Black Individuals Have Less A-fib, but When They Do, the Consequences Are More Dire

Black individuals—while less likely to have atrial fibrillation than their white counterparts—are at higher risk of adverse cardiovascular outcomes stemming from the condition, according to the results of a new study. Absolute risks of stroke, heart failure, coronary heart disease, and mortality are significantly higher among black individuals with A-fib. 

The analysis—based on data from the Atherosclerosis Risk in Communities (ARIC) study—is observational but does suggest there are racial disparities in the treatment of atrial fibrillation, say investigators. 

“When we find atrial fibrillation in blacks, we do note that they are at an increased risk of very severe adverse outcomes—in fact, two times more so than whites with atrial fibrillation,” said lead investigator Jared Magnani, MD (University of Pittsburgh Medical Center, PA). “Those are profound racial differences. We’re not able to comment based on our observational study if that’s because of disparities [in care], but this finding is within the context of a very large body of work that has identified healthcare disparities between blacks and whites so I think it’s very likely this contributes to the different outcomes we observed.”

Published June 22, 2016, in JAMA: Cardiology, the study involved 15,080 people, including 3,821 black participants. During a mean follow-up of more than 20 years, 2,348 individuals developed atrial fibrillation. The incidence rate of atrial fibrillation was 8.1 per 1,000 person-years in white individuals and 5.8 per 1,000 person-years in black individuals.

To TCTMD, Magnani said research has consistently shown that atrial fibrillation is less common in black individuals than in white individuals and studies have attempted to address the reasons for the difference. While it might be the result of access to primary healthcare, and the subsequent identification of atrial fibrillation, other studies have attempted to determine if the risk is the result of genetic differences.

In fact, in a second study published in JAMA: Cardiology, Jason Roberts, MD (University of California, San Francisco), and colleagues identified a single-nucleotide polymorphism (SNP) on chromosome 10q22 that mediates a “modest increased risk of atrial fibrillation among white individuals compared with black individuals, potentially through an effect on gene expression levels of MYOZ1.” The gene, MYOZ1, is expressed within cardiac tissue, and the researchers found the SNP increases the risk of atrial fibrillation 11% to 32% among white compared with black individuals. 

For Magnani and colleagues, their study attempted to address the impact of atrial fibrillation-related cardiovascular disease and mortality. Overall, event rates for stroke, heart failure, coronary heart disease, and all-cause mortality were significantly higher in black participants with and without atrial fibrillation compared with their white counterparts. The relative risk of atrial fibrillation-related adverse events, assessed as the rate ratio (a measure of the incidence rate of adverse outcomes in those with versus without atrial fibrillation), was similar for black and white participants.

In contrast, the absolute risk of adverse cardiovascular outcomes was significantly greater for black participants than for white participants. Individual risks of stroke, heart failure, coronary heart disease, and all-cause mortality, assessed as the rate difference (calculated by subtracting the incidence rate in those without atrial fibrillation from the incidence rate in those with the arrhythmia), were 1.5 to 2.0 times higher in black than in white participants. The rate difference for all-cause mortality was 55.9 per 1,000 person-years in white individuals versus 106.0 per 1,000 person-years in black individuals.

“What we see is that atrial fibrillation is enormously associated with mortality—about a two-fold increase in death in blacks than in whites,” said Magnani.    

Results Should Inspire More Evaluation of Differences

Speaking with TCTMD, Magnani said the study should serve as a “spark” or “catalyst” for a more in-depth evaluation of the causes of racial differences in atrial fibrillation and the associated clinical outcomes. While disparities in clinical care are definitely a contributor, developing a better understanding where the problems lie is a complex undertaking. “I think we know from other studies that blacks with atrial fibrillation are less likely to be aware of the diagnosis than whites and they’re less likely to receive anticoagulation,” he said. “I think there’s a very large body of evidence showing there’s a class system of care in this country in the way healthcare is delivered and the reasons for that are highly complex, multifactorial, and have to do with institutional racism, deprivation, and other socioeconomic factors.”

From a research standpoint, Magnani even questioned the generalizability of clinical trial results to the black population, as well as to other minority groups. For example, in the landmark AFFIRM trial, which tested a strategy of rate-control versus rhythm-control for the management of atrial fibrillation, just 11% of patients were from an ethnic minority and only 7% were black, he said. The research community needs to amplify efforts to include these patients in clinical trials, Magnani stressed.  

In an editorial, Thomas Stamos, MD, and Dawood Darbar, MD (University of Illinois, Chicago), say the study adds to the long list of other studies showing an increase in the incidence of disease or worse clinical outcomes in black compared with white individuals. The reasons for the disparity remain unclear.

“Despite an intense search over the last decade, no consistent genetic cause has been identified,” write Stamos and Darbar. “What is known is that there are a number of socioeconomic factors found more commonly among black individuals that strongly correlate with worse cardiovascular outcomes. There are many studies demonstrating the influence of neighborhood social environment and the risk of adverse health events. The possibility that these social determinants of health are playing a direct causative role through an epigenetic mechanism is an interesting, but still unproven theory.”

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