Intranodal Atrioventricular Nodal Reentrant Tachycardia Mimicking Junctional Tachycardia

Differentiating atrioventricular nodal reentrant tachycardia (AVNRT) from non-reentrant junctional tachycardia (JT) can be challenging.

In this case, regular narrow QRS complex tachycardia with simultaneous activation of the atrium and ventricle was reproducibly induced following an atrio-His interval jump by a single atrial extrastimulus, initially suggesting typical slow-fast AVNRT. During tachycardia, however, atrial activation and the His-atrial interval spontaneously changed without affecting the tachycardia cycle length. An "atrial-His-His-atrial" response to atrial overdrive pacing, late-coupled atrial premature depolarizations (APDs) that failed to reset tachycardia via slow pathway conduction, and early-coupled APDs that reset tachycardia via fast pathway conduction without terminating tachycardia, favored JT. Finally, slow pathway ablation rendered tachycardia non-inducible.

Intranodal AVNRT mimicking JT, which postulates an intranodal reentrant circuit with intervening conduction between the fast and slow pathways, can explain all of these findings and thus be differentiated from JT.