1 │ CASE PRESENTATION
A 50-year old man with a structurally normal heart presented with
recurrent palpitations for six months. This was in spite of a recent
radiofrequency ablation at another center for a presumed diagnosis of
AVNRT. Interestingly, his first radiofrequency ablation for a
tachyarrhythmia was over a decade ago, but records were unavailable. The
12 lead Electrocardiogram (ECG) (Figure 1) revealed a short RP
tachycardia at rate of 170 bpm. There was no preexcitation during sinus
rhythm. Baseline intervals were normal during the ensuing
electrophysiology study (EPS). The catheter positions with the
annotations His (His bundle), CS (coronary sinus; proximal bipole 9-10
at CS ostium and distal bipole 1-2) and RV (right ventricle apex) are
self explanatory. A regular narrow complex tachycardia with rate related
right bundle branch block (CL 280-340 ms, shortest VA 90 ms, and AH 165
ms) was reproducibly induced with a single atrial extra stimulus test
(AEST) (Figure 2a). The response to maneuvers performed during
tachycardia are denoted: i.e. right ventricular overdrive pacing (VOP)
(Figure 2b), His refractory ventricular extra stimulus (HRVES) from the
RV (Figure 2c), as well the left ventricular (LV) apex via the
radiofrequency ablation catheter (RF 1-2, Figure 2d). What can be
deciphered as the mechanism of this tachycardia?