Atrial Fibrillation Nomenclature, Definitions and Mechanisms:Position Paper from the International Working Group of the Signal Summit

The international Working Group of the Signal Summit is a consortium of experts in the field of cardiac electrophysiology, dedicated to advancing knowledge on understanding and clinical application of signal recording and processing techniques. In 2023, the working group met in Reykjavik, Iceland and lay the foundation for this manuscript. Atrial fibrillation (AF) is the most common arrhythmia in adults, with a rapidly increasing prevalence worldwide. Despite substantial research efforts, advancements in elucidating the underlying mechanisms of AF have been relatively modest. Since the discovery of pulmonary veins as a frequent trigger region for AF initiation over two and a half decades ago, advancements in patient care have primarily focused on technological innovations to improve the safety and efficacy of pulmonary vein isolation (PVI). Several factors may explain the limited scientific progress made. Firstly, while AF initiation usually begins with an ectopic beat, the mechanisms of initiation, maintenance, and electrical propagation have not been fully elucidated in humans, largely due to suboptimal spatiotemporal mapping. Secondly, underlying structural changes have not been clarified and may involve different types of re-entry. Thirdly, inconsistent definitions and terminology regarding fibrillatory characteristics contribute to the challenges of comparing results between studies. Fourthly, a growing appreciation for phenotypical differences likely explains the wide range of clinical outcomes to catheter ablation among patients with seemingly similar AF types. Lastly, restoring sinus rhythm in advanced phenotypic forms of AF is often not feasible or may require extensive ablation with minimal or no positive impact on quality of life. The aims of this international position paper are to provide practical definitions as a foundation for discussing potential mechanisms and mapping results, and to propose pathways toward meaningful advancements in AF research, ultimately leading to improved therapies for AF.