If QRS duration is broadened beyond normal, what may be suggested?

• A. BBB or ventricular origin
• B. Atrial fibrillation
• C. Normal conduction
• D. Re-entry pathway

Answer: (A)

A broadened QRS duration means ventricular depolarization is not using the normal His-Purkinje pathway and is instead spreading through the ventricular myocardium, which takes longer. This is most commonly seen with a bundle branch block (left or right) or when the impulse originates in the ventricles themselves. Because the width of the QRS is a direct reflection of how quickly the ventricles are being activated, a widened complex points to intraventricular conduction delay or ventricular origin of the beat. Atrial fibrillation can have a normal QRS width unless a conduction abnormality is present; normal conduction would produce a narrow QRS; and while re-entry can underlie some tachyarrhythmias, it isn’t the direct reason a QRS is widened.