The PR segment is the flat, usually isoelectric segment between the end of the P wave and the start of the QRS complex.
PR segment abnormalities
These occur in two main conditions:
- Atrial ischaemia
The characteristic changes of acute pericarditis are:
- PR segment depression.
- Widespread concave (‘saddle-shaped’) ST elevation.
- Reciprocal ST depression and PR elevation in aVR and V1
- Absence of reciprocal ST depression elsewhere.
NB. PR segment changes are relative to the baseline formed by the T-P segment.
- Typical ECG of acute pericarditis.
- PR segment depression in V5 due to acute pericarditis (note also some concave ST elevation)
- PR elevation in aVR due to acute pericarditis (note the reciprocal ST depression)
- PR segment elevation or depression in patients with myocardial infarction indicates concomitant atrial ischaemia or infarction.
- This finding has been associated with poor outcomes following MI, increased risk for the development of atrioventricular block, supraventricular arrhythmias and cardiac free-wall rupture.
Liu’s criteria for diagnosing atrial ischaemia / infarction include:
- PR elevation >0.5 mm in V5 & V6 with reciprocal PR depression in V1 & V2
- PR elevation >0.5 mm in lead I with reciprocal PR depression in leads II & III
- PR depression >1.5 mm in the precordial leads
- PR depression >1.2 mm in leads I, II, & III
- Abnormal P wave morphology: M-shaped,W-shaped,irregular,or notched (minor criteria)
PR depression in inferior STEMI indicating concomitant atrial infarction
- Profound PR-segment depression in inferior leads: (A) with clear-cut TP segment; and (B) without clear-cut TP segment; in acute inferior myocardial infarction. Note also ST-segment elevation in inferior leads. (Reproduced from Jim et al.)
Measurement of PR depression
- Measurement of PR-segment depression: (A) with clear-cut TP segment; and (B) without clear-cut TP segment. (Reproduced from Jim et al.)
- Jim MH, Siu CW, Chan AO, Chan RH, Lee SW, Lau CP. Prognostic implications of PR-segment depression in inferior leads in acute inferior myocardial infarction. Clin Cardiol. 2006 Aug;29(8):363-8. PMID: 16933578
ECG Library Basics
LITFL Further Reading
- ECG Library Basics – Waves, Intervals, Segments and Clinical Interpretation
- ECG A to Z by diagnosis – ECG interpretation in clinical context
- ECG Exigency and Cardiovascular Curveball – ECG Clinical Cases
- 100 ECG Quiz – Self-assessment tool for examination practice
- ECG Reference SITES and BOOKS – the best of the rest
- Brady WJ, Truwit JD. Critical Decisions in Emergency and Acute Care Electrocardiography
- Surawicz B, Knilans T. Chou’s Electrocardiography in Clinical Practice: Adult and Pediatric
- Wagner GS. Marriott’s Practical Electrocardiography 12e
- Chan TC. ECG in Emergency Medicine and Acute Care
- Dubin D. Rapid Interpretation of EKG’s
- Mattu A. ECG’s for the Emergency Physician
- Hampton JR. The ECG In Practice, 6e