Randomized evaluation of enoxaparin (0.5mg/kg IV) versus UFH (50-70IU/kg with GPIIb/IIIa inhibitors; 70-100IU without GPIIb/IIIa inhibitors). Anticoagulation can be continued after the procedure using the same agents as those allocated per randomization (enoxaparin SC, UHF IV or SC)

This study is a prospective, multicenter, multinational, randomized, active-control arm trial. The study population consists of subjects with ST-segment elevation MI who are randomized within 24 hours of symptom onset. Subjects presenting between 12 and 24 hours of symptom onset should present with recurrent or persisting chest pain and/or recurrent or persisting ST elevation suggesting ongoing ischemia, and an indication of primary PCI.

Approximately 850 subjects will be enrolled at approximately 50 sites in several countries including Austria, France, Germany and the United States. Informed consent will be obtained from subjects meeting all inclusion and no exclusion criteria prior to any study related procedures. Subjects will be randomized and begin treatment in the Emergency Department or in the ambulance or in the hospital room if in-patient. Eligible subjects will be randomized (1:1) to receive either UFH IV bolus (ACT-adjusted) or enoxaparin 0.50 mg/kg IV bolus without monitoring. Randomization to treatment group will be performed using an interactive voice response system (IVRS). All treatment groups will be given aspirin (160 to 500 mg/day according to local practice) and clopidogrel (300 to 900mg as loading dose according to local practice). All other concomitant medications will be consistent with local standard of care.

Inclusion Criteria:

1. Be at least 18 years of age.

2. Has experienced continuous ischemic (cardiac) symptoms for at least 20 minutes.

3. Has onset of symptoms of qualifying acute MI within the past 24 hours, and planned for primary PCI. Patients presenting between 12 and 24 hours of symptom onset should still have an indication for primary PCI, i.e. persistent ischemic symptom and/or persistent or recurrent ST elevation

4. Has an ECG indicative of an acute STEMI showing:

   • ≥ 2 mm ST elevation in 2 or more contiguous precordial ECG leads (anterior infarction); or
   • ≥ 1 mm ST elevation in 2 or more contiguous limb ECG leads (other infarction); or
   • New or presumably new left bundle branch block (LBBB)

5. Shock patients are eligible (but not patients with prolonged cardiac arrest)

6. Be willing to provide informed consent (informed consent may be provided by a legally authorized representative if the patient is not able to provide it).

7. Agree to comply with all protocol-specified procedures, including protocol-mandated follow-up

Exclusion Criteria:

1. Use of UFH or LMWH or any other anticoagulant agent (Vit K antagonists, fondaparinux, bivalirudin) within 48 hours prior to randomization
2. Thrombolytic therapy within the previous 48 hours
3. Known or suspected pregnancy in women of childbearing potential
4. History of hypersensitivity or contraindication to heparin or LMWH
5. Contraindication to primary PCI or any excessive bleeding risk (e.g. recent surgery) or suspected active internal bleeding
6. Coexistent condition associated with a limited life expectancy at short term (e.g. advanced cancer)
7. Prolonged (> 10 minutes) cardiopulmonary resuscitation (CPR)
8. Treatment with other investigational agents or devices within the previous 30 days, planned use of investigational drugs or devices, or previous enrolment in this trial