DETErmination of the Duration of the Dual Antiplatelet Therapy by the Degree of the Coverage of The Struts on Optical Coherence Tomography From the Randomized Comparison Between Everolimus-eluting Stents(EES) Versus Biolimus A9-eluting Stents(BES)

Inclusion Criteria: * Patients ≥ 20 years old * Patients with ischemic heart disease who are considered for coronary revascularization with stent implantation. * Significant coronary de novo lesion (stenosis \> 70% by quantitative angiographic analysis) treated by single DES ≤ 25mm * Reference vessel diameter of 2.5 to 3.5 mm by operator assessment Exclusion Criteria: * Complex lesion morphologies such as aorta-ostial, unprotected left main, chronic total occlusion, graft, thrombosis, and restenosis * Reference vessel diameter \< 2.5 mm or \> 4.0mm * Heavy calcified lesions (definite calcified lesions on angiogram) * Primary PCI for STEMI * Contraindication to anti-platelet agents * Treated with any DES within 3 months at other vessel * Creatinine level ≥ 2.0 mg/dL or ESRD * Severe hepatic dysfunction (3 times normal reference values) * Pregnant women or women with potential childbearing * Life expectancy \< 1 year