Fractal analysis and time- and frequency-domain measures of heart rate variability as predictors of mortality in patients with heart failure

Time-domain measures of heart rate (HR) variability provide prognostic info rmation among patients with congestive heart failure (CHF). The prognostic power of spectral and fractal analytic methods of HR variability has nor be en studied in the patients with chronic CHF. The aim of this study was to a ssess whether traditional and fractal analytic methods of HR variability pr edict mortality among a population of patients with CHF. The standard devia tion of RR intervals, HR variability index, frequency-domain indexes, and t he short-term fractal scaling exponent of RR intervals were studied from 24 -hour Halter recordings in 499 patients with CHF and left ventricular eject ion fraction less than or equal to 35%. During a mean follow-up of 665 +/- 374 days, 210 deaths (42%) occurred in this population. Conventional and fr actal HR variability indexes predicted mortality by univariate analysis. Fo r example, a short-term fractal scaling exponent <0.90 had a risk ratio (RR ) of 1.9 (95% confidence interval [CI] 1.4 to 2.5) and the SD of all RR int ervals <80 ms had an RR of 1.7 (95% CI 1.2 to 2.1). After adjusting for age , functional class, medication, and left ventricular ejection fraction in t he multivariate proportional-hazards analysis, the reduced short-term fract al exponent remained the independent predictor of mortality, RR 1.4 (95% CI 1.0 to 1.9; p < 0.05). All HR variability indexes were more significant un ivariate predictors of mortality in functional class II than in class III o r IV. Among patients with moderate heart failure, HR variability measuremen ts provide prognostic information, but all HR variability indexes fail to p rovide independent prognostic information in patients with the most severe functional impairment. (C) 2001 by Excerpta Medica, Inc.