Normal ecg in all leads. Fundamentals of electrocardiography

The electrocardiogram of the heart is the main diagnostic study that allows you to draw conclusions about the work of the organ, the presence or absence of pathologies and their severity. ECG interpretation heart examination is carried out by a cardiologist, who sees not only the curves on paper, but can also visually assess the patient's condition, analyze his complaints.

The indicators collected all together help to make the correct diagnosis. Without an accurate diagnosis, it is impossible to prescribe effective treatment Therefore, doctors carefully study the results of the patient's ECG.

Brief information about the ECG procedure

Electrocardiography examines the electrical currents that occur during the work of the human heart. This method is quite simple and accessible - these are the main advantages of the diagnostic procedure, which has been carried out by doctors for a long time and sufficient practical experience has been accumulated in relation to the interpretation of the results by doctors.

The cardiogram of the heart was developed and implemented in its modern form at the beginning of the twentieth century by the Dutch scientist Einthoven. The terminology developed by the physiologist is still used today. This once again proves that the ECG is a relevant and in-demand study, the indicators of which are extremely important for diagnosing heart pathologies.

The value of the cardiogram

An electrocardiogram is extremely important, since its correct reading allows you to detect the most serious pathologies, the patient's life depends on the timely diagnosis of which. A cardiogram is performed in both adults and children.

Upon receipt of the results, the cardiologist can assess the heart rate, the presence of arrhythmia, metabolic pathology in the myocardium, electrical conduction disturbance, myocardial pathology, localization of the electrical axis, and the physiological state of the main human organ. In some cases, the cardiogram can confirm other somatic pathologies that are indirectly related to cardiac activity.

Important! Doctors recommend doing a cardiogram if the patient feels obvious changes heart rate, suffers from sudden shortness of breath, weakness, fainting. It is necessary to do a cardiogram for primary pains in the heart, as well as for those patients who have already been diagnosed with abnormalities in the work of the organ, noises are observed.

An electrocardiogram is a standard procedure during a medical examination, in athletes during a medical examination, in pregnant women, before surgical interventions. Diagnostic value has an ECG with and without exercise. Make a cardiogram for pathologies of the endocrine and nervous systems with an increase in lipid levels. For the purpose of prevention, it is recommended to make a heart diagnosis for all patients who have reached forty-five years of age - this will help to identify abnormal performance of the organ, diagnose pathology and begin therapy.

What are the results of the study?

The results of the study for dummies will be absolutely incomprehensible, therefore it is impossible to read the cardiogram of the heart on your own. The doctor receives from the electrocardiograph a long millimeter paper with curves printed on it. Each graph reflects an electrode attached to the patient's body at a certain point.

In addition to graphs, devices can also provide other information, for example, the main parameters, the rate of one or another indicator. A preliminary diagnosis is generated automatically, so the doctor needs to independently study the results and only take into account what the device produces in terms of a possible disease. Data can be recorded not only on paper, but also on electronic media, as well as in the memory of the device.

Interesting! Holter monitoring is a type of ECG. If the cardiogram is taken in the clinic in a few minutes while the patient is lying down, then with Holter monitoring, the patient receives a portable sensor, which he attaches to his body. It is necessary to wear the sensor for a full day, after which the doctor reads the results. The peculiarity of such monitoring is the dynamic study of cardiac activity in various states. This allows you to get a more complete picture of the patient's health status.

Deciphering the results of the study: main aspects

Curves on graph paper are represented by isolines - a straight line, which means that there are no impulses at the moment. Deviations up or down from the isoline are called teeth. In one complete cycle of cardiac contraction, six teeth are laid, which are assigned standard letters of the Latin alphabet. Such teeth on the cardiogram are either directed up or down. The upper teeth are considered to be positive, and the downward ones are considered negative. Normally, the S and Q waves dip slightly down from the isoline, and the R wave is a peak rising upward.

Each tooth is not just a drawing with a letter, behind it lies a certain phase of the heart. You can decipher the cardiogram if you know which teeth mean what. For example, the P wave demonstrates the moment when the atria are relaxed, R indicates the excitation of the ventricles, and T indicates their relaxation. Doctors take into account the distance between the teeth, which also has its diagnostic value, and if necessary, entire groups of PQ, QRS, ST are examined. Each research value speaks about a certain characteristic of the organ.

For example, with an unequal distance between the R teeth, doctors talk about extrasystole, atrial fibrillation, weakness sinus node. If the P wave is elevated and thickened, then this indicates a thickening of the walls of the atria. An extended PQ interval indicates artrioventricular block, and an expansion of the QRS suggests ventricular hypertrophy, blockade of the His bundle. If there are no gaps in this segment, doctors suspect fibrillation. A prolonged QT interval indicates serious heart rhythm disturbances that can be fatal. And if this combination of QRS is presented as a flag, then doctors talk about myocardial infarction.

Table of normal values ​​\u200b\u200band other indicators

To decipher the ECG, there is a table containing the norms of values. Focusing on it, doctors can see deviations. As a rule, in the process of long work with cardiological patients, doctors no longer use the table at hand, the norm in adults is memorized by heart.

Indicator Amplitude of the norm, s QRS from 0.06 to 0.1 Rot 0.07 to 0.11 Q from 0.07 to 0.11 T from 0.12 to 0.28 PQ from 0.12 to 0.2

In addition to tabular values, doctors consider other parameters of the work of the heart:

• rhythmicity of heart contractions - in the presence of arrhythmia, i.e. failures in the rhythmicity of contractions of the heart muscle, the difference between the indicators of the teeth will be more than ten percent. In people with a healthy heart, normosistolia is noted, but pathological data make the doctor alert and look for deviations. The exception is sinus arrhythmia in combination with sinus rhythm, as often happens in adolescence, but in adults, sinus rhythm with deviations indicates the beginning of the development of pathology. A striking example deviations - extrasystole, manifested in the presence of additional contractions. It occurs with malformations of the heart, inflammation of the myocardium, ischemia,
• heart rate is the most accessible parameter, it can be assessed independently. Normally, in one minute there should be from 60 to 80 complete cycles of the heart. With a rapid cycle, more than 80 beats speak of tachycardia, but less than 60 is bradycardia. The indicator is more illustrative, since not all severe pathologies give bradycardia or tachycardia, and in single cases, the ECG of a healthy person will also show such phenomena if he is nervous during electrocardiography.

Types of heart rate

An electrocardiogram shows another important parameter - the type of heart rhythm. It means the place where the signal propagates, prompting the heart to contract.

There are several rhythms - sinus, atrial, ventricular and atrioventricular. The norm is sinus rhythm, and if the impulse occurs in other places, then this is considered a deviation.

An atrial rhythm on an ECG is a nerve impulse that occurs in the atria. Atrial cells provoke the appearance of ectopic rhythms. Such a situation arises when the sinus node malfunctions, which should produce these rhythms on its own, and now the atrial innervation centers do it for it. The immediate cause of this deviation is hypertonic disease, weakness of the sinus node, ischemic disorders, some endocrine pathologies. With such an ECG, nonspecific ST-T wave changes are recorded. In some cases, atrial rhythm is observed in healthy people.

The atrioventricular rhythm occurs in the node of the same name. The pulse rate with this type of rhythm falls below 60 beats / min, indicating bradycardia. Causes of atrioventricular rhythm - a weak sinus node, taking certain medications, blockade of the AV node. If tachycardia occurs with atrioventricular rhythm, this is evidence of a previous heart attack, rheumatic changes, such a deviation appears after surgical interventions on the heart.

Ventricular rhythm is the most severe pathology. The impulse emanating from the ventricles is extremely weak, the contractions often fall below forty beats. Such a rhythm occurs with a heart attack, circulatory failure, cardiosclerosis, heart defects, in a preadgonal state.

Deciphering the analysis, doctors pay attention to the electrical axis. It is displayed in degrees and shows the direction of the impulses. The norm for this indicator is 30-70 degrees when tilted to the vertical. Abnormalities suggest intracardiac blockade or hypertension.

When deciphering the ECG, terminological conclusions are issued, which also demonstrate the norm or pathology. A bad ECG or a result without pathology will show in a complex all indicators of the work of the heart. Atrioventricular block will be reflected as a prolonged PQ interval. Such a deviation in the first degree does not threaten the life of the patient. But with the third degree of pathology, there is a risk of sudden cardiac arrest, since the atria and ventricles work in their own incongruous rhythm.

If the conclusion contains the word "ectopic rhythm", this means that the innervation does not come from the sinus node. The condition is both a variant of the norm and a severe deviation due to cardiac pathologies, taking medicines etc.

If the cardiogram shows nonspecific ST-T wave changes, then this situation requires additional diagnostics. The reason for the deviation may be metabolic disorders, an imbalance of basic electrolytes, or endocrine dysfunctions. A high T wave may indicate hypokalemia, but is also a normal variant.

With some pathologies of the heart, the conclusion will show a low voltage - the currents emanating from the heart are so weak that they are recorded below normal. Low electrical activity is due to pericarditis or other cardiac pathologies.

Important! The borderline ECG of the heart indicates a deviation of some parameters from the norm. This conclusion is generated by the electrocardiograph system and does not mean severe violations at all. Upon receipt of such data, patients should not be upset - it is enough just to undergo an additional examination, identify the cause of the violations and treat the underlying disease.

Myocardial infarction on ECG

An ECG in myocardial infarction records extremely important diagnostic data, according to which it is possible not only to diagnose a heart attack, but also to determine the severity of the violations. The manifestation of pathology on the ECG will be noticeable already with the onset of symptoms of a crisis. There will be no R wave on the tape - this is one of the leading signs of myocardial infarction.

Electrocardiography (ECG)- one of the electrophysiological methods for recording biopotentials of the heart. Electrical impulses from the heart tissue are transmitted to skin electrodes located on the arms, legs and chest. This data is then output either graphically on paper or displayed on a display.

In the classic version, depending on the location of the electrode, the so-called standard, reinforced and chest leads are distinguished. Each of them shows bioelectric impulses taken from the heart muscle at a certain angle. Thanks to this approach, as a result, a complete characteristic of the work of each section of the heart tissue emerges on the electrocardiogram.

Figure 1. ECG tape with graphic data

What does the ECG of the heart show? Using this common diagnostic method, you can determine the specific place in which the pathological process occurs. In addition to any disturbances in the work of the myocardium (heart muscle), the ECG shows the spatial location of the heart in the chest.

Main tasks of electrocardiography

1. Timely determination of violations of rhythm and heart rate (detection of arrhythmias and extrasystoles).
2. Determination of acute (myocardial infarction) or chronic (ischemia) organic changes in the heart muscle.
3. Identification of violations of intracardiac conduction of nerve impulses (violation of the conduction of an electrical impulse along the conduction system of the heart (blockade)).
4. Definition of some acute (PE - pulmonary embolism) and chronic ( Chronical bronchitis with respiratory failure) pulmonary diseases.
5. Identification of electrolyte (potassium, calcium levels) and other changes in the myocardium (dystrophy, hypertrophy (increase in the thickness of the heart muscle)).
6. Indirect registration inflammatory diseases heart (myocarditis).

Disadvantages of the method

The main disadvantage of electrocardiography is the short-term registration of indicators. Those. the recording shows the work of the heart only at the time of taking the ECG at rest. Due to the fact that the above disorders can be transient (appear and disappear at any time), specialists often resort to daily monitoring and recording of ECG with exercise (stress tests).

Indications for an ECG

Electrocardiography is performed on a planned or emergency basis. Scheduled ECG registration is carried out during pregnancy, when a patient is admitted to the hospital, in the process of preparing a person for operations or complex medical procedures, to assess cardiac activity after certain treatment or surgical interventions.

With the preventive purpose of the ECG is prescribed:

• people with high blood pressure;
• with vascular atherosclerosis;
• in case of obesity;
• with hypercholesterolemia (increased blood cholesterol levels);
• after some transferred infectious diseases (tonsillitis, etc.);
• with diseases of the endocrine and nervous systems;
• persons over 40 years old and people prone to stress;
• with rheumatological diseases;
• people with occupational risks and hazards to assess professional suitability (pilots, sailors, athletes, drivers…).

On an emergency basis, i.e. "This very minute" ECG is assigned:

• with pain or discomfort behind the sternum or in the chest;
• in case of severe shortness of breath;
• with prolonged severe pain in the abdomen (especially in the upper sections);
• in case of persistent increase in blood pressure;
• in case of unexplained weakness;
• with loss of consciousness;
• with a chest injury (in order to exclude damage to the heart);
• at the time of or after a heart rhythm disorder;
• for pain in thoracic region spine and back (especially on the left);
• at severe pain in the neck and lower jaw.

Contraindications for ECG

There are no absolute contraindications to ECG removal. Relative contraindications to electrocardiography may be various violations of the integrity of the skin in the places where the electrodes are attached. However, it should be remembered that in the case of emergency indications, the ECG should always be taken without exception.

Preparation for electrocardiography

There is also no special preparation for an ECG, but there are some nuances of the procedure that the doctor should warn the patient about.

1. It is necessary to know if the patient is taking heart medications (should be noted on the referral form).
2. During the procedure, you can not talk and move, you must lie down, relaxed and breathe calmly.
3. Listen and follow the simple commands of the medical staff, if necessary (inhale and hold for a few seconds).
4. It is important to know that the procedure is painless and safe.

Distortion of the electrocardiogram record is possible when the patient moves or if the device is not properly grounded. The reason for incorrect recording can also be a loose fit of the electrodes to the skin or their incorrect connection. Interference in the recording often occurs with muscle tremors or electrical pickup.

Conducting an electrocardiogram or how an ECG is done

• to the right hand - a red electrode;
• to the left hand - yellow;
• to the left leg - green;
• to the right leg - black.

Then 6 more electrodes are applied to the chest.

After the patient is fully connected to the ECG device, a recording procedure is performed, which on modern electrocardiographs lasts no more than one minute. In some cases, the health worker asks the patient to inhale and not breathe for 10-15 seconds and conducts an additional recording during this time.

At the end of the procedure, the ECG tape indicates the age, full name. patient and the speed at which the cardiogram was taken. Then a specialist decrypts the recording.

ECG decoding and interpretation

The interpretation of the electrocardiogram is carried out either by a cardiologist or a doctor. functional diagnostics, or a paramedic (in an ambulance). The data is compared with a reference ECG. On the cardiogram, five main teeth (P, Q, R, S, T) and an inconspicuous U-wave are usually distinguished.

Table 1. ECG interpretation in adults is normal

Various changes in the teeth (their width) and intervals may indicate a slowdown in the conduction of a nerve impulse through the heart. T-wave inversion and/or ST interval rise or fall relative to the isometric line indicates possible damage myocardial cells.

During the decoding of the ECG, in addition to studying the shapes and intervals of all teeth, a comprehensive assessment of the entire electrocardiogram is carried out. In this case, the amplitude and direction of all teeth in standard and enhanced leads are studied. These include I, II, III, avR, avL and avF. (see Fig. 1) Having a summary picture of these ECG elements, one can judge the EOS (electrical axis of the heart), which shows the presence of blockades and helps determine the location of the heart in the chest.

For example, in obese individuals, the EOS may be deviated to the left and down. Thus, the decoding of the ECG contains all the information about the source of the heart rate, conduction, the size of the heart chambers (atria and ventricles), myocardial changes and electrolyte disturbances in the heart muscle.

Basic and most important clinical significance ECG has with myocardial infarction, cardiac conduction disorders. Analyzing the electrocardiogram, you can get information about the focus of necrosis (localization of myocardial infarction) and its duration. It should be remembered that ECG assessment should be carried out in combination with echocardiography, daily (Holter) ECG monitoring and functional stress tests. In some cases, the ECG can be practically uninformative. This is observed with massive intraventricular blockade. For example, PBLNPG ( complete blockade left bundle of Hiss). In this case, it is necessary to resort to other diagnostic methods.

Video on the topic "ECG norm"

Electrocardiography, or ECG for short, is a graphical recording of the electrical activity of the heart. It gets its name from three words: electro - electricity, electrical phenomena, cardio - heart, graphics - graphic registration. To date, electrocardiography is one of the most informative and reliable methods for the study and diagnosis of disorders of the heart.

Theoretical foundations of electrocardiography

The theoretical foundations of electrocardiography are based on the so-called Einthoven triangle, in the center of which the heart (which is an electric dipole) is located, and the vertices of the triangle form free upper and lower limbs. In the process of propagation of the action potential along the membrane of the cardiomyocyte, some of its sections remain depolarized, while the rest potential is recorded on the second. Thus, one part of the membrane is positively charged from the outside, and the second is negatively charged.

This makes it possible to consider the cardiomyocyte as a single dipole, and geometrically summing up all the dipoles of the heart (i.e., the totality of cardiomyocytes that are in different phases of the action potential), a total dipole is obtained that has a direction (due to the ratio of excited and unexcited sections of the heart muscle in different phases of the cardiac cycle ). The projection of this total dipole on the sides of the Einthoven triangle determines the appearance, size and direction of the main ECG teeth, as well as their change in various pathological conditions.

Main ECG Leads

All leads in electrocardiography are usually divided into those recording the electrical activity of the heart in the frontal plane (I, II, II standard leads and enhanced leads aVR, aVL, aVF) and recording electrical activity in the horizontal plane (thoracic leads V1, V2, V3, V4, V5 , V6).

There are also additional specialized lead circuits, such as Neb leads, etc., which are used in the diagnosis of atypical conditions. Unless otherwise provided by the attending physician, the cardiogram of the heart is recorded in three standard leads, three enhanced leads, and also in six chest leads.

ECG recording speed

Depending on the model of the electrocardiograph used, the recording of the electrical activity of the heart can be carried out both simultaneously from all 12 leads, and in groups of six or three, as well as by sequential switching between all leads.

In addition, the electrocardiogram can be recorded at two different speeds of the paper tape: at a speed of 25 mm/s and 50 mm/s. Often, in order to save the electrocardiographic tape, a registration speed of 25 mm/sec is used, but if it becomes necessary to obtain more detailed information about the electrical processes in the heart, then the cardiogram of the heart is recorded at a speed of 50 mm/sec.

Principles of ECG Waveforming

The pacemaker of the first order in the conduction system of the heart is atypical cardiomyocytes of the sinoatrial node located at the mouth of the confluence of the superior and inferior vena cava into the right atrium. It is this node that is responsible for generating the correct sinus rhythm with a frequency of impulses from 60 to 89 per minute. Arising in the sinoatrial node, electrical excitation first covers the right atrium (it is at the moment the ascending part of the P wave is formed on the electrocardiogram), and then it spreads to the left atrium through the interatrial bundles of Bachmann, Wenckenbach and Torel (at the moment the descending part of the P wave is formed) .

After excitation of the atrial myocardium, atrial systole occurs, and electrical impulse goes to the myocardium of the ventricles along the atrioventricular bundle. At the moment of passage of the impulse from the atria to the ventricles in the atrioventricular junction, its physiological delay occurs, which is reflected on the electrocardiogram by the appearance of the isoelectric PQ segment ( ECG changes, one way or another associated with a delay in the conduction of an impulse in the atrioventricular connection, will be called atrioventricular blockade). This delay in the passage of the impulse is essential for the normal flow of the next portion of blood from the atria into the ventricles. After the electrical impulse has passed through the atrioventricular septum, it is sent along the conduction system to the apex of the heart. It is from the top that the excitation of the ventricular myocardium begins, forming a Q wave on the electrocardiogram. Further, the walls of the left and right ventricles, as well as the interventricular septum, are covered by excitation, forming an R wave on the ECG. Lastly, part of the ventricles and the interatrial septum, closer to the base of the heart, will be covered by excitation, forming an S wave. After the entire myocardium of the ventricles is covered by excitation, an isoelectric line or ST segment is formed on the ECG.

At the moment, electromechanical coupling of excitation with contraction in cardiomyocytes is being carried out and repolarization processes are taking place on the membrane of cardiomyocytes, which are reflected in the T wave on the electrocardiogram. Thus formed ECG norm. Knowing these patterns of the spread of excitation along the conduction system of the heart, it is easy to determine, even with a cursory glance, the presence of gross changes on the ECG tape.

Heart rate assessment and ECG norm

After the electrocardiogram of the heart is registered, the decoding of the record begins with determining the heart rate and the source of the rhythm. To calculate the number of heartbeats, multiply the number of small cells between the R-R teeth by the duration of one cell. It should be remembered that at a registration speed of 50 mm/s, its duration is 0.02 s, and at a registration speed of 25 mm/s, it is 0.04 s.

The distance between the R-R teeth is estimated at least between three or four electrocardiographic complexes, and all calculations are carried out in the second standard lead (since in this lead the total display of I and III standard leads occurs, and the electrocardiogram of the heart, decoding its indicators is the most convenient and informative).

Table "ECG: norm"

Evaluation of rhythm correctness

The assessment of the correctness of the rhythm is carried out according to the degree of variability of changes in the above R-R interval. Variability of changes should not exceed 10%. The source of the rhythm is established as follows: if the ECG shape is correct, the wave is positive and P is at the very beginning, after this wave there is an isoelectric line and then there is a QRS complex, then it is considered that the rhythm comes from the atrioventricular junction, i.e. the ECG norm is presented. In the case of a pacemaker migration situation (for example, when one or another group of atypical cardiomyocytes takes over the function of generating excitation, the time of passage of the impulse through the atria will change, which will entail changes in the duration of the PQ interval).

ECG changes in certain types of heart pathologies

To date, an ECG can be done in almost any clinic or a small private medical center, but it is much more difficult to find a competent specialist who would decipher the cardiogram. Knowing the anatomical structure of the conduction system of the heart and the rules for the formation of the main teeth of the electrocardiogram, it is quite possible to independently cope with the diagnosis. So, an ECG table may be required as a handy auxiliary material.

The norm of the amplitude and duration of the main teeth and intervals given in it will help the novice specialist in studying and deciphering the ECG. Using such a table, or, better, a special cardiographic ruler, you can determine the heart rate in a matter of minutes, as well as calculate the electrical and anatomical axis of the heart. When deciphering, it must be remembered that the ECG norm in adults is somewhat different from that in children and the elderly. In addition, it will be quite useful if the patient takes the previous ECG tapes with him to the appointment. Thus, it will be much easier to determine the pathological changes.

It should be remembered that the duration of the P wave, the PQ segment, the QRS complex, the ST segment, as well as the duration of the T wave, if the ECG is normal in the hands, is 0.1 ± 0.02 sec. If the duration of intervals, teeth or segments changes upwards, then this will indicate a blockade of the impulse.

Holter ECG monitoring

Holter monitoring or daily recording of an electrocardiogram is one of the ECG recording methods, in which a special device is installed for the patient, which records the electrical activity of the heart around the clock. The installation of a Holter monitor and further analysis of the daily record makes it possible to identify forms of cardiac dysfunction, which are not always visible under the conditions of a single registration.

An example is the definition of extrasystole or transient rhythm disturbances.

Conclusion

Knowing the interpretation and origin of the main teeth of the electrocardiogram, you can proceed to further study of the ECG with various types pathology of the heart, including myocardial infarction of various localization. Properly evaluating and interpreting the results of the ECG, you can not only identify deviations in the conductivity and contractility of the myocardium, but also determine the presence of ion imbalance in the body.

An electrocardiograph (ECG) is a device that allows you to evaluate cardiac activity, as well as to diagnose the state of this organ. During the examination, the doctor receives data in the form of a curve. How to read an ECG trace? What are the types of teeth? What changes are visible on the ECG? Why do doctors need this diagnostic method? What does the ECG show? These are far from all the questions that interest people who are faced with electrocardiography. First you need to know how the heart works.

The human heart consists of two atria and two ventricles. The left side of the heart is more developed than the right, as it has a greater load. It is this ventricle that most often suffers. Despite the difference in size, both sides of the heart must work stably, harmoniously.

Learning to read an electrocardiogram on your own

How to read an ECG correctly? This is not as difficult to do as it might seem at first glance. First you need to look at the cardiogram. It is printed on special paper with cells, and two types of cells are clearly visible: large and small.

The conclusion of the ECG is read by these cells. teeth, cells These are the main parameters of the cardiogram. Let's try to learn how to read an ECG from scratch.

Meaning of cells (cells)

There are two types of cells on the paper for printing the examination result: large and small. All of them consist of vertical and horizontal guides. Vertical is voltage, and horizontal is time.

Large squares consist of 25 small cells. Each small cell is 1 mm and corresponds to 0.04 seconds in the horizontal direction. Large squares are 5 mm and 0.2 seconds. In the vertical direction, a centimeter of the strip is equal to 1 mV of voltage.

teeth

There are five teeth in total. Each of them on the graph displays the work of the heart.

1. P - Ideally, this tooth should be positive in the range from 0.12 to two seconds.
2. Q - negative wave, shows the state of the interventricular septum.
3. R - displays the state of the myocardium of the ventricles.
4. S - negative wave, shows the completion of processes in the ventricles.
5. T - positive wave, shows the restoration of potential in the heart.

All ECG teeth have their own reading characteristics.

Prong P

All teeth of the electrocardiogram are of some importance for the correct diagnosis.

The very first tooth of the graph is called P. It denotes the time between heartbeats. To measure it, it is best to highlight the beginning and end of the tooth and then count the number of small cells. Normally, the P wave should be between 0.12 and 2 seconds.

However, measuring this indicator in only one area will not give accurate results. To make sure that the heartbeat is even, it is necessary to determine the interval of the P wave in all areas of the electrocardiogram.

R wave

Knowing how to read an ECG the easy way, you can understand if there are pathologies of the heart. The next important tooth on the graph is R. It is easy to find - this is the highest peak on the graph. This will be the positive wave. Its highest part is marked on the R cardiogram, and its lower parts are Q and S.

The QRS complex is called the ventricular or sinus complex. In a healthy person, the sinus rhythm on the ECG is narrow, high. The ECG R waves are clearly visible in the figure, they are the highest:

Between these peaks, the number of large squares points to This indicator is calculated using the following formula:

300/number of large squares = heart rate.

For example, there are four full squares between the peaks, then the calculation will look like this:

300/4=75 heart beats per minute.

Sometimes on the cardiogram there is an elongation of the QRS complex for more than 0.12 s, which indicates a blockade of the bundle of His.

PQ wave interval

PQ is the interval from the P wave to Q. It corresponds to the time of excitation through the atria to the ventricular myocardium. The norm of the PQ interval at different ages is different. Usually it is 0.12-0.2 s.

With age, the interval increases. So, in children under 15 years of age, PQ can reach 0.16 s. At the age of 15 to 18 years, PQ increases to 0.18 s. In adults, this indicator is equal to a fifth of a second (0.2).

When the interval is extended to 0.22 s, they speak of bradycardia.

Interval between QT waves

If this complex is longer, then we can assume coronary artery disease, myocarditis or rheumatism. With a shortened type, hypercalcemia may occur.

ST interval

Normally, this indicator is located at the level of the midline, but may be two cells higher than it. This segment shows the process of restoration of depolarization of the heart muscle.

In rare cases, the indicator can rise three cells above the midline.

Norm

The decoding of the cardiogram normally should look like this:

• The Q and S segments should always be below the midline, i.e. negative.
• The R and T waves should normally be located above the midline, i.e., they will be positive.
• The QRS complex should be no wider than 0.12 s.
• Heart rate should be between 60 and 85 beats per minute.
• There should be sinus rhythm on the ECG.
• The R must be above the S wave.

ECG in pathologies: sinus arrhythmia

And how to read an ECG for various pathologies? One of the most common heart diseases is sinus rhythm disorder. It can be pathological and physiological. The latter type is usually diagnosed in people involved in sports, with neuroses.

With sinus arrhythmia, the cardiogram has the following form: sinus rhythms are preserved, fluctuations in the R-R intervals are observed, but during the breath hold the graph is even.

With pathological arrhythmia, the preservation of the sinus impulse is observed constantly, regardless of breath holding, while wave-like changes are observed at all R-R intervals.

The manifestation of a heart attack on the ECG

When a myocardial infarction occurs, the changes on the ECG are pronounced. Signs of pathology are:

• increase in heart rate;
• the ST segment is elevated;
• there is a fairly persistent depression in the ST leads;
• the QRS complex increases.

In case of a heart attack, the cardiogram is the main means of recognizing the zones of necrosis of the heart muscle. With its help, you can determine the depth of damage to the organ.

In a heart attack, the ST segment is elevated on the graph, and the R wave will be lowered, giving the ST a cat-like shape. Sometimes with pathology, changes in the Q wave can be observed.

Ischemia

When it occurs, you can see in which part it is located.

• Location of ischemia at the anterior wall of the left ventricle. Diagnosed with symmetrical peaked T-teeth.
• Location near the epicardium of the left ventricle. The T-tooth is pointed, symmetrical, directed downwards.
• Transmural type of left ventricular ischemia. T pointed, negative, symmetrical.
• Ischemia in the myocardium of the left ventricle. T is smoothed, slightly raised up.
• Damage to the heart is indicated by the state of the T wave.

Changes in the ventricles

An ECG shows changes in the ventricles. Most often they appear in the left ventricle. This type of cardiogram occurs in people with prolonged additional stress, such as obesity. With this pathology, the electric axis deviates to the left, against which the S wave becomes higher than R.

Holter method

But how to learn to read an ECG, if it is not always clear which teeth are located and how? In such cases, continuous registration of the cardiogram using a mobile device is prescribed. It constantly records ECG data on a special tape.

This method of examination is necessary in cases where the classical ECG fails to detect pathologies. During the diagnosis of Holter, a detailed diary is necessarily kept, where the patient records all his actions: sleep, walks, sensations during activity, all activity, rest, symptoms of the disease.

Typically, data registration occurs within a day. However, there are cases when it is necessary to take readings up to three days.

ECG decoding schemes

1. The conduction and rhythm of the heart is analyzed. To do this, the regularity of heart contractions is assessed, the number of heart rates is calculated, and the conduction system is determined.
2. Axial rotations are detected: the position of the electric axis in the frontal plane is determined; around the transverse longitudinal axis.
3. The R wave is analyzed.
4. The QRS-T is analyzed. At the same time, the state of the QRS complex, RS-T, T wave, as well as the Q-T interval are assessed.
5. A conclusion is made.

According to the duration of the R-R cycle, they speak about the regularity and norm of the heart rhythm. When evaluating the work of the heart, more than one gap R-R, and all. Normally, deviations within 10% of the norm are allowed. In other cases, an irregular (pathological) rhythm is determined.

To establish the pathology, the QRS complex and a certain period of time are taken. It counts how many times the segment is repeated. Then the same period of time is taken, but further on the cardiogram, it is again calculated. If at equal time intervals the number of QRS is the same, then this is the norm. At different amounts, pathology is assumed, while P waves are oriented. They should be positive and stand in front of the QRS complex. Throughout the graph, the shape of P should be the same. This option speaks of sinus rhythm hearts.

With atrial rhythms, the P wave is negative. Behind it is the QRS segment. In some people, the P wave on the ECG may be absent, completely merging with the QRS, which indicates the pathology of the atria and ventricles, which the impulse reaches at the same time.

The ventricular rhythm is shown on the electrocardiogram as a deformed and extended QRS. In this case, the connection between P and QRS is not visible. There are large distances between the R waves.

cardiac conduction

ECG determines cardiac conduction. The P wave determines the atrial impulse, normally this indicator should be 0.1 s. The P-QRS interval displays the overall atrial conduction velocity. The norm of this indicator should be in the range of 0.12 to 0.2 s.

The QRS segment shows conduction through the ventricles, the limit is considered to be the norm from 0.08 to 0.09 s. With an increase in intervals, cardiac conduction slows down.

What the ECG shows, patients do not need to know. This should be dealt with by a specialist. Only a doctor can correctly decipher the cardiogram and make the correct diagnosis, taking into account the degree of deformation of each individual tooth, segment.

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Equipment for recording electrocardiogram

Electrocardiography - a method of graphic registration of changes in the potential difference of the heart that occur during the processes of myocardial excitation.

The first registration of an electrocardiosignal, a prototype of a modern ECG, was undertaken by W. Einthoven in 1912 . in Cambridge. After that, the ECG recording technique was intensively improved. Modern electrocardiographs allow both single-channel and multi-channel ECG recording.

In the latter case, several different electrocardiographic leads (from 2 to 6-8) are synchronously recorded, which significantly shortens the study period and makes it possible to obtain more accurate information about the electrical field of the heart.

Electrocardiographs consist of an input device, a biopotential amplifier and a recording device. The potential difference that occurs on the surface of the body when the heart is excited is recorded using a system of electrodes attached to different parts of the body. Electrical vibrations are converted into mechanical displacements of the electromagnet armature and are recorded in one way or another on a special moving paper tape. Now they use directly both mechanical recording with a very light pen, to which ink is supplied, and thermal ECG recording with a pen, which, when heated, burns out the corresponding curve on a special thermal paper.

Finally, there are such capillary type electrocardiographs (mingographs), in which ECG recording is carried out using a thin jet of spraying ink.

A gain calibration of 1 mV, which causes a 10 mm deviation of the recording system, allows comparison of ECGs recorded from a patient at different times and / or different devices.

Tape drives in all modern electrocardiographs provide paper movement at different speeds: 25, 50, 100 mm s -1, etc. Most often in practical electrocardiology, the ECG registration rate is 25 or 50 mm s -1 (Fig. 1.1).

Rice. 1.1. ECG recorded at a speed of 50 mm·s -1 (a) and 25 mm·s -1 (b). Calibration signal is shown at the beginning of each curve

Electrocardiographs should be installed in a dry room at a temperature not lower than 10 and not higher than 30 °C. During operation, the electrocardiograph must be grounded

Electrocardiographic leads

Changes in the potential difference on the surface of the body that occur during the work of the heart are recorded using various ECG lead systems. Each lead registers the potential difference that exists between two specific points of the electric field of the heart, where the electrodes are installed. Thus, different electrocardiographic leads differ among themselves, first of all, in areas of the body on which the potential difference is measured.

Electrodes placed at each of the selected points on the body surface are connected to the galvanometer of the electrocardiograph. One of the electrodes is attached to the positive pole of the galvanometer (positive or active lead electrode), the second electrode is connected to its negative pole (negative lead electrode).

Today, in clinical practice, 12 ECG leads are most widely used, the recording of which is mandatory for each electrocardiographic examination of the patient: 3 standard leads, 3 enhanced unipolar leads from the extremities and 6 chest leads.

Standard leads

Three standard leads form an equilateral triangle (Einthoven's triangle), the vertices of which are the right and left arms, as well as the left leg with electrodes installed on them. The hypothetical line connecting the two electrodes involved in the formation of an electrocardiographic lead is called the lead axis. The axes of standard leads are the sides of Einthoven's triangle (Fig. 1. 2).

Rice. 1.2. Formation of three standard limb leads

Perpendiculars drawn from the geometric center of the heart to the axis of each standard lead divide each axis into two equal parts. The positive part faces the positive (active) lead electrode, and the negative part faces the negative electrode. If the electromotive force (EMF) of the heart at some point in the cardiac cycle is projected onto the positive part of the abduction axis, a positive deviation is recorded on the ECG (positive R, T, P waves), and if it is negative, negative deviations are recorded on the ECG (Q waves, S, sometimes negative T-waves or even P-waves). To record these leads, electrodes are placed on the right hand (red marking) and left (yellow marking), as well as the left leg (green marking). These electrodes are connected in pairs to the electrocardiograph to record each of the three standard leads. Standard limb leads are recorded in pairs by connecting electrodes:

Lead I - left (+) and right (-) hand;

II lead - left leg (+) and right hand (-);

III lead - left leg (+) and left hand (-);

The fourth electrode is installed on the right foot to connect the ground wire (black marking).

The signs "+" and "-" here indicate the corresponding connection of the electrodes to the positive or negative poles of the galvanometer, that is, the positive and negative poles of each lead are indicated.

Strengthened limb leads

Amplified limb leads were proposed by Goldberg in 1942 . They register the potential difference between one of the limbs on which the active positive electrode of a given lead is installed (right arm, left arm or leg) and the average potential of the other two limbs. As a negative electrode in these leads, the so-called combined Goldberg electrode is used, which is formed when two limbs are connected through additional resistance. Thus, aVR is an enhanced lead from the right hand; aVL - enhanced abduction from the left hand; aVF - enhanced abduction from the left leg (Fig. 1.3).

The designation of enhanced limb leads comes from the first letters of the English words: “ a "- augmented (reinforced); "V" - voltage (potential); "R" - right (right); "L" - left (left); "F" - foot (leg).

Rice. 1.3. Formation of three reinforced unipolar limb leads. Below - Einthoven's triangle and the location of the axes of three reinforced unipolar limb leads

Six-axis coordinate system (according to BAYLEY)

Standard and enhanced unipolar limb leads make it possible to register changes in the EMF of the heart in the frontal plane, that is, in the one in which the Einthoven triangle is located. For a more accurate and visual determination of various deviations of the EMF of the heart in this frontal plane, in particular, to determine the position of the electrical axis of the heart, the so-called six-axis coordinate system was proposed (Bayley, 1943). It can be obtained by combining the axes of three standard and three enhanced leads from the limbs, conducted through the electrical center of the heart. The latter divides the axis of each lead into positive and negative parts, directed, respectively, to the positive (active) or negative electrodes (Fig. 1.4).

Rice. 1.4. Formation of a six-axis coordinate system (according to Bayley)

The direction of the axes is measured in degrees. The reference point (0 °) is conditionally taken as a radius drawn strictly horizontally from the electrical center of the heart to the left towards the active positive pole of standard lead I. The positive pole of standard lead II is at +60°, aVF is +90°, standard lead III is +120°, aVL is -30°, and aVR is -150°. The axis of lead aVL is perpendicular to the axis II of the standard lead, the axis I of the standard lead is perpendicular to the axis aVF, and the axis aVR is perpendicular to the axis III of the standard lead.

chest leads

Thoracic unipolar leads proposed by Wilson in 1934 ., register the potential difference between the active positive electrode installed at certain points on the surface of the chest and the negative combined Wilson electrode. This electrode is formed by connecting three limbs (right and left hands, as well as the left leg) through additional resistances, the combined potential of which is close to zero (about 0.2 mV). To record an ECG, 6 generally accepted active electrode positions are used on the anterior and lateral surfaces of the chest, which, in combination with the combined Wilson electrode, form 6 chest leads (Fig. 1.5):

lead V 1 - in the fourth intercostal space on the right edge of the sternum;

assignment V 2 — in the fourth intercostal space on the left edge of a breast;

assignment V 3 — between positions V 2 and V 4, approximately at the level of the fourth edge on the left parasternal line;

assignment V 4 - in the fifth intercostal space on the left mid-clavicular line;

assignment of V 5 — at the same level across, as V 4, on the left front axillary line;

Rice. 1.5. Location of chest electrodes

Thus, 12 electrocardiographic leads (3 standard, 3 reinforced unipolar limb leads, and 6 chest leads) are the most widely used.

Electrocardiographic deviations in each of them reflect the total EMF of the whole heart, that is, they are the result of simultaneous exposure to a given lead of a changing electrical potential in the left and right parts of the heart, in the anterior and posterior walls of the ventricles, in the apex and base of the heart.

Additional Leads

It is sometimes advisable to expand the diagnostic possibilities of an electrocardiographic study by using some additional leads. They are used in cases where the usual program for recording 12 generally accepted ECG leads does not allow for a sufficiently reliable diagnosis of a particular electrocardiographic pathology or requires clarification of some changes.

The method of recording additional chest leads differs from the method of recording 6 conventional chest leads only by the localization of the active electrode on the surface of the chest. The combined Wilson electrode is used as the electrode connected to the negative pole of the cardiograph.

Rice. 1.6. Location of additional chest electrodes

Leads V7-V9. The active electrode is installed along the posterior axillary (V 7), scapular (V 8) and paravertebral (V 9) lines at the level of the horizontal, on which the electrodes V 4 -V 6 are located (Fig. 1.6). These leads are usually used for more accurate diagnosis of focal myocardial changes in the posterior basal LV.

Lead V 3R-V6R. The chest (active) electrode is placed on the right half of the chest in positions symmetrical to the usual points of the electrodes V 3 -V 6 . These leads are used to diagnose right heart hypertrophy.

Leads according to Neb. Bipolar chest leads, proposed in 1938 by Neb, fix the potential difference between two points located on the surface of the chest. To record three leads according to Nab, electrodes are used that are designed to record three standard leads from the limbs. The electrode, usually placed on the right hand (red marking), is placed in the second intercostal space along the right edge of the sternum. The electrode from the left leg (green marking) is moved to the position of the chest lead V 4 (at the apex of the heart), and the electrode located on the left arm (yellow marking) is placed at the same horizontal level as the green electrode, but along the posterior axillary line . With the electrocardiograph lead switch in position I of the standard lead, record the Dorsalis lead (D).

By moving the switch to the II and III standard leads, the Anterior (A) and Inferior (I) leads are recorded respectively. The Nab leads are used to diagnose focal myocardial changes in the posterior wall (lead D), the anterior lateral wall (lead A), and the upper sections of the anterior wall (lead I).

ECG recording technique

To obtain a high-quality ECG recording, it is necessary to adhere to some rules for its registration.

Conditions for conducting an electrocardiographic study

ECG is recorded in a special room, remote from possible sources of electrical interference: electric motors, physiotherapy and X-ray rooms, electrical distribution boards. The couch should be at least 1.5-2 m away from the mains wires.

It is advisable to shield the couch by placing a blanket under the patient with a sewn-in metal mesh, which must be grounded.

The study is carried out after a 10-15-minute rest and not earlier than 2 hours after eating. The patient must be undressed to the waist, the shins are also freed from clothing.

ECG recording is usually performed in the supine position, which allows for maximum muscle relaxation.

Application of electrodes

4 plate electrodes are applied to the inner surface of the legs and forearms in their lower third with the help of rubber bands, and one or more (for multi-channel recording) chest electrodes are placed on the chest using a rubber suction cup. To improve the quality of the ECG and reduce the amount of inductive currents, good contact of the electrodes with the skin should be ensured. To do this, you must: 1) preliminarily degrease the skin with alcohol in the places where the electrodes are applied; 2) with significant hairiness of the skin, moisten the places where the electrodes are applied with soapy water; 3) use electrode paste or abundantly moisten the skin at the electrode sites with 5-10% sodium chloride solution.

Connecting wires to electrodes

Each electrode installed on the limbs or on the surface of the chest is connected to a wire coming from the electrocardiograph and marked with a certain color. The generally accepted marking of input wires is: right hand - red; left hand - yellow; left leg - green, right leg (patient grounding) - black; chest electrode is white. In the presence of a 6-channel electrocardiograph, which allows you to simultaneously register an ECG in 6 chest leads, a wire with a red color on the tip is connected to the V 1 electrode; to the electrode V 2 - yellow, V 3 - green, V 4 - brown, V 5 - black and V 6 - blue or purple. The marking of the remaining wires is the same as in single-channel electrocardiographs.

Choice of electrocardiograph gain

Before starting an ECG recording, it is necessary to set the same gain of the electrical signal on all channels of the electrocardiograph. To do this, each electrocardiograph provides the possibility of supplying a standard calibration voltage (1 mV) to the galvanometer. Typically, the gain of each channel is selected so that a voltage of 1 mV causes a deviation of the galvanometer and the recording system, equal to 10 mm . To do this, in the position of the lead switch "0", the gain of the electrocardiograph is adjusted and the calibration millivolt is recorded. If necessary, you can change the gain: reduce if the amplitude of the ECG waves is too large (1 mV = 5 mm) or increase if their amplitude is small (1 mV = 15 or 20 mm).

ECG recording

ECG recording is carried out with quiet breathing, as well as at the height of inspiration (in lead III). First, an ECG is recorded in standard leads (I, II, III), then in enhanced leads from the extremities (aVR, aVL and aVF) and chest (V 1 -V 6). At least 4 PQRST cycles are recorded in each lead. ECG is recorded, as a rule, at a paper speed of 50 mm·s -1 . A lower speed (25 mm·s -1) is used if a longer ECG recording is required, for example, for diagnosing arrhythmias.

Immediately after the end of the study, the last name, first name and patronymic of the patient, year of birth, date and time of the study are recorded on a paper tape.

Normal ECG

Prong P

The P wave reflects the process of depolarization of the right and left atria. Normally, in the frontal plane, the average resulting atrial depolarization vector (vector P) is located almost parallel to the standard lead axis II and is projected onto the positive parts of the lead axes II, aVF, I, and III. Therefore, in these leads, a positive P wave is usually recorded, which has a maximum amplitude in leads I and II.

In lead aVR, the P wave is always negative, since the P vector is projected onto the negative part of the axis of this lead. Since the axis of lead aVL is perpendicular to the direction of the average resulting vector P, its projection on the axis of this lead is close to zero, on the ECG in most cases a biphasic or low-amplitude P wave is recorded.

With a more vertical location of the heart in the chest (for example, in people with an asthenic physique), when the P vector is parallel to the aVF lead axis (Fig. 1.7), the P wave amplitude increases in leads III and aVF and decreases in leads I and aVL. The P wave in aVL may even become negative.

Rice. 1.7. P-wave formation in limb leads

On the contrary, with a more horizontal position of the heart in the chest (for example, in hypersthenics), the P vector is parallel to the I axis of the standard lead. At the same time, the amplitude of the P wave increases in leads I and aVL. P aVL becomes positive and decreases in leads III and aVF. In these cases, the projection of the P vector on the III axis of the standard lead is equal to zero or even has a negative value. Therefore, the P wave in lead III can be biphasic or negative (more often with left atrial hypertrophy).

Thus, in a healthy person, the P wave is always positive in leads I, II, and aVF; in leads III and aVL, it can be positive, biphasic, or (rarely) negative; and in lead aVR, the P wave is always negative.

In the horizontal plane, the average resulting vector P usually coincides with the direction of the axes of the chest leads V 4 -V 5 and is projected onto the positive parts of the axes of the leads V 2 -V 6, as shown in Fig. 1.8. Therefore, in a healthy person, the P wave in leads V 2 -V 6 is always positive.

Rice. 1.8. P wave formation in chest leads

The direction of the mean vector P is almost always perpendicular to the lead axis V 1 , while the direction of the two depolarization moment vectors is different. The first initial moment vector of atrial excitation is oriented forward, towards the positive lead electrode V 1 , and the second final moment vector (smaller) is turned back towards the negative pole of lead V 1 . Therefore, the P wave in V 1 is more often biphasic (+-).

The first positive phase of the P wave in V 1 , due to excitation of the right and partially left atria, is greater than the second negative phase of the P wave in V 1 , reflecting a relatively short period of final excitation of the left atrium only. Sometimes the second negative phase of the P wave in V 1 is weakly expressed and the P wave in V 1 is positive.

Thus, in a healthy person, a positive P wave is always recorded in chest leads V 2 -V 6, and in lead V 1 it can be biphasic or positive.

The amplitude of the P waves normally does not exceed 1.5-2.5 mm, and the duration is 0.1 s.

P interval‒ Q(R)

The P-Q(R) interval is measured from the beginning of the P wave to the beginning ventricular complex QRS (Q or R wave). It reflects the duration of AV conduction, that is, the time of propagation of excitation through the atria, AV node, bundle of His and its branches (Fig. 1.9). The P-Q(R) interval does not follow with the PQ(R) segment, which is measured from the end of the P wave to the beginning of Q or R

Rice. 1.9. P-Q(R) interval

The duration of the P-Q (R) interval ranges from 0.12 to 0.20 s and in a healthy person it depends mainly on the heart rate: the higher it is, the shorter the P-Q (R) interval.

Ventricular QRS complex T

The ventricular QRST complex reflects the complex process of propagation (QRS complex) and extinction (RS-T segment and T wave) of excitation through the ventricular myocardium. If the amplitude of the QRS complex teeth is large enough and exceeds 5 mm , they are denoted by capital letters of the Latin alphabet Q, R, S, if small (less than 5 mm ) - lowercase q, r, s.

The R wave is any positive wave that is part of the QRS complex. If there are several such positive teeth, they are designated as R, Rj, Rjj, etc., respectively. The negative wave of the QRS complex immediately preceding the R wave is denoted by the letter Q (q), and the negative wave immediately following the R wave is called S (s).

If only a negative deviation is recorded on the ECG, and there is no R wave at all, the ventricular complex is designated as QS. The formation of individual teeth of the QRS complex in different leads can be explained by the existence of three moment vectors of ventricular depolarization and their different projections on the axes of the ECG leads.

Q wave

In most ECG leads, the formation of the Q wave is due to the initial moment vector of depolarization between the ventricular septum, lasting up to 0.03 s. Normally, the Q wave can be registered in all standard and enhanced unipolar limb leads and in the chest leads V 4 -V 6 . The amplitude of the normal Q wave in all leads, except for aVR, does not exceed 1/4 of the height of the R wave, and its duration is 0.03 s. In lead aVR, a healthy person may have a deep and wide Q wave or even a QS complex.

R wave

The R wave in all leads, with the exception of the right chest leads (V 1 , V 2) and lead aVR, is due to the projection of the second (middle) QRS moment vector, or conditionally vector 0.04 s, on the lead axis. The 0.04 s vector reflects the process of further spread of excitation through the RV and LV myocardium. But, since the LV is a more powerful part of the heart, the R vector is oriented to the left and down, that is, towards the LV. On fig. 1.10a it can be seen that in the frontal plane the 0.04 s vector is projected onto the positive parts of the lead axes I, II, III, aVL and aVF and onto the negative part of the lead axis aVR. Therefore, in all leads from the extremities, with the exception of aVR, high R waves are formed, and with a normal anatomical position of the heart in the chest, the R wave in lead II has a maximum amplitude. In the aVR lead, as mentioned above, a negative deviation always predominates - the S, Q or QS wave, due to the projection of the 0.04 s vector onto the negative part of the axis of this lead.

At vertical position of the heart in the chest, the R wave becomes maximum in leads aVF and II, and in the horizontal position of the heart - in standard lead I. In the horizontal plane, the 0.04 s vector usually coincides with the direction of the V 4 lead axis. Therefore, the R wave in V 4 exceeds the R wave in the other chest leads in amplitude, as shown in Fig. 1.10b. Thus, in the left chest leads (V 4 -V 6), the R wave is formed as a result of the projection of the main moment vector of 0.04 s onto the positive parts of these leads.

Rice. 1.10. R wave formation in limb leads

The axes of the right chest leads (V 1 , V 2) are usually perpendicular to the direction of the main moment vector of 0.04 s, so the latter has almost no effect on these leads. The R wave in leads V 1 and V 2, as shown above, is formed as a result of the projection on the axis of these leads of the initial moment of choice (0.02 s) and reflects the spread of excitation along the interventricular septum.

Normally, the amplitude of the R wave gradually increases from lead V 1 to lead V 4, and then again slightly decreases in leads V 5 and V 6. The height of the R wave in the limb leads usually does not exceed 20 mm, and in the chest leads - 25 mm. Sometimes in healthy people, the r wave in V 1 is so weakly expressed that the ventricular complex in lead V 1 takes the form of QS.

For comparative characteristics the time of propagation of the excitation wave from the endocardium to the epicardium of the RV and LV, it is customary to determine the so-called interval of internal deviation (intrinsical defl ection), respectively, in the right (V 1, V 2) and left (V 5, V 6) chest leads. It is measured from the beginning of the ventricular complex (the Q or R wave) to the top of the R wave in the appropriate lead, as shown in Figure 1. 1.11.

Rice. 1.11. Measuring the interval of internal deviation

In the presence of R wave splits (RSRj or qRsrj complexes), the interval is measured from the beginning of the QRS complex to the top of the last R wave.

Normally, the interval of internal deviation in the right chest lead (V 1) does not exceed 0.03 s, and in the left chest lead V 6 -0.05 s.

S wave

In a healthy person, the amplitude of the S wave in different ECG leads varies widely, not exceeding 20 mm.

In the normal position of the heart in the chest, the S amplitude in the limb leads is small, except for the aVR lead. In the chest leads, the S wave gradually decreases from V 1, V 2 to V 4, and in the leads V 5, V 6 has a small amplitude or is absent.

The equality of the R and S waves in the chest leads (transitional zone) is usually recorded in the lead V 3 or (less often) between V 2 and V 3 or V 3 and V 4 .

The maximum duration of the ventricular complex does not exceed 0.10 s (usually 0.07-0.09 s).

The amplitude and ratio of positive (R) and negative teeth (Q and S) in various leads largely depend on the rotation of the axis of the heart around its three axes: anteroposterior, longitudinal and sagittal.

RS-T segment

The RS-T segment is a segment from the end of the QRS complex (the end of the R or S wave) to the beginning of the T wave. It corresponds to the period of complete excitation coverage of both ventricles, when the potential difference between different parts of the heart muscle is absent or small. Therefore, in normal standard and reinforced unipolar leads from the limbs, the electrodes of which are located at a great distance from the heart, the RS-T segment is located on the isoline and its displacement up or down does not exceed 0.5 mm . In the chest leads (V 1 -V 3), even in a healthy person, a slight shift of the RS-T segment upwards from the isoline is often noted (no more 2 mm).

In the left chest leads, the RS-T segment is more often recorded at the level of the isoline, the same as in the standard leads (± 0.5 mm).

The point of transition of the QRS complex to the RS-T segment is designated as j. Deviations of point j from the isoline are often used to quantify the displacement of the RS-T segment.

T wave

The T wave reflects the process of rapid final repolarization of the ventricular myocardium (phase 3 of the transmembrane PD). Normally, the total resulting ventricular repolarization vector (T vector) usually has almost the same direction as the average ventricular depolarization vector (0.04 s). Therefore, in most leads where a high R wave is recorded, the T wave has a positive value, projecting onto the positive parts of the electrocardiographic lead axes (Fig. 1.12). In this case, the largest R wave corresponds to the largest T wave in amplitude, and vice versa.

Rice. 1.12. T wave formation in limb leads

In lead aVR, the T wave is always negative.

In the normal position of the heart in the chest, the direction of the T vector is sometimes perpendicular to the III axis of the standard lead, and therefore a biphasic (+/-) or low-amplitude (smoothed) T wave in III can sometimes be recorded in this lead.

With a horizontal location of the heart, the T vector can even be projected onto the negative part of the III axis, and a negative T wave in III is recorded on the ECG. However, in lead aVF, the T wave remains positive.

With a vertical location of the heart in the chest, the T vector is projected onto the negative part of the aVL lead axis, and a negative T wave in aVL is recorded on the ECG.

In chest leads, the T wave usually has a maximum amplitude in lead V 4 or V 3 . The height of the T wave in the chest leads usually increases from V 1 to V 4, and then decreases slightly in V 5 -V 6 . In lead V 1, the T wave can be biphasic or even negative. Normally, T in V 6 is always greater than T in V 1.

The amplitude of the T wave in the limb leads in a healthy person does not exceed 5-6 mm, and in the chest leads - 15-17 mm. The duration of the T wave ranges from 0.16 to 0.24 s.

Q-T Interval (QRST)

The Q-T interval (QRST) is measured from the beginning of the QRS complex (Q or R wave) to the end of the T wave. The Q-T interval (QRST) is called ventricular electrical systole. During electrical systole, all parts of the ventricles of the heart are excited. The duration of the Q-T interval primarily depends on the heart rate. The higher the rhythm rate, the shorter the proper QT interval. The normal duration of the Q-T interval is determined by the formula Q-T \u003d K√R-R, where K is a coefficient equal to 0.37 for men and 0.40 for women; R-R is the duration of one cardiac cycle. Since the duration of the Q-T interval depends on the heart rate (lengthening as it slows down), it must be corrected relative to the heart rate to evaluate it, so the Bazett formula is used for calculations: QTc \u003d Q-T / √R-R.

Sometimes on the ECG, especially in the right chest leads, immediately after the T wave, a small positive U wave is recorded, the origin of which is still unknown. There are suggestions that the U wave corresponds to a period of short-term increase in the excitability of the ventricular myocardium (exaltation phase), which occurs after the end of the LV electrical systole.

O.S. Sychev, N.K. Furkalo, T.V. Getman, S.I. Deyak "Fundamentals of Electrocardiography"