IVUS Versus FFR for Non-infarct Related Artery Lesions in Patients With Multivessel Disease and Acute MI

Inclusion Criteria: * Subject must be at least 19 years of age * Acute ST-segment elevation myocardial infarction (STEMI) \*STEMI: ST-segment elevation ≥0.1 mV in ≥2 contiguous leads or documented newly developed left bundle-branch block * Acute non-ST-segment elevation myocardial infarction (NSTEMI) \*NSTEMI: NSTEMI is defined as a combination of criteria with mandated elevation of a cardiac biomarker, preferably high-sensitive cardiac troponin with at least one value above 99th percentile of the upper reference limit and at least one of the following: 1. Symptoms of ischemia. 2. New or presumed new significant ST-T wave changes 3. Development of pathological Q waves on electrocardiography. 4. Imaging evidence of new or presumed new loss of viable myocardium or regional wall motion abnormality. 5. Intracoronary thrombus detected on angiography. * Successful primary percutaneous coronary intervention (PCI) in \< 12 h after the onset of symptoms for STEMI patients (In case of NSTEMI, PCI should be performed within 72 hours of symptom onset) * Multivessel disease (at least one stenosis of \>50% in a non-IRA ≥2.25 mm by visual estimation) * Subject is able to verbally confirm understandings of risks, benefits and treatment alternatives of receiving invasive physiologic evaluation and PCI and he/she or his/her legally authorized representative provides written informed consent prior to any study related procedure. Exclusion Criteria: * Non-IRA stenosis not amenable for PCI treatment by operators' decision * Cardiogenic shock (Killip class IV) already at presentation or the completion of IRA PCI * Intolerance to Aspirin, Clopidogrel, Prasugrel, Ticagrelor, Heparin, or Everolimus * Known true anaphylaxis to contrast medium (not allergic reaction but anaphylactic shock) * Pregnancy or breast feeding * Non-cardiac co-morbid conditions are present with life expectancy \<2 year or that may result in protocol non-compliance (per site investigator's medical judgment) * Other primary valvular disease with severe degree: severe mitral regurgitation, mitral stenosis, severe aortic regurgitation, or aortic stenosis * Unwillingness or inability to comply with the procedures described in this protocol.