Understanding the ECG
English and Chinese Terminology Interpretation Resting ECG resting electrocardiograph is classified according to the requirements of the ECG environment. It requires the patient to lie quietly on the hospital bed, and the acquisition time is 10 seconds to 300 seconds. It is suitable for the primary screening of most heart diseases. The Holter/Dynamic ECG machine is used as a supplement to the resting ECG machine. The patient can carry out all normal activities in life. The collection box is worn on the patient and can be monitored for 24/48/72 hours. The doctor can perform a full range of data through powerful analysis software Analysis; suitable for long-term cardiac monitoring, especially for some chronic heart diseases that cannot be stimulated under the condition of quiet lying down. The Stress ECG exercise electrocardiograph is a supplement to the first two electrocardiographs. The patient gradually accelerates the exercise through a treadmill or a pedal bicycle. The collection box is worn on the patient and connected to the exercise ECG analysis software on the PC to analyze the patient's exercise condition in real time. It is suitable for cardiac examinations that can only be stimulated under intense exercise. The electrophysiological signal generated in the process of cardiac depolarization and repolarization of lead lead, the positive and negative electrodes are placed at any two points on the body surface separated by a certain distance, in principle, the potential change of the ECG can be measured, and these two points constitute a lead. The Channel channel corresponds to the printing function, which refers to the maximum number of channel waveforms that can be printed at the same time during printing; the ECG machine has 12 leads, and the ECG report needs to print out all 12 leads. If printing: at most one time Print one lead, divide it into twelve groups, and complete 12 leads, which is called a single-channel electrocardiograph; print up to three leads at a time, divide it into four groups, and complete 12 leads, which is called a three-channel electrocardiograph; Print 6 leads, divide them into two groups, complete 12 leads, called 6-channel ECG machine; can complete 12-lead printing at one time, called 12-channel ECG machine; can complete 15-lead printing at one time, called 15-channel electrocardiograph; P waveP wave The electrical excitation of the normal heart starts from the sinoatrial node. Since the sinus node is located at the junction of the right atrium and the superior vena cava, the excitation of the sinoatrial node is first transmitted to the right atrium and then to the left atrium through the interatrial bundle, forming a P wave on the ECG. The P wave represents the excitation of the atrium, the first half represents the right atrial excitation, and the second half represents the left atrial excitation. The P wave duration is 0.12 seconds and the height is 0.25mv. When the atrium is enlarged and the conduction between the two chambers is abnormal, the P wave can be expressed as a high-pointed or double-peaked P wave. The QRS complexQRS complex is excited downward through the His bundle and the left and right bundle branches simultaneously activate the left and right ventricles to form a QRS complex. The QRS complex represents the depolarization of the ventricle, and the activation duration is less than 0.11 seconds. When there is conduction block of the left and right bundle branches of the heart, ventricular enlargement or hypertrophy, etc., the QRS complex appears widened, deformed, and prolonged. The T wave following the T wave represents the repolarization of the ventricle. In leads with an upward dominant QRS complex, the T wave should be in the same direction as the main QRS complex. Changes in T waves on the ECG are affected by many factors. For example, myocardial ischemia can be manifested as a low level inversion of the T wave. The towering T wave can be seen in hyperkalemia, hyperacute phase of acute myocardial infarction, etc. PR interval PR interval excitation is conducted to the atrioventricular node along the anterior, middle, and posterior interfascicular bundles. Due to the slow conduction velocity of the atrioventricular node, the PR segment on the ECG is formed, also known as the PR interval. The normal PR interval is 0.12 to 0.20 seconds. When the conduction from the atrium to the ventricle is blocked, it is manifested as a prolongation of the PR interval or the disappearance of the ventricular wave after the P wave. QT interval The QT interval represents the time from depolarization to repolarization of the ventricle. The normal QT interval is 0.44 seconds. Prolongation of the QT interval is often associated with the occurrence of malignant arrhythmias. PR segment The PR segment represents the atrial repolarization process and the electrical activity of the atrioventricular node, bundle of His, and bundle branches. ST segment ST segment ventricular myocardium is completely depolarized, and repolarization has not yet started. At this time, the ventricular myocardium at each site is in a depolarized state, and there is no potential difference between cells. Therefore, the ST segment should be on the equipotential line under normal circumstances. When there is ischemia or necrosis in a certain part of the myocardium, and there is still a potential difference in the ventricle after depolarization, it is manifested as a shift in the ST segment on the ECG. Frank system Frank lead system In 1956, Frank proposed a set of correction The orthogonal lead system has a total of 7 electrodes. Five electrodes were placed on the chest, and the other two electrodes were placed on the left foot and the back of the neck 1 cm to the right. Each electrode is connected with different resistances, which to a certain extent corrects the inhomogeneity of the heart in the thoracic cavity and the conduction of the human body. Because of its sound physical foundation and reasonable design, it is widely used in electrocardiogram technology. In order to mark the space ECG vector, it is assumed that three axes intersect each other perpendicularly in the center of the heart, and then the three axes respectively constitute the horizontal plane, sagittal plane and frontal plane of Frank's lead system. Wilson system Wilson lead system Wilson lead system is a center-end connection lead system proposed by Wilson. The probe electrode is placed on any limb of the standard lead, and the lead electrodes on the other two limbs are respectively connected with 5000 ohm resistance. connected in series as irrelevant electrodes. The ECG voltage recorded by this lead is about 50% higher than that of the unipolar limb lead, hence the name of the pressurized unipolar limb lead. Named according to the location of the probe electrode placement, if the probe electrode is on the right arm, it is the unipolar right upper extremity lead (aVR), the left arm is the compressed unipolar left upper extremity lead (aVL), and the left leg is the lead. It is a pressurized unipolar left lower extremity lead.
VCG ECG vector The potential difference formed by cardiomyocytes in the process of depolarization and repolarization has both magnitude and direction, which is called ECG vector. The electrocardiogram and the electrocardiogram are complementary and complementary to each other and used to diagnose heart disease. The ECG on a certain lead is a curve that unfolds with time t, while the vector diagram on a certain surface is a complex plane curve with t as the parameter. The vector diagram has three electrical axes X, Y, and Z, which form a plane in pairs, called the transverse plane (H), the frontal plane (F), and the right plane (s). AD converter AD conversion AD conversion is analog-to-digital conversion, which is to convert an analog signal into a digital signal, the unit is bits, and the number of bits is used to measure the conversion accuracy. Common ones are 12-bit, 16-bit, and 24-bit. Sampling rate The sampling rate is the sampling frequency, which defines the number of samples per second extracted from the continuous signal to form a discrete signal, in Hertz (Hz); the higher the frequency, the more the number of samples, and the better the accuracy. CMRR (Common mode rejection ratio) refers to the ratio of the differential mode signal (ECG signal) magnification Ad of the electrocardiograph to the common mode signal (interference and noise) magnification Ac, indicating the size of the anti-interference ability. The larger the ratio, the stronger the ability of the differential amplifier circuit to suppress common mode signals and the better the anti-interference ability. Noise level Noise level is also called internal noise. It refers to the noise generated by the electronic thermal movement when the internal components of the electrocardiograph are working, rather than the noise caused by improper use of external interference. If it is too large, it will not only affect the appearance of the graphics, but also affect the normality of the ECG. Therefore, the noise should be as small as possible, and no noise waveform should be seen in the tracing curve. Frequency response frequency range The human ECG waveform is not a single frequency, but can be decomposed into sine wave components of different frequencies and different proportions, which means that the ECG signal is rich in high-order harmonics. If the electrocardiograph has the same gain for signals of different frequencies, the traced waveform will not be distorted. However, the amplifying ability of the amplifier to signals of different frequencies is not necessarily exactly the same. When the electrocardiograph inputs signals of the same amplitude and different frequencies, the relationship between the amplitude of the output signal and the frequency is called the frequency response characteristic. The frequency response characteristics of the electrocardiograph mainly depend on the frequency response characteristics of the amplifier and recorder. The wider the frequency response, the better. Polarization voltage Polarization voltage A polarization voltage is generated between the skin and surface electrodes due to polarization. This is mainly due to the phenomenon of voltage stagnation formed after the flow of cardiac current. The polarization voltage has a great influence on the ECG measurement and will cause baseline drift and other phenomena. The highest polarization voltage can reach tens of millivolts or even hundreds of millivolts. If the polarization voltage is not handled well, the interference will be very serious. Although the electrodes used in the electrocardiograph have been made of special materials, the electrodes still generate a polarization voltage, generally 200-300mV, due to temperature changes and the influence of electric and magnetic fields. Amplifier and recording device. The requirement is greater than 300mV, and internationally it is greater than 500mV. Input impedance The input impedance is the input resistance of the pre-amplifier. The larger the input resistance, the smaller the waveform distortion caused by the different electrode contact resistance, and the higher the common mode rejection ratio. Generally, it is required to be greater than 2MΩ, and internationally, it is greater than 50MΩ. Sensitivity is also called gain; it refers to the amplitude of the recorded waveform when a 1mV standard voltage is input. It is usually expressed in mm/mV, which reflects the magnification of the amplifier of the whole machine. The standard sensitivity of the electrocardiograph is 10mm/mV. The purpose of specifying the standard sensitivity is to facilitate the comparison of various ECGs. Paper speed The paper speed is used to reflect the speed of the ECG drawing, the unit is mm/s
