Non-linear analysis of heart rate variability in patients with coronary heart disease

The article emphasizes clinical and prognostic significance of non-linear measures of the heart rate variability, applied on the group of patients with coronary heart disease (CHD) and age-matched healthy control group. Three different methods were applied: Hurst exponent (H), Detrended Fluctuation Analysis (DFA) and approximate entropy (ApEn). Hurst exponent of the R-R series was determined by the range rescaled analysis technique. DFA was used to quantify fractal long-range-correlation properties of heart rate variability. Approximate entropy measures the unpredictability of fluctuations in a time series. It was found that the short-term fractal scaling exponent (α₁) is significantly lower in patients with CHD (0.93 ± 0.07 vs. 1.09 ± 0.04; p < 0.001). The patients with CHD had lower Hurst exponent in each program of exercise test separately, as well as approximate entropy than healthy control group (P < 0.001).