What is the appropriate evaluation and management of an arterial‑to‑venous shunt identified on echocardiography?

Management of Intracardiac Shunt Identified on Echocardiography

When an arterial-to-venous (or more commonly, venous-to-arterial) shunt is detected on echocardiography, immediate comprehensive evaluation with cardiac catheterization is indicated to assess hemodynamics, quantify the shunt, and determine candidacy for closure or surgical intervention. 1

Initial Diagnostic Characterization

Complete Echocardiographic Assessment Required

The echocardiogram must document the following parameters to guide management 1:

• Shunt pathway direction: Right-to-left versus left-to-right versus bidirectional 1
• Anatomic location: Atrial septal defect (ASD), ventricular septal defect (VSD), patent foramen ovale (PFO), or systemic-to-pulmonary artery connections 1
• Shunt size and hemodynamic significance: Number and dimensions of defects 1
• Ventricular function and hypertrophy: Both right and left ventricular assessment 1
• Valvular abnormalities: Regurgitation or stenosis that may complicate management 1
• Pulmonary artery anatomy and size: Including presence of stenosis or coarctation 1

Bubble Study Interpretation

Agitated saline contrast echocardiography is mandatory to confirm and characterize any suspected shunt 2, 3:

• Intracardiac shunt: Microbubbles appear in the left atrium within 3 cardiac cycles after right atrial opacification 2, 3
• Intrapulmonary shunt: Microbubbles appear after 3-8 cardiac cycles, suggesting pulmonary arteriovenous malformations rather than cardiac defect 3, 4
• Quantification: Grade 0-3 based on number of bubbles; higher grades correlate with larger shunts and increased risk of complications 3

Advanced Imaging When Transthoracic Echo Is Inadequate

Transesophageal echocardiography (TEE) should be performed when 1, 2:

• Transthoracic windows are inadequate (common with lung disease) 1
• Detailed anatomic assessment is needed for procedural planning 2, 3
• Sinus venosus ASD is suspected (missed in ~75% of cases on transthoracic echo) 2
• Evaluation for left atrial thrombus or other embolic sources is required 2

Cardiac MRI or CT should be obtained to 1, 5:

• Quantify pulmonary-to-systemic flow ratio (Qp/Qs) non-invasively 5
• Assess ventricular volumes, ejection fraction, and degree of hypertrophy 1
• Image complex systemic and pulmonary vascular anatomy 1
• Obviate need for diagnostic catheterization in selected cases 1

Mandatory Cardiac Catheterization for Hemodynamic Assessment

Class I indication for catheterization exists to evaluate all patients with identified shunts being considered for definitive repair 1:

Essential Hemodynamic Data to Obtain

• Intracardiac pressures: Right atrial, right ventricular, pulmonary artery, and left-sided pressures 1
• Oxygen saturations: In all cardiac chambers and great vessels 1
• Qp/Qs ratio: Pulmonary-to-systemic blood flow ratio 1, 5
• Pulmonary vascular resistance (PVR): Absolute value and ratio to systemic vascular resistance 1

Critical Thresholds That Determine Operability

Shunt closure is contraindicated when 1, 2, 5:

• Pulmonary arterial systolic pressure is >2/3 of systemic pressure 2, 5
• Pulmonary vascular resistance is >2/3 of systemic resistance 2, 5
• PVR >4.6 Wood units without demonstrated vasoreactivity 6
• Eisenmenger syndrome is present (Qp/Qs <1 with right-to-left shunting) 5

Assessment and Elimination of Collateral Vessels

Class I recommendation to identify and occlude 1:

• Systemic-to-pulmonary vein collaterals 1
• Systemic-to-pulmonary artery connections 1
• Aortopulmonary collaterals 1
• These collaterals are amenable to transcatheter coil occlusion at the time of catheterization 1

Management Algorithm Based on Shunt Type and Hemodynamics

Left-to-Right Shunts (ASD/VSD)

Surgical or device closure is indicated when 5:

• Qp/Qs ratio ≥1.5:1 5
• Right atrial and right ventricular enlargement is present 5
• PVR is <1/3 of systemic resistance 5

Medical management only when:

• Qp/Qs <1.5:1 without chamber enlargement 5
• PVR exceeds operative thresholds 2, 5
• Patient has significant comorbidities precluding intervention 1

Right-to-Left Shunts (PFO with Paradoxical Embolism)

Percutaneous PFO closure is Class I indicated for 2:

• Patients ≤60 years old with cryptogenic stroke 2
• Presence of atrial septal aneurysm or large shunt (>25 microbubbles) 2
• Documented paradoxical embolism 2

Evidence from randomized trials 2:

Trial	Stroke Recurrence with Closure	Stroke Recurrence with Medical Therapy	Number Needed to Treat
CLOSE (2017)	0%	6%	20 over 5 years
REDUCE (2017)	1.4%	5.4%	28 over 3.2 years
RESPECT (2017)	3.6%	5.8%	42 over 5.9 years

Medical therapy with aspirin 81-325 mg daily is indicated when 2:

• Patient is >60 years old 2
• PFO closure is declined or contraindicated 2
• No high-risk features are present 2

Systemic-to-Pulmonary Artery Shunts

Transcatheter shunt exclusion should be examined perioperatively for patients with 1:

• Previous palliative systemic-to-pulmonary shunts (e.g., Blalock-Taussig) 1
• Planned definitive repair of complex congenital heart disease 1

Surgical options include 1:

• Bidirectional Glenn (cavopulmonary anastomosis) for staged palliation 1
• Complete Fontan procedure for definitive single-ventricle palliation 1
• Direct shunt ligation when appropriate 1

Special Considerations for Pulmonary Hypertension

When PH is present with a shunt, determine if the shunt is causative or consequential 1, 7:

• Screening for intracardiac shunts is reasonable when RVSP >45 mmHg on echo 3
• True right-to-left shunting in precapillary PH is usually NOT due to PFO reopening (only 12% of hypoxemic PH patients have intracardiac shunting) 7
• Intrapulmonary shunts (hepatopulmonary syndrome, pulmonary AVMs) are more common causes of hypoxemia in PH than cardiac shunts 4, 7

Echocardiographic predictors of operability in ASD-PAH 6:

• TAPSE/PASP ratio positively predicts PVR ≤4.6 WU (correctable shunt) 6
• Pulmonary valve peak velocity >1 m/s suggests lower PVR 6
• Combined model achieves 86% AUC for predicting operability 6

Critical Pitfalls to Avoid

Age-Related Contraindications

Do not close PFO in patients >60 years old—evidence does not support benefit and medical therapy is preferred 2

Misdiagnosis of Shunt Type

• Late bubble appearance (>3-5 cycles) indicates intrapulmonary rather than intracardiac shunt; requires pulmonary evaluation, not cardiac intervention 2, 3, 4
• Positive bubble study does not equal hemodynamically significant shunt—must quantify with catheterization 1, 5

Procedural Risks

• PFO closure complications occur in 5.9% of cases, most commonly transient atrial fibrillation (4.6%) 2
• Serious device-related events occur in 1.4% 2
• TEE has 0.0098% mortality and 0.88% complication rate 3

Contraindications to Contrast Agents

Commercial ultrasound contrast agents are FDA-contraindicated in patients with known right-to-left shunts due to systemic embolization risk 2

Surgical Expertise Requirement

Class I recommendation: All operations for single-ventricle anatomy, complex shunts, or congenital heart disease must be performed by surgeons with specialized training and expertise in congenital heart disease 1

Long-Term Monitoring

Extended cardiac monitoring (30-day event monitor or implantable loop recorder) is Class I indicated to detect paroxysmal atrial fibrillation, which would mandate anticoagulation regardless of shunt status 2