The QRS complex on an ECG corresponds to which cardiac event?

The QRS complex on an ECG corresponds to which cardiac event?

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

Answer: (B)

The QRS complex marks ventricular depolarization. When the electrical impulse spreads through the His-Purkinje system into the ventricular muscle, the ventricles depolarize rapidly, producing the sharp, rapid deflections we see as the QRS complex. The P wave represents atrial depolarization, which occurs earlier, and the T wave represents ventricular repolarization that follows. Atrial repolarization does happen during the QRS interval but is hidden by the much larger ventricular depolarization, so it isn’t seen as a separate wave.

The QRS complex marks ventricular depolarization. When the electrical impulse spreads through the His-Purkinje system into the ventricular muscle, the ventricles depolarize rapidly, producing the sharp, rapid deflections we see as the QRS complex. The P wave represents atrial depolarization, which occurs earlier, and the T wave represents ventricular repolarization that follows. Atrial repolarization does happen during the QRS interval but is hidden by the much larger ventricular depolarization, so it isn’t seen as a separate wave.