ECG stands for electrocardiogram, meaning electrocardiogram, and refers to the graphical representation of the heart's successive excitation by the pacing point, atria, and ventricles during each cardiac cycle, accompanied by bioelectrical changes, and the many forms of potential changes elicited from the body surface by means of an electrocardiographic tracer. The electrocardiographic measurement technology has been developed to eighteen leads.
Basic introduction Chinese name: electrocardiogram Foreign name: ECG Meaning: examination of the heart Principle: capacitance-voltage Overview, Meaning, Principle, Methods, Common Terms, Applied, Classification, Applied Scope, Electrocardiograph, Overview The electrocardiogram is an objective indicator of the onset, propagation, and recovery of cardiac excitation. The relationship of ECG waves to myocardial action potentials The pattern of action electric dots traced during the excitation of a single cardiomyocyte is significantly different from that of the ECG traced during each cardiac cycle. This is due to the fact that the cardiomyocyte action potential is a change in the membrane potential of a single cell, whereas the ECG is an instantaneous change in the potential of a large number of cardiomyocytes constituting a functional syncytium, which changes in response to the onset of transmission and recovery of excitation of the whole heart as a functional syncytium. Not only is the action potential different from that of a single cardiomyocyte, but the waveforms traced in multiple leads are also different. Nevertheless, there is a clear correspondence between the generation and disappearance of action potentials in individual cardiomyocytes and the waves of the electrocardiogram. In ventricular myocardium, for example, the "0" phase (ascending branch) of the action potential of a single cell of ventricular myocardium corresponds to the QRS complex wave of the electrocardiogram. Because of the sequence of the time of the beginning of depolarization of the myocytes of each ventricle, the duration of the QRS complex wave is longer than that of the "0" phase of a single ventricular myocyte, but the duration of the two is basically corresponding. The "2" phase of repolarization of a single ventricular myocyte corresponds to the S-T segment of the ECG. When a single ventricular myocyte begins to enter rapid repolarization, phase 3, it corresponds to the T wave of the electrocardiogram. Electrocardiogram Significance The significance of the electrocardiogram is that it is used to examine various arrhythmias, ventricular and atrial hypertrophy, myocardial infarction, myocardial ischemia, and other conditions. The electrocardiogram is a process of electrical activity that reflects the excitement of the heart, which has an important reference value in the study of the basic function of the heart and its pathology. ECG can analyze and identify various arrhythmias; it can also reflect the degree and development of myocardial damage and the functional structure of the atria and ventricles. It has reference value in guiding the conduct of cardiac surgery and indicating the necessary drug treatment. However, ECG is not essential for checking the functional status of the heart. This is because sometimes a seemingly normal ECG does not necessarily prove normal cardiac function; on the contrary, myocardial injuries and functional defects do not always show any changes in the ECG. Therefore, ECG examination must be combined with a variety of indicators and clinical data for a comprehensive and integrated analysis in order to make a correct judgment on the functional structure of the heart. Principle The tissues and body fluids surrounding the heart are capable of conducting electricity, so the human body can be viewed as a volume conductor with three degrees of space: length, width, and thickness. The heart acts as a power source, and the sum of action potential changes in countless cardiac muscle cells can be conducted and reflected to the body surface. There are potential differences between many points on the body surface, and there are also many points that are isoelectric without potential differences between each other. The electrical activity of the heart can be mechanistically reduced to a series of integrated vectors of instantaneous electrocardiograms. In each cardiac cycle, the trajectory of the spatial circular motion constitutes a three-dimensional electrocardiographic vector ring. The frontal, transverse, and lateral electrocardiogram vector rings seen on the screen with a cathode-ray oscilloscope are projections of the three-dimensional vector rings onto the corresponding planes. The potential changes recorded on the electrocardiogram are the reflection of a series of instantaneous integrated ECG vectors on the different lead axes, i.e., the reprojection of the planar vector rings on the relevant lead axes. The magnitude of the projected potentials is determined by the magnitude of the instantaneous ECG synthesized vectors themselves and their angular relationship to the lead axes. Positive potentials are obtained when the direction of the projection is the same as the direction of the lead axes, and negative potentials are obtained when the opposite is true. These projections are traced continuously on recording paper moving at a certain speed, and the result is the ECG waveform. The rise and fall of the ECG waveform above and below the baseline (equipotential line) is related to the direction in which the vector loop is traveling. If the direction is the same as the direction of the lead axis, the projection on the electrocardiogram has an ascending branch, and if it is the opposite, it has a descending branch. The projection of the zero point on the vector loop is the equipotential line on the ECG, and the extension of this line divides the vector loop into two parts, which are projected as positive and negative waves, respectively. Thus, the ECG is very closely related to the cardiac vector map. The strength of the ECG is the ability to quantify and analyze the projection of complex three-dimensional ECG vector loops from different angles in different planes, using relatively simple waveforms and line segments. The theoretical development of electrocardiographic vectorography has further enriched the content of electrocardiography and made it easier to understand. Conductivity animal body tissues and body fluids can conduct electricity, the recording electrodes of the ECG tracer placed on the body surface of any two non-isoelectric parts, can be recorded out of the ECG changes in the image, this measurement method is called bipolar conductivity, the measured potential changes are measured on the surface of the body of the two points of the potential changes of the algebraic sum of the analysis of the waveform is more complex. If you try to make one of the two measuring electrodes, usually the pole connected to the negative end of the tracer, its potential is always kept at zero potential, which becomes the so-called "irrelevant electrode", while the other measuring electrode is placed on the body surface at a certain point of measurement as a "probe electrode", this measurement method is called unipolar lead. This measurement method is called unipolar lead. Since the irrelevant electrode often maintains zero potential, the measured potential change only indicates the potential change of the site where the probe electrode is located, thus the interpretation of the waveform is relatively simple. Both unipolar and bipolar leads are currently used in clinical examinations of the ECG. There are 12 ECG lead methods in routine use. Methods The standard leads are bipolar leads, which can only trace the potential difference between the two electrodes. The electrode connection method is: first lead (abbreviated as I), right arm (-), left arm (+); second lead (abbreviated as II), right arm (-), left foot (+); third lead (abbreviated as III), left arm (=-), left foot (+). The pressurized unipolar limb lead placed the probe electrode on either limb of the standard lead, while the guide electrode on each of the remaining two limbs was connected in series with a 5000-ohm resistor as an extraneous electrode. The ECG voltage recorded in this lead is about 50% higher than that in the unipolar limb lead, hence the name pressurized unipolar limb lead. It is named according to the location where the probe electrode is placed, e.g., if the probe electrode is in the right arm, it is a pressurized unipolar right upper extremity lead (aVR), in the left arm it is a pressurized unipolar left upper extremity lead (aVL), and in the left leg it is a pressurized unipolar left lower extremity lead (aVF). The unipolar chest lead fixes one measurement electrode at zero potential (centroid method) and connects the centroid to the negative end of the electrocardiographic tracer, making it an irrelevant electrode. The other electrode is connected to the positive end of the tracer and serves as a probe electrode, which can be placed on different parts of the chest wall. They constitute six monopolar chest leads, and the positions of the electrodes are: V1, 4th intercostal space at the right edge of the sternum; V2, 4th intercostal space at the left edge of the sternum; V3, at the midpoint of the line connecting V2 and V4; V4, 5th intercostal space at the left midclavicular line; V5, at the same level as V4 in the left anterior axillary line; and V6, at the same level as V4 in the midaxillary line. Typical electrocardiogram waves and their time course with the standard leads led to the electrocardiogram waves, by the Dutch physiologist W. Eintraffen named P, Q, R, S, T wave, U wave is later found named. Commonly used terms 1, ECG vector: ECG activity, whether right or left atrial (P wave), or on behalf of the initiation of ventricular beats ECG activity (QRS wave group), are both the direction, but also the size (amount) of the electrical activity of the heart, known as the ECG vector. It is also reflected differently from lead to lead, due to the different angles of the leads (either frontal or transverse leads). In other words, why do we need three pressurized limb leads in the frontal plane in addition to the three standard leads, and six chest wall leads in addition? The reason is that from different angles to understand the ECG activity up and down, left and right, before and after the integrated ECG vectors, so as to observe whether it is normal or not, and so on. 2、Depolarization: atrial and ventricular muscle in the stationary interval, due to the cell inside and outside the ion (including K +, Na +, Ca2 +, cl-, etc.) concentration difference is very large, in the "polarized state". However, when excited by a self-paced cell, this polarized state is temporarily dissolved, which is called "depolarization" on the electrocardiogram (or "depolarization" by a few scholars), and electrical activity is generated as a result. Depolarization of the atrial muscle is characterized by P waves on the ECG, and depolarization of the ventricular muscle is characterized by QRS wave clusters. Of course, after a depolarization, the myocardium returns to its original state of polarization, a process known as "repolarization". Repolarization is much slower than depolarization, and the amplitude of electrical activity is lower. Repolarization of the atria is generally not evident in the P-R segment (except in the case of right atrial enlargement, when the P-R segment is mildly depressed). Ventricular muscle repolarization, on the other hand, is manifested as ST segments and T waves on the ECG. 3, electrocardiographic vector ring: the two sides of the atrium, the two sides of the ventricle and the ventricular repolarization, these three electrocardiographic activity in the thoracic cavity to form a three-dimensional vector ring. These three-dimensional vector rings are formed in the thoracic cavity by projecting parallel light rays onto the frontal plane from directly in front, forming a frontal ECG vector ring. Similarly, parallel light rays are projected from directly above these three-dimensional vector rings onto the transverse plane to form the transverse ECG vector ring. 4. Coupling interval (or coupling interval, coupling spacing): After a series of sinus excitation P-QRS-T, a premature ventricular beat occurs. The time between the onset of the QRS wave cluster preceding the premature beat and the onset of the premature ventricular beat is called the coupling time. Two consecutive atrial premature beats, their P-P time distance is also called the "coupling interval. 5, P wave: the heart's excitement originates in the sinoatrial node, and is first transmitted to the atria, so the first wave in the electrocardiogram is the P wave, which represents the excitement process of the left and right atria. In the process of propagation of excitation to the two atria, the integrated vector of electrocardiographic depolarization first points to the left lower limb, and then gradually turns to the left upper limb. If the integrated vectors of atrial depolarization are linked together, a spatial vector ring representing atrial depolarization is formed, referred to as the P ring. the projection of the P ring on the axes of the various leads results in a different P wave in each lead. the P waveform is small and rounded, and slightly different with each lead. the width of the P wave is generally no more than 0.11 seconds, and the voltage (height) is no more than 0.25 millivolts. P-R segment: the curve between the end point of the P wave and the beginning of the QRS wave, usually at the same level as the baseline. P-R segment is generated by the potential change of electrical activity to the ventricle through the atrioventricular junction is extremely weak, and it is difficult to record on the surface of the body. 7, P-R interval: is the P wave starting point to the QRS wave group starting point of the time distance, on behalf of the beginning of atrial excitation to the beginning of ventricular excitation of the time required, the general adult is about 0.12 ~ 0.20 seconds, pediatrics a little shorter. More than 0.21 seconds for atrial conduction time prolongation. 8, QRS complex wave: represents the two ventricular excitation propagation process of potential changes. The excitation wave generated by the sinus node firstly reaches the left side of the ventricular septum through the conduction system, and then propagates according to certain routes and directions and from the inner layer to the outer layer in turn. With the successive depolarization of various parts of the ventricle, multiple instantaneous integrated ECG vectors are formed, and the projection on the lead axes in the frontal plane is the QRS complex wave in the limb leads of the electrocardiogram. A typical QRS complex wave consists of three connected fluctuations. The first downward wave is the Q wave, a narrowly elevated upward wave following the Q wave is the R wave, and another downward wave in line with the R wave is the S wave. Because these three waves are closely linked and the total time does not exceed 0.10 seconds, it is collectively referred to as the QRS complex wave. the time occupied by the QRS complex wave represents the time required for the propagation of ventricular myocardial excitation, which is between 0.06 and 0.10 seconds in normal people. 9, ST segment: from the end of the QRS wave group to the beginning of the T wave of the flat line, reflecting the ventricular departments are in the excitement of the ministries in the state of depolarization, so there is no potential difference. When normal, it is close to the equipotential line, and the downward shift should not exceed 0.05 mV, and the upward shift should not exceed 0.1 mV in the limb leads, and it can be as high as 0.2～0.3 mV in the unipolar precordial leads V1, V2, and V3; and seldom higher than 0.1 mV in the leads V4 and V5. ST-segment decreases should not be less than 0.05 mV in any normal precordial lead. A high or lowered ST segment beyond the above range is considered an abnormal ECG. T-wave: It is a wave with lower amplitude and longer wave width after QRS wave group, reflecting the repolarization process after ventricular excitation. The sequence of ventricular repolarization is opposite to the depolarization process; it proceeds slowly from the outer layer to the inner layer, and the negative potential of the depolarized portion of the outer layer is first restored to the positive potential at rest, so that the outer layer is positive and the inner layer is negative, and the direction of the vectors is therefore basically the same as that of the depolarization. The trajectory formed by connecting the vectors at each instant of ventricular repolarization is the ventricular repolarization electrocardiographic vector loop, or T-loop for short, and the projection of the T-loop is the T-wave. Repolarization process is related to myocardial metabolism, so it is slower than the depolarization process and occupies a longer period of time. t-wave and S-T segment have the same important diagnostic significance. V wave: a wide and low wave appears 0.02-0.04 seconds after the T wave, with a wave height of 0.05 mV or less and a wave width of about 0.20 seconds. It is generally believed that it may be formed by the negative after-potential generated by the various departments during cardiac diastole, and it is also believed to be the result of repolarization of Purkinje's fibers. Insufficient potassium, hyperthyroidism, and the cardiac drug digitalis increase the V wave. Appropriation The electrocardiogram has been appropriated quite extensively for scientific research. Their ECGs have been traced in a variety of animals, and preliminary studies of their physiologic significance have been made. Invertebrates such as horseshoe crabs, mussels, octopuses, crayfish, and sea squirts, and vertebrates such as amphibians, reptiles, birds, and mammals can be traced using special electrodes and guidance methods. The basic patterns are generally similar, but differ in the specific waveforms and voltages, and in the length of the time period. In animals with well-developed venous sinuses, the P-wave of the ECG is preceded by a V-wave corresponding to the excitation of the venous sinuses. The ECG of fish and amphibians often has a B wave before the T wave, which reflects arterial cone excitation. The animal ECG can also be used as an objective indicator of the nature of the origin of the beat. Neurogenic beats, such as those of horseshoe crabs, often have oscillatory fast waves and a number of bursts of frontal potentials, while myogenic beats, such as those of mollusks, often consist of a number of slow waves. The animal ECG is an important reference for the study of the comparative physiology of the heart and the study of cardiac pharmacology. In addition, an ECG transmitter can be attached to a human or animal body, and changes in the ECG can be traced at a distance through a receiving system. This can be used to test changes in cardiac function in athletes and walking animals; to test changes in the heartbeat of high-altitude pilots and astronauts, and to study changes in cardiac activity in humans in response to environments such as mountains, high altitudes, and deep oceans. Classification ECG can be divided into ordinary ECG, 24-hour dynamic ECG, His bundle ECG, esophageal lead ECG, artificial heart pacing ECG and so on. The most widely used are ordinary electrocardiogram and 24-hour ambulatory electrocardiogram. Scope of application General electrocardiogram 1. Important diagnostic value for arrhythmia and conduction disorders. 2. 2, the diagnosis of myocardial infarction has high accuracy, it can not only determine the presence or absence of myocardial infarction, but also can determine the infarction of the lesion stage part scope and evolution process. 3、It is helpful for the diagnosis of atrial myocardium, myocarditis, cardiomyopathy, insufficient coronary blood supply and pericarditis. 4、It can help to understand the role of certain drugs (such as digitalis, quinidine) and electrolyte disorders on the myocardium. 5, the electrocardiogram as a kind of electrical information time sign, often for the heart sound map, echocardiography, impedance flow map and other cardiac function determination and other cardiac electrophysiology research synchronization tracing record, in order to help determine the time. 6, cardiac monitoring has been widely used in surgery, anesthesia, medication observation, aerospace, sports and other cardiac monitoring and rescue of critically ill patients. 24-hour ambulatory electrocardiogram ambulatory electrocardiogram is a method of continuous recording of dynamic cardiac activity over a long period of time (24 hours or more). It fully reflects the symptoms and changes in the heart that occur when the subject is active or asleep. It is suitable for checking transient arrhythmia and myocardial ischemia, and can qualitatively and quantitatively diagnose arrhythmia and understand the reserve capacity of the heart. However, its disadvantage is that the report is late and cannot be used in cardiac emergencies. ECG machine ECG machine is easy and convenient, can be carried to the door, ECG reading and analysis can be operated remotely, which greatly facilitates the heart disease patients who are far away from all corners of the world, as long as they have the ECG remote system contact, the cardiac patients who are recuperating at home at any time can get timely and accurate guidance from the ECG workers, so that they can better prevent and treat the heart disease. Electrocardiogram has been developed with the development of medicine, in order to comply with the development trend of human genetics and eugenics, electrocardiogram has been able to depict the bioelectrical currents generated by the fetal heart activity into a spectrum, and record the instantaneous changes of the fetus, and through the observation of fetal electrocardiogram, it can be used to dynamically monitor the development of perinatal fetuses and their growth in the uterus, which has important clinical significance and social value for early diagnosis and timely treatment of fetal diseases, and to improve the quality of perinatal babies for eugenic sterilization. important clinical significance and social value. With the development of community medical services, the role of ECG is more and more significant, ECG can help middle-aged people or young children to find potential heart disease or congenital heart disease in a timely manner.