In electrocardiography, the ST segment connects the QRS complex

QRS complex

The QRS complex is a name for the combination of three of the graphical deflections seen on a typical electrocardiogram . It is usually the central and most visually obvious part of the tracing. It corresponds to the depolarization of the right and left ventricles of the human heart...

 and the T wave

T wave

In electrocardiography, the T wave represents the repolarization of the ventricles. The interval from the beginning of the QRS complex to the apex of the T wave is referred to as the absolute refractory period. The last half of the T wave is referred to as the relative refractory period...

 and has a duration of 0.08 to 0.12 sec (80 to 120 ms).

It starts at the J point (junction between the QRS complex and ST segment) and ends at the beginning of the T wave. However, since it is usually difficult to determine exactly where the ST segment ends and the T wave begins, the relationship between the RT segment and T wave should be examined together. The typical ST segment duration is usually around 0.08 sec (80 ms). It should be essentially level with the PR and TP segment.

The ST segment represents the period when the ventricles are depolarized. It is isoelectric.

Interpretation

• The normal ST segment has a slight upward concavity.
• Flat, downsloping, or depressed ST segments may indicate coronary ischemia
  Coronary ischemia
  Coronary ischemia is a medical term for not having enough blood through the coronary arteries. Coronary ischemia is linked to heart disease as well as heart attacks.It is also known as cardiac ischemia.-Causes:...
  
  .
• ST elevation
  ST elevation
  ST elevations refers to a finding on an electrocardiogram, wherein the trace in the ST segment is abnormally high above the isoelectric line.-Measurement:...
  
   may indicate myocardial infarction
  Myocardial infarction
  Myocardial infarction or acute myocardial infarction , commonly known as a heart attack, results from the interruption of blood supply to a part of the heart, causing heart cells to die...
  
  . An elevation of >1mm and longer than 80 milliseconds following the J-point. 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%.
• ST depression
  ST depression
  -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 millimeters from the QRS complex....
  
   may be associated with hypokalemia
  Hypokalemia
  Hypokalemia or hypokalaemia , also hypopotassemia or hypopotassaemia , refers to the condition in which the concentration of potassium in the blood is low...
  
   or digitalis toxicity.