Irregular heart beat linked to increased risk of dementia

Atrial fibrillation, a particular kind of irregular heartbeat, predominantly affects older adults. In atrial fibrillation, the electrical signals in the heart muscle are disturbed, causing the heart to quiver rather than contract normally. As a result, the blood will pool in the heart, possibly forming clots which may travel to the brain and cause a stroke. Many patients with atrial fibrillation are prescribed anticoagulant drugs, which can prevent stroke by prolonging the time it takes for blood to clot. Although stroke is the most known consequence of atrial fibrillation, what remains unclear is whether atrial fibrillation could also influence cognitive function.

Therefore, to assess the connection between atrial fibrillation and cognitive function, we at the Aging Research Center, Karolinska Institutet looked at data on 2685 participants from the Swedish National Study on Aging and Care in Kungsholmen (SNAC-K). Participants underwent clinical examinations and interviews at the beginning of the study and every six years for those aged 60-72 years and every three years for those 78 years and older. All participants were free from dementia at the beginning of the study, but 243 people (9.1%) had atrial fibrillation. Over the course of 9-year follow-up, an addition of 279 people developed atrial fibrillation, and 399 people developed dementia.

We found that participants with atrial fibrillation experienced faster decline in cognitive performance, such as thinking and memorizing skills, compared to those without the condition. Notably, atrial fibrillation raises the overall risk of dementia by 40% and the risk of vascular and mixed dementia by nearly 90%. But the good news is that atrial fibrillation patients who were taking anticoagulant drugs were 60% less likely to develop dementia than those who were not taking the drug. There was no decreased dementia risk among people who took antiplatelet drugs like aspirin.
How could an irregular heartbeat lead to dementia? People with atrial fibrillation could experience massive or mini strokes, which substantially increase the risk of dementia. It is also likely that atrial fibrillation lowers the blood flow to the brain and results in brain ischemia, which in turn fastens cognitive decline and eventually the onset of dementia.

Our findings show a clear link between atrial fibrillation and dementia risk and open up the potential cognitive benefit of anticoagulant drugs, but further research is needed to understand how anticoagulant drugs benefit cognitive function. In addition, the benefit-risk balance needs to be carefully evaluated when prescribing anticoagulant drugs to older people since the drugs do increase the risk of bleeding. Therefore, in older people with atrial fibrillation, the decision to start anticoagulant therapy should be individualized.

Ding M, Fratiglioni L, Johnell K, Santoni G, Fastbom J, Ljungman P, Marengoni A, Qiu C. Atrial fibrillation, antithrombotic treatment, and cognitive aging: A population-based study. Neurology 2018 Nov 6;91(19):e1732-e1740. doi: 10.1212/WNL.0000000000006456.

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