Black Patients with Heart Failure Are Not at Lower Risk for Atrial Fibrillation

New research contradicts earlier findings that race is a risk factor for atrial fibrillation (AF) but finds that excess body fat may be riskier than anyone realized — if that fat is stored around the heart.

The separate studies, which were both presented at the 2014 Scientific Sessions of the American Heart Association, used very different techniques on very different patient populations but both reached statistically significant findings.

Several previous studies have found that black patients are less likely than white patients to develop AF after they suffer heart failure, but researchers from the Perelman School of Medicine at the University of Pennsylvania viewed such findings with suspicion.

“Even though other studies have found that black patients with heart failure have less atrial fibrillation, we didn’t think it made sense,” said lead study author Parin J. Patel, MD, an Electrophysiology Fellow at Penn. “We know that heart failure is a major risk factor for atrial fibrillation, even more than old age and high blood pressure, so we set out to understand how there could be such a disparity between races.”

Patel’s team found records in Penn’s system for 5,131 patients who had no history of AF when they arrived at the hospital with heart failure. After a median follow-up of 4.5 years, 851 of those people developed AF.

The team’s analysis found several risk factors, but race wasn’t among them. About 15% of the study’s more than 3,000 white patients and about 18% of the study’s more than 2,000 black patients were eventually diagnosed with the condition.

The study team speculated that a tendency among prior studies to have more follow-up data for white patients than for black patients may have led to apparent medical disparities.

“Our findings are important because they show that physicians should watch out for atrial fibrillation in all heart failure patients, not just those who are white,” said Patel. “Future studies in this area are needed to examine other outcomes among this patient population, including heart attack and stroke, and to further understand any differences or similarities between white and black patients.”

The second study, which was conducted by researchers at Loyola Medical Center in suburban Chicago, may significantly refine upon prior evidence that obesity is associated with increased risk of AF.

The Loyola study used new innovations in cardiac magnetic resonance imaging to precisely measure the volume of epicardial adipose tissue (EAT) and the amount of fibrosis in the left atria of 54 patients with AF.

There was a statistically significant correlation of 0.45 between EAT volume (ie, fat around the heart) and the amount of fibrosis. Indeed, that correlation was significantly stronger than the 0.30 correlation between patient body mass index (BMI) and fibrosis.

“Many people who would not be considered obese by their BMI nevertheless have high volumes of fat around their hearts, which could put them at risk for atrial fibrillation. Simple measures such as BMI may fail to completely inform us of a patient’s true cardiovascular risk,” said study co-author Mark Rabbat, MD, an assistant professor of medicine and radiology at Loyola University Medical Center.

The study authors speculated that EAT, which was once believed to be inert fat tissue, is actually a metabolically active organ that releases proteins that may trigger the fibrosis that causes AF. Rabbat also suggested that EAT may prove a viable target for medications designed to improve heart health.

First, however, the study team is planning further research to clarify the relationship between EAT, AF and other risk factors.