Anatomy and prevalence

During infancy, fibrous adhesions usually seal the atrial septum, but occasionally it does not seal completely, giving rise to a patent foramen ovale (PFO). In some individuals, excess atrial septal tissue in the region of the fossa ovalis causes increased movement of the septum during respiration. When excursion is greater than 10 mm this appearance is classified as an atrial septal “aneurysm”, which can occur in isolation, or in combination with a PFO.1

PFO is a common finding in the normal healthy population. A necropsy study of 965 normal human hearts showed an overall prevalence of 27%, with no sex differences, and a mean PFO diameter of 5 mm.2 Small PFO probably close spontaneously throughout adult life, as there is a reduction in prevalence from 34% in the first three decades compared to 20% in the ninth and 10th decades.2 Observational echocardiography studies have identified atrial septal aneurysm in about 2–4% of the normal population,3 ,4 associated with a PFO in up to 70% of cases.4

Diagnosis

Transoesophageal echocardiography (TOE) is the investigation of choice for the diagnosis of PFO. Even if the interatrial septum looks normal on two dimensional imaging, colour Doppler may show flow between the atria. Sensitivity is improved by Valsalva and coughing manoeuvres, which transiently increase right atrial pressures, with injection of microbubble contrast agents (agitated saline or gelatine). Passage of microbubbles from right to left atrium within three cardiac cycles usually identifies a PFO. Size is graded as small (up to 5 bubbles), …