Purpose of the Eustachian Valve in Utero
The Eustachian valve in fetal life directs oxygenated blood from the inferior vena cava toward the foramen ovale and away from the tricuspid valve, allowing oxygen-rich blood returning from the placenta to bypass the pulmonary circulation and enter the systemic circulation directly. 1, 2
Functional Role in Fetal Circulation
The Eustachian valve serves as a critical hemodynamic structure during intrauterine development with the following specific functions:
Blood flow direction: The valve acts as an embryological remnant of the inferior vena cava that specifically channels oxygenated blood from the IVC across the patent foramen ovale into the left atrium, effectively bypassing the non-functional fetal lungs 1, 3
Preferential streaming: By directing blood away from the tricuspid valve and toward the foramen ovale, the Eustachian valve ensures that the most oxygen-rich blood (returning from the placenta via the umbilical vein and ductus venosus) reaches the systemic circulation to supply the developing brain and myocardium 2, 4
Embryological origin: The valve represents an endocardial fold extending from the anterior margin of the inferior vena cava to the anterior part of the limbus fossa ovalis, derived from the right valve of the sinus venosus 4, 5
Postnatal Regression
Normal involution: The Eustachian valve typically regresses after birth once the foramen ovale closes and pulmonary circulation is established, becoming a benign embryological remnant in the majority of cases 1
Persistence complications: When the valve remains prominent postnatally, it can occasionally lead to complications including mimicking atrial masses, promoting paradoxical embolism in patients with patent foramen ovale, or causing neonatal symptoms requiring intensive care 1, 3, 4