What electrical event does the P wave on an ECG represent?

What electrical event does the P wave on an ECG represent?

• A. Ventricular depolarization
• B. Atrial depolarization
• C. Atrial repolarization
• D. Ventricular repolarization

Answer: (B)

The P wave reflects atrial depolarization—the spread of the electrical impulse through the atrial myocardium that triggers atrial contraction and blood flow into the ventricles. After this atrial activation, the impulse travels to the ventricles, producing the QRS complex for ventricular depolarization, and later the T wave for ventricular repolarization. Atrial repolarization is not seen as a separate wave because it occurs during the large QRS complex and is masked by the ventricle’s powerful depolarization. So the P wave specifically marks the electrical activation of the atria.

The P wave reflects atrial depolarization—the spread of the electrical impulse through the atrial myocardium that triggers atrial contraction and blood flow into the ventricles. After this atrial activation, the impulse travels to the ventricles, producing the QRS complex for ventricular depolarization, and later the T wave for ventricular repolarization. Atrial repolarization is not seen as a separate wave because it occurs during the large QRS complex and is masked by the ventricle’s powerful depolarization. So the P wave specifically marks the electrical activation of the atria.