What is a patent foramen ovale (PFO) and what causes it?
A patent foramen ovale (or PFO for short) is a flap between the top 2 chambers of the heart which has not closed the way it should do at birth. During a baby’s development in the womb, this flap is fully open as a hole called the foramen ovale, and is found in everyone. It is necessary to allow blood containing oxygen from the placenta to get the rest of the body, bypassing the lungs which are not yet working. However when a baby is born, the lungs start working and providing oxygen-rich blood to the heart; pressures inside the heart change; and the foramen ovale (which is now no longer required), usually closes within the first 2 years of life in 70-80% of people.
However in the remainder of people (20-30%), the foramen ovale does not close, and it is then known as a patent foramen ovale (PFO). There is some evidence that genetics may play a role in keeping a foramen ovale open, but generally PFOs are not thought to be inherited unless they are associated with other heart conditions.
How common is a PFO?
Studies have shown that a PFO is a relatively common finding in adult populations, being present in up to 30% of individuals. However, most people with a PFO do not even know they have it, and it is usually found by chance on investigations for other problems or during cardiac screening.
What symptoms can you get with a PFO?
Most people with a PFO don’t even know that they have it as it causes very few symptoms. Rarely in a child or young person, blue skin may develop, particularly when they strain (e.g. during crying) due to blood without oxygen mixing with oxygen-rich blood from the lungs. However, usually in this scenario, other heart abnormalities are also present. In some cases, a PFO may be associated with stroke or migraine; this is discussed below.
What problems can occur with PFOs? Can PFOs cause sudden arrhythmic death syndrome (SADS)?
In most people, a PFO will not cause any problems and they are not associated with sudden death or SADS. There are some associations, however, with other conditions, and PFOs have been linked with both stroke and migraine. Although an association of PFO with stroke is well established, there is no conclusive evidence from population-based studies that a PFO alone is associated with an increased risk of a first or recurrent stroke. Therefore no preventive treatment is recommended in individuals with an incidental finding of a PFO. In young people who have had a stroke and found to have a PFO but no other obvious cause (i.e. “cryptogenic” stroke), treatment may be indicated and this is discussed below.
Similarly, despite an association with migraines, evidence for this is conflicting and studies have not shown any benefit in PFO closure for preventing migraine attacks.
PFOs have been associated with decompression sickness from scuba diving given the pressure differences that occur in the blood and chest wall with deep sea diving. Therefore for this reason, the only lifestyle advice recommended to people with a PFO is to avoid deep sea diving.
How is a PFO diagnosed?
A PFO is generally diagnosed on an ultrasound scan of the heart called an echocardiogram, where a probe with special gel on it is connected to an ultrasound machine and passed along the chest wall. This shows the heart and its structures using sound waves and can detect blood flow through different parts of the heart. However sometimes, this type of echocardiogram may be suggestive of a PFO but not conclusive.
One of the things a PFO can look like is an atrial septal defect (ASD), which is a hole between the top 2 chambers of the heart. Therefore in order to clarify this and assess the heart further, 2 special types of echocardiogram may be needed:
- Bubble contrast echocardiogram: this is exactly the same as an ordinary echocardiogram, but in addition a small amount of agitated salt water is injected into a vein. This water forms small micro-bubbles which highlight the chambers of the heart, and can be seen crossing from one chamber to the other if a PFO is present. During the study, you may be asked to strain in order to increase the pressures in the heart and determine whether a potential PFO is present which opens when pressures in your chest increase (e.g. when coughing or sneezing).
- Sometimes, even a bubble contrast echocardiogram may be inconclusive, or may show a PFO which needs further evaluation to determine its size and structure. In this instance, another special echocardiogram called a transoesophageal echocardiogram may be needed. This uses the same principles as a transthoracic echocardiogram (i.e. sound waves) to visualise the heart, but a special, smaller probe fixed to the end of a tube is passed into the food pipe to visualise the heart from inside the body. This shows the heart in much better detail, allowing the PFO to be assessed better. Given that this test is a little more invasive and can be uncomfortable, it is usually performed with sedation (a medication which makes you feel drowsy and relaxed).
How is a PFO treated and managed?
Generally, no specific treatment is required for a PFO if found in isolation. However if found in association with a stroke where no other cause for the stroke has been established, treatment is recommended. In general, 2 options exist: medical treatment with Aspirin, or closure of the PFO with a special device.
Current guidelines do not advocate closure of the PFO over simple medical treatment, although in some centres closure using a device inserted into the heart from the groin (percutaneous closure) may be offered to patients after they are given the pros and cons of each treatment option. The National Institute of Clinical Excellence (NICE) issued guidance on percutaneous closure of a PFO in December 2013 (see http://guidance.nice.org.uk/IPG472). In this guidance, they noted that the optimal treatment for patients with PFO who have had a stroke still remains undefined. However percutaneous closure of a PFO is at least as effective as medical therapy for preventing recurrent stroke, and possibly more effective. Use of the procedure in patients for whom it would be clinically appropriate (for example, those people who cannot have blood thinning medication due to the risk of bleeding) should be strongly influenced by patient choice, taking into the consideration the risks and benefits compared with long-term blood thinning medication or Aspirin. Closure of a PFO can be associated with serious but infrequent complications, and these must be discussed with the consultant beforehand so patients can make an informed decision.
For a PFO found in isolation, open heart surgery is almost never required.
Is long-term follow-up or screening of other family members needed?
An incidentally detected PFO generally requires no long-term follow-up or monitoring, unless the individual develops symptoms suggestive of a stroke in which case reassessment and treatment as described above may be indicated.