Evaluation of Effectiveness and Safety of Antegrade and Retrograde Approach of Percutaneous Coronary Intervention for Chronic Total Occlusions

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.)