Overview
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
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:
Massive ST elevation ("tombstoning" pattern) associated with large MI:
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.
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:
Overview
ST elevation can be used to localise a cardiac lesion, while ST depression cannot.
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