1. From the Universitat Politecnica de Valencia, Valencia, Spain (M.S.G., A.M.C., J.M.); Hospital General Universitario Gregorio Marañón, Madrid, Spain (A.M.C., A.A., F.F.-A., F.A.); Department of Internal Medicine, Center for Arrhythmia Research (J.J., O.B.) and Department of Biomedical Engineering (O.B.), University of Michigan, Ann Arbor, MI; and Instituto de Investigación Sanitaria Gregorio Marañón, Madrid, Spain (A.A., F.F.A., F.A.).