ST depression
ST depression refers to a finding on an electrocardiogram.[1][2]
Measurement
ST segment depression may be determined by measuring the vertical distance between the patient's trace and the isoelectric line at a location 2[3]-3 millimeters from the QRS complex.
It is significant if it is more than 1 mm in V5-V6, or 1.5 mm in AVF or III.
In a cardiac stress test, an ST depression of at least 1 mm after adenosine administration indicates a reversible ischaemia, while an exercise stress test requires an ST depression of at least 2 mm to significantly indicate reversible ischaemia.[4]
Physiology
For non-transmural ischemia, the pathophysiological cause of ST depression is a slightly elevated resting potential in myocardial cells, but with the ST segment less affected, as it represents a depolarized state. Still, the resting potential is the reference line in ECG, making it display an apparent ST depression rather than an elevation of the other segments.
Causes
It is often a sign of myocardial ischemia, of which coronary insufficiency is a major cause. Other ischemic heart diseases causing ST depression include:
- Subendocardial ischemia[5] or even infarction.[3] Subendocardial means non full thickness ischemia. In contrast, ST elevation is transmural (or full thickness) ischemia
- Non Q-wave myocardial infarction[5]
- Reciprocal changes in acute Q-wave myocardial infarction (e.g., ST depression in leads I & aVL with acute inferior myocardial infarction)[5]
Depressed but upsloping ST segment generally rules out ischemia as a cause.
Also, it can be a normal variant or artifacts, such as:
- Pseudo-ST-depression, which is a wandering baseline due to poor skin contact of the electrode[5]
- Physiologic J-junctional depression with sinus tachycardia[5]
- Hyperventilation[5]
Other, non-ischemic, causes include:
- Side effect of digoxin[3][5]
- Hypokalemia[3][5]
- Right or left ventricular hypertrophy[5]
- Intraventricular conduction abnormalities (e.g., right or left bundle branch block, WPW, etc.)[5]
- Hypothermia[3]
- Tachycardia[3]
- Reciprocal ST elevation[3]
- Mitral valve prolapse[5]
- CNS disease[5]
Mnemonic
DEPRESSED ST ---> D - Drooping valve (MV Prolapse) E - Enlargement of the left ventricle P - Potassium loss R - Reciprocal ST Depression (e.g. Inferior MI) E - Encephalon Haemorrhage S - Subendocardial Infarct S - Subendocardial Ischaemia E - Embolism (Pulmonary) D - Dilated Cardiomyopathy S - Shock T - Toxicity (Digitalis/Quinidine
See also
ST depression be can caused by stroke (especially subarachnoid haemorrhage) (http://www.gpnotebook.co.uk/simplepage.cfm?ID=597295149)
References
- ↑ Okin PM, Devereux RB, Kors JA et al. (April 2001). "Computerized ST depression analysis improves prediction of all-cause and cardiovascular mortality: the strong heart study". Ann Noninvasive Electrocardiol 6 (2): 107–16. doi:10.1111/j.1542-474X.2001.tb00094.x. PMID 11333167.
- ↑ Okin PM, Roman MJ, Lee ET, Galloway JM, Howard BV, Devereux RB (April 2004). "Combined echocardiographic left ventricular hypertrophy and electrocardiographic ST depression improve prediction of mortality in American Indians: the Strong Heart Study". Hypertension 43 (4): 769–74. doi:10.1161/01.HYP.0000118585.73688.c6. PMID 14769809.
- ↑ 3.0 3.1 3.2 3.3 3.4 3.5 3.6 madscientist software > MicroEKG Manual Retrieved September 2010
- ↑ Yap, L. B.; Arshad, W.; Jain, A.; Kurbaan, A. S.; Garvie, N. W. (2005). "Significance of ST depression during exercise treadmill stress and adenosine infusion myocardial perfusion imaging". The International Journal of Cardiovascular Imaging 21 (2–3): 253–258; discussion 258–60. doi:10.1007/s10554-004-2458-y. PMID 16015437.
- ↑ 5.0 5.1 5.2 5.3 5.4 5.5 5.6 5.7 5.8 5.9 5.10 5.11 X. ST Segment Abnormalities Frank G. Yanowitz, MD. University of Utah School of Medicine
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