Treatment recommendations and guidelines for patients with atrial fibrillation (AF) are continuously changing. The role of catheter ablation in the treatment of AF increases and the techniques of the procedures are improving unceasingly. Responding to and evaluating the effect of these changes requires careful examination of this patient population and procedure outcomes. The aim is to create a clinical characterization platform for patients scheduled for AF ablations with the purpose to optimize health care processes and related translational research.

Study design: Prospective cohort study and research platform of patients referred for AF ablation. Clinical characteristics and results of routine tests and procedures before, during and after AF ablation are collected. In addition, the following (non-standard) tests are performed: extended surface electrocardiogram (extECG), extended rhythm monitoring, biomarker testing, genetic analysis, and questionnaires. In subgroups of patients transesophageal electrocardiogram (TE-ECG), epicardial electroanatomical mapping and/or left atrial appendage (LAA) biopsy is performed.

Inclusion Criteria:

• 18 years of age or older;
• Documented atrial fibrillation;
• Referred for any type of AF ablation: catheter ablation, stand-alone surgical AF ablation, surgical AF ablation concomitant with cardiac surgery, hybrid AF ablation, or redo AF ablation;
• Able and willing to provide written informed consent.

Exclusion Criteria:

• Conditions preventing the patient from adhering from the study protocol;
• Emergency procedures.

A subject who meets any of the following criteria will be excluded from the subset in whom additional consent for transesophageal ECG-imaging is asked:

• Severe allergic reaction against contrast agents used in the CT- or MRI-protocol
• Severe allergic reaction against body surface electrodes

A subject who meets any of the following criteria will be excluded from the subset in whom additional consent for transesophageal ECG (TE-ECG) is asked:

• Status after esophageal or gastric surgery

A subject who meets any of the following criteria will be excluded from the subset in whom additional consent for Cardiovascular Magnetic Resonance (ISOLATION CMR) is asked:

• Contraindication to MRI

A subject who meets any of the following criteria will be excluded from the subset in whom additional consent for concomitant hybrid ablation of atrial fibrillation (COMBAT-AF) is asked:

• Prior catheter or surgical AF ablation.

Specific exclusion criteria for epicardial mapping (only applicable for patients undergoing hybrid or surgical AF ablation):

• Chronic obstructive pulmonary disease (COPD) Gold 11, 111, or IV;
• Heart failure, currently in New York Heart Association (NYHA) class Ill or IV;
• Any other pulmonary, cardiac, or other condition that may compromise a safe conduct of epicardial mapping in the opinion of the treating physician or investigator, taking the prolonged duration of single lung ventilation into account.

Patients from two hospitals in the Netherlands with documented AF, referred for AF ablation.