Atrial fibrillation (AF), often referred to as an 'irregular heartbeat', is the most common abnormal heart rhythm worldwide. AF may be intermittent (termed paroxysmal) or sustained (termed persistent).Catheter ablation is increasingly being used to manage individuals with AF, however in a significant proportion of cases AF recurs. Such rhythm control interventions are known to be less effective in individuals with persistent AF compared with those with paroxysmal AF. Analysis of heart tissue of individuals with AF show deposition of scar tissue within the heart muscle and this scar tissue promotes abnormal electrical activity that is involved in causing AF. The aim of the proposed study is to evaluate the feasibility and effectiveness of combining conventional pulmonary vein isolation (PVI) during catheter ablation for AF with adjunctive substrate ablation.

This is a single-centre, non-randomized study investigating the feasibility, safety and efficacy of substrate guided ablation in persistent AF.

The study population will be patients between the ages of 18 and 80 with symptomatic, persistent atrial fibrillation (≥1 year) referred for catheter ablation on standard clinical grounds.

The catheter ablation procedure will be performed using the Precision Ensite™ three dimensional mapping system and the Advisor High Density Grid™ mapping catheter (Abbott Medical Incorporated). All patients will undergo conventional pulmonary vein isolation (PVI). As an adjunctive strategy to PVI, low voltage areas (used as a surrogate for atrial scar), as derived from the voltage map, will be targeted for ablation in order to isolate or homogenise these areas of the atrium. A pre-procedural cardiac magnetic resonance imaging scan will be performed in all patients.

All patients will undergo 12 months follow-up with an ECG and ambulatory holter monitoring at 3, 6 and 12 months.

Inclusion Criteria:

• Patients aged ≥18 years and ≤ 80 with a clinical indication for persistent atrial fibrillation ablation

Exclusion Criteria:

• Contraindication to anticoagulation
• Thrombus in the left atrium despite anticoagulation
• Cerebrovascular accident within the previous 6 months
• Patients actively participating in another research study will be not be permitted to enrol. Patients who have been involved with other research studies will be able to participate after a minimum period of 3 months after completion of prior study follow up
• Females of childbearing potential must have a negative pregnancy test on the day of the ablation procedure due to the radiation exposure during the procedure

Participants will be recruited from patients with persistent atrial fibrillation who have been referred for catheter ablation based on standard clinical grounds.