Patent Foramen Ovale (PFO) and Stroke

Patent Foramen Ovale (known as PFO) is a remnant of embryologic development. A small flap located between the upper heart chambers allows the passage of the mother's oxygen-rich blood via the umbilical cord to the developing fetus. Since the lungs are not yet developed, the blood passes across the flap and moves on to the brain and other vital organs. At birth, changes in the pressure on the left and right sides of the flap cause it to close when the lungs expand. In 25 to 30% of the general population this flap can remain open. Identification of a PFO can be made by cardiac ultrasound (ECHO). To see the PFO agitated, saline is injected into the I.V. while pictures are taken.

The majority of patients with a PFO have no symptoms and live to a normal life expectancy. Data has shown that in up to 50% of strokes and transient ischemic attacks (TIAs) the only abnormality identified is a PFO. By default, it is presumed that a clot has traveled from the venous circulation, moved across the PFO and on to the brain (known as a paradoxical embolism). It is rare to actually see a clot in transit across the defect or even find a clot in a vein in the legs. There is much controversy in the medical community as to how to manage this group of patients, the majority of which are under 60.

After a stoke or TIA has occurred in a patient with a PFO, it is important to reduce the chance of another event. The risk of a second event has been linked to the anatomical variants of the PFO. A PFO with floppy tissue (septal aneurysm) carries a greater risk for a subsequent event (repeat TIA or stroke) if the patient is taking aspirin as a medical treatment. Some have suggested that coumadin is a better medical therapy for PFO. Only one study has examined this hypothesis, and there was no difference between the chance of a second stroke or dying from a second stroke in patients who took aspirin or coumadin. Many critics point out that the study involved a small sample and that the overall event rate for PFO patients was high at 9 to 18%.

Many patients opt to have an umbrella device inserted across the PFO to prevent clots form passing across the defect. There is no data to prove that closing the PFO with this device is superior to medical therapy. Clinical trials are underway and nearing completion. As of this writing, the device had yet to earn FDA approval, although many patients have received the umbrella in "off-label" transplants. One of the interesting findings among these patients was the impact the device exerted on migraine headaches.

Data has shown that up to 65% of patients with migraine headache and aura have a PFO. After closing the PFO, many patients reported a dramatic improvement in their headaches. It is unclear whether the PFO allows the passage of a chemical that triggers the headache, or if the headaches are caused by microscopic clots crossing the defect. One study that looked at the impact of PFO closure on migraine headache has been completed in England. The study was mired in controversy, although the initial analysis looked promising. After a complete review of the data there was no real effect headaches after closing a PFO in a population that had never had a stroke.

So you might ask, "Why not close a PFO when you find it?" For a young patient with a stroke, closing the PFO may reduce the chance of another event. Unfortunately, I can't prove that it will reduce the chance of second event. I think patients should be encouraged to participate in the currently available clinical trials (such as CLOSURE I, which is closest to completion) after a first event. If a patient has experienced multiple events despite medical therapy, the defect probably should be closed. There are specific device registries through which patients can receive devices designed for PFO.

As for patients with migraine headaches, studies with different devices are being conducted to determine if PFO closure is a valid treatment for the headache. Current headache patients should not go undergo closure for a PFO outside of a clinical trial.