CHICAGO – Patients with atrial fibrillation who frequently have a supratherapeutic international normalized ratio are at sharply increased risk for developing dementia, according to a large observational study.
“We postulate that the mechanism is an accumulation of microbleeds in the brain,” Dr. T. Jared Bunch said at the American Heart Association Scientific Sessions.
“In patients with hypertension, a condition that’s extremely common with atrial fibrillation, these repetitive small bleeds are preferentially in the hippocampus, where memory is stored,” added Dr. Bunch, who is medical director for heart rhythm services at the Intermountain Medical Center Heart Institute in Salt Lake City.
He presented a study of 1,031 patients with atrial fibrillation (AF) in Intermountain’s centralized anticoagulation service. All were on dual therapy with warfarin plus aspirin or, much less commonly, another antiplatelet agent. At baseline, their average age was in the early- to mid-70s, and none of the subjects had a history of stroke or any notes in their medical record suggestive of early cognitive decline. At this dedicated anticoagulation center, their INR was measured on a weekly or biweekly basis, as a result of which their average time spent in the therapeutic range of 2.0-3.0 was relatively high at nearly 70%.
The increased risk of dementia in patients with AF has previously been recognized. The association is stronger in patients under age 75 than in those who are older. But the mechanism has been unknown. Dr. Bunch and coinvestigators decided to test their hypothesis that the mechanism involves microbleeds secondary to long-term overanticoagulation by dividing the patients into three groups based upon their percentage of INR measurements above 3.0 during a mean follow-up of more than 4 and up to a maximum of 10 years: 240 patients had a supratherapeutic INR 25% of the time or more; 374 did so less than 10% of the time; and 417 had an elevated INR 10%-24% of the time.