Abstract
A 74-year-old woman underwent diagnostic electrophysiologic study because of recurrent, symptomatic supraventricular tachycardia. Baseline atrio-His and His-ventricular intervals measured 75 ms and 50 ms, respectively. Programmed atrial extrastimulation elicited dual atrioventricular (AV) nodal physiology and ventricular pacing showed no ventriculoatrial conduction despite isoproterenol. Figure 1 shows her clinical tachycardia. The response of tachycardia to a His-refractory ventricular premature depolarization (VPD) is shown in the top section of Figure 2, while its induction twice by rapid ventricular pacing (340 ms) is shown in the middle and bottom sections of Figure 2. Based on these observations, what is the mechanism of tachycardia? Figure 2Top: Response of tachycardia to a His-refractory ventricular premature depolarization. Middle, Bottom: Induction of tachycardia by rapid ventricular pacing (340 ms). View Large Image Figure Viewer Download Hi-res image
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