CASE PRESENTATION
An 80‐year‐old man was referred to our facility for catheter ablation of an atrial tachycardia (AT) that developed after atrial fibrillation (AF) ablation. The previous procedure consisted of pulmonary vein isolation and cavotricuspid isthmus ablation. An AT with a tachycardia cycle length of 230 ms was detected on a baseline surface electrocardiogram (Fig. 1A). A decapolar catheter was positioned in the coronary sinus. The CARTO 3 system (Biosense-Webster, Inc., Diamond Bar CA) was used for electroanatomical mapping. Contact mapping was performed using a 20-pole high-density mapping catheter (PENTARAY; Biosense-Webster, Inc). The activation map suggested a dual-loop tachycardia mechanism; one circuit is a peri-mitral AT with a counterclockwise direction, and another is a roof-dependent AT around the left pulmonary veins (Fig. 1B and 1C). Since the lateral mitral isthmus was the common isthmus of the two circuits, we performed Et-VOM to create a block line on the lateral mitral isthmus. After occluding the vein of Marshall with an over-the-wire balloon catheter, 10 ml of 98% ethanol was injected in three divided doses. We did not observe the leakage of ethanol into the coronary sinus. During Et-VOM, the tachycardia cycle length was increased to 290 ms. After Et-VOM, the local staining was observed around the vein of Marshall (Fig. 2A). In the voltage map, an extensive endocardial scar was visible on the left atrial ridge and lateral mitral isthmus (Fig. 2B and 2C). Although the diaphragmatic motion was normal at baseline (Fig. 3A and 3B, and Supplementary Movie 1), the left phrenic nerve paralysis (PNP) was recognized after Et-VOM (Fig. 3C and 3D, and Supplementary Movie 2). A review of the fluoroscopic image revealed that the motion of the left diaphragm weakened immediately after the initial injection of ethanol. Seven minutes after the last ethanol injection, the left PNP gradually started to relieve. Adjunctive radiofrequency application to the lateral mitral isthmus terminated the AT, and the block line was finally created. At the end of the procedure, the left PNP was completely relieved, and no symptoms were observed after the procedure.