People with atrial fibrillation may face a higher risk for dementia if they are subjected to a drug combination for a prolonged period, researchers have found. 

Specifically, excessive treatment of warfarin (to prevent blood clotting) and antiplatelet therapy with aspirin or clopidigrel (to prevent stroke) can be harmful, noted presenters at the a recent meeting of the American Heart Association in Orlando, FL.

Atrial fibrillation is a common heart rhythm abnormality that raises the risk of stroke and all common forms of dementia. The mechanisms behind the association of atrial fibrillation and dementia remain unknown.

“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 Heart Institute in Murray, UT. “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.”

Researchers studied 1,031 patients with no previous history of stroke or dementia for up to 10 years while on the drug combination. Patients who had abnormally slow blood clotting times — International Normalized Ratio measurement above 3 — on 25% 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% of the time. The increase is higher than what researchers found in a previous study of warfarin alone.

Patients who had abnormally slow clotting times were considered to be receiving too much

“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.