What is a Patent Foramen Ovale (PFO)?
A patent foramen ovale (PFO) is a remnant of normal fetal circulation that persists after birth, creating a small interatrial communication confined to the fossa ovalis region that allows potential right-to-left shunting of blood between the atria, bypassing the pulmonary circulation. 1
Prevalence and Clinical Significance
- PFO is the most common congenital heart abnormality of fetal origin, present in approximately 25% of the general adult population. 1, 2
- Unlike a true atrial septal defect, a PFO is specifically confined to the region of the fossa ovalis without deficiency of the septum primum or septum secundum. 1
- In most cases, a PFO poses no threat to health and remains clinically silent throughout life. 3
Mechanism of Clinical Events
The primary clinical concern with PFO is its role as an anatomic substrate for paradoxical embolization, where venous thrombi can shunt directly from the right to left atrium, bypassing pulmonary filtration and reaching the systemic arterial circulation, including the brain. 1, 4
Additional mechanisms for clinical events include:
- Formation and release of thrombus from the rim of the PFO defect itself. 1
- Thrombus formation on the left atrial aspect of an associated atrial septal aneurysm. 1
- Passage of vasoactive substances that escape pulmonary degradation. 1
- Paroxysmal atrial fibrillation (which may be unrelated to the PFO itself). 1
High-Risk Anatomical Features
- An atrial septal aneurysm is a critical high-risk feature, defined as redundant and hypermobile interatrial septum demonstrating more than 10-mm excursion from the centerline during the cardiac cycle. 1, 4
- Atrial septal aneurysm is present in approximately 2.5% of the general population, most often in association with PFO. 1
- Large shunt size is another high-risk anatomical feature that increases embolic risk. 2
Diagnostic Criteria
The diagnosis of PFO is established by demonstrating right-to-left transit of contrast microbubbles within 3 to 4 cardiac cycles of right atrial opacification on echocardiography. 1, 4
- Detection modalities include transesophageal echocardiography (TEE) and transthoracic echocardiography (TTE) with contrast. 1
- Transcranial Doppler is another available diagnostic technique. 5
Association with Cryptogenic Stroke
- Approximately 45.9% of young cryptogenic stroke patients (younger than 55 years) have a PFO, versus 14.3% of young patients with stroke of known cause (odds ratio 4.70). 4
- In older patients (≥55 years), the association is weaker: 28.3% of older cryptogenic stroke patients have a PFO versus 11.9% of older patients with stroke of known cause (odds ratio 2.92). 4
- Paradoxical embolism through a PFO accounts for approximately 5% of all strokes and 10% of strokes in younger patients. 2
Other Associated Conditions
PFO has been linked to several clinical conditions beyond stroke:
- Systemic arterial embolism. 1
- Migraine with aura (though prospective randomized trials are needed to verify efficacy of PFO closure on migraine prevention). 6
- Decompression illness in divers. 3
Critical Clinical Pitfall
Do not assume all PFOs are clinically significant—the vast majority remain asymptomatic throughout life, and the presence of a PFO does not automatically indicate it is the cause of a stroke or other clinical event. 5, 3 Risk stratification tools like the RoPE score and PASCAL classification system help determine the likelihood that a PFO is causally related to a cryptogenic stroke. 2