Inclusion Criteria:  Patients with symptomatic persistent AF (defined as a sustained episode lasting ≥ 7 days) despite ≥2 previous PVI, with or without other atrial anatomical targets isolated in previous procedures (e.g. superior vena cava, coronary sinus or others). AF episodes refractory to ≥1 antiarrhythmic drug (flecainide, propofenone, amiodarone or droneradore) or adverse events related to antiarrhythmic drugs that do not allow long-term drug therapy. Age between 18-75 years old. Patients must be willing and able to comply with all peri-ablation and follow-up requirements. Signed informed consent. Confirmed pulmonary vein isolation in the index (in current protocol) procedure.  Exclusion Criteria:  Patients with paroxysmal AF (defined as a sustained episode lasting < 7 days). Patients for whom cardioversion or sinus rhythm will never be attempted/pursued. Patients with AF secondary to an obvious reversible cause. Patients with contraindications to systemic anticoagulation with heparin or coumadin or a direct thrombin inhibitor. Non-sustained AF during the mapping procedure. Severe underlying systemic disease (e.g. dementia, any end-disease stage, sepsis, etc). Severe left atrial dilation (left atrial volume >73 ml/m2). Severe underlying cardiac disease (e.g. left ventricular ejection fraction ≤35%, severe non-corrected valvular disease, severe non-corrected coronary artery disease, hypertrophic cardiomyopathy, other inherited arrhythmia syndromes, severe dilated cardiomyopathy with NYHA functional class III, IV). Hemodynamic instability due to any cardiac or non-cardiac disease. Pregnancy.