- Appropriate settings to look for Paradoxical Embolism
- Supporting evidence to suggest Paradoxical Embolism
- Diagnosis and supporting tests
- Management of immediate and ongoing risk
The pulmonary circulation provides a large filter for any 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 other form of congenital heart disease. However clots bypassing the lungs can be seen in those with pulmonary arteriovenous malformations.
Aetiology: Venous thrombi passes to the arterial circulation
|Structural Causes of Paradoxical Embolism|
|Patent Foramen Ovale||RA to LA though some feel only significant with a coexisting atrial septal aneurysm. Transcranial Doppler will be positive showing bubbles. Will be seen on transthoracic or trans oesophageal echo|
|PFO and atrial septal aneurysm||this is a protrusion of part of the atrial septum through the fossa ovalis into the right and/or left atrium, is associated with an increased risk for ischaemic stroke, especially in association with a PFO|
|Atrial Septal Defect||RA to LA. Transcranial Doppler will be positive showing bubbles. Will be seen on transthoracic or trans oesophageal echo|
|Pulmonary Arteriovenous malformation||Transcranial Doppler will be positive showing bubbles. RV to LA via shunt - suspect if bubble test positive but trans oesophageal echo negative. Get CT thorax. Usually these are well tolerated and silent but may rarely cause haemoptyisis or haemothorax or predispose to stroke or cerebral abscess.|
Proof of cardioembolism
- A stroke that is Radiologically cardioembolic - i.e. large artery and perhaps multiple territories
- Evidence of a DVT at the time - Doppler USS of legs or at least a raised Dimer
- Evidence of a shunt with Right to left flow
- It helps if there is an underlying venous procoagulant state e.g. malignancy, pregnancy etc.
- Bloods:FBC, U&E, LFTS, CRP, ESR and Raised Dimer
- USS Doppler of legs: may show evidence of DVT
- Transcranial Doppler: the MCA is studied and agitated saline (saline that is mixed with a small volume of air in a syringe) is injected in a vein in the antecubital fossa.) If there is a right to left shunt bubbles will appear in the MCA.
- Transthoracic Echocardiogram:simple test but cannot pick up small lesions. Agitated saline may be injected which can be seen moving from RA to LA. If there is a delay of a few cardiac cycles this could suggest the shunt is non cardiac and suspect a pulmonary AVM
- Transoesophageal Echocardiogram:detailed study but requires sedation. Agitated saline may be injected which can be seen moving from RA to LA. If there is a delay of a few cardiac cycles this could suggest the shunt is non cardiac and suspect a pulmonary AVM
- CTPA chest: will show a Pulmonary AVM. Paradoxical embolism is more likely if the feeder vessel is greater than 3 mm in diameter.
Management is difficult. First of all any PFO which is seen in 25% of the population may simply be a bystander and association does not mean causation. Note that the closure of PFOs is not risk free and may even increase long term risk of (P)AF and so limits any reduction, cancels or even increases any risks of stroke. Pulmonary AVM may be considered for surgery or embolisation. Before PFO closure is ever contemplated a through search for other causes particularly PAF should be performed.