Which structure provides the main delay for atrioventricular conduction?

• A. SA Node
• B. Purkinje Network
• C. Bundle of His
• D. AV Node

Answer: (D)

Atrioventricular conduction delay is produced primarily by the AV node. The AV node slows the electrical impulse between the atria and ventricles, creating a pause that allows the atria to contract and finish pumping blood into the ventricles before they start to contract. This slow conduction is due to the AV node’s cellular and structural properties—smaller fibers, fewer gap junctions, and an intrinsic decremental conduction feature that slows impulse velocity as rate increases. The SA node acts as the pacemaker, while the Purkinje network and Bundle of His conduct impulses rapidly to the ventricles to ensure coordinated, synchronized contraction, so they do not provide the main delay. That combination makes the AV node the key site of the atrioventricular conduction delay.