The Atrial Fibrillation Epidemic

Summarized by Robert W. Griffith, MD
January 21, 2005

Introduction

In atrial fibrillation (AF, or A-fib) the upper chambers of the heart quiver rather than contract, so that the lower chambers beat faster and irregularly. It's the most common of the diseases that show up as irregularity of the heartbeat. And it's becoming more common - in fact, physicians speak of "an AF epidemic".

The US is also experiencing an obesity epidemic. When two epidemics occur around the same time, scientists often look for a possible link - is one a risk factor for the other? A report has appeared studying the association between AF and obesity, based on data from the Framingham Study. It's published in the Journal of the American Medical Association, and we summarize it here.

What was done

The Framingham Heart Study and its follow-up, the Framingham Offspring Study, contain detailed medical information collected at intervals from over 5,000 inhabitants of the town of Framingham, Massachusetts. The average age at baseline was 57, and 55% of the participants were women. None of them had AF.

The body mass index (BMI) was calculated for each participant from their height and weight; they were then classified as being normal (BMI below 25), overweight (BMI 25 to 29.9), or obese (BMI 30 or above).

A full medical history, physical exam, and EKG were done routinely at each Framingham Heart Study examination, i.e. every 2-4 years. If atrial fibrillation or atrial flutter was seen on any EKG recording, the subject was diagnosed as having AF. Echocardiography was done to determine if either of the upper chambers (atria) was dilated.

The average follow-up period was 13.7 years; at the end of the study period, the numbers of new-onset AF cases in the different classes of BMI were compared. The periods that each person was in the study were added to provide total 'person-years' of study participation.

What was found

Of the 5282 participants in the study, 526 (9.9%) developed AF. Of these, 234 (45%) were women. The incidence of new AF cases, adjusted for age, increased depending on the BMI classes, as shown in the table:

	Normal BMI	Overweight	Obese
Men	9.7%	10.7%	14.3%
Women	5.1%	8.6%	9.9%

Put another way, obese men were 1.52 times as likely to develop AF as normal weight men, and obese women were 1.46 times as likely.

The link between obesity and AF was still seen after adjustments were made for the presence of high blood pressure, diabetes, and previous MI.

Although left atrial dilation was much more common in obese persons, there was no link between AF and dilated left atria. This may seem hard to understand. It can be explained by the fact that left atrial dilatation is usually a result of high blood pressure, increased left ventricle size, heart failure, or an MI, which were not, generally, linked to the incidence of AF in the study.

What the results mean

Obesity is clearly a major risk factor for AF - and so is increasing age. Also obstructive sleep apnea.¹ All these factors probably help account for the 'epidemic' of AF we are experiencing in the USA. Whether reducing obesity can influence the likelihood of AF remains to be seen; further studies are needed on the role of left atrial dilatation - if it's really relevant for AF, if it can be lessened by weight loss, and so on.

From a purely practical point of view, this study provides yet another reason for people to avoid becoming overweight in the first place, and, if already overweight, to avoid slipping into the obese category.

Source

• Obesity and the risk of new-onset atrial fibrillation. TJ. Wang, H. Parise, D. Levy,  et al., JAMA, 2004, vol. 292, pp. 2471--2477

Footnotes
1. Obstructive sleep apnea occurs in about 40% of obese people, and is strongly associated with AF. AS. Gami, G. Pressman, SM. Caples,  et al., Circulation, 2004, vol. 110, pp. 364--367

Related Links
Atrial Fibrillation -- What's New
Atrial Fibrillation - Resources for Patients
Atrial Fibrillation Foundation

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