Paradoxical embolisation

The pulmonary circulation provides a large filter for any small thrombi returning from the systemic circulation. A small microthrombus to the lungs is probably insignificant but if the pulmonary circulation can be bypassed and shunted then there is a risk of thrombi entering the systemic arterial circulation. This can happen when there are areas allowing right to left shunting in the heart such as a patent foramen ovale or Atrial septal defect or Ventricular septal defect or other form of congenital heart disease. However, clots bypassing the lungs can be seen in those with pulmonary arteriovenous malformations.

Paradoxical Embolic Stroke = DVT + Right to left shunt

Causes

Investigations

• FBC, U&E, ESR, U&E, LFTs
• ECG: AF, RBBB + Axis deviation can suggest ASD
• CXR: may show a lung AVM
• CT/MRI: Multiple territory infarcts
• CTPA: may show pulmonary AVM
• Echo and Bubble study: shows bubbles cross interatrial septum
• Transoesophageal echo

Evidence Against Repeated Paradoxical embolism

• Presence of AF or PAF or other more probable cause
• Stereotypical (identical) Strokes or TIA symptoms
• Lack of multiterritory disease on MRI

Evidence For Repeated Paradoxical embolism

• Multiple territory infarcts
• Procoagulant condition or Evidence of a DVT at the time - Doppler USS or at least a raised Dimer
• Evidence of a shunt with Right to left flow
• Sudden onset
• Clear history of a neurological deficit

Management

• Prevent DVTs +/- Occlude the shunt R/L shunt
• See Patent Foramen Ovale