In an electrocardiogram, what does the P wave represent?

In an electrocardiogram, what does the P wave represent?

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

Answer: (C)

The P wave reflects atrial depolarization—the electrical activity that spreads through the atria and triggers their contraction. On the tracing, it shows up as a small, rounded upward deflection right before the larger QRS complex. After the atria depolarize, the impulse travels to the ventricles, causing ventricular depolarization, which is what the QRS complex represents. Ventricular repolarization is seen later as the T wave. Atrial repolarization does occur, but it’s not seen as a separate wave because it’s masked by the much larger ventricular depolarization.

The P wave reflects atrial depolarization—the electrical activity that spreads through the atria and triggers their contraction. On the tracing, it shows up as a small, rounded upward deflection right before the larger QRS complex. After the atria depolarize, the impulse travels to the ventricles, causing ventricular depolarization, which is what the QRS complex represents. Ventricular repolarization is seen later as the T wave. Atrial repolarization does occur, but it’s not seen as a separate wave because it’s masked by the much larger ventricular depolarization.