Paradoxical embolisation

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Paradoxical embolism = passage of an embolus (usually thrombus from DVT) from the venous system ➝ arterial system, bypassing the pulmonary filter. This requires a right-to-left shunt (e.g. PFO, ASD, AVM) and can cause stroke, systemic emboli, or MI. ⚡ Clinical suspicion is essential, especially in young patients with cryptogenic stroke.

🔎 Etiology

• 🫀 Intracardiac shunts: PFO, ASD, VSD (Eisenmenger), complex congenital heart disease.
• 🫁 Pulmonary AVMs: direct venous → arterial connection.
• ⬆️ Raised right atrial pressure: pulmonary hypertension, Valsalva manoeuvres (cough, straining, lifting).

⚙️ Pathophysiology – “The 3 Ingredients”

1. 🩸 Source of embolus: classically DVT in legs/pelvis.
2. ➡️ Right-to-left shunt: anatomical defect bypassing lungs.
3. 🔄 Pressure gradient favouring shunt: transient ↑ RA pressure vs LA (e.g. Valsalva).

🚪 Common Shunts

• 🔹 PFO: in 25% of population; up to 50% in cryptogenic stroke. Often incidental but clinically important if DVT present. Closure ↓ recurrence in select patients.
• 🔹 ASD: usually L→R, but R→L possible if RA pressure ↑. Bubble study diagnostic.
• 🔹 VSD: R→L only if Eisenmenger physiology develops (pulmonary HTN).
• 🔹 Congenital cyanotic lesions: e.g. Tetralogy of Fallot, TGA.
• 🔹 Pulmonary AVMs: allow emboli to bypass capillary filter; classically with HHT.

🩺 Clinical Presentation

• ⚡ Stroke/TIA: sudden focal deficit, multiple vascular territories possible.
• 🦵 Peripheral embolism: acute limb ischaemia (pain, pallor, pulseless).
• ❤️ MI: rarely, coronary occlusion.
• 🌍 Multisystem emboli: simultaneous infarcts in brain + limb + other organs.
• 💨 Precipitated by Valsalva: coughing, sneezing, heavy lifting.

🧪 Investigations

• 🩸 Bloods: FBC, coagulation, thrombophilia screen if young/cryptogenic.
• 📉 ECG: AF (alternative cause); RBBB/RA strain (suggests ASD).
• 🖼 Neuroimaging: CT/MRI – multiple embolic infarcts raise suspicion.
• 🫁 CTPA: look for pulmonary AVM or PE.
• 🫀 Echocardiography:
  • TTE – chamber/valve assessment.
  • TEE – better for small shunts, LAA thrombus, vegetations.
  • Bubble study: agitated saline → bubbles in LA = shunt.
• 🔊 Transcranial Doppler with bubble study: detects microbubbles in cerebral vessels.
• 🦵 Doppler legs: exclude DVT.

✅ Evidence For vs 🚫 Against Paradoxical Embolism

• ✅ Multiple vascular territory infarcts.
• ✅ Concurrent DVT/PE.
• ✅ Positive bubble echo / R→L shunt proven.
• 🚫 AF or large artery stenosis identified instead.
• 🚫 Single-territory infarct, stereotyped recurrences.

⚕️ Management

• 💊 Anticoagulation: DOACs/warfarin if DVT/PE present. Antiplatelets alone less protective.
• 🩻 Closure procedures: percutaneous closure of PFO/ASD in selected pts with recurrent cryptogenic stroke + proven shunt.
• 🫁 AVM embolization: coil/plug closure by interventional radiology.
• 🛡 Risk factor modification: stop smoking, treat HTN, DM, dyslipidaemia.
• 🧑‍⚕️ Education: avoid excessive Valsalva, recognise DVT/stroke symptoms early.

📈 Prognosis

Recurrence risk is significant if shunt + DVT not addressed. 👉 Anticoagulation + closure in selected pts markedly improves outcomes. 👉 Without intervention, recurrent paradoxical emboli → disabling stroke or systemic ischaemia.

📚 References

• Alsheikh-Ali AA, Thaler DE, Kent DM. PFO in cryptogenic stroke. Stroke. 2009.
• Overell JR et al. Interatrial septal abnormalities and stroke: meta-analysis. Neurology. 2000.
• Mojadidi MK et al. Cryptogenic stroke & PFO. JACC. 2018.
• Rodés-Cabau J et al. Device closure of PFO. JACC. 2009.
• Kasner SE et al. Rivaroxaban vs Aspirin in ESUS & PFO. Stroke. 2021.