Paradoxical Embolism: Pathophysiology, Diagnosis, and Treatment

Pathophysiology of Paradoxical Embolism

The American Heart Association suggests that a patent foramen ovale (PFO) allows the passage of emboli from the venous to the arterial circulation when right-sided heart pressures are elevated, creating a right-to-left shunt that bypasses pulmonary circulation 1
Elevated pressures in the right heart chambers, especially during pulmonary embolism, maintain the PFO open, accommodating thrombi and promoting their passage to the left atrium 2, 3
Patients with deep vein thrombosis can develop simultaneous pulmonary embolism and paradoxical systemic embolization 1
The presence of a PFO with right-to-left shunt in patients with acute pulmonary embolism increases the risk of death by 10 times and major adverse events by 5 times, including arterial thromboembolic events 2, 3

The diagnosis of paradoxical embolism is almost always presumptive and requires specific criteria to be systematically met, according to the American Heart Association 1
The American College of Cardiology recommends that screening for PFO using echocardiography with agitated saline bubble study or transcranial Doppler may be considered for risk stratification in patients with massive or submassive pulmonary embolism (Class IIb; Level of Evidence C) 4, 5
The addition of bubble study to routine transthoracic echocardiography increases the detection of impending paradoxical embolism (bi-atrial thromboembolus trapped within the PFO) 4, 5

The American Heart Association suggests that surgical embolectomy may be considered for patients with any type of pulmonary embolism who present with impending paradoxical embolism (thrombus trapped within the PFO) (Class IIb; Level of Evidence C) 4, 5
Surgical thrombectomy may result in the lowest rate of stroke 4, 5
Thrombolysis may be associated with higher mortality compared to surgery or medical treatment with heparin 4, 5
Patients with intracardiac shunt should be considered for aggressive therapeutic options, including catheter-based techniques, surgical embolectomy, and appropriate antithrombotic therapy 4, 5

The American College of Cardiology recommends that PFO closure should be considered in carefully selected young patients (≤60 years) with high-risk PFO characteristics and cryptogenic stroke, although this carries only a Class IIb recommendation 6
High-risk PFO characteristics include atrial septal aneurysm (OR 15.59 for stroke risk in patients ≤55 years) and moderate or large right-to-left shunt 6
Significant reduction in stroke risk with PFO closure: 1.4% vs 5.4%, NNT=28 to prevent 1 stroke in 2 years 6

Patients requiring long-term anticoagulation for other indications 6
Patients older than 60 years (uncertain benefit, risk of complications may outweigh potential benefits) 6, 7
Small deep infarcts (lacunar strokes) 6
Low-risk PFO (without atrial septal aneurysm, small shunt) 6

How to screen for PFO in patients with massive or submassive pulmonary embolism, according to the American Heart Association 4
How the presence of PFO should change the management of pulmonary embolism 4
When to consider PFO closure in patients with paradoxical embolism and concurrent pulmonary embolism 4
How the size of the PFO shunt and morphology influence the risk of adverse events 5
How to stage the timing of inferior vena cava filter placement and PFO closure in patients with paradoxical embolism and pulmonary embolism 4