, Volume 1, Issue 4, pp 177-182

Approximate Entropy of Heart Rate Variability: Validation of Methods and Application in Heart Failure

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Nonlinear analysis of heart rate variability (HRV) can give additional information about the autonomic control of heart rate. This study applied the method of approximate entropy (ApEn) in a heart failure population (CHF). The influence of time series length and of adding noise on approximate entropy was examined. The method was applied to study HRV of a healthy population (N = 21) and an end stage heart failure population (N = 21). One-hour recordings during day and night were used. Regular signals showed ApEn values of 0, while adding noise increased ApEn values. Brownian noise (1/f2-noise) seemed to have the least influence on ApEn. Both heart failure patients and the control group showed no circadian difference in ApEn. Heart failure patients showed a loss of circadian variation in time and frequency domain HRV indices. ApEn was higher in the CHF population during the night. We present values of approximate entropy of heart failure patients. Heart failure results in loss of circadian variation. Higher values of ApEn in the CHF population indicate a more erratic heart rate.