Division of Cardiology, Department of Internal Medicine, Severance Hospital, Yonsei University College of Medicine, Seoul, South Korea. Department of Cardiology, Gil Hospital, Gachon University, Incheon, South Korea. Division of Cardiology, Department of Internal Medicine, Bucheon St. Mary's Hospital, The Catholic University of Korea, Seoul, South Korea. Department of Cardiology, Kyung Hee University Hospital at Gangdong, Seoul, South Korea. Department of Internal Medicine, Kyung Hee University College of Medicine, Kyung Hee University Medical Center, Seoul, South Korea. Division of Interventional Cardiology, Cardiovascular Center, Korea University Guro Hospital, Seoul, South Korea. Division of Cardiology, Department of Internal Medicine, Korea University Anam Hospital, Seoul, South Korea. Division of Cardiology, Department of Internal Medicine, Pusan National University School of Medicine, Busan, South Korea. Division of Cardiology, Department of Internal Medicine, Seoul National University College of Medicine, Seoul National University Bundang Hospital, Seongnam, South Korea. Division of Cardiology, Department of Internal Medicine, Boramae Medical Center, Seoul National University College of Medicine, Seoul, South Korea. Division of Cardiology, Department of Medicine, Inje University Ilsan Paik Hospital, Goyang, South Korea. Division of Cardiology, Department of Internal Medicine, Wonju Severance Christian Hospital, Yonsei University Wonju College of Medicine, Wonju, South Korea. Department of Cardiology in Internal Medicine, Chungnam National University Hospital, School of Medicine, Chungnam National University, Daejeon, South Korea. Division of Cardiology, Department of Internal Medicine, Chungbuk National University Hospital, Chungbuk National University College of Medicine, Cheongju, South Korea. Division of Cardiology, Chonnam National University Medical School, Chonnam National University Hopital, Gwangju, South Korea. Division of Cardiology, Department of Internal Medicine, Kosin University Gospel Hospital, Busan, South Korea. Division of Cardiology, Department of Internal Medicine, Hanyang University Seoul Hospital, Hanyang University College of Medicine, Seoul, South Korea.