Evaluation of heart rate variability in pediatric patients with beta thalassemia major: Cross-sectional study

Figure 1 Heart rate variability analysis in a thalassemia patient. A: Spectral and time-domain plots of heart rate variability (HRV) in an 8-year-old child with β-thalassemia major over 24 hours, showing both awake (06:00-22:00) and sleep (22:00-06:00) phases. The patient demonstrates a marked reduction in overall HRV with decreased root mean square of successive normal-to-normal interval differences (parasympathetic activity), percentage of successive normal-to-normal intervals differing by more than 50 ms (short-term variation) and high-frequency (HF) power, reflecting diminished parasympathetic activity; B: Corresponding 24-hour HRV spectral power distribution and RR interval histogram from the same patient shows significantly low total power (912.3 ms²) with a blunted HF (19.7) component. This pattern is consistent with significant autonomic imbalance and reduced parasympathetic modulation. VLF: Very low frequency; LF: Low frequency; HF: High frequency; SDNN: Standard deviation of all normal-to-normal intervals; SDANN: Standard deviation of the 5-minutes average normal-to-normal intervals; RMSSD: Root mean square of successive differences; pNN50: Percentage of successive normal-to-normal intervals differing by > 50 ms.