（原创）给急救员普及的AED原理（附图，英文翻译）

AED为什么可以抢救心脏骤停 

我们在救护培训中，一定会学到如何使用AED。它是个神奇的仪器，甚至可以”起死回生”。

但是，你知道AED到底是如何工作的么？

AED的全称是自动体外除颤器。为了让没有专业医疗知识的普通人可以使用，AED比除颤器减少了许多功能。下面这两张图片是AED和医用除颤器的样子。可以看到，医用除颤器配有心电图，而这个只有专业人士才能看懂， 他们会根据波形除颤。AED自动识别波形，并用彩图和语音指引急救。举个例子，医疗剧里护士拿着两个电极板，涂上导电糊，然后贴在正在抢救的病人的身上。那个就是医用除颤仪。

In AHA’s BLS certification, you will learn how to use AED. It is such an amazing device that can restart the heart and revive people. I know all of you can operate AED well, but do you know how AED works?

Well, AED stands for Automated External Defibrillator. Because it is automated, it can be used by ordinary people. From the picture below, you can see the difference. There’s an ECG strip displaying on the defibrillator’s screen, while AED comes with a colorful screen with images and voice. It detects arrythmia automatically and provide instructions according to it. 

我们都知道AED的作用是抢救心脏骤停的患者，但是其实AED对20%的心脏骤停没有效果。AED针对的心律失常是室颤（可除颤心律）。室颤和正常心律的差别一目了然，一个很规则，一个就是毫无规律的锯齿线。心脏各个部分各做各的，心肌混乱舒张和收缩，极少的血液被泵出。这个时候，AED的作用是停止心脏。对，你没听错，停止心脏。它在一瞬间让所有心肌细胞去极化，终止了这种无规律的电活动。那么，心脏不会停跳么？不会是一条直线么？不会。只要窦房结功能是正常的，它就会自发产生下一次心搏，率领心脏进行一次有效的，协调的跳动。如图，除颤之后，心律恢复为窦性（正常）心律。

We all learned that AED’s function is to resuscitate people with cardiac arrest, but in real life, AED is ineffective with approximately 20% of the cardiac arrest patients. AED can treat people with ventricular fibrillation(shockable rhythm). According to the ECG strip down there, it is clear to see that one is chaotic and one is organized. During ventricular fibrillation, there’s chaos in the heart. Every part contract on different time, so there’s almost no blood be pumped out. We have to stop the heart with AED under this situation. What you see is right, stop the heart. You may ask:” Would the heart stop and present with a flat line?” The answer is no. As long as the SA Node is normal and can generate another impulse, the heart will not stop entirely. The picture below shows the heart rhythm changes from ventricular fibrillation to sinus(normal) rhythm after defibrillation.

而那百分之二十呢？它们是不可除颤心律，包含：无脉电活动，心室停搏和全心停搏。无脉电活动就是心电图可能完全正常，只是心脏由器质性的问题没办法产生有力的跳动。心室停搏顾名思义，心室停搏，心房没有停搏，血液输出量极少。全心停搏就是一条直线，没有地方工作。在这些情况下，AED除颤没有用，它没办法重启心脏，它的用处只有中止。在这种情况下，存活率比室颤更低，不过还是可以抢救，执行不间断的CPR。经过CPR，这些心律是有机会变成可以除颤的心律。

What about that 20% of the patients? They are with unshockable rhythm. There are three types of it: Pulseless Electrical Activity (PEA), Ventricular Standstill, and asystole. PEA patients can have a completely normal ECG, but with no effective contractions. Ventricular Standstill means the ventricle stops beating but the atria keeps contracting. In this way, the cardiac output is extremely low and not enough for body to use. Asystole’s ECG is a fine flat line, no parts of the heart is contracting at all. In these situations, defibrillation of AED does not work, it cannot restart the heart. In theses situations, the survival rate is low, but we can still resuscitate and execute CPR without stopping. We have a small chance to turn these into shockable rhythm and defibrillate.

没有提及室速，和濒死心律（Agonal) ，和同步电复律。为了让内容更加精简，有大佬提一提建议么。