Where does impulse delay occur before proceeding to the ventricles, as reflected in the ECG?

The correct answer is the AV Node, which plays a critical role in the electrical conduction system of the heart. This node is located between the atria and the ventricles. Its primary function is to receive impulses from the atria and delay their transmission to the ventricles, allowing sufficient time for the atria to contract and fill the ventricles with blood before they themselves contract.

This delay is reflected on the ECG as the PR interval, which is the period between the onset of atrial depolarization and the onset of ventricular depolarization. If there were no delay at the AV Node, the ventricles might contract too soon, leading to inefficient pumping of blood and potential hemodynamic instability. Therefore, the physiological delay at the AV Node is essential for proper heart function and is a key feature in the analysis of ECGs when identifying various dysrhythmias.