Case presentation
A 72-year-old female with frequent palpitation was referred for
radiofrequency ablation. The baseline 12-lead electrocardiogram and
echocardiography results were normal. At baseline, the atrio-His (AH)
and His-ventricular (HV) intervals were 90 and 41 ms, respectively. Dual
atrioventricular (AV) nodal physiology or ventriculoatrial (VA)
conduction was not observed during programmed atrial and ventricular
stimulation. After isoproterenol infusion, VA conduction became
decremental and concentric, with
the earliest atrial activation
seen at the His bundle (HB) region during ventricular pacing. A
supraventricular tachycardia with a long RP interval (SVT) was induced
by atrial extra-stimulation, without any jump-up in the AH interval.
During the SVT, the AH and HV intervals were 180 and 180 ms,
respectively, and the earliest atrial activation was recorded in the HB
region (Figure 1A). During the SVT, transient 2:1AV conduction was
observed (Figure 1B). Ventricular overdrive pacing at a pacing cycle
length (CL) of 360 ms was performed during the SVT with a CL of 390ms
(Figures 2A and B). Based on these observations, what is the mechanism
of this tachycardia?