Clinical impact of patent foramen ovale diagnosis with transcranial Doppler

The role of patent foramen ovale (PFO) in cryptogenic stroke is still debated, but from recent follow-up studies it seems that the amount of right-to-left shunt (RLS) and the association with atrial septal aneurysm (ASA) are major determinants of stroke recurrence. PFO and RLS through the atrial chambers have been recently studied in a number of conditions not or marginally related to cerebrovascular disease. Historically the first studies addressed the presence of RLS in scuba divers as a possible abnormality related to decompression sickness (DS) of unknown aetiology. Despite initial debate there is now robust evidence to claim that patency of foramen ovale increases the risk of developing DS by two and half to four times. Patients with PFO-related DS tend to have early occurrence of symptoms after surfacing and a clinical presentation that indicates brain or upper cervical spinal cord involvement. Recent reports suggest that divers with hemodynamically significant RLS may have an increased risk of developing clinically asymptomatic multiple brain lesions. PFO has been found in patients suffering from migraine with aura with approximately the same frequency as that encountered in cryptogenic stroke patients. This finding has prompted speculations on the possible role of RLS in increasing the stroke risk in migraineurs and in the pathophysiology of the aura. Recent reports showing that migraine with aura is dramatically improved after transcatheter closure of PFO suggest that migraine with aura may indeed be triggered by humoral factors that reach the brain by escaping the pulmonary filter. A RLS is involved in a rare condition known as platypnea-orthodeoxia and perhaps underlies an increased risk of cerebral complications after major orthopedic surgery. Valsalva-like activities often precede the occurrence of attacks of transient global amnesia (TGA) and abnormalities consistent with hypoperfusion of deep limbic structures have been reported during a typical TGA episode. This had raised the hypothesis that TGA may be triggered by paradoxical embolism of platelets aggregates in the posterior circulation, but the search for an increased frequency of PFO in TGA patients has yielded conflicting results. Conditions that determine an increase in pulmonary pressure may facilitate the opening of the virtual interatrial valve and thus promoting shunting of blood to the left heart chambers which in turn might contribute to further desaturation of arterial blood. It is therefore not surprising that RLS has been found in 70% of patients with chronic obstructive pulmonary disease and increased pulmonary pressure and in the same proportion of patients with obstructive sleep apnoea, a condition that ultimately may result in pulmonary hypertension. In conclusion, from the evidence gathered so far the picture is emerging of an important role of PFO in a number of non-stroke conditions, either as causative factor or as associated condition predisposing to complications. The availability of simple diagnostic techniques such as transcranial Doppler (TCD) to assess RLS will undoubtedly contribute a great deal of knowledge on the relevance in medicine of this hitherto neglected condition.