Exercise in Atrial Fibrillation

Atrial Fibrillation (AF) is the most common sustained cardiac arrhythmia affecting 1-2% of the global population. Up until recently the treatment of the condition has been centred around either rate or rhythm control strategies in the form of pharmacological or surgical approaches. Emerging studies have demonstrated the importance of treating the underlying cause of the arrhythmia; focusing on the risk factors that are known to predispose to AF. These include obesity, obstructive sleep apnoea, type II diabetes mellitus, dyslipidaemia, alcohol and smoking. This new approach to focus on risk factor management has shown positive outcomes in the management of AF with a reduction in symptoms and burden, but also a reversal of the atrial substrate and subsequent reversal of the disease progression. Physical inactivity is increasingly recognised to contribute to many of these predisposing conditions but also as an independent risk factor for AF. Therefore, the potential role of physical activity and exercise in both the prevention and management of AF is gaining attention. This thesis focuses on the relationship of physical activity and exercise in both the prevention and management of AF and aims to extend our understanding of the role exercise can play within this emerging field. Chapter 1 presents an initial insight into the growing prevalence of AF, its related risk factors and a detailed summary on the pathophysiological remodelling within the heart that leads to AF. Then this chapter aims to provide a comprehensive literature review of the current relationship of physical activity and exercise in the causation and prevention of AF and aims to provide comprehensive insight into this relationship that currently exists. This chapter also summarises the current studies that investigate an exercise led intervention in those with AF both in persistent and non-persistent AF, which then provides the rationale of the proposed series of studies and the main part of the PhD project being the ACTIVE-AF study. Chapters 2 and 3 are meta-analyses that aim to provide important information on those studies that have assessed cardiorespiratory fitness at baseline testing and its relationship to both AF and stroke incidence. These chapters aim to provide further rationale on how exercise and improvements in cardiorespiratory fitness can reduce the risk of AF, and furthermore reduce the risk of stroke, especially that stroke is associated with AF and the risk is severely heightened in those with the cardiac arrhythmia. Chapter 4 is a study in which we assessed the use of a heart rate marker typically used to prescribe exercise target intensities in healthy populations. Heart rate reserve is a measure that assumes equivalence to one’s corresponding oxygen update or VO2 and has yet to be investigated to assess its validity in the AF patient cohort, whether the two measures are in fact equal. This study found that the use of heart rate reserve cannot assume its equivalence to a corresponding VO2 and therefore must be calculated on an individual basis following a cardiopulmonary exercise test, which can then allow for the prescription of individualised exercise targets in patients with AF. Chapter 5 is a study which evaluates the association between AF symptom burden using the University of Toronto AFSS questionnaire and cardiorespiratory fitness levels. Further to this, the study also assesses whether subjective assessment of exercise dyspnea and exercise intolerance relates to cardiopulmonary derived measures. The purpose of this study is to provide insight whether objective assessment of cardiorespiratory fitness can predict one’s degree of AF symptom severity calculated using the AFSS questionnaire. Chapter 6 then aims to further assess the role of rhythm status on cardiopulmonary gas exchange measures, with attention in VO2peak and ventilatory efficiency. There have been several studies to date which have assessed the immediate changes to VO2peak following successful restoration of sinus rhythm via direct current cardioversion or catheter ablation; however, very few have assessed for any changes also within a measure of ventilatory efficiency reflected by VE/VCO2 in patients with ‘asymptomatic’ AF. This study therefore aims to assess in more detail besides cardiorespiratory fitness changes, whether other cardiopulmonary gas exchange markers improve after 4-week after successful restoration of sinus rhythm by cardioversion in patients with ‘asymptomatic’ AF and aims to provide new insight in whether this patient cohort do in fact exhibit symptoms that can be detected during cardiopulmonary exercise testing. Finally, in Chapter 7 we assessed an exercise intervention in the management of AF. The findings of study have been to date the largest randomised controlled trial to assess a physical activity intervention in patients with symptomatic AF. The study’s primary end points showed significant improvements in exercise capacity following 6-month intervention period in those patients within the intervention group compared to controls. This study was able to further assess and validate the role of an exercise led-intervention in AF patients, as improvements to exercise capacity and subsequent volume of oxygen uptake have a direct effect in improving AF known risk factors and should be a part of the newly adopted risk factor management approach within this disease population. In conclusion, we assess and summarise the current link between exercise in the prevention and management of AF. We also address the proposed link in athletic cohorts where exercise is purported to promote AF, however there is still more to be done to effectively assess this relationship. However, for the general population where obesity and physical inactivity rates are growing there is no doubt that the benefits of engaging in regular exercise far outweigh any potential risk.Thesis (Ph.D.) -- University of Adelaide, School of Public Health, 201