Background. Atrial fibrillation (AF) is a disorganised rhythm of the upper chambers of the heart. It can lead to severe complications including stroke or heart failure. It can be treated with radiofrequency ablation (RFA). This technology works by heating heart muscle inside the heart to break the electrical circuits responsible for the abnormal rhythm.

The energy is delivered into the heart with plastic tubes that have metal electrodes, inserted through the groin veins and removed after the procedure. The patient is usually put to sleep during the intervention.

If the AF has been present for more than seven days but for less than one year it is called persistent, and it can be difficult to treat successfully with the usual methods.

Goals. The study will test a new RFA technique to treat patients with persistent AF. This involves identifying areas within the left upper chamber that have a lower electrical voltage than the surrounding heart muscle and applying RFA to the border zones of these areas.

Methods. The new technology combined with the usual procedure will be compared to the usual procedure alone. All patients will receive ablation according to the new technique and results will be compared to a historical control group from the trial institution.

Follow up. Patients will be followed up for 12 months with clinic visits and heart rhythm checks.

Potential benefit. The new technique will be assessed for success at keeping patients free from persistent AF compared to the usual methods.

The study will be performed at Imperial College Healthcare NHS Trust, at the Hammersmith Hospital. Licensed clinical software will be used from St Jude Medical to guide ablation and a special research software module will be used to analyse data from the heart following ablation. The study will be sponsored by Imperial College Healthcare NHS Trust

Inclusion Criteria:

1. Suitable candidate for catheter mapping/ablation for arrhythmias.
2. Eighteen (18) to eighty-five (85) years of age
3. Body Mass Index (BMI) < 40 (Wt. in Kgs / Ht. in m2)
4. Signed Informed Consent

Exclusion Criteria:

1. Severe cerebrovascular disease
2. Moderate to severe renal impairment (eGFR < 30)
3. Active gastrointestinal bleeding
4. Active infection or fever
5. Short life expectancy
6. Significant anemia
7. Severe uncontrolled systemic hypertension
8. Severe electrolyte imbalance
9. Ejection fraction of < 35%
10. Congestive heart failure (NYHA Class IV)
11. Unstable angina requiring emergent PTCA (percutaneous transluminal coronary angioplasty) or CABG (coronary artery bypass graft)
12. Recent myocardial infarction
13. Bleeding or clotting disorders
14. Uncontrolled diabetes
15. Inability to receive IV or oral Anticoagulants
16. Unable to give informed consent (these patients would not be recruited)
17. Previous catheter or surgical ablation treatment for atrial fibrillation.
18. Paroxysmal atrial fibrillation.
19. Pregnancy (urinary pregnancy test will be offered on the day of the procedure for all women of reproductive age)
20. Drug and/or alcohol abuse
21. Transient factors for AF
22. Severe LA enlargement of >60 mm in diameter on echocardiography
23. Patients who have participated in another study of an investigational medicinal product in the last 3 months.