What does the QRS complex represent in an ECG?

What does the QRS complex represent in an ECG?

• A. Depolarization of the ventricles and repolarization of the atria.
• B. Depolarization of the atria and repolarization of the ventricles.
• C. Repolarization of the ventricles only.
• D. Activation of the ventricles by the SA node.

Answer: (A)

The QRS complex is the rapid electrical activity that leads to ventricular depolarization—the ventricles activating to contract. The mass of ventricular muscle and the fast conduction through the bundle branches produce this sharp, distinct deflection. At the same time, the atria are repolarizing, but this signal is hidden within the large ventricular spike, so you don’t see a separate wave for atrial repolarization on the ECG. That’s why the QRS complex is associated with ventricular depolarization, with atrial repolarization occurring simultaneously but being masked. For context, the P wave marks atrial depolarization, and the T wave marks ventricular repolarization.

The QRS complex is the rapid electrical activity that leads to ventricular depolarization—the ventricles activating to contract. The mass of ventricular muscle and the fast conduction through the bundle branches produce this sharp, distinct deflection. At the same time, the atria are repolarizing, but this signal is hidden within the large ventricular spike, so you don’t see a separate wave for atrial repolarization on the ECG. That’s why the QRS complex is associated with ventricular depolarization, with atrial repolarization occurring simultaneously but being masked. For context, the P wave marks atrial depolarization, and the T wave marks ventricular repolarization.