Tachycardia cycle length alternans caused by alternate conduction velocity on the slow conduction zone in a postoperative scar-related atrial tachycardia.

The underlying mechanism for stable beat-to-beat cycle length variability (CL alternans) in scar-related atrial tachycardia (AT) had not been elucidated clearly. We described a case with postoperative dual-loop reentrant AT in right atrium. When the loop depended on cavo-tricuspid isthmus was blocked by ablation, the AT transformed into a CL alternate tachycardia. High density and resolution mapping revealed that the CL alternans was caused by the alternate conduction velocities at the slow conduct region. A further ablation line was created from the slow conduction zone to the inferior vena cave, and afterward no AT was inducible.