What are the guidelines for treating intra-pulmonary shunt (intrapulmonary shunt) in the setting of recurrent stroke?

Treatment of Intrapulmonary Shunt in Recurrent Stroke

For patients with recurrent cryptogenic stroke and documented intrapulmonary shunt (such as pulmonary arteriovenous malformations), transcatheter embolization of the feeding vessels is the definitive treatment to prevent further paradoxical embolic events. 1

Initial Diagnostic Approach

When evaluating a patient with recurrent stroke for intrapulmonary shunt:

• Perform contrast-enhanced transesophageal echocardiography (TEE) to identify both intracardiac and extracardiac shunts, as intrapulmonary shunts can mimic patent foramen ovale (PFO) with late appearance of bubbles in the left atrium 2
• If TEE shows late-appearing left atrial bubbles without identifiable intracardiac shunt, proceed to pulmonary angiography to identify pulmonary arteriovenous malformations (PAVMs) 2
• Measure peripheral oxygen saturation, as hypoxemia (e.g., SpO2 <90%) suggests significant right-to-left shunting through pulmonary vessels 2

Evidence for Intrapulmonary Shunt as Stroke Mechanism

Intrapulmonary shunt is an independent predictor of stroke and TIA:

• In cryptogenic stroke patients, intrapulmonary shunt occurs in 35% versus 7% in controls (odds ratio 6.3, P<0.005) 3
• Overall stroke/TIA patients have 22% prevalence of intrapulmonary shunt versus 10% in controls (odds ratio 2.6, P<0.0001) 3
• The mechanism involves paradoxical embolism through the pulmonary circulation, bypassing the capillary filter that normally traps venous emboli 1

Treatment Recommendations

Endovascular Management

Transcatheter embolization is the current standard of care for PAVMs causing stroke: 1

• Use coils or occlusion devices to occlude the feeding vessels of the PAVM 1
• Traditional criteria recommend embolization for PAVMs with feeding arteries ≥3 mm diameter, but smaller PAVMs (even 1.8 mm feeding arteries) have caused recurrent stroke and may require treatment 4
• Successful embolization prevents recurrent paradoxical embolic events, as demonstrated in case reports showing no recurrence after PAVM closure 4, 2

Medical Management Considerations

While awaiting definitive embolization or in patients who cannot undergo the procedure:

• Anticoagulation with warfarin may be considered, as observational data shows significantly higher warfarin use (17.4% vs 0%) in patients with intrapulmonary shunt and no recurrent events during follow-up 5
• Antiplatelet therapy alone is insufficient for preventing paradoxical embolic events through intrapulmonary shunts, as the mechanism involves venous thromboemboli bypassing pulmonary capillaries 1

Important Clinical Pitfalls

Misdiagnosis as PFO

The most critical pitfall is mistaking intrapulmonary shunt for PFO: 2

• Both conditions show bubbles in the left atrium on contrast echocardiography
• Intrapulmonary shunt shows LATE appearance of bubbles (>3-5 cardiac cycles after right atrial opacification) 2
• PFO shows IMMEDIATE appearance of bubbles within 3 cardiac cycles 2
• If the atrial septum cannot be crossed during attempted PFO closure, suspect extracardiac shunt and perform pulmonary angiography 2

Size Threshold Controversy

Do not rely solely on the traditional 3 mm feeding artery threshold for treatment decisions: 4

• PAVMs with feeding arteries as small as 1.8 mm have caused recurrent stroke 4
• In patients with recurrent cryptogenic stroke and documented small PAVM, embolization should be strongly considered regardless of feeding artery size 4

Follow-Up After Treatment

• Repeat pulmonary angiography at 6 months to confirm complete occlusion and absence of residual shunt 2
• Monitor peripheral oxygen saturation as a non-invasive marker of shunt closure 2
• Successful embolization should normalize oxygen saturation if hypoxemia was present pre-procedure 2

Context from Cardiac Shunt Guidelines

While current stroke prevention guidelines focus extensively on PFO closure for cryptogenic stroke 6, they do not specifically address intrapulmonary shunts. The PFO closure recommendations emphasize:

• Age ≤60 years with cryptogenic stroke and high-risk PFO features (large shunt, atrial septal aneurysm) benefit from device closure 6
• However, these guidelines assume intracardiac shunting, and clinicians must recognize that extracardiac (pulmonary) shunts require different diagnostic and therapeutic approaches 2