4 MIN READ | Wellness

Ellen Diamond

What Is a Defibrillator and How Do They Work?

Cite This
Ellen Diamond, (2021, October 22). What Is a Defibrillator and How Do They Work?. Psychreg on Wellness. https://www.psychreg.org/what-defibrillator-how-do-they-work/
Reading Time: 4 minutes

Have you ever wondered what they’re doing in the movies when the doctor yells ‘clear!’ and delivers an electrical shock to a patient? You’ve come to the right place. 

This article discusses defibrillators and how they work. There are three main types of defibrillators, AEDs, ICDs, and WCDs. Those who get CPR certified online understand how to use an AED, but ICDs and WCDs are only used in professional settings. 

What is a defibrillator?

When the heart goes into a sudden cardiac arrest, bystanders should do three things: contact emergency response services, begin CPR, and start searching for an AED. But what is an automated external defibrillator?

The heart spasms when it goes into cardiac arrest. This spasming action interrupts the electrical signals travelling from the brain to the heart. This process is known as ventricular fibrillation. A defibrillator delivers an electric shock to the heart to restart its function and restore its natural rhythm. 

Defibrillators come in two types: automated external defibrillators and manual external defibrillators. 

Manual external defibrillators

You will likely only find a manual external defibrillator in a medical professional setting, such as an ambulance or a hospital. On the contrary, you can locate automated external defibrillators in many public places, such as schools, public transit stations, and office spaces. 

Both strive toward the same purposes using different methods, one with manual capabilities and the other designed for civilians as an automatic defibrillator. The automated external defibrillator is designed for people without a medical background to use. These defibrillators come with a pair of adhesive electrodes and a computerized system that analyzes the heart’s rhythm. 

How does an AED work?

Fibrillation can be a symptom of a heart attack or a sign of impending sudden cardiac arrest. AEDs aim to restore a normal heartbeat to a heart that has fallen out of rhythm. The device corrects the normal heart rate by generating an electrical current that passes through the heart. 

It’s important to note that the AED doesn’t ‘restart’ the heart from a dead-stop. It can restore a normal heartbeat when the heart is in defibrillation. It fixes the pacemaker (what makes the heartbeat to a specific rhythm. 

The defibrillator delivers an electric shock via a built-in battery with a high-capacity capacitor, releasing a substantial amount of electrical energy. This energy gets released into two wires, each with an ending electrode pad known as a defibrillation pad. The pads are adhesive on the AED, meaning bystanders can quickly apply them. Since they are sticky, bystanders don’t need to hold them in place. 

What is a WCD and how does it work?

Other defibrillators are internal and help prevent high-risk patients from potentially life-threatening conditions. WCDs are wearable cardioverter defibrillators that rest on the body. Their sensors attach to the skin and deliver low or high-energy shocks. 

WCDs have belts attached to a vest and you wear them underneath your clothes. Your doctor can fit the device to your size and program it to a particular heart rhythm. These sensors can detect any time an arrhythmia occurs. 

The person who wears the device can either turn off the alert to prevent a shock, but if you do not respond, the device automatically delivers a shock to correct your heart rhythm. Typically, this process occurs within a minute. The device can also deliver repeated shocks during a fibrillation episode. 

What is an ICD and how does it work?

ICDs are surgically implanted into the patient’s chest or abdomen. Once situated, the device monitors arrhythmias. Arrhythmias can interrupt the blood flow from your heart and cause your heart to stop. ICDs can give both low or high-energy shocks to correct a fast or irregular heartbeat. 

ICDs have generators connected to wires to detect your heart’s pulses and deliver shocks when needed. ICDs continuously monitor your heart’s electrical activity and your doctor can analyze the device’s readings to fine-tune your device, so it works better to correct irregular heartbeats. 

Who needs defibrillators?

  • AEDs. AEDs save the life of someone in cardiac arrest and you can use them for children and adults alike, though you will have to use special pads for children. During cardiopulmonary resuscitation or CPR, AEDs can improve their chances of survival.
  • WCDs. WCDs protect against cardiac arrest in certain circumstances. If you are at risk of arrhythmias for a shorter period, such as recovering from a heart attack, awaiting a heart transplant, or fighting an infection, WCDs are ideal.
  • ICDs. ICDs correct more severe cases of arrhythmias. These types of arrhythmias can be fatal and can develop at any age, from newborns to adults. ICDs are used for anyone with an arrhythmia that causes your heart ventricles to quiver or spasm.

Cases that call for ICDs

  • You survived cardiac arrest.
  • You developed an arrhythmia during or after treatment for a heart attack.
  • You have genetic conditions.
  • You have a neuromuscular disorder.
  • You have an abnormally slow heart rate.
  • You have cardiac sarcoidosis.
  • You have poor heart functioning.
  • Your doctor detected an arrhythmia via an EKG scan.

Takeaway: What is a defibrillator and how do they work?

Defibrillators deliver electrical signals to the body to prevent the heart from stopping. When the heart is near cardiac arrest or in ventricular defibrillation, these devices can help restore it to its normal rhythm.

There are three different types of defibrillators. However, bystanders only need to be familiar with one, the AED. Bystanders who get their online CPR certification will learn how to use an automated external defibrillator in their course. The other two defibrillators, the ICD and the WCD are used exclusively in professional medical settings, so bystanders will not need to use them. 


Ellen Diamond did her degree in psychology at the University of Edinburgh. She is interested in mental health and well-being.


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