Which of the following best describes what the PR interval on a surface ECG represents?
- A Total duration of ventricular depolarisation and repolarisation
- B Time from onset of atrial depolarisation to onset of ventricular depolarisation ✓
- C Duration of conduction through the His-Purkinje system alone
- D Time from onset of the P wave to completion of the QRS complex
Correct answer: B. Time from onset of atrial depolarisation to onset of ventricular depolarisation
Explanation
The PR interval is measured from the beginning of the P wave to the beginning of the QRS complex, so it spans atrial depolarisation plus the deliberate AV nodal delay that allows ventricular filling. The normal range is 0.12 to 0.20 seconds. Option D is wrong because the interval ends at the start of the QRS, not its end, and option C is wrong because most of the delay lies within the AV node itself.
Reference: Ganong's Review of Medical Physiology, 26th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.