• A block is referred to any disruption or delay in normal conduction.
• A block can occur in the:
SA node: sinus node dysfunction (sick sinus syndrome)
AV node: AV block
Bundle branch: bundle branch block (interventricular conduction delay)
Infra-His: alternating left and right bundle branch block at two separate time points
Left fascicle: fascicular block
Purkinje fiber: parietal block
Ventricular myocyte: intraventricular conduction delay (IVCD)
• SA and AV blocks are frequent causes of bradyarrhythmias.
• IVCD has widened QRS's without BBB morphology.
• Parietal block has QRS's in leads V1-3 more widened than in leads V4-6 (right ventricular parietal block, seen in ARVC) or vice versa (left ventricular parietal block).
