Atrial tachycardia after atrial fibrillation ablation: what is the mechanism?

A 58-year-old male was admitted for catheter ablation of recurrent atrial tachycardia (AT; Fig. 1A) following 4 previous paroxysmal atrial fibrillation (AF) ablation procedures at other centers involving pulmonary vein (PV) isolation and linear ablations, including cavotricuspid isthmus (CTI), left mitral isthmus, left atrial (LA) roof, and LA anterior line connecting mitral annulus with the roofline. Although the linear block across LA roof and CTI had been achieved, linear block across mitral isthmus and the anterior line had not been achieved. Baseline tachycardia cycle length (TCL)