What does the P wave in an electrocardiogram (ECG) represent?

What does the P wave in an electrocardiogram (ECG) represent?

• A. Electrical changes of atrial depolarization at the SA node.
• B. Ventricular depolarization
• C. Atrial repolarization
• D. Ventricular repolarization

Answer: (A)

The P wave reflects atrial depolarization—the electrical activation and subsequent contraction of the atrial myocardium as the impulse spreads from the SA node through the atria. It occurs just before the next phase of the heartbeat, so you see it as a small wave that leads into the QRS complex. Atrial repolarization does happen, but it happens during the QRS and is not seen as a separate deflection, while ventricular depolarization is the QRS complex and ventricular repolarization is the T wave. So the P wave specifically marks the atria's electrical activation.

The P wave reflects atrial depolarization—the electrical activation and subsequent contraction of the atrial myocardium as the impulse spreads from the SA node through the atria. It occurs just before the next phase of the heartbeat, so you see it as a small wave that leads into the QRS complex. Atrial repolarization does happen, but it happens during the QRS and is not seen as a separate deflection, while ventricular depolarization is the QRS complex and ventricular repolarization is the T wave. So the P wave specifically marks the atria's electrical activation.