In a substudy of the multicenter, ongoing Swedish Obese Subjects (SOS), bariatric surgery patients had a 29% lower rate of developing atrial fibrillation compared to the non-surgery group, during nearly 20 years of follow-up (HR 0.71; 95% CI 0.60-0.83; P<0.001), according to lead author Shabbar Jamaly, MD, of the University of Gothenburg in Sweden, and colleagues.
In addition, younger patients who underwent bariatric surgery had an even lower risk reduction for the development of atrial fibrillation (P=0.001 for interaction), as well as patients with initially higher diastolic blood pressure (P=0.028).
In an interview with MedPage Today, co-author Kristjan Karason, MD, PhD, also of the University of Gothenburg, said, "To our knowledge, this is the first time weight-loss has been reported as reducing the risk of new-onset atrial fibrillation. Our findings are important since the consequences of this arrhythmia are serious, including stroke, heart failure, and increased all-cause mortality."
But in the editorial, Jonathan M. Kalman, PhD, of Royal Melbourne Hospital in Australia, and colleagues were critical of the trial, citing its "observational study design, poorly matched groups, and absence of incident AF as a predefined endpoint."
They suggested the surgery cohort might have been inherently more motivated to lose weight, since they chose surgical treatment. The results would be difficult, if not impossible, to validate since the "degree of weight loss is not replicable in a nonsurgical context," they argued.
Overall, the surgical cohort experienced a mean 25% total loss of body weight within 1 year, versus no change in the control.
Because obesity (BMI >30) is a known risk factor for cardiovascular problems, including atrial fibrillation, the researchers hoped to identify an effective "primary preventive strategy" to reduce "cardiovascular morbidity and mortality."
They highlighted the connection between obesity and AF in past studies, including a meta-analysis that identified a 49% increased risk of AF in people with obesity.
Between 1987 to 2001, a total of 4,021 Swedish adults age 37-60 were enrolled, including 2,000 who chose to undergo surgery and 2,021 matched controls who received "usual care" defined as the normal routine of their healthcare provider. Participants had a mean BMI of 36, with normal sinus rhythm and no history of atrial fibrilation at enrollment.
The majority of the surgery group underwent vertical banded gastroplasty (68%), while 13% underwent gastric bypass, and 19% had gastric banding. Weight was measured during 10 follow-up visits over the course of a median of 19 years. The participant group database was cross-referenced with the Swedish National Patient Register to gather data on incident AF.
The researchers reported post-surgical complications in about 13% of participants who underwent bariatric surgery, with 2.8% requiring additional surgery. Five people in the surgery cohort, and two in the usual care group died during the trial.
The researchers also noted an independent association between atrial fibrillation and higher free thyroxine levels during the trial. Jamaly and colleagues suggested that this might be due to a relationship between "subclinical hyperthyroidism," and "the development of supraventricular arrhythmia in obesity."
The study's observational design was a limitation, the authors noted. Additionally, because the patients were from the Swedish Obese Subjects study, the original trial's primary outcome was mortality in bariatric surgery, as opposed to incident atrial fibrillation. Karason explained to MedPage Today that the research team is planning a follow-up study to examine "the effect of long-term weight loss on other cardiac diseases such as ischemic heart disease and heart failure."
The editorialists weren't entirely dismissive of the study. They applauded it for providing novel insight to the benefits of weight loss among individuals at-risk for developing AF. They recommended future studies to identify "the categories of baseline weight that would most benefit from weight loss, quantify the degree of weight loss required to confer benefit, correlate the impact of sustained weight loss on other AF risk factors, and evaluate the mechanism of reverse atrial remodeling in AF-naive populations."
"Substantial and sustained" weight loss is key, they wrote, highlighting the fact that the variances in atrial fibrillation incident only began to differ five years into the trial. Kalman and colleagues discussed the frustrations felt within "the broader clinical community of ineffective and unsustainable weight loss among conventionally treated obese cohorts," arguing a need to identify other preventive treatments methods besides surgery in the future.
The study was funded by the Swedish Heart-Lung Foundation, and the National Institute of Diabetes and Digestive and Kidney Diseases of the National Institutes of Health. The SOS study is supported by the Swedish Research Council, the Swedish federal government under the LUA/ALF agreement, and the Swedish Diabetes Foundation.
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