Biatrial flutter circuit involving an anomalous insertion of the Bachmann bundle into the superior vena cava

Key Teaching Points•Prior cardiac surgery or atrial fibrillation ablation can predispose patients to the development of atypical atrial flutter.•Although an eccentric coronary sinus activation pattern during atrial flutter suggests a left atrial circuit, entrainment from the right atrium should still be performed to exclude a biatrial flutter circuit.•Suspicion for biatrial flutter should be heightened in the setting of prior cardiac surgery or extensive ablation in the anteroseptal left atrium, as it can promote reentry over Bachmann bundle superiorly and the interatrial septum inferiorly.•We report a unique biatrial flutter that involves an anomalous insertion of Bachmann bundle into the superior vena cava, which was successfully ablated with superior vena cava isolation. •Prior cardiac surgery or atrial fibrillation ablation can predispose patients to the development of atypical atrial flutter.•Although an eccentric coronary sinus activation pattern during atrial flutter suggests a left atrial circuit, entrainment from the right atrium should still be performed to exclude a biatrial flutter circuit.•Suspicion for biatrial flutter should be heightened in the setting of prior cardiac surgery or extensive ablation in the anteroseptal left atrium, as it can promote reentry over Bachmann bundle superiorly and the interatrial septum inferiorly.•We report a unique biatrial flutter that involves an anomalous insertion of Bachmann bundle into the superior vena cava, which was successfully ablated with superior vena cava isolation.