LETTER TO THE EDITORS Termination of the left atrial tachycardia by the ablation of epicardial critical isthmus visualized with a novel high- resolution mapping system Jedrzej Kosiuk 1 • Frank Lindemann 1 • Gehard Hindricks 1 • Andreas Bollmann 1 Received: 14 June 2016 / Accepted: 16 August 2016 Ó Springer-Verlag Berlin Heidelberg 2016 Sirs: A 71-year-old female patient with recurrent episodes of highly symptomatic persistent atrial fibrillation (AF) and organized atrial tachycardia (AT) was referred for the third catheter ablation. She previously underwent two left atrial ablation procedures consisting of pulmonary vein isolations and substrate modification [1]. The electrophysiological study was performed by means of a novel high-density mapping system (Rhythmia TM Boston Scientific) using mini-basket catheter (Intella Orion, Boston Scientific) as previously published [2, 3]. At the beginning of the procedure, the patient was in stable sinus rhythm and the previously isolated pulmonary veins did not show any signs of reconnection. However, the analysis of voltage map revealed extensive low-volt- age areas in roof and septal region. Initially, induced tachycardias were terminated by substrate-guided ablation in the roof and septal region (Fig. 1a). The ablation sights were identified with channel-based gap mapping, i.e., the detection of the conduction channel between two high- voltage regions by the gradual reduction of the voltage scale as previously described [4]. However, the third induced AT with CL of 300 ms could not be terminated by targeting previous ablation sites. A new high-resolution electroanatomic map with over 3000 mapping points was completed. It showed low-voltage area close to the basis of the left atrial appendage (Fig. 1b) which was isolated from surrounding vital tissue by the broad zone of scar regions. The potentials detected in this isolated low-volt- age region were in the range of 0.05–0.1 mV. Neverthe- less, the activation map showed the earliest activation site originating from the middle of the isolated low-voltage zone and then spreading simultaneously into three sepa- rate wavefronts implicating epicardial conduction (Fig. 1c, Movie 1). Initial ablation attempts in this region with a setting of 40 W failed to terminate tachycardia. However, by increasing the power to 45 W, it was pos- sible to alter the CL and activation sequence of tachy- cardia. Further increase of power to 50 W resulted in immediate termination of the AT, strongly suggesting a distant ablation target of an epicardial origin. No further arrhythmias were inducible [5]. Histological studies have described that the region between the left superior pulmonary vein and the appen- dage is characterized by a complex anatomy that includes the mesh of conducting epicardial fibers partially respon- sible for prevalent reconduction in this region [6]. In our case, we have presented that the high-density voltage analysis combined with activation pattern can be helpful to identify and treat tachycardias of epicardial origin. This technology might be particularly useful in the cases, where fast, detailed activation, and voltage maps are needed to better understand the mechanism of arrhythmias, as is the case of repeated left atrial procedures. In such clinical setting, the identification of epicardial focal sourced or critical isthmuses may lead to a significant improvement of outcome. J. Kosiuk and F. Lindemann contributed equally. Electronic supplementary material The online version of this article (doi:10.1007/s00392-016-1030-9) contains supplementary material, which is available to authorized users. & Jedrzej Kosiuk jedrzejkosiuk@hotmail.com 1 Department of Electrophysiology, Heart Center, Leipzig, Stru ¨mpellstr. 39, 04289 Leipzig, Germany 123 Clin Res Cardiol DOI 10.1007/s00392-016-1030-9