Taking the slower pathway.

Abstract

In this segment of the Teaching Rounds in Electrophysiology, Chen et al1 provide an instructive discussion taking us through one of the most difficult diagnostic differentiations in cardiac electrophysiology—AV nodal re-entry tachycardia (AVNRT) versus junctional tachycardia.2,3 Often the highest educational value in the electrophysiology laboratory when teaching a rule is to recognize and analyze an exception. Chen et al1 induced a slower tachycardia with similar activation sequence as an originally induced AVNRT. After slow pathway ablation and the use of isoproterenol, they had to determine whether further ablation is necessary or could potentially be harmful (slower AVNRT versus junctional tachycardia), importantly they found an exceptional response to premature atrial contractions (PACs) that span the cycle length of the arrhythmia and, with their careful analysis and stepwise logical interpretation of the data, concluded correctly that further slow pathway ablation will eliminate the arrhythmia. See Article p 232 The slow pathway is usually anatomically defined as the myocardium anterior toward the ventricle to the Eustachian ridge and tendon of Todaro, behind the tricuspid annulus septally, and just cranial to the coronary sinus ostium.4 Although exceptions exist for any diagnostic maneuver in the electrophysiology laboratory, maneuvers related to the AV nodal slow pathway can be particularly difficult because there may be anatomic variants and decrement conduction delay within the circuit. Understanding common causes of difficulty with analyzing the results of maneuvers performed and appreciating the diagnostic effect of success and failure with anatomic slow pathway ablation can be important. ### Cycle Length Variation Cycle length stability before initiating a maneuver such as introduction premature atrial beats to perturb the circuit is a paramount for accurate diagnostic interpretation. Occasionally, even if the cycle length varies, the maneuver can be executed, as long as the variation is occurring in a predictable manner. For …