Development of a Z-score equation for atrioventricular interval measurement by two-dimensional pulsed Doppler echocardiography in normal fetuses between 16 and 33+6 weeks of gestation

Abstract

Purpose: Fetal echocardiography is the primary diagnostic tool for assessing the atrioventricular (AV) time interval. Establishing a reference range for this parameter throughout pregnancy is essential for the early detection of potential abnormalities. The aim of this study was to develop a Z-score equation and establish specific percentiles for the AV time interval in normal fetuses between 16 and 33+6 weeks of gestation.

Methods: A multicenter, prospective, cross-sectional study was conducted between 2018 and 2022. A large sample of pregnant women meeting specific eligibility criteria was included, while cases with potential confounders were excluded. Two-dimensional echocardiography with pulsed Doppler techniques was employed, focusing on the left ventricular inflow and outflow. Data were rigorously analyzed with careful assessment of measurements and normalization procedures.

Results: In total, 1,309 echocardiograms were performed, and 1,183 pregnant women were included after applying the eligibility criteria. Detailed percentiles for each gestational age were determined, and a Z-score equation was formulated. A very weak correlation was observed between AV interval measurement and gestational age (r=0.16, P<0.001). In addition, the correlation between AV interval measurement and fetal heart rate was weak (r=-0.21, P<0.001). The Z-score for the AV interval measurement in milliseconds was derived as follows: Z-score=(AV interval measurement-111.3)/8.6.

Conclusion: This study provides a reference range and Z-score equation for the AV interval, which may enhance the accuracy of monitoring fetuses at risk for developing atrioventricular block-especially in pregnant women with specific antibodies-thus facilitating earlier diagnosis and treatment.

Keywords: Atrioventricular interval; Fetal heart; Reference values; Two-dimensional echocardiography.

Fig. 1.. Measurement of the atrioventricular interval using pulsed Doppler on fetal echocardiography.

Fig. 2.. Pearson correlation coefficient assessing gestational age and atrioventricular (AV) interval – very weak correlation (r=0.16), but statistically significant (P<0.001).

Fig. 3.. Pearson correlation coefficient assessing fetal heart rate and atrioventricular interval – weak correlation (r=-0.21), but statistically significant (P<0.001).

Fig. 4.. Quantile-quantile (Q-Q) plot evaluating normality of atrioventricular (AV) interval measurement.

Fig. 5.. Fetal echocardiogram showing images of how to measure the atrioventricular (AV) interval using different techniques.

A. Doppler of superior vena cava (SVC)–aorta (Ao) from the onset of the retrograde A-wave of SVC Doppler (A) to the onset of the forward S-wave of aortic flow (V). B. Pulmonary artery (PA)–pulmonary vein (PV) Doppler: note the red line showing the measurement of the AV interval from the beginning of the pulmonary venous A wave to the beginning of the pulmonary arterial ejection flow (S wave). C. Antegrade Late Diastolic Arterial blood Flow (ALDAF): from the beginning of the retrograde A wave (A) to the beginning of the forward S wave in the aortic or pulmonary arterial flow (V). D. This image shows how the Doppler sample should be positioned (red arrow) in the ventricular outflow tract to obtain the ALDAF. A, atrial contraction; V, ventricular contraction; RV, right ventricle.