Obesity is a well-established risk factor for the development of atrial fibrillation (AF), while the reduction of body weight was shown to reduce the risk of AF. However, little is known about the effect of different weight-reducing interventions on AF burden. The study will evaluate the effect of a complex program aimed at weight reduction on AF burden in subjects after catheter ablation for AF and at least 1st degree obesity. This will be investigated in randomized study design and compared with patients receiving standard care without specific obesity-related intervention. The weight loss program will consist of diet, lifestyle and exercise counselling and, in selected subjects, also bariatric surgery in order to achieve a sustained weight loss of >10% of initial body weight. Secondary aims include identification of patient phenotypes with the most benefits from weight reduction as well as elucidation of potential pathomechanisms linking obesity and AF, with the main focus being on low-grade inflammation. The project will help to define the optimal weight-reducing regimen in AF and to tailor the interventions to individual patient needs.

Inclusion Criteria:

• Paroxysmal or persistent AF scheduled for primary RF ablation
• BMI ≥30 kg/m2
• Age 18-70 years
• Informed consent to the study

Exclusion Criteria:

• Previous ablation for AF
• Myocardial infarction, stroke or pulmonary embolism < 3 months prior to inclusion
• left ventricular ejection fraction < 40%
• Left atrium diameter > 55 mm
• Active thyroid disease
• Chronic kidney disease stage IV-V (eGFR < 0.5 ml/s)
• Chronic liver disease
• Active malignancy
• Inability to comply with study procedures