Intracardiac Shunts

Evaluate suspected intracardiac shunts using two-dimensional imaging, color and spectral Doppler, chamber remodeling, and—when appropriate—agitated-saline contrast.

Atrial-Level Shunts¶

Patent foramen ovale¶

A PFO is persistence of a potential channel between the septum primum and septum secundum rather than a true deficiency of atrial septal tissue.

Associated high-risk or complex features include:

• Long tunnel ≥8 mm
• Atrial septal aneurysm
• Multiple septal fenestrations
• Thick septum secundum ≥10 mm
• Prominent Eustachian valve or Chiari network
• Large right-to-left shunt
• Distorted septal anatomy from a dilated aortic root

Atrial septal defect¶

A hemodynamically important ASD usually produces:

• RA and RV dilatation
• RV volume-overload pattern
• Predominantly diastolic septal flattening
• Increased pulmonary flow
• Dilated pulmonary artery
• Elevated Qp/Qs

Absence of right-heart enlargement makes a large chronic left-to-right atrial shunt unlikely.

Atrial Septal Imaging¶

Recommended views include:

• Subcostal four-chamber
• Subcostal short-axis
• Parasternal short-axis at the aortic-valve level
• Apical four-chamber

The subcostal window is preferred because the ultrasound beam is more perpendicular to the atrial septum.

Use color Doppler to identify:

• Defect location
• Direction of flow
• Width of the color jet
• Multiple fenestrations
• Residual flow around a closure device

TEE is superior when TTE is nondiagnostic or when detailed anatomy is required for procedural planning.

Agitated-Saline Study¶

Agitated saline detects right-to-left shunting.

1. Obtain an apical or subcostal view containing both atria.
2. Inject agitated saline through a peripheral vein.
3. Confirm dense right atrial opacification.
4. Perform a Valsalva maneuver or cough when feasible.
5. Release the maneuver as contrast reaches the right atrium.
6. Observe the left atrium for several cardiac cycles.

Timing is supportive rather than absolute. Large pulmonary shunts may appear early, while an inadequately performed Valsalva can delay or prevent passage through a PFO.

Causes of a false-negative study¶

• Inadequate right atrial opacification
• Ineffective Valsalva maneuver
• Failure to image during Valsalva release
• Elevated left atrial pressure
• Suboptimal visualization of the interatrial septum
• Flow from the IVC being directed away from an upper-extremity injection

A femoral injection may improve sensitivity when a prominent Eustachian valve directs IVC flow toward the septum, but it is not routinely required.

Ventricular Septal Defects¶

Major anatomic types include:

Evaluate a VSD for:

• Location and number of defects
• Defect size
• Direction of flow
• Peak systolic velocity and gradient
• LV volume loading
• RV and pulmonary pressures
• Aortic cusp prolapse or regurgitation
• Associated congenital abnormalities

VSD gradient¶

A small restrictive VSD usually has a high-velocity jet and large LV-to-RV gradient. A low-velocity jet may indicate a large nonrestrictive defect, elevated RV pressure, or poor Doppler alignment.

Do not determine defect significance from diameter alone.

Pulmonary-to-Systemic Flow Ratio¶

Doppler-derived Qp/Qs estimates shunt magnitude:

• Qp/Qs ≈1: no important net shunt
• Qp/Qs >1: net left-to-right shunt
• Qp/Qs ≥1.5: generally considered hemodynamically significant

The calculation is highly sensitive to outflow-tract diameter because cross-sectional area depends on the radius squared.

Reporting¶

Color Doppler demonstrates a secundum ASD measuring approximately
___ cm with predominantly left-to-right flow.

There is right atrial and right ventricular dilatation consistent
with a hemodynamically important atrial-level shunt.

Agitated-saline contrast demonstrates right-to-left passage within
___ cardiac cycles, consistent with an intracardiac shunt.

The agitated-saline study is negative for right-to-left intracardiac
shunting with and without provocation.

A restrictive [location] VSD is present with left-to-right flow.
Peak velocity is ___ m/s, corresponding to a gradient of ___ mm Hg.

No residual shunt is identified adjacent to the septal closure device.

Pitfalls¶

• Mistaking apical septal dropout for an ASD
• Calling a bubble study negative despite inadequate RA opacification
• Performing or releasing Valsalva at the wrong time
• Using bubble timing as an absolute distinction between intracardiac and intrapulmonary shunting
• Diagnosing a PFO by color Doppler alone when images are inadequate
• Missing a sinus venosus ASD in a patient with unexplained RV enlargement
• Underestimating VSD velocity because of Doppler misalignment
• Assuming a low VSD gradient means the defect is small
• Overinterpreting Doppler-derived Qp/Qs when outflow diameters are poorly measured

Key Points¶

• PFO is a flap-like channel; ASD is a true tissue defect.
• Chronic significant ASD → RA/RV dilatation and RV volume overload.
• The subcostal view is preferred for atrial septal imaging.
• Early left-sided bubbles favor an intracardiac shunt.
• Delayed bubbles favor an intrapulmonary shunt.
• Restrictive VSDs typically have high-velocity jets.
• Qp/Qs ≥1.5 suggests a hemodynamically important left-to-right shunt.

References¶

• ASE Guidelines for Echocardiographic Assessment of ASD and PFO, 2015
• ASE Guidelines for Performing a Comprehensive TTE in Adults, 2019