Background: The surface electrocardiogram (ECG) remains the cornerstone for localizing accessory pathways (APs) in WolffParkinson-White (WPW) syndrome prior to catheter ablation. The "reverse break" (or double transition) pattern in the precordial leads is a uniquely rare and highly specific finding for posteroseptal pathways.
Case Presentation: A 60-year-old female with no prior medical history presented with recurrent palpitations. Her baseline 12-lead ECG exhibited normal sinus rhythm with overt pre-excitation. Notably, the precordial leads demonstrated a distinct reverse break sign: a negative delta wave in V1, an abruptly prominent positive delta wave in V2, and a return to a negative delta wave in V3. Echocardiographic evaluation was unremarkable. Based on this specific ECG morphology, a right posteroseptal AP was suspected. An electrophysiological study utilizing 3D electroanatomical mapping (EnSite™ Precision) confirmed the earliest pre-excited ventricular activation at the right inferoposterobasal (posteroseptal) region. Subsequent targeted radiofrequency ablation was successful; the post-ablation ECG showed normal sinus rhythm and the complete disappearance of delta waves.
Conclusion: The reverse break pattern is a reliable and easily identifiable surface ECG signature that strongly predicts a right posteroseptal AP. Early recognition of this morphological shift significantly aids electrophysiologists in pre-procedural planning and improves ablation efficiency in anatomically complex regions.