Evaluating the Accuracy of Non-Invasive Pulsed-Wave Doppler Echocardiography in Measuring Fetal QT and PR Intervals: A Cross-sectional Study

Introduction: Congenital Long QT Syndrome (LQTS) is a common cause of potentially life-threatening ventricular arrhythmias and sudden cardiac death in infants and children. Fetal Magnetocardiography (fMCG) is available in only a few specialized centers worldwide and offers accurate measurements of the QT and PR intervals. The aim of this study was to assess the diagnostic accuracy of PW Doppler echocardiographic measurement of fetal QT and PR intervals compared with the available normative data for fMCG. Methods: 576 pregnant women with singleton pregnancies (16-38 weeks' gestation) were studied in this cross-sectional study between 2022 and 2023 with detailed fetal echocardiograms. Standardized pulsed-wave Doppler techniques were used to measure the PR and QT intervals. Results were compared with published normative data for fMCG, adjusted for gestational age, and were also compared with contemporaneous fMCG in a subset of 42 fetuses. results: Echocardiography demonstrated strong agreement with MCG for QT (mean 270 ± 38.82 ms) and PR (119.26 ± 16.17 ms) intervals. No significant differences were observed between methods (p > 0.05 for PR and HR; QT p = 0.017, considered non-significant after Bonferroni correction). Sensitivity and specificity were 85% and 78%, respectively. Gestational age did not correlate with interval measurements (p > 0.05). Results: Mean QT interval (echo) was 270.0 ± 38.8 and mean PR interval was 119.3 ± 16.2. In the paired subset (n = 42), strong agreement was observed (PR ICC = 0.89 [95% CI: 0.81-0.94]; QT ICC = 0.82 [95% CI: 0.72-0.89]), with mean biases of +2.1 ms and +6.8 ms on Bland-Altman analysis, respectively. Sensitivity and specificity for the full cohort for prolonged intervals (> 95th percentile of GA-adjusted fMCG norms) were 85% and 78% (PPV 68%, NPV 90%). There were no clinically significant differences for PR interval or fetal heart rate, and there was no significant correlation between measured intervals and gestational age (p > 0.05). Discussion: Pulsed-wave Doppler echocardiography is a reliable method for measuring fetal QT and PR intervals and is in good agreement with fMCG. Conclusion: It is a practical, non-invasive, and easily accessible substitute for fMCG when it is not available for prenatal screening of cardiac repolarization and conduction abnormalities.