Inclusion criteria:

• Age ≥ 18 years old.
• Absence of a prior history of atrial fibrillation or flutter.
• Patients presenting for ablation of any ventricular tachycardia related to structural heart disease or any ventricular arrhythmia with a CHA2DS2-VASc score ≥ 2.

Exclusion criteria:

• Presence of thrombus in the left atrial appendage.
• Complications related to the index procedure.
• Insufficient quality of the left atrial electroanatomical map.

Left atrial electroanatomical mapping (substrate and functional mapping)

Substrate characterization will involve measuring Low Voltage (LV) and Transition Voltage (TV) Zones (LV zone voltage cut-off of <0.5mV; TV zone voltage limits within 0.5 and 1mV). These zones will be considered if they encompass an area of at least 1cm², containing ≥3 neighboring points within ≤10mm distance. The total LVZ and TVZ surfaces will be expressed as a percentage relative to the total surface area of the left atrium (excluding the pulmonary veins and the mitral annulus).

A comparative analysis of substrate characteristics will be conducted between two groups: the study group (comprising patients without atrial fibrillation but at risk of developing it) and the control group (a historical cohort of patients with known atrial fibrillation).

Functional analysis will rely on identifying deceleration zones characterized by isochronal crowding, defined as having ≥3 isochrones within a 1cm radius, using an 8-color scale of left atrial isochronal activation mapping.

A comparative analysis of functional characteristics will be conducted between two groups: the study group (comprising patients without atrial fibrillation but at risk of developing it) and the control group (a historical cohort of patients with known atrial fibrillation).

Episodes diagnosed via a single-lead ECG tracing or a complete 12-lead ECG lasting at least 30 seconds, or AHRE episodes detected by any cardiac implantable electronic device (CIED), lasting at least 5 minutes.