1. From the Department of Thoracic and Cardiovascular Surgery, Asan Medical Center, and Division of Biostatistics, Center for Medical Research and Information (S.-C.Y.), University of Ulsan College of Medicine, Ulsan (J.S.M.), and Department of Thoracic and Cardiovascular Surgery, Seoul Saint Mary's Hospital, College of Medicine, Catholic University of Korea, Seoul (H.S.), South Korea.