High right atrial pacing (abrupt initiation and random coupling to the spontaneous rhythm) was performed in 285 pediatric cardiac patients for diagnostic purposes. Nine patients (3%) were found to have pacing-induced infra-His conduction block. In two patients this occurred following a preceding long cycle as well as a preceding short-to-long sequence cycle length change. In five patients block occurred with an abrupt shortening of the coupling H-H interval (in three patients the infra-His block initiated a series of 2:1 infra-His block). In two patients with type II second-degree atrioventricular block the initiating events were not recorded. In one of them, when the rapid atrial pacing was incremented to the same cycle length with infra-His block, the atrioventricular response became 1:1 with normal conduction. These findings of pacing-induced infra-His conduction block can be explained by the normal response of the His-Purkinje system to changes in the preceding cycle lengths, and to the abrupt shortening of the coupling interval.
ASJC Scopus subject areas
- Cardiology and Cardiovascular Medicine