Posterior Mitral Isthmus Line With Vein of Marshall Ethanolisation Compared With Anterior Mitral Lines in Patients With Persistent Atrial Fibrillation

Inclusion Criteria: * Patients between the ages of 18 and 80 years, diagnosed with symptomatic persistent AF with clinical indication for left atrial ablation with a mitral isthmus line. Pulmonary vein will be isolated in all patients before starting the mitral isthmus line (during a previous or the same procedure) Exclusion Criteria: * Previous mitral line or any other left atrial ablation beyond pulmonary vein isolation * Left atrial (LA) thrombus. LA thrombus can be determined by preprocedural imaging: CT, transesophageal echocardiography or MRI. * LA diameter greater than 60 mm on long axis parasternal view, or left atrial volume more than 250 cc. * Left ventricular ejection fraction \<25%. * Cardiac surgery within the previous 90 days. * Expecting cardiac transplantation or other cardiac surgery within 180 days. * Percutaneous transluminal coronary angioplasty/stenting or myocardial infarction within the previous 30 days. * Documented history of a thromboembolic event within the previous 60 days. * Diagnosed atrial myxoma. * Significant restrictive, constrictive, or chronic obstructive pulmonary disease with chronic symptoms. * Significant congenital anomaly or medical problem that in the opinion of the investigator would preclude enrollment * Women who are pregnant or who plan to become pregnant during the study. * Acute illness or active infection at time of index procedure * Renal insufficiency * Unstable angina. * History of blood clotting or bleeding abnormalities. * Contraindication to anticoagulation. * Life expectancy less than 1 year. * Uncontrolled heart failure. * Presence of a condition that precludes vascular access. * International normalised ratio (INR) greater than 4 within 24 hours of procedure - for patients taking warfarin. * Unwilling or unable to provide informed consent.