Basic Arrhythmias with 12-Lead EKG Practice Test 2026 – Complete Exam Prep

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What QRS duration is typically used to define a wide-complex tachycardia such as VT?

QRS duration ≥ 120 ms.

A wide-complex tachycardia is defined by a QRS duration of 120 milliseconds (0.12 seconds) or longer. The QRS duration reflects how long ventricular depolarization takes; normal QRS is typically up to about 100 ms, with some variation. When the QRS is 120 ms or more, it indicates that ventricular activation is slower or abnormal, which is common in ventricular tachycardia or in supraventricular tachycardias with aberrant conduction. This threshold helps distinguish wide-complex tachycardias from narrow-complex ones, which usually have a QRS duration less than 120 ms.

QRS duration ≤ 90 ms.

QRS duration between 100–110 ms.

QRS duration is not related.

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