Most people only know that an ECG is a piece of paper with a dense grid and some irregular curves on it. Except for a few doctors, few people can read an ECG. Here is a lesson on how to read an ECG. In order to know how to read an ECG, you must first understand the components of an ECG and the significance of each part.
1, electrogram recording paper.
The ECG is recorded on paper covered with small and large squares, so to know how to read an ECG, the first thing is to know what these squares represent. Each of these squares has a thin vertical line 1mm apart, and each thin horizontal line is also 1mm apart, and they form a 1mm square grid. The thick lines are one for every five cells, and each thick line is 5mm apart, and the horizontal and vertical thick lines form a large square. The ECG recording paper moves according to the international standard speed of 25mm/s, which means that each small horizontal grid represents 0.04s; the distance between each two thick lines represents 0.2s. There are also international regulations on the applied voltage for recording ECG, that is, when 1mV voltage is applied, the baseline should be raised exactly 10 small cells, that is, each The small horizontal frame represents 0.1mV, while each large frame represents 0.5mV, and every two large frames represent this 1mV.
2. The various waveforms on the ECG.
A single cardiac cycle will record a series of waveforms of different heights and widths on the new electrogram. These include P waves, QRS waves, T waves and (no) u waves. Understanding these waveforms and what they represent is the second step in teaching you how to read an ECG.
The P wave, the first to appear, is a circular, blunt waveform of low amplitude, which records the excitation of the right and left atria by the sinus node. Because the sinus node is located in the right atrium, the excitation of the atria starts from it first, so the first half of the P wave records the excitation of the right atrium, the middle part records the common excitation of the left and right atria while the posterior part represents the excitation of the left atrium. Except for the aVR leads, the P waves are basically upright, and the height of the P waves in the limb leads should not exceed 0.25 mV, and the height of the upright P waves in the chest leads should not exceed 0.15 mV. The width of the normal P waves should also not exceed 0.11s.
QRS wave group, a narrow but high amplitude wave group that appears after the P wave. It consists of q-wave (with or without), R-wave and S-wave. It represents the successive entry of excitation from the AV node into the myocardial cells through the AV bundle, the right and left bundle branches, and the slender Purkinje fibers, stimulating the contraction of the ventricles, and can therefore be regarded as the ECG manifestation of the onset of ventricular contraction.
The Q wave, a well-defined downward waveform, appears before the appearance of an upward wave. If it is small, less than 0.04s wide and less than 0.15mV deep, we will record it as a q wave; if it is high and wide, it is called a Q wave; of course, sometimes it is absent. Regardless of whether there is a Q wave or not, the first upward wave with a high tip is the R wave; the next downward wave is the S wave, which can also be named as S wave and s wave respectively according to the depth. The next upward wave is called R'(r’) wave, and the downward wave is called S'(s’) wave. Because of the different heights of the waves, they can be combined into many forms, but it also has limitations, the main one being the time limit. Usually, the QRS wave group of a normal person has a time of 0.08s and can fluctuate in the range of 0.06 to 0.10s. As long as this time limit is exceeded, it should be noted, especially more than 0.12s will have pathological significance.
The T wave, which appears after a pause in the previous wave group, represents the repolarization of the ventricle (diastole) in preparation for the next ventricular depolarization. To observe the T wave we have to pay attention to its direction, morphology and (height) depth.
(1) To, under normal circumstances, the T wave is upright in leads I and II; in lead III it can be upright, flat, bidirectional or even inverted; the T wave is definitely inverted in aVR leads, while in aVL and aVF leads it is in the same main direction as the QRS wave group. The T waves in the anterior thoracic leads are usually upright. Of course, V1 and V3 sometimes have inverted T waves, but their depths usually do not exceed 0.25 mV. When inverted T waves appear in the V3 leads, the T waves in the two preceding leads should also be inverted, otherwise it is an abnormal presentation.
(2) morphology, usually the waveform of T wave is rounded and has a very natural top. t wave is generally asymmetric, gently rising and slightly steeper falling to the isthmus. (3) Height (depth), which is not identical from lead to lead, but collectively appears to rarely exceed 0.5 mV in limb leads and 1.0 mV in chest leads. abnormally high sharp T waves are often seen in the early stages of myocardial infarction or in hyperkalemia.
The u wave, a very small wave after the T wave, is not obvious in every lead, and there is no definite conclusion as to what it represents.
3. The isochrones between each waveform.
There is a certain amount of time recorded between each waveform that is on the isochrones, called the P-R interval, S-T segment and Q-T interval, and they all have their own meaning. Familiarity with understanding what these intervals represent is the third step in knowing how to read an ECG.
The P-R interval, in general terms, can be expressed as the time between the start of the P wave and the start of the next group of QRS wave clusters. It includes the conduction times within the atria, the AV node, and the Hitchcock-Purkinje fibers. In normal sinus rhythm, it ranges from 0.12s to 0.20s, although it can be slightly shortened when the heart rate is accelerated. However, if there is a problem with the conduction system, it can be lengthened or shortened.
The ST segment, refers to the period of time between the termination of the QRS wave group and the beginning of the T wave. A normal ST segment is a slightly upward line connected to the T wave that is essentially on the equator. The ST segment is observed mainly for whether it is elevated or depressed, and whether his morphology is upward, horizontal or downward sloping. Under normal circumstances, the ST segment in the limb leads can be elevated by 0.1mV compared to the ischial line or slightly depressed by no more than 0.05mV; in the chest leads V1 to V3, the ST segment can also be elevated by up to 0.3mV, and in leads V4 and V5, the ST segment can be elevated by no more than 0.1mV, but the ST segment depression in all the chest leads should not exceed 0.05mV. ST-segment elevation or depression exceeding the above range should be brought to your attention. A normal ST-segment is upward-sloping; a horizontal or downward-sloping ST-segment is also abnormal.
The Q-T interval, which measures the time from the onset of the QRS wave group to the end of the T wave, reflects, to some extent, the time of depolarization and repolarization. Its length varies with the speed of the heart rate, and we commonly use Bazett’s to make the correction that Q-Tc = k?(k is a constant), with the upper limit of Q-Tc being 0.39s for men and 0.44s for women.
Quick judgment ECG tips
1. Normal ECG.
Needless to say, it is possible to chop a section of those waves and leads down, each wave gives you 3 cycles, divided into several lines for you to see, pay attention to the normal ECG should be distinguished from sinus slow sinus speed: when you see QRS waves and P waves, T waves are normal do not immediately determine the normal ECG, pay attention to look at the distance between adjacent P waves, if > 0.20S diagnosis of sinus slow; if < 0.12S diagnose sinus velocity.
2. Left ventricular hypertrophy.
First look at the entire ECG whether there is 1/2 word, to just have this can confirm the diagnosis of left ventricular hypertrophy, if not look at the V5 R wave > 2.5 MV or with ST-T changes, V5 is greater than 5 frames, also the upper and lower longitudinal 5 frames + left bias.
3. Right ventricular hypertrophy.
Just look at V1 > 2 frames, it is 2 frames of upper and lower longitudinal + right deviation.
4.Atrial fibrillation
All P – P, Q – Q, R – R, S – S, T – T are not regular, that is, chaotic, look at V1, R wave is not disproportionate, absolutely unequal, no P wave, QRS wave is normal.
Ventricular fibrillation: ventricular fibrillation needless to say is very typical, who can also recognize, but it should be noted that sometimes some examiners are more unethical to give you a inside that there is ventricular tachycardia also ventricular flutter and ventricular fibrillation, encounter such, you must answer ventricular fibrillation. (To answer the serious)
5, sinus bradycardia.
Each heartbeat cycle is greater than 5 frames. (is the left and right horizontal frame)
6, sinus tachycardia.
Each cardiac cycle is less than 3 frames (is the left and right frame), compared with paroxysmal supraventricular tachycardia with P waves.
7, atrial precontraction.
See if the P waves are all the same, the PP spacing is gradually shortened, then suddenly longer, and again gradually shortened. The first few normal waves, followed by a wave advance (note: the pQRSt shape of this wave is normal, just advance), followed by a normal wave. However, the accompanying intraventricular differential conduction v1 has an M-shaped wave, and the QRS can be widened, followed by another normal wave with P’. (Most of the compensation is incomplete)
8. Ventricular preterm contractions.
The overall appearance is messy and unevenly layered, with no P waves. The first few normal waves, followed by a wave in advance of the broad malformation of the QRS wave group (note: this time the R wave becomes wider), followed by another normal wave, T and the main wave opposite. (mostly compensated completely)
9. Typical myocardial ischemia.
ST segment of V456 is shifted down and up: v12>0.3mvv3>0.5mvv45>0.1mv, remember ST-T is shifted down or T wave is inverted. (The person is walking with head down or upside down)
10. Acute myocardial infarction.
Q-wave widening + ST-segment arch-back upward elevation, note: anterior wall look V123456; anterior wall look V456; inferior wall look II, III, aVF lateral wall, Ⅰ, v56, aVL red flags. (People walk with their heads up)
11. Complete left bundle branch conduction block.
Look at the entire ECG with QRS widening and ST-T changes. v1, V2S waves deepen. Complete right bundle branch conduction block: look at V1 with an extra large R wave (malformation), accompanied by ST-T changes.
12. Ventricular tachycardia.
There are P waves and widening of QRS aberrations. Paroxysmal supraventricular tachycardia: each cardiac cycle is less than 2 frames, the rhythm is regular, QRS is normal, no P, T. (need to be differentiated from sinus tachycardia)
13.Atrioventricular block.
Ⅰ degree AV block: RR interval > 0.20S, the rest is normal; need to be distinguished from sinus bradycardia.
Ⅱ degree type I conduction block (Mohs type): PR interval is gradually prolonged with QRS wave off.
Ⅱ degree II type II conduction block (fixed): fixed PR interval with QRS shedding and fixed PP interval.
Grade III AV block: atrial walk, ventricular walk, no relationship between P waves and QRS waves, number of P waves > QRS waves, P-P.