ABC ECG
Chapter I. Genesis of the main teeth, intervals and segments of the ECG
Additional Information for Chapter I
1. Segment details
A segment in electrocardiography is considered to be a segment of the ECG curve in relation to its isoelectric line. For example, the S-T segment is above the isoelectric line or the S-T segment is below the isoline.
2. The concept of internal deviation time
The conducting system of the heart, which was discussed above, is laid under the endocardium, and in order to embrace the excitation of the heart muscle, the impulse, as it were, “penetrates” the thickness of the entire myocardium in the direction from the endocardium to the epicardium.
It takes a certain time to cover the entire thickness of the myocardium with excitation. And this time, during which the impulse passes from the endocardium to the epicardium, is called the internal deflection time and is denoted by a capital Latin letter J.
Determining the time of internal deviation on the ECG is quite simple: for this, it is necessary to lower the perpendicular from the top of the R wave to its intersection with the isoelectric line. The segment from the beginning of the Q wave to the point of intersection of this perpendicular with the isoelectric line is the time of internal deviation.
The internal deflection time is measured in seconds and is 0.02-0.05 s.
3. Information about the excitation vector
Look carefully at fig. 14. Excitation of the thickness of the myocardium has a direction. It is directed from the endocardium to the epicardium. This is a vector quantity, that is, a vector, in addition to any of its magnitude values, also has a directionality. This vector is different from scalar quantities. Compare: the area of a rectangle is 30 cm 2 - this is a scalar value. On the contrary, the distance from point "A" to point "B", equal to 100 m, is a vector value, since there is a clear direction - from "A" to "B".
Several vectors can be summed (according to the rules of vector addition) and the result of this sum will be one summation (resulting) vector. For example, if we add three ventricular excitation vectors (interventricular septal excitation vector, apex excitation vector, and heart base excitation vector), then we get a summation (aka final, or resultant) ventricular excitation vector.
4. The concept of "recording electrode"
The recording electrode is called the electrode that connects the recording device (electrocardiograph) to the surface of the patient's body. The electrocardiograph, receiving electrical impulses from the surface of the patient's body through this recording electrode, converts them into a graphic curved line on a millimeter tape. This curved line is the electrocardiogram.
5. Graphical display of the vector on the ECG
The display (registration) of a vector or several vectors on an electrocardiographic tape occurs with certain patterns, given below.
A larger vector is displayed on the ECG with a larger wave amplitude compared to a smaller vector.
If the vector is directed to the recording electrode, then a wave is recorded upward from the isoline on the electrocardiogram.
If the vector is directed from the recording electrode, then a wave is recorded on the electrocardiogram down from the isoline.
Let's expand the concept of graphical display of vectors.
The figure shows that the right recording electrode will graphically display the vector "A" on the electrocardiogram with a tooth directed upwards ( R wave). On the contrary, the same vector "A" by the left recording electrode will be displayed on the electrocardiogram with a tooth directed downwards ( wave S).
In other words: the same vector is recorded on the ECG by recording electrodes having different locations, in different ways, in this case discordantly, i.e., in different directions.
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Similar Documents
- assessment of the regularity of heart contractions,
- counting the heart rate (HR),
- determination of the source of excitation,
- conductivity rating.
- Determination of the electrical axis of the heart.
- Analysis of atrial P wave and P-Q interval.
- Analysis of the ventricular QRST complex:
- analysis of the QRS complex,
- analysis of the RS-T segment,
- T wave analysis,
- analysis of the interval Q - T.
- Electrocardiographic conclusion.
- assessment of heart rate regularity
- heart rate count(HR)
- determination of the source of excitation
- 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.
- in leads II and III, P waves are negative,
- There are P waves before each QRS complex.
- P waves may be absent because they are superimposed on normal QRS complexes,
- P waves may be negative, located after the QRS complex.
- 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.
- conductivity assessment.
To correctly account for conductivity, the write speed is taken into account. - duration P wave(reflects the speed of the impulse through the atria), normally up to 0.1s.
- duration 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.
- duration QRS complex(reflects the spread of excitation through the ventricles). Fine 0.06-0.1s.
- internal 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).
- 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.
- 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.
- analysis of the QRS complex.
- analysis of the RS-T segment
- T wave analysis.
- analysis of the interval Q - T.
- Rhythm source (sinus or not).
- Rhythm regularity (correct or not). Usually sinus rhythm is correct, although respiratory arrhythmia is possible.
- The position of the electrical axis of the heart.
- The presence of 4 syndromes:
- rhythm disorder
- conduction disorder
- hypertrophy and/or congestion of the ventricles and atria
- myocardial damage (ischemia, dystrophy, necrosis, scars)
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Prong P. - atrial complex, reflecting the process of propagation of excitation (depolarization) of the atria. Its source is the sinus node located at the mouth of the superior vena cava (in the upper part of the right atrium). The first 0.02-0.03 s, the excitation wave propagates only through the right atrium, the next 0.03-0.06 s goes simultaneously through both atria. In the final 0.02-0.03 s, it spreads only through the left atrium, since the entire myocardium of the right atrium is already in an excited state by this time.
P wave polarity different in different leads I, II, aVF, V3-V6 always positive.
aVR is always negative.
III can be positive, two-phase or negative with the horizontal position of the electrical axis of the heart. aVL is positive, biphasic, or negative with a vertical electrical position of the heart. V1 0 is more often two-phase, it can be registered in the form of a low positive tooth. Occasionally, P has the same polarity in lead V2.
The amplitude of the P wave is 0.5-2.5mm. Its duration does not exceed 0.1 s(ranges from 0.07 to 0.1 s).
Segment P-Q.. Excitation of the atrioventricular junction, the bundle of His, the legs of the bundle of His, Purkinje fibers creates a very small potential difference, which on the ECG is represented by an isoelectric line located between the end of the P wave and the beginning of the ventricular complex.
P-Q interval.corresponds to the time of propagation of excitation from the sinus node to the contractile myocardium of the ventricles. This indicator includes the P wave and the P-Q segment and is measured from the beginning of the P wave to the beginning of the stomach.
daughter complex. The duration of the P-Q interval is normally 0.12-0.20 s (up to 0.21 s with bradycardia) and depends on the heart rate, increasing with a decrease in sinus rhythm.
QRS complex.- ventricular complex, which is formed in the process of depolarization of the ventricles. For greater clarity of explanation of the origin of the individual teeth of this complex, the continuous process of the course of excitation through the ventricles is divided into 3 main stages. I stage (initial). It corresponds to the first 0.02-0.03 s of the propagation of excitation along the ventricular myocardium and is mainly due to excitation of the interventricular septum, and also, to a lesser extent, of the right ventricle. The total (moment) initial vector is directed to the right and forward and has a small value. The projection of this vector on the lead axis determines the direction and size of the initial wave of the ventricular complex in most electrocardiographic leads. Because Since the initial moment vector of ventricular depolarization is projected onto the negative parts of the axes of leads I, II, III, aVL, aVF, then in these
assignments the small negative deviation of a wave q is registered. Its direction from the V5-V6 electrodes also explains the appearance of a small q wave in these leads. At the same time, this vector is oriented from the electrodes V1-V2, where under its influence an initial positive wave of small amplitude is formed - the R wave. Stage II (main). It takes place during the next 0.04-0.07 s, when the excitation spreads along the free walls of the ventricles. The total (momentary) main vector is directed from right to left, corresponding to the orientation of the total vector of the more powerful left ventricle. The projection of the main moment vector on the lead axis determines the main wave of the ventricular complex in each of them. It is projected onto the positive parts of the axes I, II, III, aVL, aVF of the leads, where the R waves are formed and onto the negative part of the lead aVR, which leads to the simultaneous registration of the negative S wave. The main moment vector is oriented to the electrodes V5 -V6, here under its influence there are positive teeth - teeth R. The same vector has a direction from the electrodes V1 -V2, therefore, in the same period of time, a negative tooth S tooth is formed in them. Stage III (final). The process of depolarization of the ventricles ends with excitation coverage of their basal regions. This happens at 0.08-0.10 s. The total (moment) terminal vector has a small value and varies significantly in direction. However, more often it is oriented to the right and backwards. In a number of leads from the limbs, in leads V4-V6, under its influence, terminal negative teeth - S waves are formed. In leads V1-V2, this vector, merging with the main one, contributes to the formation of deep S waves. Thus, the same electrical processes recorded simultaneously during the propagation of excitation in the ventricles in different leads can be represented by teeth of different
polarity and magnitude. This is determined by the projection of the corresponding moment vectors on the lead axes. In other words, depending on the position of the electrodes, the teeth reflecting the initial, main and final stages of ventricular depolarization can have different directions and different amplitudes. When the amplitude of the wave of the ventricular complex exceeding 5 mm, it is indicated by a capital letter. If the amplitude of the tooth is less than 5 mm - lower case. The Q wave indicates the first wave of the ventricular complex if it is directed downward. Thus, there can be only one Q wave in the ventricular complex. R wave- any prong of the ventricular complex directed upward from the isoline, i.e. positive. If there are several positive teeth, they are designated respectively as R, R", R", etc. S wave- negative tooth following the positive tooth, i.e. R wave. There can also be several S waves, and then they are designated as S", S", etc. If the ventricular complex is represented by one negative wave (in the absence of an R wave), it is designated as QS.
Characteristics of normal teeth of the ventricular complex.
Q wave. can be recorded in leads I, II, III, aVL
aVF, aVR. Its presence is mandatory in leads V4-V6. The presence of this tooth in leads V 41 0-V 43 0 is a sign of pathology.
Criteria for a normal Q wave: 1) duration no more 0,03 2) depth no more 25% amplitude of the R wave in the same lead (except lead aVR, where a QS or Qr complex can normally be recorded).
R wave.may be absent in leads aVR, aVL (in the vertical position of the electrical axis of the heart) and in lead V1. In this case, the ventricular complex takes the form of QS. The R wave amplitude does not exceed 20 mm in limb leads and 25 mm in chest leads. In practical electrocardiography, the ratio of the amplitudes of the R wave in various leads is often of great importance than its absolute value. This is due to the influence of extracardiac factors on the amplitude characteristics of the ECG (emphysema, obesity). The ratio of the height of the R waves in the limb leads is determined by the position of the electrical axis of the heart. In the chest leads, the normal R-wave amplitude gradually increases from V1 to V4, where its maximum height is usually recorded. From V4 to V6 there is a gradual decline. Thus, the dynamics of the amplitude of the R wave in the chest leads can be described by the formula: R V1< R V2< R V3< R V4>R V5 > R V6 .
S wave.- non-permanent prong of the ventricular complex. It has its maximum amplitude in lead V1 0 or V2 and gradually decreases towards leads V5-V6 (where it may normally be absent). The ratio of the S waves in the chest leads is the formula: SV1 S V3 > S V4 > SV5 > S V6. In limb leads, the presence and depth of this tooth depend on the position of the electrical axis of the heart and the rotations of the heart. As a rule, in these leads, the amplitude of the S wave does not exceed 5-6 mm. Its width is within 0.04 mm. The described dynamics of the R and S waves in the chest leads corresponds to a gradual increase in the R/S amplitude ratio from the right leads, where it< 1,0, к левым, в которых это отношение >1.0. A chest lead with equal R and S wave amplitudes (R/S = 1.0) is called transition zone. More often in healthy people this assignment V3.
The total duration of the QRS complex, representing intraventricular conduction time, is 0.07-0.1 s. An equally important indicator of intraventricular conduction is ventricular activation time or internal deviation (intrinsicoid deflection) - ID. It characterizes the propagation time of excitation from the endocardium to the epicardium of the ventricular wall located under the electrode. Internal deviation is determined for each ventricle separately. For the right ventricle, this indicator (IDd) is measured in lead V 1 by the distance from the beginning of the ventricular complex to the top of the R wave (or the top of the last R wave in the RSR complex). Normal IDd = 0.02-0.03 s. - left ventricular flexion (IDs) is assessed in lead V6 by the distance from the beginning of the ventricular complex to the top of the R wave (or the top of the last R wave when it splits) Normal IDs = 0.04-0.05 s.
S-T segment.- line from the end of the ventricular complex to the beginning of the T wave. It corresponds to the period of complete coverage of the ventricular myocardium by excitation. In this case, the potential difference in the heart muscle is absent or very small. Therefore, the S-T segment is on the isoline, or slightly offset relative to it. In the leads from the extremities and the left chest leads, the S-T segment normally shifts down and up from the isoline by a distance of no more than 0.5 mm. In the right chest leads, it can be shifted up by 1.0-2.0mm(especially with high T waves in these same leads). There is no normal downward displacement of the S-T segment in the left chest leads.
T wave.reflects the process of rapid final repolarization of the ventricular myocardium. The total vector of ventricular repolarization, the wave of which propagates from subepicardial to subendocardial layers, has the same direction as the main moment vector of depolarization. In this regard, the polarity of the T wave in most leads coincides with the polarity of the main wave of the QRS complex.
T wave in I, II, aVF, V3-V6 always positive, T wave in aVR always negative. T III can be positive, biphasic and even negative with the horizontal position of the electrical axis of the heart. T in aVL is both positive and negative - with a vertical position of the axis of the heart. T in V1 (rarely T in V2) can be either positive, biphasic, or negative. It is asymmetric, has a smoothed top. T wave amplitude in leads V5 -V6 0 is 1/3-1/4 R wave height in these leads. In lead V4 (V3), it can reach 1/2 R wave amplitude. Usually in limb leads it does not exceed 5-6 mm, in chest - 15-17 mm.
Q-T interval.- electrical systole of the heart. This indicator is measured by the distance from the beginning of the ventricular complex to the end of the T wave. Including the T wave, the systolic indicator largely reflects changes in the phase of ventricular repolarization, which have many different causes. The duration of the Q-T interval is also affected by the heart rate and gender of the patient, which is taken into account when assessing it.
The systolic indicator is estimated by comparing the actual value with the due one. The proper value can be calculated using the Bazett formula: Q-T = k ´R-R, where k is a coefficient equal to 0.37 for men and 0.40 for women; R-R - the duration of one cardiac cycle in seconds. The proper Q-T corresponding to a given heart rate and gender of the patient can be set using a special nomogram.
The Q-T interval is considered normal if its actual value does not exceed the due value by more than 0.04 s.
U wave.. There is no single view on the origin of this ECG wave. Its appearance is associated with the potentials arising from the stretching of the ventricular myocardium during the period of rapid filling, with the repolarization of the papillary muscles, Purkinje fibers. This is a small amplitude positive wave, which follows the T wave in 0.02-0.03 s. More often it can be registered in leads II, III, V1-V4.
Electrocardiogram analysis.
I. Analysis of heart rhythm and conduction.
II. Determining the position of the electrical axis of the heart. Definition of turns of the heart.
III. Analysis of teeth and segments.
IV. Formulation of the electrocardiographic conclusion.
I. Rhythm and conduction analysis. This stage consists of determining the source of the rhythm, assessing its regularity and frequency, and elucidating the conduction function. Normally, the pacemaker (source) of rhythm is the sinus (sinoatrial) node. Normal sinus rhythm is defined by the following criteria:
1) the presence of a P wave preceding each QRS complex;
2) normal for this lead and permanent form
P wave;
3) normal and stable duration of the P-Q interval;
4) rhythm frequency 60-90 per minute;
5) the difference in the intervals R-R (or R-R) is not more than 0.15.
Evaluation of the last criterion allows you to determine the rhythm as regular or irregular. In case of rhythm irregularity, its cause is specified (sinus arrhythmia, extrasystole, atrial fibrillation, etc.).
To calculate the heart rate (HR) with a regular rhythm, use the formula:
Heart rate \u003d 60 / R-R, where 60 is the number of seconds in a minute.
With an irregular rhythm, you can record an ECG in one of the leads for 3-4 minutes. On this segment, count the number of QRS complexes in 3 minutes and multiply it by 20.
To evaluate the conductivity function, the following indicators are measured:
1) the duration of the P wave (characterizes the speed of intra-atrial conduction);
2) P-Q interval, which reflects the state of atrioventricular conduction;
3) QRS complex, which gives a general idea of intraventricular conduction;
4) IDd and IDs, which make it possible to judge the spread of excitation in the right and left ventricles, respectively.
The final conclusion about the nature of the violation of intraventricular conduction is made after analyzing the morphology of the ventricular complex.
A segment in electrocardiography is considered to be a segment of the ECG curve in relation to its isoelectric line. For example, the S-T segment is above the isoelectric line or the S-T segment is below the isoelectric line.
2. The concept of internal deviation time
The conducting system of the heart, which was discussed above, is laid under the endocardium, and in order to embrace the excitation of the heart muscle, the impulse, as it were, “penetrates” the thickness of the entire myocardium in the direction from the endocardium to the epicardium.
It takes a certain time to cover the entire thickness of the myocardium with excitation. And this time, during which the impulse passes from the endocardium to the epicardium, is called the internal deflection time and is denoted by a capital letter J.
Determining the time of internal deviation on the ECG is quite simple: for this, it is necessary to lower the perpendicular from the top of the R wave to its intersection with the isoelectric line. The segment from the beginning of the Q wave to the point of intersection of this perpendicular with the isoelectric line is the time of internal deviation.
The internal deflection time is measured in seconds and is 0.02-0.05 s.
3. Information about the excitation vector
Look carefully at fig. 14. Excitation of the thickness of the myocardium has a direction. It is directed from the endocardium to the epicardium. This is a vector quantity, that is, a vector, in addition to any of its magnitude values, also has a directionality. This vector is different from scalar quantities. Compare: the area of a rectangle is 30 cm 2 - this is a scalar value. On the contrary, the distance from point "A" to point "B", equal to 100 m, is a vector value, since there is a clear direction - from "A" to "B".
Several vectors can be summed (according to the rules of vector addition) and the result of this sum will be one summation (resulting) vector. For example, if we add three ventricular excitation vectors (interventricular septal excitation vector, apex excitation vector, and heart base excitation vector), then we get the summation (it is also final, it is also resultant) ventricular excitation vector.
4. The concept of "recording electrode"
The recording electrode is called the electrode that connects the recording device (electrocardiograph) to the surface of the patient's body. The electrocardiograph, receiving electrical impulses from the surface of the patient's body through this recording electrode, converts them into a graphic curved line on a millimeter tape. This curved line is the electrocardiogram.
5. Graphical display of the vector on the ECG
The display (registration) of a vector or several vectors on an electrocardiographic tape occurs with certain patterns, given below.
A larger vector is displayed on the ECG with a larger wave amplitude compared to a smaller vector.
If the vector is directed to the recording electrode, then a wave is recorded upward from the isoline on the electrocardiogram.
If the vector is directed from the recording electrode, then a wave is recorded on the electrocardiogram down from the isoline.
Let's expand the concept of graphical display of vectors.
The figure shows that the right recording electrode will graphically display the “A” vector on the electrocardiogram with a tooth directed upwards (R wave). On the contrary, the same vector "A" by the left recording electrode will be displayed on the electrocardiogram with a downwardly directed tooth (S wave).
Normal electrocardiogram.
1) Checking the correctness of the ECG registration
At the beginning of each ECG tape there should be 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 incorrect. 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:
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.
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 bpm
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.
In other words, they are looking for where pacemaker which causes atrial and ventricular contractions. Sometimes this is one of the most difficult stages, because various disturbances of excitability and conduction can be very intricately combined, which can lead to misdiagnosis and incorrect treatment. To correctly determine the source of excitation on the ECG, you need to know well conduction system of the heart.
Sinus rhythm(this is a normal rhythm, and all other rhythms are pathological).
The source of excitation is in sinoatrial node. ECG signs:
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:
P wave in atrial rhythm.
Rhythms from the AV junction. If the pacemaker is in the atrioventricular ( atrioventricular node) node, then the ventricles are excited as usual (from top to bottom), and the atria - retrograde (i.e., from bottom to top). At the same time on the ECG:
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:
Idioventricular rhythm. The P wave is not associated with the QRS complex.
To assess conductivity, measure:
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:
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 block there are 3 degrees:
5) Analysis of the ventricular QRST 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).
The 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.
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.
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:
Conclusion Examples(not quite complete, but real):
Sinus rhythm with heart rate 65. Normal position of the electrical axis of the heart. Pathology is not revealed.
Sinus tachycardia with a heart rate of 100. Single supragastric extrasystole.
The rhythm is sinus with a heart rate of 70 beats / min. Incomplete blockade of the right leg of the bundle of His. Moderate metabolic changes in the myocardium.
Examples of ECG for specific diseases of the cardiovascular system - next time.