(HealthDay)—Atrial fibrillation, a common condition where the heart beats abnormally, may more than double the risk of "silent" strokes, a new review suggests.
Silent strokes have no signs or symptoms, but can affect thinking and memory. In addition, recent research has shown that atrial fibrillation is associated with a 40 percent increased risk for mental impairment, the researchers noted.
"Patients with atrial fibrillation are at higher risk of developing silent strokes," said review author Dr. Shadi Kalantarian, a resident at the Yale School of Medicine in New Haven, Conn.
Previous studies have found that silent strokes are associated with a more than threefold increase in the risk for symptomatic stroke and a twofold increase in the risk for dementia, she said.
"The higher prevalence of silent strokes in patients with atrial fibrillation may put this population at a higher risk for mental impairment, future stroke and disability," Kalantarian said.
More than 2.7 million Americans, many of them elderly, experience atrial fibrillation, according to background information in the report.
Atrial fibrillation is an electrical disorder that causes the upper chambers of the heart to contract quickly and irregularly. These abnormal contractions allow blood to pool and coagulate in the heart, forming clots that can cause a stroke if they break off and are carried into the brain.
For their study, the researchers reviewed 11 previously published reports that looked at the association between atrial fibrillation and silent strokes in a total of about 5,000 patients.
In this type of study, called a meta-analysis, researchers cull published studies in hopes of finding patterns that support a conclusion or trend. By finding similar trends in a variety of studies, the conclusions can be stronger than what a single study can provide.
While the analysis found an association between atrial fibrillation and an increased risk of silent strokes, it did not prove a cause-and-effect link.
The report was published Nov. 4 in the Annals of Internal Medicine.
Dr. Gregg Fonarow is a professor of cardiology at the David Geffen School of Medicine at the University of California, Los Angeles. He said, "Atrial fibrillation is a substantial risk factor for stroke, with patients with atrial fibrillation having a fivefold increased risk of symptomatic stroke."
Studies have suggested that atrial fibrillation is also associated with an increased risk of silent strokes, which can only be detected by brain scans, he said.
To prevent strokes, patients with atrial fibrillation usually take blood-thinning drugs ranging from aspirin to warfarin to newer medications.
The use of blood thinners markedly lowers the risk of stroke, and the benefits greatly outweigh the potential risk of bleeding, Fonarow said.
"While it is highly likely that effective use of blood thinners will reduce the risk of silent stroke as well as symptomatic strokes, further studies are needed to prove the point," he said.
Kalantarian, who conducted the study while at Massachusetts General Hospital in Boston, said that clinical trials are needed to investigate whether diagnosing silent strokes should be a factor in whether blood thinners should be started at the first signs of atrial fibrillation.
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