Atrial pacing-induced alternating Wenckebach periodicity and multilevel conduction block in children.

Multilevel block within the atrioventricular (AV) node has not been previously described in children. Six children with atrial pacing-induced repetitive block are presented. The conduction patterns satisfy the requisites for alternating Wenckebach periodicity or multilevel AV block. In 2 patients the block is documented in the AV node and infra-His region. In 4 patients multilevel block within the AV node is postulated by deductive reasoning. In this study, 2 patterns of alternating Wenckebach periodicity are reported for the first time: sequences of 3:1 block with progressive prolongation of the conducted impulses terminating in 4:1 block; and sequences of 2:1 block with progressive prolongation of the conducted impulses terminating in 2 series of 3:1 block, in which the first conducted impulse following the first 2 blocked beats is not the shortest one, whereas that following the second 2 blocked beats is the shortest.