|A patent foramen ovale (PFO) is a relatively common heart defect characterized by an unsealed tunnel between the right and left atria of the heart. Remarkably, this defect is present in up to 25% of people, although it is often benign.
The PFO is actually a remnant of the fetal circulation. As the chambers of the heart begin to form in a human fetus, a tunnel is created between the newly-formed right and left atria (the foramen ovale) that allows blood to pass directly from the venous circulation to the arterial circulation, circumventing the non-functioning fetal lungs. After birth, the pressure differential between the right and left atria changes with the introduction of blood flow to the now-functioning lungs. As a result, the tunnel collapses and eventually closes completely within the first few months.
In about 20 to 25% of people, however, the foramen ovale does not completely seal and remains “patent” or open. In patients with a patent foramen ovale (PFO), the tunnel can reopen under circumstances of elevated right atrial pressure, such as coughing or straining.
One of the primary concerns with PFO is that it provides a pathway for blood clots (that more commonly form in the veins rather than the arteries) to pass directly to the arterial circulation without being filtered out by the capillary bed of the lungs. The PFO can also allow deoxygenated blood and certain chemical species that are more common in the venous system to cross over to the arterial side. The presence of a PFO has been linked to a number of clinical issues, especially strokes and migraines. Clinical trials are underway to definitively prove the link between PFO and stroke or migraine, and to identify the patients who are most likely to benefit from closure.