What is the primary electrical activity represented by the P wave in an ECG?

The primary electrical activity represented by the P wave in an ECG is atrial depolarization. During this phase, the electrical impulse that originates in the sinoatrial (SA) node spreads through the atria, causing them to contract and push blood into the ventricles. This process is depicted on the ECG as the P wave, which indicates that the atrial myocardium is being activated electrically. It is crucial for initiating the heart's rhythm and ensuring proper blood flow.

The other options represent different phases of the cardiac cycle. Atrial repolarization occurs after atrial depolarization, but it is typically not visible on the ECG due to the overlapping QRS complex. Ventricular depolarization, which is indicated by the QRS complex, shows electrical activation of the ventricles as they prepare to contract. Finally, ventricular repolarization, represented by the T wave, occurs after the ventricles contract and shows the recovery phase of the ventricles as they reset for the next cycle. Understanding these distinctions is key to reading ECGs accurately and recognizing the heart's electrical activity.