Modifiable risk factors may account for half the cases of AF

Study results suggest that controlling certain risk factors could help in prevention of AF.

Although it has been well established that preventing traditional risk factors for CVDs such as HF and MI could prevent most cases, research looking into the role of risk factors in atrial fibrillation has been less frequent and far less conclusive. However, a new study in Circulation has shown that having at least one of the established risk factors for atrial fibrillation, including high BP, elevated BMI and diabetes, could explain more than 50% of the cases.

According to Alvaro Alonso, MD, PhD, assistant professor of epidemiology and community health at University of Minnesota School of Public Health in Minneapolis and co-author on the study, previous research into this topic had been performed using patients from the Framingham Study, but the generalization of the results to the general US population was limited because the population was primarily white.

“However, in our study, we have a large African-American population, so it’s a more diverse sample in terms of geography,” Alonso told Cardiology Today. “So we were able to look at this question and come up with results that we believe might be more applicable to the general US population.”

‘Not surprising’ findings

Alvaro Alonso

The study, conducted by Alonso and fellow researchers from the University of Minnesota, Minneapolis; the University of North Carolina, Chapel Hill; and the Wake Forest University School of Medicine, Winston-Salem, N.C., included 15,792 men and women who were members of the Atherosclerosis Risk in Communities (ARIC) study cohort and aged 45 to 64 years. The investigators looked for previously established AF risk factors, including high BP, diabetes, elevated BMI, prior cardiac disease and cigarette smoking, and characterized individuals by either optimal, borderline or elevated levels.

They then followed the participants for a mean of 17.1 years and reported 1,520 cases of incident AF. Overall, age-adjusted incidence rates were highest in white men (7.45 per 1,000 person-years) and lowest in black women (3.67 per 1,000 person-years). According to their findings, 56.5% of AF cases could be explained by having at least one borderline or elevated risk factor, with elevated BP being the most significant contributor.

“We know that for other CVDs, like HF or MI, modifying risk factors for those two conditions could prevent 70% to 80% of all cases. So our finding that AF had similar numbers is not surprising,” Alonso said. “But the highlight of this study is that in preventing AF, sometimes we are more interested in finding genetic factors and biomarkers, yet we have these basic risk factors, like high BP and obesity, that if we prevented would probably be able to prevent a lot of AF occurring in the population.”

Bernard Gersh

In fact, the results are consistent with some of the work performed by Bernard Gersh, MB, ChB, DPhil, professor of medicine with the Mayo Graduate School of Medicine, Mayo Clinic, Rochester, Minn., and colleagues and raise what Gersh said is the important question of whether comprehensively treating all of these risk factors would lead to a reduction in the incidence of AF.

“We would hope so, but I don’t know personally whether we can state with confidence that it will cut [AF incidence] by 50%,” Gersh, who is also a member of Cardiology Today’s Editorial Board, said in an interview. “But there is a real possibility that the predicted increase in the frequency of this condition is not inevitable. It will be as people age, but after adjusting for age, there is no reason why we should not be able to blunt this epidemic. And this is a good paper that suggests that.”

Possible explanation

For Gersh, AF is not nor has it ever been just one disease, and this partially explains why modifying risk factors could make a dramatic effect on the incidence of this condition.

“In younger people without risk factors and a strong family history, AF is probably caused by a genetically mediated electrical substrate. These are the people that have triggered activity and are good candidates for radiofrequency ablation,” he said. “At the other end of the spectrum are the vast majority of people with AF who are older, and there I think it is a very different mechanism. There, it is a vascular disease and not primarily an electrical disease and our own work at Mayo has very much been along those lines, and very much in agreement with this [study].”

The reason for this, he said, is “AF is a disease of arterial stiffness due to conditions like hypertension, atherosclerosis, obesity and diabetes, which lead to diastolic dysfunction and puts overload on the left atrium, which dilates. Now, how much of that is the individual respect of age is difficult to say, but it’s consistent with our own data.”

Unanswered questions

For Alonso, one of the limitations of the paper presents an important direction that future research into this topic should head.

“We included a large group of white people, as well as a group of African Americans, but we don’t have information on other ethnic or racial minorities,” he said. “The proportion of Hispanics in this country is increasing and we don’t have that information here. It may be that these numbers are different for Hispanics. So, trying to find other populations that include Hispanics and other minorities would be relevant.”

Along similar lines, Alonso would also like to see research delve into one of the key findings of this study that showed a striking racial disparity between the incidence of AF in whites and African Americans, indicating substantially lower rates in the latter population, which is the opposite seen in CHD, HF and stroke.

“We believe that there are probably some genetic risk factors that explain this, and we would like to find out what those factors are because that eventually might help us understand how AF occurs and eventually be able to develop preventive strategies that take into account how AF occurs in a population,” he said.

Still, Gersh said, there is also need for more research into AF on an even broader level. “What we need from a research perspective is incidence and prevalence data for the past 10 years, as we have the data up to 2000, but we don’t have good data thereafter,” he said. “Although there are not a lot of databases, this is something that we are going to be looking into.” – by Brian Ellis

For more information:

• Huxley R. Circulation. 2011;123:1501-1508.
• Miyasaka Y. Circulation. 2006;114:119-125.
• Wyse D. Circulation. 2004;109:3089-3095.

Disclosures: Drs. Alonso and Gersh report no relevant financial disclosures.