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PQ Interval - this is the distance (time interval) from the beginning of the P wave to the beginning of the Q wave (or R wave, if there is no q wave - then we are talking about the PR interval). In the figure, the PQ interval is indicated by a red region - it corresponds to the time of passage of excitation through the atria and the atrioventricular node to the ventricular myocardium. PQ interval (PR) depends on age, body weight, heart rate.
- Normally, the PQ interval is 0.12-0.18 (up to 0.2) seconds (6-9 cells).
- With age, the PQ interval lengthens:
- under the age of 14, the maximum PQ interval is up to 0.16 s,
- from 14 to 17 years old - 0.18 s,
- over the age of 17 years - 0.2 s.
- With an increase in heart rate, the PQ interval is reduced,
- With bradycardia, the PQ interval lengthens to 0.21-0.22 s.
- In the chest leads, the duration of the PQ interval may differ from the indications in the leads from the limbs to 0.04 s (2 cells).
- To measure the PQ interval, select the lead where the P wave and the QRS complex are well defined (usually this is the II standard lead).
- If the initial part of the P wave is isoelectric, then when measuring the PQ interval, there will be an error in the direction of decreasing from its true values.
- If the initial segment of the QRS complex is isoelectric, then when measuring the PQ interval, there will be an error in the direction of increase from its true values.
- Errors can be avoided by measuring on a multi-channel electrocardiograph.
The PQ interval can be divided into two parts:
- P wave (green sector),
- PQ segment (blue sector) - from the end of the P wave to the beginning of the QRS complex.
The ratio of the duration of the P wave to the duration of the PQ segment is called Macroose Index. Normally, the Macrouse index is 1.1-1.6. This index is used in the diagnosis of atrial hypertrophy.
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What is cardiography?
The essence of cardiography is the study of electric currents that occur during the work of the heart muscle. The advantage of this method is its relative simplicity and accessibility. Strictly speaking, a cardiogram is called the result of measuring the electrical parameters of the heart, displayed in the form of a time graph.
The creation of electrocardiography in its modern form is connected with the name of the Dutch physiologist of the early 20th century Willem Einthoven, who developed the basic ECG methods and the terminology used by doctors today.
Thanks to the cardiogram, it is possible to obtain the following information about the heart muscle:
- Heart rate,
- Physical condition of the heart,
- The presence of arrhythmias,
- The presence of acute or chronic myocardial damage,
- The presence of metabolic disorders in the heart muscle,
- The presence of violations of electrical conductivity,
- The position of the electrical axis of the heart.
Also, an electrocardiogram of the heart can be used to obtain information about some vascular diseases that are not related to the heart.
An ECG is usually performed in the following cases:
- Feeling of abnormal heartbeat,
- Bouts of shortness of breath, sudden weakness, fainting,
- Heart murmurs
- Deterioration of the condition of patients with cardiovascular diseases,
- Medical Boards
- Clinical examination of people over 45 years old,
- Inspection before surgery.
An electrocardiogram is also recommended for:
- Endocrine pathologies,
- Nervous disease
- Changes in blood counts, especially with an increase in cholesterol,
- Age over 40 years (once a year).
Where can a cardiogram be made?
If you suspect that your heart is not all right, you can contact a therapist or cardiologist to give you an ECG referral. Also, on a paid basis, a cardiogram can be done in any clinic or hospital.
ECG recording is usually done while lying down. To take a cardiogram, a stationary or portable device is used - an electrocardiograph. Stationary devices are installed in medical institutions, and portable devices are used by emergency teams. The device receives information about the electrical potentials on the surface of the skin. For this, electrodes attached to the chest area and limbs are used.
These electrodes are called leads. On the chest and limbs, 6 leads are usually installed. The chest leads are designated V1-V6, the leads on the limbs are called the main (I, II, III) and reinforced (aVL, aVR, aVF). All leads give a slightly different picture of the oscillations, however, summing up the information from all the electrodes, you can find out the details of the heart as a whole. Sometimes additional leads are used (D, A, I).
Typically, the cardiogram is displayed as a graph on paper, containing millimeter markings. Each lead electrode has its own schedule. The standard belt speed is 5 cm / s, other speeds may apply. The cardiogram displayed on the tape can also indicate the main parameters, norm indicators and conclusion generated automatically. Also, data can be recorded in memory and on electronic media.
After the procedure, the decoding of the cardiogram usually requires an experienced cardiologist.
In addition to stationary devices, there are also portable devices for daily (Holter) monitoring. They are attached to the patient's body along with the electrodes and record all the information received over a long period of time (usually during the day). This method gives much more complete information about the processes in the heart compared to a conventional cardiogram. So, for example, when taking a cardiogram in stationary conditions, the patient should be at rest. Meanwhile, some deviations from the norm can occur during physical exertion, in a dream, etc. Holter monitoring provides information on such phenomena.
Other types of procedures
There are several more methods of the procedure. For example, it is monitoring with physical activity. Deviations from the norm are usually more pronounced on the ECG with a load. The most common way to provide the body with the necessary physical activity is a treadmill. This method is useful in cases where pathologies can occur only in the case of increased heart function, for example, with suspected coronary disease.
With phonocardiography, not only the electrical potentials of the heart are recorded, but also the sounds that arise in the heart. The procedure is prescribed when it is necessary to clarify the occurrence of noise in the heart. This method is often used for suspected heart defects.
Recommendations for completing the standard procedure
The patient must be calm during the procedure. A certain period of time must elapse between physical activity and the procedure. It is also not recommended to undergo the procedure after eating, drinking alcohol, drinks containing caffeine, or cigarettes.
Reasons that can affect the ECG:
- Times of Day,
- Electromagnetic background,
- Physical exercise ,
- The position of the electrodes.
First you need to talk a little about how the heart works. It has 4 chambers - two atria, and two ventricles (left and right). The electrical impulse, due to which it is reduced, is formed, as a rule, in the upper part of the myocardium - in the sinus pacemaker - the nervous sinoatrial (sinus) node. The impulse spreads down the heart, first affecting the atria and causing them to contract, then the atrioventricular nerve node and the other nerve node, the bundle of His, travels and reaches the ventricles. It is the ventricles that take the main burden of pumping blood, especially the left one, which is involved in a large circle of blood circulation. This stage is called heart contraction or systole.
After the reduction of all parts of the heart, it is time for their relaxation - diastole. Then the cycle repeats again and again - this process is called the heartbeat.
The state of the heart, in which there is no change in the propagation of impulses, is reflected on the ECG in the form of a straight horizontal line called the isoline. Deviation of the graph from the contour is called a tooth.
One heart beat on the ECG contains six teeth: P, Q, R, S, T, U. The teeth can be directed either up or down. In the first case, they are considered positive, in the second - negative. The teeth Q and S are always positive, and the tooth R is always negative.
The teeth reflect the various phases of the contraction of the heart. P reflects the moment of atrial contraction and relaxation, R - ventricular arousal, T - ventricular relaxation. Special designations are also used for segments (gaps between adjacent teeth) and intervals (plot sections, including segments and teeth), for example, PQ, QRST.
Correspondence of the stages of heart contraction and some elements of cardiograms:
- P - atrial contraction,
- PQ - horizontal line, transition of the discharge from the atria through the atrioventricular node to the ventricles. Q wave may be absent,
- QRS is the ventricular complex, the element most often used in diagnostics,
- R is the excitation of the ventricles,
- S - myocardial relaxation,
- T - ventricular relaxation,
- ST - horizontal line, myocardial repair,
- U - may be absent. The reasons for the appearance of the tooth are not unambiguously clarified, however, the tooth has value for the diagnosis of some diseases.
Below are some abnormalities on the ECG and their possible explanations. This information, of course, does not negate the fact that it is more advisable to entrust the decryption to a professional cardiologist who knows better all the nuances of deviations from the norms and related pathologies.
Major abnormalities and diagnosis
|The distance between the R teeth is not the same||atrial fibrillation, cardiac block, sinus node weakness, extrasystole|
|P wave too high (more than 5 mm), too wide (more than 5 mm), consists of two halves||thickening of the atria|
|Prong P is absent on all leads except V1||rhythm does not come from the sinus node|
|PQ interval extended||atrioventricular block|
|QRS extension||ventricular hypertrophy, blockade of the legs of the bundle of His|
|No gaps between QRS||paroxysmal tachycardia, ventricular fibrillation|
|QRS as a flag||heart attack|
|Deep and wide Q||heart attack|
|Wide R (more than 15 mm) in leads I, V5, V6||hypertrophy of the left ventricle, blockade of the legs of the bundle of His|
|Deep S in III, V1, V2||left ventricular hypertrophy|
|S-T above or below contour more than 2 mm||ischemia or heart attack|
|Tall, two-humped, spiky T||heart overload, ischemia|
|T merging with R||acute heart attack|
Cardiogram parameters table in adults
The norm of the duration of the elements of the cardiogram in children
The heart rate may be regular or irregular.
Irregular rhythms can be:
- Regularly irregular (i.e., the pattern of irregularity is repeated).
- Irregularly irregular (rhythm completely disorganized).
You can distinguish a regular rhythm from an irregular one as follows: Several consecutive R-R intervals are marked on a piece of paper. Then, rhythm bands move along them to check if the following intervals coincide.
The nuance of decoding the ECG: If there is a suspicion that there is some kind of atrioventricular block, you need to specify separately the rate of contractions of the atria and ventricles (that is, P-waves and R-waves are noted separately. When there is movement along the rhythm strip, then you can see whether the PR interval is changing.
A similar change can be observed in the absence of QRS complexes or complete dissociation between them. If we additionally measure the R-R intervals, then we can find out if the rhythm is regular or irregular.
The cardiac axis represents the general direction of the electrical arrangement of the heart.
In a healthy person, the axis should go from 11 hours to 5 hours (if judged by the dial).
To determine the cardiac axis, you need to look at the standard leads I, II and III.
With a normal cardiac axis:
- II lead has the most positive deviation compared with the leading I and III leads
In case of deviation to the right:
- Lead III has the most positive deviation, and lead I should be negative.
A similar change is usually observed in individuals with right ventricular hypertrophy.
If the axis deviates to the left:
- I lead has the largest positive deviation.
- Leads II and III are negative.
Left axis deviation is observed in individuals with cardiac conduction disorders.
Video: ECG norm (Russian voice acting)
Key Features and ECG Changes
The following issues are often associated with P-wave analysis:
- Are there P waves?
- If so, is each P-wave accompanied by a QRS complex?
- Do P-waves look normal? (duration of inspection, direction and form)
- If not, is there any atrial activity, such as a sawtooth baseline → flutter waves / chaotic baseline → fibrillation waves / flat line → no atrial activity at all?
The nuance of decoding the ECG: If P-waves are absent and there is an irregular rhythm, this can provoke atrial fibrillation.
The P-R interval should be between 120 and 200 ms (3-5 small squares)
Long PR interval is over 0.2 seconds. Its presence may be associated with atrioventricular delay (AV block).
First degree heart block
Cardiac blockade of the first degree includes a fixed long interval of PR (more than 200 ms).
Cardiac block of the second degree (type Mobitz 1)
If the PR interval slowly increases, then the resettable QRS complex occurs, which corresponds to the AV block type Mobitz 1.
Cardiac block of the second degree (type Mobitz 2)
If the PR interval is fixed, but there is a decrease in the contour, then they talk about the AV blockade of the Mobitz 2 type, while the frequency of the falling strokes should be specified, for example, 2: 1, 3: 1, 4: 1.
Third degree cardiac block (complete heart block)
If the P-waves and QRS complexes are not completely connected, this is the third degree of AV block.
Tips for remembering heart block types
1. In order to remember the presented degrees of AV blockade, it is useful to visually perceive the anatomical location of the blockade in the conduction system of the heart:
1.1 AV block of the first degree occurs between the sinoatrial node (SA node) and the AV node (that is, inside the atrium).
1.2 AV block of the second degree (Mobitz I) is determined at the level of the AV node. This is the only segment of the conduction system of the heart that has the ability to translate incoming pulses from a higher speed to a lower one. Mobitz II - occurs after the AV node in the bundle of His or Purkinje fibers.
1.3 The third level of AV blockade occurs lower in relation to the AV node, which leads to a complete blockage of the conductivity of the pulses.
Shortened PR Interval
If the PR interval is short, this means one of two things:
- The P-wave emanates from a closer site with respect to the AV node, so the conductivity takes less time (the SA node is not in a fixed place, and some atria are smaller than others!).
- The atrial impulse gets to the ventricle faster, rather than slowly passing through the wall of the atrium. This may be an auxiliary path associated with the delta wave. Such an ECG is often observed in patients with Wolff-Parkinson-White syndrome.
There are several characteristics of the QRS complex that need to be evaluated:
QRS complex width
The width can be described as narrow (NARROW, less than 0.12 seconds) or wide (BROAD, more than 0.12 seconds).
A narrow QRS complex occurs when an impulse is conducted along the bundle of His and Purkinje's fiber into the ventricles. This leads to a well-organized synchronous ventricular depolarization.
A wide QRS complex occurs if there is an abnormal sequence of depolarization - for example, ventricular ectopia, when the impulse slowly spreads along the myocardium from the focus of excitation in the ventricle. With ectopic atria, the narrow QRS complex is most often determined, because the impulse passes through the normal cardiac conduction system. Similarly, branch blockage leads to wide QRS, because the impulse quickly enters one ventricle through the internal conduction system, and then slowly spreads through the myocardium to the other ventricle.
QRS complex height
Described as small (SMALL) and high (TALL).
Small ventricular complexes are determined at a height below 5 mm in the main leads or less than 10 mm in the chest leads.
High QRS complexes most often indicate ventricular hypertrophy (although changes can be associated with the human constitution, for example, with growth pain). There are many algorithms for measuring ventricular hypertrophy, mainly the left, among which the Sokolov-Lyon index or the Cornell index are most often used.
QRS complex morphology
During the decoding of the ECG, individual elements of the QRS complex are evaluated.
The appearance of a delta wave is a sign that the ventricles are activated earlier than usual. Early activation followed by a slow propagation of the impulse along the myocardium causes an indistinct burst of the QRS complex. При этом наличие дельта-волны не позволяет однозначно говорить о синдроме Вольфа-Паркинсона-Уайта. В таких случаях для подтверждения должны быть определены тахиаритмии в сочетании с дельта-волнами.
Изолированные волны Q могут определяться в нормальном состоянии. The pathological wave Q is more than 25% of the size of the wave R that follows it, or more than 2 mm in height and more than 40 ms in width. Sometimes it’s enough to see the Q waves on different ECG leads to get evidence of a previous myocardial infarction.
Q-waves (V2-V4), with T-wave inversion, may indicate a previous anterior myocardial infarction.
The R-wave is characterized by progression in the chest leads (starting small in V1 and ending with large in V6). The transition from the wave S> R to R> S should occur in leads V3 or V4. Poor progression (i.e., S> R to leading V5 and V6) may be a sign of a previous MI. It is also sometimes determined in people of very high growth due to the peculiarities of location.
J-point is when the S-wave connects the ST segment. This point can be raised, as a result of which the ST segment that follows it also rises and then they say “high take-off”.
High take-off (or benign early repolarization) is a normal ECG that causes a lot of different negative interpretations, since they mostly look at the height of the ST segment.
- Benign early repolarization occurs mainly at the age of up to 50 years (in people older than 50 years, ischemia is more common, which should be suspected in the first place).
- As a rule, the J-point is combined with an increase in ST in many leads, which makes ischemia less likely.
- T waves also increase (unlike STEMI, that is, myocardial infarction, when the T wave remains unchanged, and the ST segment rises).
- Changes associated with benign repolarization practically do not change over time, in contrast to myocardial infarction, since during STEMI changes will be observed in a week or two or more.
The ST segment is a part of the ECG, located between the end of wave S and the beginning of wave T. In a healthy person, this segment is comparable to the isoelectric line, which is neither high nor low. Anomalies of the ST segment are investigated to exclude pathology.
ST segment elevation
The ST height is considered significant when it exceeds 1 mm (1 small square) in two or more adjacent segments of standard leads or more than 2 mm in two or more chest leads. This is most often associated with acute large-focal myocardial infarction.
ST segment depression
Depression of the ST segment is indicated when it decreases relative to the contour by more than 0.5 mm in two or more adjacent leads, which indicates myocardial ischemia.
T wave formation is associated with ventricular repolarization.
High T waves
T teeth are considered high if they:
- More than 5 mm in standard leads.
- More than 10 mm in the chest leads (the same criteria as in the case of “small” QRS complexes).
High T waves may be associated with:
- Acute myocardial infarction.
Inverted T waves
T waves are usually inverted in V1, that is, in the first chest lead, and inversion in the standard III lead is a normal option.
Inverted T waves in other leads are nonspecific signs of a wide range of diseases:
- Blockade of Purkinje fibers.
- Pulmonary embolism.
- Left ventricular hypertrophy (in the lateral leads).
- Hypertrophic cardiomyopathy (widespread).
- Generalized pathological process.
When decoding the ECG, a comment may be added regarding the distribution of the T wave inversion, for example. front / side / rear.
Two-phase T waves
Biphasic T waves have two peaks and may indicate ischemia and hypokalemia.
Another non-specific sign, which may indicate ischemia or an imbalance of electrolytes.
U-teeth have a deviation of more than 0.5 mm after T-waves are best defined in the chest leads V2 or V3.
The teeth become larger when the rhythm slows down (bradycardia). In classical cases, U-waves are determined with various imbalances of electrolytes, hypothermia, or antiarrhythmic therapy with drugs such as digoxin, procainamide or amiodarone.
- The heart can have a different position in the chest, which depends a lot on the physique of a person, the state of the heart cavities (their dilatation or hypertrophy), the presence of concomitant pathologies from the pulmonary system, etc.
- V1-V3 can become “right ventricular” if the right ventricle is enlarged, because of which the heart turns and the right ventricle is ahead.
- Severe dilatation of the left ventricle may otherwise be decrypted on an ECG, for example, V5-V6 will show the apex of the heart.
- When decoding the ECG in different medical facilities, the chest leads may be slightly different, since nurses often install electrodes in different ways.
Video: Normal ECG. All intervals and teeth: p, QRS, T, PR, ST