Conventional electrode catheter placement can miss crucial atypical atrioventricular nodal reentrant tachycardia circuit details. -New insights into the retrograde slow pathways-

Background During atypical atrioventricular nodal reentrant tachycardia (AVNRT), the earliest atrial activation site following retrograde slow pathway (SP) conduction is at the atrial exit of the left inferior extension of the compact node (LIE) in the coronary sinus (CS) or the right inferior extension (RIE) on the tricuspid annulus (TA). We tested the validity of conventional electrode placement-based mapping of the atrial ends of these extensions. Methods We retrospectively evaluated the efficiency of the two catheter (His bundle and CS) mapping method for localization of LIE and RIE in atypical AVNRT patient using electroanatomical 3D mapping validation. Results Among 19 atypical AVNRTs (15 fast/slow and 4 slow/slow) in 14 patients (9 females, age 59±17), 8 AVNRTs had LIE involvement and 11 had RIE. The 8 LIE exits were inside the CS, and localization by 3D mapping and CS electrode catheter matched in all. In contrast, RIE exits were on the posterior TA where electrode catheters are conventionally not placed. All RIE exits required 3D mapping for accurate localization. During retrograde RIE conduction, comparison of the activation time of the CS ostium and HBE showed that the CS ostium was earlier in 7 RIEs, HBE was earlier in 1, and they were simultaneous in 3, resulting in the presence of RIE being missed in 4/11 (36%) AVNRTs using current diagnostic criteria. Activation time of the CS ostium and His bundle were determined by their relative closeness to the RIE exit. Conclusions Conventionally placed electrode catheter mapping in atypical AVNRT was able to identify 100% of LIE, but only 64% of RIE. It is critical to place a catheter on or use a 3D mapping system for the posterior TA in cases of suspected atypical AVNRT, so that all inferior extensions of the AV node can be identified and targeted for treatment.