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What Is a Defibrillator and How Does It Work?

What Is a Defibrillator and How Does It Work?

A defibrillator is a device used in emergencies to restore the normal rhythm of the heart. This happens in a situation when the heart has stopped beating due to a sudden cardiac arrest or is beating irregularly due to ventricular fibrillation or other types of arrhythmia.

A study by the U.S. National Institutes of Health has shown that individuals have better chances of surviving a sudden cardiac arrest if a defibrillator is used by a bystander while waiting for EMTs to arrive. Up to 1,700 additional lives are saved by bystanders’ use of defibrillators yearly in the U.S. alone.

Below, we’ll explore the defibrillation treatment in-depth and explain how defibrillators work and help in critical situations.

What Is a Defibrillator?

So, what is a defibrillator and how does it work? Defibrillators are machines that shock or discharge an electric shock or current to the heart to get it to beat normally again.

A defibrillator can be used to help or correct ventricular fibrillation or heart arrhythmia, which are irregular heartbeats that manifest as too-slow, too-fast, or out-of-rhythm beating of the heart.

Defibrillators are used in emergencies when the heart’s electrical system malfunctions and causes the heart to stop beating or to beat irregularly. This condition is known as sudden cardiac arrest, and a defibrillator is used to treat and restart an abruptly stopped pulse.

How Do Defibrillators Work?

Defibrillators work by delivering an electric shock or current to the heart, which depolarizes the heart muscle cells and resets the heart’s electrical rhythm. The electric shock is delivered through two electrode shock paddles that are placed on the chest of the patient.

The shock paddles detect the heart’s electrical activity and deliver a shock if necessary. This is done by its built-in computer, which analyzes the patient’s heart rhythm. After the shock is delivered, the defibrillator re-analyzes the patient’s heart rhythm and determines if another shock is required.

A key component for a defibrillator device is a capacitor, which is used to store built-up energy in the form of an electrical charge, which is then released in a short period. There are two distinct types of electrical energy mechanisms for a defibrillator device, presented below:

    • Monophasic defibrillators utilize electrical current flow in one direction, and the recommended dose for electrical shocks is around 360 joules.

Types of Defibrillators

There are three types of defibrillators available on the market:

    • Automated external defibrillators (AEDs)

    • Implantable cardioverter defibrillators (ICDs)

    • Wearable cardioverter defibrillators (WCDs).

All types of defibrillators work in different ways, and each is presented below in more detail:

External Defibrillators

External defibrillators, also known as automated external defibrillators (AEDs), are the most common type of defibrillator used in emergency situations. External defibrillators are portable devices that can be found in public places such as airports, shopping malls, sports facilities, workplaces, retirement homes, and other public spots.

Since an external defibrillator can now be found in a lot of public spaces, the odds of cardiac arrest victims surviving a sudden out-of-the-hospital cardiac arrest have increased in the past decade. That is why AEDs are often referred to as life-saving devices.

In addition, AEDs are specifically made to have easy and simple use that requires minimal training so that anyone can use them and save a life. Even untrained bystanders are able to operate these first-aid devices if an emergency arises.

Implantable Cardioverter Defibrillators

Implantable cardioverter defibrillators (ICDs) are surgically placed defibrillators inside your body or under the skin and are used to treat patients with a high risk of sudden cardiac arrest.

Implantable defibrillators continuously monitor the patient’s heart rhythm and deliver an electric shock if necessary, and are typically used in patients with heart conditions such as heart failure, ventricular fibrillation, or other forms of arrhythmia.

This type of defibrillator is used as a prevention measure against sudden death for individuals with a high risk of a life-threatening heart condition. In addition, ICDs are used as an after-heart attack treatment; in cases of congenital heart disease, inherited conduction disorder, neuromuscular disorder, cardiac sarcoidosis, and for improving heart function and blood flow.

Wearable Cardioverter Defibrillators

Wearable cardioverter defibrillators (WCDs) are portable devices that rest outside the body. Like ICDs, they are used to monitor heart rhythms and deliver electrical shocks to the heart to correct potentially life-threatening arrhythmias or other heart conditions.

WCDs can deliver a shock within seconds of detecting an abnormal rhythm, record the heart activity of the patient, and transmit the data to the patient’s healthcare provider for further analysis.

These devices, worn typically over the chest, are prescribed as a temporary measure for patients at risk of sudden cardiac arrest but are still not suitable for patients requiring an implantable cardioverter defibrillator (ICD).

WCDs are often prescribed for patients with acute myocardial infarction and heart failure. They are sometimes applicable after a recent cardiac surgery or other cardiac conditions that may increase the risk of cardiac arrest.

While WCDs are very useful, getting used to living with a wearable defibrillator can be difficult. WCDs are no substitute for long-term therapy with an ICD or other interventions to manage underlying cardiac conditions.

Who Can Use a Defibrillator?

Defibrillators can be used by anyone, regardless of their training or experience. That includes trained medical professionals to non-medical personnel that have been familiarized with basic knowledge of how to operate an automated external defibrillator (AED).

However, it is recommended that individuals receive some basic training on how to use a defibrillator properly or follow the user’s manual carefully. Most AEDs come with voice prompts and even visual guides with step-by-step instructions on how to save a life with an AED device. Many public places that have defibrillators also have instructions on how to use them.

In addition, many organizations offer training courses on how to use a defibrillator. In recent years, automated external defibrillators (AEDs) have become more widely available in public places to secure the possibility of a timely response in an emergency if someone witnesses a sudden cardiac arrest.

When to Use a Defibrillator if an Emergency Arises

In a cardiac arrest emergency, the first step to take as a bystander is to call 911. After that, you should administer CPR (it doesn’t matter if you aren’t trained) and use an AED if present on the premises. If not, wait for EMTs to arrive.

The external defibrillator comes with specific instructions that should be followed to analyze the heart rhythm and determine if an electric shock is needed. If there is a need for an electrical shock treatment, the device will guide the user on how to administer it safely and effectively.

With more AEDs available in public places and increased awareness of how to use them, more lives can be saved in cases of out-of-the-hospital cardiac arrest, which reach a number of 350,000 people each year in the U.S. alone.


So, what is a defibrillator and how does it work? A defibrillator is a medical device used to treat sudden cardiac arrest by delivering electric shocks or currents to the heart. This is done according to a careful analysis of the heart’s rhythm.

An external defibrillator can often be found in public places and can be used by both medical professionals as well as non-medical personnel or even bystanders who have basic knowledge of how to operate an AED device.

When using an external defibrillator, it is vital to abide by the provided instructions to ensure the device is operated safely and effectively. In addition, it is also crucial to call for emergency medical services and perform CPR before using a defibrillator, as these actions can increase the chances of survival.

The other two types of defibrillators, implantable cardioverter-defibrillators (ICDs) and wearable cardioverter defibrillators (WCDs), are both implant types of defibrillators, either in or outside the body.

All the defibrillator types are life-saving devices that can help restore a normal heartbeat in cases of sudden cardiac arrest and potentially save lives. Therefore, it’s crucial to raise awareness and get more people familiarized with these life-saving devices.