[Atrioventricular block at nodal and infrahissian level during atrial tachycardia. Apropos of a case].

The authors report the case of a patient with atrial tachycardia and surface electrocardiographic signs of left anterior hemiblock and complete right bundle branch block with 10/3 atrioventricular block. The regularity of the RR intervals which were an exact multiple of the atrial cycle suggested the absence of a Wenckebach phenomenon. The sequence of atrioventricular conduction cannot be explained by classical models of intranodal conduction. Endocavitary recordings confirmed this hypothesis. They showed block at 2 levels: supra- and infrahisian. The suprahisian block functioned in the 2/1 mode and the infrahisian block in the 5/3 mode without incremental conduction distal to the His potential before the apparition of block. A double zone of intrahisian block could explain the observed sequence of atrioventricular conduction. The absence of Wenckebach phenomenon on the surface ECG during tachycardia could be a sign of infrahisian block. The authors suggest that the association of this sequence of atrioventricular conduction with intraventricular conduction defects is a formal indication for electrophysiological studies.