Which statement correctly describes the relationship of the P wave to atrial contraction?

Which statement correctly describes the relationship of the P wave to atrial contraction?

• A. The P wave marks atrial depolarization leading to atrial contraction
• B. The P wave marks ventricular depolarization
• C. The P wave marks atrial repolarization
• D. The P wave marks ventricular repolarization

Answer: (A)

The P wave shows atrial depolarization, the electrical change that triggers atrial contraction. When the impulse starts in the SA node and spreads through the atria, the atrial myocardium depolarizes, and this electrical event appears as the P wave on the ECG. That depolarization leads to atrial systole, the atrial kick that helps fill the ventricles. In contrast, the QRS complex reflects ventricular depolarization, and the T wave reflects ventricular repolarization; atrial repolarization is not seen as a separate deflection because it is obscured within the QRS complex. Therefore, the P wave correctly describes atrial depolarization leading to atrial contraction.

The P wave shows atrial depolarization, the electrical change that triggers atrial contraction. When the impulse starts in the SA node and spreads through the atria, the atrial myocardium depolarizes, and this electrical event appears as the P wave on the ECG. That depolarization leads to atrial systole, the atrial kick that helps fill the ventricles. In contrast, the QRS complex reflects ventricular depolarization, and the T wave reflects ventricular repolarization; atrial repolarization is not seen as a separate deflection because it is obscured within the QRS complex. Therefore, the P wave correctly describes atrial depolarization leading to atrial contraction.