Electrocardiography [+ Greek kardia heart + grapho to write, represent electro-(from «electricity»)]:
- a method of registration of the electric activity of a myocardium extending on heart during a cardial cycle;
- the section of cardiology studying genesis of electric activity of heart its characteristic is normal also at pathology, and also clinicodiagnostic value. Nek-ry researchers designate E. in the second value as electrocardiology, but this term was not widely adopted.
The electrocardiogram (ECG) — the curve reflecting dynamics of potential difference in two points of electric field of heart during a cardial cycle. The ECG (or assignment of an ECG) is registered the electrocardiograph by obtaining information on potentials by means of the electrodes placed in the chosen two points of electric field of heart. Sometimes an ECG call scalar as it unlike the vector ECG (see Vektorkardiografiya) does not allow on the basis of the analysis in one assignment to judge the direction of the electromotive force (EMF) of heart, providing only information on its size. To gain as much as possible complete idea of the space nature of electric processes in heart, assignments of an ECG can be removed at various provision of electrodes. Each assignment is characterized by the provision of an axis (the line between two electrodes) and polarity of each of electrodes (poles) of assignment.
Existence of the electric phenomena in the reduced cardiac muscle was found for the first time by R. Kelliker and I. Müller (1856) on nerve-muscle preparation of a frog. Sharp (W. Sharpey, 1880) and Waller (A. D. Waller, 1887) the first wrote down an ECG of the person the capillary electrometer designed by G. Lippmann in 1873 Waller (1887 — 1889) offered the scheme of electric field of heart (fig. 1), put forward idea of dipolar structure of heart and an electrical axis. Development E. it is inseparably linked with a name of the Dutch physiologist V. Eyntkhoven, to-ry in 1903 created the first electrocardiograph on the basis of the string galvanometer invented by J. S. Schweigger. V. Eyntkhoven's electrocardiograph allowed in details, without essential distortions to write down an ECG and to widely implement E. in fiziol. researches and wedge. medicine.
V. Eyntkhoven with sotr. offered three standard leads from extremities, described the normal ECG, developed bases of the vector analysis of the ECG which is based on studying of projections of a vector of the electromotive force of heart to axes of standard leads, offered a method of definition of an electrical axis of heart and a corner and, formulated the rule of a triangle, etc. An essential contribution in E. the domestic physiologist A. F. Samoylov who described dependence of an ECG on phases of breath and presented experimental justification of a possibility of circular motion of an excitation wave on a myocardium of auricles at a ciliary arrhythmia brought. A. F. Samoylov studied questions of genesis of an ECG, together with And. 3. Draft in 1930 described a reciprocal rhythm at the person. Great value for justification of a method E. and its implementations in clinic had works F. Kpayca, Nikolay (G. Nicolai, 1910), Lewis (Th. Lewis, 1920).
Development clinical E. it is connected with names of V. F. Zelenin who described an ECG at increase in departments of heart (1910) and disturbances of a cordial rhythm (1915); Smith (R. M. of Smith, 1918), Pardey (N. E. V. of Pardee, 1920), Bailey (R. Bayley, 1942), shown a possibility of diagnosis of a myocardial infarction; Rotberger and Vinterberg (Page J. Rothberger, N. of Winterberg, 1917), Venkebakh and Vinterberg (To. Wenckebach, N. of Winterberg, 1927), profoundly studied ECGs at disturbances of a rhythm and conductivity. In 1932 Mr. F. N. Wilson offered single-pole assignments. In 1942 Goldberger (V. of Goldberger) developed the strengthened single-pole assignments from extremities. Since the same time practice included the chest assignments of an ECG which significantly expanded possibilities of diagnosis.
The first Soviet guides and monographs to an electrocardiography are written by L. I. Fogelson (1928, 1948), P. E. Lukomskim (1943), V. E. Nezlin and S. E. Karpay (1948, 1959), G. Ya. Dekhtyar (1951), A. V. Goltsman and I. T. Dmitriyeva (1960).
Wilson (1935) entered a concept about the integral vector of heart reflecting the total EMF as the sum of elementary EMFs of all excited elements (dipoles) of a myocardium. It showed change of an integral vector during a cardial cycle. Schaefer (N. of Schaefer, 1951) and Grant (R. Grant, 1951 — 1957) developed the vector analysis of an ECG, connected change of orientation of an integral vector with spread of activation on various departments of heart, gave the characteristic of an ECG in any assignment as the curve registering dynamics of a projection of an integral vector to an axis of the given assignment during a cardial cycle (fig. 2, 3).
Theoretical bases of an electrocardiography
an ECG — periodically repeating curve representing graphic display of the time histories of potential difference between various points of a body arising owing to electric processes to-rymi is followed spread of activation on the working heart. Spread of activation on heart is followed by emergence in the volume conductor (body) of electric field surrounding it. The form, amplitude and a sign of elements of the electrocardiogram depend on spatio-temporal characteristics of excitement of heart (a hronotopografiya of excitement), on geometrical characteristics and passive electric properties of a body as volume conductor, on properties of assignments of an ECG as measuring system.
Frequency and a rhythm of cordial reductions are defined by the excitement rhythmic generated by the so-called pacemaker (see the Pacemaker) extending on the carrying-out system of heart (see) and involving a wave of reduction of a myocardium.
The carrying-out system of heart consists of muscle fibers of a special structure. In it distinguish nodes and bunches. It is normal a pacemaker at the highest animals and the person the sinus and atrial node located between an upper vena cava and the right auricula atrii is. From here excitement extends on intra atrial conduction paths, a myocardium of auricles and covers an atrioventricular (atrioventricular) node, then, later nek-dig delays — a ventriculonector (an atrioventricular, or atrioventricular bunch) with its branchings and Purkinye's fibers, and also a «working» myocardium of ventricles.
The priority of excitement and a delay of an excitation wave created in the course of evolution in an atrioventricular node create the sequence of reduction of its departments, necessary for the most effective ensuring pumping function of heart, and the time term which is required for filling by their blood. Desequencing of excitement of different departments of heart finds a certain reflection on an ECG. It gives the chance to use E. for very exact diagnosis of various disturbances of a rhythm and blockade of carrying out excitement unavailable to other types of a research, allows to define localization of a source of premature ventricular contraction, to diagnose a hypertrophy of auricles and ventricles, to reveal diffusion and focal changes of a myocardium and others patol. conditions of heart.
Feature of an electrocardiographical method consists that pickup electrodes are always located in a distance from the excited cells. Thus the potential difference in corresponding, being at more or less considerable distance one from another, points of electric field of heart is registered. In practice this distance is minimum at record of an endocardial or epicardial elektrogramma and is most big at registration of standard leads of an ECG from extremities. Information on the electric generator of heart, to-ruyu at the same time receive, it is directly connected with the accuracy of idea of its field provided with the analysis of the ECG registered in these or those assignments.
The total electric generator of heart consists of a set of elementary generators — the excited cells distributed in space and components the front of an excitation wave. The number of these cells and the nature of their distribution and the course of spread of activation continuously change. The total generator has therefore very complex variable structure, the exact quantitative description a cut it is almost impracticable. For the approximate description use the equivalent generators (EG) — simple mathematical models of the known, set by the researcher structure in the form of set of sources of current, to-rye at their arrangement in heart would have to lead to emergence of the electric field reproducing the field of heart. EG of subjects is more perfect, than more precisely its field matches the field of heart. For assessment of accuracy of coincidence choose criterion of equivalence. Adequacy of model is defined by in what degree its components can be unambiguously defined in the settlement way on the basis of the analysis of an ECG in these assignments (a so-called return problem of an elektrografiya, i.e. creation of the EG model of the available ECGs).
From a set of the offered models the solution of the return task is best developed for EG of multipolar type. Multi-zero represents set of final number of the dipolar sources of current with incoincident dipolar axes located in one point. At the accepted assumptions about properties of a body as volume conductor (accept that the body — the homogeneous isotropic volume conductor having active electric resistance) the potential of multipolar EG in any point of a body (φ) is expressed as the sum of the sizes depending on the characteristic of a multipole determined, in turn, by sizes of potentials and the directions of axes of the dipoles making it:
where h(i) — the characteristic of a multipole. l(i) — the coefficients determined by measuring characteristics of assignments, localization of points of assignments and properties of the carrying-out environment, і — the order of a multipole (a multipole of the first orders — a dipole, the second order — a quadrupole, the third order — oktapol etc.) used in this model and determined by the set criterion of equivalence.
The first theoretical concept of genesis of an ECG which received the name «concept of a cordial dipole» was offered by Waller (1887) and developed by V. Eyntkhoven (1912). According to Waller's theory — Eyntkhovena a moment electric condition of the working heart can be presented by a so-called equivalent cordial dipole. A dipole call set of two dot electric charges equal in size and opposite on a sign, being on nek-rum distance from each other; the last can be as much as small. Around a dipole electric field is formed. Consider that its power lines proceed from a positive pole (source) and enter a negative pole (drain). Perpendicularly to power lines there pass so-called isopotential lines, i.e. lines, in any point to-rykh the size of electric potential is identical. Absolute value of potential for isopotential lines is caused by their arrangement concerning poles of a dipole (fig. 1). The straight line passing through poles of a dipole is called a dipolar axis. V. Eyntkhoven considered an equivalent cordial dipole as a hypothetical source of current in the volume conductor, having made at the same time a number of assumptions, in particular having assumed that the equivalent dipole is located in the center of a thorax as in the volume conductor, and this conductor gomogenen also has the form of the sphere of infinite radius. These assumptions allow to consider heart as an equivalent dipole of immeasurably small size. If at the same time to register potential difference from tops of an equilateral triangle, for to-rye V. Eyntkhoven accepted the right hand, the left hand and a pubic joint, or a pubic symphysis (in a practical electrocardiography as the third top the left leg is used), it is possible by means of simple calculations to determine the size and the direction (i.e. vectors) the electromotive forces. the creating ECGs. In the course of cardiac performance the size and the direction of the electromotive forces continuously change, according to it also value of a so-called integral vector of heart changes, the point corresponding to the middle of distance between poles of a dipole is taken for the beginning to-rogo.
According to Wilson (F. N. Wilson, 1935), to-ry entered idea of an integral vector of heart, the last is the vector sum of the electromotive forces of a huge set of dipoles though, from the point of view of physics, quite naturally to consider it as a vector of EMF of a uniform equivalent dipole. Projecting the integral vector of heart located in space on Eyntkhoven's triangle lying in the frontal plane of a body receive the so-called demonstrating axis of heart (which is also a vector in this plane). If to project the demonstrating axis on each of the parties of a triangle of Eyntkhoven, scalar size EMF of heart three standard leads of time turns out at present. These scalar sizes registered throughout a cardial cycle also create an ECG (fig. 2, and, b).
For the I standard lead the arrangement of the registering electrodes on the right and left hands, for II — on the right hand and the left leg, for III — on the left hand and the left leg is accepted. The straight line connecting points of an arrangement of two electrodes of opposite polarity is called an axis of this assignment. Scalar sizes of a projection of a cordial vector to the parties of a triangle of Eyntkhoven in each timepoint are defined by the equation:
where eI, eII, eIII — the algebraic size of the signals registered respectively in I, II and III standard leads. The specified ratio carries the name Eyntkhovena governed; its justice is confirmed by simple trigonometrical calculations. A referral of an average projection of an integral vector of heart to the frontal plane of a body was got by the name «electrical axis of heart». It is determined by a ratio of positive and negative teeth of a complex in I and III assignments and consider one of the ECG important parameters. In clinical E. standard leads keep the value to a crust. time. Later three single-pole assignments from extremities, and also six single-pole chest assignments were offered. The last are intended for registration of a projection of a vector of dipole moment of heart for the transversal plane of a body. The indifferent electrode of these assignments (terminal Wilson) combines through the potentials mixing resistors both upper and left lower extremities. The imagined axes of unipolar assignments connect points of imposing of trimming electrodes to the center of heart, to-ry has the potential close to zero, i.e. very little changing during a cardial cycle. Twelve listed assignments are standard in clinical E. Actually these assignments are sensitive also to not dipolar components of electric field of heart, but do not provide a possibility of quantitative definition of the last. For exact registration of dipolar components systems of orthogonal korrigirovanny assignments are developed. They differ in the fact that registration of an ECG is made in three-dimensional system of coordinates, axes X, U, Z to-rykh (axes of assignments) are mutually perpendicular. Scale factors on axes are equal in well korrigirovanny systems among themselves, and sensitivity to not dipolar components of electric field of heart is absent. The dipolar theory gained wide recognition. Nevertheless for improvement of the obtained diagnostic information many other systems of assignments of an ECG are created. Among them there are systems of multiple assignments of an ECG allowing to study distribution of potential of a body surface and its time history. The researches executed with use of various systems of multiple assignments showed that on the structure electric field of heart is much more difficult than the field, a cut would have to arise under the influence of a dipolar source of current and that the dipolar description of electric field of heart — quite rough approach. Therefore the systems of orthogonal korrigirovanny assignments sensitive only to dipolar components of the field contain though important, but not exhaustive diagnostic information. Creation of the optimum equivalent generator of heart — one of the major tasks modern biophysical. directions of an electrocardiography.
For registration of an ECG in clinic the system including 12 assignments is accepted: three standard leads from extremities (I, II III), three strengthened single-pole assignments (on Goldbergera) from extremities (aVR, aVL, aVF) and six single-pole chest (V1, V2, V3, V4, V5, V6) assignments (according to Wilson).
Standard leads. For registration of assignments from extremities (frontal plane of projection of an integral vector of heart) electrodes establish on the right and left forearms and the left shin. At record ECG in the I assignment the electrode of the right hand is connected to minus of the electrocardiograph (a negative electrode), an electrode of the left hand — to plus (a positive electrode), the axis of assignment is located horizontally. The II assignment is registered at an arrangement of a negative electrode on the right hand, positive — on the left leg, the axis of assignment is directed from top to down and from right to left. For record ECG in the III assignment the negative electrode of the electrocardiograph is placed on the left hand, positive — on the left leg, the axis of assignment goes from top to down and from left to right. Still V. Eyntkhoven with sotr. (1913) defined axes of standard leads as the parties of an equilateral triangle; in this case corners between axes are equal 60 °. However, as showed the Burgher and sotr. (1948), actually the arrangement of axes of assignments, including standard, differs from their geometrical situation because of not homogeneous conductivity of fabrics in the direction of assignments a little, an irregular geometrical shape of a body (in ideal model of Eyntkhoven the assumption is accepted that heart is located in the center of the homogeneous sphere of infinite radius) and other factors. The true arrangement of axes of three standard leads (a triangle of the Burgher) is under construction for each assignment taking into account these factors (a vector of assignment) on a formula of the Burgher: the projection of a vector of heart to an axis of assignment increased by length of a vector of assignment.
The strengthened single-pole assignments from extremities (fig. 2, b). Assignment of aVR: minus — combined (indifferent, on Goldberger's terminology) an electrode of the left hand and left leg, plus (active electrode) — an electrode of the right hand, an axis goes from the middle of distance between the left electrodes (the integrated electrode) through the center of heart (triangle) to the right hand. Assignment of aVL: minus — the integrated electrode of the right hand and left leg, plus — an electrode on the left hand, passes an axis from below up and on the left. Assignment of aVF: minus — the integrated electrode of both hands, plus — an electrode on the left leg, the axis is located vertically positive half between positive poles of axes of assignments of II and III. Thus, so-called single-pole assignment from extremities actually are bipolar, and call them single-pole by tradition. Poles of these assignments lie on one axis with «the electric center» of heart (the center of the line of zero potential of electric field). The analysis of an ECG in assignments from extremities allows to characterize the direction of a vector of EMF in the frontal plane.
Chest assignments. So-called chest assignments also are bipolar (the name «single-pole» remains by tradition). Their negative pole (to it there corresponds the negative electrode of the electrocardiograph) combines electrodes of the right hand, left hand and left leg (an indifferent electrode, on Wilson's terminology). Its potential is close to zero, but is not equal to it. Topographical it can be combined with the center of heart. Positive poles correspond to the provision of chest electrodes, axes pass between the center of heart and chest electrodes. Chest (positive) electrodes of assignments of V1 — V6 are located as follows (fig. 3): assignment of V1 in the fourth mezhreberye on the right edge of a breast, V2 — at the same level on the left edge of a breast, V3 — at the level of IV edges on the left okologrudinny (parasternal) line, V4 — in the fifth mezhreberye on the left sredneklyuchichny line, V5 — at the V4 level on the left front axillary line and V6 at the same level on left to average axillary stick. Axes of chest assignments lie in the plane close to horizontal; they are a little lowered towards positive electrodes of axes of assignments of V5 and V6. The analysis of the ECG registered in chest assignments allows to estimate deviations of a vector of EMF in the horizontal plane. Twelve standard assignments of an ECG give the main and in most cases sufficient information about the EMF of heart is normal also at pathology.
In an electrocardiography also additional assignments in cases when the standard assignments are insufficient are applied. Take away need to use additional a niya arises, e.g., at a misplaced of heart in a thorax if typical a wedge. the picture of a myocardial infarction does not find accurate reflection in 12 standard assignments of an ECG, at disturbances of a cordial rhythm, to-rye it is not possible to identify on the basis of the analysis of an ECG in the standard assignments and in nek-ry other cases. Extreme right chest assignments of V3R — V6R register to the right of a breast symmetrically V3 — V6 at a dextrocardia. Extreme left chest assignments — V7 (at the V4 level — on the back axillary line), V8 and V9 (at the same level respectively on the left scapular and juxtaspinal lines) — at back and side myocardial infarctions. High chest assignments — V2/1, V2/2, V2/3, V3/4, V3/5, V3/6 (electrodes are located on two or one mezhreberye is higher, than in assignments of V1 — V6; the nadstrochny index designates a mezhreberye) — at basal front heart attacks and low chest assignments — V1/6, V6/2, V6/3, V7/4, V7/5, V7/7. The last are used at the shift of heart in a chest cavity in case of low standing of a diaphragm.
Assignment on the Liana (L) or S5 is applied to specification of the diagnosis of difficult arrhythmias: it is registered at position of the handle of the switch on the I assignment, an electrode for the right hand have in the second mezhreberye at the right edge of a breast, an electrode for the left hand — at the basis of a xiphoidal shoot, on the right or to the left of it, depending on at what provision of an electrode the tooth of River comes to light better.
Assignments on W. Nehb are written down at provisions of the handle of the switch on standard leads, electrodes to-rykh place on a thorax (fig. 4): an electrode for the right hand in the second mezhreberye at the right edge of a breast (2), an electrode for the left hand (LA) — in the point which is at the level of an apical beat on the left back axillary line (2) for the left leg — on area of an apical beat (3). Register three assignments: D (dorsalis) in position of the switch on the I assignment, A (anterior) — on the II assignment, I (inferior) — on the III assignment. Axes of these assignments make a small triangle of the Sky. Assignments of the Sky often apply during the carrying out veloergometrichesky and other functional electrocardiographic exercise tolerance tests. Their value as local damages of a myocardium, additional for diagnosis, diskutabelno. Three assignments (triangle) of Arrigi are located in the sagittal plane of a body. They were not widely used. Quite seldom esophageal assignments of Eo are registered. As an active electrode of assignments of Eo serves the olive of the duodenal probe connected by a wire to a positive pole of the electrocardiograph; a negative pole is the integrated electrode of Wilson. The olive is consistently established at three levels: at distance of 33 cm (Eo33), 35 — 45 (Eo33 — Eo45) and 45 — 50 cm (Eo45 — Eo50) from upper cutters. In these assignments well are registered an atrial tooth P and changes of an ECG at a myocardial infarction of a back wall of a left ventricle. Most often esophageal assignments apply to diagnosis of the disturbances of a heart rhythm which are badly identified on an ECG in the standard assignments. Changes of an atrial tooth well come to light also in endobronchial assignments. Other additional assignments of an ECG have even more limited use.
In scientific a wedge. researches the method of registration of an ECG in 35 single-pole chest assignments across Morocco (P. Maroko, 1972) and electrocardiotopography — the synchronous registration of an ECG in 50 chest assignments offered R. 3 is widely applied. Amirov (1965). It is reasonable to carry out registration of an ECG in multiple assignments on multichannel electrocardiographs, the analysis of such ECGs is extremely labor-consuming and is usually carried out using electronic computer facilities. The specified methods most often apply to impact assessment of these or those pharmaceuticals on intensity of scarring of the center of a myocardial infarction.
Synchronous registration of an ECG in several assignments and development of a problem of automation of the analysis of an ECG showed a possibility of replacement of 12 standard assignments with three korrigirovanny orthogonal assignments of an ECG. These assignments are developed taking into account asymmetry of electric field of heart on a body surface. Irregularity of potentials under electrodes is compensated by the additional chest electrodes and electric resistance to poles of assignments located close to heart. As a result three korrigirovanny assignments of X, Y, Z turn out truly orthogonal (mutually perpendicular) in physical sense, i.e. teeth of an ECG in these assignments are exact projections of an equivalent cordial dipole to three mutually perpendicular axes of space. The last allows to carry out the quantitative space analysis of korrigirovanny ECGs sufficient for the description EMFs loudspeakers of heart are normal also at pathology. Usually apply the systems of korrigirovanny assignments offered by Frank (E. Frank, 1956). and also IAC-Fi and Parungao (R. McFee, A. Parungao, 1961).
the Driver of a cordial rhythm at healthy people is a sinus and atrial node (fig. 5), from to-rogo excitement extends on a sokratitelny myocardium of auricles below and a few to the left (it is reflected in an ECG formation of an atrial tooth P) and at the same time on internodal ways of bystry carrying out — to an atrioventricular node. Thanks to it the impulse gets to an atrioventricular node even before the end of excitement of auricles. In an atrioventricular node impulses are late a little that allows to complete a mechanical systole of auricles prior to the beginning of a ventricular systole, and then are quickly carried out on an atrioventricular band (ventriculonector), its trunk and legs, branchings to-rykh transmit excitement through Purkinye's fibers directly to fibers of a sokratitelny myocardium of ventricles. Excitement of a myocardium of ventricles begins with an interventricular partition (the first 0,01 — 0,03 sec. of time taken by the QRS complex), the integral vector to-rogo is oriented to the right and forward. In the following 0,015 — 0,07 sec. the myocardium of tops of the right and left ventricles from subendocardial to subepicardial layers, their front, back and side walls is excited, and in the last turn excitement extends to the basis of the right and left ventricles (0,06 — 0,09 sec.). The Integral Vector (IV) of heart during the period between 0,04 and 0,07 sec. from the moment of the beginning of excitement of ventricles (WILLOWS 0,06-0,09 sec.) is oriented to a positive pole of assignments of II and V4, V5 to the left and down; WILLOWS 0,06-0,09 sec. of QRS — up and slightly to the right.
Are defined on an ECG (fig. 6): the isoelectric line (isoline), the horizontal piece registering during a diastole (between a tooth of T of one of cycles and a tooth P following cycles), teeth — deviations of a curve up (positive teeth) or down (negative teeth) from the isoelectric line or other horizontal segments with the rounded-off or sharp-pointed tops. The atrial tooth P, and also teeth of T and U relating to a ventricular complex having the rounded-off tops are called sometimes waves. Temporary intervals between the teeth of the next cycles of the same name carry the name of intercyclic intervals, and between different teeth of one cycle — intra cyclic intervals. Pieces of an ECG between teeth designate as segments if not only their duration, but also a configuration is described. They can be displaced (elevation) or down (depression) in relation to the isoline up. The group of the teeth and segments reflecting process of excitement or its phase in departments of heart is designated as a complex. Distinguish the tooth P reflecting spread of activation on auricles, the QRST complex (a ventricular complex) corresponding to excitement of ventricles and consisting of the QRS complex (spread of activation, or depolarization of ventricles) and a final part (a segment of RS — T and a tooth of T — fading of excitement, or repolarization), and also the tooth of U not always registered (fading of excitement of system of Gis — Purkinye). In the QRS complex there can be no teeth of Q or (i) S (RS, QR, R form). Two teeth of R or S can be also registered, at the same time the second tooth is designated by R’ (the RSR forms' and RR') or S'.
The normal electrocardiogram (fig. 7) is characterized by a sinuatrial, or sinoatrial (nomotopny), regular rate with a frequency of excitement of ventricles 60 — 80 in 1 min. The sinoatrial rate is determined by existence of a positive tooth P in assignments of I, II, aVF, V6, (PI,II, aVF, V6) and two-phase with a positive first phase or positive P(V1) before the QRS complex. The characteristic of a tooth P at a sinoatrial rate depends on orientation of vectors of a tooth P down and to the left, to a positive pole of assignments of II and V3-6. The regularity of a rhythm is defined by equality of intercyclic intervals (R — P or R-R). At an irregular sinuatrial rhythm (sinus arrhythmia) intervals P — P (R — R) differ on 0,10 sec. and more. The normal duration of excitement of auricles measured on width of a tooth P is equal 0,08 — 0.10 sec. Time of atrioventricular carrying out — an interval P — Q (R) — normal is equal 0,12 — 0,20 sec. The transmission time of excitement on ventricles determined by width of a complex (QRS, makes 0,06 — 0,10 sec. Duration of an electrical systole of ventricles — the interval of QRST (Q-t) measured from the beginning of the QRS complex before the termination of a tooth of T — normal depends on the frequency of a rhythm (due duration of Q-T). It is counted on Bazett's formula: Q - ((due) = K?C where To — the coefficient making 0,37 for men and 0,39 for women and children With — duration of a cardial cycle (the size of an interval R — R) in seconds. It is increased or reduction of an interval of Q — T more than for 10% is a symptom of pathology. The normal tooth P is highest (to 2 — 2,5 mm) in the II assignment; it has the semi-oval form. A tooth P (I, aVF, V2-V6) positive, below PII. A tooth of P(aVR) negative, P(V1) two-phase with the first bigger positive phase. Teeth of P(III) and P (aVL) positive low (sometimes superficial negative). The QRS complex, according to the direction of vectors of excitement of an interventricular partition (to the right, forward), free walls of a left ventricle (to the left, down) and the bases of ventricles (up, to the right), consists in assignments of I, II, III, aVL, aVF, V5 — V6 of a small initial negative tooth of Q (no more than 0,03 sec.), a high tooth of R and a small final negative tooth of S. Such form is caused by a normal arrangement of a neutral electrical axis of heart — an average vector of QRS (AQRS) in the frontal plane of assignments from extremities down and to the left — to a positive pole of the II assignment and left chest. The tooth I in assignments of II is respectively highest, V4, V5. Also positive the normal tooth of T is registered (I, II, III, aVL, aVF, V3 — V6). Identical orientation of AQRS and AT in the frontal plane explains the big amplitude of a tooth of T in those assignments where the tooth of R is higher (e.g., in the II assignment). In assignment of aVR the main tooth of the QRS complex (a tooth of S) and a tooth of T — negative since the corresponding vectors are directed to minus of this assignment. In assignment of V1 the rS complex (a lowercase letter designate teeth of rather small amplitude when it is necessary to emphasize specially a ratio of amplitudes), in assignments of V2 and V3 — the RS or rS complex is registered. The tooth of R in chest assignments increases from right to left (from V1 to V4-5) and further decreases to V6 a little. The tooth of S decreases from right to left from V2 to V6. Equality of multidirectional teeth in one assignment (e.g., R and S) determines the transition zone by Grant — assignment in the plane, perpendicular to an average space vector of the QRS complex. Normal the transition zone of the QRS complex is between assignments of V2 and V4. The tooth can be both positive, and negative, a tooth of T(V2) usually positive. The tooth of T is highest in assignments of Vz or V4. Teeth of T(V5) and T(V6) positive; they are lower, than T(V4) but above, than T(V1). The segment of RS - T in all assignments from extremities and in the left chest assignments is registered at the level of the isoelectric line. Small horizontal shifts (down to 0,5 mm or up to 1 mm) a segment of RS — T at healthy people are possible, especially against the background of tachycardia or bradycardia, but it is necessary to exclude in all cases patol. character of similar shifts by dynamic observation, carrying out functional trials or comparison about a wedge. data. In assignments of V1, V2, V3 the segment of RS — T is located on the isoelectric line or displaced up on 1 — 2 mm.
Versions of the normal ECG are defined generally by an arrangement of heart in a thorax. They are considered conditionally as turns of heart around three axes: front-back (is determined by position of AQRS — normal, horizontal, vertical, left axis deviation and to the right), longitudinal (on and counterclockwise) and cross (turn by a top of heart forward or back).
The provision of an electrical axis (fig. 8) is determined by the size of a corner α (see fig. 2): normal situation — α from + 30 to + 69 °, horizontal — α from 0 to +29 °, vertical — α from +70 to +90 °, a deviation to the left — α from — 1 to — 90 °, to the right — α from +91 to ±180 °. At horizontal position of an electrical axis of heart a tooth of R(I) high (AQRS is parallel to axis I of assignment), above, than a tooth of R(II);< R III S III; R (aVF) ≥ S(aVF).
At left axis deviation>>< of R I R II R (aVF) S(aVF)< (r III S III). At vertical position and a deviation of AQRS to the right R I low, increases S I and R III. The corner α is determined by creation in system of axes of standard leads or by special schemes and tables after obtaining the algebraic sum of amplitudes of teeth of the MRS complex in any two assignments from extremities (usually in I and III).
On an ECG at turn of heart around a longitudinal axis clockwise the RS form is characteristic of an initial part of a ventricular complex (I, V5, V6 and qR III). At turn qR (I, V5, V6) RS III, moderate increase in R (V1V3) (RS V1, RS V3) without the shift of the transition zone counterclockwise are registered. The turn of heart a top is displayed by the qR form in assignments of I, II and III forward. For turn of heart a top back, or the type S I, S II, S III, an initial part of a ventricular complex, shaped RS I, RS II, RS III is characteristic.
Changes on the electrocardiogram at some morbid conditions. The dextrocardia owing to mirror change of topography of rather sagittal plane of heart and shift it causes orientation of AP, AQRS and AT to the right to the right, i.e. to minus of the I assignment and to a positive pole of the III assignment. On an ECG the deep tooth of S I (rS I), negative teeth of P I and T I, high teeth R III and positive teeth of P III and T of III, chest assignments reduction of a voltage of QRS in the left positions is registered during the deepening of a tooth of S(v5,6). At mutual movement of electrodes of the right and left hand of an ECG in I and III assignments teeth of a usual form and the direction are registered. Such replacement of electrodes and registration of additional chest assignments of the V (3R), V(4R), V(5R), V(6R) allow to confirm the conclusion and to reveal or exclude other pathology of a myocardium at a dextrocardia. Unlike a dextrocardia at dextroversion a tooth of P I,II,V6 positive, an initial part of a ventricular complex has the form qR1, V6 and RSV (3R).
Changes of an ECG at a hypertrophy of this or that department of heart are caused by increase in its EMF and thereof increase and a deviation towards hypertrophied department of a vector of total EMF of heart. At the same time increased average, final or (less often) the initial vector is projected on axes of assignments parallel to it by teeth of the increased amplitude (high teeth of P, R or a deep tooth of S) or the changed form. At a hypertrophy of nek-ry departments of heart small broadening of the corresponding tooth or its intrinsic (intrinsikoidny) deflection, i.e. time from the beginning of a tooth P or a ventricular complex till the moment corresponding to a maximum of their positive deviation is defined. At a hypertrophy of ventricles a final part of a ventricular complex can change: the segment of RS — T is displaced down and becomes lower or the tooth of T in assignments with high R is inverted (becomes negative). Such change of a form of a ventricular complex is designated as discordance (divergence) of a segment of RS — T and a tooth of T in relation to a tooth of R. Also discordance of a segment of RS — T and a tooth of T in relation to a tooth of S in assignments with a deep tooth of S is observed.
At a hypertrophy of the left auricle (fig. 9) the tooth P extends to 0,11 — 0,14 sec., becomes two-humped (R mitrale) in a number of assignments from extremities (I, II, aVL) and the left chest assignments, its top is less often flattened, amplitude of the second top increases. Time of intrinsic deflection of a tooth> of P I,II,V6 0,06 of sec., sometimes deviates an axis of a tooth P or an axis of its second half to the left. Increase in the negative phase PV1 is the most frequent and reliable sign of a hypertrophy of the left auricle (+< PV1 — PV1), emergence of the second negative phase P (V2,V3) is more rare.
The hypertrophy of the right auricle (fig. 10) is characterized by increase in amplitude and a sharp-pointed form of a tooth P II,III, aVF (P pulmonale), the ARE has vertical position, is less often rejected to the right, sometimes the tooth of S(V1V2) slightly increases.
At a hypertrophy of a left ventricle on an ECG (fig. 11) the high tooth of R in the left chest assignments and a deep tooth of S is registered V1V2 . At the qR and R forms of the QRSv9 complex or the usual qRs form, typical for a hypertrophy of a left ventricle, a highly specific sign is R (V6)> = R (V4); a little less reliable signs >of R (V5) R (V4), the qR form (V6) at the shift of the transition zone to the right, a number of criteria of Sokolov — Lyon — R (V5) + S (V1,2)> of 35 mm (for persons 40 years) and more than 40 — 45 mm (for persons up to 40 years are more senior), R (V5,4,6)> 25 mm, S (v 1,2)> 20 mm, R (aVL)> 11 mm, etc. At a left ventricular hypertrophy horizontal position or a deviation to the left by AQRS is more often observed, but it can be normal and even vertical. Confirmation of a hypertrophy of a left ventricle and the instruction on its expressiveness, existence of secondary dystrophic changes of a myocardium are discordant changes of a segment of RS — T and a tooth of T. In assignments of V (5,6) I, to the left the segment of RS — T is displaced by aVL at a deviation of AQRS from the isoline, in assignments with a deep tooth of S down (V1, V2,III, etc.) the segment of RS — T is displaced up, a tooth of T high positive. Less expressed changes of a final part of a ventricular complex at a left ventricular hypertrophy are characterized by decrease in a tooth of T in the left chest assignments; at the same time T> (V1) T (V6).
Significant increase in amplitude of a tooth of P(V1,V2,V3) often at normal position of AP is observed at inborn heart diseases (R by congenitale). The combined hypertrophy of both auricles quite often is reflected in an ECG (fig. 12) a combination of a number of the signs of a hypertrophy of each of auricles described above: simultaneous broadenings of a tooth P and increase in amplitude of the pointed P (II, III, aVF), splitting of P (I, V6), increase in both the positive, and negative phase P(V1).
Practical value has undertaken by Cabrera and Monroyem (E. Cabrera, J. R. Monroy, 1952) attempt to determine by changes of an ECG type hron. the hemodynamic overload of a ventricle which is the cornerstone of development of its hypertrophy. At a diastolic (isotonic) overload of a left ventricle (insufficiency of an aorta or the mitral valve and other heart diseases) the QRS (V5V6) complex often has the QR form with a high tooth of R and Q normal width are frequent with a profound tooth. The tooth of T can be high positive (T of Cabrera), is more often at young people. V. I. Makolkin (1973) noted decrease and inversion of a tooth along with reduction of depth of a tooth of Q (V5V6) in process of progressing of damage of heart at such patients. At a systolic (isometric) overload of a left ventricle (e.g., at a stenosis of the mouth of an aorta) the R (V5V6) or qR form (V5V6) with very small q(V6), the shift of a segment of RS—T(V5V6) down and a negative tooth of T (V5V6) is most often observed. In the right chest assignments rS and sometimes QS with the raised segment of RS — T and a positive asymmetric tooth of T is registered.
The hypertrophy of a right ventricle on an ECG (fig. 12) is presented by a high tooth of R (V1) (types qR, R, Rs, RS) or R (V1) (the rSR types', RSR', rR' with a normal width of QRS) and a deep tooth of S (V4) (the types rS, RS, Rs at sinistroposition of the transition zone). At the qR, R, Rs and rS types (V1) the depression of a segment of RS—T(V1) and inversion of a tooth of T(V1) usually is registered. At the RS(V1) type — amplitude< of S (V1) S (V2V3). The electrical axis of heart is usually rejected to the right or located vertically the corner> of a +100 ° is a sign to a hypertrophy of a right ventricle if there is no blockade of the left back branch of a ventriculonector. The described ECG form at a hypertrophy of a right ventricle is observed at heart diseases and in some cases heavy hron. pulmonary heart (types qR, RS, Rs(V1)). In most cases hron. a pulmonary heart the ECG S-type (see fig. 10) with the expressed tooth of S(V1) and a low tooth of r(V1) is registered. In these cases existence of a hypertrophy of a right ventricle is confirmed by the shift of the transition zone to the left or reduction of amplitude of S(V1) (<<Sv1 3 mm less Sv2v3), or the rSr type' (V1), or a deviation of AQRS to the right. Signs systolic (qRv1, RSv1) and diastolic (RSR'v1) of overloads against the background of a hypertrophy of a right ventricle have diagnostic value only at inborn heart diseases.
The combined hypertrophy of both ventricles not always finds reflection on an ECG, only signs of a hypertrophy of a left ventricle sometimes are registered. In rare instances it is possible to find the reduced signs of a right-and left ventricular hypertrophy.
The syndrome (phenomenon) of Wolff — Parkinson — Whyte, being one of kinds of a syndrome of premature excitement of ventricles (see Wolff — Parkinson — Whyte a syndrome), is caused by premature spread of activation from auricles in additional ways of bystry carrying out an impulse (Kent bunch, Makheym's fibers) in basal departments of one of ventricles or an interventricular partition. According to it premature excitement of a myocardium of ventricles on an ECG is expressed by a delta wave (low-amplitude fluctuations) at the beginning of the QRS complex widened by it and shortening of an interval P — Q (fig. 13). In typical cases of a syndrome of Wolff — Parkinson — Whyte duration of an A-wave makes 0,04 — 0,08 sec., P — Q — 0,08 — 0,11 sec., the QRS complex 0,12 — 0,15 sec. At an atypical current of this syndrome excitement is carried out to a ventricle through Makheym's fibers; at the same time the delta wave borrows 0,02 — 0,03 sec., the interval P — Q is not shortened, the QRS complex is not widened. Premature synchronous excitement of both ventricles (through Torel and James's bunches) is shown on an ECG by shortening of an interval P — Q (lower than 0,11 sec.) without change of the QRS complex. Shortening of an interval (R)) can arise also owing to other reasons (acceleration of carrying out on an atrioventricular node, on intra atrial conduction paths) therefore it is recommended to call such change of an ECG a syndrome of the shortened interval P — Q (P — R), on terminology (1980) and classification of disturbances of a heart rhythm (1982) groups of experts of WHO. At Wolff's syndrome — Parkinson — Whyte and other syndromes of a short interval P — Q often there are paroxysmal disturbances of a heart rhythm.
Disturbances of intra ventricular conductivity (see the Heart block) are classified on the basis of the concept about a trekhpuchkovy structure of the intra ventricular carrying-out system. According to this concept the ventriculonector (a trunk of an atrioventricular band) is divided into three functionally independent branches (see fig. 5): left lobby (front branch of the left leg), left back (back branch of the left leg) and right (right leg). The main branches are divided in a subendocardial layer of a myocardium into numerous small branchings, to-rye terminate in the carrying-out muscle fibers of Purkinye.
Between peripheral branchings of front and back left branches (a branch of the left leg) there is a network of an anastomosis of conduction fibers, on the Crimea in case of blockade of one of them excitement quickly (for 0,01 — 0,02 sec.) extends from not struck branch to the blocked area. It causes the normal width of a complex or its insignificant broadening (to 0,11 sec.) at blockade of one of the left branches. It becomes wider (0,11 — 0,13 sec.) at a combination of blockade of the left branch to blockade of an anastomosis. Between right and the left branches there is no anastomosis therefore at blockade of the right branch or both left branches the QRS complex is considerably widened (0,12 sec. and more). The term «blockade of a branch of a ventriculonector» designate the termination of carrying out an impulse on one branch, and the term «incomplete blockade of a branch» — delay of carrying out on it or the termination of carrying out as regards its branchings. Blockade of a branch can be a constant (on this ECG or on several) and non-constant (alternating, intermittent).
Blockade of the left front branch of a ventriculonector on an ECG (fig. 14, a) is characterized in the I assignment by the qR complex, in the III assignment — the rS complex and the expressed deviation to the left (a corner and> = — 30 °). At blockade by the maiden of a back branch the RS1 and qR III complex with right axis deviation is registered (and> = +90 °). The diagnosis of blockade of the left back branch can be made according to an ECG, only if its signs appear in dynamics during the short period between consistently registered by an ECG. In all other cases it is necessary for this conclusion on a wedge. given to exclude a hypertrophy of a right ventricle and vertical position of heart, at to-rykh on an ECG identical changes are registered. Blockade of the right leg on an ECG (fig. 14, b) is characterized by broadening of the QRS complex to 0,12 sec. and more, a wide tooth of S I, v6 (qRS I, v6) and the RSR complex' (V1) with wide and high R 1/V1. Provision of an electrical axis normal, vertical or horizontal. Tooth of T(V1) negative. At incomplete blockade of any of the left branches the form of the QRS complex in I and III assignments same, and a deviation of AQRS to the left or to the right is less, than at a total block of the corresponding branch. For their exact diagnosis it is necessary to analyze dynamics of a configuration of a complex. Incomplete blockade of the right leg is characterized by width of the QRS complex, equal 0,08 — 0,11 sec., the rSr complex (V1) or rSR (V1) with small broadening of a tooth of r (V1) or S (1,V3, aVL), or emergence of the rSr complex' + + Sr' (V1) in dynamics.
Blockade of two branches (dvukhpuchkovy blockade) of a ventriculonector leads to delay of excitement or a right ventricle and one of walls left (blockade right and one of the left branches), or all left ventricle (blockade of both branches of the left leg). At blockade right and one of the left branches on an ECG signs of blockade of each of them (fig. 14, c) are registered since the blocked wall of a left ventricle is excited with a smaller delay, than a right ventricle: width >of QRS0,12 of sec., signs of blockade of the right leg are combined with a considerable deviation of AQRS to the left (at simultaneous blockade of the left front branch) or to the right (at a combination to blockade by the maiden of a back branch). At blockade of both left branches (blockade of the left leg) both walls of a left ventricle are excited approximately with identical delay therefore on an ECG signs of blockade of each of these branches accurately are not registered, and the QRS complex has very peculiar form (fig. 14, d) — a wide tooth of R I,V6 (width> 0,12 sec.) with the flattened or jagged top (the tooth of Q (V5) is absent) and a wide deep tooth of Sv1v2 (rS or QS); the segment of RS — T and tooth of T in assignments of I, are sharply discordant V1, V2 and V3 to the main tooth of the QRS complex.
At blockade of all three branches (trekhpuchkovy blockade) there is an incomplete or total atrioventricular block of distal level. At a distal atrioventricular block of the I pla of the II degree on an ECG along with lengthening of an interval P — Q or blocking of separate ventricular complexes signs of blockade of two branches of a ventriculonector are registered. The total distal atrioventricular block is characterized by emergence of actually ventricular (idioventricular) replacing rhythm with the aberrant (sharply changed) form of a ventricular complex as dvukhpuchkovy blockade.
During an attack of stenocardia (see Stenocardia), and regarding cases after the termination of pains or in the mezhpristupny period on an ECG the depression of a segment of RS — T and decrease or inversion of a tooth of T is registered. These changes of an ECG are connected with ischemia of the most vulnerable concerning blood supply of subendocardial and partially intramural layers of a myocardium of a wall of a left ventricle. The short-term elevation of a segment of RS — T is observed at so-called stenocardia of Printsmetal (see Stenocardia). Elevation of a segment of RS — T reflects short-term transmural ischemia. At stenocardia on an ECG also different types of disturbance of a cordial rhythm and conductivity quite often come to light. However more than a half of patients with stenocardia in the mezhpristupny period on an ECG can have completely no symptoms of ischemia of a myocardium or it is difficult to identify them against the background of other changes of an ECG (e.g., changes of a segment of RS — T and a tooth of T at a hypertrophy of a left ventricle). In such cases apply to detection of the hidden coronary insufficiency funktsional ny electrocardiographic tests. The greatest distribution was gained by electrocardiographic tests with the dosed exercise stress: veloergo metric test, test on the tredmil (see Ergografiya), etc. These tests, as well as pharmacological using Dipiridamolum (curantyl), an izoprenalin or ergometrine, and also hypoxemic test model stenocardia at patients with coronary heart disease. On an ECG the positive take of test is characterized by emergence of the symptoms of ischemia of a myocardium and arrhythmias described above, and clinically — an attack of stenocardia or its equivalents. Electrocardiographic test with nitroglycerine gives multidirectional changes, to-rye it is very difficult to interpret. Apply it preferential in cases of the changed initial ECG. Orthostatic test (see. Orthostatic tests) limited use has. At this test remove an ECG of the patient in horizontal position, then in vertical — right after a rising and further in 30 sec., 3, 5, and sometimes and 10 min. motionless standing. Test is considered positive at a depression on an ECG in an ortostaza of a segment S — T and inversion of a tooth of T. All functional electrocardiographic trials carry out in the morning on an empty stomach or in 3 hours after a breakfast. The final decision on conducting test is made in day of its carrying out, after registration of the initial ECG. Removal of the following ECGs depends on time of emergence of changes in a myocardium under the influence of test.
In diagnosis of a myocardial infarction (see) the electrocardiography plays the leading role along with clinic. With its help reveal specific diagnostic symptoms, define localization, extensiveness, depth of defeat and estimate dynamics of a heart attack. The defeats developing in the center of a myocardial infarction have three zones morfol. changes: a zone of a necrosis in the center (is closer to inner layers), a zone of sharp dystrophy («damage») and a zone of ischemia of a myocardium on the periphery of the center. It causes a deviation of a vector of Q (the first half of the QRS complex) and a vector of T aside, opposite to a zone of a heart attack, and a vector S — T towards the direction of this zone. Respectively on an ECG in assignments with a positive pole (fig. 15) over the center the tooth of Q increases and broadens, the tooth of R decreases, the segment of RS — T is displaced up, the tooth of T becomes negative symmetric (coronary). In assignments with a positive pole from heart to an opposite zone of a heart attack, reciprocal (inverse) changes of teeth of an ECG are observed: the tooth of R (e.g., R (V1V2) increases at a zadnebazalny heart attack), the tooth of S decreases, the segment of RS — T is displaced from the isoline down, the tooth of T becomes high symmetric.
Dynamics of changes of an ECG corresponds to stages development of a heart attack. The most acute stage within the first hours or days of a disease in connection with transmural damage of a wall of a ventricle is followed by the sharp shift of a segment of RS — T (fig. 16) up — the monophase curve is formed (all ECG elements on the one hand from the isoline). Then amplitude and a shirila of a tooth of Q (in 4 — 12 hours, is more rare at the end of the first — on second day of a heart attack) increases. The negative coronary tooth of T appears not earlier than the end of the first days. Increase in a tooth of Q, inversion of a tooth of T match on time about a nek-eye reduction of an elevation of RS — T. M. I. Kechker's observations with sotr. (1970 — 1976) showed that on 3 — the 5th days of a myocardial infarction the tooth of T becomes less deep, and is frequent even positive or does not undergo changes during 5 — 7 dpy. On 8 — the 12th day of a disease the tooth of T is repeatedly inverted (false and ischemic changes of an ECG) or begins to go deep quickly (in cases when it remained negative). At the same time the segment of RS — T approaches the isoline. On 14 — the 18th day the provision of a segment of RS — T is normalized (its resistant elevation in a cicatricial stage of a heart attack — a symptom of aneurism of a left ventricle), and the tooth of reaches the maximum depth (the termination of acute — the beginning of a subacute stage of a myocardial infarction). Repeated inversion of a tooth of T, apparently, is caused by autoimmune reaction of the myocardium surrounding organized patol. center. In a subacute stage of a disease depth of a tooth of T decreases again; regarding cases it becomes positive or izoelektrichny.
Prevalence of a myocardial infarction well is defined by number of assignments, in to-rykh characteristic changes of an ECG are registered (direct and reciprocal). Registration multiple about cardial assignments allows to obtain more exact information on prevalence of heart attacks of front localization. As a symptom of a transmural myocardial infarction, and also aneurism of a left ventricle serves the tooth (disappearance of a tooth of R) in those assignments where the high tooth of R normal is registered. At intramural (melkoochagovy and macrofocal) a myocardial infarction the QRS complex usually does not change (amplitude of a tooth of R sometimes decreases), the main electrocardiographic sign is the negative «coronary» tooth of T registered during 3 weeks and more. Rather big duration of these changes and usually observed repeated inversion of a tooth of T allows to distinguish an intramural heart attack from acute ischemia with focal dystrophy of a myocardium. The considerable depression of a segment of RS — T with the subsequent formation of a negative tooth of T is characteristic of a subendocardial myocardial infarction. All forms of acute coronary insufficiency can lead to disturbance of intra ventricular conductivity, a cut quite often complicates diagnosis focal change. At a myocardial infarction also different types of arrhythmia and disturbance of atrioventricular conductivity are often observed.
The vegetative and dishormonal myocardial dystrophy is often shown by inversion of a tooth in T and a depression of a segment of RS — T. These changes of an ECG usually do not correspond to clinic of a disease (to emergence and disappearance of pains in heart). They quite often remain on an ECG many months and even years though their expressiveness changes. Apply to differential diagnosis of a vegetative and dishormonal myocardial dystrophy and coronary heart disease pharmakol. electrocardiographic tests with drugs of potassium and blockers of β-adrenergic receptors (Obsidanum, etc.). Disappearance of negative teeth of T and depression of a segment of RS — T in 60 — 90 min. after reception of these drugs is regarded as a positive take of test (it is considered characteristic of a vegetative and dishormonal myocardial dystrophy).
At myocarditis (see) on an ECG changes of a tooth of T from decrease in a voltage to inversion are registered. During the conducting electrocardiographic tests with drugs of potassium and β-blockers the tooth of T remains negative. Quite often disturbances of a cordial rhythm (premature ventricular contraction, a ciliary arrhythmia, etc.) and conductivity are defined.
The pericardis (see) is characterized in an acute stage by a considerable elevation of a segment of RS — T (damage of subepicardial layers of a myocardium). Often this elevation of a segment of RS — T in all standard and chest leads has the concordant (unidirectional) character. However also discordant shift can be observed. The QRS complex at a shaggy pericardium is not changed (fig. 17). Further (in 2 — 3 weeks) inversion of a tooth of T is observed. shift of a segment of RS — T gradually decreases. At accumulation of exudate amplitude of teeth of the QRS complex and other teeth in all assignments sharply decreases. Sometimes alternation of the QRS complex is registered, under a cut understand regular alternation of the ventricular complexes having two a little various amplitudes and the forms. Small deformation of one of complexes is caused by hl. obr. certain type of incomplete intra ventricular blockade. At an adhesive pericarditis the segment of RS — T and a tooth of T are quite often discordant to the main tooth of the QRS complex; signs of an overload of auricles are defined.
Thromboembolism of a pulmonary trunk and pulmonary arteries, causing a syndrome of an acute pulmonary heart (see. Pulmonary heart), causes an acute overload, a hypoxia and dystrophy of a right ventricle and an interventricular partition. Defeat of the last often leads to development of an electrocardiographic syndrome of Mac-Ginna — Whyte — SI QIII (RS I, QR III), to-ry is considered as manifestation of an incomplete or total block of the left back branch of a ventriculonector (fig. 18). There is an incomplete or total block of the right branch of a ventriculonector much less often. The most frequent electrocardiographic symptoms of a thrombembolia of large branches of a pulmonary trunk are shift of a segment of RS — T at the same time in assignments III, aVF and V 1,2 up (V3, v4), and also inversion tooth tsa T (III is more rare, than aVF, V1-V3). These changes arise quickly (during tens of minutes) and accrue within the first days. At the favorable course of a disease they disappear for 1 — 2 week, only inversion of a tooth of T remains sometimes 3 — 4 weeks.
Use of nek-ry medicines (cardiac glycosides, quinidine, novokainamid, diuretics, kordaron, etc.) can lead to changes of an ECG. One of them reflect existence of therapeutic effect (e.g., at treatment by glycosides shortening of an interval of Q — the T, a depression of a segment of RS — T, decrease in a tooth of T and normalization of heart rate), other (fig. 19) indicate intoxication owing to overdose of drug (e.g., at glikozidny intoxication emergence of ventricular extrasystoles, especially polytopic, or bigeminals pulse, an atrioventricular block and other changes of a rhythm and conductivity up to fibrillation of ventricles).
The electrocardiography in diagnosis of disturbances of a cordial rhythm and conductivity plays a paramount role. Assessment of an ECG at arrhythmias (see Arrhythmias of heart) is carried out first of all on the basis of measurement and comparison of intercyclic and intra cyclic intervals in records during 10 — 20 sec., and sometimes and longer. At the same time also the analysis of a configuration and direction of a tooth P and teeth of the QRS complex, including their vector space analysis is important. From this point of view synchronous registration of assignments of I, II, III and V1 (or I, III and V1), and also assignments the Liana is reasonable (see above). In nek-ry cases for the exact diagnosis registration elektrogramm a ventriculonector, and also intra atrial and intra ventricular elektrogramm is recommended (see. Ciliary arrhythmia, Bouveret's disease, Premature ventricular contraction).
All above indicates great diagnostic value E. concerning a wide range a wedge. forms and syndromes, especially various forms of coronary heart disease, myocarditis and pericardis, hypertrophy, acute overloads of various departments of heart and disturbances of a cordial rhythm and conductivity. The advantage of a method is the possibility of its use in any conditions and harmlessness for the patient. These qualities led to widespread introduction of an electrocardiography in applied medicine.
Feature of an electrocardiography at children
For registration of an ECG at children can use any modern single-channel or multichannel electrocardiographs; at a fruit use more sensitive devices to record ECG, napr, the domestic device EMP2-01. The ECG is written down usually in 12 standard assignments. From extremities at newborns apply rectangular or oval electrodes of 3x2 cm in size to assignments, at children up to 7-8 years — 4x3 cm in size. For registration of chest assignments at newborns use round electrodes to dia. 5 mm, children up to 3 years have electrodes to dia. 10 — 15 mm, children up to 7 — 8 years have 15 — 20 mm. At record ECG at children 8 years are more senior use electrodes of the same sizes, as well as at adults.
ECGs at a fruit register by the indirect method (both electrodes have on a front abdominal wall of the woman) combined by method (one electrode is placed on a front abdominal wall, and the second — in a rectum, a vagina or a uterus) and a direct method (electrodes establish directly on a head of the born fruit).
At healthy children of different age of an ECG has the features. It depends on anatomic position of heart in a thorax, a ratio of thickness of walls of the left and right ventricles, features of neuroendocrinal regulation of cardiovascular system. Heart rate at a fruit in early durations of gestation makes 150 — 170 in 1 min., at the end of pregnancy — 120 — 140 in 1 min.; duration of an interval P — Q at the beginning of pregnancy fluctuates from 0,06 to 0,12 sec., in late durations of gestation — from 0,08 to 0,13 sec.; duration of the QRS complex increases from 0,02 — 0,03 sec. in early durations of gestation up to 0,04 — 0,05 sec. — in its late terms. With increase in duration of gestation also amplitude of teeth of R, Q, S increases.
Registration of an ECG at a fruit is made for diagnosis of a multiple pregnancy, various disturbances of cordial activity, for the purpose of definition of the prelying part, by exceptions of a tumor, a cancelled abortion etc.
After the birth of the child on an ECG dominance of electric activity of a right ventricle of heart is noted that it is connected with features of pre-natal blood circulation (see the Fruit). The electrical axis of heart is rejected to the right, the corner and fluctuates between + 90 and +180 °. The rhythm of cordial reductions at newborns is characterized by the expressed lability. In the first days of life relative bradycardia (110 — 130 reductions in 1 min.), then increase in heart rate with considerable fluctuations is observed (from 130 to 180 reductions in 1 min.). Tooth P in I and II standard leads high and often pointed, especially at premature. The relation of its height to height of a tooth of R in the specified assignments makes 1:3. A tooth of Q deep in assignments of II, III, aVF and aVR. A tooth of R in assignments of II, III, aVF, V3-V6 high, and a tooth of S in assignments of I, aVL, V2 — V6 deep. The tooth of T in standard leads is lowered, sometimes two-phase or even negative; the relation of its amplitude to height of a tooth of R I-II makes 1: 6. In assignments of aVL and aVF it can be negative, and in assignment of aVR — positive. In chest assignments from V1 to V3 and even to V4 a tooth of T negative, the tooth of T (V5,V6) is lowered, sometimes negative.
Duration of the main intervals and width of teeth of an ECG at children increase with age. Duration of a tooth P at newborns averages 0,05 sec. (0,04 — 0,06 sec.), duration of an interval P — Q — on average 0,11 sec. (0,09 — 0,13 sec.) . Width of the QRS complex on average corresponds 0,05 sec. (0,04 — 0,06 sec.), duration of an interval of T fluctuates within 0,22 — 0,32 sec.
of an ECG at children up to two years is characterized in most cases by dominance of electric activity of a right ventricle of heart. The corner and fluctuates ranging from +40 to +120 °. Heart rate makes 110 — 120 in 1 min. The tooth P becomes rounded more off; the relation of its height to height of a tooth of R in I and II standard leads — 1:6. The tooth of Q remains deep (more than 1/4 amplitudes of a tooth of R) (II, III, aVF, aVR). In the I standard lead height of a tooth of R increases, and depth of a tooth of S decreases. In chest assignments (V2 — V6) note high teeth of R and quite deep teeth of S. The tooth of T of I, II becomes higher and makes 1/z — 1/4 part of height of a tooth of R. In assignments of aVL, aVF, V5, V6 a tooth of T positive, but below, than at the senior children, and in assignments of V1 — V3 also is frequent in assignment of V4 negative. Duration of intervals and width of teeth of an ECG at children of early age in comparison with newborns increases a little. Width of a tooth P averages 0,06 sec. (0,04 — 0,07 sec.), duration of an interval P — Q — 0,12 sec. (0,11 — 0,15 sec.), width of the QRS complex — 0,06 sec. (0,04 — 0,07 sec.), varies duration of QRST within 0,24 — 0,32 sec.
of an ECG at children from 2 to 7 years is characterized by further decrease in electric activity of a right ventricle of heart and increase in left. The corner and fluctuates ranging from + 40 to +100 °. Heart rate makes 90 — 110 in 1 min. The relation of height of a tooth of P I,II to height of a tooth of R I,II — 1: 8.
The tooth of Q in standard leads is less expressed and not the nsegda is observed. Height of a tooth of R in the left chest assignments increases, and in right — decreases while the size of a tooth of S increases in the right chest assignments and decreases in left. Tooth of T (I, II, aVL, V5,V6), as a rule, positive and above, than at children of early age; tooth of T (V1-V3), and sometimes and T(V4) negative. Width of a tooth P at children of this age averages 0,07 sec. (0,05 — 0,08 sec.), duration of an interval P — Q — 0,13 sec. (0,11 — 0,16 sec.), width — 0,07 sec. (0,05 — 0,08 sec.), duration of QRST fluctuates within 0,27 — 0,34 sec.
of an ECG at children of 7 — 15 years differs from an ECG of adults in more expressed lability of heart rate (that is connected, in particular, with existence of a considerable respiratory arrhythmia), smaller duration of the main intervals. Pulse rate varies within 70 — 90 blows in 1 min. More than in half of cases the ECG normal type is noted. The ratio between amplitudes of teeth becomes approximately same, as at adults. Width of a tooth P at children of this age averages 0,08 sec. (0,06 — 0,09 sec.), duration of an interval of P — Q 0,14 sec. (0,14 — 0,18 sec.), width of the QRS complex 0,08 sec. (0,06 — 0,09 sec.), duration of QRST fluctuates within 0,34 — 0,45 sec.
Thus, at children belong to the main features of an ECG: 1) more high frequency of cordial reductions; 2) lability of a cordial rhythm; 3) dominance of electric activity of a right ventricle over activity of left; 4) smaller width of teeth and duration of intervals; 5) existence of a negative tooth of T in the III standard and right chest assignments.
Elektrokardiograf — the device intended for strengthening and registration of the electric potentials arising on body surfaces and also in cavities of internals and in depth biol. fabrics as a result of electric processes, to-rymi spread of activation on heart is followed.
The modern electrocardiograph consists of the following main nodes: switch of assignments, amplifier of biopotentials, chart recorder and device of calibration. Its integral part are electrodes. Obob the shchenny block diagram of the electrocardiograph is submitted in fig. 20. The principle of operation of the electrocardiograph consists in the following. The electric signal removed from a body surface, cavities of internals or from depth of fabrics by means of electrodes through a cable of assignment arrives on the switch of assignments, and then on an entrance of the amplifier of biopotentials. Strengthened up to the size sufficient for actuating of a galvanometer, the signal arrives on an entrance of the chart recorder where it will be transformed to movement of the writing device (a light ray, a feather, a stream of ink). The tape drive mechanism of the chart recorder moves coordinate paper with precisely established speed, the ECG registers in a cut.
Structurally electrocardiographs carry out, as a rule, one - two - four - and six-channel. Depending on a design the main nodes or combine in the uniform case (single-channel electrocardiographs), or can be executed in the form of separate independent blocks (multichannel electrocardiographs). Idiosyncrasy of single-channel electrocardiographs — existence of the general panel, on a cut all operating controls is located. Single-channel electrocardiographs have small dimensions and weight from 0,4 to 5 kg. Multichannel electrocardiographs make in the form of separate blocks and cartridges. The block and cassette design provides interchangeability of blocks and cartridges, simplifies operation, repair, assembly and dismantling of the device. Multichannel electrocardiographs usually have horizontal configuration. Dimensions of multichannel electrocardiographs much more, than single-channel, and weight can exceed 40 kg. In single-channel electrocardiographs for switching of assignments usually use one multiposition switch, with the help to-rogo it is consistently possible to register assignments of I, II, III, AVR, AVL, AVF, V, and also a calibration signal. Multichannel electrocardiographs have two switches allowing to switch in any sequence assignments of I, II, III, aVR, aVL, AVF, V1-6. Because on an entrance of the switch of assignments the signal of low tension, the main requirement to the switch — ensuring small transfer resistance on contacts arrives. The electric signal arrives on an entrance of the switch through a cable of assignments. The cable of assignments is intended for connection to the electrocardiograph of the electrodes imposed by a pas a body of the patient. The cable of assignments consists of wires, the number to-rykh corresponds to number of electrodes; the ends of these wires are supplied with contacts for connection to electrodes. Wires of a cable of assignments are marked as follows; red — to an electrode on the right hand, yellow — to an electrode on the left hand, green — to an electrode on the left leg, black or brown — to an electrode on the right leg, white — to a chest electrode.
The signal commutated in the necessary sequence and a combination has the size about 0,03 — 5 mV in this connection it is impossible to register it on a paper strip without preliminary strengthening. Therefore the signal from the switch of assignments arrives on an entrance of the amplifier of biopotentials. Here the signal amplifies up to the size necessary for movement of a galvanometer. Amplifiers of modern electrocardiographs are most often carried out on integrated circuits. For this purpose industrial integrated circuits of operational amplifiers, the amplifiers of biopotentials of very high sensitivity allowing to construct (about 10 mkv) with the small level of own noise (5 — 10 mkv), big entrance resistance (5 megohms and above), a high noise stability, ability to suppress network hindrances in 10 thousand times and more in relation to the registered useful signal are widely used.
The strengthened signal arrives on an entrance of the chart recorder, with the help to-rogo such important characteristics of electrocardiographs as speed of the movement of a paper strip, thickness of the line of record, etc. are provided. The registration device of the electrocardiograph with ink and thermal record consists of a peryevy galvanometer and the tape drive mechanism. The galvanometer serves for transformation of an electric signal to movement of a feather. The galvanometer consists of the magnetic conductor divided by air gaps into two symmetric half, a rotor, two coils of traffic control of a feather and two constants Magni Ov. Dependence between movement of a feather and current in the coil is aimed to be made close to linear. The rotating moment, the operating rotor, rejects the feather fixed on the output end of a shaft of a rotor.
The tape drive mechanism is intended for movement of a chart tape, on a cut record ECG is made. One of options of a design of the tape drive mechanism consists of the engine, a reducer, a travel table. Rotation from the engine to the roller stretching paper is transferred by a reducer. In the bottom of a travel table there is a plug, on to-ruyu put on a roll the chart of paper. The table has three guide rolls and the directing grooves for strictly fixed movement of a paper strip. The tape is stretched by a rubber roll of a reducer. Paper nestles on a rubber roll cylindrical springs.
Many electrocardiographs have the broad range of speeds of the movement of a paper strip: 1; 2,5;; 10; 25; 50; 100; 250 mm/sec. Thickness of the line of record lies within 0,3 — 1 mm, width of record (fluctuation band of the writing device) — within 40 — 100 mm. Speed of ink and thermal record reaches 10 m/s, the speed of photorecord is almost not limited. Quality of record is influenced considerably by a design of the looking for device. The largest weight and consequently, and metal feathers for ink and thermal record have inertia; jet galvanometers have smaller inertia (in devices like Mingograf); galvanometers with beam record are least inert. Also quality of a paper strip is of great importance. The basis of a paper strip (coordinate paper) shall be mechanically strong and at the same time have the minimum thickness. Paper shall not be deformed under the influence of a tension in the tape drive mechanism.
A necessary node of any electrocardiograph is the device of calibration intended for giving on an entrance of the amplifier of calibration voltage of 1 mV relatively to-rogo the amplntuda of teeth of an ECG is measured. Electrocardiographs can have auxiliary devices: system of calm of a galvanometer, adjustment of heat of a feather (for the electrocardiograph thermal record), operating handles movement of a feather etc. Functional properties of the electrocardiograph can be expanded for couples of inclusion of various prefixes. For this purpose install output connectors, to the Crimea it is possible to connect, e.g., an oscilloscope for sighting of an ECG, etc.
According to the operating GOST electrocardiographs classify by the form the writing element and a sort of the data carrier on peryevy with record on warm sensitive paper, ink on coordinate paper, on paper with use of a copy tape and on electrosensitive paper, jet with record on paper, beam with record on photographic paper, pases, beam with record, to semiconductor paper, beam with record on paper with direct manifestation. Besides, distinguish electrocardiographs with the network, autonomous or combined food. The ECG can be received also by means of telemetry (see Telemetry, Teleelektrokardiografiya). In systems of monitoring (see. Monitor observation) is used intermediate record of biopotentials on a magnetic tape. Further improvement of electrocardiographs goes on the way of automation of management of operation of these devices, use to them automatic processing of an ECG in real time with delivery of results of processing of an ECG in the form of alphanumeric information directly on a paper strip or the display.
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M. I. Kechker, BB. H. Gavrikov; E. V. Neudakhin (ped.), P. I. Utyamyshev (tekhn.), B. M. Zuckerman (theoretical bases).