The concept and application of AED: Why does "energizing the body" save a life?
"Scenario" for AED: Cardiac arrest
When we encounter an emergency where we cannot feel the pulse of the people around us, there is a high chance of a so-called "Cardiac Arrest". The causes of cardiac arrest are mainly divided into "heart failure" (no heartbeat or weak force) and "abnormal heart rhythm"; the former mainly relies on CPR, and the latter mainly requires the assistance of AED.
The automatic external defibrillator, referred to as AED (Automated External Defibrillator), has the main function of "defibrillation", that is, to eliminate abnormal "shakes". To "rectify" the heart "strong enough but the rhythm is abnormal", that is, the abnormal heart rhythm.
Conceptually, just like when the picture tube TV signal was unclear when I was a child, I used the percussion to make the TV clearer. When encountering abnormal discharge, use external force to rectify. The external force in the AED is "high voltage", which normalizes the heartbeat through discharge and returns to a more normal heart rhythm.
So how does the "defibrillator" achieve rectification? At present, most of the researches believe that the cardiomyocytes are driven by electricity to reset the electric potential (depolarization) in the cells together with this high-voltage electricity. With powerful electrical currents, our bodies are forced to reset the electrical currents in the heart muscle.
Why does this approach work? We can look at the concept of "rectification" in this way: I still remember that before the flag was raised when I was a child, there was always a lot of noise in the class, and I had to ask the teacher to shout before I could calm down and queue up. The noisy children here are like unruly cardiomyocytes; the teacher's instructions are like the electric shock of the AED, forcing us to be quiet and follow the rules.
Use external force to make the irregular and turbulent state quiet and disciplined. The "external force" here can be simple and rude (such as teacher's instructions, AED's current, etc.), which can be effective in a very short time with limited resources. In addition, it can also be a "guide" type that is less prone to rejection and side effects, and it takes more time accordingly. As common as a traffic light to tell drivers, or a sheepdog leading a flock. Later, when many small individuals are out of control, you can think and design from this perspective.
The ECG signal usually returns to normal after the AED shock, but the strength is often still insufficient. This returns to another condition of cardiac arrest: insufficient heart strength. This is also why after using AED, we have to rely on CPR and other actions to help pump blood from the heart to the whole body.
What are the possible causes of "irregular heart rhythm"? The main problem is that there is a problem with the signal conduction between the brain and the heart. There is noise in the electrical nerve signals, causing an unstable heart rhythm. So from another perspective, the defibrillator helps to "reset the current" (Reset). Therefore, if there is a problem in the conduction path, such as the current failure, making it difficult for the signal to reach the heart, then the defibrillator cannot help.
