A broad QRS complex indicates a defect in which part of the conduction system?

• A. Aorta
• B. Ventricular conduction system
• C. Atrioventricular node
• D. Sinoatrial node

Answer: (B)

A broad QRS complex means that ventricular activation is being conducted through the ventricles more slowly than normal. The QRS complex corresponds to the depolarization of the ventricles, which in a healthy heart travels quickly via the His-Purkinje system. When the QRS is widened, it indicates that the impulse is not using that rapid pathway and is instead spreading through the ventricular myocardium itself—often due to a block or delay within the ventricular conduction system (such as a bundle branch block or other intraventricular conduction delay) or from a ventricular-originated rhythm.

The aorta isn’t involved in the electrical conduction of the heart, so defects there wouldn’t broaden the QRS. Defects in the SA node (the natural pacemaker) or the AV node (which delays conduction between atria and ventricles) affect heart rate and atrioventricular conduction (reflected in heart rate, P waves, and PR interval) rather than widening the QRS.