Division of Cardiology, Department of Internal Medicine, Seoul National University Hospital, Seoul, Republic of Korea. Division of Cardiology, Department of Internal Medicine, Asan Medical Center, Seoul, Republic of Korea. Division of Cardiology, Department of Internal Medicine, Soonchunhyang University Seoul Hospital, Seoul, Republic of Korea. Division of Cardiology, Department of Internal Medicine, Inje University Ilsan-Paik Hospital, Goyang, Republic of Korea. Division of Cardiology, Department of Internal Medicine, Dong-A University Hospital, Busan, Republic of Korea. Division of Cardiology, Department of Internal Medicine, Chungnam National University Hospital, Daejon, Republic of Korea. Division of Cardiology, Heart Center, Konyang University Hospital, Daejon, Republic of Korea. Division of Cardiology, Department of Internal Medicine, Seoul Metropolitan Government-Seoul National University Boramae Medical Center, Seoul, Republic of Korea. Division of Cardiology, Department of Internal Medicine, Wonju Christian Hospital, Wonju, Republic of Korea. Division of Cardiology, Department of Internal Medicine, Seoul St. Mary's Hospital, Seoul, Republic of Korea. Division of Cardiology, Department of Internal Medicine, DongGuk University International Hospital, Goyang, Republic of Korea. Division of Cardiology, Department of Internal Medicine, Bucheon St. Mary's Hospital, Bucheon, Republic of Korea. Department of Cardiology, CHA Bundang Medical Center, Seongnam, Republic of Korea. Department of Cardiology, Sejong General Hospital, Bucheon, Republic of Korea. Division of Cardiology, Department of Internal Medicine, Kyung Hee University Hospital, Seoul, Republic of Korea. Division of Cardiology, Department of Internal Medicine, Chuncheon Sacred Heart Hospital, Chuncheon, Republic of Korea. Division of Cardiology, Department of Internal Medicine, Gangnam Severance Hospital, Seoul, Republic of Korea. Department of Cardiology, Heart Center, Saint Carollo Hospital, Sun-cheon, Republic of Korea. Division of Cardiology, Department of Internal Medicine, Ulsan University Hospital, Ulsan, Republic of Korea. Division of Cardiology, Department of Internal Medicine, Presbyterian Medical Center, Jeonju, Republic of Korea. Division of Cardiology, Department of Internal Medicine, Kosin University Gospel Hospital, Busan, Republic of Korea. Division of Cardiology, Department of Internal Medicine, Seoul National University Hospital, Seoul, Republic of Korea. Electronic address: hyosoo@snu.ac.kr.