1. From the Cardiac Arrhythmia Service, Massachusetts General Hospital and Harvard Medical School, Boston (A.D., C.H., J.N.R., V.Y.R.); the Pathology Division, Heart Institute (InCor), University of São Paulo Medical School, São Paulo, Brazil (P.G.); Boston University School of Medicine, Boston, Mass (O.V.); and the Harvard-Thorndike Arrhythmia Institute, Beth Israel–Deaconess Medical Center and Harvard Medical School, Boston, Mass (M.E.J.).