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ECG Basics

The ST Segment



  • The ST segment on an ECG trace reflects early ventricular repolarisation, and is classically used to assess for cardiac ischaemia.
    • Look For

    • The section between the end of the QRS complex (J point) and the beginning of the T wave.

ST Elevation

  • ST elevation is classically associated with ST elevation myocardial infarction (STEMI) and as such is a medical emergency if seen on ECG. However, there are several other causes of ST elevation that it is important to be aware of.
    • Look For

      Elevation of the J point (meeting point of the QRS complex and ST segment)
    • >2mm in V1-V3
    • >1mm in limb leads
    • ST Elevation
    • Causes of ST Elevation

    • ST elevation myocardial infarction
    • Prinzmetal angina (coronary vasospasm)
    • Tako-tsubo cardiomyopathy
    • Pericarditis
    • Left bundle branch block
    • Left ventricular hypertrophy
    • Benign early repolarisation (physiological)
    • Subarachnoid haemorrhage
    • Interpretation

    • Localised ST elevation with reciprocal ST depressionST elevation myocardial infarction, prinzmetal angina, tako-tsubo cardiomyopathy
    • ST elevation discordant with the QRS complexLeft bundle branch block, left ventricular hypertrophy
    • Mild concave ST elevation with tall T waves in at least 1 precordial lead ± notch at end of QRS complex (j-point notching)Benign early repolarisation
    • Widespread ST elevationPericarditis, subarachnoid haemorrhage, tako-tsubo cardiomyopathy
    • Examples

    • Benign early repolarisation with concave ST elevation, tall T waves and J-point notching:
    • ST Elevation
  • Massive ST elevation (“tombstoning” pattern) associated with large MI:
    • ST Elevation

ST Depression

    • Look For

    • Depression of the J point (meeting point of QRS complex and ST segment) of >1mm. Note whether the ST segment is horisontal, downsloping or upsloping.
    • ST Depression
    • Causes of ST Depression

    • Exercise
    • Cardiac ischaemia without infarction - downsloping ST depression
    • Non-ST elevation MI (NSTEMI)
    • ST elevation MI (STEMI) - reciprocal to ST elevation
    • Hypokalaemia - widespread downsloping ST depression
    • Digoxin - reverse tick ST depression
    • Left ventricular hypertrophy - downsloping
    • Left bundle branch block
    • Example

    • ST depression, T wave flattening and QT prolongation associated with hypokalaemia:
    • ST Depression


  • ST elevation can be used to localise a cardiac lesion, while ST depression cannot.
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