The aim of this randomized trial is to compare the efficacy of high dose tirofiban administered as either an intracoronary bolus alone or as an intravenous bolus followed by a maintenance infusion with respect to microvascular perfusion and long term left ventricular infarct size, volumes and function.

Primary percutaneous coronary intervention (PCI) is currently the treatment of choice for patients with acute ST elevation myocardial infarction (STEMI). Nevertheless, despite restoration of normal epicardial flow, myocardial perfusion remains impaired in approximately half of patients and is associated with a poor prognosis. A variety of invasive and non-invasive techniques have been proposed to evaluate microvascular perfusion and several invasive hemodynamic measures have been closely associated with microvascular damage.In order to improve microvascular perfusion after primary PCI, a variety of treatment strategies have been developed, such as adjunctive administration of glycoprotein IIb/IIIa inhibitors (GPIs). Although current ACC/AHA guidelines recommend that small molecule GPIs should be administered as a bolus followed by 18 hours of continuous infusion, changes in clinical practice may obviate the need for a maintenance infusion in current practice.

We hypothesized that when tirofiban is administered via intracoronary route, a bolus-only strategy may even be superior to intravenous bolus plus infusion strategy in maintaining myocardial perfusion. In order to evaluate microvascular function, we used a guidewire tipped with pressure and temperature sensors and measured the coronary hemodynamic parameters, as the index of microvascular resistance and coronary flow reserve, measures which have been closely associated with microvascular damage. In order to increase the predictive value of these indices, we performed these measurements four to five days after MI, because it has been shown that the extent of microvascular dysfunction changes, particularly within first 48 hours after reperfusion and stabilizes between 2 days and 1 week after perfusion

Inclusion Criteria:

• Typical ongoing ischemic chest pain for longer than 30 minutes
• ST segment elevation of 0,1 mV or greater in at least two contiguous leads or a new left bundle branch block on the initial ECG.

Exclusion Criteria:

• Cardiogenic shock and / or clinical instability
• previous STEMI
• Malignant life threatening diseases
• Presence of an additional lesion causing more than 50% narrowing distal to the culprit lesion
• Contraindications to aspirin, clopidogrel, or heparin
• inability to give informed consent.