Background: Atrial fibrillation (AF) is the most frequent cardiac arrhythmia and represents a high priority public health problem, as in a few decades it will become a possibly unsustainable load for the national health system. Preventive and therapeutic strategies based on the best possible scientific evidence are required. Ablation therapy, despite being the most effective approach, is associated with a 30-35% arrhythmic recurrence rate. An intervention with Mediterranean diet and extra virgin olive oil (EVOO) has proven effective in primary prevention and reduced the incidence of AF in high-risk subjects in a recent, large, randomized trial (PREDIMED).

Methods: Parallel, randomized, multicenter nutritional intervention trial in 640 patients with AF treated with catheter ablation. Two groups will be randomized in a 1:1 ratio: 1) intervention with Mediterranean diet and EVOO; 2) usual care (control group). The primary objective will be the incidence of atrial tachyarrhythmias for two years after ablation. At least 190 recurrences are expected after 2 years (median) of follow-up. A relative risk of 0.7 is assumed and statistical power of 80%. Follow-up visits will be scheduled at 3, 6, 12, 18 and 24 months. In addition to the in-person visits, event monitors will be used to document episodes. Dietary intervention will be carried out by nutritionists who will use methods adapted from the PREDIMED trial with contacts every 2 months. 1 liter of EVOO per week will be provided for free in the intervention arm. Inflammatory markers will be analyzed in both groups during follow-up. Cox models will be used to estimate adjusted hazard ratios.

Inclusion Criteria:

• Patients with symptomatic paroxysmal AF (with evidence of more than one symptomatic episode in the last year and at least one documented episode) upon whom catheter ablation is performed.
• Patients with persistent symptomatic AF upon whom catheter ablation is performed.

Exclusion Criteria:

• Serious medical condition that prevents dietary intervention (gastrointestinal disease with intolerance to fats, advanced malignancy, neurological, psychiatric or severe endocrine disease)
• Any other pathology or medical condition that limits survival to less than one year; Immunodeficiency or HIV-positive,
• Consumption of illegal drugs,
• Chronic alcoholism or total consumption of alcohol >80 g/d
• Body mass index > 40 kg/m 2,
• Difficulty or major inconvenience with changing dietary habits, inability to follow a style of Mediterranean diet, low probability of changing dietary habits according to the models of Prochaska and Diciemente (Nigg, 1999)
• History of food allergy or hypersensitivity to any component of EVOO
• Participation in a clinical trial carried out with drugs or use of a drug in experimental state during the year prior to inclusion
• Institutionalized patients for chronic treatment, with lack of autonomy and with inability to perform the clinical follow-up,
• Impossibility of telephone contact
• Patients with acute infection or inflammatory process (e.g. pneumonia) may be included in the study three months after the resolution of the infectious symptoms.