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Diagnosis and management of patent foramen ovale.

What is a patent foramen ovale? The fossa ovalis is an overlap flap between the two layers of the atrial septum (septum primum on the left atrial side and septum secondum on the right atrial side). In the fetus there is communication between the left and right atria. Oxygenated blood drains from the umbilical vein via the ductus venosus to the inferior vena cava and then the right atrium. Blood does not flow to the fetal lungs as the pulmonary vascular resistance is high and instead goes via the foramen ovale and ductus arteriosus to the systemic circulation (Figure 1). After the fetus is delivered, breathing causes the pulmonary vasculature resistance to fall with a subsequent increase in cardiac blood flow and increase in left atrial pressure. This causes the primum and secondum septae to fuse together, closing the foramen ovale. In 25–40% of individuals this closure is not complete and a flap or tunnel between the atria remains – the patent foramen ovale (Hagen et al, 1984) (Figure 2). In around 1% of the population, the septae are large and mobile and an atrial septal aneurysm exists (Silver and Dorsey, 1978). The definition of an atrial septal aneurysm varies but a consensus view is that