1. Division of Cardiology, Department of Internal Medicine, Uijeongbu St. Mary's Hospital, The Catholic University of Korea College of Medicine, Uijeongbu, Korea.
2. Department of Cardiology, Seoul St. Mary's Hospital, The Catholic University of Korea College of Medicine, Seoul, Korea.
3. Severance Cardiovascular Hospital, Yonsei University College of Medicine, Seoul, Korea.
4. Cardiovascular Center, Korea University Guro Hospital, Korea University College of Medicine, Seoul, Korea.