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, R 2 = 0.15, p , 0.0001, mean bias 8.0 ms) than did in/out (R 2 = 0.10, p = 0.002, bias 18.7 ms) and V/AO (R 2 = 0.06, p = 0.02, bias 12.4 ms). Gestational age and AV intervals were positively correlated with all imaging modalities (R 2 = 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. I solated congenital complete atrioventricular (AV) block is associated with maternal anti-Ro/SSA and anti-La/SSB autoantibodies, which may trigger inflammatory destruction of the AV node in the susceptible fetus. Related to this insult, electrical AV conduction is progressively prolonged to complete heart block at around 20 weeks' gestation. Complete AV block may be preventable if the disease can be recognised and treated at an early stage of AV nodal damage, which is clinically characterised by a short-lived appearance of first-or second-degree AV block.1 2 Thus, a simple, precise diagnostic tool that allows reliable detection of subtle electrical AV conduction anomalies is indispensable for the surveillance of at-risk fetuses.Although recording fetal electrophysiological signals is possible by transabdominal fetal magnetocardiography and signal-averaged ECG, 3-5 their use is limited to a few centres. Alternatively, simultaneous pulse-wave Doppler (PD) interrogation of the mitral valve and left ventricular inflow/ outflow (in/out) or the superior vena cava/ascending aorta (V/AO) have been used to study the chronology of atrial and ventricular systolic events indirectly by their mechanical consequences.6-11 The accuracy of measurements of flowderived AV time intervals is influenced by loading condition, intrinsic myocardial properties, heart rate and the speed of pulse-wave propagation. [12][13][14] In addition, there is a tendency...

Interference with pacemaker function could not be shown with iPod or MP3 players. No additional precaution beyond standard is necessary for patients with pacemakers when they are using these players.

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