LAUSR

A 55-year-old male was referred to our center for catheter ablation of recurrent episodes of atrial tachycardia (AT). He had congenital heart disease with persistent left superior vena cava, and interatrial septum defect that was corrected surgically. In the years following surgery, he underwent multiple catheter ablation procedures of AT at the cavotricuspid isthmus (CTI) and the lateral right atrium (RA). Successively, he underwent a single chamber atrial pacemaker implantation because of severe sinus dysfunction. The atrial leadwas implanted via the right subclavian vein, while a ventricular lead could not be inserted due to subocclusive stenosis of the RA–superior vena cava junction. Electrophysiological study was performed and multipolar diagnostic catheters were placed within the coronary sinus (CS) and around the tricuspid annulus (Orbiter catheter). Selective angiography revealed the presence of amega CS (MCS) that was also shown on 3D anatomical map using the CARTO system (Fig. 1A and B). Though the atrial lead looped widely inside the MCS (white arrows–Fig. 1A), it did not appear to be proarrhythmic under fluoroscopy check. AT with a median cycle length of 280 millisecond was reproducibly induced by programmed atrial stimulation. Intracardiac recordings showed counter-clockwise peritricuspid activation, while nearly simultaneous activation was observed through the CS (Fig. 1C). Entrainment maneuvers excluded the participation of the CTI or other parts of the RA in the AT circuit. High-density activation mapping using the PentaRay catheter (Biosense Webster, Inc, Diamond Bar, CA, USA) and CARTO system showed the presence of a small reentry circuit at the inferolateral portion of the posterior wall of the MCS. At this site, PentaRay recordings showed fragmented potentials scanning nearly the entire tachycardia cycle length (the gray window—Fig. 1C) within a very limited anatomical area (∼ 1 cm2) indicating the presence of a small “localized” reentry (Fig. 1D). Moreover, this area was also characterized by a very low bipolar voltage (< 0.1 mV) consistent with diseased or fibrotic myocardium (red zone—Fig. 1E). Irrigated radiofrequency application at this level terminated tachycardia and rendered it not inducible anymore. This case highlights the utility of high-density anatomical and activation mapping to define and successfully ablate the critical arrhythmic substrate, particularly when approaching complex and challenging anatomy.