Background
Peri-mitral flutter is a common cause of recurrent tachyarrhythmia following atrial fibrillation (AF) ablation, accounting for up to 60% of post-ablation atrial tachycardias (AT)1-5. As with other atypical atrial flutters, its pathogenesis is dependent on the presence of abnormal electrical substrate resulting in areas of slow conduction. Accordingly, while occasionally seen de novo in the ablation-naïve, the exponential rise in the incidence of peri-mitral flutter has paralleled the rapid increase in AF ablations being performed worldwide as well as techniques incorporating substrate modification beyond pulmonary vein isolation (PVI).6,7The incidence of left atrial flutter steadily increases from approximately 5% with PVI alone, to about 25% with the addition of linear lesions and ablation of complex electrograms, to up to 50% with the extensive stepwise approach to persistent AF ablation.4,8-11 In the context of frequent recurrence post cardioversion and generally inadequate control with anti-arrhythmic drugs, cardiac electrophysiologists are increasingly called upon to perform catheter ablation for post-procedural peri-mitral flutter. While successful in eliminating recurrent tachyarrhythmia in the majority of patients, achieving bidirectional block with catheter ablation is challenging due to complex anatomic relationships. The importance of attaining this endpoint has been previously highlighted by the significant incidence of recurrent atrial flutters when the mitral isthmus line is incomplete.12 Prior studies report the majority of re-entrant left ATs post AF ablation traverse prior ablation lines.13 The aim of this report is to review the anatomic considerations and approaches to catheter ablation for peri-mitral flutter.