Contribution of Doppler atrioventricular flow waves to ventricular filling in the human fetus

The normal fetal flow velocity profile across the atrioventricular valves is characterized by an early peak (E), which is related to preload and to active ventricular muscle relaxation, and a higher late peak (A), which is caused by the atrial contraction and also influenced by ventricular compliance. The purpose of this study was to determine how these two elements of ventricular filling change during gestation in both ventricles. A total of 485 normal fetuses from 17 weeks to term were examined by Doppler echocardiography. We measured E and A peak velocities and E/A ratio for both mitral and tricuspid valves. Simple regression analysis was applied to assess possible correlation between Doppler variables and gestational age. Moreover, E and A peak velocities were compared using paired Student's t-test. With the advance of gestation a significant linear increase in the E wave and E/A ratio was found for both mitral and tricuspid valves. The A wave shows little change throughout pregnancy. We found significantly higher Doppler velocities for the tricuspid valve than for the mitral valve. The relationship between the E/A ratios for the two valves and gestational age diverge slightly, with higher values for the mitral E/A ratio. This study shows that the A wave velocity remains constant throughout gestation, suggesting little or no change in ventricular compliance. The E wave is mainly responsible for the change in E/A ratio for both atrioventricular valves during gestation. These findings suggest progressive enhancement of relaxation and elastic recoil, an increase in preload, or both, throughout gestation, rather than a change in myocardial compliance as an explanation for the observed increase in the E/A ratio.