ABNORMAL WAVEFORMS IN THE

INFERIOR VENA CAVA

In the healthy fetus, a significant decrease in the amount of reversed flow that occurs during atrial contraction occurs with advancing gestation. This is thought to be due to both improved ventricular compliance and to the reduction of right ventricular afterload (due to reduced placental resistance).

IUGR

• Increased reverse flow during atrial contraction.
• Percentage of reverse flow (1) is quantified as the percentage of time velocity interval during atrial contraction (reverse flow) with respect to the total forward time velocity integral (first and second wave). This index relates to the pressure gradient between the RA and RV during end diastole (this is a function of ventricular compliance and ventricular end diastolic pressure) (2).

REFERENCES

1. Reed KL, Appleton CP, Anderson CF et.al. Doppler studies of vena cava flows in human fetuses - insights into normal and abnormal cardiac physiology. Circulation 1990;91:498-505.
2. Appleton CP, Hatle LK, Propp RL. Superior vena cava and hepatic vein doppler echocardiography in healthy adults. J Am Coll Cardiol 1987;10:1032-1039.