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ST depression refers to a finding on an electrocardiogram.[1][2]

It is often a sign of myocardial ischemia.

It can be associated with acute pericarditis.[3]

Contents

ST segment depression

ST segment depression can be caused by ischemia, digitalis, rapid heart rate, and temperature or electrolyte abnormality. It can also be a “reflected” or reciprocal ST elevation (showing an inverted view of what’s happening at another place in the heart). The shape of the ST segment, and whether the abnormality is localized to leads looking at one area of the heart, often allows the cause of ST depression to be diagnosed. ST segment depression is considered significant if the ST segment is at least one box below baseline, as measured two boxes after the end of the QRS. As with infarction, the location of the ischemia is reflected in the leads in which the ST depression occurs.

Causes of ST Depression:

  • Ischemia
  • Hypothermia
  • Hypokalemia
  • Tachycardia
  • Subendocardial infarct
  • Reciprocal ST elevation
  • Ventricular Hypertrophy
  • Bundle branch block
  • Digitalis

Measure: 2 mm beyond QRS Significant: 1 mm

Ischemia:

When ST segment depression is transient, it’s almost always due to acute myocardial ischemia. The ECG signs of ischemia may come and go fairly quickly — over a matter of minutes.

ST segment depression is MOST specific for ischemia if the ST segment slopes down from the J point. Horizontal or flat STs are also quite suspicous for ischemia. Upsloping ST depression is only about 60% accurate for diagnosing ischemia.

“J point” depression at the beginning of the QRS complex is not significant if the location of measurement (two boxes past the QRS) finds the ST segment has risen back to the baseline.

Infarction:

ST depression can also be seen in infarction, typically in non Q-wave infarction, often called subendocardial infarction. This type of infarct does not extend through the ventricular wall (non-transmural). Subendocardial infarctions involve small areas of injured tissue, with larger areas of overlying ischemia. These infarctions may show ST segment depression (rather than elevation) because of the larger areas of ischemia.

ST depression can also be seen as a “mirror” of what’s happening on the other side of the heart. For example, the inferior leads may show ST depression as a reflection of what’s happening in the upper lateral side of the heart.

Ventricular hypertrophy:

Left ventricular hypertrophy or strain commonly causes ST segment depression, often with T wave inversions. These changes are seen in the “lateral” leads — those that record activity over the left ventricle. In LVH, ST and T wave abnormalities are commonly seen in leads I, L, and V4-V6.

Right ventricular hypertrophy or acute ventricular strain can produce changes in the right precordial leads, V1 and V2.

Ventricular conduction block:

Left bundle branch block produces ST depression and inverted T waves in leads I, L, and V5-V6. In general, the ST will slope away from the direction of the QRS: a large wide R wave will have a down-sloping ST ending in an inverted T, while a deep wide S wave will have an upsloping ST segment ending in an upright T.

Other causes of ST segment abnormality:

Patients on digitalis often show mild ST depression. This depression is usually less than 1 mm, and produces a “scooped” appearance — the “Salvador Dali mustache” ST. These ST abnormalities are seen in multiple leads.

Hypothermia and severe hypokalemia routinely cause ST segment depression in multiple leads. Hypothermia will tend to lengthen all ECG intervals, including the PR and QT, while hypokalemia will often lengthen the PR while shortening the ST segment slightly. ST segment depression is called “nonspecific ST abnormality” rather than “ST segment depression” if the ST segments are less than 1 mm depressed and are accompanied by a normally-oriented T wave. (madscientist)

See also

References

  1. ^ 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. PMID 11333167.  
  2. ^ 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. http://hyper.ahajournals.org/cgi/pmidlookup?view=long&pmid=14769809.  
  3. ^ Celik T, Iyisoy A, Kurşaklioğlu H (June 2008). "Reciprocal ST segment depression in a patient with acute pericarditis". Anadolu Kardiyol Derg 8 (3): E15. PMID 18524713. http://www.anakarder.com/yazilar.asp?yaziid=1254&sayiid=.  

madscientist software http://www.madsci.com/manu/ekg_st-t.htm








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