Case report: Slow conducting accessory pathway in an Ebstein's anomaly patient: Is this a Mahaim fiber?

We report a case of multiple accessory pathways (APs) in an Ebstein's anomaly patient with a history of prior ablation. Electrophysiological study demonstrated a slow conducting AP which pre-excited ventricle only during atrial tachycardia or rapid atrial pacing. The non-decremental property and a longstanding fragment potential at the ablation target site rule out Mahaim fiber. The slow conducting AP might be caused by inadequate prior ablation, and highlights that delta wave absent and prolonged AV interval in target point could not definitely indicate anterograde conduction block when we ablate a manifest AP. Rapid atrial pacing may unveil the slow conducting AP.