Circadian variations of short-term heart period irreversibility in healthy and chronic heart failure patients

We exploited time irreversibility analysis to characterize short heart period sequences (256 samples) derived from 24h Holter recordings in normal healthy (NO) subjects and chronic heart failure (CHF) patients. We found a significant presence of irreversible dynamics over short time scales, whereas over dominant, longer time scales irreversibility was marginal. Over short time scales in NO subjects the percentage of irreversible dynamics was larger during daytime than during nighttime, thus indicating a larger presence of non linear dynamics during daytime. Same circadian variation was detected in CHF patients but the percentage of irreversible series was higher. In NO subjects during daytime the non linear behavior was mostly the result of bradycardic runs shorter than tachycardic ones. In CHF population this pattern was as present as the reverse pattern (i.e. tachycardic runs shorter than bradycardic ones). Time irreversibility analysis provides useful and reliable indexes even in uncontrolled experimental conditions and during daily activities.