The P wave on an ECG represents which cardiac event?

The P wave on an ECG represents which cardiac event?

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

Answer: (A)

The P wave represents atrial depolarization—the electrical activation that spreads through the atria and triggers atrial contraction. This wave appears first on the ECG because the impulse begins in the atria (originating near the SA node) and travels through the atrial myocardium, depolarizing it just before the atria contract. If you look further, the QRS complex corresponds to ventricular depolarization, the spike you see after the P wave, while the T wave reflects ventricular repolarization. Atrial repolarization does occur, but it happens during the QRS complex and is not seen as a separate deflection on a standard ECG.

The P wave represents atrial depolarization—the electrical activation that spreads through the atria and triggers atrial contraction. This wave appears first on the ECG because the impulse begins in the atria (originating near the SA node) and travels through the atrial myocardium, depolarizing it just before the atria contract.

If you look further, the QRS complex corresponds to ventricular depolarization, the spike you see after the P wave, while the T wave reflects ventricular repolarization. Atrial repolarization does occur, but it happens during the QRS complex and is not seen as a separate deflection on a standard ECG.