1. Department of Thoracic and Cardiovascular Surgery, Guro Hospital, Korea University College of Medicine, Seoul 02841, Republic of Korea
2. Department of Thoracic and Cardiovascular Surgery, Ansan Hospital, Korea University College of Medicine, Ansan 15355, Republic of Korea
3. Department of Thoracic and Cardiovascular Surgery, Anam Hospital, Korea University College of Medicine, Seoul 02841, Republic of Korea
4. Department of Biostatistics, Korea University College of Medicine, Seoul 02841, Republic of Korea