Substrate

INCLUSION CRITERIA:

* male or female \>21 years
* reported incidence of at least two documented episodes of symptomatic paroxysmal atrial fibrillation (AF) during the three months preceding trial entry (at least 1 episode documented by 12-lead ECG or ECG rhythm strip)
* women without childbearing potential or women of childbearing potential who are not pregnant per a serum HCG test
* refractory to at least one Class I or III anti-arrhythmic medications. Drug doses must be therapeutic and stable
* willingness, ability and commitment to participate in baseline and follow-up evaluations without participation in another clinical trial (unless documented approval received from both sponsors)
* oral anticoagulation required for those subjects who have a score of two or more based on the following criteria (CHAD score):

* Congestive heart failure (1 point)
* hypertention (1 point)
* age 75 years or older (2 points)
* diabetes (1 point)
* prior stroke or transient ischemic attack (2 points)
* vascular disease (1 point)
* age 65 years or older (1 point)
* sex category: female (1 point)
* patient is willing and able to remain on anti-coagulation therapy for a minimum of 3 months post procedure for all subjects, and potentially indefinitely post procedure if the patient has CHAD score \>or=2
* signed informed consent after a full discussion of the risks and benefits of both therapy arms, and the concept of randomization
* NYHA Class 0,I, II stable on medical therapy for \> 3months
* left atrial diameter \* LVEF \>or=40%
* sustained AF during the procedure

EXCLUSION CRITERIA:

* atrial fibrillation from a reversible cause (e.g., surgery, hyperthyroidism, pericarditis)
* cardiac or thoracic surgery within the past 180 days
* AF secondary to electrolyte imbalance, thyroid disease
* contraindication to Heparin
* Contraindication to Warfarin or other novel oral anticoagulants
* history of significant bleeding abnormalities
* history of significant blood clotting abnormalities, systemic thrombi or systemic embolization
* ASD closure device, LAA closure device, prosthetic mitral or tricuspid valve
* atrial clot/thrombus on imaging such as on a trans-esophageal echocardiogram (TEE) within 72 hours of the procedure
* intramural thrombus or other cardiac mass that may adversely effect catheter introduction or manipulation
* significant pulmonary embolus within 6 months of enrollment
* acute illness or active systemic infection or sepsis that may ordinarily warrant postponement of the procedure
* history of recent cerebrovascular disease (stroke or TIA) or systemic thromboembolism within \< 6 months
* NYHA classes III, IV
* heart failure that is not stable on medical therapy
* pulmonary edema, that may make planned anesthesia or sedation difficult
* stable/unstable angina or ongoing myocardial ischemia
* myocardial infarction (MI) within the past three months
* structural heart disease of clinical significance including:

* congenital heart disease where the abnormality or its correction prohibit or increase the risk of ablation
* acquired heart disease that may increase risk of ablation, such as significant ventricular septal defect post myocardial infarction
* rheumatic valve disease, since this produces a unique AF phenotype
* extreme left atrial enlargement (LA volume index \> 60 ml/m2) in whom PVI has low success and 55 mm baskets are too small for the atria
* cardiac transplantation or other cardiac surgery planned within the 12 month followup period of the trial
* life expectancy less than 12 months (the followup period of the trial)
* significant pulmonary disease (e.g., COPD) or any other disease that significantly increase the risk to the patient from sedation or anesthesia
* untreatable allergy to contrast media
* at time of ablation procedure, clinically significant abnormalities in serum potassium, sodium, magnesium or other electrolytes that affect the suitability of the patient for ablation at that time