Common Condition Emerges as Possible Stroke Cause

Stroke is the third leading cause of death in America, after heart disease and cancer, and medical researchers expect the prevalence of stroke to grow as the overall population ages and as the number of stroke-prone minorities increases.

Of the 750,000 primary and secondary strokes that occur annually in this country, two-thirds are in older patients, and Hispanics and African Americans face a higher risk than Caucasians. Approximately one-third of all stroke survivors will have another stroke within five years, according to the National Stroke Association.

Although physicians know that risk factors for stroke are similar to those for heart disease - hypertension, smoking, heavy use of alcohol, obesity and lack of exercise - a surprisingly high 40% of strokes occur in patients with no apparent risk factors, and in younger patients. Doctors are finding increasing evidence that these so-called "cryptogenic strokes" often occur in patients with a hole in the heart, known medically as patent foramen ovale, or PFO. Between 10% and 20% of Americans have this condition.

"What happens," says David S. Marks, MD, Associate Professor of Medicine at the Medical College of Wisconsin and Director of the Cardiac Catheterization Laboratory at Froedtert & Medical College Clinics, "is that all of us have this hole or flap [called the foramen ovale] in the heart before birth, when we are developing in the womb. After birth, when the baby is breathing on its own, this flap gradually seals shut." In some people, however, the flap stays partly open, or patent, allowing blood to shunt between the right and left chambers of the heart.

For Many, No Complications
For most people with PFOs, "it's not known to be associated with any health risk," says Dr. Marks. "But in a small number of people, it's implicated in a cryptogenic stroke." In these cases, when people with PFOs develop small blood clots in their venous blood flow (arms, legs or pelvis), those clots can move through the veins to the right atrium, and from there, a clot can leak into the left atrium. It then travels to the brain and becomes lodged there, preventing blood flow to that part of the brain and resulting in a stroke. Older adults are more prone to such clots in the lower extremities, but they do occur in younger patients, he says. It's often not until they suffer an unexpected stroke that they are even aware they have the congenital condition.

"We always try to find the cause for a stroke," Dr. Marks says, to help prevent a future one. The likelihood of having a secondary stroke varies, according to the National Stroke Association. It estimates that between 3% and 10% of stroke patients suffer a second stroke within a month of having the first; another 5% to 14% have a repeat episode within the first year, and between 25% and 40% of patients suffer a second stroke within five years.

All stroke patients are encouraged to reduce their blood pressure, lose weight if they are obese, and take aspirin or other blood-thinning medication to reduce the likelihood of clot formation, he says.

Few Risk Factors
But people with PFOs often do not have the risk factors linked to stroke and other cardiovascular problem. Some have no symptoms, or the symptoms they might have - fatigue, shortness of breath, heart flutters or fibrillations - are fairly common indicators of other conditions. (Physicians at the Medical College are also looking into a link between classic migraine headaches and PFOs in younger, healthy patients, Dr. Marks says, noting that not all young migraine sufferers necessarily have PFOs.)

A diagnostic test called an echocardiogram typically reveals the presence of a PFO. And if a PFO is detected, then what?

"Until fairly recently," Dr. Marks says, "treatment options were limited to open-heart surgery, where the opening is sewn shut, or to a lifelong regimen of anticoagulant (blood-thinning) drugs like Coumadin (warfarin), Plavix or aspirin." Neither option is without risks. Open-heart surgery inherently carries certain risks. And chronic use of such blood-thinning drugs is associated with complications like ulcers, internal bleeding, cerebral bleeding, hematuria (blood in the urine) and hemorrhoidal bleeding. Thus, many younger patients and women of childbearing age were not considered candidates for the anticoagulant regimen.

New Implant Expands Treatment Options
"But now we're offering a third option - a small device that is inserted through a vein in the leg and guided to the heart, where it's implanted to assist the body in closing the flap," Dr. Marks says. The actual procedure, similar to a cardiac catheterization, typically takes a few minutes, although the preparation time and follow-up care takes about one to two hours, he notes.

The procedure is done with the aid of a real-time echocardiogram to ensure that the device is transported to the precise location of the PFO. The implant is a self-expandable double disk made from wire mesh and polyester fabric. According to the manufacturer of one of the devices, AGA Medical Corporation, when the doctor is certain the device is placed properly, the implant is released from the delivery system and opened so that the defect is blocked (or sandwiched) by the mesh discs. The implant remains in the heart and the delivery system is removed. Once the device is in place, tissue will grow over it, closing the defect. The device then becomes part of the wall of the heart.

The Medical College is one of a number of sites around the country that are conducting clinical trials in the use of the device, Dr. Marks says. "We use a team approach here," he says. In addition to the interventional cardiologist (such as Dr. Marks), a physician specializing in interpreting echocardiograms is on hand to ensure the correct placement before the implant is placed permanently." He also credits the assistance of pediatric cardiologists at the Medical College and Children's Hospital, who are experienced in using similar techniques in infants to repair a variety of congenital defects.

Not all patients with PFOs are candidates for the procedure, Dr. Marks says. Conventional surgical repair is still the best option for patients with multiple holes in the heart, or with large defects, or with defects abutting a valve.

But he is clearly enthusiastic about the new device for younger people who have experienced a stroke, and he hopes more will inquire about participating in the clinical trial at the Medical College & Froedtert.

"If you know a young person who has had a stroke, tell him or her that now there are other options besides lifelong medication."

Barbara Abel
HealthLink Contributing Writer

For more information, call the Department of Cardiovascular Medicine at 414-456-6777.

The US Food and Drug Administration provides visuals and a description of the implant device on its website.

MCW Health News presents up-to-date information on patient care and medical research by the physicians of the Medical College of Wisconsin.