Change of Peri-mitral Atrial Flutter into Single-loop Biatrial Flutter During Ablation

Anterior line ablation for peri-mitral atrial flutter (AFL) is associated with biatrial flutter due to disruption of the electrical conduction in the left atrial septum. An AFL case with valvular disease, cardiac surgery, and prior ablation was confirmed to be counterclockwise peri-mitral flutter with isthmus on the left atrial septum. Ablation on the septum of the left atrium (LA) targeting the isthmus prolonged the tachycardia cycle length (TCL) from 266 to 286 ms. Left atrial mapping during AFL with a TCL of 286 ms showed that the activation remained peri-mitral counterclockwise, but there was interruption of the local activation time (LAT) sequence. Combined mapping of the LA and the right atrium (RA) showed a counterclockwise single-loop biatrial flutter, involving the whole LA and the RA septum, with Bachmann’s bundle and the posteroinferior septum being the interatrial connections. The AFL was terminated by ablation at the right superior cavoatrial junction. RA mapping should be considered if there is prolongation of TCL but without termination of the peri-mitral AFL, and if there is interruption of the continuity of the LAT sequence during AFL with a longer TCL. The biatrial flutter can be terminated by ablation targeting the interatrial connections.