Sleep-Disordered Breathing and Atrial Fibrillation: Prevalence, Detection and Mechanistic Insights

Abstract

Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia, and its incidence, prevalence, and health- and economic-costs are expected to proliferate in the coming decades. Sleep-disordered breathing (SDB) is increasingly recognised as an important modifiable risk factor that increases AF risk and negatively affects treatment outcomes. However, our understanding of the epidemiology of SDB within AF, which AF patients are at increased SDB risk, or how SDB mediates that risk remains incomplete. This thesis focused on addressing these knowledge gaps. Chapter 2 examined the utility of self-reported symptoms of daytime sleepiness for identification of AF patients with concomitant SDB. The principal finding was that most AF patients do not experience excessive daytime sleepiness, regardless of the presence or severity of SDB. This questions the current clinical practice of assessment of SDB symptoms prior to consideration of a sleep study. Chapter 3 is a systematic review and meta-analysis of the literature aiming to quantify the prevalence of SDB in the AF population, which was found to be high. The study also reviewed the various methods with which SDB is assessed in the literature and demonstrated the need for a standardised approach in testing and reporting of SDB in AF research. Chapter 4 aims to assess the feasibility of simplifying SDB testing in the AF population. The study found that an oxygen-desaturation index, a metric derived from simple overnight oximetry, had a good diagnostic yield comparable to that of a full overnight sleep study in identifying patients with clinically-relevant SDB. The simplified test would allow for wider availability of SDB testing and therefore XII potentially improve access to diagnosis and management of SDB in the AF population. Chapter 5 studied ways to improve the patient-selection process for SDB testing by deriving and validating a clinical risk score for AF patients most likely to benefit from treatment of SDB with positive airway pressure. This study utilised two separate observational cohorts and identified multiple characteristics that can readily be ascertained in a clinical setting to help prioritise testing for SDB. Subsequently, a simplified score comprising Male gender, Overweight or Obesity, and history of Diabetes or Stroke (MOODS) was found to have a good discrimination ability to identify AF patients most likely to benefit from SDB testing. The main metric for SDB assessment, the apnoea-hypopnea index (AHI), does not consider a number of important physiological processes that accompany the respiratory events associated with SDB, such as overnight oxygenation, hypoxaemic burden, or the amplitude, nadir, and duration of respiratory events. Chapter 6 examined these metrics in a cohort of AF patients and assessed their correlation atrial remodelling and the prevalence of persistent AF as an indicator of disease progression. The main finding was that the duration of respiratory events independently predicted atrial dilatation, and that patients with longer events had a higher prevalence of persistent AF. Finally, the thesis touches on future avenues of exploration to establish the role of SDB treatment in AF-related outcomes and to address outstanding challenges in the field of concomitant SDB and AF.