LONGITUDINAL DISSOCIATION IN THE HIS-BUNDLE - A POSSIBLE MECHANISM OF2 DISTINCT CYCLE LENGTHS IN ATRIOVENTRICULAR REENTRANT TACHYCARDIA

Two wide QRS tachycardias with identical morphology but different cycl e lengths (CLs) developed in a 63-year-old man. Electrophysiological s tudy demonstrated inducible atrioventricular reentrant tachycardia (AV RT) due to a concealed left posterior accessory pathway (AP), which wa s successfully ablated by radiofrequency application. Neither dual AV nodal pathways nor other APs were documented Splitting of the His-bund le electrogram was shown, and programmed stimulation induced sudden pr olongation of intra-hisian conduction time. These results suggest long itudinal dissociation in the His bundle may be responsible for two dis tinct CLs in AVRT without dual AV nodal physiology.