The goal of this clinical trial is to compare two ablation techniques to treat patients with persistent atrial fibrillation (irregular and often very rapid heart rhythm). An ablation is a procedure during which some scars are made on the inside of the heart to break up the electrical signals that cause the irregular heartbeat. In this trial researchers will compare a new technique, which uses tiny electric shocks to make the scars, to the standard technique, which uses heat. The main question the trial aims to answer is: • Does the new technique work as well as the standard technique to prevent the irregular heartbeat from returning within one year of the procedure? Participants will: * Undergo an ablation with either the new or the standard technique * Visit the hospital 1, 3, 6, 9 and 12 months after the procedure for a check-up * Wear a device to register their heart rhythm for 24 hours before the 3 month visit and for 72 hours before the 6, 9 and 12 month visit * Record their heart rhythm at home every week * Complete a questionnaire 3, 6, 9 and 12 months after the procedure