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.
ASJC Scopus subject areas
- Cardiology and Cardiovascular Medicine