ST elevation refers to a finding on an electrocardiogram wherein the trace in the

ST segment In electrocardiography, the ST segment connects the QRS complex and the T wave and has a duration of 0.005 to 0.150 sec (5 to 150 ms). It starts at the J point (junction between the QRS complex and ST segment) and ends at the beginning of the ...

is abnormally high above the baseline.

Electrophysiology

The ST segment starts from the J point (termination of

QRS complex The QRS complex is the combination of three of the graphical deflections seen on a typical electrocardiogram (ECG or EKG). It is usually the central and most visually obvious part of the tracing. It corresponds to the depolarization of the ri ...

and the beginning of ST segment) and ends with the

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 ...

. The ST segment is the plateau phase, in which the majority of the myocardial cells had gone through

depolarization In biology, depolarization or hypopolarization is a change within a cell, during which the cell undergoes a shift in electric charge distribution, resulting in less negative charge inside the cell compared to the outside. Depolarization is ess ...

but not

repolarization In neuroscience, repolarization refers to the change in membrane potential that returns it to a negative value just after the depolarization phase of an action potential which has changed the membrane potential to a positive value. The repolarizat ...

. The ST segment is the isoelectric line because there is no voltage difference across

cardiac muscle Cardiac muscle (also called heart muscle, myocardium, cardiomyocytes and cardiac myocytes) is one of three types of vertebrate muscle tissues, with the other two being skeletal muscle and smooth muscle. It is an involuntary, striated muscle th ...

cell membrane during this state. Any distortion in the shape, duration, or height of the

cardiac action potential The cardiac action potential is a brief change in voltage ( membrane potential) across the cell membrane of heart cells. This is caused by the movement of charged atoms (called ions) between the inside and outside of the cell, through proteins c ...

can distort the ST segment.

Abnormalities

Pathologic ST elevation (CardioNetworks ECGpedia)

An ST elevation is considered significant if the vertical distance inside the ECG trace and the baseline at a point 0.04 seconds after the J-point is at least 0.1 mV (usually representing 1 mm or 1 small square) in a limb lead or 0.2 mV (2 mm or 2 small squares) in a

precordial lead Electrocardiography is the process of producing an electrocardiogram (ECG or EKG), a recording of the heart's electrical activity. It is an electrogram of the heart which is a graph of voltage versus time of the electrical activity of the hear ...

. The baseline is either the PR interval or the TP interval. This measure has a

false positive A false positive is an error in binary classification in which a test result incorrectly indicates the presence of a condition (such as a disease when the disease is not present), while a false negative is the opposite error, where the test resul ...

rate of 15–20% (which is slightly higher in women than men) and a

false negative A false positive is an error in binary classification in which a test result incorrectly indicates the presence of a condition (such as a disease when the disease is not present), while a false negative is the opposite error, where the test resul ...

rate of 20–30%.

Myocardial infarction

12 Lead EKG ST Elevation tracing color coded

When there is a blockage of the

coronary artery The coronary arteries are the arterial blood vessels of coronary circulation, which transport oxygenated blood to the heart muscle. The heart requires a continuous supply of oxygen to function and survive, much like any other tissue or organ ...

, there will be lack of oxygen supply to all three layers of

(transmural ischemia). The leads facing the injured cardiac muscle cells will record the action potential as ST elevation during systole while during

diastole Diastole ( ) is the relaxed phase of the cardiac cycle when the chambers of the heart are re-filling with blood. The contrasting phase is systole when the heart chambers are contracting. Atrial diastole is the relaxing of the atria, and ventri ...

, there will be depression of the PR segment and the PT segment. Since PR and PT interval are regarded as baseline, ST segment elevation is regarded as a sign of myocardial ischemia. The opposing leads (such as V3 and V4 versus posterior leads V7–V9) always show reciprocal ST segment changes (ST elevation in one lead is followed by ST depression in the opposing lead). This is highly specific for myocardial infarction. An upsloping, convex ST segment is highly predictive of a myocardial infarction ( Pardee sign) while a concave ST elevation is less suggestive and can be found in other non-ischaemic causes. Following infarction,

ventricular aneurysm Ventricular aneurysms are one of the many complications that may occur after a heart attack. The word aneurysm refers to a bulge or 'pocketing' of the wall or lining of a vessel commonly occurring in the blood vessels at the base of the septum, o ...

can develop, which leads to persistent ST elevation, loss of S wave, and T wave inversion. Weakening of the electrical activity of the cardiac muscles causes the decrease in height of the R wave in those leads facing it. In opposing leads, it manifests as Q wave. However, Q waves may be found in healthy individuals at lead I, aVL, V5 and V6 due to left to right depolarisation.

Myocarditis/pericarditis

In these conditions, there will mostly be concave ST elevations in almost all the leads except for aVR and V1. These two leads, ST depression will be seen because they are the opposing leads of the cardiac axis. PR segment depression is highly suggestive of pericarditis. R wave in most cases will be unaltered. In two weeks after pericarditis, there will be upward concave ST elevation, positive T wave, and PR depression. After several more weeks, PR and ST segments normalised with flattened T wave. At last, there will be T wave inversion which will take weeks or months to vanish.

Associated conditions

The topology and distribution of the affected areas depend on the underlying condition. Thus, ST elevation may be present on all or some leads of ECG. It can be associated with: *

Myocardial infarction A myocardial infarction (MI), commonly known as a heart attack, occurs when blood flow decreases or stops to the coronary artery of the heart, causing damage to the heart muscle. The most common symptom is chest pain or discomfort which may ...

(see also ECG in myocardial infarction). ST elevation in select leads is more common with myocardial infarction. ST elevation only occurs in full thickness infarction *

Prinzmetal's angina Variant angina, also known as Prinzmetal angina, vasospastic angina, angina inversa, coronary vessel spasm, or coronary artery vasospasm, is a syndrome typically consisting of angina (cardiac chest pain). Variant angina differs from stable angina ...

* Acute pericarditis ST elevation in all leads (diffuse ST elevation) is more common with acute pericarditis. * Left ventricular aneurysm * Blunt trauma to the chest resulting in a cardiac

contusion A bruise, also known as a contusion, is a type of hematoma of tissue, the most common cause being capillaries damaged by trauma, causing localized bleeding that extravasates into the surrounding interstitial tissues. Most bruises occur clos ...

Hyperkalemia Hyperkalemia is an elevated level of potassium (K+) in the blood. Normal potassium levels are between 3.5 and 5.0mmol/L (3.5 and 5.0mEq/L) with levels above 5.5mmol/L defined as hyperkalemia. Typically hyperkalemia does not cause symptoms. Occasi ...

* Acute myocarditis *

Pulmonary embolism Pulmonary embolism (PE) is a blockage of an artery in the lungs by a substance that has moved from elsewhere in the body through the bloodstream ( embolism). Symptoms of a PE may include shortness of breath, chest pain particularly upon breathin ...

* Brugada syndrome *

Hypothermia Hypothermia is defined as a body core temperature below in humans. Symptoms depend on the temperature. In mild hypothermia, there is shivering and mental confusion. In moderate hypothermia, shivering stops and confusion increases. In severe ...

* J-point elevation * Early repolarization * Subarachnoid hemorrhage

References