PR interval and QRS of Junctional Rhythm

• A. PR ≤0.10 s and QRS ≤0.10 s
• B. PR >0.12 s and QRS >0.12 s
• C. PR ≤0.10 s and QRS >0.12 s
• D. PR >0.12 s and QRS ≤0.10 s

Answer: (A)

Junctional rhythm arises from the AV junction, so ventricular depolarization travels through the normal His-Purkinje system, producing a narrow QRS complex. Atrial activation can occur retrogradely or be hidden within the QRS, so P waves may be absent or inverted; when a P wave is visible before the QRS, the time from atrial to ventricular depolarization (the PR interval) is shortened, typically around 0.10 seconds or less. This combination—a short PR interval with a narrow QRS—best matches junctional rhythm. Longer PR intervals or a wide QRS point to other conduction problems rather than a junctional focus.