Contemporary pacemakers allow quantification of atrial high-rate episodes (AHREs) and atrial fibrillation burden (AFB) accurately. It is generally believed that left atrial (LA) remodelling may precede the development of atrial arrhythmias (AA), and AHRE precede the clinical manifestation of atrial flutter or fibrillation. However, the relationship between LA remodelling with AHRE has not been studied. Furthermore, the relationship of AFB to progressive LA remodelling and how this relates to indices of thrombogenesis is unclear. The aim of my study is to investigate the inter-relationship between LA remodelling, AA burden and indices of thrombogenesis in patients with pacemakers. My findings suggest that the incidence of AHRE was 35%. Increased frequency of right ventricular pacing is associated with LA enlargement and reduced global left and right ventricular function. However, there was no clear association between the right atrial pacing with cardiac remodelling. The cumulative percentage right ventricular pacing and increased LA volume are associated with the development of AHREs, but AFB is independently associated with changes in LA function, left ventricular diastolic function and indices of platelet activation and thrombosis. In addition, I demonstrated the feasibility and reproducibility of a novel method of IACT measurement in patients with permanent pacemakers.