The conduction system of the heart includes. Av knot of the heart

An important role in the rhythmic work of the heart and in the coordination of the activity of the muscles of the individual chambers of the heart is played by the so-called conduction system of the heart. Although the muscles of the atria are separated from the muscles of the ventricles by fibrous rings, however, there is a connection between them through the conduction system, which is a complex neuromuscular formation. The muscle fibers that make up its composition (conductive fibers) have a special structure: their cells are poor in myofibrils and rich in sarcoplasm, therefore they are lighter. They are sometimes visible to the naked eye in the form of light-colored threads and represent a less differentiated part of the original syncytium, although they are larger than ordinary muscle fibers of the heart. In a conducting system, nodes and bundles are distinguished.

1. Sinoatrial node, nodus sinuatrialis, is located in the area of ​​the wall of the right atrium, corresponding to sinus venosus cold-blooded (in sulcus terminalis, between the superior vena cava and the right ear). It is associated with the muscles of the atria and is important for their rhythmic contraction.

2. Atrioventricular node, nodus atrioventricularis, located in the wall of the right atrium, near cuspis septalis tricuspid valve. The fibers of the node, directly connected with the muscles of the atrium, continue into the septum between the ventricles in the form of p atrioventricular bundle, fasciculus atrioventricularis (bundle of His). In the ventricular septum, the bundle divides into two legs - crus dextrum et sinistrum, which go into the walls of the same ventricles and branch under the endocardium in their muscles. Atrioventricular bundle is very important for the work of the heart, since it transmits a wave of contraction from the atria to the ventricles, due to which the regulation of the systole rhythm - the atria and ventricles - is established.

Therefore, the atria are connected to each other by the sinoatrial node, and the atria and ventricles are connected by the atrioventricular bundle. Usually, irritation from the right atrium is transmitted from the sinoatrial node to the atrioventricular node, and from it along the atrioventricular bundle to both ventricles.

Fig.1. Jan Purkinje

Fig.2. The structure of the conduction system of the heart

The rhythmic activity of the heart is carried out automatically with the help of a special system of fibers close to muscle in morphological and physiological properties. It bears the name - conducting system of the heart.

conduction system of the heart

The conduction system of the heart includes:
1) Keys-Fleck node, or sinus node, located in the wall of the PP between the mouths of the inferior and superior vena cava;
2) the atrioventricular section of the conduction system, which includes the atrioventricular node, or the Ashof-Tavar node, located in the right atrium between the attachment point of the tricuspid valve leaflet and the mouth of the coronary sinus, its continuation is the His bundle, which lies in the lower part of the atrial septum and the upper part of the ventricular septum ;
3) left, right legs of the bundle of His, as well as their branching in the walls of the corresponding ventricles. The legs of the bundle of His lie in the wall of the interventricular septum - in its subendocardial layers: the right leg is located on the right side of the septum, the left leg is on the left side. The terminal branches of the conducting system are the Purkinje fibers, which are located in the form of a network in the subendocardial layer of the muscles of the ventricles.
The sinus node is called the automatic center of the first order - normally it produces 60 - 80 impulses per minute.
The atrioventricular node is referred to as an automatic center of the second order with a pulse frequency of 40-50 per minute.
The automatic center of the third order are the legs of the bundle of His (30 pulses per minute).

Functions of the conduction system of the heart

conduction system of the heart has a specific ability to automatically generate impulses to contract the heart. The sinus node has the highest degree of this function, which is the site of the wave of excitation of the heart under normal conditions, and therefore the normal rhythm is called sinus. To a lesser extent, the atrioventricular node and the underlying parts of the system have the ability to generate impulses. All the named elements of the conducting system, including its terminal branches, have some degree of automatism. Normally, the automatism of the underlying departments is suppressed by the automatic function of the sinus node; in a number of pathological conditions, this automatism begins to manifest itself in various forms.

A variety of rhythm and conduction disorders in humans can be reduced to four groups.

1) Violation of the automatic function of the sinus node - sinus bradycardia, sinus tachycardia - or other parts of the conduction system: nodal rhythm, interfering dissociation, migration of the source of the heart rate, idioventricular rhythm.

2) Violation of the excitability of the conduction system: paroxysmal tachycardia, extrasystole.

3) Violation of conduction: intra-atrial blockade, various forms of atrioventricular blockade, sinoauricular blockade, intraventricular conduction disorder.

Cardiac arrhythmias occur for a variety of reasons. These include heart diseases of an infectious-inflammatory and dystrophic nature: heart defects, thyrotoxicosis, various forms of coronary insufficiency, toxic, including pharmacological effects, etc.

Disturbances in the nervous regulation of the heart rhythm play a very large role in the origin of these disorders. It is known that neurotic states can be accompanied by such heart rhythm disorders as extrasystole, etc.

It must be borne in mind that rhythm disturbances, especially extrasystoles, can occur reflexively, for example, under the influence of pathological irritations from the gastrointestinal tract.

Module 1. FunctionsandonalIdandagnostic

ELECTROCARDIOGRAPHIC EXAMINATION METHOD

conduction system of the heart

Functions of the heart

There are the following main functions of the heart:

Automatismis the ability of the heart to produce impulses that cause excitation. Normally, the sinus node has the greatest automatism.

Conductivity- the ability of the myocardium to conduct impulses from their place of origin to the contractile myocardium.

Excitability- the ability of the heart to be excited under the influence of impulses. During excitation, an electric current arises, which is recorded by a galvanometer in the form of an ECG.

Contractility- the ability of the heart to contract under the influence of impulses and provide pump function.

refractoriness- the impossibility of excited myocardial cells to be activated again when additional impulses occur. It is divided into absolute (the heart does not respond to any excitation) and relative (the heart responds to very strong excitation).

Electrocardiography allows get an idea directly about automatism, conduction and excitability functions. These functions are provided conducting system hearts, which includes centers of automatism and pathways.

Knowledge of the conduction system of the heart is essential for mastering the ECG and understanding cardiac arrhythmias.

The heart has automatism- the ability to independently contract at certain intervals. This is made possible by the occurrence of electrical impulses in the heart itself. It continues to beat while cutting all the nerves that come to it.

Impulses arise and are conducted through the heart with the help of the so-called conducting system of the heart . Consider the components of the conduction system of the heart:

• sinoatrial node,
• atrioventricular node,
• bundle of His with its left and right legs,
• Purkinje fibers.

Diagram of the conduction system of the heart .

Now more.

1) sinoatrial node(= sinus, sinoatrial, SA; from lat. atrium- atrium) - the source of electrical impulses is normal. It is here that impulses originate and from here spread through the heart (drawing with animation below). C The inusoidal node is located in the upper part of the right atrium, between the confluence of the superior and inferior vena cava. The word "sinus" in translation means "sinus", "cavity".

Phrase " sinus rhythm” in the ECG decoding means that the impulses are generated in the correct place - the sinoatrial node. The normal resting heart rate is 60 to 80 beats per minute. A heart rate (HR) below 60 per minute is called bradycardia, and above 90 - tachycardia. Trained people usually have bradycardia.

It is interesting to know that normally impulses are not generated with perfect accuracy. Exists respiratory sinus arrhythmia(The rhythm is called irregular if the time interval between individual contractions is ≥ 10% greater than the mean). With respiratory arrhythmias Inspiratory heart rate increases, and on exhalation it decreases, which is associated with a change in the tone of the vagus nerve and a change in the blood filling of the heart with an increase and decrease in pressure in the chest. As a rule, respiratory sinus arrhythmia is combined with sinus bradycardia and disappears when holding the breath and increasing the heart rate. Respiratory sinus arrhythmia is mostly in healthy people especially young ones. The appearance of such an arrhythmia in persons recovering from myocardial infarction, myocarditis, etc., is a favorable sign and indicates an improvement in the functional state of the myocardium.

2) atrioventricular node(atrioventricular, AV; from lat. ventriculus- ventricle) is, one might say, a “filter” for impulses from the atria. It is located near the septum itself between the atria and ventricles. At the AV node the slowest propagation speed electrical impulses throughout the conduction system of the heart. It is approximately 10 cm / s (for comparison: in the atria and bundle of His, the impulse propagates at a speed of 1 m / s, along the legs of the bundle of His and all underlying sections up to the myocardium of the ventricles - 3-5 m / s). The impulse delay in the AV node is about 0.08 s, it is necessary, for the atria to contract earlier and pump blood into the ventricles.

conduction system of the heart .

3) Bundle of His(= atrioventricular bundle) does not have a clear border with the AV node, runs in the interventricular septum and has a length of 2 cm, after which it divides on left and right legs to the left and right ventricles, respectively.Since the left ventricle works more intensively and is larger in size, the left leg has to be divided into two branches - anterior and back.

Why know this? Pathological processes (necrosis, inflammation) can disrupt impulse propagation along the legs and branches of the bundle of His, as seen on the ECG. In such cases, in the conclusion of the ECG, they write, for example, “complete blockade of the left leg of the bundle of His”.

4) Purkinje fibers connect the terminal branches of the legs and branches of the bundle of His with the contractile myocardium of the ventricles.

The ability to generate electrical impulses (i.e. automatism) is possessed not only by the sinus node. Nature has taken care of reliable reservation of this function. The sinus node is first order pacemaker and generates pulses at a frequency of 60-80 per minute. If for some reason the sinus node fails, the AV node will become active - 2nd order pacemaker, generating pulses 40-60 times per minute. pacemaker third order are the legs and branches of the bundle of His, as well as Purkinje fibers. The automatism of the pacemaker of the third order is 15-40 pulses per minute. The pacemaker is also called a pacemaker (pacemaker, from the English. pace- speed, pace).

Conduction of an impulse in the conduction system of the heart .

Normally, only the first-order pacemaker is active, the rest are sleeping. This happens because the electrical impulse reaches the other automatic pacemakers before they have time to generate their own. If the automatic centers are not damaged, then the underlying center becomes a source of heart contractions only with a pathological increase in its automatism (for example, with paroxysmal ventricular tachycardia, a pathological source of constant impulses arises in the ventricles, which causes the ventricular myocardium to contract in its rhythm with a frequency of 140-220 per minute) .

It is also possible to observe the work of a third-order pacemaker when the conduction of impulses in the AV node is completely blocked, which is called complete transverse blockade(= 3rd degree AV block). At the same time, the ECG shows that the atria contract in their rhythm with a frequency of 60-80 per minute (SA-node rhythm), and the ventricles - in their own with a frequency of 20-40 per minute.

BASICS OF HEART ELECTROPHYSIOLOGY

excitability function.

Excitability is the ability of the heart to be excited under the influence of impulses. The function of excitability is possessed by the cells of both the conduction system of the heart and the contractile myocardium. Excitation of the heart muscle is accompanied by the appearance of a transmembrane action potential (TMAP) and, ultimately, an electric current.

In different phases of TMPD, the excitability of the muscle fiber when a new impulse arrives is different. At the onset of TMPD, cells are completely non-excitable, or refractory to an additional electrical impulse (1,2). This is the so-called absolute refractory period of the myocardial fiber, when the cell is generally unable to respond with new activation to any additional electrical stimulus. how a weak impulse remains unanswered (3). During diastole, the excitability of the myocardial fiber is completely restored, and its refractoriness is absent (4).

Significance of active forces in the formation of membrane potential.

The movement of ions occurs by diffusion. Active transport is carried out by Na + - K + pump (R. Dean - 1941). Na + - K + pump carries out the movement of ions against the concentration gradient (K + inward, Na + - outward). The pump requires energy, which is generated when ATP is broken down under the influence of ATPase, which is activated when the concentration of K + and Na + changes, which happens constantly, so the Na + - K + pump works constantly. According to Dean, the movement of ions is carried out by carrier molecules (proteins inside cell membranes). After performing the function, the X-protein (carrier of K + ions), thanks to the energy of ATP, changes its structure and turns into a Y-protein (carrier of Na + ions). Na + - K + pump is not the same under different conditions. At rest, there are 2 K+ ions for every 3 Na+ ions. When the state of the cell changes, the activity of the Na + - K + pump changes.

So at rest due to the release of K + ions from the cell, the outer surface of the cell is positively charged, and the inner one is negatively charged (in relation to the outer surface). This state is called polarization; the membrane potential is the equilibrium potassium potential; other ions and active forces participate in the appearance of the membrane potential.

The mechanism of action potential formation.

The action potential arises in the tissue under the influence of threshold and suprathreshold stimuli and is an impulsive excitation. The action potential can be registered in the same way as the membrane potential by a transmembrane method. Under the influence of threshold stimuli, the permeability of the cell membrane changes - it increases for all potential-forming ions, but most of all for N a + ions (500 times). Sodium ions move into the cell. The movement of sodium ions into the cell exceeds the exit of K + ions from the cell. As a result, there is a change in the charge of the cell membrane by opposite, then there is a gradual restoration of the initial charge of the membrane.

Components of the action potential and the mechanism of their occurrence .

With the transmembrane method of registration, an action potential arises, consisting of 3 main components:

1 component: local (local response);

2 component: peak (spike);

3rd component: trace potentials (negative and positive).

Spike (peak) - the most constant part. It consists of an ascending limb (depolarization phase) and a descending limb (repolarization phase). The remaining components are variable and may be absent.

Local (local) response occurs and continues until the stimulus will not reach threshold value. If the stimulus (its strength) is less than 50-75% of the threshold value, the membrane permeability changes slightly and is balanced for all ions (non-specific). After the strength of the stimulus reaches 50-75%, sodium permeability begins to predominate, since sodium channels are released from Ca2 + ions. There is a decrease in the membrane potential when the threshold value is reached, the potential difference reaches a critical level of depolarization.

Critical level of depolarization (Ek) - this is the potential difference that must be achieved in order for local changes to pass into the peak of the action potential. Ek is the threshold value at which local changes become widespread. Ek value is almost constant and equal to - 40 - -50 mV. The difference between the membrane potential and the threshold value characterizes the threshold of irritation and reflects the excitability of the tissue.

Peak action potential consists of the following phases.

The depolarization phase occurs as a result of an avalanche-like movement of N a + into the cell. Two reasons contribute to this: voltage-gated Na+ channels open. In this case, depolarization occurs according to the type of process with positive feedback (self-reinforcing process).

Release of sodium channels from Ca2 +.

The charge of the cell membrane first decreases to 0 (this is actually depolarization), and then changes to the opposite (inversion or overshoot). To characterize the phase of depolarization, the concept of reversion is introduced - this is the potential difference by which the action potential exceeds the resting potential.

R\u003d (action potential) - (membrane potential) 20-30 \u003d 50-60 mV.

R(reversion) is the amount of mV by which the membrane was recharged. The depolarization phase continues until electrochemical equilibrium in N a+ is reached. Then comes the next phase. The amplitude of the action potential does not depend on the strength of the stimulus. It depends on the concentration of N a + (both outside and inside the cell), on the number of sodium channels, and on the characteristics of sodium permeability.

The repolarization phase is characterized by:

a decrease in the permeability of the cell membrane for N a + (Na-inactivation). Sodium accumulates on the outer surface of the cell membrane;

an increase in the permeability of the membrane for K +, as a result, the release of K + from the cell increases with an increase in the positive charge on the membrane;

a change in the activity of the Na + - K + pump.

Repolarizationis the process of restoring the charge on the membrane. But there is no complete recovery, since trace potentials arise.

Trace potentials are divided into:

Negative trace potential - slowing down the repolarization of the cell membrane. This is the result of penetration into the cell of a certain amount of N a +, thus, a negative trace potential is a trace depolarization.

Positive trace potential - increase in potential difference. This is the result of an increased release of K + ions from the cell. A positive trace potential is a trace hyperpolarization. As soon as the potassium permeability returns to its original level, the membrane potential is recorded.

Conductivity function

Conductivity - the ability of cells to conduct electrical impulses

electrical impulses are conducted by the cells of the conduction system of the heart and cardiomyocytes.

Normally, the conduction system of the heart for conducting electrical impulses from the sinus node includes atrial cardiomyocytes, the AV node, the bundle of His, the right and left legs of the bundle of His, Purkinje fibers.

The speed of impulse conduction in the atria is 1 m/s, the AV node is 0.2 m/s, the bundle of His is 1 m/s, in the legs and Purkinje fibers 3-4 m/s.

Normally, such a conduction system determines the sequence of excitation in the heart of the sinus node. From the sinus node, electrical impulses are conducted to atrial cardiomyocytes.

In the atria, electrical impulses are conducted from the right atrium to the left atrium along the Bachmann bundle, and all atria are excited in 0.1 s.

Atrial cardiomyocytes conduct electrical impulses to the AV node.

Through the AV node, electrical impulses are conducted at a low speed - there is a delay in conduction. This delay is physiological - as a result, ventricular systole occurs after atrial systole.

From the AV node, electrical impulses are conducted to the bundle of His, the legs of the bundle of His, Purkinje fibers and further to the ventricular cardiomyocytes.

In the ventricles, electrical impulses propagate from the middle part of the interventricular septum to the apex of the right ventricle, then to the apex of the left ventricle, then to the basal part of the ventricles and septum

All ventricles are excited in 0.1 s, and it spreads from the endocardium to the epicardium.

An electrocardiograph can, to one degree or another, reflect all these functions, except for the function of contractility

Electrocardiograph fixes total electrical activity of the heart, or more precisely - the difference in electrical potentials (voltage) between 2 points.

Where in the heart there is a potential difference? Everything is simple. At rest, myocardial cells are negatively charged on the inside and positively charged on the outside, while a straight line (= isoline) is fixed on the ECG tape. When an electrical impulse (excitation) arises and propagates in the conduction system of the heart, the cell membranes pass from a state of rest to an excited state, changing the polarity to the opposite (the process is called depolarization). At the same time, the membrane becomes positive from the inside, and negative from the outside due to the opening of a number of ion channels and the mutual movement of K + and Na + ions (potassium and sodium) from the cell and into the cell. After depolarization, after a certain time, the cells go into a state of rest, restoring their original polarity (minus from the inside, plus from the outside), this process is called repolarization.

An electrical impulse sequentially propagates through the heart, causing depolarization of myocardial cells. During depolarization, part of the cell is positively charged from the inside, and part is negatively charged. Arises potential difference. When the entire cell is depolarized or repolarized, there is no potential difference. stages depolarization corresponds to contraction cells (myocardium), and stages repolarization - relaxation. The ECG records the total potential difference from all myocardial cells, or, as it is called, electromotive force of the heart(EMF of the heart). The EMF of the heart is a tricky but important thing, so let's get back to it a little lower.

Schematic arrangement of the EMF vector of the heart (in the center)
at one point in time.

EKG LEADS

As stated above, the electrocardiograph records the voltage (electrical potential difference) between 2 points, that is, in some abduction. In other words, the ECG machine captures on paper (screen) the value of the projection of the electromotive force of the heart (EMF of the heart) on any lead.

StandardThe ECG is recorded in 12 leads:

• 3 standard(I, II, III),
• 3 enhanced from limbs (aVR, aVL, aVF),
• and 6 chest(V1, V2, V3, V4, V5, V6).

Standard leads (proposed by Einthoven in 1913).

I - between the left hand and the right hand,

II - between the left leg and right hand,

III - between the left leg and left hand.

Protozoa(single-channel, i.e. recording no more than 1 lead at any time) the cardiograph has 5 electrodes: red(applies to right hand) yellow(left hand), green(left leg), black(right leg) and thoracic (suction cup). If you start with the right hand and move in a circle, you can say that you have a traffic light. The black electrode means “ground” and is only needed for safety purposes for grounding so that a person is not shocked if the electrocardiograph is possible to break down.

Multichannel portable electrocardiograph .

All electrodes and suction cups differ in color and place of application.

2) Strengthened limb leads(proposed by Goldberger in 1942).

The same electrodes are used as for recording standard leads, but each of the electrodes in turn connects 2 limbs at once, and a combined Goldberger electrode is obtained. In practice, these leads are recorded by simply switching the handle on a single-channel cardiograph (i.e., the electrodes do not need to be rearranged).

aVR- enhanced lead from the right hand (short for augmented voltage right - enhanced potential on the right).
aVL- enhanced abduction from the left hand (left - left)
aVF- enhanced abduction from the left leg (foot - leg)

3) chest leads(proposed by Wilson in 1934) are recorded between the chest electrode and the combined electrode from all 3 limbs.

The points of location of the chest electrode are located sequentially along the anterior-lateral surface of the chest from the midline of the body to the left hand.

I do not specify in too much detail, because for non-specialists it is not necessary. The principle itself is important (see fig.).

V1 - in the IV intercostal space along the right edge of the sternum.
V2
V3
V4 - at the level of the apex of the heart.
V5
V6 - on the left mid-axillary line at the level of the apex of the heart.

Location of 6 chest electrodes when recording an ECG .

The 12 leads indicated are standard. If necessary, "write" and additional leads:

• by Nebu(between points on the surface of the chest),
• V7 - V9(continuation of chest leads to the left half of the back),
• V3R-V6R(mirror image of chest leads V3 - V6 on the right half of the chest).

SIGNIFICANCE OF LEADS

For reference: quantities are scalar and vector. Scalars have only magnitude(numerical value), for example: mass, temperature, volume. Vector quantities, or vectors, have both magnitude and direction; for example: speed, force, electric field strength, etc. Vectors are indicated by an arrow above the Latin letter.

Why invented so many leads? EMF of the heart is vector heart emf in 3d world(length, width, height) taking into account time. On a flat ECG film, we can only see 2-dimensional values, so the cardiograph records the projection of the EMF of the heart on one of the planes in time.

Body planes used in anatomy .

Each lead records its own projection of the EMF of the heart. First 6 leads(3 standard and 3 reinforced from the limbs) reflect the EMF of the heart in the so-called frontal plane(see. Fig.) and allow you to calculate the electrical axis of the heart with an accuracy of 30 ° (180 ° / 6 leads = 30 °). The missing 6 leads to form a circle (360°) are obtained by continuing the existing lead axes through the center to the second half of the circle.

Mutual arrangement of standard and reinforced leads in the frontal plane .
But there is an error in the picture:aVL and lead III are NOT in line.Below are the correct drawings.

6 chest leads reflect the emf of the heart in the horizontal (transverse) plane(it divides the human body into upper and lower halves). This allows you to clarify the localization of the pathological focus (for example, myocardial infarction): the interventricular septum, the apex of the heart, the lateral sections of the left ventricle, etc.

When parsing an ECG, projections of the EMF vector of the heart are used, so this ECG analysis is called vector.

Note. The material below may seem very complex. This is fine. When studying the second part of the cycle, you will return to it, and it will become much clearer.

Electrical axis of the heart (EOS)

If draw a circle and draw lines through its center corresponding to the directions of three standard and three reinforced leads from the limbs, then we get 6-axis coordinate system. When recording an ECG in these 6 leads, 6 projections of the total EMF of the heart are recorded, which can be used to assess the location of the pathological focus and the electrical axis of the heart.

Formation of a 6-axis coordinate system .
Missing leads are replaced by extensions of existing ones.

Electrical axis of the heart - this is the projection of the total electrical vector of the ECG QRS complex (it reflects the excitation of the ventricles of the heart) onto the frontal plane. Quantitatively, the electrical axis of the heart is expressed angle α between the axis itself and the positive (right) half of the axis I of the standard lead, located horizontally.

It is clearly seen that the same EMF of the heart in projections
on different assignments gives various forms of curves.

Definition rules the positions of the EOS in the frontal plane are as follows: the electrical axis of the heart matches with that of the first 6 leads, in which highest positive teeth, and perpendicular to the lead in which the size of the positive teeth is equal to the size of the negative teeth. Two examples of determining the electrical axis of the heart are given at the end of the article.

Options for the position of the electrical axis of the heart:

• normal: 30° > α< 69°,
• vertical: 70° > α< 90°,
• horizontal: 0° > α < 29°,
• sharp right axis deviation : 91° > α< ±180°,
• sharp left axis deviation : 0° > α < −90°.

Options for the location of the electrical axis of the heart
in the frontal plane.

Fine electrical axis of the heart roughly corresponds to anatomical axis(for thin people it is directed more vertically from the average values, and for obese people it is more horizontally).For example, when hypertrophy(growth) of the right ventricle, the axis of the heart deviates to the right. At conduction disorders the electrical axis of the heart can deviate sharply to the left or right, which in itself is a diagnostic feature. For example, with complete blockade of the anterior branch of the left branch of the bundle of His, there is a sharp deviation of the electrical axis of the heart to the left (α ≤ −30°), the posterior branch to the right (α ≥ +120°).

Complete blockade of the anterior branch of the left leg of the bundle of His .
EOS sharply deviated to the left (α ≅ − 30°), because the highest positive waves are seen in aVL, and the equality of the waves is noted in lead II, which is perpendicular to aVL.

Complete blockade of the posterior branch of the left leg of the bundle of His .
EOS sharply deviated to the right (α ≅ +120°), because the highest positive waves are seen in lead III, and the equality of the waves is noted in lead aVR, which is perpendicular to III.

The principle of operation of the electrocardiograph

Front view contemporary panels electrocardiograph

Potential difference fluctuations , arising from the excitation of the heart muscle, is perceived by electrodes located on the body of the subject, and is fed to the input of the electrocardiograph. This extremely small voltage is passed through the cathode lamp system, due to which its magnitude increases by 60 0- 700 times. Since the magnitude and direction of the EMF during the cardiac cycle are constantly changing, the galvanometer needle reflects voltage fluctuations, and its fluctuations, in turn, are recorded as a curve on a moving tape.

Recording vibrations galvanometer is carried out on a moving tape directly at the time of registration. The movement of the tape for recording ECG can occur at different speeds (from 25 to 100 mm / s), but most often it is 50 mm / s. Knowing the speed of the tape, you can calculate the duration of the ECG elements.

So if ECG recorded at a typical speed of 50 mm/s, a 1 mm curve would correspond to 0.02 s.

For ease of calculation in devices with direct recording, the ECG is recorded on paper with millimeter divisions. The sensitivity of the galvanometer is selected so that a voltage of 1 mV causes a deviation of the recording device by 1 cm. The sensitivity or amplification of the device is checked before recording the ECG, it is carried out using a standard voltage of 1 mV (control millivolt), the supply of which to the galvanometer should cause deviation of the beam or pen by 1 cm. The normal millivolt curve resembles the letter P, the height of its vertical lines is 1 cm.

Electrocardiographic leads. Changes in the potential difference on the surface of the body that occur during the work of the heart are recorded using various ECG lead systems. Each lead registers the potential difference existing between two different points of the electric field of the heart, where the electrodes are installed.

Thus, different ECG leads differ among themselves primarily in areas of the body from which potentials are removed.

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

ELECTROCARDIOGRAM REGISTRATION TECHNIQUE.

An electrocardiogram is recorded using electrocardiographs.

To record the ECG, the patient is laid on the couch. To obtain good contact, gauze pads moistened with alcohol are placed under the electrodes. The ECG is recorded in a special room, remote from possible sources of electrical interference.

The couch must be at least 1.5- 2 m from the mains wires. It is advisable to shield the couch by placing a blanket under the patient with a sewn-in metal mesh, which must be grounded. An ECG recording is usually performed with the patient lying on his back, which allows for maximum muscle relaxation.

Preliminarily fix the surname, name and patronymic of the patient, his age, date and time of the study, the number of the medical history

Application of electrodes Hand 4 plate electrodes are applied to the inner surface of the legs and forearms in their lower third with the help of rubber bands or special plastic clips, and one or more (for multichannel recording) chest electrodes are placed on the chest using a rubber pear - suction cup or adhesive disposable chest electrodes.

To improve the contact of the electrodes with the skin and reduce interference and inductive currents at the places where the electrodes are applied, it is necessary to first degrease the skin with alcohol and cover the electrodes with a layer of special conductive paste, which allows you to minimize the interelectrode resistance. Connecting wires to electrodes Each electrode is connected to a wire coming from the electrocardiograph and marked with a certain color.

The following marking of input wires is generally accepted: right hand - red; left hand - yellow; left leg green; right leg (patient grounding) - black; chest electrode - white.

In the presence of a 6-channel electrocardiograph, which allows you to simultaneously record an ECG in 6 chest leads, a wire with a red tip marking is connected to the V electrode; to the electrode V2 - yellow, uz - green, V4 - brown, V5 - black and Vg - blue or purple.

The marking of the remaining wires is the same as in single-channel electrocardiographs

Electrocardiogram reflects only electrical processes in the myocardium: depolarization (excitation) and repolarization (recovery) 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, I will sometimes use “contraction-relaxation” instead of “depolarization-repolarization”, 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.

ELEMENTS OF A NORMAL ECG

Before moving on to deciphering the ECG, you need to figure out 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.

Every ECG is made up of teeth, segments and intervals.

TEETHare convexities and concavities on the electrocardiogram.
The following teeth are distinguished on the ECG:

• P(atrial contraction)
• Q, R, S(all 3 teeth characterize the contraction of the ventricles),
• T(ventricular relaxation)
• U(non-permanent tooth, rarely recorded).

SEGMENTS
A segment on an ECG is called straight line segment(isolines) between two adjacent teeth. The P-Q and S-T segments are of the greatest importance. For example, the P-Q segment is formed due to a delay in 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.

Teeth, segments and intervals on the ECG.
Pay attention to large and small cells (about them below).

Waves of the QRS complex

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 pick out the teeth?

Before total estimate amplitude (dimensions) of individual teeth QRS complex. If the amplitude exceeds 5 mm, the prong denote capital (big) letter Q, R or S; if the amplitude is less than 5 mm, then lowercase (small): q, r or s.

The tooth R (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. The negative (downward) wave of the QRS complex located before the R wave, denoted as Q (q), and after - as 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 R- the bulk of the myocardium of the ventricles, tooth S- basal (i.e., near the atria) sections of the interventricular septum. The R wave V1, V2 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 widening and deepening of the Q wave, so this wave is always paid close attention.

ECG analysis

General ECG decoding scheme

1. Checking the correctness of ECG registration.

2. Heart rate and conduction analysis:

oassessment of the regularity of heart contractions,

ocounting the heart rate (HR),

odetermination of the source of excitation,

oconductivity rating.

3. Determination of the electrical axis of the heart.

4. Analysis of atrial P wave and P-Q interval.

5. Analysis of the ventricular QRST complex:

oanalysis of the QRS complex,

oanalysis of the RS-T segment,

o T wave analysis,

oanalysis of the interval Q - T.

6. Electrocardiographic conclusion.

Normal electrocardiogram.

1) Checking the correctness of the ECG registration

At the beginningeach ECG tape must have calibration signal- so-called control millivolt. To do this, at the beginning of the recording, a standard voltage of 1 millivolt is applied, which should display on the tape a deviation of 10 mm. Without a calibration signal, the ECG recording is considered invalid. Normally, in at least one of the standard or augmented limb leads, the amplitude should exceed 5 mm, and in the chest leads - 8 mm. If the amplitude is lower, it is called reduced EKG voltage which occurs in some pathological conditions.

Reference millivolt on the ECG (at the beginning of the recording).

2) Heart rate and conduction analysis:

a.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 correct.

b.P heart rate counting (HR)

Large squares are printed on the ECG film, each of which includes 25 small squares (5 vertical x 5 horizontal). For a quick calculation of heart rate with the correct rhythm, the number of large squares between two adjacent R-R teeth is counted.

At 50 mm/s belt speed: HR = 600 / (number of large squares).
At 25 mm/s belt speed: 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 /m in.

At a speed of 25 mm/s each little cell is equal to 0.04s, and at a speed of 50 mm/s - 0.02 s. This is used to determine the duration of the teeth and intervals.

With an incorrect rhythm, they usually consider maximum and minimum heart rate according to the duration of the smallest and largest R-R interval, respectively.

c.determination of the source of excitation

Sinus rhythm(this is a normal rhythm, and all other rhythms are pathological).
The source of excitation is in sinoatrial node. ECG signs:

• in standard lead II, the P waves are always positive and are in front of each QRS complex,
• P waves in the same lead have a constant identical shape.

P wave in sinus rhythm.

ATRIAL Rhythm . If the source of excitation is in the lower sections of the atria, then the excitation wave propagates to the atria from the bottom up (retrograde), therefore:

• in leads II and III, P waves are negative,
• There are P waves before each QRS complex.

P wave in atrial rhythm.

Rhythms from the AV junction . If the pacemaker is in 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 may be negative, located after the QRS complex.

Rhythm from the AV junction, P wave overlapping the QRS complex.

Rhythm from the AV junction, the P wave is after the QRS complex.

The heart rate in the rhythm from the AV connection is less than sinus rhythm and is approximately 40-60 beats per minute.

Ventricular, or IDIOVENTRICULAR, rhythm (from lat. ventriculus [ventriculus] - ventricle). In this case, the source of rhythm is the conduction system of the ventricles. Excitation spreads through the ventricles in the wrong way and therefore more slowly. Features of idioventricular rhythm:

• the QRS complexes are dilated and deformed (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 fire 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.

d.conductivity assessment .
To correctly account for conductivity, the write speed is taken into account.

To assess conductivity, measure:

oduration P wave(reflects the speed of the impulse through the atria), normally up to 0.1s.

oduration interval P - Q(reflects the speed of the impulse from the atria to the myocardium of the ventricles); interval P - Q = (wave P) + (segment P - Q). Fine 0.12-0.2s.

oduration QRS complex(reflects the spread of excitation through the ventricles). Fine 0.06-0.1s.

ointernal deflection interval in leads V1 and V6. This is the time between the onset of the QRS complex and the R wave. Normally in V1 up to 0.03 s and in V6 to 0.05 s. It is mainly used 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).

Measurement of the interval of internal deviation.

3) Determination of the electrical axis of the heart.
In the first part of the cycle about the ECG, it was explained what electrical axis of the heart and how it is defined in the frontal plane.

4) Atrial P wave analysis.
Normal in leads I, II, aVF, V2 - V6 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 0.1s, 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 "cor pulmonale".
• A split with 2 peaks, an extended P wave in leads I, aVL, V5, V6 is typical for left atrial hypertrophy such as mitral valve disease.

P wave formation (P-pulmonale) with right atrial hypertrophy.

P wave formation (P-mitrale) with left atrial hypertrophy.

P-Q interval: fine 0.12-0.20s.
An increase in this interval occurs with impaired conduction of impulses through the atrioventricular node ( atrioventricular block, AV block).

AV blockthere 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 in the AV node. The atria and ventricles contract in their own rhythm, independently of each other. Those. an idioventricular rhythm occurs.

5) Analysis of the ventricular QRST complex:

a.analysis of the QRS complex .

The maximum duration of the ventricular complex is 0.07-0.09 s(up to 0.10 s). The duration increases with any blockade of the legs of the bundle of His.

Normally, the Q wave can be recorded in all standard and augmented limb leads, as well as in V4-V6. Q wave amplitude normally does not exceed 1/4 R wave height, and the duration is 0.03 s. Lead aVR normally has a deep and wide Q wave and even a QS complex.

The R wave, like Q, can be recorded in all standard and enhanced limb leads. From V1 to V4, the amplitude increases (while the r wave of V1 may be absent), and then decreases in V5 and V6.

The S wave can be of 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) is usually recorded “ transition zone” (equality of the R and S waves).

b.analysis of the RS-T segment

CThe ST segment (RS-T) is the segment from the end of the QRS complex to the beginning of the T wave. The ST segment is especially carefully analyzed in CAD, as it reflects a lack of oxygen (ischemia) in the myocardium.

Normally, the S-T segment is located in the limb leads on the isoline ( ± 0.5mm). In leads V1-V3, the S-T segment can be shifted upward (no more than 2 mm), and in V4-V6 - downward (no more than 0.5 mm).

The transition point of the QRS complex 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.

c.a 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.

d.a analysis of the interval Q - T .

The Q-T interval is called electrical ventricular systole, because at this time all departments of the ventricles of the heart are excited. Sometimes after the T wave, a small U wave, which is formed due to a short-term increased excitability of the myocardium of the ventricles after their repolarization.

6) Electrocardiographic conclusion.
Should include:

1. Rhythm source (sinus or not).

2. Rhythm regularity (correct or not). Usually sinus rhythm is correct, although respiratory arrhythmia is possible.

3. heart rate.

4. The position of the electrical axis of the heart.

5. The presence of 4 syndromes:

o rhythm disorder

oconduction disorder

ohypertrophy and/or congestion of the ventricles and atria

omyocardial damage (ischemia, dystrophy, necrosis, scars)

LOAD TESTS

A test with dosed physical activity is an ideal method of functional diagnostics, which allows assessing the usefulness of the physiological compensatory-adaptive mechanisms of the body, and in the presence of an obvious or latent pathology, the degree of functional inferiority of the cardiorespiratory system].Stress test (NP) is considered one of the types of natural provocation, which is used to diagnose various diseases, and in cases where the pathology is already known, with the help of NP it is possible to determine the degree of its severity or compensatory possibilities. cardiovascular systems. NP is one of several types stress testing(along with transesophageal pacing, stress echocardiography), therefore, the term NP more accurately reflects the essence of the technique than the often used definition of a stress test.

The main point of application of NP is the diagnosis of coronary artery disease. The most important advantages of NP are non-invasiveness, almost unlimited availability and low cost of research. The significance of NP is also emphasized by the fact that this technique allows you to identify a risk group, that is, patients at risk of developing cardiovascular complications and death. It is no coincidence that in the recommendations for coronary angiography under class I, the following indication is indicated - “criteria for high risk cardiovascular complications identified by non-invasive testing, regardless of the severity of angina." However, the provocative nature of the test implies the possibility of various complications, many of which can be serious.

Treadmill .

Treadmill test– function research method cardiovascular systems with physical activity on a treadmill - treadmill. Alternatively, an ECG stress test can also be performed on a bicycle ergometer - a special exercise bike.

How is the treadmill test done?

Before routine treadmill test for each patient, the maximum load level is calculated taking into account age, gender, height and weight.

When conducting treadmill test with gas analysis the load continues until the patient reaches the anaerobic threshold, determined by the concentration of gases exhaled by the patient (individual maximum tolerated load).

The patient is exposed to the waist, electrodes attached to the measuring equipment are applied to the chest. An ECG of the heart is performed at rest. Throughout the test, there is a constant measurement of blood pressure and ECG recording.

When conducting a load test, various research protocols can be used, mainly a protocol is used in which there is a gradual increase in load at certain time intervals (most often after 3 minutes). Functional diagnostics doctor can increase the load by controlling the speed of the walkway and the angle of inclination.

Types of treadmill test

Routine treadmill test with ECG

Capabilities

Early diagnosis and assessment of severity ischemic heart disease(CHD), arterial hypertension, heart rhythm disturbances ( arrhythmias).

Evaluation of the effectiveness of the surgical treatment of cardiac vessels.

Assessment of the adequacy of drug treatment.

Treadmill test with gas analysis

Capabilities
Along with the above possibilities, the anaerobic threshold is determined, lung function is assessed, oxygen consumption, carbon dioxide release, oxygen and carbon dioxide concentrations on exhalation.

The level of physical development of the patient is determined, the correspondence of his biological and actual age, an individual safe training regimen is selected.

Stress test with echocardiography (stress echocardiography)

The load can be dosed with treadmill test or a bicycle ergometer.

Capabilities

Examination of the degree of contractility of the walls of the left ventricle, assessment of intracardiac circulation.

Diagnosis of myocardial ischemia, assessment of myocardial viability after myocardial infarction or prolonged ischemia, assessment of the contractility of various segments of the heart muscle

Treadmill test with dopplerography of arterial blood flow

Capabilities

Assessment of the severity of ischemia, arterial insufficiency of the vessels of the lower extremities

Benefits of the treadmill test

Simplicity and accessibility of the method for the patient

Non-invasiveness and absolute safety of the method

Accurate diagnosis of the level of individual exercise tolerance

The possibility of selecting and evaluating the effectiveness of drug therapy

Diagnostics diseases cardiovascular systems in the early stages (including coronary heart disease, angina pectoris, etc.)

Preparing for the treadmill test

Refrain from eating 3 hours before the event treadmill test

No stress and physical activity before the procedure treadmill test

Cardiologist's consultation to identify possible contraindications to the treadmill test

It is necessary to inform the doctor about the medications taken. Cancellation of nitrates and long-acting beta-blockers 2 days before the study.

Comfortable walking shoes are required

Treadmill Test Results can be used for early diagnosis of heart diseases (in particular, to establish the functional class of angina pectoris, determine indications for surgical treatment, etc.), evaluate the effectiveness of surgical treatment of heart vascular diseases, and make recommendations on the amount of physical activity for patients with diseases cardiovascular systems, etc.

BIKE ERGOMETRY

Bicycle ergometry (ECG) - This is an electrocardiogram recording against the background of physical activity. It is carried out on a special bicycle - a bicycle ergometer. The method allows you to determine the reaction cardiovascular systems for physical activity, the degree of endurance of the body to the load, to reveal the hidden pathology of the cardiovascular system.

This study is carried out with the aim:

• diagnosis of latent pathology of the cardiovascular system, including in the absence of characteristic symptoms, especially in patients with risk factors - smoking, arterial hypertension, hypercholesterolemia, etc.
• provocation of latent arrhythmias;
• determination of exercise tolerance in healthy individuals, athletes, patients with pathology of the respiratory system, as well as in individuals with cardiac and extracardiac pathology;
• to assess the risk of surgical treatment or assess the ability to work;
• evaluation of the prognosis in the early postinfarction period.

Bicycle ergometry is mandatory :

• in the presence of atypical pain in the chest, especially associated with physical activity;
• in the presence of fuzzy clinical manifestations of coronary heart disease (shortness of breath, palpitations, weakness, dizziness associated with physical activity);
• with typical exertional angina to determine exercise tolerance;
• after an acute myocardial infarction;
• with non-specific changes in ECG rest, even in the absence of pain syndrome or its atypical character;
• from public transport drivers, pilots to ensure public safety.

Contraindications to bicycle ergometry :

1. Complicated acute myocardial infarction (only after 3 weeks).

2. Uncomplicated acute myocardial infarction (only after 7-14 days).

3. Unstable angina, including progressive and variant, with uncontrolled pain syndrome.

4. Heart failure 2-B and 3 stages.

5. Severe respiratory failure.

6. Dangerous rhythm and conduction disturbances, paired extrasystoles, early extrasystoles, paroxysm of atrial fibrillation, tachycardia over 100 beats / min.

7. Active inflammatory diseases (infectious and non-infectious, febrile conditions, thrombophlebitis, endocarditis, pericarditis, myocarditis - 3 months).

8. Thromboembolism of the pulmonary artery, blood clots in the cavities of the heart, pulmonary infarction.

9. Critical valve stenoses.

10. Dissecting aortic aneurysm; post-infarction aneurysm of the left ventricle with ventricular fibrillation and a history of clinical death.

JERELA INFORMATION:

A. Basics:

1. http:// www. happydoctor. en

Vershigora A.V., Zharinov O.Y., Kuts V.O., Nesukai V.A. Fundamentals of electrocardiography. - Lviv. - 2012. - 130 p.

2. Shved M.I., Grebenik M.V. Fundamentals of practical electrocardiography. - Ternopil. Ukrmedkniga, 2000. - P.7 - 25.

3 . Posіbnik z normalї fіzіologiї / For red. V.G. Shevchuk, D.G. Nalivayka. - K., 1995. - S.150-160.

4 . Physiology of people: assistant / V.I. Filimonov. - K., VSV "Medicine", 2010. - S. 522-535.

5 . Fundamentals of functional diagnostics (manual guide) / Vadzyuk S.N., 1997. - S. 13-14.

6 . Dovіdnik osnovnyh pokaznikіv zhittєdіyalnostі zdoroї lyudiny / Z and ed. prof. S.N. Vadzyuk - Ternopil, 1996. - S. 21-23.

B. Dodatkov:

1. Murashko V.V., Strutynsky A.V. Electrocardiography. - M., 1987. - S. 16-97.

2. Zharinov O.I., Kuts V.O., Thor N.V. Navantage trials in cardiology. - Kiev: "Medicine of the World", 2006. - P.6 - 14.

The conduction system of the heart (PSS) is a complex of anatomical formations (nodes, bundles and fibers) that have the ability to generate an impulse of heart contractions and conduct it to all parts of the atrial and ventricular myocardium, ensuring their coordinated contractions.

The conduction system of the heart includes:

• 1. Sinus node - Kisa-Flex. The sinus node is located in the right atrium on the back wall at the confluence of the superior vena cava. He is a pacemaker, impulses arise in it that determine the heart rate. This is a bundle of specific tissues, 10-20 mm long, 3-5 mm wide. The node consists of two types of cells: P-cells (generate impulses of excitation), T-cells (conduct impulses from the sinus node to the atria).
• 2. Atrioventricular node - Ashof-Tovar.

It is located in the lower part of the interatrial septum on the right, anterior to the coronary sinus. In recent years, instead of the term "atrioventricular node", a broader concept is often used - "atrioventricular connection". This term refers to the anatomical region, which includes the atrioventricular node, specialized atrial cells lying in the region of the node, and part of the conductive tissue, from which the potential H of the electrogram is recorded. There are four types of cells of the atrioventricular node, similar to the cells of the sinus node:

• P-cells, which are present in small numbers and are located mainly in the area of ​​​​the transition of the atrioventricular node to the bundle of His;
• transitional cells that make up the bulk of the atrioventricular node;
• · cells of the contractile myocardium, located mainly at the atrionodal edge;
• Purkinje cells
• 3. Bundle of His, which is divided into right and left legs, passing into Purkinje fibers.

The bundle of His consists of penetrating (initial) and branching segments. The initial part of the Hiss bundle has no contacts with the contractile myocardium, but is easily involved in the pathological processes occurring in the fibrous tissue that surrounds the Hiss bundle. The length of the Hiss bundle is 20 mm. The bundle of His is divided into 2 legs (right and left). Further, the left leg of the bundle of His is divided into two more parts. The result is a right pedicle and two branches of the left pedicle that descend down both sides of the interventricular septum. The right leg goes to the muscle of the right ventricle of the heart. As for the left leg, the opinions of researchers differ here. It is believed that the anterior branch of the left bundle of His bundle supplies fibers to the anterior and lateral walls of the left ventricle; the posterior branch is the posterior wall of the left ventricle, and the lower sections of the lateral wall. The branches of the intraventricular conduction system gradually branch out to smaller branches and gradually pass into Purkinje fibers, which communicate directly with the contractile myocardium of the ventricles, penetrating the entire heart muscle.