Origin of the Eustachian Valve
The Eustachian valve originates from the anterior rim of the inferior vena cava orifice at its junction with the right atrium, representing an embryologic remnant of the right valve of the sinus venosus. 1, 2
Embryologic Development
The Eustachian valve develops from the right sinus venosus valve during fetal cardiac development 1, 2. During embryogenesis:
- The right sinus venosus valve normally regresses during fetal life, leaving only a thin ridge or crescent-shaped fold of endocardium at the anterior rim of the inferior vena cava orifice 1
- The valve's embryologic function was to redirect blood flow from the inferior vena cava through the foramen ovale during fetal circulation 3
- Complete regression typically occurs before birth, though persistence into adulthood is common 2, 3
Anatomic Location and Variations
The valve's specific anatomic position is:
- Located at the junction between the inferior vena cava and the right atrium 1, 2
- Arises from the anterior rim of the inferior vena cava orifice 1
- When prominent, it can extend as a mobile membrane within the right atrium 3
Clinical Significance of Persistence
Persistent Eustachian valves are found in approximately 4.2% of adults undergoing transesophageal echocardiography (46 out of 1100 consecutive patients), with an average length of 23.6 ± 9.7 mm 3. The prevalence is similar between men and women 3.
Important Anatomic Distinctions
- When the right sinus venosus valve has partly regressed without septal attachments and without dividing the atrium, it is termed a "prominent Eustachian valve" 1
- When there are attachments on the atrial septum creating the appearance of a divided atrium, it is called cor triatriatum dexter rather than simply a prominent Eustachian valve 1, 4
- This distinction is critical because giant Eustachian valves with high septal insertion can mimic cor triatriatum dexter on echocardiography 1, 4
Clinical Complications
Large persistent Eustachian valves can be associated with:
- Thrombosis and embolization 3
- Bacterial endocarditis (particularly in immunocompromised states or with indwelling devices) 5, 3
- Simulation of atrial tumors on imaging 2
Relevance to Electrophysiology
The Eustachian valve and ridge serve as an important anatomic landmark in cardiac electrophysiology, forming the posterior boundary of the cavotricuspid isthmus used in atrial flutter ablation procedures 6. The cavotricuspid isthmus is bounded anteriorly by the tricuspid valve annulus and posteriorly by the Eustachian valve and ridge 6.