Objective of this study is to 1) analyze the clinical, anatomical and periprocedural differences of patients who underwent a procedure related to coronary CTO through the antergrade approach and retrograde approach; 2) analyze the success rate of the procedures and the incidence and patterns of complications; 3) compare and analyze long-term performances after the successful procedure; and 4) identify the independent factors that require a retrograde approach and the prognostic factor regarding long-term performances after use of each approach.

Inclusion Criteria:

• Patients aged>=19
• Patients who have a CTO lesion in at least one or more epicardial coronary artery 2.5 mm in blood vessel diameter
• Patients who have symptoms of angina or objectively proven myocardial ischemia (asymptomatic myocardial ischemia, stable or unstable angina, non - -ST-segment elevation myocardial infarction)
• Patients who voluntarily agreed to the protocol and the clinical follow-up plan (or let their representative do this), and signed the informed consent form approved by the IRB of each study institute

Exclusion Criteria:

• Patients who are pregnant or lactating or have childbearing potential Patients in whom contrast medium and heparin are contraindicated or who are hypersensitive to them
• Patients in whom aspirin, clopidogrel, ticagrelor and prasugrel, cilostazol are contraindicated
• Patients scheduled to undergo a surgery, etc. that requires discontinuance of an antiplatelet drug within 12 months after participation in the study
• Acute ST elevation myocardial infarction at the time of hospitalization
• Terminally ill patients with their life expectancy < one year
• Patients who have serious diseases other than cardiac diseases that may affect limitation of residual life time or observation of the protocol (e.g. oxygen-independent chronic obstructive pulmonary disease, persisting hepatitis or serious hepatic insufficiency, severe renal disease, etc. Be left up to the discretion of the investigator.)

Subject selection will be determined after screening patients who undergo PCI for CTO lesions and completing the evaluation of all inclusion/exclusion criteria.