1. From the Department of Medicine and the Cardiac Arrhythmia Service, Massachusetts General Hospital, Boston, MA (N.A.C., G.A.U., J.P.S.); the Division of Cardiology, Virginia Commonwealth University School of Medicine, Richmond, VA (K.A.E.); the Division of Internal Medicine, University of Alberta Hospital, Edmonton, Canada (F.A.M.); and the Division of Pharmacoepidemiology and Pharmacoeconomics, Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, MA (N.K.C.).