Patient Population: Patients with AF that is symptomatic and refractory to at least one antiarrhythmic medication. Patients must have AF that is paroxysmal (>4 episodes within 6 months, two episodes >6 hours within 1 year) or persistent (sustained episode <6 months terminated by cardioversion or drug).

Purpose: To compare a trigger-based technique (pulmonary vein isolation) to a substrate-based technique (high-frequency, fractionated EGMs) to a combined approach for AF ablation

Interventions: Patients will be randomized to either wide circumferential pulmonary vein isolation ("trigger") or ablation of high-frequency, fractionated electrograms during AF ("substrate"), or a hybrid approach combining trigger and substrate. Both techniques will be performed with NavX mapping system and a standardized ablation catheter. Endpoint of PVI will be isolation of all four PVs documented by circular catheter. Endpoint for substrate-based ablation will be termination and noninducibility of AF. Up to 2 procedures will be allowed within 6 months. A 2 month blanking period will be allowed after each procedure during which early recurrences will not be counted.

Outcomes:

• Recurrence of atrial fibrillation or other atrial tachycardia at 3, 6, and 12 months post-initial procedure.
• Recurrence will be defined by symptoms and/or ECG/Holter data showing AF > 2 mins
• Occurrence of adverse events in each group post-procedure.
• Quality of life assessment at 6 and 12 months post-initial procedure.

Followup:

• 3, 6, and 12 months post-initial procedure.
• Clinical data, ECG, Holter, loop recorder at baseline and at each visit.
• QOL at baseline, 3, 6 and 12 months post-initial procedure.

Inclusion Criteria:

• Patients age 18 or greater.
• "high burden" of paroxysmal atrial fibrillation or persistent atrial fibrillation
• candidates for AF ablation based on AF that is symptomatic and refractory to at least one antiarrhythmic medication.
• At least one episode of AF must have been documented by ECG or Holter within 12 months of randomization in the trial.
• continuous anticoagulation with warfarin (INR 2-3) for >4 weeks prior to the ablation.
• Patients must be able and willing to provide written informed consent to participate in the clinical trial.

Exclusion Criteria:

• chronic atrial fibrillation.
• Patients with AF felt to be secondary to an obvious reversible cause.
• inadequate anticoagulation as defined in the inclusion criteria.
• left atrial thrombus or spontaneous echo contrast on TEE prior to procedure.
• contraindications to systemic anticoagulation with heparin or coumadin.
• previously undergone atrial fibrillation ablation.
• left atrial size > 55 mm.
• Patients who are or may potentially be pregnant