[Contribution of specific potential monitoring in the expression of accessory pathways].

The electrocardiographic expression of preexcitation results from the electrophysiological behaviour of the 2 conduction pathways: the normal pathway and the accessory pathway (AP). Its interpretation can only be deductive since the electrical activities of these 2 pathways are not recorded simultaneously. The validation of a K potential likely to represent Kent's bundle activation is based on criteria of exclusion of other origins (atrium, His bundle, ventricle). The K potential could be obtained in 16 of 32 consecutive studies. In 2 cases the unusual behaviour of the AP could be reliably studied owing to recording of the K potential. In case n. 1 a 35 ms increment in conduction was reproducibly observed by atrial extrastimulation at the atrium-Kent's bundle interface. In case n. 2 preexcitation was expressed on ECG only when the atrial rate was 70 to 100/mn. With lower atrial rates conduction in the AP was impaired by a 1st degree block with an atrium-Kent's bundle delay of 100 ms. Atrial acceleration reduced this delay to 40 ms, showing that this improvement in conduction reflected an initial block on the AP in phase IV. With higher atrial rates a block was observed on the AP in phase III either as an abrupt rupture of the atrium-Kent's bundle conduction, or as a block following progressive increment of the Luciani-Wenckebach type. Injection of ATP 20 mg produced and anterograde block on the AP at the atrium-Kent's bundle interface. Retrograde conduction seemed to be lacking in the AP since atrial activity was completely dissociated from induced ventriculograms.(ABSTRACT TRUNCATED AT 250 WORDS)