What is a defining feature of narrow complex tachycardia in terms of QRS duration?

What is a defining feature of narrow complex tachycardia in terms of QRS duration?

• A. QRS Duration Less Than 120 ms
• B. QRS Duration Greater Than 120 ms
• C. QRS Duration Equal To 160 ms
• D. QRS Duration Not Measured

Answer: (A)

A narrow complex tachycardia is characterized by a QRS duration under about 120 milliseconds. This narrow width shows that ventricular activation is happening through the normal His-Purkinje system, meaning the impulse likely originates above the ventricles (a supraventricular mechanism such as AV nodal reentrant tachycardia or AV reentrant/atrial tachycardia). If the QRS is wide (greater than 120 ms), it suggests ventricular involvement or aberrant conduction, which would not be a narrow complex tachycardia. So the defining feature is a QRS duration less than 120 ms.

A narrow complex tachycardia is characterized by a QRS duration under about 120 milliseconds. This narrow width shows that ventricular activation is happening through the normal His-Purkinje system, meaning the impulse likely originates above the ventricles (a supraventricular mechanism such as AV nodal reentrant tachycardia or AV reentrant/atrial tachycardia). If the QRS is wide (greater than 120 ms), it suggests ventricular involvement or aberrant conduction, which would not be a narrow complex tachycardia. So the defining feature is a QRS duration less than 120 ms.