PR segment

PR segment abnormalities occur in two main conditions:

• Pericarditis
• Atrial ischaemia

Pericarditis

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 there is also some concave ST elevation)

PR elevation in aVR due to acute pericarditis (note the reciprocal ST depression)

Atrial ischaemia

• 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 with (A) and without (B) 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 with (A) and with- out (B) clear-cut TP segment. (Reproduced from Jim et al.)

Further Reading

• ECG BASICS — Waves, Intervals, Segments and Clinical Interpretation
• ECG CLINICAL CASES — Your favourite ECG’s placed in clinical context with a challenging Q&A approach
• ECG and Cardiology Eponymous Syndromes — Cheats guide to eponymous emancipation
• ECG Exam Template — a framework for the FACEM part 2 exam.
• ECG Reference Sites on the WEB — the best of the rest

Author Credits

References

• 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 [Full text]