Which patient with a patent foramen ovale should be referred for closure?

A patent foramen ovale (PFO) occurs in approximately one quarter of the population. It is a vestige of the fetal circulation, with an orifice varying in size from 1 to 19mm, allowing right-toleft or bidirectional shunting at atrial level and the potential for paradoxical embolism. The development of better imaging techniques (e.g. transoesophageal echocardiography, contrast agents) and the fact that 35% of ischaemic strokes remain unexplained has generated interest in the potential for paradoxical thromboembolism through a PFO.

Studies of patients with cryptogenic stroke give a higher incidence of PFO (up to 56%)1 than in a control population, suggesting, but not proving, causality. Stroke due to paradoxical embolism involves the passage of material across a PFO, at a time when right atrial pressure exceeds left atrial pressure, to the brain. In one study the incidence of venous thrombosis as the sole risk factor for presumed embolic stroke in patients with PFOs was 9.5% and was clinically silent in 80% of patients,2 adding support to the concept of paradoxical embolism. The detection of venous thrombosis is not without difficulty and venous thrombi may resolve with time, such that a negative study does not exclude prior thrombosis. There is evidence that PFOs allow right-to-left shunting under normal physiological conditions, during coughing, straining and similar manoeuvres and especially in patients with raised right heart pressures and tricuspid regurgitation.

There are no completed prospective trials comparing aspirin, warfarin and percutaneous closure to guide management of patients with an ischaemic stroke presumed to be cardioembolic in origin. Opinion is divided in the case of a single ischaemic lesion on MR imaging and an isolated PFO – there is no evidence in favour of any particular strategy. Aspirin therapy is an uncomplicated option, and easier and safer than life-long warfarin. If there is evidence of more than one ischaemic lesion, no indication for warfarin (e.g. a procoagulant state), preferably a history of a Valsalva manoeuvre or equivalent immediately preceding the stroke and no alternative cause for the stroke then I would consider percutaneous closure, which has rapidly developed as a highly effective and technically straightforward procedure for closure of PFOs and many atrial septal defects.