1. From the National Heart Institute, Inaba, Cairo, Egypt (A.E.-S.); Montreal General Hospital, Montreal, Quebec, Canada (T.H.); and the Clinical Cardiac Electrophysiology Laboratories of the Harvard Thorndike Electrophysiology Institute and Arrhythmia Services at Beth Israel Deaconess Medical Center, Boston, Mass (P.P., K.M., L.E., M.E.J.).