The heart, like industrial pumps, air pumps, oil pumps, etc., are a class of power pumps with the ability to transmit fluids. Unlike a mechanical pump, which is a device that drives fluid in one direction, the heart is a muscular pump located in the human body that squeezes blood out of the heart by muscle contraction and valve activity to move it in one direction. Unlike the mechanical pump, which is driven by electricity or other power to drive fluid in one direction without stopping, the heart is driven by muscle contraction (narrowing, tightening) to drive blood out of the arteries of the heart, after which the heart dilates (expands, relaxes) to accept blood inflow from the veins, and when the diastole ends, it starts again with the next cycle of contraction activity, thus forming the circulation of blood in the body. flow. Unlike the mechanical pump, the process of transferring blood to the veins is not continuous, but intermittent, meaning that only during systole does blood from the heart flow to the arteries, and during diastole no blood flows to the arteries. What initiates the contraction of the heart? Electricity. It is well known that when an electric current stimulates a muscle, the muscle contracts. The heart has a node called the sinus node, which is specifically responsible for the intermittent emission of electrical impulses (pacing point), which are transmitted successively to the atria and ventricles, causing them to contract. Along with this periodic electrical change in the heart, which is transmitted not only in the human heart, but also on the surface of the body, causing changes in the electrocardiographic bioelectricity, which can be recorded from the body surface potential changes graphically through the electrocardiographic tracer, which represents the electrocardiogram graph ( ECG for short). ECG is usually recorded on a special ECG recording paper. We all know that the paper is moving when doing ECG, the paper speed is 25mm/sec, so the width on the horizontal line represents the length of time, called the time line, a small frame for 0.04 seconds (s), imagine that 1 large frame for 5 small frames is 0.2 seconds, 1 second is 5 large frames. The vertical line represents the voltage, also called voltage line, in fact, and our daily use of electricity, the voltage used for electric lights is 220 volts, the voltage of cell phone electricity is 3.7 volts, etc.. However, the voltage of ECG is much smaller. 1 small cell in the longitudinal direction of ECG paper is 0.1 mV (1 volt = 1000 mV), and 10 small cells or two large cells are 1 mV (mV). Below is a blank ECG paper. Normal ECG When looking at an ECG, it is important to know the normal chart first. The first wave semicircular is P wave, caused by atrial activity; the second Q wave, direction downward, mostly seen in abnormal graphs, normal can be without this wave; the third R wave, direction upward; the fourth S wave, direction downward; the first three can appear in a very short period of time, so they can also be commonly called QRS wave group; the fifth wave is T wave. Due to the different angular electrode placement for measuring ECG, different graphs, that is, different leads, will appear. It will not be detailed here. From the above, it is easy to see that ECG is a continuous record of the electrical changes on the surface of the heart from the electrical impulses spontaneously emitted by the heart is the ECG. It is a functional examination of the electrical activity of the heart, such as our house, which plays the role of being evaluated such as electrical wiring appliances, less accurate and intuitive than imaging methods, the latter is to evaluate the structure of the heart, like our usual house where there is a wall and where there is a door that can be seen exactly. Clinically, it is called the anatomical structure of the heart. However, ECG has its own unique advantages, the main advantage is that it has been used in medicine for a long time, its results are easy to judge, fast, easy and inexpensive, it still has some application in the initial screening on the diagnosis of precardiac disease, and it is listed as a mandatory test before and after surgery. By doing ECG, congenital heart disease can be screened out, and one or several chambers of the heart can be indirectly judged to be hypertrophically enlarged according to voltage changes, and abnormalities in electrical conduction pathways accompanying congenital heart disease patients can also be detected, which is equivalent to laying the wrong wires and placing the wrong appliances in your home. Therefore, the use of ECG in combination with other imaging tests can accurately determine the diagnosis of heart disease. ECG is a fairly good adjunctive test to determine congenital heart disease. It is important to note that a normal ECG does not exclude congenital heart disease. It is equivalent to having the right electrical circuit in your house renovation and not being completely sure that there are holes in the walls of the house, too wide door gaps, etc.