Afib.no network member Lars Elnan Garnvik defended his thesis “Physical activity and cardiorespiratory fitness as determinants of atrial fibrillation incidence and prognosis. Observational findings from the HUNT study” for the degree of PhD at the Faculty of Medicine and Health Sciences, NTNU – Norwegian University of Science and Technology, March 24, 2020.

Before the defense, he gave a trial lecture entitled “Cardiovascular disease prevention: sit less, move more or become fitter?”

Supervisors: Bjarne Martens Nes and Jan Pål Loennechen, NTNU.

Evaluation committee:
Thijs Eijsvogels, Radboud University Medical Center, the Netherlands
Bente Morseth, UiT – The Arctic University of Norway
Anja Bye, CERG/Department of Circulation and Medical Imaging, NTNU

Summary
Atrial fibrillation is a cardiac arrhythmia characterized by rapid and irregular electrical activity in the atria. It is the most common cardiac rhythm disorder with a prevalence of 2-3% in the adult population. Atrial fibrillation is associated with increased mortality, mainly due to increased risk of stroke, ischemic heart disease and heart failure. In addition to the serious burden the disease poses on the individual patient, it represents a major challenge for the public health and health care system. In this project, we have utilized data from the Nord-Trøndelag Health Study (The HUNT study) to investigate the relationship between physical activity, estimated cardiorespiratory fitness and atrial fibrillation.

In paper I, we present data on 43 602 men and women from the third wave of the HUNT study (HUNT3). The purpose of the study was to investigate the risk of atrial fibrillation associated with different levels of physical activity and body mass index, and to assess how physical activity affected the risk of atrial fibrillation imposed by obesity. The main findings from the study was that people with obesity had a significantly increased risk of developing atrial fibrillation. However, this increased risk was attenuated in obese individuals who undertook regular physical activity.

Furthermore, in paper II we investigated the association between estimated cardiorespiratory fitness and risk of atrial fibrillation in 39 844 men and women from HUNT2 and HUNT3. The study had two primary aims: (1) to investigate the association between estimated cardiorespiratory fitness measured in HUNT3 and atrial fibrillation risk, and (2) to examine the effect of change in estimated cardiorespiratory fitness from HUNT2 to HUNT3 on future risk of atrial fibrillation. The results of the study showed that men and women with the highest estimated fitness had 31% and 47% lower atrial fibrillation risk, respectively, compared to men and women with the lowest estimated fitness. Furthermore, we found that those who increased their fitness over a 10-year period from HUNT2 to HUNT3 had half the
risk of atrial fibrillation compared to those who had reduced their fitness levels.

Finally, in paper III, we investigated the impact of physical activity and estimated cardiorespiratory fitness on mortality and morbidity in individuals diagnosed with atrial fibrillation. The major findings were that regular physical activity and high estimated cardiorespiratory fitness were associated with lower incidence of mortality and cardiovascular disease in individuals with AF.
Lars Elnan Garnvik

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