Patent foramen ovale (PFO) is an anatomical interatrial communication with potential for right-to-left shunt. Foramen ovale has been known since the time of Galen. In 1564, Leonardi Botali, an Italian surgeon, was the first to describe the presence of foramen ovale at birth. However, the function of foramen ovale in utero was not known at that time. In 1877, Cohnheim described paradoxical embolism in relation to PFO.
PFO is a flaplike opening between the atrial septa primum and secundum at the location of the fossa ovalis that persists after age 1 year. In utero, the foramen ovale serves as a physiologic conduit for right-to-left shunting. Once the pulmonary circulation is established after birth, left atrial pressure increases, allowing functional closure of the foramen ovale. This is followed by anatomical closure of the septum primum and septum secundum by the age of 1 year.
The Mayo Clinic autopsy study revealed that the size of a PFO increases from a mean of 3.4 mm in the first decade to 5.8 mm in the 10th decade of life, as the valve of fossa ovalis stretches with age.1
With increasing evidence that PFO is the culprit in paradoxical embolic events, the relative importance of the anomaly is being reevaluated. James Lock, MD, postulated that PFO anatomy results in a cul-de-sac between the septa primum and secundum, predisposing individuals to hemostasis and clot formation. Any conditions that increase right atrial pressure more than left atrial pressure can induce paradoxical flow and may result in an embolic event.
This reasoning has greatly altered the previous conception of PFO and is changing current management of the condition.
PFO is detected in 10-15% of the population by contrast transthoracic echocardiography. Autopsy studies show a 27% prevalence of probe-patent foramen ovale.1 This difference is probably due to the ability to directly visualize PFO on autopsy study, while contrast echocardiography relies on detection of secondary physiologic phenomena.
The prevalence and size of probe-patent PFO is similar in males and females.
The prevalence of PFO declines progressively with age â 34% up to age 30 years, 25% for age 30-80 years, and 20% older than 80 years.
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