Fractional Flow Reserve Versus Angiography for Treatment-Decision and Evaluation of Significant Left MAIN Coronary Artery Disease

Inclusion Criteria: 1. The subject must be ≥20 years of age with angina and/or evidence of myocardial ischemia. 2. Significant de novo LMCA disease, defined as ≥ 50% diameter stenosis by visual estimation with or without concomitant non-left main major epicardial coronary artery disease, amenable to PCI with drug-eluting stent(DES) implantation. 3. The patient or guardian agrees to the study protocol and the schedule of clinical follow-up, and provides informed, written consent, as approved by the appropriate Institutional Review Board/Ethical Committee of the respective clinical site. Exclusion Criteria: 1. left anterior descending coronary artery (LAD) or left circumflex coronary artery (LCx) chronic total occlusion (CTO) 2. Extremely calcified or tortuous vessels precluding FFR measurement. 3. The presence of complex coronary disease anatomy or lesion characteristics or other cardiac condition(s) which leads the participating interventional cardiologist to believe that PCI is not suitable (i.e. the subject should be managed with coronary artery bypass graft or medical therapy alone). 4. Recent ST Elevation Myocardial Infarction(\<7 days prior to randomization). 5. Cardiogenic shock and/or need for mechanical/pharmacologic hemodynamic support. 6. Severe left ventricular dysfunction (ejection fraction \<30%). 7. Requirement for other cardiac surgical procedure (e.g., valve replacement or aorta surgery). 8. Contraindication or inability to take aspirin or P2Y12 inhibitors (clopidogrel, ticagrelor, or clopidogrel). 9. Prior PCI of the left main trunk. 10. Prior coronary artery bypass graft surgery. 11. Subjects requiring or who may require additional surgery (cardiac or noncardiac) within 1 year. 12. End-stage renal disease requiring renal replacement therapy. 13. Liver cirrhosis. 14. Pregnant and/or lactating women. 15. Concurrent medical condition with a limited life expectancy of less than 2 years. 16. Subjects who are actively participating in another drug or device investigational study, which have not completed the primary endpoint follow-up period. However, where at least one or more conditions are satisfied, it could be an exception according to an investigator's discretion; 1\) Participated in the observational study expected no effect on the safety and/or effectiveness evaluation of this trial. 2\) Screening failed before any interventional factor is involved. 3\) Participated in academic trials like strategic comparison studies conducted under standard therapy provided that there is no additional risk or a specific procedure to a subject and no interference between this trial and other studies.