Abstract
The features of the classic atrioventricular (A-V) nodal Wenckebach phenomenon are attributed to a conduction delay in the A-V nodal region. Changes in the P-R intervals merely represent the variations of the H-H intervals. The characteristic abnormalities of the latter consist of: (1) a gradual increase in P-H intervals; (2) a progressive decrease of the P-H increments; (3) a progressive diminution of the H-H intervals; (4) the long H-H interval produced by the nonconducted P wave is equal to the sum of the increments subtracted from twice the P-P intervals; and (5) the H-H interval after the intermission is longer than the H-H interval preceding the pause.
Tracings from 4 patients with atypical characteristics are presented. Case 1 showed an increase of the H-H intervals. In addition, the pause was terminated by an atrial echo. In Case 2 there was premature (retrograde) excitation of the His bundle. The last 2 patients had an A-V nodal Wenckebach phenomenon co-existing with a block below the His bundle (type II Mobitz block). In one, this double conduction disturbance occurred during forward propagation, whereas in the other it appeared during retrograde conduction.
