In junctional escape rhythm, what is the PRI typically?

• A. Wide PRI >0.20 s
• B. PRI is variable
• C. Narrow PRI <0.12 s
• D. PRI cannot be measured

Answer: (C)

In a junctional escape rhythm the impulse originates near the AV node, so the signal to the ventricles takes a very direct path. This proximity to the ventricles makes the time from the start of atrial depolarization to the start of ventricular depolarization quite short, giving a narrow PR interval. P waves may be absent or appear after the QRS due to retrograde atrial activation, but when you can measure it, the PRI is typically less than 0.12 seconds. A wide PR interval would suggest delayed conduction or AV block, and a variable PRI would indicate inconsistent conduction timing, neither of which describes a stable AV-junctional escape rhythm. Therefore, the typical PR interval is narrow, less than 0.12 seconds.