Which statement correctly describes the normal sequence of ventricular conduction and the effect on QRS duration?

• A. AV node → His-Purkinje system; short duration; lengthens with slow conduction
• B. SA node → AV node; duration constant
• C. Bundle of His → AV node; duration lengthens with rapid conduction
• D. Purkinje fibers → AV node; duration unaffected

Answer: (A)

The key idea is that ventricular conduction travels quickly through the AV node into the His-Purkinje system, producing a short QRS duration. In normal physiology, the impulse reaches the ventricles via the AV node and then spreads rapidly through the His bundle and Purkinje fibers to depolarize the ventricles almost simultaneously. Because this pathway conducts electricity very fast, the time taken to depolarize the ventricles is brief, reflected as a short QRS complex. If conduction through this system slows down—due to blocks or delays—the ventricles take longer to depolarize, and the QRS duration widens. Starting with the SA node or misordering the conduction path would not describe ventricular activation, and saying the duration is constant or unaffected contradicts how QRS duration changes with intraventricular conduction speed.