Which rhythm commonly shows a QRS duration of 0.10 seconds or less?

• A. Junctional Escape Rhythm
• B. Ventricular Tachycardia
• C. Idioventricular Rhythm
• D. Premature Junctional Contraction

Answer: (A)

A narrow QRS complex (0.10 seconds or less) points to ventricular depolarization traveling through the heart’s normal His-Purkinje conduction system, which is typical for rhythms that originate above the ventricles. A junctional escape rhythm arises from the AV junction, and its impulse uses the standard conduction pathways to activate the ventricles. That results in a fast, coordinated depolarization with a normally narrow QRS complex, usually within the normal range.

In contrast, rhythms that begin in the ventricles—such as ventricular tachycardia or idioventricular rhythm—depolarize the ventricles through slower, abnormal pathways, producing a widened QRS complex well beyond 0.10 seconds. Premature junctional contractions can also have a narrow QRS, but they are isolated premature beats rather than a sustained rhythm, so the sustained junctional escape rhythm is the one most consistently associated with a narrow QRS duration.