1. From the Section of Pacing and Electrophysiology, Department of Cardiovascular Medicine, The Cleveland Clinic Foundation, Cleveland, Ohio (N.F.M., A.N., O.W., A.V.); Thoracic and Cardiovascular Institute, Lansing, Mich (J.C.); and Department of Pathology (H.P., P.U.) and Section of Cardiac Electrophysiology, Department of Cardiology (Y.Y., M.M.S.), University of California at San Francisco.