QTc reference ranges in eastern European children aged 6 to 18 years: a large-scale population study and comparison with international normative datasets

BACKGROUND: QT interval corrected for heart rate (QTc) is important. Appropriate reference ranges support ECG interpretation, but data for Eastern European children remain limited. We aimed to derive age- and sex-stratified QTc reference ranges, estimate proportions exceeding cut-offs, and compare results with normative datasets. METHODS: 12‑lead ECGs from 22,335 children aged 6-18 years were obtained through the CARDIOPED screening programme in northwestern Transylvania, Romania. QTc was calculated using Bazett's formula. Age- and sex-stratified percentile curves (P2.5-P97.5) were derived using spline regression. Correlations with anthropometric variables and proportions exceeding QTc cut-offs of 440, 460, and 480 ms were assessed. Results were compared with the Davignon, Rijnbeek, Saarel, Bratincsák, and Mason datasets. RESULTS: Overall median QTc was 408.2 ms in males and 409.9 ms in females. Upper reference limits (P97.5) were 451.4 ms and 457.0 ms, respectively. The sex difference increased from 2.6 ms in the 6-12-year group to 5.7 ms in the 12-18-year group. Obesity and anthropometric variables showed weak, non-significant correlations with QTc. Values were closely aligned with Rijnbeek et al. QTc exceeded 440 ms in 6.0% of males and 460 ms in 1.2% of females; 14 children (0.06%) had a single screening QTc measurement ≥480 ms. CONCLUSIONS: QTc reference ranges in this Eastern European cohort were consistent with European paediatric normative data. Upper reference limits were approximately 450 ms in males and 460 ms in females. Proportions exceeding cut-offs describe cohort distributions, not diagnostic false-positive rates. Percentiles are statistical reference limits rather than validated clinical decision or diagnostic thresholds.