Characteristic diameter pulse waveform patterns of the inferior vena cava in fetuses with abnormalities of cardiac structure

BackgroundChanges in the vessel lumen diameter pulse waveform closely follow changes in the transmural pressure pulse waveform.AimTo study diameter pulse waveform recorded noninvasively from the fetal inferior vena cava (IVC) in fetuses with cardiac abnormality.Study designA paired ultrasonic phase-locked echo tracking system with a high sampling frequency (3000 Hz) was used to follow the movement of diametrically opposite points of the IVC. The lumen was measured as the interval between these points.SubjectsWe studied 80 normal fetuses (20 to 40 weeks) and 11 fetuses with cardiac abnormality.ResultsThe four component waves of the IVC diameter pulse waveform (A, X, V, Y) were identified and measured in the fetal recording. In the normal group, the A and V values increased linearly with advancing gestation. There was an increase in the depth of X and Y descents. Each cardiac abnormality produced characteristic changes in the A, X, V and Y waves of the IVC diameter pulse waveform. The most impressive IVC diameter pulse waveform pattern in fetal cardiac abnormality was the depth of the X descent from the A crest to X trough. In the circumstance of pulmonary stenosis, the A wave was large and prominent (deeper X descent, high pulsatility waveform). In the presence of a dilated right ventricle, or an incompetent tricuspid valve, the X descent was shallow (low pulsatility waveform).ConclusionThe fetal IVC diameter pulse waveform can be simply recorded. The high pulsatility waveform may result from increased end-diastolic pressure with a consequent increased resistance to flow into the ventricle from the atrium. The low pulsatility waveform may indicate depressed myocardial function.