What can an electrocardiogram determine? Electrocardiogram: interpretation of results and indications for implementation
In the diagnosis of diseases of the cardiovascular system, electrocardiographic (ECG) research methods play a leading role, being an integral part of clinical studies of patients with cardiovascular diseases.
Purpose of ECG studies:
- assessment of the most important cardiac functions: automaticity, excitability, conductivity;
- diagnosis of coronary heart disease (CHD), including coronary insufficiency;
- determination of the functional class of angina pectoris;
- selection of the most effective drug therapy;
- monitoring the progress of myocardial infarction;
- detection of cardiac conduction and rhythm disturbances;
- identification of other cardiac pathologies (pericarditis, electrolyte and metabolic disorders of the myocardium, etc.).
Options for ECG studies can be divided into two classes:
- ECG at rest- the electrical activity of the heart muscle of a patient at rest (lying down) is recorded;
- ECG under stress- bicycle ergometer test (VEM), treadmill test, Master's test, abnormal load.
Carrying out ECG studies at rest is described in detail in the ECG section.
VEM, Treadmill test
Both of these tests are similar in essence - measuring the electrical activity of the heart during physical activity on a bicycle ergometer or treadmill.
The patient walks on a treadmill, the speed and incline of which are increased stepwise every 3 minutes (the load during VEM is increased every 2 minutes). The subject must stop taking beta blockers and nitrates the day before the test, the last meal should be no later than 4 hours before the test, the patient should be dressed in comfortable clothes that do not restrict his movement.
The studies are carried out in compliance with all precautions under the supervision of a specialist, in order to avoid the development of arrhythmias, an attack of prolonged angina, excessive rise (fall) in blood pressure, and loss of consciousness of the patient.
The purpose of these tests is to determine the amount of load tolerated and assess the threshold at which signs of the disease begin to appear. Having the results of a treadmill test (TEM) in hand, the attending physician can select the most effective treatment tactics for the patient, adjust drug therapy if necessary, and make a more accurate prognosis of the course of the disease.
Indications for performing a treadmill test (TMT):
- in healthy people:
- determination of exercise tolerance;
- professional selection;
- identification of individuals at risk of developing hypertension, when blood pressure increases sharply during physical activity;
- identification of initial manifestations of atherosclerotic lesions of the coronary arteries and ischemic heart disease;
- identification of hidden insufficiency of cardiac blood supply with high cholesterol.
- in persons with heart and vascular diseases:
- detection and identification of arrhythmias;
- identification of “hidden” ischemia;
- determination of individual exercise tolerance in patients with coronary artery disease;
- determination of the functional class of angina pectoris;
- selection and evaluation of the effectiveness of treatment measures for people who have suffered an MI;
- examination of the working capacity of patients with heart and vascular diseases.
Absolute contraindications for performing a treadmill test (TEM):
- acute MI;
- uncontrolled arrhythmias accompanied by hemodynamic disturbances;
- heart defects;
- severe heart failure;
- acute vascular conditions;
- acute myocarditis (pericarditis);
- acute dissecting aortic aneurysm.
Clinical criteria for stopping the treadmill test (TMT):
- increase in heart rate to a certain age value;
- development of a classic attack of angina;
- an increase in blood pressure above the maximum limit (systolic blood pressure above 230 mm Hg; diastolic blood pressure - 120 mm Hg);
- blood pressure drop by 25-30% from the original;
- development of an attack of suffocation or pronounced shortness of breath (more than 30 respiratory movements per minute);
- dizziness, severe headache, severe weakness, pallor, cyanosis, severe sweating;
- inappropriate behavior;
- sudden severe fatigue of the subject.
ECG criteria for stopping the treadmill test (TEM):
- downward displacement of the ST segment of an ischemic nature (horizontal; obliquely descending; trough-shaped by 1 mm or more; obliquely ascending by 2 mm or more, lasting more than 0.08 sec after the junction point (J), with a displacement of the J point by 2 mm or more relative to the isoline (more 0.06 sec at heart rate more than 130 beats/min);
- ST segment elevation by 1 mm or more compared to baseline;
- development of arrhythmias: extrasystoles (more than 1:10 extrasystoles), paroxysmal tachycardia, atrial fibrillation;
- cardiac conduction disturbance - appearance (progression) of AV block, bundle branch block;
- change in the QRS complex: R wave volts increased by more than a third; deepening (widening) of q waves (qR); transition of the Q wave to QS;
- development of WPW syndrome, migration of the pacemaker through the atria.
Rice. Ischemic displacements of the ST segment: a) horizontal; b) oblique; c) trough-shaped.
Rice. Oblique displacements of the ST segment: a) no displacement; b) displacement 2 mm.
Rice. Options for ST segment elevation: a) in a calm state; b) at the peak of physical activity.
Evaluation of the results of the treadmill test (TEM)
At each load level of the treadmill test (TEM), the patient’s heart rate and blood pressure are recorded.
- patient complaints before the start of the study;
- medications that the patient took on the eve of the test;
- data on the load size, duration of work at each stage of the test;
- test results recorded by the doctor:
- reason for stopping the test;
- maximum heart rate achieved by the patient;
- the presence of clinical signs of myocardial ischemia (the presence of changes in the ST segment (their nature); the appearance of arrhythmias and cardiac conduction disorders).
Options for a medical opinion based on the results of exercise tests:
- negative test: the subject has reached “his” age heart rate, while no clinical or electrocardiographic signs of ischemia (myocardial dysfunction) were recorded;
- negative test with features: when the age-appropriate heart rate is reached, an extrasystole of less than 4 per 1 minute is recorded; dizziness, headache, shortness of breath, calf pain; significant increase in blood pressure (250/120 or more); reversion (inversion) of the T wave - these symptoms, as signs of coronary artery disease, are nonspecific, as a rule, associated with the patient’s lack of training and lack of experience in performing heavy physical activity;
- positive test: ECG criteria for the presence of myocardial ischemia are recorded, regardless of the simultaneous development (absence) of angina attacks;
- questionable sample:
- the patient developed pain in the chest characteristic of angina pectoris, which was not confirmed by ischemic changes on the ECG;
- The ECG recorded a horizontal decrease in the ST segment by 0.5 mm, a slowly ascending decrease in the ST segment to 1 mm;
- arrhythmias and cardiac conduction disturbances were recorded;
- at the height of the action of the provoking factor, a decrease in blood pressure of 20 mm Hg was recorded. Art. and more.
- unreliable sample: the patient failed to achieve the required age level of heart rate.
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Back in the 19th century, scientists, studying the anatomical and physiological characteristics of the heart of animals and humans, came to the conclusion that this organ is a muscle capable of generating and conducting electrical impulses. The human heart consists of two atria and two ventricles. Correct conduction of electrical signals through them ensures good contractility of the myocardium (heart muscle) and ensures the correct rhythm of contractions.
Initially, the impulse occurs in the cells of the sinoatrial (atrial) node, located on the border of the right atrium and the superior vena cava. It then spreads through the atria, reaching the atrioventricular node (located between the right atrium and the ventricle), here there is a slight delay in the impulse, then passes through the His bundle in the thickness of the interventricular septum and spreads along the Purkinje fibers in the walls of both ventricles. It is this path of conducting an electrical signal through the conduction system of the heart that is correct and ensures full cardiac contraction, since under the influence of the impulse the muscle cell contracts.
Conduction system of the heart
A little later, scientists were able to create a device that allows them to record and read the processes of electrical activity in the heart by placing electrodes on the chest. A huge role here belongs to Willem Uythoven, a Dutch scientist who designed the first apparatus for electrocardiography and proved that in people with various heart diseases, the indicators of cardiac electrophysiology change during the recording of an ECG (1903). So, what is electrocardiography?
is an instrumental method for studying the electrophysiological activity of the heart, based on recording and graphically depicting the potential difference that occurs during the contraction of the heart muscle for the purpose of diagnosing heart diseases.
An ECG is performed by placing electrodes on the anterior wall of the chest in the projection of the heart and limbs, then using the ECG device itself, the electrical potentials of the heart are recorded and displayed as a graphic curve on a computer monitor or thermal paper (using an ink recorder). Electrical impulses generated by the heart propagate throughout the body, so for ease of reading, leads were developed - circuits that make it possible to record potential differences in different parts of the heart. There are three standard leads - 1, 11, 111; three enhanced leads – aVL, aVR, aVF; and six chest leads - from V1 to V6. All twelve leads are displayed on the ECG film and allow you to see the work of a particular part of the heart in each specific lead.
In modern times, the electrocardiography method is very widespread due to its availability, ease of use, low cost and lack of invasiveness (violation of the integrity of body tissues). An ECG makes it possible to timely diagnose many diseases - acute coronary pathology (myocardial infarction), hypertension, rhythm and conduction disorders, etc., and also allows you to evaluate the effectiveness of drug or surgical treatment of heart disease.
The following ECG methods are distinguished:
- Holter (24-hour) ECG monitoring– the patient is fitted with a portable small device on the chest, which records the slightest deviations in the activity of the heart during the day. The good thing about this method is that it allows you to monitor the work of the heart during the patient’s normal everyday activities and for a longer period of time than when taking a simple ECG. Helps in recording cardiac arrhythmias and myocardial ischemia that were not detected with a single ECG.
- ECG with stress– medication (with the use of pharmacological drugs) or physical activity (treadmill test, bicycle ergometry) is used; as well as electrical stimulation of the heart when a sensor is inserted through the esophagus (TEPS - transesophageal electrophysiological study). Allows you to diagnose the initial stages of coronary artery disease, when the patient complains of pain in the heart during physical activity, but the ECG at rest does not reveal any changes.
- transesophageal ECG– as a rule, it is performed before TEE, as well as in cases where an ECG through the anterior chest wall turns out to be uninformative and does not help the doctor establish the true nature of heart rhythm disturbances.
Indications for ECG
Why is an ECG necessary? Electrocardiography allows you to diagnose many cardiac diseases. Indications for ECG are:
1. Routine examination of children, adolescents, pregnant women, military personnel, drivers, athletes, people over 40 years of age, patients before surgery, patients with other diseases (diabetes mellitus, thyroid diseases, lung diseases, digestive system diseases, etc.);
2. Diagnosis of diseases:
- arterial hypertension;
- coronary heart disease (CHD), including acute, subacute myocardial infarction, post-infarction cardiosclerosis;
- endocrine, dysmetabolic, alcohol-toxic cardiomyopathies;
- chronic heart failure;
- heart defects;
- rhythm and conduction disorders - SVC syndrome, atrial fibrillation, extrasystole, tachycardia - and bradycardia, sinoatrial and atrioventricular blockade, bundle branch block, etc.
- pericarditis
3. Control after treatment of the listed diseases (drug or cardiac surgery)
Contraindications for ECG
There are no contraindications for standard electrocardiography. However, the procedure itself can be difficult in persons with complex chest injuries, with a high degree of obesity, with severe chest hair (the electrodes simply will not be able to fit tightly to the skin). The presence of a pacemaker in the patient’s heart can also significantly distort ECG data.
There are contraindications for performing an ECG with stress: acute period of myocardial infarction, acute infectious diseases, worsening of arterial hypertension, coronary heart disease, chronic heart failure, complex rhythm disturbances, suspicion of dissection of the aortic aneurysm, decompensation (worsening of the course) of diseases of other organs and systems – digestive, respiratory, urinary. Contraindications for transesophageal ECG are diseases of the esophagus - tumors, strictures, diverticula, etc.
Preparing for the study
An ECG does not require special preparation for the patient. There are no restrictions on normal household activities, eating or drinking. It is not recommended to consume coffee, alcohol or large amounts of cigarettes before the procedure, as this will affect the functioning of the heart at the time of the study, and the results may be misinterpreted.
How is electrocardiography performed?
An ECG can be performed in a hospital or clinic. In the hospital, a study is carried out on patients delivered by an ambulance team with cardiac symptoms, or on patients already hospitalized in a hospital of any profile (therapeutic, surgical, neurological, etc.). In the clinic, an ECG is performed as a routine examination, as well as for patients whose health condition does not require urgent hospitalization.
Carrying out an ECG
The patient comes at the appointed time to the ECG diagnostic room, lies down on the couch on his back; the nurse wipes the chest, wrists and ankles with a sponge moistened with water (for better conductivity) and places electrodes - one “clothespin” on the wrists and feet and six “suction cups” on the chest in the projection of the heart. Next, the device is turned on, the electrical activity of the heart is read, and the result is recorded in the form of a graphic curve on thermal film using an ink recorder or immediately saved in the doctor’s computer. The entire study lasts about 5 - 10 minutes, without causing any discomfort in the patient.
Next, the ECG is analyzed by a functional diagnostics doctor, after which the conclusion is given to the patient or sent directly to the attending physician’s office. If the ECG does not reveal any serious changes requiring further observation in the hospital, the patient can go home.
ECG interpretation
Now let's take a closer look at the analysis of the electrocardiogram. Each complex of a normal electrocardiogram consists of waves P, Q, R, S, T and segments - PQ and ST. The teeth can be positive (directed upward) or negative (directed downward), and the segments are above and below the isoline.
The patient will see the following indicators in the ECG protocol:
1. Source of excitation. During normal heart function, the source is located in the sinus node, that is, the rhythm is sinus. Its signs are the presence of positive P waves in the 11th lead in front of each ventricular complex of the same shape. Non-sinus rhythm is characterized by negative P waves and appears with sinoatrial block, extrasystole, atrial fibrillation, atrial flutter, fibrillation and ventricular flutter.
2. Correctness (regularity) of the rhythm. It is determined when the distance between the R waves of several complexes differs by no more than 10%. If the rhythm is abnormal, the presence of arrhythmias is also indicated. A sinus but irregular rhythm occurs with sinus (respiratory) arrhythmia, and a sinus regular rhythm occurs with sinus brady and tachycardia.
3. HR - heart rate. Normally 60 – 80 beats per minute. A condition with a heart rate below this value is called bradycardia (slow heartbeat), and above it is called tachycardia (rapid heartbeat).
4. Determination of EOS (rotation of the electrical axis of the heart). EOS is the summing vector of the electrical activity of the heart, coinciding with the direction of its anatomical axis. Normally, the EOS varies from semi-vertical to semi-horizontal position. In obese people, the heart is located horizontally, while in thin people it is more vertical. EOS deviations may indicate myocardial hypertrophy (proliferation of the heart muscle, for example, with arterial hypertension, heart defects, cardiomyopathies) or conduction disorders (blockade of the legs and branches of the His bundle).
5. Analysis of the P wave. The P wave reflects the occurrence of an impulse in the sinoatrial node and its conduction through the atria. Normally, the P wave is positive (the exception is lead aVR), its width is up to 0.1 sec, and its height is from 1.5 to 2.5 mm. Deformation of the P wave is characteristic of pathology of the mitral valve (P mitrale) or diseases of the bronchopulmonary system with the development of circulatory failure (P pulmonale).
6. PQ segment analysis. Reflects the conduction and physiological delay of the impulse through the atrioventricular node and is 0.02 - 0.09 sec. A change in duration is characteristic of conduction disorders - shortened PQ syndrome, atrioventricular block.
7. Analysis of the QRS complex. Reflects the conduction of an impulse along the interventricular septum and ventricular myocardium. Normally, its duration is up to 0.1 seconds. A change in its duration, as well as deformation of the complex, is characteristic of myocardial infarction, bundle branch block, ventricular extrasystole, and paroxysmal ventricular tachycardia.
8. ST segment analysis. Reflects the process of complete coverage of the ventricles by excitation. Normally it is located on the isoline; a shift up or down by 0.5 mm is allowed. Depression (decrease) or elevation of ST indicates the presence of myocardial ischemia or the development of myocardial infarction.
9. Analysis of the T wave. Reflects the process of attenuation of ventricular excitation. Normally positive. A negative T also indicates the presence of ischemia or small focal myocardial infarction.
The patient must remember that independent analysis of the ECG protocol is not acceptable. Interpretation of electrocardiogram indicators should only be carried out by a functional diagnostics doctor, cardiologist, therapist or emergency physician, since only a doctor, during an in-person examination, can compare the data obtained with clinical symptoms and the risk of conditions requiring treatment, including in a hospital. Otherwise, underestimating the ECG conclusion can harm a person’s health and life.
ECG complications
Are there possible complications during electrocardiography? The ECG procedure is quite harmless and safe, so there are no complications. When performing an ECG with stress, an increase in blood pressure, rhythm and conduction disturbances in the heart may occur, but this, rather, can be attributed not to complications, but to diseases, for the clarification of which provocative tests were prescribed.
General practitioner Sazykina O.Yu.
Electrocardiography is a method of graphically recording the potential difference in the electrical field of the heart that arises during its activity. Registration is carried out using a device - an electrocardiograph. It consists of an amplifier that allows it to capture currents of very low voltage; a galvanometer that measures voltage; power systems; recording device; electrodes and wires connecting the patient to the device. The waveform that is recorded is called an electrocardiogram (ECG). Registration of the potential difference in the electric field of the heart from two points on the surface of the body is called lead. As a rule, the ECG is recorded in twelve leads: three bipolar (three standard leads) and nine unipolar (three unipolar enhanced limb leads and 6 unipolar chest leads). With bipolar leads, two electrodes are connected to the electrocardiograph; with unipolar leads, one electrode (indifferent) is combined, and the second (different, active) is placed at a selected point on the body. If the active electrode is placed on a limb, the lead is called unipolar, limb-amplified; if this electrode is placed on the chest - with a unipolar chest lead.
To record an ECG in standard leads (I, II and III), cloth napkins moistened with saline are placed on the limbs, on which metal electrode plates are placed. One electrode with a red wire and one raised ring is placed on the right, the second - with a yellow wire and two raised rings - on the left forearm, and the third - with a green wire and three raised rings - on the left shin. To record leads, two electrodes are connected to the electrocardiograph in turn. To record lead I, the electrodes of the right and left hands are connected, lead II - electrodes of the right hand and left leg, lead III - electrodes of the left hand and left leg. Switching leads is done by turning the knob. In addition to the standard ones, unipolar reinforced leads are removed from the limbs. If the active electrode is located on the right arm, the lead is designated as aVR or UP, if on the left arm - aVL or UL, and if on the left leg - aVF or UL.
Rice. 1. The location of the electrodes when registering the anterior chest leads (indicated in numbers corresponding to their serial numbers). The vertical stripes crossing the numbers correspond to the anatomical lines: 1 - right sternal; 2 - left sternal; 3 - left parasternal; 4-left midclavicular; 5-left anterior axillary; 6 - left middle axillary.
When recording unipolar chest leads, the active electrode is placed on the chest. The ECG is recorded in the following six electrode positions: 1) at the right edge of the sternum in the IV intercostal space; 2) at the left edge of the sternum in the IV intercostal space; 3) along the left parasternal line between the IV and V intercostal spaces; 4) along the midclavicular line in the 5th intercostal space; 5) along the anterior axillary line in the 5th intercostal space and 6) along the middle axillary line in the 5th intercostal space (Fig. 1). Unipolar chest leads are designated by the Latin letter V or in Russian - GO. Less commonly recorded are bipolar chest leads, in which one electrode is located on the chest and the other on the right arm or left leg. If the second electrode was located on the right arm, the chest leads were designated by the Latin letters CR or Russian - GP; when the second electrode was located on the left leg, the chest leads were designated by the Latin letters CF or Russian - GN.
The ECG of healthy people is variable. It depends on age, physique, etc. However, normally it is always possible to distinguish certain teeth and intervals on it, reflecting the sequence of excitation of the heart muscle (Fig. 2). According to the available time stamp (on photographic paper the distance between two vertical stripes is 0.05 sec., on graph paper at a broaching speed of 50 mm/sec 1 mm is 0.02 sec., at a speed of 25 mm/sec - 0.04 sec. ) you can calculate the duration of ECG waves and intervals (segments). The height of the teeth is compared with a standard mark (when a 1 mV pulse is applied to the device, the recorded line should deviate from the original position by 1 cm). Excitation of the myocardium begins from the atria, and the atrial P wave appears on the ECG. Normally, it is small: 1-2 mm high and lasting 0.08-0.1 seconds. The distance from the beginning of the P wave to the Q wave (P-Q interval) corresponds to the time of propagation of excitation from the atria to the ventricles and is equal to 0.12-0.2 seconds. During excitation of the ventricles, the QRS complex is recorded, and the size of its waves in different leads is expressed differently: the duration of the QRS complex is 0.06-0.1 seconds. The distance from the S wave to the beginning of the T wave - the S-T segment, is normally located at the same level with the P-Q interval and its displacement should not exceed 1 mm. When excitation in the ventricles fades, a T wave is recorded. The interval from the beginning of the Q wave to the end of the T wave reflects the process of excitation of the ventricles (electrical systole). Its duration depends on the heart rate: when the rhythm increases, it shortens, when it slows down, it lengthens (on average it is 0.24-0.55 seconds). The heart rate can be easily calculated from an ECG, knowing how long one cardiac cycle lasts (the distance between two R waves) and how many such cycles are contained in a minute. The T-P interval corresponds to the diastole of the heart; at this time the device records a straight (so-called isoelectric) line. Sometimes after the T wave a U wave is recorded, the origin of which is not entirely clear.
Rice. 2. Electrocardiogram of a healthy person.
In pathology, the size of the waves, their duration and direction, as well as the duration and location of ECG intervals (segments), can vary significantly, which gives rise to the use of electrocardiography in the diagnosis of many heart diseases. Using electrocardiography, various heart rhythm disturbances are diagnosed (see), inflammatory and dystrophic lesions of the myocardium are reflected on the ECG. Electrocardiography plays a particularly important role in the diagnosis of coronary insufficiency and myocardial infarction.
Using an ECG, you can determine not only the presence of a heart attack, but also find out which wall of the heart is affected. In recent years, to study the potential difference in the electric field of the heart, the method of teleelectrocardiography (radioelectrocardiography), based on the principle of wireless transmission of the electric field of the heart using a radio transmitter, has been used. This method allows you to register an ECG during physical activity, in motion (for athletes, pilots, astronauts).
Electrocardiography (Greek kardia - heart, grapho - writing, recording) is a method of recording electrical phenomena occurring in the heart during its contraction.
The history of electrophysiology, and therefore electrocardiography, begins with the experiment of Galvani (L. Galvani), who discovered electrical phenomena in the muscles of animals in 1791. Matteucci (S. Matteucci, 1843) established the presence of electrical phenomena in an excised heart. Dubois-Reymond (E. Dubois-Reymond, 1848) proved that in both nerves and muscles the excited part is electronegative relative to the resting part. Kolliker and Muller (A. Kolliker, N. Muller, 1855), applying a frog neuromuscular preparation consisting of a sciatic nerve connected to the gastrocnemius muscle to the contracting heart, obtained a double contraction during heart contraction: one at the beginning of systole and the other (non-constant ) at the beginning of diastole. Thus, the electromotive force (EMF) of the naked heart was recorded for the first time. Waller (A. D. Waller, 1887) was the first to record the EMF of the heart from the surface of the human body using a capillary electrometer. Waller believed that the human body is a conductor surrounding the source of EMF - the heart; different points of the human body have potentials of different magnitudes (Fig. 1). However, the recording of cardiac EMF obtained by a capillary electrometer did not accurately reproduce its fluctuations.
Rice. 1. Scheme of the distribution of isopotential lines on the surface of the human body, caused by the electromotive force of the heart. The numbers indicate the potential values.
An accurate recording of the EMF of the heart from the surface of the human body - an electrocardiogram (ECG) - was made by Einthoven (W. Einthoven, 1903) using a string galvanometer, built on the principle of devices for receiving transatlantic telegrams.
According to modern concepts, cells of excitable tissues, in particular myocardial cells, are covered with a semi-permeable membrane (membrane), permeable to potassium ions and impermeable to anions. Positively charged potassium ions, which are in excess in cells compared to their surrounding environment, are retained on the outer surface of the membrane by negatively charged anions located on its inner surface, impenetrable to them.
Thus, a double electrical layer appears on the shell of a living cell - the shell is polarized, and its outer surface is charged positively in relation to the internal contents, which are negatively charged.
This transverse potential difference is the resting potential. If microelectrodes are applied to the outer and inner sides of the polarized membrane, a current arises in the outer circuit. Recording the resulting potential difference gives a monophasic curve. When excitation occurs, the membrane of the excited area loses its semi-permeability, depolarizes, and its surface becomes electronegative. Registration of the potentials of the outer and inner shell of the depolarized membrane with two microelectrodes also gives a monophasic curve.
Due to the potential difference between the surface of the excited depolarized area and the surface of the polarized one, which is at rest, an action current arises - an action potential. When excitation covers the entire muscle fiber, its surface becomes electronegative. The cessation of excitation causes a wave of repolarization, and the resting potential of the muscle fiber is restored (Fig. 2).
Rice. 2. Schematic representation of polarization, depolarization and repolarization of a cell.
If the cell is at rest (1), then on both sides of the cell membrane there is an electrostatic equilibrium, consisting in the fact that the surface of the cell is electropositive (+) in relation to its inner side (-).
The excitation wave (2) instantly disrupts this balance, and the surface of the cell becomes electronegative with respect to its interior; This phenomenon is called depolarization or, more correctly, inversion polarization. After the excitation has passed through the entire muscle fiber, it becomes completely depolarized (3); its entire surface has the same negative potential. This new equilibrium does not last long, since the excitation wave is followed by a repolarization wave (4), which restores the polarization of the resting state (5).
The process of excitation in a normal human heart - depolarization - proceeds as follows. Arising in the sinus node, located in the right atrium, the excitation wave propagates at a speed of 800-1000 mm per 1 second. radially along the muscle bundles of first the right and then the left atrium. The duration of excitation coverage of both atria is 0.08-0.11 seconds.
The first 0.02 - 0.03 sec. Only the right atrium is excited, then 0.04 - 0.06 seconds - both atria and the last 0.02 - 0.03 seconds - only the left atrium.
Upon reaching the atrioventricular node, the spread of excitation slows down. Then, at a high and gradually increasing speed (from 1400 to 4000 mm per 1 second), it is directed along the bundle of His, its legs, their branches and branches and reaches the final ends of the conduction system. Having reached the contractile myocardium, excitation spreads through both ventricles at a significantly reduced speed (300-400 mm per 1 second). Since the peripheral branches of the conduction system are scattered mainly under the endocardium, the inner surface of the heart muscle is the first to become excited. The further course of excitation of the ventricles is not related to the anatomical location of the muscle fibers, but is directed from the inner surface of the heart to the outer. The time of excitation in the muscle bundles located on the surface of the heart (subepicardial) is determined by two factors: the time of excitation of the branches of the conduction system closest to these bundles and the thickness of the muscle layer separating the subepicardial muscle bundles from the peripheral branches of the conduction system.
The interventricular septum and the right papillary muscle are the first to be excited. In the right ventricle, excitation first covers the surface of its central part, since the muscle wall in this place is thin and its muscle layers are in close contact with the peripheral branches of the right leg of the conduction system. In the left ventricle, the apex is the first to become excited, since the wall separating it from the peripheral branches of the left leg is thin. For various points on the surface of the right and left ventricles of a normal heart, the period of excitation begins at a strictly defined time, and most of the fibers on the surface of the thin-walled right ventricle and only a small number of fibers on the surface of the left ventricle become excited first due to their proximity to the peripheral branches of the conduction system (Fig. .3).
Rice. 3. Schematic representation of normal excitation of the interventricular septum and outer walls of the ventricles (according to Sodi-Pallares et al.). Excitation of the ventricles begins on the left side of the septum in its middle part (0.00-0.01 sec.) and then can reach the base of the right papillary muscle (0.02 sec.). After this, the subendocardial muscle layers of the outer wall of the left (0.03 sec.) and right (0.04 sec.) ventricles are excited. The last to be excited are the basal parts of the outer walls of the ventricles (0.05-0.09 sec.).
The process of cessation of excitation of the muscle fibers of the heart - repolarization - cannot be considered fully studied. The process of atrial repolarization coincides for the most part with the process of depolarization of the ventricles and partly with the process of their repolarization.
The process of ventricular repolarization is much slower and in a slightly different sequence than the process of depolarization. This is explained by the fact that the duration of excitation of the muscle bundles of the superficial layers of the myocardium is less than the duration of excitation of the subendocardial fibers and papillary muscles. Recording the process of depolarization and repolarization of the atria and ventricles from the surface of the human body gives a characteristic curve - an ECG, reflecting the electrical systole of the heart.
The EMF of the heart is currently recorded using slightly different methods than those recorded by Einthoven. Einthoven recorded the current generated by connecting two points on the surface of the human body. Modern devices - electrocardiographs - directly record the voltage caused by the electromotive force of the heart.
The voltage caused by the heart, equal to 1-2 mV, is amplified by radio tubes, semiconductors or a cathode ray tube to 3-6 V, depending on the amplifier and recording apparatus.
The sensitivity of the measuring system is set so that a potential difference of 1 mV gives a deviation of 1 cm. Recording is done on photographic paper or film or directly on paper (ink, thermal recording, inkjet recording). The most accurate results are obtained by recording on photographic paper or film and inkjet recording.
To explain the peculiar shape of the ECG, various theories of its genesis have been proposed.
A.F. Samoilov considered the ECG as the result of the interaction of two monophasic curves.
Considering that when two microelectrodes record the outer and inner surfaces of the membrane in states of rest, excitation and damage, a monophasic curve is obtained, M. T. Udelnov believes that the monophasic curve reflects the main form of bioelectrical activity of the myocardium. The algebraic sum of two monophasic curves gives the ECG.
Pathological ECG changes are caused by shifts in monophasic curves. This theory of the genesis of the ECG is called differential.
The outer surface of the cell membrane during the period of excitation can be represented schematically as consisting of two poles: negative and positive.
Immediately before the excitation wave at any point in its propagation, the cell surface is electropositive (resting state of polarization), and immediately after the excitation wave, the cell surface is electronegative (depolarization state; Fig. 4). These electric charges of opposite signs, grouped in pairs on one side and the other of each place covered by the excitation wave, form electric dipoles (a). Repolarization also creates an innumerable number of dipoles, but unlike the above dipoles, the negative pole is in front and the positive pole is behind in relation to the direction of wave propagation (b). If depolarization or repolarization is complete, the surface of all cells has the same potential (negative or positive); dipoles are completely absent (see Fig. 2, 3 and 5).
Rice. 4. Schematic representation of electric dipoles during depolarization (a) and repolarization (b), arising on both sides of the excitation wave and the repolarization wave as a result of changes in the electrical potential on the surface of the myocardial fibers.
Rice. 5. Diagram of an equilateral triangle according to Einthoven, Faro and Warth.
The muscle fiber is a small bipolar generator that produces a small (elementary) EMF - an elementary dipole.
At each moment of cardiac systole, depolarization and repolarization occurs of a huge number of myocardial fibers located in different parts of the heart. The sum of the resulting elementary dipoles creates the corresponding value of the EMF of the heart at each moment of systole. Thus, the heart represents, as it were, one total dipole, changing its magnitude and direction during the cardiac cycle, but not changing the location of its center. The potential at different points on the surface of the human body has different values depending on the location of the total dipole. The sign of the potential depends on which side of the line perpendicular to the dipole axis and drawn through its center the given point is located: on the side of the positive pole the potential has a + sign, and on the opposite side it has a - sign.
Most of the time the heart is excited, the surface of the right half of the torso, right arm, head and neck has a negative potential, and the surface of the left half of the torso, both legs and left arm has a positive potential (Fig. 1). This is a schematic explanation of the genesis of the ECG according to the dipole theory.
The EMF of the heart during electrical systole changes not only its magnitude, but also its direction; therefore, it is a vector quantity. A vector is depicted as a straight line segment of a certain length, the size of which, given certain data from the recording apparatus, indicates the absolute value of the vector.
The arrow at the end of the vector indicates the direction of the cardiac EMF.
The EMF vectors of individual heart fibers that arise simultaneously are summed up according to the vector addition rule.
The total (integral) vector of two vectors located parallel and directed in one direction is equal in absolute value to the sum of its constituent vectors and is directed in the same direction.
The total vector of two vectors of the same magnitude, located parallel and directed in opposite directions, is equal to 0. The total vector of two vectors directed to each other at an angle is equal to the diagonal of a parallelogram constructed from its constituent vectors. If both vectors form an acute angle, then their total vector is directed towards its constituent vectors and is greater than any of them. If both vectors form an obtuse angle and, therefore, are directed in opposite directions, then their total vector is directed towards the largest vector and is shorter than it. Vector analysis of an ECG consists of determining from the ECG waves the spatial direction and magnitude of the total EMF of the heart at any moment of its excitation.
The electrocardiogram reflects electrical processes only in the myocardium: depolarization (excitation) and repolarization (restoration) of myocardial cells.
Ratio ECG intervals With 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 a concept “ electromechanical dissociation“, in which depolarization and repolarization of the myocardium do not lead to its visible contraction and relaxation. I wrote a little more about this phenomenon earlier .
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 P-Q interval is usually called P-R.
Any ECG consists of teeth, segments And intervals.
TEETH- these are convexities and concavities on the electrocardiogram. The following waves are distinguished on the ECG:
P(atrial contraction)
Q, R, S(all 3 teeth characterize contraction of the ventricles),
T(ventricle relaxation)
U(non-permanent tooth, rarely recorded).
SEGMENTS A segment on an ECG is called straight line segment(isolines) between two adjacent teeth. The most important segments are P-Q and S-T. For example, the P-Q segment is formed due to a delay in the conduction of excitation in the atrioventricular (AV-) node.
INTERVALS The interval consists of tooth (complex of teeth) and segment. Thus, interval = tooth + segment. The most important are the P-Q and Q-T 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 complex QRS on the ECG. How to do it right highlight the teeth in it?
First of all they evaluate amplitude (sizes) of individual teeth QRS complex. If the amplitude exceeds 5 mm, the tooth indicates 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 called any positive(upward) wave that is part of the QRS complex. If there are several teeth, subsequent teeth indicate strokes: R, R’, R”, etc. Negative (downward) wave of the QRS complex, located before the R wave, is denoted as Q(q), and after - like 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.
Normal tooth Q reflects depolarization of the interventricular septum, tooth R- the bulk of the ventricular myocardium, tooth S- basal (i.e. near the atria) sections of the interventricular septum. The R V1, V2 wave reflects the excitation of the interventricular septum, and R V4, V5, V6 - the excitation of the muscles of the left and right ventricles. Necrosis of areas of the myocardium (for example, with myocardial infarction ) causes the Q wave to widen and deepen, so close attention is always paid to this wave.
ECG analysis
General ECG decoding diagram
Checking the correctness of ECG registration.
Heart rate and conduction analysis:
assessment of heart rate regularity,
heart rate (HR) counting,
determination of the source of excitation,
conductivity assessment.
Determination of the electrical axis of the heart.
Analysis of the atrial P wave and P-Q interval.
Analysis of the ventricular QRST complex:
QRS complex analysis,
analysis of the RS - T segment,
T wave analysis,
Q-T interval analysis.
Electrocardiographic report.
Normal electrocardiogram.
1) Checking the correct ECG registration
At the beginning of each ECG tape there must be calibration signal- so-called reference millivolt. To do this, at the beginning of the recording, a standard voltage of 1 millivolt is applied, which should display a deviation of 10 mm. 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, it is called reduced ECG voltage, which occurs in some pathological conditions.
Reference millivolt on the ECG (at the beginning of the recording).
2) Heart rate and conduction analysis:
assessment of heart rate regularity
Rhythm regularity is assessed by R-R intervals. If the teeth are at an equal distance from each other, the rhythm is called regular, or correct. The variation in the duration of individual R-R intervals is allowed no more than ± 10% from their average duration. If the rhythm is sinus, it is usually regular.
heart rate counting(heart rate)
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 teeth R - R.
At belt speed 50 mm/s: HR = 600 / (number of large squares). At belt speed 25 mm/s: HR = 300 / (number of large squares).
On the overlying ECG, the R-R interval is approximately 4.8 large cells, which at a speed of 25 mm/s gives 300 / 4.8 = 62.5 beats/min.
At a speed of 25 mm/s each small cell 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 incorrect, it is usually considered maximum and minimum heart rate according to the duration of the smallest and largest R-R interval, respectively.
determination of the excitation source
In other words, they are looking for where pacemaker, 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 know well conduction system of the heart .
Sinus rhythm(this is a normal rhythm, and all other rhythms are pathological). The source of excitation is in 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.
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 in the atrioventricular ( atrioventricular node) node, then the ventricles are excited as usual (from top to bottom), and the atria - retrograde (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(from Latin ventriculus [ventrikulyus] - ventricle). 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.
conductivity assessment. To properly account for conductivity, the recording speed is taken into account.
To assess conductivity, measure:
duration P wave(reflects the speed of impulse transmission through the atria), normally up to 0.1 s.
duration interval P - Q(reflects the speed of impulse conduction from the atria to the ventricular myocardium); interval P - Q = (wave P) + (segment P - Q). Fine 0.12-0.2 s.
duration QRS complex(reflects the spread of excitation through the ventricles). Fine 0.06-0.1 s.
internal deviation interval in leads V1 and V6. This is the time between the beginning of the QRS complex and the R wave. Normal in V1 up to 0.03 s and in V6 up to 0.05 s. Used mainly to recognize bundle branch blocks and to determine the source of excitation in the ventricles in the case of ventricular extrasystole (extraordinary contraction of the heart).
Measuring the internal deviation interval.
3) Determination of the electrical axis of the heart. In the first part of the series about ECG it was explained what it is electrical axis of the heart and how it is determined in the frontal plane.
4) Atrial P wave analysis. Normally, in leads I, II, aVF, V2 - V6, the P wave 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 right atrial hypertrophy, for example, with “pulmonary heart”.
Split with 2 apexes, widened P wave in leads I, aVL, V5, V6 is characteristic of left atrial 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 hypertrophy of the left atrium.
P-Q interval: fine 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).
AV block There are 3 degrees:
I degree - the P-Q interval is increased, but each P wave has its own QRS complex ( 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) Ventricular QRST analysis:
QRS complex analysis.
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.
Normally, the Q wave can be recorded in all standard and enhanced limb leads, as well as in V4-V6. The amplitude of the Q wave normally does not exceed 1/4 R wave height, and the duration is 0.03 s. In lead aVR, there is normally a deep and wide Q wave and even a QS complex.
The R wave, like the Q wave, can be recorded in all standard and enhanced limb leads. From V1 to V4, the amplitude increases (in this case, the r wave of V1 may be absent), and then decreases in V5 and V6.
The S wave can have very different amplitudes, but usually no more than 20 mm. The S wave decreases from V1 to V4, and may even be absent in V5-V6. In lead V3 (or between V2 - V4) “ transition zone” (equality of R and S waves).
RS - T segment analysis
The S-T segment (RS-T) is a segment from the end of the QRS complex to the beginning of the T wave. The S-T segment is especially carefully analyzed in case of coronary artery disease, since it reflects the lack of oxygen (ischemia) in the myocardium.
Normally, the S-T segment is located in the limb leads on the isoline ( ± 0.5 mm). In leads V1-V3, the S-T segment may shift upward (no more than 2 mm), and in leads V4-V6 - downward (no more than 0.5 mm).
The point at which the QRS complex transitions to the S-T segment is called the point j(from the word junction - connection). The degree of deviation of point j from the isoline is used, for example, to diagnose myocardial ischemia.
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. Normally, the T wave is always positive in I, II, aVF, V2-V6, with T I > T III, and T V6 > T V1. In aVR the T wave is always negative.
Q-T interval analysis.
The Q-T 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 there is a small U wave, which is formed due to short-term increased excitability of the ventricular myocardium after their repolarization.
6) Electrocardiographic report. Should include:
Source of rhythm (sinus or not).
Regularity of rhythm (correct or not). Usually sinus rhythm is normal, although respiratory arrhythmia is possible.
Position of the electrical axis of the heart.
Presence of 4 syndromes:
rhythm disturbance
conduction disturbance
hypertrophy and/or overload of the ventricles and atria
myocardial damage (ischemia, dystrophy, necrosis, scars)
Examples of conclusions(not quite complete, but real):
Sinus rhythm with heart rate 65. Normal position of the electrical axis of the heart. No pathology was identified.
Sinus tachycardia with heart rate 100. Single supraventricular extrasystole.
Sinus rhythm with heart rate 70 beats/min. Incomplete blockade of the right bundle branch. Moderate metabolic changes in the myocardium.
Examples of ECG for specific diseases of the cardiovascular system - next time.
ECG interference
Due to frequent questions in the comments about the type of ECG, I’ll tell you about interference which may appear on the electrocardiogram:
Three types of ECG interference(explained below).
Interference on an ECG in the lexicon of health workers is called tip-off: a) inrush currents: network pickup 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).
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Electrocardiogram is a widely used method of objective diagnostics various pathologies of the human heart, which is used almost everywhere today. An electrocardiogram (ECG) is taken in a clinic, in an ambulance, or in a hospital department. ECG is a very important recording that reflects the condition of the heart. That is why the reflection of various types of cardiac pathology on the ECG is described by a separate science - electrocardiography. Electrocardiography also deals with the problems of correct ECG recording, decoding issues, interpretation of controversial and unclear points, etc.Definition and essence of the method
An electrocardiogram is a recording of the heart, which is presented as a curved line on paper. The cardiogram line itself is not chaotic; it has certain intervals, teeth and segments that correspond to certain stages of the heart.To understand the essence of an electrocardiogram, you need to know what exactly is recorded by a device called an electrocardiograph. The ECG records the electrical activity of the heart, which changes cyclically in accordance with the onset of diastole and systole. The electrical activity of the human heart may seem like fiction, but this unique biological phenomenon exists in reality. In reality, the heart contains so-called cells of the conduction system, which generate electrical impulses that are transmitted to the muscles of the organ. It is these electrical impulses that cause the myocardium to contract and relax with a certain rhythm and frequency.
The electrical impulse propagates through the cells of the conduction system of the heart strictly sequentially, causing contraction and relaxation of the corresponding sections - the ventricles and atria. The electrocardiogram reflects precisely the total electrical potential difference in the heart.
decryption?
An electrocardiogram can be taken in any clinic or multidisciplinary hospital. You can contact a private medical center where there is a specialist cardiologist or therapist. After recording the cardiogram, the tape with curves is examined by the doctor. It is he who analyzes the recording, deciphers it and writes a final report, which reflects all visible pathologies and functional deviations from the norm. An electrocardiogram is recorded using a special device - an electrocardiograph, which can be multi-channel or single-channel. The speed of ECG recording depends on the modification and modernity of the device. Modern devices can be connected to a computer, which, with a special program, will analyze the recording and issue a final conclusion immediately after the procedure is completed.
Any cardiograph has special electrodes that are applied in a strictly defined order. There are four clothespins in red, yellow, green and black that are placed on both arms and both legs. If you go in a circle, then the clothespins are applied according to the rule “red-yellow-green-black”, from the right hand. It's easy to remember this sequence thanks to the student saying: "Every-Woman is an Eviler Trait." In addition to these electrodes, there are also chest electrodes, which are installed in the intercostal spaces.
As a result, the electrocardiogram consists of twelve waveforms, six of which are recorded from the chest electrodes, and are called chest leads. The remaining six leads are recorded from electrodes attached to the arms and legs, with three of them called standard and three more called enhanced. The chest leads are designated V1, V2, V3, V4, V5, V6, the standard ones are simply Roman numerals - I, II, III, and the reinforced leg leads - the letters aVL, aVR, aVF. Different leads of the cardiogram are necessary to create the most complete picture of the activity of the heart, since some pathologies are visible on the chest leads, others on the standard ones, and still others on the enhanced ones.
The person lies down on the couch, the doctor attaches the electrodes and turns on the device. While the ECG is being written, the person must be absolutely calm. We must not allow the appearance of any irritants that can distort the true picture of the work of the heart.
How to correctly perform an electrocardiogram followed by
transcript - video
The principle of decoding an ECG
Since the electrocardiogram reflects the processes of contraction and relaxation of the myocardium, it is possible to trace how these processes occur and identify existing pathological processes. The elements of the electrocardiogram are closely related and reflect the duration of the phases of the cardiac cycle - systole and diastole, that is, contraction and subsequent relaxation. Decoding the electrocardiogram is based on the study of the teeth, their position relative to each other, duration, and other parameters. The following elements of the electrocardiogram are studied for analysis:1. Teeth.
2. Intervals.
3. Segments.
All sharp and smooth convexities and concavities on the ECG line are called teeth. Each tooth is designated by a letter of the Latin alphabet. The P wave reflects contraction of the atria, the QRS complex – contraction of the ventricles of the heart, the T wave – relaxation of the ventricles. Sometimes after the T wave on the electrocardiogram there is another U wave, but it has no clinical and diagnostic role.
An ECG segment is considered to be a segment enclosed between adjacent teeth. For diagnosing heart pathology, the P – Q and S – T segments are of great importance. The interval on the electrocardiogram is a complex that includes a tooth and an interval. The P–Q and Q–T intervals are of great importance for diagnosis.
Often in the doctor’s report you can see small Latin letters, which also indicate teeth, intervals and segments. Small letters are used if the prong is less than 5 mm long. In addition, several R waves may appear in the QRS complex, which are usually designated R’, R”, etc. Sometimes the R wave is simply missing. Then the entire complex is designated by only two letters - QS. All this has important diagnostic value.
ECG interpretation plan - general scheme for reading results
When deciphering an electrocardiogram, the following parameters reflecting the work of the heart must be established: - position of the electrical axis of the heart;
- determining the correctness of the heart rhythm and conductivity of the electrical impulse (blockades, arrhythmias are identified);
- determining the regularity of contractions of the heart muscle;
- determination of heart rate;
- identifying the source of the electrical impulse (whether sinus rhythm is determined or not);
- analysis of the duration, depth and width of the atrial P wave and the P – Q interval;
- analysis of the duration, depth, width of the QRST ventricular wave complex;
- analysis of parameters of the RS – T segment and T wave;
- analysis of Q – T interval parameters.
In the conclusion on the electrocardiogram, the doctor must reflect the following parameters:
- sinus rhythm or not;
- rhythm regularity;
- heart rate (HR);
- position of the electrical axis of the heart.
Example of deciphering an electrocardiogram
At the very beginning of the electrocardiogram tape there should be a calibration signal, which looks like a large letter “P” 10 mm high. If this calibration signal is not present, then the electrocardiogram is uninformative. If the height of the calibration signal is below 5 mm in standard and enhanced leads, and below 8 mm in chest leads, then there is a low voltage of the electrocardiogram, which is a sign of a number of heart pathologies. For subsequent decoding and calculation of some parameters, you need to know what period of time fits into one cell of graph paper. At a belt speed of 25 mm/s, one cell 1 mm long is equal to 0.04 seconds, and at a speed of 50 mm/s – 0.02 seconds.Checking the regularity of heart contractions
It is assessed by the intervals R - R. If the teeth are located at the same distance from each other throughout the entire recording, then the rhythm is regular. Otherwise it is called correct. Estimating the distance between the R - R teeth is very simple: the electrocardiogram is recorded on graph paper, which makes it easy to measure any gaps in millimeters.Heart rate (HR) calculation
It is carried out using a simple arithmetic method: count the number of large squares on graph paper that are placed between two R waves. Then the heart rate is calculated using the formula, which is determined by the speed of the tape in the cardiograph: 1. The tape speed is 50 mm/s - then the heart rate is 600 divided by the number of squares.
2. The tape speed is 25 mm/s - then the heart rate is 300 divided by the number of squares.
For example, if 4.8 large squares fit between two R teeth, then the heart rate, at a belt speed of 50 mm/s, will be equal to 600/4.8 = 125 beats per minute.
If the heart rate is abnormal, then the maximum and minimum heart rate is determined, also taking as a basis the maximum and minimum distances between the R waves.
Identifying the source of the rhythm
The doctor studies the rhythm of heart contractions and finds out which node of nerve cells causes the cyclic processes of contraction and relaxation of the heart muscle. This is very important for identifying blockages.Decoding ECG - rhythms
Normally, the pacemaker is the sinus node. And such a normal rhythm itself is called sinus - all other options are pathological. In various pathologies, any other node of the nerve cells of the cardiac conduction system can act as a pacemaker. In this case, the cyclic electrical impulses become confused and the heart rhythm is disrupted - an arrhythmia occurs.In sinus rhythm on the electrocardiogram in lead II there is a P wave before each QRS complex, and it is always positive. In one lead, all P waves should have the same shape, length and width.
With atrial rhythm the P wave in leads II and III is negative, but is present before each QRS complex.
Atrioventricular rhythms are characterized by the absence of P waves on cardiograms, or the appearance of this wave after the QRS complex, and not before it, as is normal. With this type of rhythm, the heart rate is low, ranging from 40 to 60 beats per minute.
Ventricular rhythm characterized by an increase in the width of the QRS complex, which becomes large and quite frightening. The P waves and the QRS complex are completely unrelated to each other. That is, there is no strict correct normal sequence - the P wave, followed by the QRS complex. Ventricular rhythm is characterized by a decrease in heart rate - less than 40 beats per minute.
Detection of pathology of electrical impulse conduction through the structures of the heart
To do this, measure the duration of the P wave, the P–Q interval and the QRS complex. The duration of these parameters is calculated from the millimeter tape on which the cardiogram is recorded. First, count how many millimeters each tooth or interval occupies, after which the resulting value is multiplied by 0.02 at a recording speed of 50 mm/s, or by 0.04 at a recording speed of 25 mm/s.The normal duration of the P wave is up to 0.1 seconds, the P – Q interval is 0.12-0.2 seconds, the QRS complex is 0.06-0.1 seconds.
Electrical axis of the heart
Denoted as the alpha angle. It can have a normal position, horizontal or vertical. Moreover, in a thin person the axis of the heart is more vertical relative to the average values, while in a fat person it is more horizontal. The normal position of the electrical axis of the heart is 30–69 o, vertical – 70–90 o, horizontal – 0–29 o. The alpha angle, equal to 91 to ±180 o, reflects a sharp deviation of the electrical axis of the heart to the right. The alpha angle, equal to 0 to –90 o, reflects a sharp deviation of the electrical axis of the heart to the left. The electrical axis of the heart can deviate under various pathological conditions. For example, hypertension leads to a deviation to the right; a conduction disorder (blockade) can shift it to the right or left.
Atrial P wave
The atrial P wave should be:- positive in I, II, aVF and chest leads (2, 3,4, 5, 6);
- negative in aVR;
- biphasic (part of the tooth lies in the positive region, and part in the negative) in III, aVL, V1.
Pathological forms of the P wave may indicate the following pathologies:
1.
Tall and sharp teeth in leads II, III, aVF appear with hypertrophy of the right atrium (“cor pulmonale”);
2.
A P wave with two peaks and a large width in leads I, aVL, V5 and V6 indicates hypertrophy of the left atrium (for example, mitral valve disease).
P–Q interval
The P–Q interval has a normal duration of 0.12 to 0.2 seconds. An increase in the duration of the P–Q interval is a reflection of atrioventricular block. On the electrocardiogram, three degrees of atrioventricular block (AV) can be distinguished:- I degree: simple lengthening of the P–Q interval while preserving all other complexes and waves.
- II degree: prolongation of the P–Q interval with partial loss of some QRS complexes.
- III degree: lack of connection between the P wave and QRS complexes. In this case, the atria work in their own rhythm, and the ventricles - in their own.
Ventricular QRST complex
The ventricular QRST complex consists of the QRS complex itself and the S – T segment. The normal duration of the QRST complex does not exceed 0.1 seconds, and its increase is detected with blockades of the Hiss bundle branches. QRS complex consists of three waves, Q, R and S, respectively. The Q wave is visible on the cardiogram in all leads except 1, 2 and 3 chest leads. A normal Q wave has an amplitude up to 25% of that of an R wave. The duration of the Q wave is 0.03 seconds. The R wave is recorded in absolutely all leads. The S wave is also visible in all leads, but its amplitude decreases from the 1st thoracic to the 4th, and in the 5th and 6th it may be completely absent. The maximum amplitude of this tooth is 20 mm.
The S–T segment is very important from a diagnostic point of view. It is by this tooth that myocardial ischemia can be detected, that is, a lack of oxygen in the heart muscle. Usually this segment runs along the isoline, in the 1st, 2nd and 3rd chest leads; it can rise up by a maximum of 2 mm. And in the 4th, 5th and 6th chest leads, the S-T segment can shift below the isoline by a maximum of half a millimeter. It is the deviation of the segment from the isoline that reflects the presence of myocardial ischemia.
T wave
The T wave is a reflection of the process of eventual relaxation in the cardiac muscle of the ventricles of the heart. Typically, when the amplitude of the R wave is large, the T wave will also be positive. A negative T wave is normally recorded only in lead aVR.Q-T interval
The Q–T interval reflects the process of eventual contraction in the myocardium of the ventricles of the heart.ECG interpretation - normal indicators
The transcript of the electrocardiogram is usually recorded by the doctor in conclusion. A typical example of a normal cardiac cardiogram looks like this:1. PQ – 0.12 s.
2. QRS – 0.06 s.
3. QT – 0.31 s.
4. RR – 0.62 – 0.66 – 0.6.
5. Heart rate is 70 - 75 beats per minute.
6. sinus rhythm.
7. The electrical axis of the heart is located normally.
Normally, the rhythm should be only sinus, the heart rate of an adult is 60 - 90 beats per minute. The P wave is normally no more than 0.1 s, the P – Q interval is 0.12-0.2 seconds, the QRS complex is 0.06-0.1 seconds, Q – T is up to 0.4 s.
If the cardiogram is pathological, then it indicates specific syndromes and deviations from the norm (for example, partial blockade of the left bundle branch, myocardial ischemia, etc.). The doctor can also reflect specific violations and changes in the normal parameters of the waves, intervals and segments (for example, shortening of the P wave or Q-T interval, etc.).
Interpretation of ECG in children and pregnant women
In principle, children and pregnant women have normal heart electrocardiogram readings - the same as in healthy adults. However, there are certain physiological characteristics. For example, the heart rate of children is higher than that of an adult. The normal heart rate of a child up to 3 years of age is 100–110 beats per minute, 3–5 years old – 90–100 beats per minute. Then gradually the heart rate decreases, and in adolescence it is compared with that of an adult - 60 - 90 beats per minute.In pregnant women, there may be a slight deviation of the electrical axis of the heart in late gestation due to compression by the growing uterus. In addition, sinus tachycardia often develops, that is, an increase in heart rate to 110 - 120 beats per minute, which is a functional condition and goes away on its own. An increase in heart rate is associated with a greater volume of circulating blood and increased workload. Due to the increased load on the heart, pregnant women may experience overload in various parts of the organ. These phenomena are not a pathology - they are associated with pregnancy and will go away on their own after childbirth.
Decoding the electrocardiogram during a heart attack
Myocardial infarction is a sudden cessation of oxygen supply to the heart muscle cells, resulting in the development of necrosis of a tissue area that is in a state of hypoxia. The reason for the disruption of oxygen supply can be different - most often it is a blockage of a blood vessel, or its rupture. A heart attack involves only part of the muscle tissue of the heart, and the extent of the damage depends on the size of the blood vessel that is blocked or ruptured. On an electrocardiogram, myocardial infarction has certain signs by which it can be diagnosed. In the process of development of myocardial infarction, four stages are distinguished, which have different manifestations on the ECG:
- acute;
- acute;
- subacute;
- cicatricial.
Sometimes it is possible to detect the phase of myocardial ischemia preceding the acute phase, which is characterized by high T waves.
Acute stage A heart attack lasts 2–3 weeks. During this period, a wide and high-amplitude Q wave and a negative T wave are recorded on the ECG.
Subacute stage lasts up to 3 months. The ECG shows a very large negative T wave with a huge amplitude, which gradually normalizes. Sometimes a rise in the S-T segment is detected, which should have leveled off by this period. This is an alarming symptom, as it may indicate the formation of a cardiac aneurysm.
Scar stage heart attack is final, since connective tissue is formed at the damaged site, incapable of contraction. This scar is recorded on the ECG as a Q wave, which will remain for life. Often the T wave is smoothed, has a low amplitude, or is completely negative.
Interpretation of the most common ECGs
In conclusion, doctors write the result of the ECG interpretation, which is often incomprehensible because it consists of terms, syndromes and simply statements of pathophysiological processes. Let's consider the most common ECG conclusions, which are incomprehensible to a person without a medical education. Ectopic rhythm means not sinus - which can be either a pathology or a norm. The norm is ectopic rhythm when there is a congenital malformation of the conduction system of the heart, but the person does not present any complaints and does not suffer from other cardiac pathologies. In other cases, an ectopic rhythm indicates the presence of blockades.
Changes in repolarization processes on the ECG reflects a violation of the process of relaxation of the heart muscle after contraction.
Sinus rhythm This is the normal heart rate of a healthy person.
Sinus or sinusoidal tachycardia means that a person has a correct and regular rhythm, but an increased heart rate - more than 90 beats per minute. In young people under 30 years of age, this is a variant of the norm.
Sinus bradycardia- this is a low heart rate - less than 60 beats per minute against the background of a normal, regular rhythm.
Nonspecific ST-T changes mean that there are minor deviations from the norm, but their cause may be completely unrelated to heart pathology. It is necessary to undergo a full examination. Such nonspecific ST-T changes can develop with an imbalance of potassium, sodium, chlorine, magnesium ions, or various endocrine disorders, often during menopause in women.
Biphasic R wave in combination with other signs of a heart attack indicates damage to the anterior wall of the myocardium. If no other signs of a heart attack are detected, then a biphasic R wave is not a sign of pathology.
QT prolongation may indicate hypoxia (lack of oxygen), rickets, or overexcitation of the child’s nervous system, which is a consequence of birth trauma.
Myocardial hypertrophy means that the muscular wall of the heart is thickened and works under enormous load. This can lead to the formation of:
- heart failure;
- arrhythmias.
Moderate diffuse changes in the myocardium mean that tissue nutrition is impaired and cardiac muscle dystrophy has developed. This is a fixable condition: you need to see a doctor and undergo an adequate course of treatment, including normalizing your diet.
Deviation of the electrical axis of the heart (EOS) left or right is possible with hypertrophy of the left or right ventricle, respectively. EOS can deviate to the left in obese people, and to the right - in thin people, but in this case this is a variant of the norm.
Left type ECG– EOS deviation to the left.
NBPNG– an abbreviation for “incomplete right bundle branch block.” This condition can occur in newborns and is a normal variant. In rare cases, RBBB can cause arrhythmia, but generally does not lead to the development of negative consequences. Block of the Hiss bundle branch is quite common in people, but if there are no complaints about the heart, then it is not at all dangerous.
BPVLNPG– an abbreviation meaning “blockade of the anterior branch of the left bundle branch.” Reflects a violation of the conduction of electrical impulses in the heart, and leads to the development of arrhythmias.
Small growth of the R wave in V1-V3 may be a sign of interventricular septal infarction. To accurately determine whether this is the case, it is necessary to do another ECG study.
CLC syndrome(Klein-Levy-Kritesco syndrome) is a congenital feature of the conduction system of the heart. May cause the development of arrhythmias. This syndrome does not require treatment, but it is necessary to be regularly examined by a cardiologist.
Low voltage ECG often recorded with pericarditis (a large amount of connective tissue in the heart that has replaced muscle tissue). In addition, this sign may be a reflection of exhaustion or myxedema.
Metabolic changes are a reflection of insufficient nutrition of the heart muscle. It is necessary to be examined by a cardiologist and undergo a course of treatment.
Conduction slowdown means that the nerve impulse travels through the tissues of the heart more slowly than normal. This condition itself does not require special treatment - it may be a congenital feature of the conduction system of the heart. Regular monitoring by a cardiologist is recommended.
Blockade 2 and 3 degrees reflects a serious disturbance of cardiac conduction, which is manifested by arrhythmia. In this case, treatment is necessary.
Rotation of the heart by the right ventricle forward may be an indirect sign of the development of hypertrophy. In this case, it is necessary to find out its cause and undergo a course of treatment, or adjust your diet and lifestyle.
Price of an electrocardiogram with interpretation
The cost of an electrocardiogram with interpretation varies significantly, depending on the specific medical institution. Thus, in public hospitals and clinics the minimum price for the procedure of taking an ECG and interpreting it by a doctor is from 300 rubles. In this case, you will receive films with recorded curves and a doctor’s conclusion on them, which he will make himself, or using a computer program.If you want to receive a thorough and detailed conclusion on the electrocardiogram, a doctor’s explanation of all the parameters and changes, it is better to contact a private clinic that provides such services. Here the doctor will be able not only to write a conclusion after deciphering the cardiogram, but also to calmly talk to you, taking his time to explain all the points of interest. However, the cost of such a cardiogram with interpretation in a private medical center ranges from 800 rubles to 3,600 rubles. You should not assume that bad specialists work in an ordinary clinic or hospital - it’s just that a doctor in a public institution, as a rule, has a very large amount of work, so he simply does not have time to talk with each patient in great detail.
When choosing a medical institution for taking a cardiogram with interpretation, first of all, pay attention to the qualifications of the doctor. It is better for this to be a specialist - a cardiologist or therapist with good experience. If a child needs a cardiogram, then it is better to contact specialists - pediatricians, since “adult” doctors do not always take into account the specifics and physiological characteristics of children.
Before use, you should consult a specialist.
