Reproducibility of the heart rate variability regularity index in chronic heart failure patients

Among non linear analysis of HRV, information domain analysis has recently gained wide interest, allowing to evaluate regularity, defined as the degree of recurrence of a pattern in a signal. The reproducibility of this method, however, is not known and in this study we addressed this issue in the population of chronic heart failure (CHF) patients. We analyzed three 24-hour ECG Holter recordings in 25 clinically stable CHF patients by a regularity index, based on the evaluation of the conditional entropy. We studied the mean values over 24 hours and, separately, during the nighttime and daytime periods to assess the regularity index reproducibility by the standard error of within-patient variability. Results suggest the need of an appropriate signal detrending to fulfill stationarity criteria and to obtain a better reproducible regularity indexes in long-term recordings.