1. Department of Cardiology, Gangneung Dong-in Hospital, Gangneung, Korea.
2. Department of Cardiology, Pyeongtaek St. Mary's Hospital, Pyeongtaek, Korea.
3. Department of Statistics and Actuarial Science, Soongsil University, Seoul, Korea.
4. Cardiovascular Division, Department of Internal Medicine, Kyung Hee University Medical Center, Kyung Hee University, Seoul, Korea.