The “patent oval shape” (also known by the acronym FOP) is a small hole or tunnel that connects two heart chambers, the atria, which are usually separated by a partition called the interatrial septum.
How is a FOP formed?
We can consider it as a small “memory” or “remnant” of our intrauterine life, that is, from when we were still developing inside our mothers' wombs. Inside the uterus, the fetus has a circulation and oxygenation different from what we have when we are born since, during intrauterine life, we do not breathe and oxygenated blood comes to us directly from our mother through the umbilical cord.
In this period of life, oxygenated blood has to pass from the right atrium to the left in order to carry oxygen and nutrients to the rest of the small developing body and for this reason the septum or interatrial septum is not yet closed and the atria communicate with each other. When we are born, just after delivery, our lungs begin to work and the blood, which no longer receives oxygen from the mother, has to pass from the veins and therefore from the right atrium to the lungs to be oxygenated and from there to the left atrium and arteries. At this time there is no longer a need for the atria to communicate with each other and the septum or interatrial septum closes, completely separating the two cavities, usually in the first year of life. However, this does not always happen and in up to 25% of people (1 in 4... much more frequently than one can imagine...) a small tunnel-like communication remains open at the level of the interatrial septum, known as “patent foramen ovale” or PFO.
What problems can a FOP cause us?
Having a patent foramen ovale (PFO) is therefore much more common than we think, and in the vast majority of people it goes unnoticed. Only in a small percentage of cases is it associated with symptoms or complications. In fact, the diagnosis of PFO is usually an incidental finding in tests performed for other reasons, and in most cases it doesn't cause any problems.
The main complication that can be associated with the presence of a PFO, as already mentioned in a minimal percentage of people, is the development of what is known as “paradoxical embolism”, that is, the passage of small clots that can form in the venous system and pass to the arterial system through the PFO, causing ischemic events such as a stroke. When the interatrial septum is closed, without the presence of any direct communication between the atria, the clots that can form in certain circumstances in the veins, usually in the legs, migrate to the lung, which functions as a large reservoir and allows them to be eliminated, in the majority of cases without symptoms. Also in the presence of FOP, the small thrombi that can form in the veins do not usually pass into the arteries since the pressure in the left atrium is greater than in the right atrium and this allows the entrance door to the atrium to be “closed.” left. However, in the presence of certain characteristics of the interatrial septum, such as a septal aneurysm, or in some work or sports activity that causes increased pressure in the right atrium, the entrance door to the left atrium into which the PFO can “open up” and allow small clots to pass through, causing stroke or other systemic ischemia.
Another much less common complication that can cause a PFO is a “deoxygenation” of the arterial blood when non-oxygenated blood from the right atrium mixes with the left atrium. It is very rare since, as we have explained, the communication between the atria is very small and the higher pressure on the left side prevents the mixing of blood from both sides.
How is a FOP diagnosed?
PFO can be diagnosed with a conventional transthoracic echocardiogram, although it is not always possible to see it since the tunnel-like communication between the atria is small and the flow passage at the level of the interatrial septum may go unnoticed. When the clinical suspicion of having a PFO is high, such as in young patients with a “cryptogenic stroke”, it is decided without apparent causes, a “bubble test” can be performed. An agitated saline solution is injected into a peripheral vein to form bubbles that can be seen with the echocardiogram and it is monitored whether these bubbles pass from the right to the left atrium, both in the baseline situation and with Valsalva maneuvers: if there is an early passage and evident bubbles then we do have a PFO. The same test can be performed with a transcranial Doppler echocardiogram or a transesophageal echocardiogram, since in certain situations they may be more sensitive than the transthoracic echocardiogram in terms of the passage of bubbles.
When and how should a FOP be treated?
In most cases, the presence of FOP does not require specific treatment, nor does it imply limitations for the person who has it. However, in certain circumstances it may be considered to close the FOP.
The clearest indication is in young patients who have had an ischemic event or a stroke without another apparent cause. In older patients, usually over 50 years of age, the indications for PFO closure tend to be stricter since stroke may be more likely to occur due to other causes.
There are then sports activities such as diving in which the presence of a PFO can cause problems, especially if in addition to the PFO we have other characteristics of the interatrial septum that help the passage of blood between the atria, such as an aneurysm of the interatrial septum. People who practice diving at a professional level would always have to undergo a specific study to rule out FOP and in certain cases consider closure in order to continue with the sporting activity.
The presence of migraines, associated with certain characteristics of the interatrial septum, can also be an indication of FOP, although a complete neurological and cardiological evaluation must be carried out beforehand since we must be strict in this indication.
Finally, we would consider PFO closure in those rare cases in which there is a mixture of venous and arterial blood through the PFO, causing poor oxygenation of the arterial blood. It can occur, for example, in older people with a dilated aorta who, when standing, have low oxygenation that improves when they lie down (“platypnea-orthodeoxia syndrome”).
Today, patent foramen ovale (PFO) closure in adults is usually performed percutaneously via catheterization. A double-disc or diabolo-shaped device is advanced through the femoral vein and implanted at the level of the interatrial septum, with one disc in the left atrium and the other in the right atrium. It is a relatively simple procedure with a relatively low risk of complications, requiring only a very short hospital stay.
In summary, having a FOP is much more common than we consider and does not usually cause any problems nor does it have to limit us in our daily lives. However, there is a small percentage of people who may have complications and therefore it is always appropriate to have at least an initial evaluation by a cardiologist to assess attitude and follow-up if necessary.
By Dr. Daniele Gemma
The closure of a patent foramen ovale is performed by the Hemodynamics and Interventional Cardiology Unit of UICAR.