Which statement about AV blocks is true?

• A. They can involve conduction tissue from the AV node through the bundle branches
• B. They never affect ventricular rate
• C. They always cause tachycardia
• D. They only occur in disease of the SA node

Answer: (A)

AV blocks arise from impaired conduction along the atrioventricular pathway, from the AV node down through the His-Purkinje system. Because the disturbance can occur at different points along this pathway, blocks can involve tissue from the AV node through the bundle branches. This explains why higher-grade blocks often slow the ventricular rate and may rely on a ventricular or junctional escape rhythm. They do not typically cause tachycardia, and they are not limited to disease of the SA node. So the true statement is that blocks can involve conduction tissue from the AV node through the bundle branches.