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SECTION III: Abnormal Rhythms
Atrioventricular
(
AV
)
block
refers to an abnormality in electrical conduction between the
atria and ventricles. The term
heart block
has also been used to describe this abnormality.
Normal AV conduction was discussed in Chapter 3, and the parts of the cardiac pacemak-
ing and conduction system that electrically connect the atrial and ventricular myocardia
are illustrated in Figure 22.1. The term
degree
is used to indicate the severity of AV block.
This severity varies from minor (first degree), in which all impulses are conducted with
delay; through moderate (second degree), in which some impulses are not conducted; to
complete (third degree), in which no impulses are conducted. Any of these three levels of
severity of AV block can be caused by conduction abnormality in the AV node (level A in
Fig. 22.1), His bundle (level B in Fig. 22.1), or both the right bundle branch (RBB) and left
bundle branch (LBB) (level C in Fig. 22.1).
(A)
(B)
(C)
F I G U R E 2 2 . 1 .
Figure 6.1 is reproduced here to schematically illustrate the anatomic layers of
AV-junctional (AV node [
A
] and His bundle [
B
]
)
and ventricular (RBB and LBB [
C
]) structures poten-
tially capable of causing AV block. The numbers
1
,
2
, and
3
are anatomic structures in the ventricles
incapable of initiating a narrow ( 0.12 second) QRS complex.
