Anatomical Relationship Between the Eustachian Valve and Chiari Network
The Chiari network is an embryological remnant that represents incomplete resorption of the right valve of the sinus venosus, and it is directly connected to and extends from the Eustachian valve in the right atrium. 1, 2
Embryological Origin and Structural Connection
Both the Eustachian valve and Chiari network originate from the same embryological structure—the right valve of the sinus venosus—with the Chiari network representing a fenestrated, reticulated membrane of threads and strands that extends from the Eustachian valve 1, 3, 2
The Eustachian valve forms the posterior boundary of the cavotricuspid isthmus (an important landmark in atrial flutter ablation), while the Chiari network extends as a web-like structure from this valve into the right atrium 4
This anatomical relationship means that a prominent or redundant Chiari network is essentially an extensive, incompletely resorbed Eustachian valve that has persisted as a reticulated network rather than regressing completely during fetal development 5
Clinical Significance of This Anatomical Relationship
Impact on Congenital Heart Disease Interventions
The presence of an extensive Eustachian valve and Chiari network can preclude percutaneous device closure of atrial septal defects, as these structures may interfere with device deployment and proper rim characterization 6
During evaluation for ASD closure, the description must specifically include whether extensive Eustachian valve and Chiari network are present, as tissue strands crossing the defect can preclude device placement 6
The Chiari network can become entangled with catheter-based devices during interventional procedures, requiring transesophageal echocardiographic guidance for safe deployment and potential disentanglement 3
Association with Patent Foramen Ovale and Stroke Risk
Patient characteristics associated with ischemic stroke in patent foramen ovale include the presence of both Eustachian valve and Chiari network, along with larger-sized PFO, right atrial pressure overload with right-to-left shunting, and atrial septal aneurysms 6
A redundant Chiari network may favor persistence of a patent foramen ovale, formation of an atrial septal aneurysm, and paradoxical embolism 1, 5
Clinical Complications in Younger Patients
In neonates and young infants, a prominent Chiari network can prolapse into the right ventricle and cause intense right-to-left shunting across a patent foramen ovale, resulting in persistent cyanosis that mimics cyanotic congenital heart disease 1, 5, 7
This cyanosis typically resolves spontaneously within the first weeks to months of life as the right ventricular pressures normalize and the network becomes less prominent 5, 7
Fetal hydrops has been reported as a rare prenatal complication of redundant Chiari network, though outcomes are generally positive with spontaneous resolution 5
Diagnostic Considerations
The Chiari network can be confused with other curvilinear, highly mobile pathologic structures in the right atrium, including vegetation, flail tricuspid leaflet, ruptured chordae tendineae, thrombus, or tumor, making accurate echocardiographic identification essential 1, 2
Transesophageal echocardiography is the diagnostic technique of choice for demonstrating the relationship between the Eustachian valve, Chiari network, and any associated atrial septal pathology 6, 3
Large persistent Eustachian valves and Chiari networks can be associated with thrombosis and embolization, bacterial endocarditis, and simulation of atrial tumors on imaging 4
Key Clinical Pitfalls to Avoid
Do not assume the Chiari network is always benign—while found in 2-4% of the population and generally of little clinical consequence, it can cause arrhythmias, compromise cardiovascular function, harbor thrombi, or interfere with interventional procedures 1, 3, 5
Avoid surgical intervention in neonates with cyanosis attributed to Chiari network, as symptoms generally resolve spontaneously and surgery should be avoided 5
During pre-procedural evaluation for ASD closure, specifically assess for extensive Eustachian valve and Chiari network using multiplane transesophageal echocardiography, as their presence may necessitate surgical rather than percutaneous closure 6, 3