Atrial fibrillation and exercise
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Atrial fibrillation (AF) is the most common persistent arrhythmia, with a prevalence of 2-3% in the adult population and is associated with an increased morbidity and mortality. This is caused by an increased risk of stroke and heart failure, in addition to the associated comorbidities. Many AF patients also experience burdening symptoms that cause a reduced quality oflife. Increased age and male sex are two of the most important risk factors. In addition, modifiable risk factors like hypertension, obesity, diabetes mellitus, inactivity and heart failure are associated with an increased AF risk. Exercise training is important in treating and preventing many cardiovascular diseases, but the effect in AF patients has not been clear. It seems that large volumes of endurance exercise for many years increases AF risk, while more moderate amounts can be protective. The underlying mechanisms are not fully elucidated. The knowledge on AF mechanisms is limited and the treatment options are restricted. There is thus a need for more knowledge on AF, and the effects of exercise training on AF needs further investigation. This thesis shows that aerobic interval training with relatively high intensity reduces AF burden in patients without profound cardiovascular disease, and the effect seems to be evident shortly after heavy exercise. Twelve weeks of exercise training also caused improvements in quality of life and symptoms of AF, lipid values and cardiac function. The positive effect of exercise is supported by an experimental study in rats. There, we show that the increased susceptibility to AF caused by increased age might be caused by increased atrial fibrosis, reduced conduction velocity in the atria, and changes in expression of connexins, which are important for fast signal propagation between cardiomyocytes. In rats, aerobic interval training prevented the increased AF susceptibility seen with aging. This might be mediated through increased conduction velocity and prolonged action potential duration in the atria. This supports the concept that modification of AF risk factors, with exercise training as an important part, should be central in AF care and prevention. As part of a future plan to examine the relationship between exercise and AF in the population based HUNT study, we examined the validity of self-reported and hospital diagnosed AF, which are the most commonly used endpoints in epidemiological studies. We showed that use of self-reported AF had a very low sensitivity in finding persons with a true diagnosis of AF, and the positive predictive value was also low. Hospital diagnosed AF yields better results, but the sensitivity was also low for those diagnoses, so supplementary methods should be considered in studies where the sensitivity is important, like prevalence studies.