What does the P Wave on an ECG represent?

What does the P Wave on an ECG represent?

• A. The electrical stimulation of the ventricles
• B. The AV node delay
• C. The electrical stimulation (contraction) of the atria
• D. The recovery phase of the myocardium

Answer: (C)

The P wave shows atrial depolarization—the electrical activation of the atrial myocardium that triggers atrial contraction. This impulse starts in the sinus node and spreads through the atria, producing the small, rounded deflection you see on the ECG. This depolarization occurs before the ventricles depolarize, which is the QRS complex, and before ventricular repolarization, which is the T wave. The AV node delay shows up as the PR interval, not the P wave. Also, atrial repolarization happens as part of the cycle but is usually masked by the QRS complex.

The P wave shows atrial depolarization—the electrical activation of the atrial myocardium that triggers atrial contraction. This impulse starts in the sinus node and spreads through the atria, producing the small, rounded deflection you see on the ECG. This depolarization occurs before the ventricles depolarize, which is the QRS complex, and before ventricular repolarization, which is the T wave. The AV node delay shows up as the PR interval, not the P wave. Also, atrial repolarization happens as part of the cycle but is usually masked by the QRS complex.