1 Cardiovascular Research Center, Massachusetts General Hospital, Boston, Cardiac Arrhythmia Service, Massachusetts General Hospital, Boston.
2 Boston University and National Heart, Lung and Blood Institute's Framingham Heart Study, MA, Boston University School of Medicine, MA, Department of Neurology, Boston Medical Center, MA.
3 Boston University and National Heart, Lung and Blood Institute's Framingham Heart Study, MA, Cardiology Section, Department of Medicine, Boston Medical Center, MA, Preventive Medicine Section, Department of Medicine, Boston University School of Medicine, MA, Department of Epidemiology, School of Public Health, Boston University, MA.