The heart has two sides, right and left. The septa separate these sides from each other, preventing deoxygenated blood on the right side from mixing with oxygenated blood on the left side. When there is a hole in a septum, blood from the right side leaks into the left side, or vice versa. As a result, the heart cannot pump blood as efficiently as it was designed to.

The atrial septum separates the top chambers of the heart, the right and left atria. The foramen ovale (fore-AY-men oh-VAL-ee) is a naturally occurring hole in the atrial septum of a fetus. Because a fetus does not use its lungs—it gets oxygen from its mother—this naturally occurring hole allows a fetus to circulate its blood while bypassing its lungs. Although the foramen ovale usually closes a few years after birth, in about 10 to 20 percent of people it remains leaky, allowing tiny amounts of deoxygenated and oxygenated blood to mix. More than 99 percent of people with a “patent” (PAY-tent, meaning “open”) foramen ovale (PFO) do not show symptoms and do not need treatment. However, in some patients, the PFO allows blood clots and other debris to pass from the venous (deoxygenated) system to the arterial (oxygenated) system. (Normally these clots and debris are filtered by the lungs.) Once a clot or particle enters the arterial system, it can cause a stroke or cut off circulation to a limb or vital organ.

Less than 1 percent of the time, a baby will be born with a hole in its atrial septum, called an atrial septal defect (ASD). Like a PFO, an ASD results from a developmental abnormality. (A PFO is like a leaky tunnel; an ASD is an actual hole.) An ASD allows significant quantities of deoxygenated and oxygenated blood to mix, causing fatigue and shortness of breath. If the hole is small, these symptoms can be subtle; sometimes patients do not recognize them until their physical stamina improves after the hole is fixed.

PFOs and ASDs are usually closed only if they cause symptoms like fatigue or shortness of breath, or are suspected of having caused a stroke. (Fewer than 1 percent of PFOs require closure; ASDs are closed much more frequently.) Although traditional open-heart surgery is still occasionally performed, most patients undergo a less-invasive procedure in which the surgeon makes a small incision and snakes a narrow tube (catheter) through a blood vessel into the heart. The surgeon then sends a collapsible “patch”—a metal prosthesis—through the catheter, and inserts it at the leak point.

There are three types of prostheses used to fix PFOs. One type looks like two umbrellas connected by a post; another, like two disks connected by a post; and the third, like an Oreo cookie. The size and shape of the leak determines which prosthesis is used. Because ASDs are usually larger than PFOs, only the Oreo-cookie-shaped device is used to patch an ASD.

PFO/ASD closure with a catheter is an outpatient procedure that takes about an hour. The surgeon inserts a catheter into a vein, usually in the groin, and moves it into the right side of the heart through the vena cava, which delivers deoxygenated blood to the heart. The patient receives a local anesthetic and can usually return to work in a few days.

Several studies have found that people with PFOs who had a stroke were more likely than average to suffer from migraine headaches. After their PFOs were closed, many of these patients’ migraines disappeared. (One recent study demonstrated a 50 percent reduction in migraine severity and frequency after patients’ PFOs were closed, compared to a placebo group that underwent a fake procedure.) Although no causal link has been proved between PFOs and migraines, researchers speculate that certain types of migraines may be caused by chemicals in venous blood that pass through PFOs—bypassing the lungs’ filtration system—and travel to the brain. Little research has been done on any connection between ASDs and migraines.

Most patients are put on mild anti-clotting medications, such as aspirin and Plavix, for a few months following the procedure.

In considering whether to have an atrial leak closed, patients should talk to their doctor. Patients with a PFO but without any history of stroke or migraine should probably not have their PFO closed. PFO patients with a history of stroke may be eligible to participate in a randomized trial in which they either have their PFO closed or take blood-thinning medications. (Researchers are trying to determine which therapy is most effective.) Patients with a PFO and migraines may be eligible for a similar trial. For patients with a PFO and a variety of other conditions, such as decompression illness from scuba-diving (“the bends”), a decision to close the PFO should be individualized after discussion with a doctor.

Patients with an ASD should consider whether their leak is large enough to put excess strain on their heart and whether they are experiencing symptoms that affect their lifestyle.

PFO/ASD closure via catheter can almost always stop blood shunting in the upper heart. PFO closure helps to prevent strokes in most patients. Approximately 1 to 3 percent of patients who have a PFO closed after having suffered a stroke will have a “mini-stroke” called a transient ischemic attack, in which symptoms last less than a day and no permanent brain damage results. About 50 to 70 percent of migraine sufferers appear to benefit from closing their PFO, but these observations remain preliminary. Most ASD closures successfully reduce fatigue and increase energy.

As with any catheter-based procedure, there is a small risk that the patient may bleed or bruise at the puncture site. Occasionally the procedure can induce a heart arrhythmia, which is almost always correctible with a few days of medication.

Patients with untreated PFOs may put themselves at risk of a stroke. Those with symptoms will continue to experience symptoms. If an ASD is left untreated, the efficiency of heart function may worsen, which can lead to progressive fatigue and hospitalizations.

Unless a patient has had a series of rapid strokes caused by an atrial leak, the procedure can usually be scheduled at the patient’s convenience.