Patent Fossa Ovale
20% of adults may have intermittently patent fossa ovale (PFO). That patency, with potential right-to-left shunt demonstrable on TEE by color doppler imaging shown on the left, or intravenous agitated saline contrast injection, may account for paradoxic embolus and stroke. PFO shunting may be continuous left to right, or right to left by provokable maneuvers that raise right atrial pressure (cough, Valsalva, straining). Redundant (aneurysmal) interatrial fossa tissue carries a higher likelihood of PFO.
General comments:
During fetal life, systemic venous return from the lower part of the body, including the newly oxygenated blood returning from the placenta, is directed toward the foramen ovale by a flap of tissue at the mouth of the inferior vena cava, called the Eustachian valve. This allows the relatively well-oxygenated blood to enter the left heart circulation to be delivered to the coronary arteries as well as vessels supplying the developing central nervous system.
The foramen ovale is maintained patent in the fetus because the right atrial pressure is higher than the left atrial pressure. At birth, the organ of oxygenation is transferred from the placenta to the aerated lungs. This results in a dramatic increase in the volume of blood delivered to the lungs. As a result, blood volume returning from lungs to left atrium through the pulmonary veins increases leads to increased left atrial pressure which forces the septum primum against the septum secundum, thus effectively closing the foramen ovale. This fusion is complete in most infants by a month of age, although perhaps 20% of adults may have a probe patent, or intermittently patent foramen ovale. Therapeutic implications of this finding is an important but unresolved medical issue.
Color doppler transesophageal echo shows a left-to-right shunt across a patent fossa ovale (blue jet in mid - screen) probably due to excess mobility of the thin membrane.
Intravenous agitated saline is injected into the brachial vein and arrives first in the right atrium. Evidence of intermittent right to left shunting is shown by the few bright echo 'bubbles' that traverse the slit opening of the fossa and enter the left atrium (above and to the right).
Subcostal 2D view of the thin region of the fossa ovale.
Subcostal color doppler of the thin region of the fossa ovale showing the small left-to-right shunt at its edge.