Atrial Septal Defect

We locally follow infants with an inter-atrial shunt ≥4 mm size. Otherwise, we consider the shunt a patent foramen ovale (depending also on its anatomy and presence of flap). See some examples of the patent foramen ovale in the subcostal section.

• Superior Sinus Venosus Defect

  • Located between the base of the superior vena cava (SVC) and the right upper pulmonary vein (RUPV).

  • Frequently associated with abnormal right pulmonary venous (RPV) return to the SVC or RA.

  • In the subcostal sagittal view, the SVC appears to "override" the defect.

4. Unroofed Coronary Sinus

• A rare and unusual type of left-to-right shunt.

• Suspect this defect when a large coronary sinus is present without a left superior vena cava (LSVC), along with signs of right ventricular volume overload (RVVO).

• The defect results from incomplete formation of the wall covering the coronary sinus, allowing a shunt from the LA → coronary sinus (CS) → RA.

5. Patent Foramen Ovale (PFO) - Most frequent. 

• A persistent, flap-like opening between the atria due to incomplete fusion of the septum primum and septum secundum. 

• Though not a true ASD (as the septal tissue is present but not sealed), it can allow right-to-left shunting under certain conditions.

• PFO is a physiological remnant of normal fetal circulation where the septal tissue is present but not sealed, usually remaining functionally closed unless right atrial pressure increases (e.g., Valsalva maneuver). Ostium Secundum ASD, on the other hand, is a structural defect where there is actual missing atrial septal tissue, leading to continuous left-to-right shunting and potential volume overload in the right atrium and right ventricle. Small atrial septal defects of secundum type or PFO type tend to close in infancy but up to 25% of the population remains with an inter-atrial shunt of various significance. 

Hemodynamic Consequences of an Atrial Septal Defect (ASD)

• An atrial septal defect (ASD), with or without partial anomalous pulmonary venous return (PAPVR), leads to a left-to-right shunt at the atrial level under normal circumstances. The shunt may change depending on the relationship between LA and RA pressure. This may depend on RV-end diastolic and LV end-diastolic pressure, as well as degree of pulmonary/systemic venous return. 

• A left to right inter-atrial shunt eventually results (typically after months/years) in right ventricular volume overload (RVVO). This does not usually happen in the neonatal period since there is still a transitional aspect to the physiology. The RVVO causes:

  • Right ventricular (RV) dilation and hyperdynamic function.

  • Flattening or paradoxical motion of the interventricular septum (IVS).

  • Main pulmonary artery (MPA) enlargement due to increased pulmonary blood flow.

  • Eventually the excess pulmonary blood flow leads to chronic remodelling of the pulmonary vasculature (usually in the 30s - 40s). Eisenmenger syndrome is the late-stage consequence of an untreated atrial septal defect (ASD) or other congenital heart defects that cause a left-to-right shunt. Over time, chronic volume overload and increased pulmonary blood flow lead to pulmonary vascular remodeling and progressive pulmonary hypertension. As pulmonary vascular resistance rises beyond systemic levels, the shunt direction reverses (bidirectional and eventually right-to-left), resulting initially in attenuation of symptoms (paradoxical balance in Qp:Qs) and eventually in cyanosis and systemic hypoxemia. This leads to right ventricular failiure and increased mortality. This typically develops in adulthood, often in the third or fourth decade of life, though the timeline varies based on defect size and pulmonary vascular response. Once Eisenmenger physiology is established, closure of the ASD is contraindicated due to the risk of worsening right ventricular failure.

Echocardiographic Goals for Atrial Septal Defects (ASD)

1. Assess Defect Characteristics

   • Measure size, location, and number of defects using imaging and color Doppler.

2. Evaluate ASD Flow

   • Assess ASD flow using color Doppler in all views.

   • In views with an acceptable interrogation angle:

     • Use Pulsed-Wave (PW) Doppler (preferred) and Continuous-Wave (CW) Doppler to measure the mean pressure gradient.

3. Identify Pulmonary Venous Connections

   • Pay special attention to:

     • Right upper pulmonary vein (RUPV) in superior sinus venosus defects.

     • Right lower pulmonary vein (RLPV) in inferior sinus venosus defects. Best views are the subcostal short (sagittal / bicaval) axis view. 

4. Measure Septal Rims and Total Atrial Septal Length (if secundum ASD)

   • Total septal length from:

     • Subcostal in-between and short-axis (bicaval) views.

     • Right sternal border bicaval view.

     • Apical 4-chamber view - although the angle of insonnation typically is parallel and may create acoustic shadows - as such it is not a good view to measure the actual defect.

   • Specific septal rims:

     • Retroaortic rim – Assessed in parasternal short-axis (PSAX) view.

     • Posterior rim – Assessed in PSAX view.

     • Inferior septum – Assessed in apical 4-chamber (A4C) and subcostal sagittal views.

     • Superior rim – Assessed in subcostal sagittal and right sternal border bicaval views.

5. Assess Septal Motion and Right Ventricular Volume Overload (RVVO)

   • Use M-mode to evaluate interventricular septal (IVS) motion and identify paradoxical motion due to RV volume overload.

6. Estimate Right Ventricular (RV) Pressure

   • Assess tricuspid regurgitation (TR) jet and pulmonary regurgitation (PR) jet for RV pressure estimation.

7. Evaluate Right Ventricular (RV) Size and Function

   • Obtain high-quality views of the RV to assess chamber size and contractility.

8. Post-ASD Device Closure Assessment

   • Focus on:

     • Residual atrial-level shunting.

     • Atrioventricular valves, assessing for any new regurgitation or dysfunction.

     • Pulmonary and systemic venous drainage, ensuring no interference from the device.

     • Aortic valve function, checking for any impact from device placement.

Ostium secundum ASD, left to right.

ASD osteum primum (in the context of an AVSD)

Silvestry, Frank E., et al. "Guidelines for the echocardiographic assessment of atrial septal defect and patent foramen ovale: from the American Society of Echocardiography and Society for Cardiac Angiography and Interventions." Journal of the American Society of Echocardiography 28.8 (2015): 910-958.