Autonomic function evaluated by entropy measures of the heart rate variability

Measurements of the system complexity analysis have been applied based on the Renyi and Shannon entropies, in order to describe the Heart Rate Variability (HRV). The RR series were obtained from ECG recordings of 117 subjects: Group IDC, containing 53 patients with idiopathic dilated cardiomyopathy; Group NRM, formed by 64 healthy people. Only the night period (O:OO-5:00 h) was considered for time-series analysis. The entropies were calculated in four spectral bands: very low frequency VLF (0-0.04 Hz), low frequency LF (0.04-0.15 Hz), high frequency HF (O.15-0.45 Hz) and in the total band TF (0-0.45 Hz). A study of the lags involved in the calculation of the entropies was carried out. All entropies showed significant statistical differences (p<0.001) comparing IDC and NRM groups, independently of the lag, except those obtained in the VLF band. A linear combination of the entropies, calculated in the HF, LF and VLF bands, permitted the IDC and NRM groups to be characterised.