New York, Nov 19 (IANS): More than body mass index (BMI) which is commonly used to determine if a person is obese, it is the layer of fat around heart which is more closely associated with atrial fibrillation or irregular heart beat, finds research.

“Simple measures such as BMI may fail to completely inform us of a patient's true cardiovascular risk," said Mark Rabbat, assistant professor of medicine and radiology at Loyola University Medical Center in Illinois, US.

"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,” Rabbat explained.

The study found a statistically significant correlation between the fat layer and scarring in the left atrium that causes atrial fibrillation.

By contrast, there was not a statistically significant correlation between BMI and scarring in the left atrium, which is one of the four chambers of the heart.

Atrial fibrillation, or a-fib, occurs when the upper chambers of the heart contract very fast and irregularly.

It is thought to be caused by inflammation and scarring (fibrosis) in the left atrium.

The fat layer around the outside of the heart is called epicardial adipose tissue (EAT).

"Our study is the first of its kind to demonstrate the association of EAT and the extent of left atrial fibrosis in patients with a-fib," Rabbat said.

The study included 54 patients who had a-fib. The average amount of fat around the heart (EAT volume) was 120 cubic centimeters.

"Fat tissue around the heart may be a novel target to reduce the risk of a-fib and its recurrence," Rabbat added.

The findings were presented at the American Heart Association 2014 Scientific Sessions in Chicago.