Can a Patent Foramen Ovale Cause a Pulmonary Embolism?
No, a patent foramen ovale (PFO) does not cause pulmonary embolism—the relationship is reversed: a PFO allows thrombi from the venous system to bypass the lungs and enter the arterial circulation (paradoxical embolism), while pulmonary embolism itself elevates right heart pressures that can open the PFO and worsen outcomes. 1
Understanding the Pathophysiology
The critical distinction here is directional flow and causation:
- PFOs create right-to-left shunts, not left-to-right, meaning they allow venous blood to bypass pulmonary circulation when right-sided heart pressures exceed left atrial pressure 2, 1
- Pulmonary embolism causes the PFO to open wider by elevating right heart chamber pressures, which maintains the foramen patent and accommodates thrombus passage to the left atrium 2
- The source of emboli is typically deep vein thrombosis in the lower extremities, which can simultaneously cause both pulmonary embolism (through normal venous return) and paradoxical systemic embolization (through the PFO) 3, 4, 5
Clinical Significance When Both Coexist
When a patient has both PE and PFO, mortality and morbidity increase dramatically:
- PFO-related right-to-left shunts in patients with acute major PE increase death risk by 10-fold and major adverse events (including arterial thromboembolic events) by 5-fold during hospitalization 2, 1
- The PFO worsens hypoxemia already present from PE by allowing deoxygenated blood to bypass the lungs entirely 6
- Paradoxical embolization can cause stroke, myocardial infarction, renal infarction, or limb ischemia—all while the patient is simultaneously experiencing PE 2, 4
Diagnostic Approach
When you suspect this dangerous combination:
- Screen for PFO using echocardiography with agitated saline bubble study or transcranial Doppler in patients with massive or submassive PE (Class IIb recommendation) 1
- Look for evidence of deep vein thrombosis as the common source 1, 5
- Maintain high clinical suspicion for paradoxical embolism when a patient with confirmed DVT presents with simultaneous PE and arterial embolic events (stroke, MI, limb ischemia) 2, 3, 4
- The diagnosis of paradoxical embolism is almost always presumptive and requires systematic criteria 1
Management Considerations
For patients with impending paradoxical embolism (thrombus trapped within the PFO):
- Surgical embolectomy may be considered (Class IIb; Level of Evidence C) and may result in the lowest stroke rate 1
- Thrombolysis carries higher mortality compared to surgery or medical treatment with heparin 1
- Patients with intracardiac shunt should receive aggressive therapeutic options including catheter-based techniques, surgical embolectomy, and appropriate antithrombotic therapy 1, 7, 5
Common Pitfall to Avoid
Do not confuse the direction of causation. The PFO is present in 25-27% of the general population as a benign remnant of fetal circulation 2. It does not generate thrombi or cause PE. Rather, when PE occurs in someone with a PFO, the elevated right heart pressures from the PE transform the PFO from an incidental finding into a potentially lethal conduit for paradoxical embolization 2, 6.
PFO Closure After PE with Paradoxical Embolism
There are no established guidelines for PFO closure in patients with non-cerebral paradoxical embolism (including those with PE and systemic embolization), requiring individualized assessment after careful consideration 2, 1. This represents "no-guidelines land" where the presumptive causal connection between PFO and life-threatening peripheral embolism lacks evidence-based medicine support 2, 8.