Subclinical atrial fibrillation (SCAF) is the occurrence of brief episodes of AF, a fast atrial arrhythmia, in the absence of any symptoms. The asymptomatic nature of the arrhythmia means it often goes undetected and untreated. Conversely, clinical AF presents itself, and is swiftly managed with anticoagulation therapy to minimise the risk of stroke. The link between clinical AF and stroke has been well-established, however, research into SCAF is only just beginning. It is widely suspected that SCAF is the cause of many cryptogenic stroke admissions. If this is found to be true then methods of risk stratification and screening, to boost detection and early management of SCAF, should have a significant effect on reducing stroke and AF-related hospital admissions. This study will use records of patients with permanent pacemaker (PPM) devices to investigate the incidence of SCAF. In addition, the data will be used to establish the clinical relevance of SCAF, particularly in relation to stroke, and aim to identify useful screening and risk stratification methods.