What is a Patent Foramen Ovale (PFO)?
A patent foramen ovale (PFO) is a flap-like opening between the upper chambers of your heart (the right and left atrium) that failed to seal after birth—it's essentially a leftover from fetal circulation that normally closes but persists in about 25-30% of adults 1, 2.
The Basic Anatomy
During fetal development, there's an opening between the two upper heart chambers that allows blood to bypass the lungs (since the fetus gets oxygen from the placenta, not from breathing). After birth, this opening—called the foramen ovale—is supposed to seal shut. When it doesn't completely close, you have a PFO 1.
Think of it as a small door or flap between the right and left atrium that can open under certain conditions, particularly when pressure increases on the right side of the heart 1.
Why It Matters in the Context of Pulmonary Embolism
In the setting of a pulmonary embolism (PE), a PFO becomes particularly dangerous because it can allow blood clots to bypass the lungs and travel directly into the arterial circulation—a phenomenon called paradoxical embolism 1.
Here's what happens:
- Normally, blood flows from right atrium → right ventricle → lungs (where clots get filtered out) → left atrium → left ventricle → body
- With a PFO and elevated right heart pressures (which occur with PE), the shunt can reverse direction
- Blood clots from veins or the right heart can pass through the PFO directly into the left atrium, bypassing the lung's natural filter
- These clots can then travel to the brain (causing stroke), kidneys, limbs, or other organs 1, 3, 4
Research shows that patients with major pulmonary embolism who have a PFO face significantly worse outcomes: 33% mortality versus 14% in those without PFO, plus dramatically higher rates of stroke (13% vs 2.2%) and peripheral arterial embolism (15% vs 0%) 4.
Detection
PFO is diagnosed using echocardiography with bubble contrast (microbubbles injected into a vein). If the bubbles appear in the left atrium within 3-4 heartbeats of appearing in the right atrium, a PFO is present. Transesophageal echocardiography (TEE) is more sensitive than transthoracic imaging and is recommended for younger adults with unexplained strokes or embolic events 1.
Clinical Significance
The presence of a PFO is particularly concerning when:
- There's a large shunt (significant amount of blood crossing)
- An atrial septal aneurysm is present (bulging, floppy septum)
- Right heart pressures are elevated (as with PE)
- There's evidence of deep vein thrombosis or clotting disorders 1, 4
In your situation with recent PE, the PFO represents a potential pathway for clots to cause systemic complications, making it a critical finding that requires careful management consideration 3, 4.