[Unusual supraventricular tachycardias in Wolff-Parkinson-White syndrome].

Two unusual types of narrow-QRS tachycardias were initiated during electrophysiological investigation of a patient with the Wolff-Parkinson-White syndrome. In the first type, the QRS complexes were preceded by atrial activation, the chronological sequence of depolarisation of which was similar to the sinus rhythm, suggesting the mechanism of sino-atrial reentry. The narrow QRS complex during tachycardia was related to the fact that the refractory period of the accessory pathway was longer than the tachycardia cycle. The second type of tachycardia was associated with I/I retrograde atrial activation within the QRS complex, suggesting the mechanism of intranodal reentry. The main point of interest of this case is that the accessory pathway, which only conducted in the anterograde direction, did not participate in the mechanism of either of these tachycardias.