Sex Differences in QT Interval and Beat-to-Beat Temporal QT Variability at Rest and After Submaximal Exercise in Young Adults With and Without Obesity: A Cross-Sectional Study

BackgroundObesity increases arrhythmia risk by altering QT dynamics.However, sex-specific differences during rest and exercise remain insufficiently characterized in young adults, representing a critical gap in cardiovascular risk research. ObjectivesThis study aimed to (1) evaluate sex differences and the potential interaction between sex and obesity in heart rate-corrected QT interval (QTc) and single-lead temporal beat-to-beat QT variability (QTvar) at rest and following submaximal exercise and (2) explore subgroup-specific relationships between body mass index (BMI) and repolarization parameters. MethodsA cross-sectional observational study was conducted on 200 healthy young adults (aged 18-25 years) categorized into obese and non-obese groups based on World Health Organization Asia-Pacific BMI criteria.Participants underwent resting and post-exercise (50% VO2max) continuous Lead II electrocardiogram (ECG) recordings following a standardized submaximal treadmill protocol.QTc (using Bazett's formula) and temporal beat-to-beat QTvar (QTvar = QTmax -QTmin across 10 consecutive complexes) were quantified from Lead II.Statistical comparisons with Bonferroni adjustments and correlation analyses between BMI and QT parameters were performed. ResultsObese females demonstrated significantly higher resting QTvar values than obese males both at rest (227.2 ± 68.5 vs. 174.6 ± 57.2 ms, p = 0.0002, Cohen's d = 0.83) and post-exercise (214.0 ± 25.4 vs. 184.6 ± 81.6 ms, p = 0.045, Cohen's d = 0.48).QTc intervals were numerically longer in females across groups, though differences were not statistically significant (p > 0.05).Following Bonferroni correction for multiple comparisons across correlation analyses (α = 0.0031), a significant positive correlation between BMI and post-exercise QTc was observed in obese females (r = 0.572, p = 0.0004), whereas correlations between BMI and resting QTc in females (r = 0.402, p = 0.018) and recovery QTc in obese males (r = 0.370, p = 0.005) represented exploratory associations that did not meet strict multiplicity adjustment. ConclusionsObese young females exhibit greater temporal beat-to-beat QTvar than obese males, suggesting sex-specific differences in dynamic ventricular repolarization stability under conditions of elevated adiposity.The emergence of a robust positive correlation between BMI and recovery QTc in obese females highlights the potential for differential autonomic and electrophysiological responses following physical exertion, providing hypothesis-generating evidence that warrants prospective longitudinal study.