Figure 206-8
His bundle (HB) electrograms in atrioventricular
(AV) block. The tracings are from three different patients with second-degree
AV block. In A and B, the conducted QRS complexes are wide and associated
with bundle branch block.
In A, the block is within the AV node (i.e., the A wave on the HB is
not followed by an HB deflection).
In B, it can be appreciated that the block is distal to the HB even
though the surface electrocardiogram (ECG) demonstrates a Wenckebach
phenomenon. The latter can obviously occur in the His-Purkinje system
as well, as depicted in this figure.
C. The Site of the block is within the HB. This is suggested by split
HB potentials (labeled H and H'), and the block is distal to the H but
proximal to the H'. Intra-His block is difficult to diagnose from the
surface ECG but can be suspected when a Mobitz type II occurs in association
with a normal PR interval and a narrow QRS complex.
(From Akhtar.Reproduced with permission
from the publisher and author.)