Electrocardiography (Electrocardiography, ECG, or EKG) is a diagnosis and treatment technique that records the electrophysiological activity of the heart in units of time through the body wall, and captures and records it through electrodes that touch the skin. This is a non-invasive recording method. The etymology of Electrocardiography comes from three Greek words: “electro”, because it is related to electrophysiological activities, “cardio”, the Greek “heart”, and “graph”, a Greek root meaning: “description” .
The working principle of the electrocardiogram: each time the heartbeat depolarization of the myocardial cells will cause a small electrical change on the skin surface, this small change is captured by the electrocardiogram recording device and magnified to describe the electrocardiogram. When the cardiomyocytes are in a resting state, there is a potential difference formed by the difference in the concentration of positive and negative ions on both sides of the myocardial cell membrane. Depolarization is the process in which the potential difference of the cardiomyocytes rapidly changes to zero and causes the myocardial cells to contract. In a cardiac cycle of a healthy heart, the depolarization waves generated by the sinoatrial node cells propagate in the heart in an orderly manner, first to the entire atrium, and then to the ventricle through the “internal conduction pathway”. If two electrodes are placed on any two sides of the heart, then the minute voltage changes between the two electrodes can be recorded during this process and can be displayed on the ECG paper or monitor. The electrocardiogram can reflect the rhythm of the entire heart beat, as well as the weak part of the heart muscle.
Usually more than 2 electrodes can be placed on the limbs, and they can be used as a pair for measurement (such as the left arm electrode (LA), the right arm electrode (RA), and the left leg electrode (LL) can be combined as follows: LA+RA, LA+LL, RA+LL). The output signal of each electrode pair is called a set of leads. Simply put, the lead is to look at the changes in the heart current from different angles. The types of ECG can be distinguished by leads, such as 3-lead ECG, 5-lead ECG and 12-lead ECG, etc. The 12-lead electrocardiogram is the most common type in clinical practice. It can record the potential changes of 12 sets of leads on the body surface at the same time, and depict the 12 sets of lead signals on the electrocardiogram. It is often used for one-time electrocardiogram diagnosis. 3-lead and 5-lead electrocardiograms are mostly used in situations where the electrical activity of the heart needs to be continuously monitored by a monitor, such as during surgery or during monitoring during ambulance transfer of patients. Depending on the instrument, the results of this continuous monitoring may sometimes not be recorded completely.
The electrocardiogram is the best way to measure and diagnose abnormal heart rhythms. It is used to diagnose abnormal heart rhythms when the electrical conduction tissue of the heart is damaged, as well as changes in heart rhythm caused by electrolyte imbalance. In the diagnosis of myocardial infarction (MI), it can specifically distinguish the area of myocardial infarction (but not all changes in the electrical activity of the heart can be recorded). The electrocardiogram cannot fully assess the pumping ability of the heart, which is usually done by echocardiography or nuclear medicine. In some cases, patients with normal ECG images may have cardiac arrest (a condition called electromechanical separation).
