Concealed WPW Syndrome with Longitudinal Dissociation in the His Bundle Exhibiting Five Different Electrocardiographic Waveforms During Tachycardia

We examined a patient with concealed WPW syndrome who exhibited five different electrocardiographic waveforms during tachycardia. With the intracardiac electrogram, all tachycardia were artrioventricular reciprocating tachycardia with retrograde conduction through only the accessory pathway where each artrioventricular conduction form varied: i.e., one with anterograde conduction through the fast pathway, one with anterograde conduction through the slow pathway, one with anterograde conduction through the fast pathway and slow pathway alternately, and an irregular R‐R interval, one with anterograde conduction through the fast pathway and wide QRS tachycardia with the right bundle branch block type, and one with anterograde conduction through the fast pathway and wide QRS tachycardia with left bundle branch block. His bundle electrogram might be split and H, H′ was recorded at the time of sinus rhythm. Furthermore, the right and left bundle branches exhibited a different refractory period because of longitudinal dissociation in the His bundle. Therefore wide QRS tachycardia with both right and left bundle branch block might appear without complete atrioventricular block. In addition to the association between fast pathway and slow pathway, right and left bundle branch block patterns appeared.