Timing of critical isthmus from end of P wave and usefulness of activation mapping with window of interest from end to end of P wave in reentrant atrial tachycardias

Introduction: In activation mapping of reentrant atrial tachycardia (AT), there was no reference for window of interest (WOI). We assumed that the critical isthmus will exhibit the slowest conduction velocity, and thus, may be located in an isoelectric line after prominent P wave . We examined the timing of a successful termination site from end of the P wave and attempted to determine whether the critical isthmus can be identified using activation mapping when WOI was set as end to end of the P wave. Methods: Forty patients with 54 reentrant ATs who underwent 3D electroanatomic mapping and radiofrequency catheter ablation were evaluated retrospectively. The critical isthmus was defined as a successful termination site. We evaluate critical isthmus timing from end of the P wave and ratio of critical isthmus timing from end of the P wave to tachycardia cycle length. Results: In 54 reentrant ATs, macroreentry was identified in 46 (85.2%) and microreentry was identified in eight (14.8%). The timing of the critical isthmus site from end of the P wave was -4.0 ± 31.1 msec (Macroreentry vs. Microreentry; -8.9 ± 29.4 msec vs. 24.0 ± 26.7 msec; P = 0.005). The ratio of critical isthmus timing from end of the P wave to tachycardia cycle length was -1.4 ± 10.5% (Macroreentry vs. Microreentry; -3.1 ± 9.8% vs. 8.3 ± 9.3%, P = 0.004) Conclusion: The critical isthmus of reentrant AT is located within 10% backward and forward from end of the P wave to tachycardia cycle length. Setting the WOI from end to end of the P wave is useful for identification of the critical isthmus through activation mapping in reentrant AT.