Brain Volume and Stroke Risk in Patients with Atrial Fibrillation

New analysis of data from the Framingham Heart Study found a significant association between atrial fibrillation (AF) and reduced volume in the brain’s frontal lobe.

Investigators studied magnetic resonance imaging (MRI) scans from 2,144 participants in the study offspring cohort’s 7^th examination cycle between 1999 and 2005. The mean age of cohort members was 61.8 years ± a standard deviation of 9.3 years, and 54% of cohort members were women. None of the patients had a history of stroke or dementia, but 73 of them (3.4%) had been diagnosed with prevalent AF by the time they underwent MRI.

Investigators began by using MRI results to measure total cerebral volume, frontal lobe volume, temporal lobe volume, temporal horn volume, hippocampal volume, and white matter hyperintensity volume. They then looked for associations between those measurements and prevalent AF.

In models adjusted for age and sex only, AF was inversely associated with total cerebral brain volume, frontal brain volume and temporal brain volume. When the investigators also adjusted for vascular risk factors and APOE4 — a gene that’s known to be independently associated with reduced brain size — AF was still inversely associated with frontal brain volume.

“After accounting for vascular risk factor burden, prevalent AF was associated with lobar indices of vascular brain aging but not with expected white matter changes,” the study authors wrote in Heart Rhythm.

The study authors believe their work is the first to explore the association between AF and the physical structure of the brain. They plan to undertake further research to determine whether the link between AF and frontal lobe volume impacts cognitive skills such as language, memory and problem solving.

“We believe that good heart health also contributes to good brain health and given that the incidence of AF is expected to more than double in the next three decades, we are interested in understanding the association between AF and brain anatomy,” said corresponding author Rhoda Au, PhD, Director of Neuropsychology for the Framingham Heart Study and a professor of anatomy, neurobiology, neurology and epidemiology at Boston University’s schools of Medicine and Public Health.

The findings of the new study may shed some light on the long-observed association between AF and cognitive decline.

Part of that association certain stems from the tendency of AF to precipitate brain-crippling strokes, but the association almost certainly involves several other factors. A number of studies have found that even AF patients who never suffer a stroke still experience unusual rates of cognitive decline.

Discovering the true size of the relationship between AF and cognitive impairment has been difficult because they share so many risk factors: age, hypertension, diabetes, cardiac failure and, of course, stroke. Still, a meta-analysis published 3 years ago in the Annals of Internal Medicine used data from 21 studies to estimate that AF was associated with higher risk for developing cognitive impairment in patients with or without a history of stroke (relative risk [RR], 1.40; 95% CI, 1.19 to 1.64).

To test reliability of this estimate, the authors of that study then restricted their analysis to prospective studies and obtained similar results (RR, 1.36; 95% CI, 1.12 to 1.65). They then looked only at studies of dementia and, again, obtained a similar estimate of the association between incident AF and the increased risk of later cognitive impairment (RR, 1.38; 95% CI, 1.22 to 1.56).