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INFERIOR VENA CAVA
WAVEFORM |
The IVC has a triphasic pulsatile waveform. The longitudinal section of the IVC is obtained from a sagittal section of the fetal trunk with the sample volume placed equidistant between the outlet of the renal vein and the ductus venosus.
- First component (S).
- Largest.
- Represents forward flow during late diastole (atrial relaxation) and ventricular systole.
- Second component (D).
- Forward flow during early diastolic filling.
- Third component (A).
- Late diastolic retrograde flow due to atrial contraction.
- Percentage reversal at 11-12 weeks = 25-30%. (six times higher than in the late third trimester).
- Reversal thought to be due to low cardiac compliance coupled with a decreased ventricular relaxation time.
Time Velocity Integral (TVI) is the most common index used to measure the percentage of retrograde flow of the A wave with respect to the antegrade
flow (S and D waves).
Inferior vena cava PLI
(Table)– Rizzo et.al. 1992
Inferior vena cava PLI (Graph)– Rizzo et.al. 1992
% reverse flow in IVC = TVI (A wave) / TVI (S + D waves).100
Table of % reverse flow in IVC
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