1. From the Division of Cardiology, Department of Medicine (Z.S., J.A.S., J.K.H., J.K., P.S.D., E.J.V.), Cardiac Diagnostic Unit (Z.S., S.M., A.A., A.T., B.S., K.S., S.M.H., P.S.D., E.J.V.), and Duke Clinical Research Institute (Z.S., S.M.H., P.S.D., E.J.V.), Duke University Medical Center, Durham, NC.