BARCELONA – The obesity paradox is alive and well in the rapidly growing population with atrial fibrillation, Samuel Z. Goldhaber, MD, reported at the annual congress of the European Society of Cardiology.
In an analysis of 22,541 participants in the international registry known as GARFIELD-AF (Global Anticoagulation Registry in the Field-Atrial Fibrillation) – the largest ongoing prospective AF registry in the world – all-cause mortality during the first 2 years after diagnosis of the arrhythmia paradoxically decreased as body mass index increased all the way up to a ceiling of 40 kg/m2, according to Dr. Goldhaber, professor of medicine at Harvard Medical School and section head of vascular medicine and director of the thrombosis research group at Brigham and Women’s Hospital, Boston.
“It’s pretty impressive. This degree of mortality reduction with overweight and obesity is of about the same magnitude you might get with thrombolytic therapy for an acute MI, or with beta blocker therapy or statins post-MI,” the cardiologist said in an interview.
This newly described obesity paradox in AF is all the more baffling in light of the heavy cardiovascular risk factor burden that accompanied increased BMI. For example, the prevalence of type 2 diabetes rose from 14.1% among normal-weight individuals with AF, to 19.7% in the overweight, 27.5% in the obese, 34.6% in those with a BMI of 35 to less than 40 kg/m2, and 41.6% in patients with a BMI of 40 kg/m2 or more.
“It’s perplexing,” Dr. Goldhaber confessed. “I think there’s some hidden message here that we haven’t decoded yet.”
Patients with AF who were at the low extreme of the BMI spectrum -- the 3.3% who were underweight, with a BMI below 20 kg/m2 – fared particularly poorly. Their 2-year all-cause mortality rate of 8.71 per 100 person-years was by far the highest of any BMI class in the study. But that’s relatively straightforward to understand, as it’s likely that many underweight patients with AF were frail and/or had cancer. Indeed, only 49% of deaths in the underweight group were due to cardiovascular disease, in contrast to 64% of deaths in persons whose BMI was 40 kg/m2 or more.
Interestingly, only 5%-6% of all deaths in GARFIELD-AF were due to stroke; deaths from heart failure were far more common.
Overall, 71% of patients who presented with newly diagnosed AF in GARFIELD-AF were overweight or obese. The only contributory factor to the obesity paradox that Dr. Goldhaber could spot was that the heavier patients were younger at diagnosis of AF. But this age disparity seems unlikely to overcome their massive burden of multiple other cardiovascular risk factors. So he solicited theories from his audience. One physician argued that morbidly obese individuals are sedentary, so they don’t leave the house as much as leaner AF patients.
“You stay at home because you cannot move. You don’t get into fatal car accidents. You don’t get into conflicts and get murdered,” the physician postulated.
Dr. Goldhaber wasn’t convinced.
“When I go out to bars or dancing, I look around at people, and I estimate that a lot of them have a BMI of 35,” he commented.
Another proposed theory was that overweight and obese AF patients exercise less, so they inhale less of the airborne toxic fine particulates present in the urban environment. The adverse health impact of air pollution is a particularly hot topic of late among European cardiologists, but the notion that obese AF patients fare better because they don’t exercise runs contrary to a wealth of data supporting the health benefits of working out.
The GARFIELD-AF registry is funded by Bayer AG. Dr. Goldhaber reported receiving research grants and/or serving as a consultant to Bayer and numerous other entities, including the National Heart, Lung and Blood Institute.