Wagner_Marriot's Practical Electrocardiography, 12e

(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.

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).

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SECTION III: Abnormal Rhythms