Demonstration of accessory pathway interaction by computerized mapping in preexcitation syndrome.

While interaction between the normal conduction system and an accessory pathway (AP) has been reported, interaction between two APs has not been well documented. With the assistance of computerized mapping techniques, we recently operated on a patient with two APs. One of these two APs had slow anterograde conduction velocity and was concealed during sinus rhythm and atrial pacing. Intraoperative computerized mapping studies revealed that the interaction between the APs was responsible for the anterograde conduction block of the slow AP during sinus rhythm and atrial pacing. This is the first direct demonstration of inhibition of conduction of one AP by the other AP in a patient with preexcitation syndrome.