On an ECG, which feature marks atrial depolarization?

On an ECG, which feature marks atrial depolarization?

• A. P wave
• B. QRS complex
• C. T wave
• D. U wave

Answer: (A)

The main idea is that different parts of the ECG trace correspond to the timing of electrical activity in the heart’s chambers. Atrial depolarization is represented by the P wave. This small, rounded upward deflection occurs as the impulse spreads across the atria from the SA node, triggering atrial contraction. It appears before the ventricular activity, which is why it sits before the QRS complex. The QRS complex reflects ventricular depolarization, and the T wave reflects ventricular repolarization. The U wave, when present, is not a reliable indicator of atrial activity. Atrial repolarization is actually hidden within the QRS complex and not seen as a separate wave. So the feature that marks atrial depolarization is the P wave.

The main idea is that different parts of the ECG trace correspond to the timing of electrical activity in the heart’s chambers. Atrial depolarization is represented by the P wave. This small, rounded upward deflection occurs as the impulse spreads across the atria from the SA node, triggering atrial contraction. It appears before the ventricular activity, which is why it sits before the QRS complex. The QRS complex reflects ventricular depolarization, and the T wave reflects ventricular repolarization. The U wave, when present, is not a reliable indicator of atrial activity. Atrial repolarization is actually hidden within the QRS complex and not seen as a separate wave. So the feature that marks atrial depolarization is the P wave.