Time-interval between maternal hepatic vein Doppler and ECG is longer in late than in early pregnancy

Abstract

Objectives: Venous Wave Protraction Time (VWPT) is defined as the time-interval between the electrocardiographic P-wave and the corresponding venous Doppler A-wave, as obtained by Duplex Ultrasonography. This study aims to evaluate the gestational evolution of VWPT during uncomplicated pregnancy.

Materials and Methods: Cross-sectional study in 4 groups of 10 women at gestations (1) 10-14 weeks, (2) 18-23 weeks, (3) 28-33 weeks and (4) ≥ 37 weeks. Three consecutive venous Doppler waves were recorded at the craniocaudal midportion of the liver from each of the three main branches of hepatic veins, simultaneously with an electrocardiogram (ECG). The time-interval between the ECG P-wave and corresponding A-deflection of venous Doppler waves was measured, without or with correction for changing heart rate (PA and PA/RR respectively). For each group, means and standard deviations were calculated and compared statistically using conventional F-tests for linear mixed-effects models (SAS procedure MIXED).

Results: PA and PA/RR were significantly larger at term than in the first trimester [337±74 versus 220±47 msec, p=0.0008 and 0.48±0.15 versus 0.29±0.09, p=0.0009 respectively]. When groups at early-, mid- and late gestation were compared, VWPT increased gradually with gestational age.

Conclusions: VWPT is significantly longer in late than in early pregnancy, and our results provide evidence for an increase in VWPT with advancing pregnancy. This observation probably relates to maternal cardiovascular adaptation mechanisms, as an increase of venous distensibility during normal pregnancy has been reported. This pilot study invites for further studies to directly link VWPT to venous tone.