Patent Foramen Ovale (PFO)

The foramen ovale has been found in studies to be patent in about 25% of people. A patent foramen ovale has been implicated in stroke, in migrane headaches, in decompression sickness in divers, and in altitude sickness.

PFO and stroke

A number of case control studies have found increased prevalence of PFO in patients with cryptogenic stroke.

A number of mechanisms have been postulated that might increase risk of stroke in those with PFO:

• paradoxical embolism of venous thrombi through the PFO
• formation of thrombi on associated atrial septal aneurysms that embolise to the brain
• allowing the passage of vasoactive chemicals through the PFO to the systemic circulation, chemicals that normally might pass to the lung and be inactivated there.

One widely quoted study (N Engl J Med 2001;345:1740-6) studied 581 patients aged between 18 and 55 years who had had an ischaemic stroke of unknown origin. The study found:

• the highest risk of recurrent stroke was in those with both a PFO and an atrial septal aneurysm
• the risk of recurrent stroke was not higher in those with PFO alone compared with those without a PFO

There is considerable interest in determining if those with large PFOs are at increased risk of recurrent stroke.

Randomised trials are underway to try to determine if event rates are reduced by closure of PFO with devices delivered via the femoral veins. Many would recommend initial treatment with low dose aspirin or warfarin and if there are recurrent events than consider closure with devices. Not surprisingly, as the experience with device closure increases, PFOs are being closed after first events in those deemed to be at higher risk for recurrent events.

PFO and Migrane

PFO and Decompression sickness in Divers

PFO and Increased Risk of Stroke and TIA in those with Large Pulmonary Emboli

PFO and Altitude Sickness

Hitesh Patel, Cardiologist
3rd July, 2005