What is a Defibrillator? Types, Uses, & Considerations

The heart muscle pumps blood to the rest of the body by an electrical conduction system that coordinates the contraction of the four chambers of the heart (the two upper chambers called the right and left atrium and the two lower chambers called the right and left ventricle). This electrical system helps to control the timing of the heartbeat and the heart rhythm. It is responsible for the synchronized pumping of the heart’s chambers, which is called the normal sinus rhythm.

A defibrillator is a device that detects an arrhythmia and delivers an electrical shock to the heart. It can stop an abnormal rhythm and make the heart go back to a normal rhythm. It can also restart a heart that has suddenly stopped beating.

A defibrillator can save lives in people with potentially fatal ventricular arrhythmias (heart rhythm abnormalities) called ventricular tachycardia (VT) and ventricular fibrillation (VF). These are fast or irregular heartbeats that start in the lower chambers of the heart (the ventricles). 

In people experiencing cardiac arrest, the controlled electric shock from a defibrillator can restart the heart and prevent sudden cardiac death.

Types of Defibrillators

Manual External Defibrillators (MEDs)

A manual external defibrillator (MED) consists of a pair of hand paddles connected with wires to a machine and monitor. 

It is designed for use by trained medical personnel and is typically stored in a crash cart in the hospital. A MED has several treatment modes and allows doctors to assess how much electric shock energy should be delivered to a patient with an abnormal heart rhythm and when and how many shocks should be administered. It can perform both defibrillation and synchronized cardioversion, and some models might include advanced monitoring features such as ECG, pacemaker function, and capnography.

You may have seen manual defibrillation being performed in movies and TV shows where an emergency room doctor places the defibrillator paddles on a person’s chest and yells “Clear!” before delivering an electrical shock.

Automated External Defibrillators (AEDs)

An automated external defibrillator (AED) is a small, lightweight, portable device that is available in many public places, such as airports, malls, and schools. It can be used to treat a person experiencing a sudden cardiac arrest, a life-threatening emergency where the heart suddenly stops working. 

Even people without any medical training can use an AED and save a life. The device automatically analyzes a person’s heart rhythm and provides verbal instructions to bystanders about when and how to use it. An AED alone may not be enough to restart the heart immediately, so CPR must be performed to help maintain circulation until a normal rhythm is restored.

Healthcare providers sometimes recommend having a personal defibrillator (AED) at home for people who are at risk of sudden cardiac arrest due to severe heart disease.

Implantable Cardioverter Defibrillators (ICDs)

An implantable cardioverter-defibrillator (ICD) is a small device that is placed in a person’s chest under the skin. It consists of a battery-powered pulse generator and electrodes (also called leads) that connect the device to the heart. It continuously monitors heart rhythms and is used for patients with a history of sudden cardiac arrest, ventricular arrhythmias, and genetic arrhythmia syndromes. Patients at high risk of arrhythmias with advanced heart failure or hypertrophic cardiomyopathy are also candidates for this device.

An ICD can detect a life-threatening abnormal heart rhythm (arrhythmia) and quickly send an electric shock to the heart to convert it back to normal rhythm. Most ICDs have a built-in pacemaker that can pace the heart (correct a slow or fast heartbeat).

These implantable devices are of two types:

• Transvenous ICDs in which the defibrillator generator is placed under the collarbone and above the breastbone on the left side of the chest. The electrodes (ICD wires) are threaded through a vein to connect the device to the heart.

• Subcutaneous ICDs in which the pulse generator is implanted under the skin, but the leads are not in direct contact with the heart.

Note: ICD surgery for a transvenous ICD is a minimally invasive procedure done using local anesthesia. Most patients can go home the same day. A subcutaneous ICD is implanted under the skin using general anesthesia. Batteries need replacement every 8-13 years. 

Wearable Defibrillators

A wearable defibrillator, such as LifeVest, is a garment that functions as a continuous electrocardiogram (EKG or ECG) monitor. It is worn under your clothes and removed only while bathing. The vest contains electrodes that constantly monitor your heartbeat and detect abnormal electrical signals. It delivers an electric shock if an abnormal heart rhythm is detected. The device also has a monitor that can be worn with a shoulder strap or around the waist. It is worn by patients who are at a high risk for sudden cardiac arrest but are not yet candidates for an ICD. 

When the wearable defibrillator detects life-threatening arrhythmias, it sounds an alarm. If you are conscious, you have about 1 minute to press buttons and stop the treatment. If you are not responsive, the device warns bystanders that it is going to deliver an electric shock so they don’t touch you. 

What Exactly Does a Defibrillator Do?

Defibrillators monitor a person’s heartbeat and deliver an electric charge if they detect an abnormal heart rhythm or cardiac arrest. This can restore a normal heart rhythm or restart a heart that has stopped beating.

Process of Defibrillation

The process of defibrillation is the delivery of an electrical shock across the chest wall. It is done using a pair of manual paddles or adhesive hands-free pads in the hospital by healthcare professionals. The American Heart Association (AHA) guidelines are to use the manufacturer’s recommended dose for the first defibrillation shock or the maximum dose if instructions are unavailable. 

An electrical shock is delivered once healthcare providers have ensured no one is touching the patient or is in contact with anything touching the patient. 

After the electrical charge is delivered, CPR is immediately resumed. If the patient continues to have ventricular fibrillation or pulseless ventricular tachycardia, they may be shocked again. It is important to follow Advanced Cardiac Life Support (ACLS) guidelines to improve the chances of restoring a normal rhythm.

Is A Pacemaker The Same As A Defibrillator?

A pacemaker and a defibrillator are both implanted devices that help maintain a normal heart rhythm. A pacemaker regulates the heart's rhythm continuously, while a defibrillator only delivers a shock when the heart's rhythm is dangerously abnormal. Many implantable cardioverter-defibrillators (ICDs) have an in-built pacemaker. A patient might require the capabilities of both devices, which are usually supplied as an ICD with a built-in pacemaker or pacing capability. 

Usage Guidelines and Applications

When to Use a Defibrillator

You should only use a defibrillator (automated external defibrillator or AED) if a person’s heart has suddenly stopped beating and they are experiencing a sudden cardiac arrest. Symptoms of sudden cardiac arrest include: 

• Not breathing

• No pulse

• Unresponsive

• Unconscious

Step-by-Step Usage Instructions

1. Recognize cardiac arrest (see the signs and symptoms listed above).

2. Call emergency services if a patient is experiencing cardiac arrest.

3. Start and continue cardiopulmonary resuscitation (CPR).

4. Find the nearest AED.

5. Attach the two adhesive pads (electrodes) of the AED to the person’s bare and dry chest.

6. Switch on the AED and follow the verbal instructions.

The AED will analyze the heart’s electrical rhythm and respond with a shock if a life-threatening abnormal rhythm is detected (Pulseless Ventricular Tachycardia or Ventricular Fibrillation). Some devices tell bystanders not to touch the person while the shock is delivered automatically. Others tell bystanders to press a button on the device to deliver the shock. After the shock is delivered, the AED will tell rescuers to resume CPR. After 2 minutes, the AED will tell rescuers not to touch the person while it rechecks the person’s heart rhythm again. If needed, it will give a further shock.

Locations and Accessibility

Many public locations have a sign identifying the nearest AED. AEDs are usually stored in a white case with the words “AED” in large red letters, along with a red heart and lightning bolt. The 911 operator can also tell you the nearest AED location.

Benefits and Risks of Defibrillator Use

Benefits

Defibrillators protect people from dangerous, potentially fatal heart rhythms that can result in sudden death. Immediate CPR and the use of an AED can double or triple survival rates in people experiencing a cardiac arrest. Therefore, a defibrillator can save your life if you have a heart problem (abnormal rhythm) or cardiac arrest outside a hospital setting.

Potential Risks

ICD surgery is a low-risk procedure. Potential risks include heart valve infections, bleeding, or damage to the heart or lungs, but these are rare. Sometimes, the device can deliver an inappropriate shock, but again, this is uncommon. 

Rarely, the high energy shock from an AED can cause minor skin burns or tissue damage on the chest wall where the pads are placed. 

In some cases, the electrical current delivered by a defibrillator can lead to other types of arrhythmias or irregular heart rhythms, but this is extremely rare.

Some people receive shocks from their defibrillators without realizing it during sleep. The device can directly report this to the physician if there is an event detected. If a defibrillation shock occurs while the person is aware, it can be an intense sensation. Some people describe it as a feeling of being kicked in the chest. ICD shocks can cause anxiety and PTSD in some patients.

Long-Term Implications

Most patients can lead relatively normal lives with a defibrillator. There are no special precautions, including while going through airport security and getting MRI scans. You will, however, need to see your healthcare professional for regular checkups every 3-6 months. Your doctor (cardiologist or electrophysiologist) will check your ICD’s battery, lead integrity, and pacing thresholds. They will retrieve data on arrhythmias and delivered shocks and discuss any necessary treatment changes. Most ICDs have a battery life of 8 to 13 years. When a battery is nearing depletion, the provider will schedule a procedure to replace the device.

Some precautions for people with an ICD include:

• Stay away from high-arc welding equipment.

• Keep an arm’s distance from strong magnets, such as an induction stove.

• Avoid putting a cell phone within 6 inches of your defibrillator.

• Tell your doctors you have a defibrillator before any cancer radiation treatment.

Getting a Defibrillator: Key Considerations

Why Would A Person Get A Defibrillator?

Doctors usually recommend a defibrillator to people who are at a high risk of fatal ventricular fibrillation or ventricular tachycardia event. This way, if an event were to occur, the ICD can identify the arrhythmia and treat it with resynchronization of the heart’s rhythm. People who have never had an arrhythmia event but have risk factors can receive a defibrillator proactively based on their risk profile. Patients with advanced heart failure, hypertrophic or dilated cardiomyopathy, personal history of sudden cardiac arrest or syncope due to VT or VF, as well as genetic syndromes causing arrhythmias are candidates for a defibrillator.

Factors to Consider

Before recommending an ICD, your cardiologist or electrophysiology physician will likely try medications to improve heart function and lower the risk of dangerous arrhythmias. If medications don’t help in restoring a regular rhythm, they may suggest getting a defibrillator. However, there are situations that are directly indicative of ICD based on the high risk of life-threatening arrhythmia.