Cardiorespiratory fitness and atrial fibrillation: A population-based follow-up study

Background Atrial fibrillation (AF) is the most common arrhythmia worldwide and has a complex association with physical fitness. The relationship of cardiorespiratory fitness (CRF) with the risk for AF has not been previously investigated in population-based studies. Objective The purpose of this study was to determine the relationship of CRF with incident AF. Methods CRF, as assessed by maximal oxygen uptake (VO2 max) during exercise testing, was measured at baseline in 1950 middle-aged men (mean age 52.6 years, SD 5.1) from the Kuopio Ischaemic Heart Disease (KIHD) study. Results During average follow-up of 19.5 years, there were 305 incident AF cases (annual AF rate of 65.1/1000 person-years, 95% confidence interval [CI] 58.2–72.8). Overall, a nonlinear association was observed between CRF and incident AF. The rate of incident AF varied from 11.5 (95% CI 9.4–14.0) for the first quartile of CRF, to 9.1 (95% CI 7.4–11.2) for the second quartile, 5.7 (95% CI 4.4–7.4) for the third quartile, and 6.3 (95% CI 5.0–8.0) for the fourth quartile. Age-adjusted hazard ratio comparing top vs bottom fourth of usual CRF levels was 0.67 (95% CI 0.48–0.95), attenuated to 0.98 (95% CI 0.66–1.43) upon further adjustment for risk factors. These findings were comparable across age, body mass index, history of smoking, diabetes, and cardiovascular disease status at baseline. Conclusion Improved fitness as indicated by higher levels of CRF is protective of AF within a certain range, beyond which the risk of AF rises again. These findings warrant further replication.