What is a Patent Foramen Ovale (PFO) stroke?

What is a PFO Stroke?

A PFO stroke is an ischemic stroke that occurs when a patent foramen ovale (PFO)—a persistent opening between the heart's right and left atria—allows a venous blood clot to bypass the lungs and travel directly to the brain, causing paradoxical embolism. 1, 2

Understanding Patent Foramen Ovale

Anatomic Definition:

• A PFO is a remnant of fetal circulation that fails to close after birth, creating a small interatrial communication confined to the fossa ovalis region without deficiency of the septum primum or secundum 1
• It is present in approximately 25% of the general adult population, making it the most common congenital heart abnormality of fetal origin 1, 2
• The diagnosis is established by demonstrating right-to-left transit of contrast microbubbles within 3-4 cardiac cycles of right atrial opacification on echocardiography 3, 1

Stroke Mechanism

Primary Pathway:

• The PFO provides an anatomic substrate for paradoxical embolization, where venous thrombi shunt directly from the right to left atrium, bypassing pulmonary filtration and reaching the cerebral circulation 3, 1
• Paradoxical embolism accounts for approximately 5% of all strokes and 10% of strokes in younger patients 4

Alternative Mechanisms:

• In situ thrombus formation on the rim of the PFO defect or on an associated atrial septal aneurysm 3
• Paroxysmal atrial fibrillation (which may be unrelated to the PFO itself) 3, 1
• Passage of vasoactive substances that escape pulmonary degradation 3, 1

Clinical Epidemiology

Association with Cryptogenic Stroke:

• Approximately 50% of patients aged 60 years or younger with cryptogenic stroke have a PFO, compared to 25% in the general population 4
• The association is strongest in younger patients (less than 55 years): 45.9% of young cryptogenic stroke patients have a PFO versus 14.3% of young patients with stroke of known cause (odds ratio 4.70) 3
• 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) 3

Important Caveat:

• Having a PFO does not automatically mean it caused the stroke—PFO prevalence in asymptomatic individuals is high, and not all PFOs confer stroke risk 3, 2
• Deep venous thrombosis or thrombus-in-transit is identified in only a small minority of PFO stroke patients 3

High-Risk Anatomical Features

Factors Increasing Stroke Risk:

• Large right-to-left shunt magnitude 1, 4
• Presence of an atrial septal aneurysm (defined as >10mm excursion of the interatrial septum from centerline during the cardiac cycle) 3, 1
• These anatomical features help identify patients who benefit most from PFO closure 5, 4

Risk Stratification

PASCAL Classification System:

• Combines clinical characteristics (RoPE score) with anatomical features to classify PFO as "probable," "possible," or "unlikely" cause of cryptogenic stroke 5, 4
• Patients classified as PASCAL "probable" (younger patients without vascular risk factors and high-risk PFO features) have a 90% decreased relative rate of recurrent stroke with PFO closure 4
• PASCAL "unlikely" patients (older patients with vascular risk factors and no high-risk PFO features) do not benefit from closure and face higher procedural risks 4

Recurrence Risk

Natural History:

• Annual recurrent stroke rates in PFO patients range from 1.5% to 12%, depending on patient age and population characteristics 3
• In the PICSS study, the 2-year rate of death or recurrent ischemic stroke was 15.9% in patients with PFO, with no significant difference compared to patients without PFO 3