Antegrade late diastolic arterial blood flow in the fetus: insight into fetal atrial function

The purpose of this study was to examine the presence and frequency of antegrade late diastolic arterial blood flow (ALDAF) in the fetus and to determine its contribution to cardiac output.

We evaluated the presence of ALDAF in 457 fetal and 21 postnatal echocardiograms. The timing of ALDAF to the ventricular systolic Doppler recording (ALDAF-V) was compared with the mechanical atrioventricular interval and, in neonates, the electrical PR interval. Velocity time integrals of ALDAF and the ventricular systolic Doppler signals were measured, and the percent contribution of ALDAF was calculated.

ALDAF was observed in 365 of 457 studies and included all <11 weeks' gestations. Strong correlation between ALDAF-V, atrioventricular interval, and electrical PR interval suggests that ALDAF coincides with atrial contraction. ALDAF contributed substantially to cardiac output in early gestation with later decline.

ALDAF results from atrial contraction. Increasing gestational age results in less ALDAF, and reduced ALDAF contribution to cardiac output likely due to improved diastolic function.