Slow pathway modification for atrioventricular node re-entrant tachycardia: fast junctional tachycardia predicts adverse prognosis

Objective-To examine the cycle length of the junctional tachycardia often s een during successful slow pathway ablation for atrioventricular (AV) node re-entrant tachycardia, to determine whether shorter cycle lengths predict imminent atrioventricular block. Design-Retrospective analysis of consecutive patients undergoing slow pathw ay modification. Intracardiac recordings were analysed after digital storag e to determine the development of junctional tachycardia, its duration and maximum, minimum, and mean cycle length, occurrence of heart block, persist ent slow pathway conduction, or later confirmed recurrence of ATT node re-e ntrant tachycardia. Setting-Regional cardiac centre. Patients-136 consecutive patients undergoing electrophysiological study fou nd to have typical "slow-fast" AV node re-entrant tachycardia and subject t o 137 slow pathway modification procedures. Results-During successful temperature feedback controlled radiofrequency en ergy application, junctional tachycardia developed in 133 of 137 procedures . During ablation, 10 patients had evidence of AV block (first degree in se ven patients and third degree in three), and 17 others had retrograde junct ional atrial (JA) block. In these 27 patients, the junctional tachycardia w as rapid, with a minimum (SD) cycle length 291 (47) ms. Conduction recovere d quickly in all but two patients, one of whom required permanent pacing. J unctional tachycardia with normal AV and JA conduction in the: other 111 pa tients tvas of a significantly slower minimum cycle length (537 (123) ms; p < 0.0001). Conclusions-Fast junctional tachycardia with cycle lengths under 350 ms see n during slow pathway modification is a predictor of conduction block, sugg esting proximity to the compact node. Radiofrequency energy application sho uld be terminated immediately to prevent development of AV block. An "auto cut off' facility for cycle lengths shorter than 350 ms could be built into radiofrequency ablation systems to increase safety.