Abstract Background Obstructive sleep apnoea (OSA) is prevalent in approximately 15% of western populations. Cardiovascular disease and arrhythmia are extremely common in this group with significant morbidity overlap. Whilst treatment of OSA with continuous positive airways pressure (CPAP) appears to reduce hypertension, bradycardia and recurrence of atrial fibrillation (AF), large randomised control trials and meta-analyses do not demonstrate a significant reduction of incident tachyarrhythmias such as atrial fibrillation or sudden cardiac death. Some smaller studies suggest that AF may have up to 20% incidence. Analysis of these studies suggest that there may be significant heterogeneity in both CPAP usage and OSA phenotype, confounding the results. Furthermore, standard arrhythmia detection often underestimates paroxysmal arrhythmias. This on-going trial investigates a treated OSA population using CPAP monitoring and implantable loop recorders (ILR). Purpose This study aims to identify the incidence of arrhythmia in a treated OSA population with comprehensive arrhythmia monitoring and CPAP usage. It also explores the mechanisms linking OSA and arrhythmia such as heart rate variability and turbulence and cardiac biomarkers in order to identify at risk sub populations. Methods Continuous moderate-to-severe OSA patients were recruited from a major UK sleep centre after ECG and medical history confirmed the absence of arrhythmia. Each patient was then randomised to receive either standard-care or standard-care with an ILR with 24-hour heart rate variability/turbulence measurements, echocardiography (where possible) and cardiac biomarkers at baseline and 12 months. All patients had remote CPAP usage monitoring (where possible). The trial ended at 36 months after enrolment. Results 200 patients were recruited to the trial. Current mean average follow-up is 28 months in this on-going trial. Mean age and apnoea hypopnea index at enrolment was 53 years and 43.8 respectively. To date we have diagnosed atrial fibrillation in 15% of the ILR group compared to 2% in the standard care group. Other arrhythmias detected in the ILR group include two with supraventricular tachycardia and 2 with significant pauses but not requiring further treatment. Final analysis of arrhythmia incidence with CPAP usage and heart rate variability/turbulence, and cardiac biomarkers is ongoing with final results due by the time of final submission. Conclusion Arrhythmias, particularly AF, are highly incident in OSA despite CPAP treatment. This study may determine if heterogenous CPAP usage confounds the above observation and whether there may be predictors of arrhythmia that may indicate a need for arrhythmia screening in the OSA population.