Which structure delays conduction of the electrical impulse from the atria to the ventricles?

• A. Sinoatrial node
• B. Bundle of His
• C. Atrioventricular node
• D. Purkinje fibers

Answer: (C)

The delay in conduction between the atria and ventricles is produced by the atrioventricular node. After the atria fire, the impulse slows markedly as it passes through this node, allowing the atria to contract and fill the ventricles before they contract. This intentional pause helps coordinate the heartbeat and optimize ventricular filling. The sinoatrial node starts the impulse, but it’s the AV node that provides the critical pause; once the delay is over, the impulse travels rapidly through the bundle of His and Purkinje fibers to activate the ventricles. If the AV node’s conduction changes, the timing reflected on the ECG as the PR interval changes, illustrating its role in timing between atrial and ventricular activity.