Which statement about the QRS complex width is correct in a normal rhythm?

• A. It is typically wide, indicating conduction delay
• B. The QRS complex width equals the duration of ventricular depolarization
• C. It reflects the duration of atrial depolarization
• D. It is normally narrow, reflecting rapid ventricular depolarization, typically less than 0.12 seconds

Answer: (D)

QRS duration reflects how long it takes ventricles to depolarize. In a normal rhythm, this depolarization occurs rapidly through the His-Purkinje system, so the QRS complex is narrow—typically less than 0.12 seconds (120 milliseconds). A narrow QRS indicates rapid ventricular activation and normal conduction. When the QRS is wide, it points to slowed or abnormal conduction, such as bundle branch block or ventricular ectopy, which is not part of a normal rhythm. While the QRS width does correspond to the time for ventricular depolarization, the key takeaway for a normal rhythm is that it is normally narrow, reflecting rapid depolarization.