What kind of tachycardia might it be?

Do you remember our riddle: https://lnkd.in/eBRG8deV? Dr. Michal Marchel & Dr Michal Peller agreed to reveal the solution! 🙂

27-year-old male with a history of palpitations for the last 10 years. Finally, ECG during tachycardia was recorded (Fig 1). The patient was scheduled for EPS and ablation. Here you can find a few of his intracardiac recordings from EPS (Fig 2-4). What kind of tachycardia might it be?

Fig.1: Narrow QRS tachycardia, in aVF negative P waves hidden in QRS complexes (red arrows). RP<PR. Sinus beats, PVCs.

Fig.2: Programed pacing 100×8 + 340ms, extrastimuli conducted by slow pathway and nodal echo is present (red square). Double pathway physiology, stepdown conduction through the slow pathway, retrograde conduction through the fast pathway. 

Fig.3: Ventricle overdrive pacing (VOP). Pacing with CL 270ms during tachycardia (CL 290ms). Tachycardia not terminated by VOP makes analysis of V and A response possible. VAV response excludes AT (figures). Late atrial capture following “transition zone” makes AVRT uncommon (red square).

Fig. 4: Para-Hisian pacing. High output pacing makes His capture possible (narrow QRS). SA short (70ms) – retrograde conduction through physiologic pathways (His-AVN) (red line). Low output pacing and loss of His bundle capture when local ventricular myocardium is captured (wide QRS) results in longer SA (120ms) – conduction through physiologic pathways (ventricle myocardium-Purkinie-His-AVN) (blue line). This kind of response excludes presence of the para-Hisian accessory pathway.

Diagnosis: Typical slow-fast AVNRT. 

Treatment: In the EPS following slow pathway ablation in the postero-septal region no tachycardia was induced. No palpitation in 6-month follow-up were reported.