ST interval




 * Associate Editor-In-Chief:

Overview
The ST interval represents the initial, slow phase of ventricular repolarization. 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.

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


 * 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.

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
 * 1) Dig effect (concave up;"reverse-checkmark")
 * 2) LV "strain"-associated with LVH (asymmetric ST depression, concave up, with slow downstroke and rapid upstroke, most often in I, aVL, V4-6)
 * 3) RV "strain"-associated with RVH (asymmetric ST depression, concave up, with slow downstroke and rapid upstroke, most often in V1-2)
 * 4) Hypokalemia (usually slight ST depression)
 * 5) Hypercalcemia

Differential Diagnosis of ST Segment Elevation

 * 1) Myocardial "injury," i.e. ongoing or recent infarction; usually concave down
 * 2) Pericarditis
 * 3) Diffuse ST segment elevation (us. 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
 * 4) T wave inversion can be seen in pericarditis but us. not until the ST elevation has resolved, so T wave inversion accompanying ST elevation is probably not due to pericarditis
 * 5) "Reciprocal changes" representing ischemia in other leads--see Ischemia
 * 6) Hyperkalemia (not necessarily in all leads)
 * 7) Ventricular aneurysm (suspect if ST elevation persists > 6 weeks after AMI)
 * 8) Prinzmetal's angina (transient, during chest pain)
 * 9) "J point" elevation aka "early repolarization" -concave-upward; normal variant; particularly in V1-3
 * 10) "Proximity effect": V2, sometimes also V1 and V3, thought to reflect an artifact of proximity to heart.

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