PR interval of IVR is

• A. Not Measurable Due To Absence Of P Waves
• B. Normal 120-200 ms
• C. Short PR
• D. Not Measurable Due To Absence Of P Waves

Answer: (D)

In idioventricular rhythm, the rhythm starts in the ventricles and often there is little or no atrial activity conducted to the ventricles, so P waves may be absent or not related to the QRS complexes. The PR interval is defined as the time from the start of a P wave to the start of the QRS complex, which requires a recognizable P wave preceding a QRS. When P waves aren’t present to mark the beginning of atrial depolarization, the PR interval cannot be measured. That’s why the correct understanding is that the PR interval is not measurable due to the absence of P waves. Normal or short PR intervals would require visible atrial activity with proper conduction, which doesn’t occur in IVR.