The QRS complex on an ECG represents which event?

The QRS complex on an ECG represents which event?

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

Answer: (A)

The QRS complex represents ventricular depolarization—the rapid spread of electrical activity through the ventricles that triggers their contraction. The atria depolarize earlier, shown as the P wave, while atrial repolarization occurs during the QRS but is masked by the much larger ventricular depolarization and thus not seen as a separate deflection. After depolarization, the ventricles repolarize, which appears as the T wave. So the QRS is the signature of ventricular activation, not atrial activity or ventricular recovery.

The QRS complex represents ventricular depolarization—the rapid spread of electrical activity through the ventricles that triggers their contraction. The atria depolarize earlier, shown as the P wave, while atrial repolarization occurs during the QRS but is masked by the much larger ventricular depolarization and thus not seen as a separate deflection. After depolarization, the ventricles repolarize, which appears as the T wave. So the QRS is the signature of ventricular activation, not atrial activity or ventricular recovery.