Assessing the impact of a new atrial fibrillation (AF) catheter ablation energy on left atrial structure and function is of crucial importance.

The goal of this clinical trial is to assess the effect of pulsed-field ablation of atrial fibrillation on left atrial structure.

Until recently, pulmonary vein ablation was performed using thermal energy; Pulmonary vein ablation (PVA) is the cornerstone of catheter ablation techniques for the treatment of atrial fibrillation (AF). In paroxysmal atrial fibrillation (PAF), PVI achieves a high rate of sustained freedom from AF recurrence, due to the predominant role of AF triggers, primarily represented by the pulmonary veins (PVs). Until recently, two main ablation energies were used to perform PVI: radiofrequency (RF) and cryoablation, both of which rely on thermal injury to the atrial cardiomyocytes surrounding the pulmonary vein ostia. Thermal lesions are associated with coagulative necrosis, oedema, and macro- and microvascular damage. Over time, thermal ablation lesions are replaced by interstitial fibrosis, a non-contractile and inflexible tissue. It has been demonstrated that extensive ablation lesions in the left atrium (LA) exacerbate atrial cardiomyopathy by impairing the LA's reservoir function, which can lead to stiff left atrium syndrome. Furthermore, thermal ablation lesions have been associated with an increased risk of stroke, particularly in patients with a low fibrosis burden in the LA.

Pulsed-field ablation of atrial fibrillation, including ablation of the posterior wall, is associated with the absence of left atrial fibrosis or fatty metaplasia, as well as the preservation of left atrial mechanics and blood flow.

Inclusion Criteria:

• Patient age ≥ 18
• Established diagnosis of persistent or paroxysmal atrial fibrillation with a I/IIa/IIb indication for catheter ablation (ESC 2020 guidelines)
• AF ablation procedure planned using pulsed-field ablation and including at least pulmonary vein isolation and posterior wall isolation
• Episode of AF documented by ECG within the last 12 months
• Patient able to give written informed consent
• If female of childbearing potential, have a negative serum pregnancy test and using effective contraception
• Be affiliated with a French social security system or entitled

Exclusion Criteria:

• Only pulmonary vein isolation is scheduled
• Atrial fibrillation present at ECG during the pre-ablation (V1a) visit
• Contraindication to oral anticoagulation
• Intracardiac thrombus
• Previous ablation in the left atrium
• Previous heart surgery
• Significant valvular heart disease defined as any moderate (grade 3) or severe (grade 4) mitral regurgitation, mitral stenosis, aortic regurgitation, aortic stenosis, tricuspid regurgitation, or tricuspid stenosis
• Contraindication to perform MRI or using the DOTAREM™ contrast product (pacemaker, defibrillator, foreign body or prosthesis, old generation heart valves, old generation ferromagnetic vascular surgical clips, percutaneous devices for endocranial aneurysms, neurosimulator, cochlear implants, automated injection device such as insulin pump, and more generally any non-removable electronic device, severe kidney disease with GFR < 30 mL/min, documented hypersensitivity to gadoteric acid or to excipients, severe claustrophobia)
• Patient on AME (state medical aid)
• Pregnant or breast-feeding female
• Patient protected by law (guardianship, tutelage measure, deprived of liberty)
• Participation in another interventional study or being in the exclusion period at the end of a previous study.