Data on the association between AF and fitness is conflicting.
The aim of this analysis was to investigate the association between fitness, obesity and incidence of atrial fibrillation (AF) among apparently healthy non-athlete adults.
We investigated 20,410 self-referred subjects who were annually screened in a tertiary medical center. All subjects were free of AF and completed maximal exercise stress test according to the Bruce protocol at baseline. Fitness was categorized into age- and sex-specific quintiles (Q) according to treadmill time. Subjects were categorized to low (Q1-Q2) and high fitness (Q3-5) groups. The primary end point was new-onset AF during follow-up.
Mean age was 48 ± 10 years, and 72% were men. A total of 463 (2.3%) events occurred during an average follow-up of 8 ± 5 years corresponding to an AF event rate of 0.3% per person year. Univariate and multivariate models showed that AF risk was similar in both fitness groups. However, AF event rate was 0.55% per person year among high fitness obese subjects, compared with 0.31% for low fitness obese subjects (p= 30 kg/m2) high fitness was independently associated with a significant 79% increased AF risk (95% CI 1.15-2.78; p=0.01), whereas among non-obese subjects the rate of events was similar between both fitness groups (p for interaction = (1)).
Our findings suggest that high fitness might be associated with increased AF risk among obese subjects.

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