Objective: To identify the normal reference ranges of the atrioventricular (AV) time interval, ventriculoatrial (VA) time interval, and VA:AV ratio in fetuses between 18 and 37 weeks of gestational age (GA) and to establish the relationship between AV and VA time intervals and VA:AV ratio with GA and fetal heart rate (FHR).

Materials and Methods: A prospective cross-sectional study was conducted at Rajavithi Hospital between December 2019 and June 2020. AV and VA time intervals and VA:AV ratio were obtained by pulse wave Doppler over inflow and outflow tract of left ventricle. The correlation of the measurement values with GA and FHR were analyzed by Spearman’s rank correlation.

Results: Three hundred seventy pregnant women were enrolled in the present study with 343 participants included in the analysis. The average values of AV and VA time intervals and VA:AV ratio, along with their 5th, 10th, 50th, 90th, and 95th percentiles were calculated from the measurement values. A correlation between each measurement value and GA was demonstrated to be linear [AV time intervals = 91.74+1×GA(weeks) (R²=0.516, p<0.001); VA time intervals = 2.58E2+1.39×GA(weeks) (R²=0.151, p<0.001); and VA:AV ratio = 2.74–8.99E–3×GA(weeks) (R²=0.063, p<0.001)]. A correlation between each measurement value and FHR was also linear [AV time intervals = 1.79E2–0.41×FHR (R²=0.181, p<0.001); VA time intervals = 6.21E2–2.23×FHR (R²=0.811, p<0.001); and VA:AV ratio = 3.9–9.64E-3×FHR (R²=0.150, p<0.001)].

Conclusion: Both AV and VA time intervals are positively correlated with GA but VA:AV ratio is negatively correlated with GA. All measurement values have negative correlation with FHR. The normal reference values of AV, VA time intervals, and VA:AV ratio from the present study may be useful for diagnosis of fetal arrhythmia.

Keywords: normal reference value, atrioventricular time intervals, ventriculoatrial time intervals, VA:AV ratio

DOI: doi.org/10.35755/jmedassocthai.2021.05.12105

Received 12 October 2020 | Revised 11 January 2021 | Accepted 18 January 2021