1. From the Cardiovascular Division, Massachusetts General Hospital, Boston (E.K., J.L.J.); Center for Arrhythmia Prevention (C.M.A., M.V.M.), Division of Preventive Medicine (C.M.A., N.R.C., M.V.M.), and Cardiovascular Division (C.M.A.), Brigham and Women’s Hospital and Department of Medicine, Harvard Medical School, Boston, Mass; and Siemens Healthcare Diagnostics Inc, Newark, Del (M.L.G.).