An ST elevation is considered significant if the vertical distance between the ECG trace and the isoelectric line at a point 0.04 seconds after the J-point is at least 0.1 mV (usually representing 1 mm or 1 small square) in a limb lead or 0.2 mV (2 mm or 2 small squares) in a precordial lead. The isoelectric line is either the PR interval or the TP interval. This measure has a false positive rate of 15-20% (which is slightly higher in women than men) and a false negative rate of 20-30%.
The ST segment corresponds to a period of ventricle systolic depolarization, when the cardiac muscle is contracted. Subsequent relaxation occurs during the diastolic repolarization phase. The normal course of ST segment reflects a certain sequence of muscular layers undergoing repolarization and certain timing of this activity. When the cardiac muscle is damaged or undergoes a pathological process (e.g. inflammation), its contractile and electrical properties change. Usually, this leads to early repolarization, or premature ending of the systole.
Associated conditions 
The exact topology and distribution of the affected areas depend on the underlying condition. Thus, ST elevation may be present on all or some leads of ECG.
It can be associated with:
- Myocardial infarction (see also ECG in myocardial infarction). ST elevation in select leads is more common with MI.
- Prinzmetal's angina
- Acute pericarditis ST elevation in all leads is more common with acute pericarditis.
- Left ventricular aneurysm
- Blunt trauma to the chest resulting in a cardiac contusion
- Acute myocarditis
- Pulmonary embolism
- Brugada syndrome
- J point elevation
See also 
- Family Practice Notebook > ST Elevation Retrieved Nov 2010
- Khandpur, R.S. (2003). Handbook of biomedical instrumentation (2nd ed.). New Delhi: Tata McGraw-Hill. p. 255. ISBN 978-0-07-047355-3.
- Sabatine MS (2000). Pocket Medicine (Pocket Notebook). Lippincott Williams & Wilkins. ISBN 0-7817-1649-7.
- Thaler, Malcolm (2009). The only EKG book you'll ever need. Lippincott Williams & Wilkins. p. 2009. ISBN 1-60547-140-2, 9781605471402 Check
- Tingle LE, Molina D, Calvert CW (November 2007). "Acute pericarditis". Am Fam Physician 76 (10): 1509–14. PMID 18052017.
- Chew HC, Lim SH (November 2005). "Electrocardiographical case. ST elevation: is this an infarct? Pericarditis". Singapore Med J 46 (11): 656–60. PMID 16228101.
- Victor F. Froelicher; Jonathan Myers (2006). Exercise and the heart. Elsevier Health Sciences. pp. 138–. ISBN 978-1-4160-0311-3. Retrieved 10 October 2010.
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