Abstract & Commentary
Synopsis: Obesity is an important, potentially modifiable risk factor for AF. The excess risk of AF associated with obesity appears to be mediated by left atrial dilatation. These prospective data raise the possibility that interventions to promote normal weight may reduce the population burden of AF.
Source: Wang JT, et al. JAMA. 2004;292:2471-2477.
Atrial fibrillation (AF) is the most common cardiac dysrhythmia currently afflicting 2½ million Americans and its frequency is expected to increase several-fold in the next one or two decades.1 Previously reported studies have demonstrated that diabetes, hypertension, advanced age, and the presence of cardiovascular disease increase the risk of developing AF2-5 and, most recently, obstructive sleep apnea which occurs in about 40% of obese individuals has also been found to be strongly associated with AF.9 Despite the fact that obesity frequently occurs in association with most of these conditions, the data from prior studies have not been clear as to whether or not obesity is a specific risk factor for AF in and of itself.2-5
Wang and associates used the data from the prospective, community-based Framingham Heart Study and the Framingham Offspring Study6,7 to collect information on 5282 participants whose mean age was 57 years (55% women) without baseline AF. Subjects were categorized as normal if their body mass index (BMI) was less than 25, overweight if it was 25-30, and obese if it was greater than 30. During the mean follow-up of 13.7 years, 526 participants (234 women) developed AF. After adjusting for cardiovascular risk factors and interim myocardial infarction or heart failure, a 4% increase in AF risk for a one unit increase in BMI was observed both in men and women. However, after adjustment for echocardiographic left atrial diameter in addition to the clinical risk factors, BMI was no longer associated with an increase in AF risk. Therefore, the excess risk of AF associated with obesity appears to be mediated by left atrial dilatation.
Comment by Harold L. Karpman, MD
Obesity has reached epidemic proportions in the United States in that nearly 65% of the population are overweight and 31% are classified as obese.8 Similarly, as indicated above, AF is also reaching epidemic proportions. Wang et al have now clearly demonstrated that obesity was correlated with a 50% increase risk of developing AF irrespective of sex. Equally important, they demonstrated that after adjusting for left atrial diameter, obesity was no longer associated with increased risk for the development of AF. Left atrial remodeling is an established mechanistically important factor in the pathogenesis of AF whether by increasing left atrial size or by other mechanisms such as allowing for the occurrence of a critical number of reentrant wavelets, by left atrial stretch or by triggering pulmonary vein foci.10,11
Although the Framingham data are observational, it clearly raises the strong possibility that weight reduction may decrease the risk of developing AF. Although the increased risk for the development of AF in patients with an increased BMI is modest, the public health implications are quite significant since AF is responsible for a 3-5-fold increase risk of stroke and a 2-fold increase risk of mortality.1 Older age is clearly the most important risk factor for the development of AF for a variety of electrophysiological reasons. Of course, one cannot change their age; however, it would now appear clear that control of diabetes and hypertension as well as lifestyle changes aimed at weight reduction in obese individuals may prove to be critically important in preventing the onset of AF, and thereby reducing the morbidity and mortality associated with that arrhythmia. Finally, it is important to note that additional prospective studies are needed to understand the influence of excessive weight on the cardiac remodeling process and to document the effects of weight loss on the risk of developing new onset AF.
Dr. Karpman, Clinical Professor of Medicine, UCLA School of Medicine, is Associate Editor of Internal Medicine Alert.
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