A broad or prolonged QRS complex (> 100 ms) would indicate which of the following?

• A. Atrial conduction delay
• B. Ventricular conduction defect
• C. Reduced left ventricle contraction
• D. Normal conduction

Answer: (B)

The key idea is that the QRS complex timing reflects how quickly the ventricles depolarize. Under normal conditions, depolarization spreads rapidly through the His-Purkinje system, producing a relatively narrow QRS complex (about up to 100 ms). If the QRS becomes broad or prolonged (greater than 100 ms), it means there’s slowed or abnormal conduction within the ventricles themselves, such as a bundle branch block or other intraventricular conduction delay—this is a ventricular conduction defect.

Atrial conduction delay would influence the PR interval, not the width of the QRS. Reduced left ventricular contraction speaks to systolic function (how hard the heart squeezes) rather than the timing of depolarization. Normal conduction would yield a normal, narrow QRS.