Narrow-complex tachycardia most likely represents:

• A. Atrial flutter
• B. Supraventricular tachycardia
• C. Ventricular tachycardia
• D. Junctional tachycardia

Answer: (B)

The main idea here is that the width of the QRS complex tells you where the tachycardia is arising. A narrow QRS tachycardia means the ventricles are being activated through the heart’s normal conduction system, so the rhythm originates above the ventricles. That places the mechanism in the supraventricular category, which includes rhythms like AV nodal reentrant tachycardia, AVRT, or atrial tachycardias.

Among the options, supraventricular tachycardia is the best fit because it covers tachycardias that start above the ventricles and produce narrow QRS complexes. Ventricular tachycardia, by contrast, typically shows wide QRS due to ventricular activation from an outside conduction path. Atrial flutter can sometimes present with a narrow QRS, but the general, most likely classification for a narrow-complex tachycardia is SVT. Junctional tachycardia is also a supraventricular rhythm with a narrow QRS, but the overarching and most common label for a narrow-complex tachycardia is supraventricular tachycardia.