Concealed and supernormal atrioventricular conduction.

THE FAILURE of a cardiac impulse to traverse the entire atrioventricular (AV) conducting system is called concealed conduction. Electrocardiographically, the effects of concealed conduction are reflected in the conduction and/or formation of subsequent beats.1 The concept of concealed conduction can be applied to explain (1) post-extrasystolic prolongation of the P-R interval, (2) the irregularity of the ventricular response during atrial fibrillation, (3) the slower ventricular response during atrial fibrillation as compared to atrial flutter in the same patient, and (4) alternation of the P-R interval, etc. The recording of His bundle electrograms has permitted us to localize more precisely the area within the A-V conduction system where the impulse is blocked and also the area where conduction of subsequent beats is prolonged.2 By means of His bundle electrogram recordings, the P-R interval can be divided into the A-H (atrium-to-His bundle) interval which is a measure of A-V nodal conduction time, and the H-V (His bundle-toventricle) interval which is a measure of conduction along the His-Purkinje system.