title: Effects and significance of premature beats on fractal correlation properties of R-R interval dynamics.
abstract: BACKGROUND
  Premature beats (PBs) have been considered as artifacts producing a bias in the traditional analysis of heart rate (HR) variability. We assessed the effects and significance of PBs on fractal scaling exponents in healthy subjects and patients with a recent myocardial infarction (AMI).
  
  
  METHODS
  Artificial PBs were first generated into a time series of pure sinus beats in 20 healthy subjects and 20 post-AMI patients. Thereafter, a case-control approach was used to compare the prognostic significance of edited and nonedited fractal scaling exponents in a random elderly population and in a post-AMI population. Detrended fluctuation analysis (DFA) was used to measure the short-term (alpha1) and long-term (alpha2) fractal scaling exponents.
  
  
  RESULTS
  Artificial PBs caused a more pronounced reduction of alpha1 value among the post-AMI patients than the healthy subjects, for example, if > 0.25% of the beats were premature a > 25% decrease in the alpha1 was observed in post-AMI patients, but 4% of the premature beats were needed to cause a 25% reduction in alpha1 in healthy subjects. Both edited (1.01 +/- 0.31 vs 1.19 +/- 0.27, P < 0.01) and unedited alpha1 (0.71 +/- 0.33 vs 0.89 +/- 0.36, P < 0.05) differed between the patients who died (n = 42) and those who survived (n = 42) after an AMI. In the general population, only unedited alpha1 differed significantly between survivors and those who died (0.96 +/- 0.19 vs 0.83 +/- 0.27, P < 0.05).
  
  
  CONCLUSIONS
  Unedited premature beats result in an increase in the randomness of short-term R-R interval dynamics, particularly in post-AMI patients. Premature beats must not necessarily be edited when fractal analysis is used for risk stratification.
authors.affiliation: Division of Cardiology, Department of Medicine, University of Oulu, Finland. misalo@paju.oulu.fi
authors.forename: Mirja A
authors.initials: MA
authors.lastname: Peltola
authors.forename: Tapio
authors.initials: T
authors.lastname: Seppänen
authors.forename: Timo H
authors.initials: TH
authors.lastname: Mäkikallio
authors.forename: Heikki V
authors.initials: HV
authors.lastname: Huikuri
mesh_terms: D000328:Adult; D000368:Aged; D005117:Cardiac Complexes, Premature / Q000401:mortality / Q000503:physiopathology*; D016022:Case-Control Studies; D002940:Circadian Rhythm / Q000502:physiology; D015716:Electrocardiography, Ambulatory; D005260:Female; D005387:Finland; D005500:Follow-Up Studies; D017709:Fractals; D006329:Heart Conduction System / Q000503:physiopathology; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D009203:Myocardial Infarction / Q000401:mortality / Q000503:physiopathology; D013223:Statistics as Topic; D016019:Survival Analysis