Supraventricular arrhythmia with discordant electrocardiographic features. What is the arrhythmia mechanism?

Junctional and AV nodal reentrant tachycardia share common electrocardiographic features, but they differ in their management and outcomes after catheter ablation. This case concerns a 60-year-old female who presented with recurrent episodes of a relatively slow, regular supraventricular arrhythmia. Electrocardiographic features of the arrhythmia were discordant regarding its underlying mechanism. However, careful analysis of 12-lead electrocardiograms, with focus on the effect of spontaneous premature beats, pointed out the arrhythmia etiology. Electrophysiological study and pacing maneuvers defined the arrhythmic substrate that was successfully treated by catheter ablation.