1. From the Department of Cardiology (R.Y., J.B., C.C., C.A., M.M., J.A.S., R.M., M.A.G.-F.) and the Unit of Experimental Medicine and Surgery (M.M.D.), Hospital General Universitario Gregorio Marañón, Madrid, Spain; the Department of Mathematical Physics and Fluids (J.C.A., L.M.), Facultad de Ciencias, Universidad Nacional de Educación a Distancia, Madrid, Spain; and the Department of Signal Theory and Communications (J.L.R.-A.), Universidad Carlos III de Madrid, Spain.