title: The "Chaos Theory" and nonlinear dynamics in heart rate variability analysis: does it work in short-time series in patients with coronary heart disease?
abstract: BACKGROUND
  Dynamic analysis techniques may quantify abnormalities in heart rate variability (HRV) based on nonlinear and fractal analysis (chaos theory). The article emphasizes clinical and prognostic significance of dynamic changes in short-time series applied on patients with coronary heart disease (CHD) during the exercise electrocardiograph (ECG) test.
  
  
  METHODS
  The subjects were included in the series after complete cardiovascular diagnostic data. Series of R-R and ST-T intervals were obtained from exercise ECG data after sampling digitally. The range rescaled analysis method determined the fractal dimension of the intervals. To quantify fractal long-range correlation's properties of heart rate variability, the detrended fluctuation analysis technique was used. Approximate entropy (ApEn) was applied to quantify the regularity and complexity of time series, as well as unpredictability of fluctuations in time series.
  
  
  RESULTS
  It was found that the short-term fractal scaling exponent (alpha(1)) is significantly lower in patients with CHD (0.93 +/- 0.07 vs 1.09 +/- 0.04; P < 0.001). The patients with CHD had higher fractal dimension in each exercise test program separately, as well as in exercise program at all. ApEn was significant lower in CHD group in both RR and ST-T ECG intervals (P < 0.001).
  
  
  CONCLUSIONS
  The nonlinear dynamic methods could have clinical and prognostic applicability also in short-time ECG series. Dynamic analysis based on chaos theory during the exercise ECG test point out the multifractal time series in CHD patients who loss normal fractal characteristics and regularity in HRV. Nonlinear analysis technique may complement traditional ECG analysis.
authors.affiliation: Institute for Cardiovascular Diseases and Rehabilitation, Zagreb, Croatia. goran.krstacic@zg.t-com.hr
authors.forename: Goran
authors.initials: G
authors.lastname: Krstacic
authors.forename: Antonija
authors.initials: A
authors.lastname: Krstacic
authors.forename: Anton
authors.initials: A
authors.lastname: Smalcelj
authors.forename: Davor
authors.initials: D
authors.lastname: Milicic
authors.forename: Mirjana
authors.initials: M
authors.lastname: Jembrek-Gostovic
mesh_terms: D016022:Case-Control Studies; D003327:Coronary Disease / Q000503:physiopathology*; D015150:Echocardiography, Doppler; D004562:Electrocardiography; D005260:Female; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D017711:Nonlinear Dynamics; D012372:ROC Curve; D012307:Risk Factors; D018709:Statistics, Nonparametric