1. Division of Cardiology, Department of Internal Medicine, Seoul St. Mary Hospital, College of Medicine, The Catholic University of Korea, Seoul 06591, Republic of Korea
2. Cardiovascular Research Institute for Intractable Disease, College of Medicine, The Catholic University of Korea, Seoul 06591, Republic of Korea
3. Cardiovascular Research Center, Massachusetts General Hospital, Boston, MA 02114, USA
4. Harvard Medical School, Boston, MA 02115, USA