Objective: To establish gestational age-specific reference values of normal fetal atrioventricular (AV) time interval by spectral tissue Doppler imaging (TDI) and pulse-wave Doppler (PD) methods, and to assess their correlation with signal-averaged fetal PR intervals (ECG).
Design: Cohort study.
Setting: Tertiary centre for fetal cardiology.
Patients and measures: 131 pregnant women between 14 and 42 weeks’ gestation underwent 196 fetal echocardiograms and 158 fetal ECG studies. TDI-derived AV intervals were measured as the intervals from atrial contraction (Aa) to isovolumic contraction (IV) and from Aa to ventricular systole (Sa) at the right ventricular free wall. PD-derived AV intervals were measured from simultaneous left ventricular inflow/outflow (in/out) and superior vena cava/aorta (V/AO) recordings.
Results: Measurements were possible by ECG in 61%, by TDI in 100%, by in/out in 100% and by V/AO in 97% of examinations. Aa-IV correlated significantly better with PR intervals (y = 0.67x + 38.29, R2 = 0.15, p < 0.0001, mean bias 8.0 ms) than did in/out (R2 = 0.10, p = 0.002, bias 18.7 ms) and V/AO (R2 = 0.06, p = 0.02, bias 12.4 ms). Gestational age and AV intervals were positively correlated with all imaging modalities (R2 = 0.19–0.31, p < 0.0001).
Conclusion: This study showed the feasibility of fetal AV interval measurements by TDI, and established gestational age-specific reference data. TDI-derived Aa-IV intervals track ECG PR intervals more closely than PD-derived AV intervals and thus should be used as the ultrasound method of choice in assessing fetal AV conduction.
- Aa, atrial contraction
- AV, atrioventricular
- in/out, inflow/outflow
- FEMO, fetal ECG monitor
- IV, isovolumic contraction
- PD, pulse-wave Doppler
- Sa, ventricular systole
- TDI, tissue Doppler imaging
- V/AO, superior vena cava/aorta
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