Blocks that occur within the sinoatrial node (SA node) are described as SA nodal blocks.
Blocks that occur within the atrioventricular node (AV node) are described as AV nodal blocks.
This is because if an individual had complete block at this level of the conduction system (which is uncommon), the secondary pacemaker of the heart would be at the AV node, which would fire at 40 to 60 beats a minute, which is enough to retain consciousness in the resting state.
When bundles are injured, as in a myocardial infarction, or because of underlying heart disease, a bundle or a branch of a bundle may cease normal function.
Right bundle branch blocks typically cause some prolongation of the last part of the QRS wave complex, and may cause the heart's electrical axis to be more rightward.
However, when bundle blocks are complex and diffuse in the bundle systems, or associated with additional and significant ventricular muscle damage, they may be a sign of serious underlying heart disease.
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