In which transthoracic echocardiography (TTE) view is a sinus venosus atrial septal defect (ASD) best appreciated?

Sinus Venosus ASD is Best Appreciated in the Subcostal View on Transthoracic Echocardiography

Sinus venosus atrial septal defects are best visualized using the subcostal view on transthoracic echocardiography, which allows visualization of the entire atrial septum from the superior vena cava to the inferior vena cava orifices. 1

Diagnostic Challenges of Sinus Venosus ASD

Sinus venosus ASDs present unique diagnostic challenges compared to other types of ASDs:

• They are located outside the confines of the fossa ovalis
• They involve either the superior vena cava (more common) or inferior vena cava junction with the right atrium
• They are frequently associated with partial anomalous pulmonary venous connections

Why Subcostal View is Superior

The subcostal view offers several advantages for visualizing sinus venosus ASDs:

1. It provides direct visualization of the entire atrial septum from the SVC to the IVC orifices 1
2. With deep inspiration, the subcostal window improves, allowing better visualization of superior structures 1
3. The pathognomonic feature of SVC overriding across the upper rim of the oval fossa can be demonstrated from this position 2

Imaging Protocol for Suspected Sinus Venosus ASD

When evaluating for a sinus venosus ASD, the TTE examination should include:

• Subcostal views with deep inspiration to optimize imaging
• High right parasternal views as a complementary approach
• 2D imaging of the entire atrial septum with special attention to SVC and IVC junctions
• Color Doppler demonstration of shunting
• Assessment of pulmonary venous connections

Diagnostic Pitfalls

Despite optimal technique, sinus venosus ASDs are frequently missed on TTE:

• False-negative diagnoses are common in adults with poor-quality transthoracic images 1
• The superior sinus venosus defect is most often missed due to its posterior location 1
• Unexplained right ventricular volume overload should prompt further investigation 1

When to Consider TEE

If TTE is inconclusive or inadequate:

• TEE should be performed when there is unexplained right heart enlargement 3
• TEE has superior diagnostic accuracy for sinus venosus ASDs due to the proximity of the transducer to the defect 3
• TEE can accurately identify associated anomalous pulmonary venous connections 3

Parasternal Short-Axis View as a Complementary Approach

For inferior sinus venosus ASDs specifically:

• The parasternal short-axis view can help distinguish inferior sinus venosus ASDs from secundum ASDs 4
• Absence of the posterior rim in the parasternal short-axis view (a "bald" posterior wall) is a consistent finding in inferior sinus venosus ASDs 4

Clinical Implications

Early and accurate diagnosis is crucial:

• Proper identification of sinus venosus ASDs requires surgical rather than percutaneous closure 1
• Associated anomalous pulmonary venous connections must be identified for appropriate surgical planning
• Missed diagnosis can lead to progressive right heart enlargement, pulmonary hypertension, and arrhythmias

In summary, while the subcostal view is the most valuable TTE approach for visualizing sinus venosus ASDs, a comprehensive echocardiographic assessment should include multiple views. When TTE findings are inconclusive but clinical suspicion remains high, TEE should be performed as it provides superior diagnostic accuracy for this challenging defect.