Supraventricular tachycardia with cycle length variation and apparent VA dissociation: what is the mechanism?

We report on a 33-year-old woman who underwent an electrophysiologic study because of a documented supraventricular tachycardia. The induced tachycardia presented with cycle length variations and an apparent ventriculo atrial (VA) dissociation on the surface ECG. Careful analysis of the activation sequence revealed the correct diagnosis of an atrioventricular nodal re-entrant tachycardia using two different slow pathways in an antergrade and retrograde directions. A 33-year-old woman was referred for an electrophysiologic study because of a documented supraventricular tachycardia. The patient suffered from paroxysmal tachycardias with a typical on/off-phenomenon for 2 years. Structural heart disease had been ruled out. Stimulation from the RV-apex showed retrograde conduction over the bundle of His without any evidence of an accessory pathway. Programmed atrial stimulation with one extra stimulus revealed a dual atrioventricular (AV) nodal physiology. Under isoprenaline, a supraventricular tachycardia was inducible. On the first glance, this tachycardia presented with VA dissociation on the surface ECG (Figure 1). Is that true? What is the correct diagnosis?