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 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.
- 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
Measurement of PR depression
- ECG BASICS — Waves, Intervals, Segments and Clinical Interpretation
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- 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