Impact of Intravascular Ultrasound(IVUS)-Guided Chronic Total Occlusion Intervention With Drug-eluting Stents

Inclusion Criteria: 1. Patient is ≥ 20 years or ≤ 80 years old 2. On coronary angiography, complete obstruction of coronary blood flow (TIMI grade 0) with estimated occlusion duration ≥ 3months. 3. On coronary angiography, Reference vessel diameter of 2.5 to 4.0mm by operator assessment 4. On coronary angiography, Total length of total occluded lesion and main lesion is less than 80mm and lesions can be treated less than 4 stents. 5. Guide wire can be passed through occluded lesion without complications 6. Patients who can keep the dual antiplatelet treatment (aspirin, clopidogrel) more than 6 months after procedure Exclusion Criteria: 1. Hypersensitivity reaction or side effects to Aspirin, Clopidogrel, Biolimus A9 and Zotarolimus 2. unprotected Left main disease 3. Cardiogenic shock or LV ejection fraction ≤ 30% 4. Previous stent restenotic lesion 5. Treated within 2 weeks at the same lesion. 6. Creatinine level ≥ 2.0 mg/dL or ESRD 7. Severe tortuous and calcified lesion (Unobtainable IVUS image) 8. Life expectancy \< 1 year 9. Severe hepatic dysfunction (3 times normal reference values) 10. Pregnant women or women with potential childbearing