Conventional heart rate variability analysis of ambulatory electrocardiographic recordings fails to predict imminent ventricular fibrillation - Vybiral, T; Glaeser, DH; Goldberger, AL; Rigney, DR; Hess, KR; Mietus, J; Skinner, JE; Francis, M; Pratt, CM (J Am Coll Cardiol, 1993)