Key Measurements to Report for Atrial Septal Defect (ASD)
When evaluating an ASD, you must report defect type, quantitative defect size, evidence of right ventricular volume overload, pulmonary artery pressure, shunt direction, and rim measurements if considering device closure. 1, 2
Essential Core Measurements
1. Defect Characterization
Defect Type - Specify the anatomical classification:
- Secundum ASD (80% of cases, fossa ovalis region)
- Primum ASD (15%, near crux with AV valve involvement)
- Superior sinus venosus (5%, near SVC entry)
- Inferior sinus venosus (<1%, near IVC entry)
- Unroofed coronary sinus (<1%) 2
Defect Size - Report both qualitative and quantitative measurements:
- Quantitative maximum diameter in millimeters (most critical measurement) 1
- Qualitative assessment: small (hemodynamically insignificant) vs. moderate-to-large (hemodynamically significant) 1
- For adults, defects ≥10 mm generally produce relevant shunting 2
- Consider reporting defect size relative to total atrial septal length (ratio ≤0.35 predicts successful device closure) 3
2. Hemodynamic Assessment
Right Ventricular Volume Overload - This is the key finding that characterizes hemodynamic significance, more important than shunt ratio alone 2:
- RV size and function
- RV/LV dimension ratio
- Presence of RV dilation
Pulmonary Artery Pressure (PAP):
- Estimate systolic PAP from tricuspid regurgitation jet velocity
- Document presence and severity of pulmonary hypertension
- Critical for determining operability (PVR <5 Wood units indicates closure candidacy) 2
Shunt Direction and Magnitude:
- Document left-to-right, right-to-left, or bidirectional flow
- Qp/Qs ratio (pulmonary to systemic flow ratio) when feasible, though echocardiography tends to overestimate compared to catheterization 4, 5
- Presence of significant shunt defined as Qp/Qs >1.5 2
3. Device Closure Planning Measurements (When Applicable)
For secundum ASDs being considered for transcatheter closure, TEE is required to measure 2, 6:
Septal Rim Measurements (width in mm):
- Superior (aortic) rim
- Anterosuperior rim - ratio to defect size >0.75 predicts successful closure 3
- Anteroinferior rim
- Inferior (IVC) rim
- Inferoposterior rim - ratio to defect size >1.0 predicts successful closure 3
- Posterior rim
A rim width <5 mm (except at the aortic side) generally precludes device closure 6. Document adequacy of rims for device anchoring.
Additional Anatomical Details:
- Total atrial septal length (transverse and longitudinal axes)
- Presence of multiple defects
- Atrial septal aneurysm
- Tissue strands crossing the defect
- Eustachian valve or Chiari network prominence
4. Associated Findings
Mandatory assessments:
- Pulmonary venous connection (confirm normal drainage; sinus venosus defects have anomalous pulmonary venous return) 2
- Tricuspid regurgitation severity
- Mitral valve function (prolapse association)
- Left atrial size and pressure indicators
- Associated lesions: persistent left SVC, pulmonary stenosis 2
For primum ASDs specifically:
- AV valve morphology and regurgitation severity
- Presence of subaortic obstruction 7
Imaging Modality Considerations
Transthoracic echocardiography (TTE) is the primary diagnostic tool and provides most measurements 2. However, transesophageal echocardiography (TEE) is essential for:
- Accurate diagnosis of sinus venosus defects
- Pre-device closure evaluation of secundum defects
- Rim assessment and sizing 2, 6
3D echocardiography offers superior spatial orientation and en-face views of the defect, improving accuracy of size and rim measurements 6, 8, 9.
Cardiac MRI or CT serve as alternatives when echocardiography is insufficient, particularly for RV volume assessment and confirming pulmonary venous anatomy 2, 5.
Common Pitfalls
- Do not rely on defect size alone - RV volume overload is the best indicator of hemodynamic significance 2
- Avoid missing sinus venosus defects - these require TEE for accurate diagnosis and are associated with anomalous pulmonary venous drainage 2
- Do not confuse residual LV-to-RA shunt with tricuspid regurgitation in post-repair patients, as this leads to erroneous PAH diagnosis 7
- Fixed cut-off values may be inadequate in children - consider defect size relative to body size and cardiac structures 4