A Case of WPW Syndrome Exhibiting a Retrograde Accessory Pathway with Decremental Conduction Property after Ablation of an Anterograde Conduction over the Same Accessory Pathway

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A surface electrocardiogram of a sixty-year old woman showed typical delta waves of type-A at a sinus rhythm, and a narrow QRS duration during tachycardia at a rate of 150. Electrophysiologic studies were performed. Right ventricular apical pacing showed a ventriculoatrial (VA) conduction with the shortest interval of 37 msec recorded at coronary sinus of lateral side of mitral annulus. This VA conduction had no decremental property, and the retrograde atrial activation sequence was the same as that during atrioventricular tachycardia. Via a transaortic approach, an anterograde accessory pathway located at the left lateral side of mitral annulus was ablated at a sinus rhythm, when delta waves on electrocardiogram disappeared. However, a narrow QRS tachycardia with longer VA conduction interval but with the same atrial activation sequence as clinical tachycardia was induced. Right ventricular pacing at a sinus rhythm showed the same atrial activation sequence as seen in the tachycardia. This VA conduction interval was elongated by 50 msec compared with that recorded before anterograde accessory pathway ablation. The VA conduction was blocked with a 10-mg infusion of adenosine and furthermore, showed decremental property by ventricular extra stimuli. Finally, this retrograde conduction pathway was ablated at a similar lateral side of the mitral annulus.