Atrioventricular block pathophysiology

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Edzel Lorraine Co, DMD, MD [2]

Overview

Atrioventricular (AV) block is caused by one of the following mechanisms i.e. fibrosis or degeneration of the conduction system, ischemic heart disease, or medications.

First-degree atrioventricular block
- A delay in electrical heart conduction without significant interruption occurs from atria to ventricle.
- This occurs at the level of atrioventricular node (AV node) or slightly below it.
- In this situation, no hemodynamic instability happens.
Second-degree atrioventricular block Mobitz type 1 (Wenckebach)
- A block in the normal electrical conduction system occurs at the crest of AV node]as a result of failure of AV nodal cells to transmit the cardiac impulse to the ventricles.
- This is related to a progressive fatigue of the cells and result is manifested as a dropped beat.
Second-degree atrioventricular block Mobitz type 2
- The electrical conduction system blockage occurs at the level below the AV node (His bundle, bundle branches, and heart fascicles.
Third-degree atrioventricular block
- There are two possible locations in this block with impulse conduction depending on the location of the block.
- A narrow QRS complex with AV node intrinsic rate of 40 to 55 beats per minute is observed when the block is at the crest of AV node or above it.
- A wide QRS complex with a ventricular pacemaker intrinsic rate of 20 to 40 beats per minute is observed when the block is below the AV node.^[1]