Study of retrograde conduction in complete heart block using His bundle recordings.

Two patients with complete anterograde A V block without retrograde P' waves are described in whom regular retrograde conduction across the blocked area was shown by recording the His bundle electrogram. When an atrial depolarization (A) occurred after the QRS complex within a certain period, A was followed either by no H potential or by a prolonged AH interval, indicating concealed retrograde penetration of the His bundle. Thefact that retrograde conductionaffectedanterograde conduction indicates that the anterograde and retrograde pathways are not totally independent. Atropine significantly improved retrograde conduction; this suggests that the retrograde conduction occurs through the conduction system in a retrograde fashion rather than through a muscular pathway, bypassing a blocked area of the conduction system, as the latter should not be affected by atropine.