Electrocardiography - what is it and why do ECG of the heart?

ECG - instrumental diagnostic method used in various heart diseases. The procedure is based on the study of the electrophysiological functioning of the heart. It is based on the registration and graphical representation of the potential difference that occurs during myocardial contraction.

During the manipulation, special electrodes connected to the ECG apparatus are superimposed on the front wall of the chest, arms and legs of the patient. After this, the electric cardiac potentials are fixed, followed by the derivation of a graphic curve on a computer monitor, or by recording on a special thermal paper.

Electrocardiography is a non-invasive diagnostic technique that is simple to carry out and accessible to each patient. With its help, it is possible to quickly identify many diseases - myocardial infarction, arterial hypertension, cardiac arrhythmia, impaired cardiac conduction, etc. Along with this, this diagnosis makes it possible to evaluate the effectiveness of the treatment or treatment of cardiac pathologies - medicamentous or surgical.

What it is?

With the contraction of the heart muscle, electric currents are generated. It is on their fixation and graphic image based electrocardiography. The undeniable advantage of this technique is its simplicity and accessibility. The result obtained during the study is called a cardiogram.

Modern electrocardiography was developed in the early 20th century by the Dutch physiologist Willem Einthoven. He developed not only the ECG methodology, but also terminology, which is now widely used by doctors all over the world.

Thanks to electrocardiography, you can evaluate:

  • Heart rate (heart rate);
  • physical condition of the heart;
  • heart rhythm (the method allows to detect arrhythmia);
  • the position of the electrical cardiac axis;
  • electrical conductivity of the heart.

After examining the radiograph, the doctor may note the presence of acute or chronic lesions of the heart muscle, or metabolic disorders in it.

In some cases, an ECG is assigned to detect certain vascular pathologies that are not related to cardiac activity.

ECG Holter

This technique allows you to identify abnormalities in the work of the heart that cannot be diagnosed at rest. With the help of a special apparatus (holter-ECG), daily monitoring of the organ's activity is performed when performing physical activities, feelings and stresses, at rest, etc. Holter research allows:

  • to identify the moments when heart activity is disturbed, and to understand what exactly provoked the disorder;
  • detect factors that cause pain, burning, feeling of squeezing in the chest, dizziness and fainting.

With this method, ischemia can be fixed at the earliest stages of its development.

Stress ECG

This procedure is based on the assessment of the work of the heart during physical exertion (when exercising on exercise bikes or a treadmill). Such manipulation is necessary if the patient has periodic irregularities in the work of the heart, which cannot be detected by an ECG performed in a state of rest.

Thanks to stress ECG, it becomes possible:

  • the identification of factors under the influence of which the work of the heart is disrupted during physical exertion;
  • determining the cause of arterial hypertension or heart rhythm disorders;
  • Exercise careful control of loads after surgical interventions or heart attacks.

Often, based on the results of such research, a scheme of drug treatment is developed, and the effectiveness of the therapy is monitored.

Indications for ECG

Electrocardiography may be planned or emergency. A planned ECG is performed when:

  • pregnancy;
  • admission of the patient to the hospital;
  • preparation for surgery or complex diagnostic / therapeutic procedures;
  • the need to assess the work of the heart after the treatment or surgery.

An emergency ECG is necessary for:

  • pain, discomfort in the chest or chest;
  • severe shortness of breath;
  • prolonged pain in the upper abdomen;
  • persistent hypertension;
  • causeless weakness;
  • syncope;
  • chest injuries (to avoid damage to the heart);
  • heart rhythm disorder;
  • intense pains in the neck, lower jaw, thoracic spine, or back.

ECG can be prescribed for prophylactic purposes in patients with:

  • high blood pressure;
  • atherosclerotic disease;
  • obesity;
  • high blood cholesterol levels;
  • postponed infectious diseases (in particular, after sore throat or tonsillitis);
  • pathologies of the endocrine or nervous system;
  • rheumatological diseases;
  • occupational risks and possible harm to health (in order to confirm professional suitability: pilots, sailors, athletes, etc.).

People older than 40 years and those subject to frequent stress should also undergo such a diagnosis from time to time.

There are no absolute contraindications for prescribing ECG. The procedure is limited in the presence of skin lesions in the area of ​​attachment of electrodes. But this precaution is not taken into account if the ECG is performed on an emergency basis.

Preparation for electrocardiography

Specific preparation for ECG is not required, but there are a few nuances that must be remembered:

  • the doctor must find out whether the patient is taking any medications that affect the CVS;
  • during the manipulation, the patient must find in a state of complete physical rest (it is also forbidden to talk);
  • it is important to come to the procedure about half an hour earlier before the scheduled time to sit down and rest for a while (during this time the heart rhythm will have time to normalize);
  • During the manipulation, the person must carefully listen and follow all the recommendations of the specialist.

If the patient moves or talks during the procedure, its results may be distorted - just like in the case of incorrect grounding of the device. Incorrect or loose connection of electrodes, muscle trembling or electrical noise are factors that can also lead to inaccurate ECG data.

How is electrocardiography performed

Carrying out an electrocardiogram can be carried out in the conditions of a hospital, or in policlinic. In the first case, the procedure is often of an emergency nature, especially if the patient was taken to hospital by an ambulance team, or to a department of any therapeutic profile (cardiological, endocrinological, etc.).

In the clinic, electrocardiography is usually carried out routinely for the purpose of prophylaxis, or if the patient has any diseases that are not related to emergency cases and do not require hospitalization.

Features of ECG

Diagnosis is carried out by appointment. The patient comes to the electrocardiography room at the appointed time, removes outer clothing and lies down on the couch on his back. With the help of a fleece, a nurse rubs parts of the skin on the chest, as well as wrists and ankles. This is necessary for better conductivity of the electrodes, which are superimposed on the treated zone. 6 suckers are placed on the chest, and special "clothespins" are put on the arms and legs.

After the preparatory stage, the procedure itself is carried out. The health worker includes an ECG machine that reads information about the electrical activity of the heart and records it in the form of a graphical curve on thermal paper. When using modern equipment, all information can be stored directly to the computer.

The manipulation is completely painless, and does not take more than 10 minutes. After graduation, the specialist analyzes the results obtained, writes the data into a patient’s form or card, after which the conclusion is given to him for further study by the attending physician and an accurate diagnosis.

ECG analysis: transcript in adults

Each of the teeth shown on the ECG has its letter designation (P, Q, R, S, T, U), where each of the letters represents the functioning of a specific heart section:

  • P stands for atrial depolarization;
  • Q, R, S - a combination of ventricular depolarization;
  • T - ventricular repolarization;
  • U is an underexposed ecg wave, which may indicate repolarization of the distal portions of the conductive ventricular system.

When deciphering the ECG in adults, it is taken into account that the teeth pointing upwards are considered positive, and those whose edges look downward are considered negative. The pronounced Q and S teeth, being always negative, in all cases follow a positive R wave.

For ECG recording, 12 leads are commonly used:

  • standard - І, ІІ, ІІІ;
  • reinforced single pole leads from the arms and legs (3 pcs.);
  • 6 reinforced chest monopolar leads (according to Wilson).

However, there are separate cases in which additional unipolar chest and bipolar leads D, A, I (according to Heaven) are used. This method of conducting an ECG is used primarily for arrhythmias or abnormal location of the heart. ads3

How is decryption done?

While deciphering the results of an ECG in adults, the cardiologist takes into account the length of the intervals between the components of the ECG. This is important for heart rate assessment. It is carried out by studying the shape and size of the teeth in different leads. Through this, you can find out how the heart functions in a certain period of time.

In special cases, a more rigorous, intent decoding of the electrocardiogram is performed. It is based on the use of special leads (vector theory). But in most cases, studying the total vector of QRS is enough to assess the activity of the heart.

We must not forget that each patient has its own individual characteristics of the structure of the chest and the location of the heart. Consequently, the indicators of his work may also have some differences. In this regard, during the decoding of ECG results, the direction of the total QRS vector is indicated - horizontal or vertical.

Electrocardiogram analysis is performed according to a specific algorithm:

  1. Heart rate is assessed and heart rate is determined. Normally, the rhythm should be sinus, and the heart rate can fluctuate within 60-8 beats per minute.
  2. Calculate the intervals characterizing the duration of the systolic phase (mainly according to the Bazett formula). The norm is from 390 to 450 ms. At prolongation of this interval, we can talk about atherosclerosis, ischemic disease, rheumatic heart disease or myocarditis. With hypercalcemia, by contrast, the QT interval is shortened. The duration of the pulses, reflected by such intervals, is calculated using a special computer program, which significantly reduces the risk of obtaining unreliable results.
  3. Calculation of the position of EOS. It begins from the isoline at the height of the teeth. In a healthy person, the R-wave is always higher than S. If the patient’s S-tooth rises above R when the axis deviates to the right side, a violation of the right ventricle can be suspected. It happens and vice versa: the axis is rejected to the left, while the height S is greater than the height R in 1-2 leads, we can talk about left ventricular hypertrophy.
  4. The study of the QRS complex, which occurs during the conduct of electrical impulses to the ventricular muscles, and is the identifier of the activity of the latter. Normally, there should be no pathological Q wave, and the width of the complex does not exceed 120 ms. If this interval is shifted, we can talk about blockades of the bundle of the His bundle or conduction disturbances. A partial block of the right leg of the bundle of His is an electrocardiographic identifier of right ventricular hypertrophy, and an incomplete blockade of the left leg may indicate a hypertrophy of the left cardiac ventricle.
  5. Description of ST segments, which are indicative of the recovery period of the initial position of the myocardium after its complete depolarization (in a healthy person they are on the isoline). The T wave displays the repolarization process of both heart ventricles. It is directed upwards, asymmetrical, and in its duration from longer than the QRS complex.

In young children, ECG results differ from those in adults. And only by 12 years old they will begin to approach the above described norms.

Normal ECG values ​​in adults

Interpretation of the ECG of the heart and the norms of indicators in adults are presented in this table:

IndicatorsNorm
Teeth
PAlways positive in leads I, II, aVF, in aVR negative, and in V1 two-phase. Width - up to 0, 12 s, height - up to 0.25 mV (up to 2.5 mm), but in the II lead the wave duration should be no more than 0.1 s
QQ is always negative, in leads III, and VF, V1 and V2 are normally absent. Duration up to 0.03 seconds. Height Q: in leads I and II no more than 15% of the P wave, in III no more than 25%
RHeight from 1 to 24 mm
SNegative. The deepest in lead V1, gradually decreases from V2 to V5, may be absent in V6
TAlways positive in leads I, II, aVL, aVF, V3-V6. AVR is always negative
USometimes it is recorded on a cardiogram 0.04 seconds after T. Absence of U is not a pathology.
Interval
Pq0.12-0.20 sec
Complex
QRS0.06 - 0.008 sec
Segment
STIn leads V1, V2, V3 is shifted up by 2 mm

Usually there are 5 teeth on the ECG - P, Q, R, S, T. But sometimes you can see the inconspicuous U wave. It is noteworthy that the opinions of experts regarding the nature of its origin diverge dramatically.

One researchers believe that the appearance of this wave is associated with the repolarization of papillary muscles. Other experts believe that the occurrence of this wave has a connection with the entry of potassium ions into the cells of the heart muscle during its contraction phase. According to Gorshkov-Kantakuzena, this tooth appears at a time when part of the charge is carried away by blood through the coronary arteries. This process is directly affected by potassium and magnesium ions.

The repolarization phase is characterized by the restoration of the initial resting potential of the cell membrane after passing through the action potential. When a pulse passes through it, a temporary change in the molecular membrane structure occurs, as a result of which ions can easily penetrate through it. At the time of repolarization, the ions diffuse in the opposite direction, which contributes to the restoration of the former electric membrane charge. After that, the cell again becomes capable of further electrical activity.

Total

ECG is a safe and accessible diagnostic procedure, with which you can assess the activity of the heart and identify abnormalities in the first stages of their development.

In public hospitals, manipulation is carried out free of charge, at the direction of the attending physician. In private medical institutions ECG fee. Its cost depends on the methodology and general pricing policy of the clinic.

Watch the video: How to Interpret Heart Rhythms on ECGs (November 2019).

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