How can I assess an atrial septal defect using only echocardiography?

Echocardiographic Assessment of Atrial Septal Defects

Start with transthoracic echocardiography (TTE) for initial diagnosis and characterization, but recognize that transesophageal echocardiography (TEE) is essential for complete evaluation of the entire atrial septum, rim adequacy, and pulmonary venous connections in adults. 1

Initial TTE Assessment

Begin with standard TTE views to identify and characterize the ASD:

Defect Identification and Location

• Secundum ASD: Located in the fossa ovalis region, centrally positioned—best visualized in subcostal and apical four-chamber views
• Primum ASD: Located adjacent to AV valves with no offset between mitral and tricuspid valves 2
• Sinus venosus defects: Superior type (5% of ASDs) near SVC; inferior type (<1%) near IVC—these are NOT true septal defects but interatrial communications 2
• Use color Doppler from off-axis apical four-chamber view to demonstrate flow across the defect 2

Critical Measurements

• Defect size: Measure maximum diameter in multiple views
• Shunt direction: Color Doppler to assess left-to-right vs. bidirectional flow
• Right heart volume overload: RV dilation, paradoxical septal motion, RA enlargement
• Pulmonary artery pressure: Estimate from tricuspid regurgitation velocity

Hemodynamic Significance

• Assess for moderate-to-large left-to-right shunt
• Document RV size and function
• Measure pulmonary artery systolic pressure

When TTE Is Insufficient

TTE has significant limitations in adults: poor visualization of superior and posterior atrial septum, inability to assess anomalous pulmonary venous connections adequately 1. Proceed to TEE when:

• Defect anatomy unclear on TTE
• Planning percutaneous closure
• Suspected sinus venosus defect
• Need to evaluate pulmonary venous connections

TEE for Complete Evaluation

TEE is excellent for visualizing the entire atrial septum and is considered standard of care for guiding closure procedures 1:

Pre-Procedural Assessment

• Defect morphology: Single vs. fenestrated, shape, exact location
• Rim adequacy: Measure all rims (aortic, IVC, SVC, AV valve, posterior)—critical for device closure eligibility
• Defect size: More accurate than TTE, particularly for complex defects
• Pulmonary venous connections: Identify anomalous drainage (especially with sinus venosus defects where right upper/middle lobe veins may drain to RA or SVC) 1
• Left atrial appendage: Rule out thrombus before intervention
• Associated lesions: Patent foramen ovale, other septal defects

Specific Advantages

• Superior visualization of sinus venosus defects and associated anomalous pulmonary venous drainage 1
• Accurate measurement for device sizing
• Assessment of surrounding structures (coronary sinus, vena cavae)

3D Echocardiography Enhancement

3D TEE provides superior anatomic visualization with "en-face" views of the interatrial septum from both RA and LA perspectives 2:

• Renders the defect in anatomically oriented views
• More reliable sizing of complex defects compared to 2D TEE 2
• Can predict device size through validated equations 2
• Creates common visual language between echocardiographer and interventionalist
• Allows direct planimetry of defect area

3D Advantages for Intervention

• Significantly decreases radiation exposure during catheterization 2
• Monitors defect crossing, device deployment, and proper seating
• Confirms device position without compression of neighboring structures (coronary sinus, vena cavae) 2
• Detects complications: residual shunts, device thrombosis

Intraprocedural Guidance

Echocardiography (TEE or intracardiac echo) is standard of care for guiding ASD closure 1:

• Device sizing by direct visualization or balloon "stop-flow" diameter
• Real-time monitoring of catheter/wire position
• Immediate assessment of device deployment
• Detection of pericardial effusion
• Identification of thrombi on wires or devices

Adjunctive Techniques

Contrast Echocardiography

• Agitated saline injection via peripheral vein
• Visualize right-to-left shunting (bubbles appearing in LA within 3-5 beats)
• Useful when defect not clearly seen on standard imaging 3

Pulse Oximetry Integration

• Perform at rest and with exercise
• Identifies shunt reversal (oxygen saturation dropping to <90% with activity despite resting >90%) 1
• Suggests increased pulmonary vascular resistance

Common Pitfalls to Avoid

1. Don't rely solely on TTE in adults—you will miss sinus venosus defects and anomalous pulmonary venous connections 1

2. Don't assume all ASDs are suitable for device closure—inadequate rims (particularly aortic and AV valve rims) require surgical closure 4

3. Don't forget to assess for pulmonary hypertension—elevated PA pressures change management and prognosis

4. Don't overlook associated anomalies—particularly anomalous pulmonary venous drainage with sinus venosus defects

5. In older adults, evaluate for left atrial hypertension from diastolic dysfunction—this may worsen after ASD closure when the "pop-off" to the RA is eliminated 1

Follow-Up Echo Assessment

Post-closure echocardiography should document:

• Device position and stability
• Residual shunts
• RV size normalization
• Pulmonary artery pressure reduction
• Device-related complications (rare)

Serial follow-up at 1,3,6, and 12 months is standard 5