Determinants of the Doppler flow velocity profile through the mitral valve of the human fetus.

Abstract

Objective-A normal fetal flow velocity profile through the atrioventricular valves early in gestation is characterised by a higher late peak (A) than early peak (E) velocity waveform, whereas the E/A ratio is known to increase throughout pregnancy. This study aims firstly to identify which of the two variables, E or A, is the contributory factor to the increased E/A ratio and secondly to assess the relative influence of gestational age, heart rate, and stroke volume on the flow velocity profile through the fetal mitral valve. Design-Eighty normal fetuses from 18 to 38 weeks of gestation were examined by Doppler echocardiography. The variables measured were E and A waves, the early and late flow velocity integrals (EI and AI), and the total filling velocity integral (TI). The ratios E/A and EI/AI were also calculated. Transvalvar flow was obtained by multiplying TI by mitral area. Associations between Doppler variables and gestational age, heart rate, and stroke volume were assessed by multifactorial Anova and simple or multiple stepwise regression analyses. Results-The results showed that the heart rates found did not affect flow velocity variables. There were only weak correlations between both A and AI values and gestational age (negative) and volume load (positive). With the advance in gestation, a significant increase in the early filling E -wave was found. The E wave was also positively correlated with stroke volume. what is normally found during extrauterine life, the fetal profile is characterised by a higher last peak (A) than early peak (E) velocity waveform. This waveform has been interpreted as an indication of a decrease in compliance of the fetal myocardium. With advancing gestational age, the fetal ratio E/A has been shown to increase progressively which has been interpreted as an improvement in myocardial compliance.2 Doppler derived indices of left ventricular function, however, are complex phenomena affected by the interaction of multiple factors." Whereas the E wave is related to active ventricular muscle relaxation, the A wave is caused by atrial contraction and also influenced by ventricular compliance. The respective velocity profiles of the E and A waves are interrelated with each other. It is theoretically possible that during fetal life, an inadequate myocardial relaxation could impair early ventricular filling thereby allowing more blood to remain in the atrium for the last part of diastole, which would result in a higher A wave. This event would not necessarily be due primarily to a lack of myocardial compliance. Furthermore, in adult life other variables such as heart rate and loading conditions are known to influence the relation between the two ventricular diastolic filling waves independently of muscular diastolic function. Attention has not been given to the influence of these variables on fetal myocardial diastolic function. ConclusionIt is the purpose of this study therefore, firstly to find which of the two elements of left ventricular filling dynamics, the E or A wave, ...

Fetal cardiac performance in uncomplicated and well‐controlled maternal type I diabetes

“…In accordance with a previous study 20 , the atrioventricular E /A flow ratios of FODW increased normally towards the end of pregnancy, mainly via a predominant rise in peak E flow velocities. This augmentation of early diastolic filling is believed to be associated with improved active ventricular relaxation, and may be an important mechanism to elevate fetal cardiac output during gestation 21 .…”

Alternative parameters for echocardiographic assessment of fetal diastolic function

“…The waveforms obtained in diastole by pulsed Doppler echocardiography at the tip of both atrioventricular valves are biphasic, with an E wave representing early ventricular filling velocity, and an A wave related to flow velocity during atrial contraction in presystole. The normal E/A ratio during pregnancy is below 1, which means that the fetal myocardium is relatively "stiff" compared to that of newborns and older children (16)(17)(18)(19)(20)(21)(22). An increase or inversion of the E/A ratio is related to ventricular diastolic dysfunction (23)(24)(25)(26)(27).…”

Profiling fetal cardiac function in twin–twin transfusion syndrome

“…The MPI was calculated as (IVRT + IVCT)/ET. Doppler interrogation of AV flow in an apical four-chamber view was used to measure the E/A ratio 15,16 . Color flow mapping of the AV valve and atrium was used to assess the presence of AV regurgitation.…”