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Paradoxical Embolism

Lasted edited: 15/4/2018

Learning objectives

  • Appropriate settings to look for Paradoxical Embolism
  • Causes of Paradoxical Embolism
  • Investigations of Paradoxical Embolism
  • Treatment options


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


PFOMost are entirely innocent and seen in 25% of population but 50% with cryptogenic stroke. Closed by catheter if felt to be causative
ASDFlow will usually go Left to right but here can be reversal.Get Echo. Bubble study. May be surgically closed
VSDFlow will usually go Left to right but here can be reversal with Eisenmenger's syndrome. Get Echo. Bubble study. May be surgically closed
Other Congenital heart disease with R/L shuntFlow will usually go Left to right but here can be reversal with Eisenmenger's syndrome. Get Echo. Bubble study. May be surgically closed
Pulmonary AVMA lesion may be seen on CXR. Needs CTPA. Bubble study will show bubbles in LA after several cardiac cycles. Can be considered for occlusion by interventional radiologists


  • 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


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