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Address reprint requests and correspondence: Dr. Gregory M. Marcus, Division of Cardiology, Section of Electrophysiology, UCSF, 500 Parnassus, MUE 434, San Francisco, California 94143.
A 53-year-old man with palpitations, one episode of syncope, and ventricular preexcitation
on surface ECG presented for electrophysiologic study. Baseline sinus cycle length
was 1,010 ms, atrial-His (AH) interval 111 ms, and His-ventricular (HV) interval 28
ms. With delivery of atrial extrastimuli, a discrete “jump” in the AH interval was
observed (>50 ms with decrement of the extrastimulus by 10 ms), indicating dual node
physiology. However, neither echo beats nor supraventricular tachycardia based on
this mechanism alone was observed. A premature ventricular complex (PVC) initiated
an antidromic atrioventricular reciprocating tachycardia (AVRT) (Figure 1). What is the most likely mechanism of the initiation of this tachycardia?
Figure 1Induction of an antidromic atrioventricular reciprocating tachycardia with a premature
ventricular complex. CS p, CS d, CS 3-4, CS 5-6, and CS 7-8 = proximal, distal, bipole
3-4, bipole 5-6, and bipole 7-8 coronary sinus electrogram, respectively; HIS d and
HIS p = distal and proximal His-bundle electrogram, respectively; RVA p = proximal
right ventricular electrogram.
