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Dual‐Loop Bi‐Atrial Macroreentrant Atrial Tachycardia in a Patient With Modified Cox Maze IV: Where Is the Initial Ablation Target?

A 75-year-old man with atrial fibrillation, who underwent valve (mitral and tricuspid) plasty with a modified Cox-Maze IV, was referred for the ablation of atrial tachycardia (AT). At the beginning of the procedure, the baseline tachycardia cycle length (TCL) was 300 milliseconds. No pulmonary vein potentials were recorded, and a 3-dimensional (3D) activation map (CARTO, Biosense Webster Inc., Diamond Bar, CA, USA) showed a clockwise peri-mitral atrial tachycardia (PMAT) pattern (Fig. 1). With the entrainment pacing from the multiple sites at the left atrium (LA) in the 7–2 o’clock direction of the mitral annulus (MA), a postpacing interval (PPI)–TCL was 20 milliseconds (Fig. 1). The PPI–TCL at the multiple sites of the coronary sinus (CS) opposite of LA 3–6 o’clock direction of MA was 20 milliseconds, although the PPI–TCL at the LA 3–6 o’clock direction of MA was >20 milliseconds. Interestingly, the PPI–TCL at both the CS ostium and the right atrial septum was 20 milliseconds. Furthermore, the RA activation map showed that the counter-clockwise cavotricuspid isthmus (CTI) dependent AT although the PPI–TCL at the CTI was >20 milliseconds (Fig. 1). Based upon these observations, where is the initial ablation target?