A patent foramen ovale (PFO) is a common condition present from birth, characterized by a small opening between the upper two chambers of the heart. This opening, called the foramen ovale, is a normal part of fetal development but closes shortly after a baby is born. When this flap-like opening fails to seal completely, it is termed a patent foramen ovale. This condition is prevalent, with estimates suggesting that it persists in about one out of every four people. For the overwhelming majority of individuals, a PFO is an incidental finding that causes no adverse health effects.
The Role of the Foramen Ovale in Circulation
During fetal development, the foramen ovale serves an important function in circulation. Because a fetus does not use its lungs to breathe, its oxygenated blood comes directly from the mother’s placenta. The foramen ovale allows this oxygen-rich blood to flow from the heart’s right upper chamber (right atrium) directly to the left upper chamber (left atrium), bypassing the non-functioning lungs. This shunt ensures that the most highly oxygenated blood is pumped by the left ventricle to the rest of the body, including the developing brain.
At the moment of birth, a significant physiological shift occurs with the baby’s first breath. As the lungs inflate with air, the pressure dynamics within the heart change dramatically. Pressure in the left atrium rises, becoming higher than the pressure in the right atrium. This change pushes a flap of tissue, known as the septum primum, against the opening, acting like a one-way door. Over time, this flap fuses with the atrial wall, permanently sealing the foramen ovale.
A PFO results when this fusion process is incomplete, leaving a small, tunnel-like passageway between the atria. It is different from an atrial septal defect (ASD). An ASD is a true hole in the wall separating the atria, meaning tissue is missing from the septal wall. In contrast, a PFO is simply the failure of the flap-like opening to seal, not a structural absence of tissue.
Associated Health Conditions
In certain circumstances, a PFO can contribute to health issues, most notably in relation to stroke. When a stroke occurs without a clearly identifiable cause, it is termed a cryptogenic stroke. In some of these cases, particularly in patients younger than 60, a PFO is considered a contributing factor. The connection is based on a mechanism known as a paradoxical embolism.
A paradoxical embolism occurs when a blood clot, formed in the deep veins of the legs (deep vein thrombosis), travels to the right side of the heart. Normally, such a clot would be pumped into the lungs and filtered out. If a PFO is present, a temporary increase in right-sided heart pressure from an event as simple as coughing or straining can push the clot through the opening into the left atrium. From the left side of the heart, the clot can then travel to the brain, block a blood vessel, and cause a stroke.
A less definitive association has been observed between PFOs and migraine with aura. The exact nature of this link is still under investigation. One theory suggests that small clots or deoxygenated blood may cross from the right to the left side of the heart and travel to the brain, triggering the neurological events that characterize an aura.
Another condition linked to PFOs is decompression sickness, which affects scuba divers. During a diver’s ascent, nitrogen that was absorbed by body tissues at depth comes out of solution and can form bubbles in the bloodstream. The lungs filter these bubbles, but a PFO can allow them to pass directly into the arterial circulation. If these bubbles travel to the brain or spinal cord, they can cause the symptoms of decompression sickness.
Diagnosis Process
A patent foramen ovale is diagnosed using a cardiac ultrasound, known as an echocardiogram, combined with a saline contrast study. This procedure, often called a “bubble study,” uses sound waves to create moving images of the heart’s structure and visualize blood flow between its chambers.
The bubble study involves injecting a sterile saline solution with harmless microbubbles into a vein. These bubbles then travel through the bloodstream and enter the right atrium. The clinician uses the echocardiogram to watch the path of these bubbles. In a heart without a PFO, the bubbles will travel from the right atrium to the right ventricle and then to the lungs, where they are filtered out.
If a PFO is present, some bubbles will be seen crossing from the right atrium to the left atrium. To enhance the detection of a PFO, the patient may be asked to perform a Valsalva maneuver, which involves bearing down. This action temporarily increases the pressure in the right atrium, which can push the flap of the PFO open and allow bubbles to pass through more easily, confirming the diagnosis.
This diagnostic test can be performed in two ways. A transthoracic echocardiogram (TTE) involves placing an ultrasound transducer on the chest wall. A transesophageal echocardiogram (TEE) is a more sensitive method where a specialized probe is passed down the esophagus, which lies directly behind the heart. This proximity provides a much clearer and more detailed view of the atrial septum, making the TEE a more definitive test for identifying a PFO.
PFO Management and Closure
The management for a patent foramen ovale depends on an individual’s symptoms and clinical history. For the vast majority of people who are asymptomatic and have a PFO discovered incidentally, no treatment is necessary. The standard approach is observation, as the condition is unlikely to cause any problems.
For patients who have experienced a cryptogenic stroke that is believed to be linked to a PFO, medical therapy is often a first-line approach. This can include antiplatelet drugs, such as aspirin or clopidogrel. In other cases, anticoagulant medications, or blood thinners like warfarin, may be prescribed.
In specific situations, a procedure to close the PFO may be recommended. PFO closure is reserved for patients who have had a PFO-associated stroke, as a measure to prevent recurrence. This is a minimally invasive procedure performed using a catheter. A long, flexible tube is inserted into a large vein, usually in the groin, and guided to the heart.
Through the catheter, a specially designed closure device is delivered to the site of the PFO. This device consists of two small, umbrella-like discs that are deployed on either side of the atrial septum, effectively plugging the opening. The heart tissue then grows over the device in the following months, permanently sealing the PFO.