No consensus exists about which coronary artery should be firstly catheterized in primary percutaneous coronary intervention (PCI). The aim of the present study was to compare door-to-balloon time (D2B) of ECG guided immediate infarct-related artery (IRA) PCI with traditional complete coronary angiography followed by PCI for the treatment of ST segment elevation myocardial infarction (STEMI) patients. Primary endpoint is door to device (D2D) time. Secondary end-points are: puncture to device (P2D) time,first medical contact to device (FMC2D) time,incidence of radial artery spasm and occlusion, contrast amount, fluoroscopy time, cumulative air kerma(CAK) and dose area product(DAP).

Inclusion Criteria:

• Patient must be > 18 years of age
• Patients have typical chest pain for at least 20 minutes and have ECG changes typical for STEMI (ST elevation≥2mm in two continuous precordial leads or ST elevations≥1mm in two limb leads or new left bundle branch block) or ECG changes compatible with true posterior MI
• Symptoms ≥ 30 min and ≤12 hours
• Patient and treating interventional cardiologist agree for randomization
• Patient provides written informed consent
• Diagnostic and therapeutic intervention performed through transradial artery approach
• Palpable radial artery.

Exclusion Criteria:

• Concurrent participation in other investigational study
• Current platelet count <100 x 10^9cells/L or Hgb <10 g/dL
• Absence of radial artery pulsation
• Active bleeding or significant increased risk of bleeding, severe hepatic insufficiency, current peptic ulceration, proliferative diabetic retinopathy
• Uncontrolled hypertension
• Prior CABG surgery
• Fibrinolytic therapy for current MI treatment
• patient have a life expectancy of <180days