Case presentation
A 72-year-old man without overt structural heart disease was referred to
our institution for catheter ablation of a narrow QRS tachycardia. A
12-lead electrocardiogram recorded during sinus rhythm showed no
ventricular preexcitation. Multielectrode catheters were placed in the
high right atrium, His bundle (HB) region, coronary sinus (CS), and
right ventricular (RV) apex. During sinus rhythm, the cycle length (CL),
atrio-His interval, and His-ventricular interval were 758, 102, and 52
ms, respectively. A narrow QRS complex tachycardia with a CL of 270 ms
was induced without atrio-His jump by atrial extrastimulation. The
intracardiac electrograms with RV overdrive pacing during the
tachycardia are shown in Figure 1A-B. What is the mechanism of this
tachycardia?