Final answer:
The AV node delay on an ECG occurs between the P wave and QRS complex, known as the PR interval, which is a critical time for ventricular filling. The correct option is B.
Step-by-step explanation:
The AV node delay occurs on the ECG during the time between the P wave and QRS complex, which corresponds to option B. The P wave on the ECG represents the depolarization of the atria, initiating atrial contraction. Following this, there is a brief pause which is the AV nodal delay, reflecting the time the electrical impulse takes to travel from the atria to the ventricles through the AV node.
This interval is critical in allowing the ventricles to properly fill with blood before contracting. On a standard ECG, this delay is represented by the PR interval, which starts at the beginning of the P wave and ends with the beginning of the QRS complex.