of investigational product on Day 3 for subject to take home * Local laboratory Assessments: - Blood draw for Creatine Kinase-MB (CK-MB) and troponin I - Blood pregnancy (females of childbearing potential only) FOLLOW UP PROCEDURES: Day 5 * Vital signs (e.g., blood pressure, heart rate, respiration rate, temperature) * Review for Adverse Events and Serious Adverse Events (only AEs possibly related to study procedures and SAEs are collected) * Cardiac MRI * Left Ventricular Ejection Fraction (LVEF), Left Ventricular End-Diastolic Volume (LVEDV), Left Ventricular End-Systolic Volume (LVESV) calculations * Serum creatinine, Complete Blood Count (CBC) * Documentation of concomitant medications and investigational product compliance Day 30 (+/- 1 day), Day 60 (+/- 2 days) * Vital signs (e.g., blood pressure, heart rate, respiration rate, temperature) * Review for Adverse Events and Serious Adverse Events (only AEs possibly related to study procedures and SAEs are collected) * LVEF, LVEDV, LVESV calculations * Serum creatinine, CBC * Documentation of concomitant medications and investigational product compliance * Investigational Product Dispensing Day 14, Day 44, Day 74 (+/- 2 days): Phone calls will be performed to ensure drug compliance, review concomitant medications and review any events. On Day 74, study staff will confirm whether or not the subject has seen their regular cardiologist. Subject will be instructed to bring this information with them at the Day 90 visit so that their cardiologist can be told what arm they participated in for continuation of care and medication therapy. Day 90 or Termination/End of Study (+/- 2 days) : * Vital signs (eg, sitting blood pressure, heart rate, respiration rate, temperature) * Review for Adverse Events and Serious Adverse Events (only AEs possibly related to study procedures and SAEs are collected) * Cardiac MRI * LVEF, LVEDV, LVESV calculations * Serum creatinine, CBC * Documentation of concomitant medications and investigational product compliance * If available and subject consents, subject's cardiologist will be informed what arm of the study they participated in for continuation of care and medication therapy.