Atrial fibrillation: A preventable lifestyle disease!

The Nord-Trøndelag Health Study (the HUNT study) is one of the largest cohort studies worldwide combining data from 120,000 people from a central rural region in Norway, the Nord-Trøndelag County. Starting with the first survey in 1984–1986 (HUNT1) several follow-up examinations have been performed since (HUNT2 to HUNT4) assessing socioeconomic conditions, health-related behaviors, clinical symptoms, illnesses and disease states, also addressing cardiovascular risk factors, morbidity and mortality. The advantage of this study is the confined region, large percentage (50%) of the population investigated and the registry data of the two county hospitals, which makes the study a unique population-based approach. In the publication of the journal, the group from the K.G. Jebsen Center for Exercise in Medicine at Trondheim University leading the investigation have addressed an important issue in preventive cardiology, the role of obesity and physical activity on the incidence of atrial fibrillation. The topic is not new and has been investigated before in different regions of the world. However, the HUNT investigation provides important data, particularly on a detailed questionnaire of the frequency, duration and intensity of physical activity per week. Results of the HUNT3 survey assessing data between 2006 and 2008 and follow-up until the end of 2015 clearly confirm the notion that obesity is a risk factor for atrial fibrillation and flutter, whereas high physical activity has preventive potential. In detail, overweight and obesity were associated with an 18% and 59% higher risk of atrial fibrillation, respectively, when compared to the population with normal body mass index between 18 and 25 kg/m. However, data also show that obesity seems to be more important than physical inactivity. Although data reveal that active obese individuals have a 22% lower risk of atrial fibrillation than sedentary obese subjects, these data were not significant. Therefore, the conclusion of the Norwegian authors ‘our results suggest that obese individuals are likely to benefit the most from being physically active concerning AF risk’ should be extended also addressing weight reduction as an important intervention strategy. Nonetheless, increasing physical activity has to be included in a weight reduction programme in order to extend maintenance successfully, but weight reduction seems to be at least as important from a pathophysiological perspective. The mechanisms for the deleterious influence of obesity on the pathophysiology of atrial fibrillation are multifactorial, as also explained by the authors. They are mediated by obesity itself as well as obesityassociated cardiovascular risk factors. Present over several decades this risk factor profile eventually leads to myocardial changes, including disturbances of the atrial conduction pathways and autonomic control, leading to a significantly increased incidence of atrial fibrillation as observed in the HUNT study (4% incidence per 1000 person-years). Two different strains of pathophysiology can be distinguished, ‘pressure overload’ and ‘metabolic overload’ (Figure 1). On the one hand arterial hypertension (pressure overload) is the leading risk factor for the development of atrial fibrillation, even independently of obesity. However, it is particularly prevalent in overweight and obese individuals, leading to myocardial remodeling over time inducing ventricular diastolic dysfunction, left ventricular hypertrophy, mitral valve regurgitation and left atrial enlargement (Figure 1), which will eventually lead to disturbances in sinus node, adjacent atrial and pulmonary vein electrical conduction. On the other hand, obesityassociated metabolic disorders such as insulin resistance or type 2 diabetes not only favour systemic