When and how to diagnose patent foramen ovale

Patent foramen ovale (PFO) is a common finding in the healthy population, with a prevalence of 27% in one necropsy study of 965 normal hearts from patients with no history of cardioembolic events.1 It is also the most common cardiac finding in young patients (< 55 years of age) with an unexplained cerebrovascular event, presumably caused by paradoxical emboli.2 The presumed mechanism is the migration of a thrombus (or less commonly air or fat) from the venous system to the left atrium via a PFO, with subsequent systemic embolisation. Determining whether paradoxical embolism has occurred through a PFO ideally requires the presence of the PFO “triad”, which combines raised right atrial pressure, venous source of thrombosis, and the presence of PFO. The larger size of a PFO and greater number of microbubbles passing through a shunt during echocardiography has also been associated with an increased incidence of cerebrovascular events3,4 Although PFO is becoming increasingly recognised as a cause for cryptogenic cerebrovascular events, there are other situations in which documenting a right to left shunt is important. The presence of a large PFO has been associated with severe unexplained decompression sickness caused by paradoxical gas embolism.5 Torti and colleagues showed in 250 scuba divers that the presence of a PFO was related to a low absolute risk of suffering five major decompression illness (DCI) events per 10 000 dives, the odds of which were five times as high as in divers without PFO.6 In addition they showed that the risk of suffering …