Recurrent focal electrical activation (or ectopy) superseding sinus activation is the only mechanism proven to drive paroxysmal atrial fibrillation (AF). However, it has not been possible to show similar focal drivers during AF, owing to the limitations of mapping in persistent AF. RETRO-Mapping has been developed as a method to generate activation maps during AF to test the hypothesis that persistent AF is also maintained by focal drivers. RETRO-Mapping is able to locate sites of focal activation that were isolated, intermittent, or recurrent during persistent AF. However, a 30-second segment of AF can have approximately 150 wavefronts in a small area of myocardium. Screening for focal activation and manually validating these prior to ablation was not feasible using current commercial systems. RETRO-Mapping can automatically detect focal activation and a recording system that enables the intracardiac signals to be directly analysed by the RETRO-Mapping software. This will allow RETRO-Mapping to build a detailed classification of focal activation types and study the impact of ablation of these sites on the AF cycle length, to address the hypothesis that persistent AF is maintained by focal drivers.