Longitudinal Trajectories of Autonomic Maturation in Preterm Infants Using Serial 24-Hour Heart Rate Variability Monitoring

Heart rate variability (HRV) is a non-invasive measure reflecting cardiac autonomic regulation and has been used to investigate developmental changes in preterm infants. Short-term HRV recordings have demonstrated developmental changes with advancing postmenstrual age (PMA), but are highly susceptible to transient physiological conditions, limiting reproducibility. We prospectively performed serial 24 h electrocardiographic recordings in 50 preterm infants born at 24–35 weeks’ gestation from postnatal life until before 37 weeks’ PMA to characterize longitudinal HRV trajectories. A total of 879 recordings were analyzed using a 24 h single-window approach, and developmental trajectories were evaluated using linear mixed-effects models. All HRV indices increased progressively with advancing PMA. Infants born at ≥32 weeks’ gestation exhibited significantly higher HRV values after approximately 33 weeks’ PMA than those born at <32 weeks, indicating distinct maturational trajectories according to gestational age. PMA remained independently associated with multiple HRV indices after adjustment for major clinical factors, whereas body weight z-score, respiratory support, oxygen supplementation, and caffeine exposure showed little or no independent association after adjustment. These findings characterize longitudinal 24 h HRV trajectories in preterm infants and suggest that serial 24 h HRV monitoring may provide a framework for assessing developmental changes in cardiac autonomic regulation during neonatal intensive care.