Abstract
An 83-year-old woman with a history of frequent paroxysmal supraventricular tachycardia underwent radiofrequency catheter ablation. Baseline electrophysiological study showed that the atrioventricular node had dual pathways and the earliest atrial activation during right ventricular pacing was located at the His-bundle（His）recording site with decremental property. Narrow QRS regular tachycardia at a cycle length（CL）of 470ms induced by atrial burst pacing was consistent with slow-fast atrioventricular nodal reentrant tachycardia（s/f AVNRT）. We ablated the slow pathway（SP）with the anatomical and electrogram-guided methods, but a tachycardiawith a similar intracardiac activation pattern to s/f AVNRT was still inducible by rapid atrial pacing during infusion of isoproterenol（ISP）with a dosage of 0.5µg/min. During the tachycardia, a premature atrial contraction（PAC）occurring when His was refractory advanced the following His, which indicated s/f AVNRT. On the other hand, an earlier PAC advanced the immediate His without termination of the tachycardia, which indicated junctional tachycardia. Although these were conflicting, the latter observation could be explained by double ventricular responses to a single PAC via the fast pathway and the SP. Therefore, further ablation for SP was continued until no tachycardia could be induced with ISP. The patient remained free from arrhythmic recurrence during the follow-up of 3 months.
