The aim of this observational, retrospective study is to evaluate, comparatively, procedural outcomes of APs (Accessory pathway) ablation according to the conduction properties (i.e., manifest vs. concealed) and to assess both short- and long-term outcomes of RFA (RF ablation).

Inclusion Criteria:

1. Patients who consecutively underwent an electrophysiological (EP) study between 2005 and 2023 at San Raffaele Scientific Institute are included if they met one of the following criteria:

   Patients referred for EP study due to:

   • EITHER clinical suspicion of paroxysmal supraventricular tachycardia without prior documentation of ventricular pre-excitation and/or supraventricular arrhythmia (SVA) on 12-lead surface electrocardiogram, OR with electrocardiographic evidence of SVA, AND electrophysiological confirmation of atrioventricular re-entrant tachycardia (AVRT) as the arrhythmic mechanism.
   • Ventricular pre-excitation documented on serial 12-lead surface ECGs, with or without clinical episodes suggestive of AVRT, who underwent catheter ablation of the accessory pathway based on:

   The presence of high-risk electrophysiological features (e.g., short antegrade effective refractory period of the AP, rapid conduction during atrial fibrillation), or Induction of sustained AVRT during the EP study.

2. Aged between 5 to 60 years old

Exclusion Criteria:

1. Lack of pre-specified follow-up: only patients with at least 1 years follow-up ambulatory visit will be included in the study
2. REDO CA procedure

Patients who consecutively underwent an electrophysiological (EP) study at San Raffaele Scientific Institute for EP study due to paroxysmal SVT with documented acessory pathway