Timing of FFR-guided PCI for Non-IRA in STEMI and MVD (OPTION-STEMI)

Inclusion Criteria: * Age ≥ 19 years old * ST-segment elevation myocardial infarction * ST-segment elevation in at least 2 contiguous leads or, * New onset left bundle branch block * Primary PCI within 12 hours after symptom development * Multivessel disease: Non-IRA with at least 2.5 mm diameter and 50% diameter stenosis by visual estimation * Patient's or protector's agreement about study design and the risk of PCI Exclusion Criteria: * Cardiogenic shock at initial presentation or after treatment of IRA * Unprotected left main coronary artery disease with at least 50% diameter stenosis by visual estimation * TIMI (Thrombolysis in Myocardial Infarction) flow at non-IRA ≤ 2 * Severe procedural complications (e.g. persistent no-reflow phenomenon, coronary artery perforation) which restricts study enrollment by operators' decision * Non-IRA lesion not suitable for PCI treatment by operators' decision * Chronic total occlusion at non-IRA * History of anaphylaxis to contrast agent * Pregnancy and lactation * Life expectancy \< 1-year * Severe valvular disease * History of CABG (coronary artery bypass graft), or planned CABG * Fibrinolysis before admission * Severe asthma * Patient's refusal to participate in study