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.