PR segment

The PR segment is the flat, usually isoelectric segment between the end of the P wave and the start of the QRS complex.

waves of the ecg

PR segment abnormalities occur in two main conditions:


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 depression in 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

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

pr depression due to atrial ischaemia

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 in atrial ischaemia

Measurement of PR-segment depression with (A) and with- out (B) clear-cut TP segment. (Reproduced from Jim et al.)

Further Reading

Author Credits


  • 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]
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