Which ECG interval represents ventricular depolarization?

Which ECG interval represents ventricular depolarization?

• A. P wave
• B. QRS complex
• C. T wave
• D. PR interval

Answer: (B)

The main concept is that different parts of the ECG map to specific electrical events in the heart. Ventricular depolarization is represented by the QRS complex—the rapid, large deflections that occur after the P wave. This reflects the ventricles activating and contracting, driven by the His-Purkinje system and the bulk of ventricular muscle. The other features correspond to different events: the P wave is atrial depolarization, the T wave is ventricular repolarization, and the PR interval is the time from the start of atrial depolarization to the start of ventricular depolarization (including AV nodal conduction), not the depolarization itself.

The main concept is that different parts of the ECG map to specific electrical events in the heart. Ventricular depolarization is represented by the QRS complex—the rapid, large deflections that occur after the P wave. This reflects the ventricles activating and contracting, driven by the His-Purkinje system and the bulk of ventricular muscle.

The other features correspond to different events: the P wave is atrial depolarization, the T wave is ventricular repolarization, and the PR interval is the time from the start of atrial depolarization to the start of ventricular depolarization (including AV nodal conduction), not the depolarization itself.