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.

ECG basics: waves, segments and intervals LITFL ECG library

PR segment abnormalities

These 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.

ECG Pericarditis

ECG pericarditis PR segment depression

PR segment depression in V5 due to acute pericarditis (note also some concave ST elevation)

ECG pericarditis aVR PR 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
ECG Atrial Ischaemia

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
  • Measurement of PR-segment depression: (A) with clear-cut TP segment; and (B) without clear-cut TP segment. (Reproduced from Jim et al.)


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BA MA (Oxon) MBChB (Edin) FACEM FFSEM. Emergency physician, Sir Charles Gairdner Hospital.  Passion for rugby; medical history; medical education; and asynchronous learning #FOAMed evangelist. Co-founder and CTO of Life in the Fast lane | Eponyms | Books | Twitter |

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