1. From the Section of Cardiology (J.W.M., K.M.M., E.J.B.), Division of Medicine (M.A.W.), Division of Preventive Medicine (E.J.B.), Whitaker Cardiovascular Institute (E.J.B.), Boston University School of Medicine; Department of Epidemiology (E.J.B.), School of Public Health, Boston, Mass; the National Heart Lung and Blood Institute’s Framingham Study (E.J.B.), Framingham, Mass; and Cardiovascular Research Center and Cardiac Arrhythmia Service (P.T.E.), Massachusetts General Hospital, Boston, Mass.