Long-term overtreatment with the anti-clotting drug warfarin, combined with antiplatelet therapy with aspirin or clopidigrel to prevent stroke, may increase the risk of dementia in people with atrial fibrillation, according to a new research.

Atrial fibrillation is a common heart rhythm abnormality that raises the risk of stroke and all common forms of dementia, according to researchers, who presented their findings at the American Heart Association’s Scientific Sessions 2014.

“The dual drug regimen is often used to prevent strokes in people with coronary artery disease or peripheral vascular disease, but we have to consider that long-term exposure to anti-clotting drugs such as warfarin, if not well controlled, can significantly increase bleeding risk,” said T. Jared Bunch, M.D., lead author of the study and director of electrophysiology at the Intermountain Medical Center Heart Institute in Murray, Utah.

“This may result in micro bleeds in the brain that don’t cause symptoms right away, but accumulate over time, raising the risk of dementia.”

For the study, researchers examined 1,031 patients with no previous history of stroke or dementia for up to 10 years while on the drug combination.

After adjusting for traditional stroke and bleeding risk factors, patients who had abnormally slow blood clotting times — an International Normalized Ratio (INR) measurement above three — on 25 percent or more of their monitoring tests were more than twice as likely to be diagnosed with dementia than patients whose tests showed overtreatment less than 10 percent of the time.

The increase is higher than what researchers found in a previous study of warfarin alone, the scientists note.

Patients with abnormally slow clotting times are considered to be receiving too much medication, the researchers explained.

Researchers previously found that atrial fibrillation patients taking warfarin were more likely to develop dementia if lab measurements of their clotting time were frequently too slow — raising the risk of bleeding — or too fast — raising the risk of blood clots.

From those results, they concluded that brain injury from both small bleeds and clots was important in the development of dementia in atrial fibrillation patients.

“Even at skilled centers, it’s very common to have INR outside the ideal range up to 40 percent of the time, and over the years there may be an accumulative negative impact on cognitive ability,” Bunch said.

The researcher advise that patients taking warfarin and an antiplatelet drug such as aspirin or clopidgrel should check with their doctors to make sure they need one or both of the long-term antiplatelet medications.

“If your INRs are consistently too high, for stroke prevention your doctor may want to consider switching you to one of the newer anti-clotting drugs that is easier to regulate or a device placed into the heart that prevents clots from forming or exiting the area in the heart chamber where most clots develop in people with atrial fibrillation,” he said.

He added that most patients in the study were Caucasian, so the researchers aren’t sure if the results would apply to other ethnic groups.

Source: American Heart Association