A patent foramen ovale (PFO) is a relatively common and often asymptomatic heart defect that is present at birth (congenital). During fetal development, the heart’s two upper chambers (atria) are connected by a hole through the wall of muscle that separates them (septum). This hole, along with a blood vessel connecting the pulmonary artery (artery going to the lungs) and the aorta (the main artery going to the body), must be present in the fetus in order to detour blood away from the lungs. Without these two connections the fetus would not survive and a miscarriage often occurs. This hole is called the foramen ovale, and it normally closes shortly after birth. When it remains open after birth, it is said to be “patent,” which is another away of saying “open.”
In about 15-20 percent of the general population, however, the foramen ovale remains open (patent), allowing blood to potentially or actually mix between the two atria. Many people do not know they have PFO because it does not give any symptoms. PFO does not have adverse effects on most people and therefore, it does not require treatment.
However, even a small, untreated patent foramen ovale can cause heart-related difficulties such as labored breathing or recurrent respiratory infections. Other medical conditions, such as migraine headaches, have also been associated with a PFO. If closure is recommended as treatment, the hole may be closed with an inserted device or, rarely, by surgery.
The cause of patent foramen ovale is unknown but health experts believe it may be related to genetic and hereditary factors. PFO also has been associated with other cardiac conditions, such as septal or valve defects.
PFO is considered a possible risk factor for stroke and systemic embolism because of the potential formation of blood clots. These clots may form in veins and subsequently pass into circulation through the PFO, without being filtered in the lungs. The relationship between PFO and stroke remains somewhat controversial and it continues to be studied by researchers.
Because of the pressure of the water and its effect on the circulation especially during surfacing, scuba divers also seem to face a slightly higher risk of stroke if they have a PFO.
About patent foramen ovale
A patent foramen ovale (PFO) is a type of heart defect that is present in about 15 to 20 percent of the population. It is a congenital defect that usually causes no symptoms or ill effects.
The foramen ovale is a hole between the two upper chambers of the heart (atria) that forms naturally during gestation.
Beginning in about the fourth week of pregnancy, tissue flaps begin to form in the upper portion heart, dividing the right and left atrium. The first such tissue barrier to form is known as the septum primum. A small hole develops in this septum primum called the ostium secundum, allowing blood to mix freely between the right and left atria. Soon after, however, a second septum, called the septum secundum, forms on the right atria side of the heart. The septum secundum covers up the original hole in the septum primum, but does not totally divide the developing atria. Instead, this septum secundum has a hole in it. This hole is the foramen ovale.
In the fetal heart, these two septa act as a pressure valve. When the pressure in the right atria exceeds the pressure in the left atria, the septum primum, which is located on the left atria side of the heart, swings open. This action allows blood to flow from the right side of the heart to the left side. At this point in development, the baby's lungs are not functioning. When oxygenated blood is introduced into the right side of the heart, a steady supply of this blood flows from the right side of the heart through the foramen ovale into the left side of the heart. From here, the blood flows out into the general circulation.
After birth, a number of conditions change that alter the pressure gradient. The lungs begin to function and blood can flow into the left atria through the pulmonary veins. At the same time, the pressure in the right side of the heart decreases as blood naturally flows toward the lungs. This change in pressure acts like a hand pressing against a door--it holds the flap of the septum primum closed, thus shutting off the foramen ovale. In response, the flaps begin to naturally fuse, and by age two, the two flaps should be joined, creating the atrial septum as a solid wall.
In about 15 to 25 percent of children, however, the flaps do not properly fuse, resulting in a patent (open) foramen ovale. This condition sometimes occurs in conjunction with other defects of the atrial septum, including a septal aneurysm, an atrial septal defect or a malformation of the tricuspid valve called Ebstein's anomaly.
Signs and symptoms of PFO
Depending on the size of the hole, most people with PFOs have no signs or symptoms. However, people with large holes(which is sometimes classified as a secundum atrial defect rather than a PFO) may experience some difficulties because of the volume of blood traveling from the right side of the heart to the left (right to left shunt), or vice versa, through the valve created by the septum primum.
These difficulties may include labored breathing, recurrent respiratory infections and other problems. Rarely, larger PFOs can lead to heart failure or even death. Depending on the size of the diameter of the opening, PFOs have also been associated with a greater risk of pulmonary embolism and stroke, although studies have recently shown that PFO is not linked to the occurrence of a second stroke, as was once suspected. Migraine headaches have also been linked to PFOs.
Diagnosis methods for PFO
In many cases, patent foramen ovale (PFO) may be discovered when physicians are conducting tests for another cardiac problem, such as a heart murmur. The condition also may be suspected if an individual suffers a transient ischemic attack (TIA) or a stroke. However, PFO is not typical a cause of a cerebrovascular event.
Individuals with low blood oxygen levels also may be suspected of having PFO. This is especially true of patients with severe lung conditions, such as emphysema. Lung conditions can cause higher pressure on the right side of the heart. With the increased pressure, oxygen-poor blood to flows through the hole from the right side of the heart to the left side. This action further lowers oxygen levels in the blood and can lead physicians to suspect PFO.
To diagnose PFO, physicians may use the following tests:
Transthoracic echocardiogram. This test uses sound waves (ultrasound) to visualize the structures and functions of the heart. A moving image of the patient’s beating heart is played on a video screen, where a physician can study the heart’s thickness, size and function. This test does not involve radiation and is completely painless. No preparation is necessary prior to performing an echo. It may be done at the bedside.
Transesophageal echocardiogram. This test uses a flexible tube similar to the endoscopes used to image the esophagus and stomach with a device that captures and records ultrasound images of the heart. It is a more sensitive test for detecting PFO and may be used in patients with an unexplained stroke. Additionally, this test can detect other cardiac conditions that may cause stroke. This test requires some sedation and specialized monitoring. It usually is only performed in specialized testing regions of a hospital.
Transcranial doppler. This is often done in conjunction with both the transthoracic and transesophageal echocardiogram. A monitoring device is held against the side of the head over one of the arteries supplying the brain. A special liquid with extremely small bubbles is injected in a vein and the flow of this liquid through the heart is imaged. The tiny bubbles also will give a certain signal that can be picked up by the device held over the cerebral artery. This may help confirm the potential of a PFO to account for a stroke, TIA, or migraine headache.
Treatment options for PFO
In most cases of asymptomatic PFO, treatment is unnecessary. In a small number of cases, however, intervention may be required to close the hole. Physicians may opt for either open-heart surgery or a catheter-based treatment. During the catheter-based treatment, a catheter is introduced into the body, usually through the groin, and guided all the way up into the heart. Once the catheter is in the correct position, the physician can measure the PFO and insert a device to plug the hole. There, it is used to close the PFO with a special plug. This procedure is called a transcatheter closure and is the most frequently used method of closing PFOs.
Because the shape and location of a PFO is often different than another defect in this region, the secundum atrial septal defect, there are now specialized devices specifically designed for closing PFOs.
In surgical closure, the procedure is performed in open-heart surgery. It is more invasive than device closure through a catheter. Some patients who are receiving surgery for another cardiac condition, such as a valve defect, may have a PFO closed at the same time. It is extremely unusual for open-heart surgery to be performed just for a PFO.
The recovery from PFO closure varies with the type of procedure and the general health of the patient. Patients may have some restrictions on physical activities for a few weeks following the procedure. In addition, patients may be placed on aspirin or anti-platelet drugs for six months or more after a closure device has been implanted. The treating physicians will provide detailed instructions following the procedure, including necessary follow-up visits and tests.
Early success has also been noted with robotically assisted surgery. Robotic surgery involves a voice-activated robot at the operating table and a cardiac surgeon in another room who manipulates hand controls that direct the robot where to cut and sew inside the chest. The surgeon directing the operation can view the procedure via an endoscope (a slim optical tube with an attached camera that is positioned inside the chest cavity). The advantage of using a robot is that the “hands” are smaller than human hands and require a much smaller incision. These techniques are reported to be safe and reliable, causing less pain to the patient, less surgical trauma and a shortened recovery time.
Prevention methods for PFO
Like other congenital heart defects, there are no definite prevention strategies for patent foramen ovale (PFO). However, people with PFOs can take certain steps to reduce possible complications that might result from the defect. Studies have shown an increased risk of deep vein thrombosis and stroke among people with PFOs on long airplane flights, compared to people without PFOs. Although the absolute risk is small, people with PFOs are encouraged to reduce this risk by drinking plenty of nonalcoholic fluids during the flight, as well as wearing nonconstricting clothing and shoes. It is also recommended these individuals take a walk up and down the aisle, or do simple leg stretches while seated.
Scuba diving and PFO
People with a patent foramen ovale (PFO) may be at slightly greater risk of decompression sickness – a potentially fatal condition associated with scuba diving. Normally, gas bubbles travel through the veins during decompression. In individuals with a PFO, however, gas bubbles can travel from the right side of the heart to the left side and out to the rest of the body. When these gas bubbles travel through the arteries, they could cause a stroke or other life-threatening event. Research has shown that divers who have a PFO are more likely to have wounds or lesions in their brains.
To reduce the risk of serious health problems, divers who have a patent foramen ovale are encouraged to swim to the surface of the water slowly and not dive as deeply or as long as other divers. Depending on the size of the PFO, divers may also consider a procedure to have it closed. If they experience severe shortness of breath, they are encouraged to contact their physician right away.
German researchers have developed a fairly inexpensive test to help predict whether or not people are at risk before they dive. During the test, harmless bubbles are injected into a vein and then a painless ultrasound is performed to see if the bubbles are able to reach the brain. People who have a PFO should discuss the hazards of scuba diving with their physician before participating in diving activities.
Questions for your doctor
Preparing questions in advance can help patients to have more meaningful discussions with their physicians regarding their conditions. Patients or parents may wish to ask their doctor the following questions related to patent foramen ovale (PFO):
Why do you suspect a PFO in me (or my child)?
What tests will be used to diagnose this condition?
Can these tests find any other structural abnormalities?
If I do not have any problems, is treatment for PFO necessary?
If necessary, what type of procedure is available to close the PFO?
What are the risks with this type of procedure?
How quickly does the procedure need to be performed?
What is the recovery from this procedure?
Will medications be necessary following the closure? If so, why type and for how long?
What are the risks if the PFO is not closed?
Should I avoid any activities with a PFO?
How will my condition be monitored?
What signs indicate a medical emergency with a PFO?
What steps can I take to reduce the risk of a stroke?
If I have a PFO, what are the chances my child will be born with one?
