A patent foramen ovale (PFO) is best thought of as a communication at the level of the atrial septum between the left heart and the right heart. It is found in 25-30% of a normal healthy population and usually does not cause any symptoms, impact on quality of life or lifespan. Many people refer to it as a ‘hole in the heart’ although strictly speaking, a PFO is more like a flap or a partially open door rather than a gaping hole.
To understand, why this happens we need to understand what happens during fetal development.
In adults, oxygen deprived blood is pumped back from the body into the right heart from where it is pumped into the lungs where it becomes enriched with oxygen and then comes back to the left heart from where this oxygen rich blood is pumped to the body.
However before birth, our lungs are collapsed and not functional and therefore all the oxygen is obtained from the placenta. So oxygen rich blood comes from the placenta into the right heart. From here it would be a complete waste and a huge effort to pump it all into non functional/collapsed lungs and therefore most of the blood is directed through this gap in the atrial septum into the left heart from where the oxygen rich blood is then pumped around the embryos body.
When the baby is born the lungs become functional and suddenly the resistance to blood gets less and more blood goes the lungs and therefore more blood comes back to the left heart and this increased pressure has the effect of closing the ‘door’
Because the door is closed, the flap fuses and therefore the door becomes permanently locked by 2 years of age in 70-75% of children. The remaining are left with a patent foramen ovale which basically means that the door is closed but not locked. We don’t know for sure why the door doesn’t lock in some people but there may be some genetic factors. In one study they found that the prevalence of PFO in siblings of a patient with a PFO was 77% compared to only 25% in a patient without a PFO
Most patients with PFO are asymptomatic.
However there are 4 situations in which a PFO may be important and partially be responsible for harm.
1) Cryptogenic stroke.
Cryptogenic stroke is defined a stroke which occurs without an obvious aetiology. Most of such strokes are believed to be due to small blood clots going into the brain from somewhere else. In these patients there is a higher prevalence of PFO and it has therefore been hypothesized that a blood clot could form anywhere in the body, travel to the right heart, and then go through the partially open door (The PFO) to the left heart and from there go to the brain and cause the stroke. Some research indicates that it is not people who just have a PFO who are at risk as much as people who have an interatrial septal aneurysm which could actually allow stagnation of blood and formation of clot.
2) Migraine and vascular headache
There is some low quality evidence that migraine is more common in patients with PFO and the theory is that the venous circulation contains vasoactive substances whixh could trigger migraine but these are destroyed in the lungs. However if the substances can bypass the lungs by crossing through the PFO then they could get to the brain and trigger migraine. However there is no real evidence to categorically confirm this or show that closure of the PFO will improve migraine
3) Decompression sickness and air embolism
There is a 2-5 fold increase of serious decompression illness with a PFO and therefore this can be a contraindication to diving. However with closure, patients can dive again.
4) Platypnoea- orthodeoxia syndrome
This is a very rare and very interesting condition in which patients complain of something called platypnoea. In this condition, people get breathless when they satnd up but feel better whn they lie down. When you measure their oxygen levels, their oxygen levels fall when they satnd up and normalise when they lie down. It is seen in people who have had lung disease or part of the lung removed and therefore for some reason, blood returning from the rest of the body is in some way preferentially directed towards the ‘door’ and therefore bypasses the lungs and enters the left heart and this is why the oxygen levels in the blood fall and the patient feels breathless.
How do we diagnose it?
The easiest way is to detect it is through ultrasound. As this is like a door which may only be very slightly open, you can often miss it unless you can push the door open and demonstrate that blood flows through it to the other side. The easiest way to do this is injecting tiny air bubbles in through a vein whilst the patient is straining and this has the effect of pushing the door open in which case the air bubbles are seen on the other side.
What do we do about it?
If it is incidental and not causing any symptoms then it is best left alone.
For cryptogenic stroke, there is some evidence that closing the PFO is associated with better outcomes. Closure can usually be done via a keyhole procedure.
For platypnoea orthodeoxia syndrome and in scuba divers, keyhole closure is also a recommended option.
Here is a video I have done on this subject