Which statement describes narrow-complex tachycardia versus wide-complex tachycardia?

• A. Narrow-complex tachycardia has QRS duration < 120 ms; wide-complex tachycardia has QRS ≥ 120 ms
• B. Narrow-complex tachycardia has QRS duration > 120 ms; wide-complex tachycardia has QRS < 120 ms
• C. Both have QRS duration < 100 ms
• D. Wide-complex tachycardia confirms atrial tachycardia

Answer: (A)

The key idea is how the QRS duration reflects where the electrical impulse is coming from and how it’s conducted to the ventricles. Narrow-complex tachycardia means the QRS complexes are run through the normal His-Purkinje system, so the ventricular activation is rapid and the QRS duration is short, typically less than 120 milliseconds. Wide-complex tachycardia means the ventricular activation is abnormal or delayed—due to a ventricular origin or aberrant conduction through the ventricles—so the QRS duration is 120 milliseconds or longer.

That makes the statement correct: narrow-complex tachycardia has QRS duration less than 120 ms, while wide-complex tachycardia has QRS duration of 120 ms or more. The other options either flip the cutoff, claim an incorrect universal QRS range, or imply that wide QRS always points to atrial tachycardia, which isn’t true since wide complexes can arise from ventricular tachycardia or SVT with aberrancy.