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The Eustachian Valve (EV) also called «valvulae venae cavae inferioris» has been described for the first time by the Italian anatomist: Bartolomeo Eustachi (born between 1500 and 1513, died 1574 ).

Picture 1: Bartolomeo Eustachi

Anatomy: The Eustachian valve is a crescent-shaped endocardial fold that extents from the anterior margin of the inferior vena cava ostium to the anterior part of the limbus fossa ovalis.

Picture 2: Schematic internal view of the right atrium (after removal of the lateral wall of the right atrium) showing the ostium of superior and inferior vena cava (SVCO and IVCO ), the foramen ovale (FO), the coronary sinus (CS) and Eustachian Valve (EV).

Sonographic aspects: During an ultrasound examination, the Eustachian valve can be recognized on a sagittal section near the bicaval section. It appears as a mobile echogenic line at the anterior part of the inferior vena cava close to the junction with the right atrium.

Pictures 3a,b,c: On a magnified view, we can see the relationships of the Eustachian valve with the others adjacent structures (HV = hepatic veins, ICV = inferior vena cava, RV = right ventricle, RA = right atrium, TV = tricuspid valve). The TV is closed on the top picture and opened on the botton picture.

Picure 4: Color Doppler showing the Eustachian valve directing the flow of the ductus venosus segment of the inferior vena cava across to the foramen ovale towards the left atrium

Physiology: The Eustachian valve is an important element of the fetal circulation. The oxygenated venous blood comes from the placenta via umbilical vein and then joins the terminal part of the inferior vena cava by two different ways:

• The ductus venosus
• The hepatic veins

Picture 5: Arriving in the right atrium, this oxygenated blood is redirected toward the left atrium thought the foramen ovale. Then it is ejected in the ascending aorta via the left ventricle.

This right-to-left shunt allows an adequate oxygenation of two important organs:

1. The heart (via the coronary arteries)
2. The brain (via the brachiocephalics arteries emerging from the aortic arch)

In the absence of this streaming of the blood flow, the heart does not receive as oxygenated blood and there is usually signs of hydrops.

There are two mechanisms used for redirecting blood flow:

1. Anatomic mechanism:The mechanism is characterized by a parallel movement of the flap of the foramen ovale and of the Eustachian valve.At the onset of ventricular systole, the flap valve of the foramen ovale moves towards the left atrial cavity whereas the Eustachian valve moves towards the atrial septum.The Eustachian valve appears to form a conduit within the right atrium directing the inferior vena cava blood into the left atrium. It also prevents the flow coming from the superior vena cava from crossing into the left atrium. The flow coming from the superior vena cava is now directed toward the right ventricle through the tricuspid valve.
2. Hemodynamic mechanism:Beside this “anatomic” explanation, another hemodynamic element seems to favor the passage of the ductus venosus blood through the foramen ovale.The ductus venosus (with a high velocity flow) joins the left side of the inferior vena cava (with low velocity flow). This high velocity permits the ductus venosus stream to remain separated from the low velocity inferior vena cava stream until the foramen ovale.These 2 mechanisms (mechanical and hemodynamically) appears to works simultaneously.

References:

1.David N : “The fetal circulation” in “ Echocardiographie foetale “, ed Masson Paris,1996

2. Schmidt K.G, Silverman N.H, Rudolph A.M : “Assessment of flow events at the ductus venosus, inferior vena cava junction and at the foramen ovale in fetal sheep by use of multimodal ultrasound “ Circulation.1996;93:826-833

3.Kiserud T, Eik-Nes S.H, Blaas H.G, Hellevik L.R : “ Foramen ovale : an ultrasonographic study of its relations to the inferior vena cava, ductus venosus and hepatic veins” Ultrasound Obstet Gynecol .1992 Nov1;2(6):384-5

4.Edelstone D.I, Rudolph A.M : “ Preferential streaming of ductus venosus blood to the brain and heart in fetal lambs” Am J Physiol.1979 Dec;237(6):H724-9

5.Huisman T.W, Stewart P.A, Wladimiroff J.W, Stijnen T : “ Flow velocity waweforms in the ductus venosus, umbilical vein and inferior vena cava in normal human fetus at 12-15 weeks of gestation “ Ultrasound Med Biol.1993;19(6):441-5

6.Rudolph A.M : “ Hepatic and ductus venosus blood flows during fetal life” Hepatology.1983 Mar-Apr;3(2):254-8

7.Yavuz T, Nazli C, Kinay O, Kuts A “ Giant eustachian valve with echographic appearance of divided right atrium” Tex Heart Inst J.2002; 29(4):336.338