Single-loop incisional atrial tachycardia encircling the entire right atrium: Where is the critical isthmus?

Figure 1. Fluoroscopic image and intracardiac electrograms. A,B: Fluoroscopic image showing the position of electrode catheters around the tricuspid valve and intracardiac electrograms during the cavotricuspid isthmus (CTI) ablation. AT1 was a common atrial flutter (A, white arrow), and CTI linear ablation was performed after pulmonary vein isolation, resulting in a shift from AT1 to AT2 (A, yellow arrow). Then, entrainment pacing from the anterior lateral (denoted by ①), lateral (②), superior posterior (③), inferior posterior (④), and anterior (⑤) regions of the right atrium revealed that the postpacing interval was almost equal to the tachycardia cycle length. In addition, the activation sequences of the catheter electrodes during pacing and the tachycardia were the same. Those findings indicated that there was an orthodromic capture of the placed catheter electrodes by the entrainment pacing. C: Examples of intracardiac electrograms during entrainment at sites ①, ②, and ③. II and V3 represent the surface electrocardiogram leads; HALO 1-2 to 9-10 represent the distal-to-proximal recordings of the Halo catheter positioned around the tricuspid annulus; CS 1-2 to 7-8 represent the…

Figure 2. CARTO (Biosense Webster, Diamond Bar, CA) images describing the atrial tachycardia (AT2) circuit. Three-dimensional images of the right atrium constructed using ripple mapping during AT2 are described (see Supplementary Video). The bipolar voltage threshold to identify low-voltage areas was set to 0.2–0.5 mV. The surface color projection and points were collected aiming for a complete right atrial coverage (ie, with no areas >5 mm from a data point), and the number of points collected for this map was 3892. The white arrows indicate the direction of the wavefront propagation. The results of the entrainment at each point (yellow arrow) are shown. The postpacing interval (PPI) was approximately equal to the tachycardia cycle length (TCL), and entrainment with concealed fusion was observed at multiple locations within the right atrium (denoted by ①–⑤); thus, estimating the circuit using a conventional entrainment maneuver is challenging. The light blue tag points indicate double potentials associated with the right lateral incision. AP = anteroposterior; LAO = left anterior oblique; LPO = left posterior oblique; PA = posteroanterior; RAO = right anterior oblique; RPO = right…

Figure 3. Method to identifying the slow conduction area. Coherent mapping with conduction velocity (CV) vectors during atrial tachycardia (AT2) are described. CV thresholds of 10, 20, and 30 mean that the slowest 10%, 20%, and 30% of the vectors are highlighted by thicker vectors, respectively. By gradually increasing the CV threshold, the areas where CV slows relative to the entire map are visualized (red circle). The area that is highlighted first across the circuit is a potential deceleration zone with a calculated conduction velocity of 0.37 m/s. Linear ablation across this area successfully terminated AT2. RAO = right anterior oblique.