michael s
(Michael S)
#1
74 Which patient with a patent foramen ovale
should be referred for closure?
Diana Holdright
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-to-
left 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 unex-
plained 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
