What is the ST segment in an electrocardiogram?

This is an automatically translated article.

The article was professionally consulted by Specialist Doctor II Nguyen Quoc Viet - Department of Medical Examination & Internal Medicine - Vinmec Danang International General Hospital. The doctor has more than 20 years of experience in the examination and treatment of cardiovascular diseases and Cardiovascular Interventions (Including angiography, dilation, stenting of coronary arteries, renal arteries...), placing temporary pacemakers , forever...
The normal ST segment lies on the isoelectric line, with very little difference up or down the isoelectric line. The image of ST-segment elevation or ST-segment depression on electrocardiogram results is valuable in the diagnosis of some cardiovascular diseases.

1. What is an ST segment?

On the electrocardiogram, the ST segment does not consist of a single wave but is a straight line from the end of the QRS to the beginning of the T wave. The ST segment represents the end of depolarization to the beginning of repolarization. pole.
ST segment is normal when 75% of ST segment is above the isoelectric line, if elevation is not more than 0.1 mV and depression is not more than 0.05 mV. In general, the ST segment does not curve but goes straight and smoothly continues into the T, nor does it ever go downhill, but only sideways or slightly uphill.
ST segment duration is relatively long and depends on heart rate. However, ST segment duration is of little clinical use. On the contrary, the shape and position of the ST segment relative to the isoelectric line is a new feature that is noticeable and meaningful in diagnosis.

Vị trí đoạn ST trên kết quả điện tâm đồ
Vị trí đoạn ST trên kết quả điện tâm đồ

2. ST segment elevation in what cases?

ST segment elevation is defined as ST elevation in at least two consecutive leads and the following conditions are met:
> 0.1 mV in the periphery and V4-V6 > 0.2 mV in V1-V3 ST segment elevation in the following conditions:
Acute ST-elevation myocardial infarction (acute STEMI): can produce short convex or concave ST elevation or indirect morphology, often with depression in the contralateral leads. Coronary vasospasm: causes ST-segment elevation similar to acute STEMI, but the ECG changes are transient, and the ST segment usually returns to normal when pain subsides or vasodilators are used. Electrocardiographic changes may not be distinguished. Benign early repolarization: causes mild ST elevation with T waves, often with a V-shaped notch of the J point. This is a normal variant, common in children and healthy patients. Left bundle branch block: Produces high ST with vertical T waves in leads with negative QRS (dominant S waves), while negative ST inversion reverses T waves in leads with positive QRS complexes. Acute pericarditis: Causes ST elevation but depression with PR depression in multiple leads. Commonly seen in I, II, III, aVF, aVL and V2-V6. In leads aVR and V1 there is reciprocal ST depression. Left ventricular hypertrophy: Causes an appearance similar to left bundle branch block, high ST in leads with deep S waves, usually V1-V3, and deep ST/T inversion in leads with high R (I, aVL) , V5-V6).

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Phì đại tâm thất trái
Phì đại tâm thất trái
Ventricular septal bulge: ECG results in ST elevation with deep Q waves and T wave inversion. Often associated with extensive myocardial damage and paradoxical left ventricular wall motion on echocardiography in patients after myocardial infarction. Autoventricular rhythm: causes ST segment abnormality, ST segment and T wave contrast to the main QRS vector, similar to images in left bundle branch block Brugada syndrome: ST segment elevation and partial right bundle branch block in V1- V2 with dome-shaped, saddle-shaped morphology.. Increased intracranial pressure due to traumatic brain injury, intracranial hemorrhage,... can cause ST elevation or undulation. In addition, ST segment elevation can also appear in a number of other diseases such as: acute pulmonary embolism, parasympathetic hypertonia, hyperkalemia, myocarditis, heart tumor, septic shock, shock anaphylaxis ,...

3. In what cases does ST segment depression appear?

ST-segment depression >0.5mm has diagnostic significance. There are many types of ST segment depression such as: oblique depression, horizontal depression, concave depression, descending depression, cup-shaped concave depression.
ST segment depression is common in the following conditions:
Myocardial ischemia: ST depression may be present in some leads, most commonly in the left precordial leads V4-V6 with wide ST depression and ST elevation in aVR in left main coronary artery occlusion. The corresponding ST elevation may be difficult to see but should be sought. Posterior MI: acute ST-segment elevation myocardial infarction causes symmetrical St depression in the anterior lead in V1-V3, along with a dominant R wave and a vertical T wave. ST elevation in lead V7-V9. Digoxin toxicity causes ST depression with a “hammock” appearance. Hypokalemia: causes wide ST-segment depression, flat/inverted T waves, prominent U waves, and a prolonged QU interval. Right ventricular hypertrophy: causes ST depression, T wave inversion in the right precordial lead V1-V3. Right bundle branch block: ST depression and T wave inversion in V1-V3. Supraventricular tachycardia: usually causes wide ST elevation and depression, prominent in the left precordial leads V4-V6.

Hình ảnh nhịp nhanh trên thất
Hình ảnh nhịp nhanh trên thất
In addition, ST segment depression is also seen in other diseases such as typical angina, asymptomatic coronary artery disease, acute myocardial necrosis, myocarditis, secondary cardiomyopathy,...
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