Atrial fibrillation (AF) is the commonest condition affecting the rhythm of the heart. Tablets to try to normalise the heart rhythm rarely work well. As a result, doctors have devised a treatment called catheter ablation in which special wires are used to deliver heat energy (called ablation lesions) on the inside surface of the heart. Unfortunately, in many patients (almost 1 in 2), some of these ablation lesions recover, and this leads to AF recurrence. Many of these patients then need a second procedure to deliver further ablation at these recovered areas.

Recent research has shown that monitoring of heat delivery with a factor called Ablation Index may be useful in predicting which ablation lesions are less likely to recover. Therefore, we aim to carry out AF ablation guided with Ablation Index (AI) and observe whether this will be associated with better durability of ablation lesions, and thereby better freedom from AF.

This study will include patients with persistent AF, those whose AF episode(s) last for longer than seven days. All patients participating in the study will undergo an initial ablation treatment guided by ablation Index . All patients will undergo a repeat procedure 8-10 weeks after their initial treatment. Any gaps found during the second procedure will be closed again by delivery of ablation.

All participants will be issued with a simple to use handheld heart rhythm monitor, and asked to make a 30-second recording of their heart rhythm each day and also whenever they have symptoms. The monitor stores these recordings and they will be downloaded at review appointments arranged 6 weeks, 3 months, 6 months and 12 months after the initial ablation procedure.

The study is a prospective cohort study in 40 patients with Persistent AF. It will comprise two groups:

1. Active Group (AI guided ablation): An initial pulmonary vein isolation (PVI) procedure will be performed guided by AI targets. All patients (regardless of AF recurrence) will undergo a repeat EP study at 8-10 weeks to identify and re-ablate site(s) of PV reconnection
2. Historical control group (Contact Force Guided Ablation): will be formed by the 40 patients enrolled to the repeat study arm of the PRESSURE study (ClinicalTrials.gov Identifier: NCT01942408). All 40 patients underwent contact force-guided PVI followed by a repeat EP study after 8-10 weeks.

End-points

Primary outcome measure:

The proportion of patients with pulmonary vein (PV) reconnection seen at repeat EP study

Secondary outcome measures:

• The proportion of reconnected PVs seen at repeat electrophysiology (EP) study
• The proportion of patients maintaining freedom from atrial tachyarrhythmia for 12 months (after an initial 12 week blanking period)
• QOL 6 and 12 months after initial ablation, as quantified by the validated atrial Fibrillation Effect on QualiTy-of-life (AFEQT) and EQ-5D-5Lquestionnaires.
• Rates of major complications occurring within 60 days after a PVI procedure, measured in composite numbers and percentage.

Inclusion Criteria:

• Aged over 18 years
• Persistent AF (defined, according to the ESC/EHRA Guidelines for the Management of Atrial Fibrillation 2010, as AF episode that either lasts longer than 7 days or requires termination by cardioversion, either with drugs or by direct current cardioversion (DCC) ).
• Symptomatic in spite of drug treatment
• Due to undergo pulmonary vein isolation by RF ablation

Exclusion Criteria:

• Inability or unwillingness to receive oral anticoagulation with a Vitamin K antagonist (VKA) or non-VKA (NOAC) agent
• Previous catheter or surgical ablation procedure for AF
• Unwillingness or inability to complete the required follow-up arrangements
• Current pattern of paroxysmal AF
• Long standing persistent AF (continuous AF longer than 12 months before ablation)
• Prior prosthetic mitral valve replacement or severe structural cardiac abnormality
• Known infiltrative cardiomyopathy
• Known severe left ventricular systolic function (ejection fraction <35%)
• Pregnancy