[Automatic activity of the pre-excitation pathways].

The possibility of preexcitation pathways exhibiting automatic activity was demonstrated in 3 cases: in two cases electrophysiological studies supported this diagnosis which was confirmed in the third case by histological examination of the preexcitation pathway. During sinus node dysfunction, spontaneous or induced (by rapid right atrial pacing or by a reciprocating tachycardia), the substitute rhythm arose from the Kent Bundle either transiently or for a longer period: rhythms arising from the Kent Bundle can only be diagnosed after eliminating the possibility of an atrioventricular junctional rhythm conducted to the ventricles by Mahaïm fibres.