SUPERIOR VENA CAVA (SVC)

INFERIOR VENA CAVA (IVC)

• The majority of blood passes through the fetal liver and into the IVC via the hepatic veins.
• 10-50% bypasses the liver and enters the IVC via the ductus venosus.
• 60% of oxygenated blood in the IVC is directed towards the atrial septum via the eustachian valve (which communicates directly with the lower edge of septum secundum). A smaller percentage remains in the RA and mixes with blood from the SVC
• IVC widens in the proximal portion and enters the RA in a slightly anterior direction. The funnel-like venous confluence is at the end of the abdominal part (venous vestibulum), contains the IVC and orifices of the hepatic veins and ductus venosus.
• It has the appearance of a vertical Y-shaped unit with "2 branches":
• Long branch to LA
• Short branch to RA
• Separated by a cleft between the branches = crista dividens (atrial septum).
• IVC continues as a tube between LA and RA. Walls of this tube are formed by:
• Eustachian valve (also called valve of the IVC) on the right side
• Foramen ovale flap on the left side.
• 2 separate blood pathways result so that the better-oxygenated blood (in the ductus venosus) is directed preferentially towards the brain and coronary arteries.

1. Left sided ductus venosus - foramen ovale pathway that delivers blood directly to the foramen ovale and LA circumventing the RA (oxygenated blood from ductus and left hepatic vein).

2. Right sided IVC - RA pathway - blood is delivered directly to the RA. (poorly saturated blood in IVC enters RA together with SVC blood).

• The left and medial hepatic veins enter the ductus venosus - foramen ovale pathway. The right hepatic veins enter the IVC - RA pathway.
• Inferior Vena Cava Waveform