ST interval: Difference between revisions
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*There is diffuse [[ST segment]] elevation (usually flat or concave up) together with [[PR segment depression]]. ST elevation reflects inflammation of the ventricular subepicardial layer and [[PR segment]] depression reflects inflammation of the atrial subepicardial layer. | *There is diffuse [[ST segment]] elevation (usually flat or concave up) together with [[PR segment depression]]. ST elevation reflects inflammation of the ventricular subepicardial layer and [[PR segment]] depression reflects inflammation of the atrial subepicardial layer. | ||
*[[T wave inversion]] can be seen in [[pericarditis]] but usually not until the ST elevation has resolved, so *[[T wave inversion]] accompanying ST elevation is probably not due to [[pericarditis]] | *[[T wave inversion]] can be seen in [[pericarditis]] but usually not until the ST elevation has resolved, so *[[T wave inversion]] accompanying ST elevation is probably not due to [[pericarditis]] | ||
====Hyperkalemia==== | |||
[[Hyperkalemia]] may not affect all leads. | |||
====Ventricular Aneurysm==== | ====Ventricular Aneurysm==== | ||
*Ventricular aneurysm should be suspected if the ST segment elevation persists > 6 weeks after acute MI and if there is a wall motion abnormality on echocardiography. | *Ventricular aneurysm should be suspected if the ST segment elevation persists > 6 weeks after acute MI and if there is a wall motion abnormality on echocardiography. | ||
Revision as of 11:24, 23 September 2012
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor-In-Chief: Cafer Zorkun, M.D., Ph.D. [2]
Overview
The ST interval represents the initial, slow phase of ventricular repolarization.[1] The ST segment commonly refers to the morphology of the segment between the end of the S wave (the terminal deflection of the QRS) and the beginning of the T wave.
ST Segment Changes
EKG manifestations of acute myocardial injury or ischemia
EKG manifestations of acute myocardial injury or ischemia in absence of left ventricular hypertrophy and LBBB as follow[2] [3]
- ST segment elevation
In general, ST segment elevation reflects myocardial injury, which may be irreversible (unlike ischemia which may be reversible) and which is associated with a risk of necrosis. ST elevation is defined as new ST segment elevation at the J point in two contiguous leads with the cut off points ≥0.2 mV in men or ≥0.15 mV in women in V2-V3 and ≥0.1 mV in other leads.
- ST segment depression and T wave changes
In general, ST depresstion represents reversible ischemia (less likely to result in irreversible necorsis). One exception is the presence of ST depression in the anterior precordial leads that can reflect posterior injury rather than anterior ischemia. Ischemia is defined as new horizontal or downsloping ST segment changes as ≥0.05 mV in two contiguous leads and/or T wave inversion ≥0.1 mV in two contiguous leads with prominent R wave or in situations which R wave amplitude / S wave amplitude ratio is >1.
Althought it is not observed in women, the J point elevation in men decreases with increasing age.[4]
The term of contiguous lead represents lead groups such as anterior leads (V1-V6), inferior leads (II, III, and aVF), or lateral/apical leads (I and aVL).
Measurements
The optimal time after the J point to measure ST elevation is debated. This example shows the technique of measuring the magnitude of ST elevation 60 milliseconds or 1.5 small boxes after the J point.
Differential Diagnosis of ST Segment Depression
- Ischemia particularly if the ST segment is downsloping
- "Reciprocal changes" which are associated with a pattern of injury (ST segment elevation) in other leads. It is unclear if the ST depression is truly simply a reciprocal change which is a mirror image electrically of the injury in the other leads or if the ST depression is due to active ischemia in the other territory. Reciprocal changes are associated with a poorer prognosis. Reciprocal changes in the anterior precordial leads in association with an inferior MI are associated with slower flow in the LAD
- Dig effect (concave up;"reverse-checkmark")
- LV "strain"-associated with LVH (asymmetric ST depression, concave up, with slow downstroke and rapid upstroke, most often in I, aVL, V4-6)
- RV "strain"-associated with RVH (asymmetric ST depression, concave up, with slow downstroke and rapid upstroke, most often in V1-2)
- Hypokalemia (usually slight ST depression)
- Hypercalcemia
Differentiating the Causes of ST Segment Elevation
Myocardial Injury
- The ST elevation is usually localized to an anatomic distribution that follows the coronary arteries (e.g. leads II,III, aVF).
- In the setting of myocardial injury, "reciprocal changes" representing ischemia in other leads or a mirror like effect of the ST elevation presenting as ST depression in other leads, may be present. For example, ST elevation in the anterior leads in acute MI may be accompanied by ST depression in the inferior leads.
- Prinzmetal's angina can cause transient ST elevation during chest pain.
- Contact of the needle can cause a "current of injury" and ST segment elevation during pericardiocentesis.
Pericarditis
- There is diffuse ST segment elevation (usually flat or concave up) together with PR segment depression. ST elevation reflects inflammation of the ventricular subepicardial layer and PR segment depression reflects inflammation of the atrial subepicardial layer.
- T wave inversion can be seen in pericarditis but usually not until the ST elevation has resolved, so *T wave inversion accompanying ST elevation is probably not due to pericarditis
Hyperkalemia
Hyperkalemia may not affect all leads.
Ventricular Aneurysm
- Ventricular aneurysm should be suspected if the ST segment elevation persists > 6 weeks after acute MI and if there is a wall motion abnormality on echocardiography.
Early Repolarization
- "J point" elevation aka "early repolarization" is a concave-upward ST segment deflection.
- It is a normal variant
- Vaulting ST segment or J point elevation is a normal variant in leads V1-V3
Distinguishing Early Repolarization and Other Normal Variants from Pathologic ST Elevation
References
- ↑ Hammill S. C. Electrocardiographic diagnoses: Criteria and definitions of abnormalities, Chapter 18, MAYO Clinic, Concise Textbook of Cardiology, 3rd edition, 2007 ISBN 0-8493-9057-5
- ↑ Wong C-K, French JK, Aylward PEG, Stewart RAH, Gao W, Armstrong PW, Van De Werf FJJ, Simes RJ, Raffel OC, Granger CB, Califf RM, White HD. Patients with prolonged ischemic chest pain and presumed-new left bundle branch block have heterogenous outcomes depending on the presence of ST-segment changes. J Am Coll Cardiol. 2005;46:29–38. PMID 15992631
- ↑ Sgarbossa EB, Pinsky SL, Barbagelata A, Underwood DA, Gates KB, Topol EJ, Califf RM, Wagner GS. Electrocardiographic diagnosis of evolving acute myocardial infarction in the presence of left bundle branch block. N Engl J Med. 1996;334:481–87. PMID 8559200
- ↑ Mcfarlane PW. Age, sex, and the ST amplitude in health and disease. J Electrocardiol. 2001; 34: 235–241. PMID 11781962
Additional resources
- ECGpedia: Course for interpretation of ECG
- The whole ECG - A basic ECG primer
- 12-lead ECG library
- Simulation tool to demonstrate and study the relation between the electric activity of the heart and the ECG
- ECG information from Children's Hospital Heart Center, Seattle
- ECG Challenge from the ACC D2B Initiative
- National Heart, Lung, and Blood Institute, Diseases and Conditions Index
- A history of electrocardiography
- EKG Interpretations in infants and children