This will be a prospective multi-centre randomised controlled trial with two treatment arms. We plan to include up to 15 UK centres. Patients that have been referred for catheter ablation of symptomatic persistent AF will be recruited. Patients will be consented and have their baseline review after having been listed for AF ablation on the hospital waiting list. They will be randomized to one of two treatment arms. All patients will undergo their procedure using a 3D mapping system. Standard catheters will be used during the ablation procedure. Because the STAR mapping™ system will be configured for use with a special version of the 3D mapping system Carto (BIosense Webster) the study will mandate use of clinically approved Carto catheters: Smarttouch thermocool ablation catheter and the Pentarray mapping catheter. Ablation procedures will be carried out using the usual policies and protocols of the institutions involved except for the specific points below. The two treatment arms include:

1. Control arm - PVI alone After PVI, no further ablation in AF will be allowed. If the patient organizes into an atrial tachycardia (AT) during PVI this will be mapped and ablated. Otherwise, in accordance with common clinical practice, a 30 minute waiting period will be observed following PVI to watch for acute pulmonary vein reconnection. During this waiting period, mapping data will be acquired using the multipolar pulmonary vein mapping catheter to acquire STAR mapping™ data. The operator will be blinded to these data. This is done using the pentarray mapping catheter to acquire a minimum of 10 widely spaced globally distributed left atrial recordings of 30 seconds each outside the pulmonary veins. If the patient has remained in AF post PVI then electrical cardioversion will be performed, the pulmonary veins checked and re-isolated if needed, and the procedure terminated.
2. Experimental arm - PVI followed by STAR guided ablation. If the patient organises to sinus rhythm after PVI alone then a 30 minute wait will be observed to ensure sustained PVI and the procedure terminated. If patients remain in AF following PVI, the left atrium will be mapped using a multipolar mapping catheter to acquire a minimum of 10 widely spaced globally distributed recordings outside the pulmonary veins. STAR mapping™ data will be exported and maps generated. Ablation will then be targeted at the leading sites identified by STAR mapping™ in order of ranking (1st first, 2nd second, etc.) with the end-point of AF termination. If AF terminates further sites will not be targeted. If patients terminate to an atrial tachycardia then this will be mapped and ablated as per standard clinical practice.

If AF persists following ablation of all STAR mapping™ identified sites then mapping of the right atrium may be considered if the septum consistently activates early and the coronary sinus activation is predominantly proximal to distal, and further ablation permitted in the right atrium if indicated. If patients remain in AF following ablation then they will be electrically cardioverted.

Follow-up All patients will undergo 12 months follow-up with an ECG at 3, 6, 9 and 12 months, and a 48h ambulatory Holter monitor at 6 and 12 months. Patients will routinely continue anti-arrhythmic therapy for up to 3 months post procedure which will be considered a blanking period. After 3 months rhythmically active antiarrhythmic drugs will be stopped.