Inclusion Criteria:  Scheduled to undergo elective catheter ablation of AF History of persistent or longstanding persistent AF (see definitions below) Able to provide written informed consent prior to the procedure Age ≥18 years  Exclusion Criteria:  Ineligible to undergo elective atrial fibrillation ablation procedure due to medical illness or poor medical condition Presence of a permanent endocardial pacemaker or ICD (implantable cardioverter defibrillator) Presence of a prosthetic mitral heart valve Known reversible causes of AF including clinical hyperthyroidism, pericarditis/pleuritis or other active systemic inflammatory disease including post pericardiotomy syndrome, systemic lupus erythematosus, sarcoidosis and rheumatoid arthritis Decompensated clinical heart failure (NYHA class 4) Any cerebral ischemic event (strokes or transient ischemic attacks) which occurred during the 6-month interval preceding the consent date History of systemic thromboembolic event defined as clinical and arteriographic evidence of thromboembolism to any distal arterial vascular bed within the past 6 months, or evidence of intracardiac thrombus at the time of the procedure Pregnancy (pre-procedure pregnancy serum test will be performed in all premenopausal women) Unable to provide own informed consent due to cognitive impairment