title: Prediction of sudden cardiac death by fractal analysis of heart rate variability in elderly subjects.
abstract: OBJECTIVE
  The aim of this study was to test the hypothesis that abnormal scaling characteristics of heart rate (HR) predict sudden cardiac death in a random population of elderly subjects.
  
  
  BACKGROUND
  An abnormality in the short-term fractal scaling properties of HR has been observed to be related to a risk of life-threatening arrhythmias among patients with advanced heart diseases. The predictive power of altered short-term scaling properties of HR in general populations is unknown.
  
  
  METHODS
  A random sample of 325 subjects, age 65 years or older, who had a comprehensive risk profiling from clinical evaluation, laboratory tests and 24-h Holter recordings were followed up for 10 years. Heart rate dynamics, including conventional and fractal scaling measures of HR variability, were analyzed.
  
  
  RESULTS
  At 10 years of follow-up, 164 subjects had died. Seventy-one subjects had died of a cardiac cause, and 29 deaths were defined as sudden cardiac deaths. By univariate analysis, a reduced short-term fractal scaling exponent predicted the occurrence of cardiac death (relative risk [RR] 2.5, 95% confidence interval [CI], 1.9 to 3.2, p < 0.001) and provided even stronger prediction of sudden cardiac death (RR 4.1, 95% CI, 2.5 to 6.6, p < 0.001). After adjusting for other predictive variables in a multivariate analysis, reduced exponent value remained as an independent predictor of sudden cardiac death (RR 4.3, 95% CI, 2.0 to 9.2, p < 0.001).
  
  
  CONCLUSIONS
  Altered short-term fractal scaling properties of HR indicate an increased risk for cardiac mortality, particularly sudden cardiac death, in the random population of elderly subjects.
authors: Division of Cardiology, University of Miami, School of Medicine,  Florida 33101, USA. Tmakikia@med.miami.edu
authors: T H
authors: TH
authors: Mäkikallio
authors: H V
authors: HV
authors: Huikuri
authors: A
authors: A
authors: Mäkikallio
authors: L B
authors: LB
authors: Sourander
authors: R D
authors: RD
authors: Mitrani
authors: A
authors: A
authors: Castellanos
authors: R J
authors: RJ
authors: Myerburg
mesh_terms: D000368:Aged; D002423:Cause of Death; D016757:Death, Sudden, Cardiac / Q000453:epidemiology / Q000209:etiology*; D015716:Electrocardiography, Ambulatory / Q000706:statistics & numerical data*; D005260:Female; D005387:Finland / Q000453:epidemiology; D005500:Follow-Up Studies; D017709:Fractals; D015577:Geriatric Assessment; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008297:Male; D011237:Predictive Value of Tests; D012306:Risk; D012815:Signal Processing, Computer-Assisted