Nearly 11 percent of middle-aged people in the United States suffered a stroke without knowing it, and atrial fibrillation more than doubled the risk for these so-called "silent strokes," according to a study published recently in the journal Stroke.

Nationwide, an estimated 15 to 20 percent of all strokes -- with and without symptoms -- are associated with atrial fibrillation, the most common form of irregular heartbeat. Dr. Bruce Solomon, of Pinehurst Neurology, thinks that is pretty accurate because 15 to 20 percent of his stroke patients have a history of atrial fibrillation.

Atrial fibrillation (a-fib) is the rapid, irregular contracting of the atria, the upper chambers of the heart. This chaotic quivering prevents the lower chambers, the ventricles, from filling completely with blood.

Blood stagnates in the atria, sometimes resulting in clots that can cause stroke.

"If a clot is in the left atrium and it breaks off, it can go to the brain, and that is what causes a stroke," says Dr. Andy Kiser, a cardiothoracic surgeon at FirstHealth Moore Regional Hospital.

While a-fib is not a direct cause of strokes, it can be a major contributing factor. Depending on their age, a-fib patients are two to seven times more likely to have a stroke than are people with regular heartbeats.

"If no one had atrial fibrillation, there would be significantly fewer people with strokes," Solomon says.

According to Solomon, most people who are diagnosed with a-fib are given blood-thinning medications, such as Coumadin, to reduce the risk of stroke and other serious problems that can result from clotting.

But blood thinners are not safe for people who have certain medical conditions or who are about to have surgery. And most people would rather not have to be on blood thinners for the rest of their lives because of side effects that can include too-low blood pressure or unusual bleeding or bruising.

Physicians have several options for either curing a-fib or keeping it reasonably well controlled. They can prescribe medications to slow the rapid heart rate associated with a-fib, and they sometimes use electric shock to try to jolt the heart back into normal rhythm.

Various methods have been developed to block the stray electrical impulses that cause the heart to beat erratically and to guide this electricity back onto the correct pathways through the heart. Maze-like patterns of scar tissue, which is a barrier to electrical conduction, are created by cutting or cauterizing the heart muscle.

The newest version of the maze procedure, which Kiser developed in collaboration with other surgeons, is called the Ex-Maze. It creates a more extensive pattern of scar tissue and controls the heart's electrical impulses more effectively.

The Ex-Maze is still so new that Moore Regional is one of only a few places in the country where it is being performed. Because of that, cardiologists in other states are sending some of their patients to Moore Regional, where Kiser and his colleagues have created the FirstHealth Arrhythmia Center.

Kiser describes the Arrhythmia Center as a "virtual clinic."

"Patients don't necessarily have to come to our clinic before or after their operation," he says. "We work with their cardiologists, wherever they are, to evaluate them to see if they are candidates for the Ex-Maze. Then, after the procedure, we follow up with their cardiologists at home so they don't have to come all the way back here to be seen."

The Arrhythmia Center's nurse coordinator handles much of that, working with cardiologists to get their patients prepared for the operation and then following up to make sure that the outcomes are as expected.

The Ex-Maze can be done at the same time as another type of heart procedure, such as open-heart surgery, or as a minimally invasive procedure.

Anyone needing more information on the FirstHealth Arrhythmia Center or the Ex-Maze procedure for atrial fibrillation can visit www.firsthealth.org.