Fitness and Atrial Fibrillation | Journal Scan

Study Questions:

What is the relationship between cardiorespiratory fitness (CRF) and the risk of atrial fibrillation (AF)?


The FIT project study group consisted of 64,561 adults (mean age, 55 years; 46% female; 64% whites) who underwent clinically indicated exercise treadmill testing (ETT). Using medical claim files, diagnosis of AF was confirmed via the 9th International Classification of Diseases (ICD-9) code. CRF was stratified with respect to the metabolic equivalents of task (METs) achieved on ETT: <6 METs, 6-9 METs, 10-11 METs, and >11 METs.


There were 4,616 new cases of AF over a median follow-up period of 5.4 years. The unadjusted 5-year cumulative incidence of AF with respect to the level of CRF (<6 METs, 6-9 METs, 10-11 METs, and >11 METs) was 19%, 10%, 5%, and 4%, respectively. Each additional MET achieved on stress testing was associated with a 7% lower risk of developing AF (hazard ratio, 0.93; 95% confidence interval, 0.92-0.94; p < 0.001). The inverse relationship between CRF and AF was stronger in obese patients.


The authors concluded that there is an inverse relationship between performance on ETT and incidence of AF.


It is noteworthy that a simple treadmill test may be helpful in predicting the patient’s risk of AF during long-term follow-up. However, the mechanisms underlying the inverse relationship between fitness and AF risk remain unclear. AF is perpetuated by structural remodeling of the atria, manifested by fibrosis, which not only affects the left atrium, but also other atrial regions, such as the sinus node. It is possible that some patients with poor CRF were unable to exercise further due to chronotropic incompetence, in addition to other causes, such as deconditioning and coexisting comorbidities. Recent studies have also suggested that elite athletes may be more likely to develop AF. The current study cannot address this finding since such individuals would be very unlikely to have been referred for exercise testing.

Clinical Topics: Arrhythmias and Clinical EP, Diabetes and Cardiometabolic Disease, Prevention, Implantable Devices, EP Basic Science, SCD/Ventricular Arrhythmias, Atrial Fibrillation/Supraventricular Arrhythmias, Exercise

Keywords: Arrhythmias, Cardiac, Atrial Fibrillation, Comorbidity, Exercise, Exercise Test, Follow-Up Studies, Incidence, International Classification of Diseases, Metabolic Equivalent, Obesity, Primary Prevention, Risk, Sinoatrial Node

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