- The definition of an electrocardiogram.
Electrocardiography (electrocardiogram, ECG or EKG) is a kind of diagnosis and treatment technique which records the electrophysiological activity of the heart in units of time through the chest and cavity and records it through the electrode on the skin. This is a non-invasive recording method.
- How ECG works.
The working principle of ECG is simply as follows: every time the heartbeat cardiomyocytes are depolarized, they cause a little electrical change on the surface of the skin. This small change is captured by the electrocardiograph and amplified to depict the electrocardiogram. When the cardiomyocytes are in a resting state, there is a potential difference formed by the difference of positive and negative ion concentration on both sides of the myocardial cell membrane. Depolarization is a process in which the myocardial cell potential difference rapidly changes to 0 and causes myocardial cell contraction. In a cardiac cycle of a healthy heart, the depolarized waves produced by the sinoatrial node cells are sequentially transmitted in the heart, first to the entire atrium, and propagate through the “inner conduction pathway” to the ventricles. If two electrodes are placed on either side of the heart, a small voltage change between the two electrodes can be recorded during this process and can be displayed on an ECG drawing or monitor. The electrocardiogram can reflect the rhythm of the entire heartbeat and the heart muscle’s weak part.
Usually, more than two electrodes can be placed on the limb, and they are paired for measurement (such as left arm electrode (LA), right arm electrode (RA), left leg electrode (LL) can be combined like this: LA+RA, LA+LL, RA+LL. The output signal of each electrode pair is referred to as a set of leads. The lead is simply to look at changes in heart current from different angles. The types of electrocardiograms can be distinguished by leads, such as 3-lead ECG, 5-lead ECG, and 12-lead ECG, and so on. The 12-lead ECG is the most common clinical type. It can simultaneously record the electrical changes of the 12 groups of leads in the body surface, and draw 12 sets of lead signals on the ECG drawings, which are often used for one-time ECG diagnosis. 3-lead and 5-lead ECGs are often used to continuously detect ECG activity through a monitor, such as during surgery or during ambulance transport. Depending on the instrument, the results of this continuous monitoring may not be fully documented at sometimes.
The heart is a three-dimensional structure. In order to reflect the electrical activity of different parts of the heart, electrodes are placed in different parts of the body to record and reflect the electrical activity of the heart. In routine electrocardiography, only 4 limb lead electrodes and V1 to V6 thoracic lead electrodes are usually placed, and a conventional 12-lead electrocardiogram is recorded.
- The application of ECG.
An electrocardiogram is one of the most commonly used tests in the clinic, and its wide range of applications as follows:
（1）Record the electrical activity of the normal heart of the human body.
（2）Help diagnoses an arrhythmia.
（3）Help diagnoses myocardial ischemia, myocardial infarction, and its location.
（4）Diagnose the heart to enlarge and hypertrophy.
（5）Determine the effect of the drug or electrolyte on the heart.
（6）Determine the artificial heart pacing condition.