Cycle Length Alternans During Ablation of Cavotricuspid Isthmus-Dependent Atrial Flutter

A 55-year-old man was referred for ablation of symptomatic typical counterclockwise atrial flutter. Concealed entrainment from the cavotricuspid isthmus (CTI) and electroanatomic CARTO activation mapping confirmed the arrhythmia to be typical CTI-dependent atrial flutter. During radiofrequency ablation, a regular irregularity in the tachycardia cycle length (ie, cycle length alternans [250 and 210 milliseconds]), but with the same activation sequence in the right atrium, and fixed cycle length at 250 milliseconds in the left atrium were subsequently noted. This report addresses potential mechanisms and explanations for the cycle length alternans that may be observed during ablation of cavotricuspid isthmus-dependent atrial flutter.