Atrial Tachycardia Utilizing Bachmann's Bundle as an Epicardial Bypass: A Case Suggestive of a Dual-Loop Mechanism.

A 70-year-old man with a history of prior ablation for atrial fibrillation presented with atrial tachycardia (AT). Electrophysiological studies revealed roof-dependent and localized-reentrant ATs. During each AT, widespread breakthrough activation was observed just anterior to the low-voltage area on the anterior wall, suggesting that Bachmann's bundle served as an epicardial bypass within the tachycardia circuits. This case highlights the potential role of Bachmann's bundle in the development of ATs in the remodeled left atrium.