Association Between Heart Rate Variability and Ventricular Repolarization Parameters in Children: Insights from 24-Hour Holter Monitoring

Background/Objectives: Heart rate variability (HRV) and ventricular repolarization parameters are non-invasive markers of cardiac autonomic regulation and electrical stability. Although these parameters un-dergo significant maturational changes during childhood, normative data and their physiological interac-tions in healthy pediatric populations remain insufficiently explored. This study aimed to evaluate the rela-tionship between HRV and ventricular repolarization indices (QT, QTc, QTd, QTcd) in healthy children and to establish age-stratified normative reference values for HRV parameters across four distinct age groups. Methods: This cross-sectional study included 254 healthy children (145 males, 57.1%; mean age 12.51 ± 3.55 years, range 5–18 years). All participants underwent 24-hour ambulatory electrocardiographic (Holter) monitoring. HRV parameters (SDNN, SDANN, RMSSD, pNN50, LF, HF, and LF/HF ratio) and ventricular repolarization indices (QT, QTc, QTd, QTcd) were derived. Participants were stratified into four age groups: 5–8, 9–12, 13–15, and 16–18 years. Normative percentile distributions (5th–95th) were generated for all HRV parameters. Results: Significant maturational increases were observed in all time- and frequency-domain HRV parame-ters across the four age groups (p < 0.001), accompanied by a decline in heart rate (r = -0.471, p < 0.001). The uncorrected QT interval showed strong positive correlations with all HRV indices, particularly SDNN (r = 0.434, p < 0.001) and RMSSD (r = 0.426, p < 0.001), while heart rate correction (QTc) attenuated these associations. Repolarization heterogeneity (QTd) correlated significantly with SDNN (r = 0.269, p < 0.001) and HF (r = 0.186, p = 0.004). Females exhibited significantly higher QTc values (r = 0.294, p < 0.001) and lower mean HRV values compared to males. Multivariate regression identified sex as the only significant independent predictor of QTc (β = 0.294, p < 0.001). Conclusion: Cardiac autonomic modulation, as reflected by HRV, significantly influences ventricular re-polarization dynamics in healthy children. The age-specific normative percentile charts established in this study provide a robust physiological reference for pediatric cardiac autonomic and electrophysiological assessment, facilitating improved clinical interpretation and arrhythmic risk stratification in children and adolescents.