Nonspecific ST-T changes on the ECG. What is it in an adult, a child, during pregnancy, how to treat it

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Kuzhel, G.V. Matyushin, T.D. Fedorova E.A., Savchenko, T.M. Zadoenko KGUZ "Krasnoyarsk Regional Hospital No. 2" GOUVPO "Krasnoyarsk State Medical Academy"
An electrocardiogram in 12 standard leads is the method of choice in the diagnosis of acute myocardial infarction (AMI). Quick and accurate diagnosis of AMI is vital, as it makes it possible to immediately begin reperfusion therapy, which reduces the area of ​​necrosis and improves the patient's prognosis. One of the generally accepted criteria for myocardial infarction is ST segment elevation in two or more anatomically adjacent leads [10]. The importance of timely identification of ST segment elevation associated with AMI is emphasized by the fact that neither ST segment depression nor increased biochemical markers of cardiac necrosis (MCN) in the blood serum are indications for thrombolytic therapy [4, 9].

In the early stages of AMI, diagnosis can be significantly difficult, since the ECG is often normal or has minimal abnormalities. Moreover, only half of patients with AMI have obvious diagnostic changes on the first ECG. At the same time, approximately 10% of patients with proven AMI (based on clinical data and positive MCI) will not develop typical changes on the ECG, such as ST segment elevation or depression [4]. However, in most cases, serial ECGs in individuals with AMI show a characteristic evolution that usually corresponds to the typical changes observed in myocardial infarction. In the domestic school of cardiology, it is customary to distinguish four stages of the course of AMI [1].

I.
The most acute stage
. In this stage, which lasts from several hours to several days, changes in the ECG affect only the ST segment and the T wave. The earliest signs of acute myocardial infarction are difficult to distinguish and usually include an increase in the amplitude of the T wave in the affected area, which becomes symmetrical and directional ( hyperacute). Typically, hyperacute T waves are most evident in the anterior precordial leads and are most noticeable when an older ECG is available for comparison. Changes in T wave amplitude can be observed within a few minutes of the onset of infarction and are accompanied by corresponding changes in the ST segment. The optimal time for delivery of a patient to a medical facility is considered to be an interval of up to four hours from the onset of AMI. Unfortunately, ECG changes in the acute stage of myocardial infarction are often not properly assessed, which significantly increases the time it takes for the patient to be delivered to a specialized facility and prolongs the start of reperfusion therapy.

II. Acute stage.

In the acute stage, which usually lasts up to one week, ST segment elevation is recorded and Q waves begin to form. In practice, ST segment elevation is often the earliest sign of AMI and usually becomes noticeable within a few hours from the onset of symptoms. At the initial stages, the angle between the T wave and the ST segment, characteristic of a normal ECG, is lost. The T wave becomes wide and the ST segment rises, losing its normal concavity. During further ascent, the ST segment becomes convex upward. The degree of ST segment elevation varies between small changes of less than 1 mm to pronounced elevation of more than 10 mm. Sometimes the QRS complex, ST segment and T wave merge, forming the so-called monophasic curve.

III. Subacute stage.

The subacute stage of myocardial infarction lasts up to several weeks. During this stage, the ST segment begins to approach the isoline, and negative T waves are formed. In the case of transmural myocardial infarction, the necrosis process is accompanied by changes in the QRS complex, which include a decrease in the amplitude of the R waves and the development of pathological Q waves. Such changes develop as a result of the loss of viable myocardium under recording electrode, therefore Q waves are the only ECG criterion that verifies myocardial necrosis. Q waves can develop within 1 to 2 hours of the onset of AMI symptoms, although this often takes 12 to 24 hours. The presence of pathological Q waves, however, does not necessarily indicate a completed infarction. If ST segment elevation and Q waves are detected on the ECG and the chest pain is of recent onset, the patient may still benefit from thrombolysis or interventional therapy.

IV. Scar stage.

Consolidation of scar tissue ends on average 8 weeks after myocardial infarction. At this stage, the ST segment reverts to the isoline and the amplitude of negative T waves decreases. In the case of extensive myocardial infarction, pathological Q waves are a stable marker of cardiac necrosis. In small infarcts, scar tissue may include viable myocardium, which may reduce the size of the electrically inert region and even cause the eventual disappearance of Q waves.

One of the curious features of the ECG in AMI is the so-called pseudonormalization phenomenon. Wilson's theory of the formation of Q waves implies the formation of a so-called electrical window in case of necrosis, through which the recording electrode records the electrical potentials of the opposite wall. However, despite necrosis, some of the myocardial fibers in the infarction zone remain viable, which explains the characteristic flattening of Q waves during myocardial infarction. However, the potentials of these fibers remain hidden behind the powerful electric vector of the opposite wall. With a repeated infarction, which involves the opposite wall, this vector is significantly reduced, which, in turn, makes it possible to record the potentials of myocardial fibers in the area of ​​the old scar. As a result, in the area of ​​the old scar with pathological Q waves (for example, in the anterior wall), in the event of a re-infarction of the opposite wall (for example, the posterior wall), R waves begin to be recorded. Thus, the registration of R waves in the area where pathological Q waves were previously observed, strongly suggests the formation of an infarction in the opposite wall.

The T wave on the ECG is normal in children and adults

The beginning of the T wave coincides with the repolarization phase, that is, with the reverse transition of sodium and potassium ions through the membrane of heart cells, after which the muscle fiber becomes ready for the next contraction. Normally, T has the following characteristics:

• begins on the isoline after the S wave;
• has the same direction as the QRS (positive where R is dominant, negative when S is dominant);
• smooth in shape, the first part is flatter;
• amplitude T up to 8 cells, increases from 1 to 3 chest leads;
• may be negative in V1 and aVL, always negative in aVR.

In newborns, T waves are low in height or even flat, their direction is opposite to the adult ECG. This is due to the fact that the heart turns in direction and takes a physiological position by 2 - 4 weeks. At the same time, the configuration of the teeth on the cardiogram gradually changes. Typical features of a pediatric ECG:

• negative T in V4 persists up to 10 years, V2 and 3 – up to 15 years;
• adolescents and young adults may have negative T waves in the 1st and 2nd chest leads; this type of ECG is called juvenile;
• height T increases from 1 to 5 mm; in schoolchildren it is 3–7 mm (as in adults).

We recommend reading about how an ECG is performed. You will learn about the principles of operation of an electrocardiograph, preparation for an ECG, methods of conducting, and interpretation of indicators. And here is more information about what myocardial ischemia looks like on an ECG.

ECG interpretation

ECG interpretation plan

An electrocardiogram reflects only electrical processes in the myocardium: depolarization (excitation) and repolarization (restoration) of myocardial cells.

Correlation of ECG intervals with the phases of the cardiac cycle (ventricular systole and diastole).

Normally, depolarization leads to contraction of the muscle cell, and repolarization leads to relaxation.

To simplify further, instead of “depolarization-repolarization” I will sometimes use “contraction-relaxation”, although this is not entirely accurate: there is the concept of “electromechanical dissociation”, in which depolarization and repolarization of the myocardium do not lead to its visible contraction and relaxation.

Elements of a normal ECG

Before moving on to deciphering the ECG, you need to understand what elements it consists of.

Waves and intervals on the ECG. It is curious that abroad the PQ interval is usually called PR.

Any ECG consists of waves, segments and intervals.

Teeth are convex and concave areas on the electrocardiogram. The following waves are distinguished on the ECG:

• P (atrial contraction),
• Q, R, S (all 3 teeth characterize ventricular contraction),
• T (ventricular relaxation),
• U (non-permanent wave, rarely recorded).

SEGMENTS A segment on an ECG is a segment of a straight line (isoline) between two adjacent teeth. The PQ and ST segments are of greatest importance. For example, the PQ segment is formed due to a delay in the conduction of excitation in the atrioventricular (AV) node.

INTERVALS An interval consists of a tooth (a complex of teeth) and a segment. Thus, interval = tooth + segment. The most important are the PQ and QT intervals.

Waves, segments and intervals on the ECG. Pay attention to large and small cells (more about them below).

QRS complex waves

Since the ventricular myocardium is more massive than the atrial myocardium and has not only walls, but also a massive interventricular septum, the spread of excitation in it is characterized by the appearance of a complex QRS complex on the ECG.

How to correctly identify the teeth in it?

First of all, the amplitude (size) of individual waves of the QRS complex is assessed. If the amplitude exceeds 5 mm, the tooth is designated by a capital (capital) letter Q, R or S; if the amplitude is less than 5 mm, then lowercase (small): q, r or s.

The R wave (r) is any positive (upward) wave that is part of the QRS complex. If there are several teeth, subsequent teeth are indicated by strokes: R, R', R”, etc.

The negative (downward) wave of the QRS complex, located before the R wave, is designated as Q (q), and after - as S (s). If there are no positive waves at all in the QRS complex, then the ventricular complex is designated as QS.

Variants of the QRS complex.

Fine:

the Q wave reflects depolarization of the interventricular septum (the interventricular septum is excited)

R wave - depolarization of the bulk of the ventricular myocardium (the apex of the heart and adjacent areas are excited)

S wave - depolarization of the basal (i.e. near the atria) parts of the interventricular septum (the base of the heart is excited)

The RV1, V2 wave reflects the excitation of the interventricular septum,

and RV4, V5, V6 - excitation of the muscles of the left and right ventricles.

Necrosis of areas of the myocardium (for example, during myocardial infarction) causes expansion and deepening of the Q , so close attention is always paid to this wave.

ECG analysis

General scheme of ECG decoding

1. Checking the correctness of ECG registration.
2. Heart rate and conduction analysis:
   assessment of heart rate regularity,
3. heart rate (HR) counting,
4. determination of the source of excitation,
5. conductivity assessment.
6. Determination of the electrical axis of the heart.
7. Analysis of the atrial P wave and P-Q interval.
8. Analysis of the ventricular QRST complex:
   QRS complex analysis,
9. analysis of the RS - T segment,
10. T wave analysis,
11. Q-T interval analysis.
12. Electrocardiographic report.

Normal electrocardiogram.

1) Checking the correctness of ECG registration

At the beginning of each ECG tape there must be a calibration signal - the so-called control millivolt. To do this, a standard voltage of 1 millivolt is applied at the beginning of the recording, which should display a deviation of 10 mm on the tape. Without a calibration signal, the ECG recording is considered incorrect.

Normally, in at least one of the standard or enhanced limb leads, the amplitude should exceed 5 mm, and in the chest leads - 8 mm. If the amplitude is lower, this is called reduced ECG voltage, which occurs in some pathological conditions.

2) Heart rate and conduction analysis:

1. assessment of heart rate regularity

   Rhythm regularity is assessed by RR intervals. If the teeth are at an equal distance from each other, the rhythm is called regular, or correct. The spread of the duration of individual RR intervals is allowed no more than ± 10% of their average duration. If the rhythm is sinus, it is usually regular.

2. heart rate (HR) counting

   The ECG film has large squares printed on it, each of which contains 25 small squares (5 vertical x 5 horizontal).

   To quickly calculate heart rate with the correct rhythm, count the number of large squares between two adjacent R-R waves.

   At a belt speed of 50 mm/s: HR = 600 / (number of large squares). At a belt speed of 25 mm/s: HR = 300 / (number of large squares).

   At a speed of 25 mm/s, each small cell is equal to 0.04 s,

   and at a speed of 50 mm/s - 0.02 s.

   This is used to determine the duration of the teeth and intervals.

   If the rhythm is abnormal, the maximum and minimum heart rate is usually calculated according to the duration of the shortest and longest RR interval, respectively.

3. determination of the excitation source

   In other words, they are looking for where the pacemaker is located, which causes contractions of the atria and ventricles.

   Sometimes this is one of the most difficult stages, because various disorders of excitability and conduction can be very confusingly combined, which can lead to incorrect diagnosis and incorrect treatment.

   To correctly determine the source of excitation on an ECG, you need to have a good knowledge of the conduction system of the heart.

   SINUS rhythm (this is a normal rhythm, and all other rhythms are pathological). The source of excitation is located in the sinoatrial node.

   Signs on the ECG:

   • in standard lead II, the P waves are always positive and are located before each QRS complex,

   P waves in the same lead have the same shape at all times.

P wave in sinus rhythm.

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ATRIAL rhythm. If the source of excitation is located in the lower parts of the atria, then the excitation wave propagates to the atria from bottom to top (retrograde), therefore:

• in leads II and III the P waves are negative,
• There are P waves before each QRS complex.

P wave during atrial rhythm.

Rhythms from the AV connection. If the pacemaker is located in the atrioventricular (atrioventricular node) node, then the ventricles are excited as usual (from top to bottom), and the atria are excited retrogradely (i.e. from bottom to top).

At the same time, on the ECG:

• P waves may be absent because they are superimposed on normal QRS complexes,
• P waves can be negative, located after the QRS complex.

Rhythm from the AV junction, superimposition of the P wave on the QRS complex.

Rhythm from the AV junction, the P wave is located after the QRS complex.

Heart rate with a rhythm from the AV junction is less than sinus rhythm and is approximately 40-60 beats per minute.

Ventricular, or IDIOVENTRICULAR, rhythm

In this case, the source of rhythm is the ventricular conduction system.

Excitation spreads through the ventricles in the wrong way and is therefore slower. Features of idioventricular rhythm:

• QRS complexes are widened and deformed (they look “scary”). Normally, the duration of the QRS complex is 0.06-0.10 s, therefore, with this rhythm, the QRS exceeds 0.12 s.
• There is no pattern between QRS complexes and P waves because the AV junction does not release impulses from the ventricles, and the atria can be excited from the sinus node, as normal.
• Heart rate less than 40 beats per minute.

Idioventricular rhythm. The P wave is not associated with the QRS complex.

Measuring the internal deviation interval.

3) Determination of the electrical axis of the heart.

4) Analysis of the atrial P wave.

• Normally, in leads I, II, aVF, V2 - V6, the P wave is always positive.
• In leads III, aVL, V1, the P wave can be positive or biphasic (part of the wave is positive, part is negative).
• In lead aVR, the P wave is always negative.
• Normally, the duration of the P wave does not exceed 0.1 s, and its amplitude is 1.5 - 2.5 mm.

Pathological deviations of the P wave:

• Pointed high P waves of normal duration in leads II, III, aVF are characteristic of hypertrophy of the right atrium, for example, with “cor pulmonale”.
• Split with 2 apexes, widened P wave in leads I, aVL, V5, V6 is characteristic of left atrium hypertrophy, for example, with mitral valve defects.

Formation of the P wave (P-pulmonale) with hypertrophy of the right atrium.

Formation of the P wave (P-mitrale) with left atrial hypertrophy.

4) PQ interval analysis:

normally 0.12-0.20 s.

An increase in this interval occurs when the conduction of impulses through the atrioventricular node is impaired (atrioventricular block, AV block).

There are 3 degrees of AV block:

• I degree - the PQ interval is increased, but each P wave corresponds to its own QRS complex (there is no loss of complexes).
• II degree - QRS complexes partially fall out, i.e. Not all P waves have their own QRS complex.
• III degree - complete blockade of conduction in the AV node. The atria and ventricles contract at their own rhythm, independently of each other. Those. idioventricular rhythm occurs.

5) Analysis of the ventricular QRST complex:

1. analysis of the QRS complex.
   • The maximum duration of the ventricular complex is 0.07-0.09 s (up to 0.10 s).

   The duration increases with any bundle branch block.

2. Normally, the Q wave can be recorded in all standard and enhanced limb leads, as well as in V4-V6.
3. The amplitude of the Q wave normally does not exceed 1/4 of the height of the R wave, and the duration is 0.03 s.
4. In lead aVR, there is normally a deep and wide Q wave and even a QS complex.
5. The R wave, like the Q wave, can be recorded in all standard and enhanced limb leads.
6. From V1 to V4, the amplitude increases (while the rV1 wave may be absent), and then decreases in V5 and V6.
7. The S wave can have very different amplitudes, but usually no more than 20 mm.
8. The S wave decreases from V1 to V4, and may even be absent in V5-V6.
9. In lead V3 (or between V2 - V4), a “transition zone” is usually recorded (equality of the R and S waves).
10. RS-T segment analysis
    • The ST segment (RS-T) is the segment from the end of the QRS complex to the beginning of the T wave. — — The ST segment is analyzed especially carefully in case of coronary artery disease, since it reflects the lack of oxygen (ischemia) in the myocardium.

    Normally, the ST segment is located in the limb leads on the isoline (± 0.5 mm).

11. In leads V1-V3, the ST segment may shift upward (no more than 2 mm), and in leads V4-V6 - downward (no more than 0.5 mm).
12. The transition point of the QRS complex to the ST segment is called point j (from the word junction - connection).
13. The degree of deviation of point j from the isoline is used, for example, to diagnose myocardial ischemia.
14. T wave analysis.
    • The T wave reflects the process of repolarization of the ventricular myocardium.

    In most leads where a high R is recorded, the T wave is also positive.

15. Normally, the T wave is always positive in I, II, aVF, V2-V6, with TI> TIII, and TV6> TV1.
16. In aVR the T wave is always negative.
17. Q-T interval analysis.
    • The QT interval is called electrical ventricular systole, because at this time all parts of the ventricles of the heart are excited.

    Sometimes after the T wave a small U wave is recorded, which is formed due to short-term increased excitability of the ventricular myocardium after their repolarization.

6) Electrocardiographic report. Should include:

1. Source of rhythm (sinus or not).
2. Regularity of rhythm (correct or not). Usually sinus rhythm is normal, although respiratory arrhythmia is possible.
3. Heart rate.
4. Position of the electrical axis of the heart.
5. Presence of 4 syndromes:
   rhythm disturbance
6. conduction disturbance
7. hypertrophy and/or overload of the ventricles and atria
8. myocardial damage (ischemia, dystrophy, necrosis, scars)

ECG interference

In connection with frequent questions in the comments about the type of ECG, I will tell you about the interference that may be on the electrocardiogram:

Three types of ECG interference (explained below).

Interference on an ECG in the lexicon of health workers is called interference: a) induction currents: network interference in the form of regular oscillations with a frequency of 50 Hz, corresponding to the frequency of alternating electric current in the outlet. b) “swimming” (drift) of the isoline due to poor contact of the electrode with the skin; c) interference caused by muscle tremors (irregular frequent vibrations are visible).

ECG analysis algorithm: determination method and basic standards

ECG changes and their meanings

Most often, changes are suspected of coronary heart disease, but such a disorder may be a sign of other diseases:

• thromboembolism,
• myocarditis, pericarditis,
• tumors, infections and injuries,
• ventricular hypertrophy,
• intoxication, including cardiac glycosides, antiarrhythmic drugs, aminazine, nicotine,
• stress, neurocirculatory dystonia,
• diseases of the endocrine system,
• potassium deficiency,
• decreased blood circulation in the brain,
• osteochondrosis.

Therefore, to make a diagnosis, all clinical signs and changes in the cardiogram are taken into account as a whole.

Two-phase

On the cardiogram, T first decreases below the isoline, and then crosses it and becomes positive. This symptom is called the “roller coaster” syndrome. May occur in the following pathologies:

• left ventricular hypertrophy;
• Hiss bundle branch block;
• increased calcium levels in the blood;
• intoxication with cardiac glycosides.

Biphasic T wave with left ventricular hypertrophy

Smoothed

Flattening of the T wave can be caused by:

• taking alcohol, Cordarone or antidepressants;
• diabetes mellitus or eating a lot of sweets;
• fear, excitement;
• cardiopsychoneurosis;
• hypokalemia;
• myocardial infarction in the scarring stage.

Decrease in indicator

A reduced T is indicated by its amplitude, which is less than 10% of the QRS complex. This symptom on the ECG causes:

• coronary insufficiency,
• cardiosclerosis,
• obesity,
• elderly age,
• hypothyroidism,
• dishormonal cardiomyopathy,
• myocardial dystrophy,
• taking corticosteroids,
• anemia,
• tonsillitis.

The T wave on the ECG is smoothed

The T wave can be smoothed in the same conditions as an absent wave, since both definitions characterize low-amplitude oscillations. It should be taken into account that violation of the rules for ECG registration can also cause smoothing of T. It also occurs in metabolic diseases - low function of the thyroid gland (myxedema, hypothyroidism). It can be found in completely healthy people throughout the day in several cardiac cycles (according to Holter monitoring).

Inversion

Inversion (turning over) of the T wave means a change in its position relative to the isoline, that is, in leads with a positive T, it changes its polarity to negative and vice versa. Such deviations can also be normal - in the right chest leads with a juvenile ECG configuration or a sign of early repolarization in athletes.

T wave inversion in leads II, III, aVF, V1-V6 in a 27-year-old athlete

Diseases that are accompanied by T inversion:

• myocardial or cerebral ischemia,
• influence of stress hormones,
• bleeding in the brain,
• attack of tachycardia,
• violation of impulse conduction along the branches of the Hiss bundle.

Negative T wave

For coronary heart disease, a characteristic sign is the appearance of negative T waves on the ECG, and if they are accompanied by changes in the QRS complex, then the diagnosis of a heart attack is considered confirmed. In this case, changes in the cardiogram depend on the stage of myocardial necrosis:

• acute – abnormal Q or QS, ST segment above the line, T positive;
• subacute – ST on the isoline, negative T;
• in the scar stage, weakly negative or positive T.

A negative T wave in leads V5-V6 (highlighted in red) indicates ischemia.
A variant of the norm may be the appearance of negative T wave with frequent breathing, excitement, after a heavy meal, which contains a lot of carbohydrates, as well as with individual characteristics in some healthy people. Therefore, the detection of negative values ​​cannot be considered a serious illness.

Pathological conditions that are accompanied by negative T waves:

• heart disease - angina pectoris, heart attack, cardiomyopathy, inflammation of the myocardium, pericardium, endocarditis, mitral valve prolapse;
• violation of hormonal and nervous regulation of cardiac activity (thyrotoxicosis, diabetes mellitus, diseases of the adrenal glands, pituitary gland);
• pulmonary heart;
• after paroxysmal tachycardia or frequent extrasystoles;
• subarachnoid hemorrhage.

Subarachnoid hemorrhage is accompanied by negative T waves

Absence of T wave on ECG

The absence of T on the ECG means that its amplitude is so low that it merges with the isoelectric line of the heart. This happens when:

• drinking alcohol;
• against the backdrop of excitement, anxiety;
• cardiomyopathy in patients with diabetes mellitus;
• neurocirculatory dystonia (with a sudden change in body position or after rapid breathing);
• insufficient intake of potassium or its loss through sweat, urine, intestinal contents (diarrhea);
• scarring of myocardial infarction;
• use of antidepressants.

High rate

Normally, in those leads where the highest R is recorded, the maximum amplitude is noted; in V3 - V5 it reaches 15 - 17 mm. Very high T can occur when the influence on the heart of the parasympathetic nervous system, hyperkalemia, subendocardial ischemia (first minutes), alcoholic or menopausal cardiomyopathy, left ventricular hypertrophy, and anemia predominate.

Changes in the T wave on the ECG during ischemia: a - normal, b - negative symmetrical "coronary" T wave, c - high positive symmetrical "coronary" T wave, d, e - biphasic T wave, f - reduced T wave, g - smoothed T wave, z - weakly negative T wave.

Flat

A slightly inverted or flattened T may be either a normal variant or a manifestation of ischemic and dystrophic processes in the heart muscle. It occurs with complete blockade of the conduction pathways in the ventricles, myocardial hypertrophy, acute or chronic pancreatitis, taking antiarrhythmic medications, and hormonal and electrolyte imbalance.

Coronary

When the heart muscle is hypoxic, the fibers located under the inner membrane, the endocardium, are most affected. The T wave reflects the ability of the endocardium to maintain a negative electrical potential, therefore, in case of coronary insufficiency, it changes its direction and becomes this shape:

• isosceles;
• negative (negative);
• pointed.

These signs characterize the ischemic wave, or it is also called coronary. Manifestations on the ECG are maximum in those leads where the greatest damage is localized, and in mirror (reciprocal) leads it is sharp and isosceles, but positive. The more pronounced the T wave, the deeper the degree of myocardial necrosis.

Rise of the T wave on the ECG

Moderate physical stress, hyperkalemia, infectious processes in the body, thyrotoxicosis, and anemia lead to an increase in the amplitude of T waves. Elevated T without changes in well-being can occur in healthy people, and can also be a symptom of vegetative-vascular disorders with a predominance of vagal tone.

Depression

A reduced T wave can be a manifestation of cardiomyodystrophy; it occurs with pneumonia, rheumatism, scarlet fever, acute inflammatory process in the kidneys, cor pulmonale and hypertrophic increase in the muscular layer of the myocardium.

The T wave is positive

Normally, T waves in leads should be positive: first, second standard, aVL, aVF, V3-V6. If it appears where in healthy people it is negative or close to the isoelectric line, then this indicates a lack of blood flow through the arteries of the heart (myocardial ischemia), blockade of the branches of the His bundle. Temporary changes are caused by stress, an attack of rapid heartbeat, and intense exercise in athletes.

Heart ST depression

Depression of the ST segment, or its decrease relative to the isoline by more than 1 mm, is a clinically significant sign. Such a change can be caused by both nonspecific and specific reasons, which are discussed below.

Non-cardiac and physiological causes include:

• errors on the part of medical staff when taking an ECG - incorrect application of electrodes or their poor contact with the patient’s skin;
• water and electrolyte disturbances that occur when drinking sea water in large quantities, dehydration, alcohol abuse, salt-free diet, anorexia, heavy physical activity, use of diuretics, as well as certain pathologies (diseases of the kidneys, gastrointestinal tract, thyroid gland, burns, significant blood loss);
• drinking very cold water;
• hyperventilation (increased air exchange in the human body).

What does ECG mean in decoding?

Nonspecific ST-T changes on the ECG in the form of its decrease relative to the isoelectric line are primarily associated with cardiac ischemia, as the most dangerous condition that can lead to death.

However, this change is nonspecific and can also occur with other disorders of the heart. To correctly interpret this deviation, differential diagnosis is necessary.

Why is the ST segment reduced in adults and children?

A decrease in the ST area on the ECG in adults and children can occur in the following cases:

• Myocardial infarction with absence of ST elevation. In this case, depression of the segment is observed in two or more leads (by lead is meant the difference in biopotentials between two points of the body, for example, right hand - left hand). This type of coronary insufficiency is less common than elevation of the segment infarction (about 28% of all cases), but in recent years there has been an increase in incidence. The cause of this disorder is most often blockage of the coronary artery by a thrombus, which leads to a significant deterioration in the blood supply to the heart muscle and the development of necrosis in the tissues. The development of this condition can be triggered by stress, anemia, and infectious and inflammatory pathologies.
• Unstable angina (58% of all cases) is an intermediate condition in coronary heart disease, when the risk of developing myocardial infarction is high. The most common cause is atherosclerotic plaques in the coronary vessels of the heart, closing their lumen by ¾ or more. Risk factors are arterial hypertension, tachycardia, physical and emotional stress, consumption of heavy food and alcohol, which increases the load on the heart and causes a lack of oxygen.
• Inflammatory lesions of the heart muscleappearing against the background of infectious diseases (including influenza and respiratory pathologies).

• Toxic effects of ethanol in alcohol abuse. In this case, there is an accumulation of fatty tissue in the heart muscle and an expansion of all the cavities of the heart. At the initial stage, this disorder can be reversible, that is, giving up alcoholic beverages contributes to a significant improvement in function.
• Changes in hormonal levels during menopause in women. The main factor in menopausal cardiomyopathy is a decrease in estrogen production, which contributes to the formation of protein deficiency in the myocardium.
• Dilated cardiomyopathy , in which stretching of the cavities of the heart develops. At the same time, heart failure progresses, the rhythm and conductivity of this organ are disrupted.
• Enlargement of the right chambers of the heart due to embolism (blockage) of the pulmonary artery, severe attack of bronchial asthma, pneumonia, accumulation of air in the pleural cavity.
• Intoxication with cardiac glycosides. Heart failure does not occur immediately, but as the drug accumulates in the blood.
• Paroxysmal tachycardia , detected in elderly people.

In pregnant women, disorders associated with the ST segment are most often caused by physiological reasons - changes in the anatomical position of the heart. Therefore, if such a condition is not accompanied by complaints or a history of cardiac pathologies, then treatment is not required. In doubtful cases, the doctor may prescribe an echocardiogram.

Types of segment reduction

There are 3 types of ST depression:

• obliquely ascending, occurring against the background of tachycardia and being a variant of the norm;
• horizontal, often serving as a sign of ischemic processes in the myocardium;
• oblique, also a symptom of cardiac muscle dysfunction.

To accept the above-described phenomena as normal, the doctor must first exclude possible pathological causes.

Symptoms of deviation

Patients may experience the following symptoms as subjective symptoms:

• Myocardial ischemia:

1. severe pain, feeling of pressure, heaviness behind the sternum;
2. in women, pain can often radiate to the neck and arm;
3. dyspnea;
4. arrhythmia;
5. general weakness;
6. cough;
7. in more rare cases - nausea, vomiting, bloating, dizziness, darkening of the eyes, cold sweat, swelling.

• Unstable angina:

1. painful attacks lasting 1-10 minutes, similar in nature to the previous case;
2. increased symptoms when walking, physical and emotional stress;
3. signs subside when taking nitroglycerin.

• Alcoholic cardiomyopathy:

1. heartache;
2. dyspnea.

• Menopausal cardiomyopathy:

1. pressing pain in the upper region of the heart;
2. At the same time, other symptoms occur - facial redness, sweating, feeling hot;
3. increased symptoms are not associated with physical activity and are not relieved by nitroglycerin.

• Intoxication with glycosides:

1. nausea, vomiting, diarrhea;
2. severe arrhythmia;
3. tachycardia.

Differential diagnosis

Nonspecific ST-T changes require differential diagnosis taking into account medical history, additional studies and analysis of other indicators on the ECG.

To detect acute myocardial infarction, rapid determination of cardiac markers in the blood (globular protein troponin, oxygen-binding protein myoglobin, creatine kinase-MB) is used. For angina pectoris, this test shows negative results.

With alcoholic cardiomyopathy, making a diagnosis usually does not cause difficulties even after interviewing the patient. Painful attacks usually occur the day after alcohol abuse.

Pulmonary embolism is accompanied by a sharp increase in pressure in the right parts of the heart and their expansion, coronary insufficiency occurs, and on the ECG graph the electrical axis of the heart deviates to the right.

In case of an overdose of cardiac glycosides, the ECG shows a rarer heart rhythm, short electrical systole, and a trough-shaped appearance of the ST segment.

Emergency (first) aid for depression

As medical statistics show, about 70% of patients with acute myocardial infarction die in the first 6 hours.

First aid consists of the following activities:

1. Call an emergency medical team.
2. If the patient is conscious, give him 1 tablet of nitroglycerin under the tongue.

3. Provide the patient with peace and fresh air, unfasten his clothes.
4. If the patient is alone in the house, open the door to provide free access to the ambulance team, sit down and cough forcefully to induce blood flow to the heart.

Treatment of conditions accompanied by ST depression

Treatment of the most severe and dangerous condition - myocardial infarction - is carried out using the basic means indicated in the table below.

All patients also undergo oxygen therapy - oxygen supply through a mask or catheter, which is inserted into the nasal passages. This procedure allows you to saturate the blood with oxygen and reduce the degree of ischemic damage to the myocardium.

Nonspecific T wave changes

Nonspecific changes in the T wave include all its deviations from the norm that cannot be associated with any disease. There are such ECG descriptions:

• variant of the norm;
• with strong compression of the limbs with electrode cuffs;
• after taking cardiac glycosides, diuretics, and some drugs to lower blood pressure;
• with frequent and intense breathing;
• due to abdominal pain;
• associated with an imbalance of the main blood electrolytes (sodium, potassium, calcium, magnesium) with vomiting, diarrhea, dehydration, and drinking alcohol on the eve of diagnosis.

In the absence of symptoms (heart pain, shortness of breath, rapid resting pulse, rhythm disturbances, swelling, enlarged liver), such changes are considered minor and do not require treatment. If there are signs of cardiac disease, then daily Holter ECG monitoring is necessary to clarify the diagnosis. It will show whether the restoration of cardiac polarity will be impaired during normal physical activity.

In some cases, nonspecific disturbances in the shape and size of the T wave occur when:

• insufficient nutrition of the myocardium (ischemic disease);
• increased blood pressure, especially with concomitant hypertrophy (thickening of the heart muscle) of the left ventricle;
• violation of intraventricular conduction (branch block).

A synonym for nonspecific changes in the T wave is a doctor’s conclusion: a violation of ventricular repolarization.

Double-humped T wave

Double-humped T waves are their shape, in which instead of one dome-shaped tip, 2 waves appear on the ECG. Such changes most often occur with a lack of potassium. This is manifested by the appearance of a distinct U wave, which is normally indistinguishable. With a pronounced lack of a microelement, this rise is so pronounced that the wave reaches the T level and can even overtake it in amplitude.

Possible causes of double-humped T include:

• the use of diuretics that remove potassium;
• laxative abuse;
• diarrhea, vomiting due to infection;
• long-term use of antibiotics, hormones;
• profuse sweating;
• diseases of the kidneys, adrenal glands, intestines;
• overdose of vitamin B12 and folic acid.

Discordant T wave

A T wave is called discordant if its direction is opposite to the ventricular QRS complex. It happens with bundle branch block, as well as during the period of restoration of blood circulation in the heart muscle after a heart attack.

Discordant T-waves may also appear in cases of severe hypertrophy of the left ventricular myocardium, as well as Wellens syndrome - blockage of the left anterior coronary artery. The latter condition is characterized by attacks of angina-type pain, a high risk of heart attack and the absence of other significant ECG changes, except for the direction of T, and normal blood tests.

Tall T waves in precordial leads

Tall T waves in the chest leads are accompanied by angina pectoris. It can be both stable and progressive, that is, threatening the development of myocardial infarction. In this case, it is important to take into account the clinical picture and other ECG changes. A typical sign of ischemic waves is their symmetry.

High T can also manifest itself as:

• hyperkalemia (excessive intake of potassium, taking drugs that inhibit its excretion);
• anemia;
• circulatory disorders in the brain;
• left ventricular hypertrophy.

Dynamics of changes in the ST segment and T wave in AMI

The ECG picture during myocardial infarction has its own characteristic development. Firstly, ST segment elevation, as a rule, leads to the formation of Q waves. Secondly, the formation of negative T waves occurs against the background of a characteristic arcuate ST segment elevation.

ST segment elevation associated with myocardial infarction in the anterior wall can persist for a long time if dyskinesia or left ventricular (LV) aneurysm develops. Negative T waves can also persist for a long period and sometimes remain a permanent sign of myocardial infarction. It should be noted that the absence of formation or “restoration” of pre-inverted T waves in the acute stage of myocardial infarction strongly suggests the development of post-infarction pericarditis [11].

T wave alternation

T wave alternans is understood as any change during exercise: on a treadmill, exercise bike, or administration of medications compared to the ECG at rest. One of the options is to analyze the daily recording (monitoring) of the cardiogram.

The doctor may discover that the shape, direction, duration of T, and its amplitude (height) have changed. But there are also micro-changes that are found when analyzed with special equipment - signal-averaged ECG.

By identifying T wave alternans, the electrical instability of the heart muscle is determined. This means that under the influence of stress or stress, a life-threatening arrhythmia with cardiac arrest can occur. Studying the characteristics of T is necessary if you have:

• changes in the duration of the QT interval;
• cardiomyopathy due to arrhythmia;
• ventricular tachycardia;
• ventricular fibrillation.

For information on changes in the T wave on an ECG, watch this video:

Normal QT interval

Normally, the QT interval does not have a constant value. The distance from the beginning of Q to the end of T depends on:

• gender and age of the subject;
• time of day;
• states of the nervous system;
• use of medications, especially analogues of stress hormones (Adrenaline, Dopamine, Hydrocortisone);
• calcium, magnesium and potassium levels in the blood.

The most significant dependence can be traced to heart rate. Therefore, the calculation formulas that take this indicator into account have been continued. The faster the heart rate, the shorter the QT. When mathematically analyzing ECG data from healthy people, an approximate pattern was derived and is reflected in the table.

What is the ST segment?

The ST segment is one of the sections of the electrocardiogram - a recording on which the electrical impulses of the heart are recorded. The work of this organ is regulated with the help of a pacemaker in the sinus node, which produces 60-90 impulses every minute.

The latter cover various areas of the heart muscle (myocardium) with excitation and are recorded on paper tape in the form of an ECG curve.

The segment of the graph, marked with the Latin letters ST, displays the part of the heart cycle when slow repolarization of the ventricles occurs, that is, their relaxation before subsequent contraction. Cardiac muscle cells cannot remain excited for a long time.

The leading role in the processes of extinction of myocardial activity is played by the coordinated work of the potassium-sodium pump, the return of sodium ions to their original state. Since electrical activity is low during this period, the ST segment should normally be in a straight line between two adjacent teeth.

Its duration (length on the graph) depends on the heart rate; the higher it is, the shorter the segment. The exact duration is difficult to measure and has little clinical significance.

Shortening of the QT interval on the ECG

Shortening the QT interval on the ECG is dangerous, as it provokes complex types of rhythm disturbances. This syndrome can be a congenital feature, and also appears when:

• treatment with cardiac glycosides in the usual dose, progresses with its increase;
• increased concentrations of potassium and calcium in the blood;
• fever;
• a shift in the blood reaction to the acidic side (acidosis).

Short QT syndrome can be constant and repeated from cycle to cycle or paroxysmal due to changes in heart rate. Patients with such disorders are prone to dizziness, lightheadedness, and sudden loss of consciousness. In severe cases, there is a risk of sudden cardiac arrest.

Nonspecific ST-T changes

Nonspecific ST-T changes include all minor violations of ST height, smoothing or the opposite direction of T. They “do not reach” obvious pathologies, but the doctor pays attention to them when deciphering them. This can be important, since if there are complaints of heart pain, further examination is necessary. It is also carried out with risk factors:

• high pressure,
• smoking,
• elderly age,
• high cholesterol,
• sedentary lifestyle.

The main causes of nonspecific symptoms include:

• imbalance of electrolytes (potassium, magnesium, calcium);
• use of medications;
• angina pectoris;
• infectious diseases, pulmonary pathology;
• pain attack;
• consumption of large amounts of food, alcoholic beverages;
• left ventricular hypertrophy;
• cerebrovascular accident.

Since all these factors are diverse, when making a diagnosis, the doctor takes into account the symptoms and, if necessary, prescribes blood tests, an ECG using the Holter method (24-hour monitoring), and stress tests with exercise.

What are nonspecific ST-T changes on an ECG?

Nonspecific ST-T changes on the ECG can occur with various disorders - from infectious diseases to myocardial infarction. This ECG parameter is sensitive to the influence of many factors, that is, it cannot serve as the only diagnostic criterion for a certain pathology. Therefore, its changes are called nonspecific.

They do not have much diagnostic value, but their occurrence requires additional research, since in combination with other characteristics they can indicate serious diseases that lead to serious complications.

As mentioned above, this section should be on an isoline.

However, its deviation is allowed in the following cases:

• a decrease of 0.5 mm, especially if the T wave, reflecting the ability of the myocardium to hold the electrical potential, is characterized by a small amplitude or it is negative, that is, the phenomenon of inversion is observed (inversion relative to the isoline);
• an increase of 1.5-2 mm with a high positive T wave, while the segment has a concave shape;
• ST elevation up to 3-3.5 mm with a deep S wave and a high positive T wave. Its elevation occurs in this case gradually, that is, the segment actually turns into a T wave.

Sometimes doctors mistake these variants of the norm for deviations and make an incorrect diagnosis.

ST segment elevation

ST segment elevation occurs in the following diseases:

Increasing the segment is a variant of the norm. In this case:

• the ST dome is directed downward, turns into a unipolar (concordant) T;
• T extended;
• changes can be traced in all leads and cycles.

Rising (elevation) can be caused by an increased concentration of potassium in the blood, inflammation (myocarditis) and a tumor process in the heart.

We recommend reading about the normal ECG in children. From the article you will learn about why children undergo an ECG, indications for examination, rules of conduct, decoding of indicators in children of different ages. And here is more information about ECG for myocarditis.

ST segment elevation

Nonspecific ST-T changes on the ECG in the form of elevation, or a higher position of the segment, in some cases are also a variant of the norm. This deviation can reach 3.5 mm in persons under 40 years of age. However, this nonspecific sign also serves as a criterion for damage to the basal sections or septum of the heart.

What does the ECG mean?

Pathological upward displacement of the ST segment above the isoelectric line is accompanied by a change in its shape:

• combination of a pronounced rise with an unrounded surface;
• horizontal flow with convexity upward;
• the excess of the amplitude of the T wave over the rise of the segment is no more than 1 mm.

  
  Nonspecific ST-T changes on ECG

Normally, the ST is a straight horizontal or gently rising line that merges with the T, or has a convexity that faces downwards (crescent shape). In healthy people, segmental displacement with a deep S wave and a high T wave in the right precordial leads may also be observed. In doubtful cases, the patient undergoes a dynamic electrocardiographic study.

Causes in adults, children

The reasons for the higher position of this segment may be the following violations:

• Acute myocardial infarction. This is the most common pathology in which ST elevation is observed. During an attack, the segment on the ECG graph has a convex shape (“cat’s back”) and smoothly passes into the left knee of the positive T wave. Subsequently, the segment acquires a curved shape, and the T wave becomes negative, and a deep pathological Q wave appears. The rise of this section of the graph indicates about ischemic myocardial damage with complete blockage of one of the coronary arteries.
• Prinzmetal's angina. This disorder is rare in patients with chest pain - in 2-3% of cases. This deviation is based on spasm of the coronary arteries, which occurs due to an imbalance between constrictor and dilating factors (constricting and relaxing blood vessels) and the increased sensitivity of the coronary vessels to them.
• Dressler syndrome , developing in 1-3% of patients after a major myocardial infarction. The cause of this disease is autoimmune aggression and damage to the connective tissue lining of the heart.
• Early ventricular repolarization syndrome , detected in 1-9% of patients. At risk are athletes and men leading a sedentary lifestyle, people with diseases of the connective tissue and cardiovascular system. This condition can be provoked by taking alpha-adrenergic agonists, hypothermia, and lipid metabolism disorders. The severity of the disease also depends on genetic predisposition.
• Post-infarction ventricular aneurysm , when a section of the wall can gradually protrude outward during the ejection of blood into the aorta. Ultimately, part of the left ventricle expands and heart failure develops.
• Brugada syndrome , which is a genetic disorder of the heart rhythm.

Clinical manifestations

Nonspecific ST-T changes on the ECG during elevation may be accompanied by the following symptoms:

• Myocardial infarction:

1. a few weeks before an acute condition - angina pectoris and rest, increased frequency of attacks;
2. Otherwise, the symptoms are similar to those of a heart attack with segment depression.

• Dressler's syndrome:

1. pain or discomfort in the heart;
2. general malaise;
3. temperature increase;
4. chills;
5. increased sweating;
6. shallow breathing;
7. red or pink skin rash;
8. cough with moist wheezing.

• Early ventricular repolarization syndrome is often asymptomatic, and arrhythmia occurs in some patients.
• Prinzmetal's angina is angina that occurs regardless of external factors.
• Brugada syndrome - frequent short-term fainting.

Diagnostics

Diagnosis of acute myocardial infarction in this case is made in the same way as in the previous case. A dynamic ECG study, determination of cardiac markers, and echocardiography are performed. For Prinzmetal's angina, coronary angiography is done to study blood flow in the coronary arteries.

Dressler's syndrome is detected using laboratory blood tests (increased ESR, leukocytosis, eosinophilia, C-reactive protein), echocardiography (marked dilatation of the left ventricle, fluid in the pericardial cavity), radiography (pleural effusion). Left ventricular aneurysm is also determined using echocardiography.

Features of treatment

Features of the treatment of the above diseases are the following:

• Prinzmetal's angina – use of calcium channel blockers (Nifedipine, Diltiazem, Verapamil), long-acting nitrovasodilators (Cardiket, Monomak and others);

• Dressler's syndrome - diuretic, antiarrhythmic, antibacterial drugs, anticoagulants, cardiac glycosides, low dosage NSAIDs (Aspirin cardio, Diclofenac), glucocorticosteroids (Prednisolone);
• early ventricular repolarization syndrome - antiarrhythmic drugs (specific therapy has not been developed);
• Ventricular aneurysms – surgical treatment.

ST Down Shift

A pronounced downward ST shift is a sign of insufficient myocardial nutrition - coronary heart disease. It is clinically manifested by angina pectoris, heart attack, and post-infarction cardiosclerosis. Similar changes, but without clear localization, are characteristic of:

• overdose of cardiac glycosides;
• use of diuretics;
• tachycardia;
• increased and frequent breathing;
• hypertrophy of the ventricles of the heart;
• intraventricular conduction disorders.

The T wave reflects the process of ventricular repolarization after their contraction. This is the most labile wave on the ECG; its changes may be the first sign of impaired blood supply to the myocardium in coronary heart disease. To make a diagnosis, you need to compare the clinical symptoms and other signs on the cardiogram.