Final answer:
The P wave indicates atrial depolarization and the PR segment is a delay in the AV node that allows ventricles to fill with blood. Ventricular depolarization is displayed by the QRS complex and ventricular repolarization by the T wave. Atrial repolarization is masked by ventricular depolarization on the ECG.
Step-by-step explanation:
The P wave on an ECG represents atrial depolarization, which is the electrical activity that leads to the contraction of the atria. This phase is crucial as it marks the beginning of the heartbeat, when the atria pump blood into the ventricles. The PR segment, which follows, is caused by the delay in the AV node. This delay allows the ventricles to fill completely with blood before they contract.
The QRS complex signifies ventricular depolarization and indicates the point at which the ventricles begin to contract, pumping blood to the lungs and body. The T wave, following the QRS complex, represents ventricular repolarization, signaling the time when the ventricles start to relax after contraction. Notably, the repolarization of the atria is not visible on an ECG because it occurs during the QRS complex and is consequently masked by the more dominant electrical activity of the ventricles.