The P wave on an ECG corresponds to which event?

• A. Ventricular depolarization leading to ventricular contraction
• B. Atrial repolarization
• C. Atrial depolarization leading to atrial contraction
• D. No electrical activity

Answer: (C)

The P wave represents atrial depolarization and the subsequent atrial contraction. It shows the spread of the electrical impulse through the atria after the SA node fires, which triggers the atrial muscles to depolarize and contract. This happens before the ventricles depolarize, so the P wave appears before the QRS complex. Atrial repolarization does occur, but it’s hidden within the QRS complex and not seen as a separate deflection. There is indeed electrical activity during the P wave, so the option stating no electrical activity isn’t correct.