Despite the emergence of expensive and complex cardiac tests, ECG remains the most reliable method for confirming acute infarction, various types of arrhythmias, and myocardial ischemia. Every healthcare worker needs to have the ability to interpret an ECG, especially in emergency situations. Can a person far from medicine master the basics of deciphering an ECG? Understand how the doctor functional diagnostics interprets the ECG results, and the cardiologist makes a diagnosis based on the ECG? If you know what the main ECG parameters mean and master the ECG analysis algorithm, then you can learn the basics of deciphering an ECG even for a person without a medical education. Let's try to figure out what the “life line” is on a cardiograph film?
1 The essence of the ECG recording method
The heart works in a certain mode: contraction of the atria - contraction of the ventricles. When the chambers of the heart contract, the cells become excited. An action potential is formed between cardiomyocytes due to the appearance of opposite charges between excited cells carrying a “-” charge and cells with a “+” charge, which are still at rest and have not had time to contract. Such electrical phenomena as the arising action potential are recorded by the electrocardiograph. If we imagine in a very simplified way the description of the method of recording an ECG, then this is a method of recording the work of the heart, namely the excitation of heart cells, the frequency and rhythm of contractions.
2 What is an electrocardiograph?
A device that records electrical impulses coming from the heart is called an electrocardiograph. It consists of:
- electrodes,
- amplifier,
- recording device.
Electrocardiographs can be mains powered or equipped with a battery (for example, portable cardiographs). ECG recording is carried out on paper tape, similar to graph paper. The speed of movement of such a belt is usually 50 mm/sec or half that. To prevent the doctor from making mistakes in the calculations, the speed is automatically indicated on the tape itself when recording an ECG.
3 How to take an ECG correctly?
The electrocardiogram is usually recorded in 12 leads: three standard (I, II, III), three enhanced (aVR, aVL, aVF) from the limbs and six thoracic (V1-6). The examination is carried out with the patient lying on his back with his torso exposed and his legs free from clothing. Electrodes are applied to the surface of the patient’s body in a certain clockwise order: Red - right hand, Yellow - left hand, Green - left leg, Black - right leg.
To make it easier for medical staff to memorize electrodes, there is a humorous phrase, the first letter of each word of which indicates the color of the desired electrode: Rabbit (red) Chews (yellow) Green (green) Garlic (black). 6 chest electrodes are applied to specific areas chest.
The contact of the electrodes with the skin should be maximum, so it is necessary to moisten the skin with water or soapy water, degrease with alcohol, and sometimes, with thick hair in men, it is recommended to shave off the hair on the chest. After applying the electrodes and connecting the wires, ECG recording begins. The potential difference is captured by an amplifier, entered into a recording device, and then displayed on tape in the form of an ECG graph. After recording the cardiogram, it is time to analyze it.
4 Electrocardiogram Basics
Decoding an ECG is a difficult science, which, perhaps, only a functional diagnostics doctor is fluent in. All doctors and senior medical students are required to be able to analyze cardiograms and have a good knowledge of ECG parameters. But the basics and basics of reading can also be learned by people who are far from medicine. So, the ECG consists of such parameters as:
- teeth (p, q, r, s, t, u),
- segments (st, pq),
- intervals (rr, qt, qrs).
Let us dwell on the description of these parameters in more detail. The P wave characterizes the excitation coverage of the atria; from the beginning of the P wave to the next Q wave, the segment pq extends, characterizing the conduction of excitation from the atria to the ventricles along the elements of the conduction system. The Q wave characterizes the beginning of the excitation coverage of the interventricular septum and the ventricular wall, and the qrs complex characterizes their systole.
The T wave shows the electrical phenomena that occur when the ventricles relax. You should pay attention to the pq segment on the ECG. The pq segment characterizes the process of excitation and subsequent relaxation of the ventricular myocardium. The meaning of the U wave is unclear. The rr interval indicates the time between heartbeats; the rr interval is used to judge the heart rate.
5 Important ECG standards
Numerous terms and ECG indicators make your head spin, so when deciphering an ECG, doctors use a certain scheme or algorithm that allows them to conduct a full analysis of the heart’s function without forgetting or losing sight of anything. Before analyzing the diagnostic algorithm, you should note such ECG indicators as the width or duration of waves and intervals (determined vertically) and the amplitude of waves and segments (determined horizontally).
If the speed of the paper tape is 25 mm per second, then when determining the width, 1 small cell (1 mm) = 0.04 s., 1 large (5 small) = 0.2 s. Height 10 mm = 1 mV. The doctor needs this data for calculations, since a normal ECG is characterized by certain, clearly established figures for the duration and amplitude of waves, intervals and segments, and a pathological ECG is characterized by deviations from normal values. You can present important ECG standards for an adult (speed 25 mm/s) in the form of a table.
| P wave | Less than 0.12 s in width and less than 3 mm in amplitude. Positive in lead I and negative in aVR. | ||
| QRS complex | Duration from 0.04 to 0.1 s. | ||
| Q wave | Available in aVR, sometimes in aVL or v1. In duration less than or equal to 0.04 s and less than or equal to 3 mm in amplitude, in lead I less than or equal to 1.5 mm in persons over 30 years of age. In persons under 30 years of age, q depth can reach 5 mm in several leads |
||
| r wave | V1: from 0 to 15 mm at the age of 12-20 years, from 0 to 8 mm at the age of 20-30 years, from 0 to 6 mm at the age of over 30 years. V2: from 0.2 to 12 mm over the age of 30 V3: 1 to 20 mm over 30 years of age |
||
| Segment st | On the isoline or up to 1 mm above it in the limb leads, a displacement above the isoline by less than 2 mm in the precordial leads | ||
| t wave | Negative in aVR, positive in I, II, v3-6 | ||
| Position of the electrical axis of the heart | From 0 to +110 degrees for persons under 40 years of age, from -30 to +90 for persons over 40 years of age | ||
| qt interval | Heart rate per minute | men | women |
| 45-65 66-100 More than 100 | Less than 0.47 Less than 0.41 Less than 0.36 | Less than 0.48 Less than 0.43 Less than 0.37 |
|
If the indicators of certain parameters do not fit into the norms, the functional diagnostics doctor will write in the conclusion about the alleged disturbances in the functioning of the heart.
6 ECG reading algorithm
In general terms, the algorithm for reading all ECG indicators can be presented step by step.
- 1 STEP. DETERMINATION OF RHYTHM AND ITS FREQUENCY.
Normally, the heart rhythm is sinus, which means that the p wave on the ECG always precedes the qrs complex. Heart rate is judged by the duration of the interval rr. There is a formula by which the heart rate is determined: heart rate = 60/rr. Where rr is the duration of the interval in seconds. - STEP 2. DETERMINATION OF THE ELECTRICAL AXIS OF THE HEART.
The position of the EOS in an adult is usually from 0 to +90 degrees. Vertical EOS (+70-+90) is more common in asthenic patients, horizontal (0-+30) in stocky patients. But in some diseases, deviation of EOS from normal values may be observed. - STEP 3. ASSESSMENT OF INTERVALS, SEGMENTS.
The doctor carefully studies the duration of intervals and segments; for more accurate measurements, he can use a ruler. Based on the calculations and by correlating them with normal indicators, the doctor makes a conclusion. For example, an increase in the pr interval by more than 0.2 s. may indicate a pathology such as AV block, and a rise of more than 1 mm in two or more limb leads (II, III, aVF) of the st segment indicates acute coronary syndrome. - STEP 4 ASSESSMENT AND ANALYSIS OF TEETH.
The appearance of a pathological q wave may indicate the development of myocardial infarction. By analyzing a combination of other indicators, the doctor can differentiate a recent heart attack from an old one. If the p wave is pointed, more than 3 mm in amplitude, this indicates problems with the right atrium, and if the p wave is wide (more than 2.5 mm) and double-humped in II, this indicates an enlargement of the left atrium. T changes are not specific. T wave inversion combined with ST depression or elevation indicates ischemia.
7 ECG at rest and more?
To clarify the diagnosis of hidden cardiac problems, the doctor may prescribe functional stress tests. Under the influence of physical activity, pressure and heart rate increase, the work of the heart increases, and hidden heart problems can “come to the surface”: ischemia, arrhythmias, and other disorders that could not be visualized on an ECG at rest. To the most popular load functional tests include:
- bicycle ergometry (or, as patients like to say, a bicycle. Indeed, the patient pedals a special “bicycle”, while experiencing a certain load, while simultaneously recording an ECG);
- treadmill test (stress test with walking).
It wouldn’t hurt for any patient to know the basics of an ECG, but it’s still best to entrust the analysis of a cardiogram to a specialist.
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Electrocardiography is considered the most simple method determining the quality of the heart, both in normal and pathological conditions. The essence of this method is to capture and record the electrical impulses of the heart that arise during its operation.
But in order to determine the degree of disturbance, it is necessary to decipher the ECG of the heart, since the recording of these impulses is carried out using a specific graphic image over a period of time.
Indications for ECG:
- For preventive purposes;
- Directed determination of the frequency of contractions of the heart muscle and the rhythm of the organ;
- Definition of acute and chronic heart failure;
- Detection of various conduction disorders inside the heart;
- To determine the physical condition of the heart;
- Diagnostics ;
- Obtaining information about pathologies that occur outside the heart (for example, complete or partial).
Principles of ECG interpretation
The electrocardiogram schematically shows three main indicators:
- Teeth are convexities with an acute angle, directed upward or downward and are designated P, Q, R, S, T;
- Segments – are the distance between nearby teeth;
- Interval – a gap that includes both a tooth and a segment.
Thanks to the above indicators, the cardiologist determines the level of contraction and recovery of the heart muscle. In addition to these indicators, during an electrocardiogram, the electrical axis of the heart can also be determined, which indicates the approximate location of the organ in chest cavity. The latter depends on the constitution of the human body and chronic pathology. The electrical axis of the heart can be: normal, vertical and horizontal.
Main indicators of ECG decoding
When deciphered, the norm indicators will be as follows:
- The distance between the R and R waves should be even throughout the entire length of the cardiogram;
- The intervals between PQRST should be from 120 to 200 m/s, graphically this is determined by 2-3 squares. This is an indicator of the passage of the impulse through all parts of the heart from the atria to the ventricles;
- The interval between Q and S indicates the passage of the impulse through the ventricles (60-100 m/s);
- The duration of ventricular contractility is determined using Q and T, normally 400-450 m/s;
At the slightest shift from the specified parameters, one can judge the beginning or development pathological process in the heart muscle. Such parameters change especially pronouncedly in rheumatism.
It should also be noted that in some cases ECG norms transcripts may vary slightly due to the presence of some disorders that are considered normal, since their presence does not affect the development of heart failure (for example, respiratory arrhythmia). It is important to note that for ECG decoding in adults, the norm can be presented in different tables describing the speed of passage between the elements of the cardiogram.
ECG decoding for adults norm in the table
ECG decoding norm table
Such tables are official document to identify possible pathological changes in the heart muscle.
Video: ECG interpretation
In some cases, when re-analyzing the ECG, deviations from previously obtained results are revealed. With what it can be connected?
- Different times of the day. Typically, an ECG is recommended to be done in the morning or afternoon, when the body has not yet been exposed to stress factors.
- Loads. It is very important that the patient is calm when recording an ECG. The release of hormones can increase heart rate and distort indicators. In addition, it is also not recommended to engage in heavy physical labor before the examination.
- Eating. Digestive processes affect blood circulation, and alcohol, tobacco and caffeine can affect heart rate and blood pressure.
- Electrodes. Incorrect application or accidental displacement can seriously change the indicators. Therefore, it is important not to move during recording and to degrease the skin in the area where the electrodes are applied (the use of creams and other skin products before the examination is highly undesirable).
- Background. Sometimes extraneous devices can affect the operation of the electrocardiograph.
A patient's ECG data can sometimes differ, so if you know how to interpret a heart ECG, but see different results in the same patient, one should not make a premature diagnosis. Accurate results will require taking into account various factors:
- Often distortions are caused by technical defects, for example, inaccurate gluing of the cardiogram.
- Confusion can be caused by Roman numerals, which are the same in the normal and inverted directions.
- Sometimes problems arise as a result of cutting the diagram and losing the first P wave or the last T wave.
- Preliminary preparation for the procedure is also important.
- Electrical appliances operating nearby affect the alternating current in the network, and this is reflected in the repetition of the teeth.
- The instability of the zero line may be affected by the patient’s uncomfortable position or anxiety during the session.
- Sometimes the electrodes become dislodged or incorrectly positioned.
Therefore, the most accurate measurements are obtained using a multichannel electrocardiograph.
It is with them that you can test your knowledge of how to decipher an ECG yourself, without fear of making a mistake in making a diagnosis (treatment, of course, can only be prescribed by a doctor).
An ECG is a necessary examination if heart disease is suspected. Electrocardiography is used in the diagnosis of ischemic changes in the heart muscle, i.e. changes from lack of oxygen, the most serious manifestation of which is the death of heart cells due to lack of oxygen - myocardial infarction.
In addition, ECG analysis may show arrhythmia - a disorder heart rate.
Conclusion The ECG also reveals dilatation of the heart in case of heart failure or pulmonary embolism. A cardiogram is usually performed as part of the preoperative examination before a planned procedure under general anesthesia, or during general examination.
There is no need to follow any special regime before the examination. All that matters is calmness.
Normal indicators for adults and children
Diagnosing the location of the teeth on the graph and calculating the width between the large R waves are the main data for analysis, on the basis of which conclusions can be drawn about the functioning of the heart of an adult.
The difference in height between the R waves should not be more than 10%. In an ideal situation, the indicators should be the same throughout the graph.
Under load, the indicators will change, so other standards should be applied, and they will differ depending on age.
For example, at 20 years old, heart rate after exercise on a simulator can reach within the normal range of 180 beats per minute, while at 40 years old this figure is no longer acceptable.
Children's norms will be completely different. This is due to the fact that during the process of growth and development the organ undergoes certain changes.
It's important to keep track proper development CVS in children as they grow up and conduct preventive examinations.
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. Normal heart rate a child under 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, it often develops sinus tachycardia, that is, an increase in heart rate to 110 - 120 beats per minute, which is a functional state 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. .
How to determine pathologies in the heart
When answering this question, the doctor pays attention to the person’s diagram and, based on the basic symbols, can guess which particular department has begun to malfunction.
We will display all the information in table form.
Taking into account all of the above, you can learn how to decipher a tape using at least the simplest parameters. Although many serious abnormalities in the functioning of the heart will be visible to the naked eye even with this set of knowledge.
For clarity, we will describe several of the most disappointing diagnoses so that you can simply visually compare the norm and deviations from it.
Myocardial infarction
Judging by this ECG, the diagnosis will be disappointing. The only positive here is the duration Q-R-S interval, which is normal.
In leads V2 - V6 we see ST elevation.
This is the result of acute transmural ischemia (AMI) of the anterior wall of the left ventricle. Q waves are visible in the anterior leads.
On this tape we see a conduction disturbance. However, even with this fact, acute anteroseptal myocardial infarction is noted against the background of right bundle branch block.
The right chest leads dismantle the S-T elevation and positive T waves.
Rhythm - sinus. There are high, regular R waves, and pathology of the Q waves in the posterolateral regions.
ST deviation is visible in I, aVL, V6. All this indicates posterolateral myocardial infarction with coronary heart disease (CHD).
- tall T wave
- elevation or depression of the S-T segment
- pathological Q wave or its absence
Signs of myocardial hypertrophy
Cardiogram analysis
A more rigorous interpretation of the ECG is made by analyzing and calculating the area of the teeth using special leads (vector theory), however, in practice, they mainly make do with such an indicator as the direction of the electrical axis, which represents the total QRS vector.
It is clear that everyone’s chest is structured differently and the heart does not have such a strict arrangement, the weight ratio of the ventricles and the conductivity inside them are also different for everyone, therefore, when deciphering, the horizontal or vertical direction of this vector is indicated.
Doctors carry out ECG analysis in a sequential order, determining the norm and violations:
- Assess the heart rhythm and measure the heart rate (with a normal ECG - sinus rhythm, heart rate - from 60 to 80 beats per minute);
- Intervals (QT, norm – 390-450 ms) are calculated, characterizing the duration of the contraction phase (systole) using a special formula (I often use Bazett’s formula). If this interval lengthens, then the doctor has the right to suspect ischemic heart disease, atherosclerosis, myocarditis, rheumatism. Hypercalcemia, on the contrary, leads to a shortening of the QT interval. The conductivity of the pulses reflected through the intervals is calculated using a computer program, which significantly increases the reliability of the results;
- The position of the EOS begins to be calculated from the isoline along the height of the teeth (normally R is always higher than S) and if S exceeds R and the axis deviates to the right, then they think about disturbances in the activity of the right ventricle, if on the contrary - to the left, and the height of S is greater than R in II and III leads – left ventricular hypertrophy is suspected;
- The QRS complex is studied, which is formed during the conduction of electrical impulses to the ventricular muscle and determines the activity of the latter (the norm is the absence of a pathological Q wave, the width of the complex is not more than 120 ms). If this interval shifts, then we speak of blockades (full or partial) of the bundle branches or conduction disturbances. Moreover, incomplete blockade of the right bundle branch is an electrocardiographic criterion of right ventricular hypertrophy, and incomplete blockade of the left bundle branch may indicate left ventricular hypertrophy;
- They describe the ST segments, which reflect the period of restoration of the initial state of the heart muscle after its complete depolarization (normally located on the isoline) and the T wave, which characterizes the process of repolarization of both ventricles, which is directed upward, asymmetrical, its amplitude is lower than the wave in duration and is longer than the QRS complex.
The decoding work is carried out only by a doctor, however, some ambulance paramedics perfectly recognize common pathologies, which is very important in emergency cases. But first, you still need to know the ECG norm.
This is what the cardiogram of a healthy person looks like, whose heart works rhythmically and correctly, but not everyone knows what this record means, which can change under various physiological conditions, such as pregnancy.
In pregnant women, the heart takes a different position in the chest, so the electrical axis shifts. In addition, depending on the duration, the load on the heart is added.
An ECG during pregnancy will reflect these changes.
The cardiogram indicators in children are also excellent; they will “grow” with the baby, and therefore will change according to age; only after 12 years, the child’s electrocardiogram begins to approach the ECG of an adult.
The entire set of ECG lines is examined and measured mathematically, after which the doctor can determine some parameters of the work of the heart muscle and its conduction system: heart rhythm, heart rate, pacemaker, conductivity, electrical axis of the heart.
Today, all these indicators are studied by high-precision electrocardiographs.
Sinus rhythm of the heart
The ECG records cardiac activity in twelve leads: 6 limb leads (aVR, aVL, aVF, I, II, III) and six chest leads(V1-V6). The P wave reflects the process of excitation and relaxation of the atria. Teeth Q,S show the depolarization phase of the interventricular septum. R - wave, indicating depolarization of the lower chambers of the heart, and T-wave - relaxation of the myocardium.
The QRS complex shows the time of ventricular depolarization. The time it takes for an electrical impulse to travel from the SA node to the AV node is measured by the PR interval.
Computers built into most ECG devices are capable of measuring the time it takes for an electrical impulse to travel from the SA node to the ventricles. These measurements can help your doctor evaluate your heart rate and certain types of heart block.
Computer programs can also interpret ECG results. And as we improve artificial intelligence and programming they are often more accurate. However, ECG interpretation has many subtleties, so human factors still remain an important part of the assessment.
There may be abnormalities in the electrocardiogram that do not affect the patient’s quality of life. However, there are standards for normal cardiac performance that are accepted by the international cardiological community.
Based on these standards, a normal electrocardiogram in a healthy person looks like this:
- RR interval – 0.6-1.2 seconds;
- P-wave – 80 milliseconds;
- PR interval – 120-200 milliseconds;
- PR segment – 50-120 milliseconds;
- QRS complex – 80-100 milliseconds;
- J-wave: absent;
- ST segment – 80-120 milliseconds;
- T-wave – 160 milliseconds;
- ST interval – 320 milliseconds;
- The QT interval is 420 milliseconds or less if the heart rate is sixty beats per minute.
- ind.juice – 17.3.
Indications for an ECG
The cardiogram contains 12 curves. When deciphering it, you should pay attention to the most important diagnostic indicators: the characteristics of the teeth, the duration and periodicity of the ST, QT, PQ segments, QRS complexes, and you also need to track the specific conductivity of the intervals, the electrical axis, the frequency and rhythm of heart contractions.
Each cell on the graph represents a period of time. When creating an ECG, a standard speed of 25 mm/s is assumed. A 1 mm cell in the figure is equal to 0.04 seconds.
By studying the RQ, PQ and QT intervals and calculating the sums of cells between the R waves, it is possible to calculate the main features of the patient's heartbeat.
The normal heart rate is 60 – 90 beats per minute. Naturally, this indicator will be normal only at rest. After the load, the data will be completely different.
During and immediately after a bicycle ergometer test, heart rate under load should not exceed the result calculated using the formula: 200 – patient’s age (the formula is not designed for children).
IN clinical practice There are several indications for electrocardiography:
- strong pain in the chest;
- constant fainting;
- dyspnea;
- exercise intolerance;
- dizziness;
- heart murmurs.
During a routine examination, an ECG is a mandatory diagnostic method. There may be other indications determined by the attending physician. If you experience any other alarming symptoms, consult your doctor immediately to determine their cause.
An electrocardiographic study is a fairly simple and effective diagnostic method used by cardiologists around the world to study the activity of the heart muscle. The results of the procedure in the form of graphs and numerical symbols, as a rule, are transferred to specialists for further data analysis. However, if, for example, the necessary doctor is not available, the patient has a desire to independently decipher his heart parameters.
Preliminary interpretation of an ECG requires knowledge of special basic data, which, due to its specificity, is not within the power of everyone. In order to make correct calculations of the ECG of the heart, a person who is not related to medicine needs to become familiar with the basic principles of processing, which are combined for convenience into appropriate blocks.
Introduction to the basic elements of a cardiogram
You should know that the interpretation of the ECG is carried out thanks to elementary, logical rules that can be understood even by the average person. For a more pleasant and calm perception of them, it is recommended to start familiarizing yourself first with the simplest principles of decoding, gradually moving to a more complex level of knowledge.
Tape marking
The paper on which data on the functioning of the heart muscle is reflected is a wide ribbon of a soft pink shade with a clear “square” marking. Larger quadrangles are formed from 25 small cells, and each of them, in turn, is equal to 1 mm. If a large cell is filled with only 16 dots, for convenience you can draw parallel lines along them and follow similar instructions.
The horizontal lines of the cells indicate the duration of the heartbeat (seconds), and the vertical lines indicate the voltage of individual ECG segments (mV). 1 mm is 1 second of time (in width) and 1 mV of voltage (in height)! This axiom must be kept in mind throughout the entire period of data analysis; later its importance will become obvious to everyone.
The paper used allows you to accurately analyze periods of time
Teeth and segments
Before moving on to the names of specific departments of the dentate graph, it is worth familiarizing yourself with the activity of the heart itself. Muscular organ consists of 4 compartments: the 2 upper ones are called atria, the 2 lower ones are called ventricles. Between the ventricle and the atrium in each half of the heart there is a valve - a valve responsible for accompanying the flow of blood in one direction: from top to bottom.
This activity is achieved thanks to electrical impulses that move through the heart according to a “biological schedule”. They are directed to specific segments of the hollow organ using a system of bundles and nodes, which are miniature muscle fibers.
The birth of the impulse occurs in the upper part of the right ventricle - the sinus node. The signal then passes to the left ventricle and excitation is observed upper sections heart, which is recorded by the P wave on the ECG: it looks like a gently sloping inverted bowl.
After the electrical charge reaches the atrioventricular node (or AV node), located almost at the junction of all 4 pockets of the heart muscle, a small “point” appears on the cardiogram, directed downwards - this is the Q wave. Just below the AV node there is the following point the destination of the impulse is the His bundle, which is fixed by the highest R wave among others, which can be imagined as a peak or mountain.
Having overcome half the path, an important signal rushes to the lower part of the heart, through the so-called branches of the His bundle, which externally resemble long octopus tentacles that hug the ventricles. The conduction of the impulse along the branching processes of the bundle is reflected in the S wave - a shallow groove at the right foot of R. When the impulse spreads to the ventricles along the branches of the His bundle, their contraction occurs. The last hummocky T wave marks the recovery (rest) of the heart before the next cycle.
Not only cardiologists, but also other specialists can decipher diagnostic indicators
In front of the 5 main ones you can see a rectangular protrusion; you should not be afraid of it, since it represents a calibration or control signal. Between the teeth there are horizontally directed sections - segments, for example, S-T (from S to T) or P-Q (from P to Q). To independently make an approximate diagnosis, you will need to remember such a concept as the QRS complex - the union of the Q, R and S waves, which records the work of the ventricles.
The teeth that rise above the isometric line are called positive, and those located below them are called negative. Therefore, all 5 teeth alternate one after another: P (positive), Q (negative), R (positive), S (negative) and T (positive).
Leads
You can often hear the question from people: why are all the graphs on the ECG different from each other? The answer is relatively simple. Each of the curved lines on the tape reflects heart parameters obtained from 10-12 colored electrodes, which are installed on the limbs and in the chest area. They read data on the cardiac impulse, located at different distances from the muscle pump, which is why the graphs on the thermal tape are often different from each other.
Only an experienced specialist can competently write an ECG report, but the patient has the opportunity to review general information about your health.
Normal cardiogram values
Now that it has become clear how to decipher the cardiogram of the heart, we should begin to directly diagnose normal readings. But before you get acquainted with them, you need to evaluate the ECG recording speed (50 mm/s or 25 mm/s), which, as a rule, is automatically printed on paper tape. Then, based on the result, you can view the norms for the duration of teeth and segments, which are listed in the table (calculations can be carried out using a ruler or checkered markings on a tape):
Among the most significant provisions for ECG interpretation are the following:
- Segments S-T and P-Q should “merge” with the isometric line without going beyond it.
- The depth of the Q wave cannot exceed ¼ of the height of the slenderest wave - R.
- The exact parameters of the S wave have not been approved, but it is known that it sometimes reaches a depth of 18–20 mm.
- The T wave should not be higher than R: its maximum value is ½ the height of R.
Control of heart rhythm is also important. It is necessary to pick up a ruler and measure the length of the segments between the vertices R: the results obtained must coincide with each other. To calculate heart rate (or heart rate), you should count the total number of small cells between the 3 vertices of R and divide the digital value by 2. Next, you need to apply one of 2 formulas:
- 60/X*0.02 (at a recording speed of 50 mm/sec).
- 60/X*0.04 (at a recording speed of 25 mm/sec).
If the number is in the range from 59–60 to 90 beats/min, then the heart rate is normal. An increase in this index implies tachycardia, and a clear decrease implies bradycardia. If for a mature person a heart rate of more than 95–100 beats/min is a rather dubious sign, then for children under 5–6 years old this is one of the varieties of the norm.
Each of the teeth and intervals indicates a certain period of time the heart muscle is working
What pathologies can be identified when decoding data?
Although the ECG is one of the extremely simple studies in structure, there are still no analogues for such a diagnosis of cardiac abnormalities. You can become familiar with the most “popular” diseases recognized by ECG by examining both the description of their characteristic indicators and detailed graphic examples.
This disease often recorded in adults during ECG, but in children it occurs extremely rarely. Among the most common “catalysts” of the disease are the use of drugs and alcohol, chronic stress, hyperthyroidism, etc. PT is distinguished, first of all, by a frequent heartbeat, the indicators of which range from 138–140 to 240–250 beats/min.
Due to the occurrence of such attacks (or paroxysms), both ventricles of the heart do not have the opportunity to fill with blood in time, which weakens the overall blood flow and slows down the delivery of the next portion of oxygen to all parts of the body, including the brain. Tachycardia is characterized by the presence of a modified QRS complex, a weakly expressed T wave and, most importantly, the absence of a distance between T and P. In other words, groups of waves on the electrocardiogram are “glued” to each other.
The disease is one of the “invisible killers” and requires immediate attention to a number of specialists, since if left untreated it can lead to death
Bradycardia
If the previous anomaly implied the absence T-P segment, then bradycardia is its antagonist. This disease reveals precisely the significant T-P extension, indicating weak conduction of the impulse or its incorrect accompaniment through the heart muscle. Patients with bradycardia have an extremely low heart rate index - less than 40–60 beats/min. If people who prefer regular physical activity have mild manifestation illness is the norm, then in the vast majority of other cases we can talk about the onset of an extremely serious disease.
If obvious signs of bradycardia are detected, you should undergo comprehensive examination.
Ischemia
Ischemia is called a harbinger of myocardial infarction, for this reason early detection anomalies contribute to the relief of fatal illness and, as a result, a favorable outcome. It was previously mentioned that the S-T interval should “lie comfortably” on the isoline, but its descent in the 1st and AVL leads (up to 2.5 mm) signals precisely IHD. Sometimes ischemic disease the heart produces only the T wave. Normally, it should not exceed ½ the height of R, however, in in this case it can either “grow” to the senior element or fall below the middle line. The remaining teeth do not undergo significant changes.
Atrial flutter and fibrillation
Atrial fibrillation is an abnormal condition of the heart, expressed in the erratic, chaotic manifestation of electrical impulses in the upper chambers of the heart. It is sometimes not possible to make a qualitative superficial analysis in such a case. But knowing what you should pay attention to first, you can calmly decipher the ECG indicators. The QRS complexes are not of fundamental importance, since they are often stable, but the gaps between them are key indicators: when flickering, they resemble a series of notches on a handsaw.
Pathologies are clearly distinguishable on a cardiogram
Not so chaotic, large-sized waves between QRS already indicate atrial flutter, which, unlike flicker, is characterized by a slightly more pronounced heartbeat (up to 400 beats/min). Contractions and excitations of the atria are to a small extent subject to control.
Thickening of the atrial myocardium
Suspicious thickening and stretching of the muscle layer of the myocardium is accompanied by a significant problem with the internal blood flow. At the same time, the atria perform their main function with constant interruptions: the thickened left chamber “pushes” blood into the ventricle with greater force. When trying to read an ECG graph at home, you should focus your attention on the P wave, which reflects the condition of the upper parts of the heart.
If it is a kind of dome with two bulges, most likely the patient is suffering from the disease in question. Since thickening of the myocardium in the long-term absence of qualified medical intervention provokes a stroke or heart attack, it is necessary to make an appointment with a cardiologist as soon as possible with the provision of detailed description discomfort symptoms, if any.
Extrasystole
It is possible to decipher an ECG with the “first signs” of extrasystole if you have knowledge about the special indicators of a particular manifestation of arrhythmia. By carefully examining such a graph, the patient may detect unusual abnormal surges that vaguely resemble QRS complexes - extrasystoles. They occur in any area of the ECG, and are often followed by a compensatory pause, allowing the heart muscle to “rest” before starting a new cycle of excitations and contractions.
Extrasystole in medical practice often diagnosed in healthy people. In the vast majority of cases, it does not affect the usual course of life and is not associated with serious illnesses. However, when arrhythmia is detected, you should play it safe by contacting specialists.
With atrioventricular heart block, an expansion of the gap between the P waves of the same name is observed, in addition, they can occur at the time of analysis of the ECG conclusion much more often than QRS complexes. Registration of such a pattern indicates low conductivity of the impulse from the upper chambers of the heart to the ventricles.
If the disease progresses, the electrocardiogram changes: now the QRS “falls out” of the general row of P waves in some intervals
Bundle branch block
Failure in the operation of such an element of the conduction system as the His bundle should in no case be ignored, since it is located in close proximity to the Myocardium. In advanced cases, the pathological focus tends to “spill over” to one of the most important areas of the heart. Decipher the ECG yourself if there is extreme unpleasant disease It’s quite possible, you just have to carefully examine the highest tooth on the thermal tape. If it does not form a “slender” letter L, but a deformed M, this means that the His bundle has been attacked.
Damage to its left leg, which transmits the impulse into the left ventricle, entails the complete disappearance of the S wave. And the place of contact of the two vertices of the split R will be located above the isoline. The cardiographic image of the weakening of the right bundle branch is similar to the previous one, only the connection point of the already designated peaks of the R wave is located under the midline. T is negative in both cases.
Myocardial infarction
The myocardium is a fragment of the densest and thickest layer of the heart muscle, which is last years exposed to various ailments. The most dangerous among them is necrosis or myocardial infarction. When deciphering electrocardiography, it is sufficiently distinguishable from other types of diseases. If the P wave, which registers the good condition of the 2 atria, is not deformed, then the remaining ECG segments have undergone significant changes. Thus, a pointed Q wave can “pierce” the isoline plane, and a T wave can be transformed into a negative wave.
The most indicative sign of a heart attack is an unnatural elevation of R-T. There is a mnemonic rule that allows you to remember its exact appearance. If, when examining this area, one can imagine the left, ascending side of R in the form of a rack tilted to the right, on which a flag is flying, then we are really talking about myocardial necrosis.
The disease is diagnosed as acute phase, and after the attack subsides
Ventricular fibrillation
Otherwise, an extremely serious illness is called atrial fibrillation. Distinctive feature This pathological phenomenon is considered to be the destructive activity of conductive bundles and nodes, indicating uncontrolled contraction of all 4 chambers of the muscle pump. Reading the ECG results and recognizing ventricular fibrillation is not at all difficult: on a checkered tape it appears as a series of chaotic waves and valleys, the parameters of which cannot be correlated with classical indicators. In none of the segments is it possible to see at least one familiar complex.
If a patient with atrial fibrillation is not given early medical attention, he will soon die.
WPW syndrome
When, in the complex of classical pathways for conducting an electrical impulse, an abnormal bundle of Kent is unexpectedly formed, located in the “comfortable cradle” of the left or right atrium, we can confidently speak about such a pathology as WPW syndrome. As soon as the impulses begin to move along the unnatural cardiac highway, the rhythm of the muscle is lost. The “correct” conducting fibers cannot fully supply the atria with blood, because the impulses prefer a shorter path to complete the functional cycle.
The ECG with SVC syndrome is characterized by the appearance of a microwave at the left foot of the R wave, a slight widening of the QRS complex and, of course, a significant reduction in the P-Q interval. Since deciphering the cardiogram of a heart that has undergone WPW is not always effective, the HM - Holter method of diagnosing the disease - comes to the aid of medical personnel. It involves wearing a compact device with sensors attached to the skin around the clock.
Long-term monitoring provides better results with fixation reliable diagnosis. In order to timely “catch” an anomaly localized in the heart, it is recommended to visit the ECG room at least once a year. If regular medical monitoring of the treatment of cardiovascular disease is necessary, more frequent measurements of cardiac activity may be required.
An electrocardiograph (ECG) is a device that allows you to evaluate cardiac activity, as well as diagnose the condition of this organ. During the examination, the doctor receives data in the form of a curve. How to read an ECG waveform? What types of teeth are there? What changes are visible on the ECG? Why do doctors need this diagnostic method? What does the ECG show? These are not 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 bears a greater load. It is this ventricle that most often suffers. Despite the difference in size, both sides of the heart must work stably and 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 should look at the cardiogram. It is printed on special paper that has cells, and two types of cells are clearly visible: large and small.
The ECG conclusion is read from these cells. teeth, cells? These are the main parameters of the cardiogram. Let's try to learn how to read an ECG from scratch.
The 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. The vertical ones are voltage, and the horizontal ones are time.
Large squares consist of 25 small cells. Each small cell is equal to 1 mm and corresponds to 0.04 seconds in the horizontal direction. Large squares equal 5 mm and 0.2 seconds. In the vertical direction, a centimeter of strip is equal to 1 mV of voltage.
Prongs
There are five teeth in total. Each of them displays the work of the heart on a graph.
- P - ideally, this wave should be positive in the range from 0.12 to two seconds.
- Q - negative wave, shows the condition of the interventricular septum.
- R - displays the state of the ventricular myocardium.
- S - negative wave, shows the completion of processes in the ventricles.
- T - positive wave, indicates restoration of potential in the heart.
All ECG waves have their own reading characteristics.
P wave
All waves of the electrocardiogram have a certain significance for making the correct diagnosis.
The very first tooth of the graph is called P. It indicates the time between heartbeats. To measure it, it is best to isolate 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 two 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 P wave interval in all parts of the electrocardiogram.
R wave
Knowing how to read an ECG the easy way, you can understand whether there are heart pathologies. The next important peak on the chart is R. It is easy to find - it is the highest peak on the chart. This will be the positive tooth. Its highest part is marked on the cardiogram as R, and its lower parts as 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 and high. The ECG R waves are clearly visible in the figure, they are the highest:
Between these peaks, the number of large squares indicates 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 the cardiogram shows a prolongation of the QRS complex by more than 0.12 s, which indicates a blockade of the His bundle.
PQ tooth spacing
PQ is the interval from the P wave to the Q wave. It corresponds to the time of excitation through the atria to the ventricular myocardium. PQ interval norm in different ages various. Usually it is 0.12-0.2 s.
With age, the interval increases. Thus, in children under 15 years of age, PQ can reach 0.16 s. Between the ages of 15 and 18 years, PQ increases to 0.18 s. In adults, this figure is equal to a fifth of a second (0.2).
When the interval lengthens to 0.22 s, they speak of bradycardia.
QT wave interval
If this complex is longer, then we can assume ischemic heart disease, myocarditis or rheumatism. With the shortened type, hypercalcemia may be observed.
ST interval
Normally, this indicator is located at the level of the midline, but can be two cells higher than it. This segment shows the process of restoring depolarization of the heart muscle.
In rare cases, the indicator may rise three cells above the midline.
Norm
The transcript of the cardiogram should normally look like this:
- The Q and S segments must 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 should be higher than the S wave.
ECG for pathologies: sinus arrhythmia
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 and with neuroses.
At sinus arrhythmia the cardiogram has the following form: sinus rhythms are preserved, fluctuations in the R-R intervals are observed, but during breath holding the graph is smooth.
With pathological arrhythmia, preservation of the sinus impulse is observed constantly, regardless of breath holding, while wave-like changes are observed at all R-R intervals.
Manifestation of a heart attack on an ECG
When myocardial infarction occurs, changes in the ECG are pronounced. Signs of pathology are:
- increase in heart rate;
- 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 main means of recognizing zones of necrosis of the heart muscle is a cardiogram. It can be used to determine the depth of organ damage.
During a heart attack, the ST segment will be elevated and the R wave will be depressed, giving the ST a cat's back 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.
- The location of ischemia at the anterior wall of the left ventricle. Diagnosed with symmetrical pointed T-waves.
- Location at the epicardium of the left ventricle. The T-wave is pointed, symmetrical, and directed downward.
- Transmural type of left ventricular ischemia. T is pointed, negative, symmetrical.
- Ischemia of the left ventricular myocardium. T is smoothed, slightly raised upward.
- Heart damage is indicated by the state of the T wave.
Changes in the ventricles
ECG shows changes in the ventricles. Most often they appear in the left ventricle. This type of cardiogram occurs in people with long-term additional stress, for example, obesity. With this pathology, there is a deviation of the electrical axis to the left, against the background of which the S wave becomes higher than R.
Holter method
How can you learn to read an ECG if it is not always clear which waves are located and how they are located? In such cases, continuous recording of the cardiogram is prescribed using mobile device. It continuously records ECG data on a special tape.
This examination method is necessary in cases where classical ECG fails to detect pathologies. During a Holter diagnosis, a detailed diary is necessarily kept, where the patient records all his actions: sleep, walks, sensations during activities, all activities, rest, symptoms of the disease.
Typically, data recording occurs within 24 hours. However, there are times when it is necessary to take readings for up to three days.
ECG interpretation schemes
- The conductivity and rhythm of the heart are analyzed. To do this, the regularity of heart contractions is assessed, the number of heart rates is calculated, and the conduction system is determined.
- Axial rotations are detected: the position of the electric axis in the frontal plane is determined; around the transverse, longitudinal axis.
- The R wave is analyzed.
- QRS-T is analyzed. In this case, the state of the QRS complex, RS-T, T wave, as well as the Q-T interval are assessed.
- A conclusion is made.
The duration of the R-R cycle indicates the regularity and normality of the heart rhythm. When assessing heart function, more than one is assessed R-R gap, and all. Normally, deviations within 10% of the norm are allowed. In other cases, an incorrect (pathological) rhythm is determined.
To establish pathology, the QRS complex and a certain period of time are taken. It counts the number of times a segment is repeated. Then the same period of time is taken, but further on the cardiogram, it is calculated again. If at equal periods of time the number of QRS is the same, then this is the norm. At different quantities- pathology is assumed, and they focus on the P waves. They must be positive and stand before the QRS complex. Throughout the entire graph, the shape of P should be the same. This option speaks about 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 pathology of the atria and ventricles, which the impulse reaches simultaneously.
Ventricular rhythm is shown on the electrocardiogram as a deformed and widened QRS. In this case, the connection between P and QRS is not visible. There are large distances between the R waves.
Cardiac conduction
The ECG determines cardiac conduction. The P wave determines the atrial impulse; normally this indicator should be 0.1 s. The P-QRS interval reflects the overall conduction velocity through the atria. The norm of this indicator should be within 0.12 to 0.2 s.
The QRS segment shows conduction through the ventricles; the normal range is 0.08 to 0.09 s. As the intervals increase, cardiac conduction slows down.
Patients do not need to know what the ECG shows. A specialist should understand this. Only a doctor can correctly decipher the cardiogram and make the correct diagnosis, taking into account the degree of deformation of each individual tooth or segment.
