Atrioventricular accessory pathway with anterograde decremental conduction property.

We report a case of atrioventricular (AV) accessory pathway with anterograde decremental conduction property. The δ wave polarity suggested the presence of a right posteroseptal accessory AV pathway. During atrial pacing, Wenckebach-type AV block over the accessory pathway was observed with prolongation of the local AV conduction time without the change in QRS morphology. No retrograde ventriculoatrial conduction was observed. During mapping of the right midseptal area, mechanical conduction block at the level of the proximal input to the accessory pathway was induced repeatedly by catheter manipulation. Radiofrequency energy delivery eliminated the accessory pathway. In this case only the bump phenomenon was the best marker of successful ablation.