P wave on an ECG represents depolarization of which chamber?

P wave on an ECG represents depolarization of which chamber?

• A. Atria
• B. Ventricles
• C. Interventricular septum
• D. Atrioventricular node

Answer: (A)

The P wave reflects atrial depolarization. When the electrical impulse starts in the SA node and spreads through the atrial muscle, the atria depolarize and then contract, which shows up as the P wave on the ECG. Ventricular depolarization occurs after that and is represented by the QRS complex, not by the P wave. The depolarization of the interventricular septum contributes to the QRS complex as part of its overall spread, and the AV node’s activity isn’t seen as a separate wave on the surface ECG—the AV node mainly causes a delay that lengthens the PR interval. So the P wave specifically corresponds to atrial depolarization.

The P wave reflects atrial depolarization. When the electrical impulse starts in the SA node and spreads through the atrial muscle, the atria depolarize and then contract, which shows up as the P wave on the ECG. Ventricular depolarization occurs after that and is represented by the QRS complex, not by the P wave. The depolarization of the interventricular septum contributes to the QRS complex as part of its overall spread, and the AV node’s activity isn’t seen as a separate wave on the surface ECG—the AV node mainly causes a delay that lengthens the PR interval. So the P wave specifically corresponds to atrial depolarization.