What is an implantable cardioverter-defibrillator (ICD)?

Jun 24, 2020 | Katrina Sorensen, Research Coordinator | @katrinasorensen | Comments (2)


What is an implantable cardioverter-defibrillator (ICD)?

An implantable cardioverter-defibrillator (ICD) is a small, battery-powered device surgically placed in a patient's chest to monitor and detect irregular heartbeats (arrhythmias). If an ICD detects a dangerous heart rhythm, it delivers an electric shock via one or more wires (leads) connected to the heart to restore its regular rhythm.

How does an implantable cardioverter-defibrillator (ICD) work?

When an ICD detects a dangerous heart rhythm, it sends an electrical pulse to the heart. An ICD can be programmed by a physician for different things.

  1. Low-energy pacing: This is used when the ICD senses a mild disruption in a heart's rhythm. It sends regular pulses to "pace" the heart and return it to normal. Most patients don't feel anything when they are being paced.
  2. High-energy shock: This is for more serious heart rhythms or if the heart stops completely. A strong shock is delivered to restart the heart or return it to a normal rhythm. Because a patient's heart isn't working properly, they often pass out and are unconscious for a high-energy shock. It is possible for a patient to be awake. If the patient is awake, the shock can be painful; it is often described as feeling like a kick to the chest. Usually, only one shock is needed to restore a normal heartbeat. However, some patients can experience two or more shocks if their heartbeat doesn't return to normal.

If an ICD needs to restore a normal heartbeat, whether with low-energy pacing or a high-energy shock, the heart rhythm is recorded. This is transmitted to a device specialist for interpretation and communicated to the patient's physician.

Are there different kinds of implantable cardiovertS-ICDer-defibrillators (ICDs)?

Yes. Standard ICDs are surgically placed under the skin, usually just below the left collarbone, and one or more flexible leads run from the ICD through the veins to the heart (pictured above).

A subcutaneous ICD (S-ICD) is a newer type of ICD. An S-ICD is implanted under the skin at the side of the chest below the armpit (pictured right). Instead of having leads inserted into the heart, it is attached to one long electrode that runs along the patient's breastbone. An S-ICD is less invasive than a traditional ICD.

Is an implantable cardioverter-defibrillator (ICD) different than a pacemaker?

Yes. A pacemaker is a small device implanted in a patient's chest that is able to regulate a heartbeat by pacing. Unlike an ICD, a pacemaker is unable to shock a heart.

Are there risks involved with an implantable cardioverter-defibrillator (ICD)?

Yes. Risks during implantation are uncommon, but can include:

  • Infection at the implant site
  • Allergic reaction to the medications used during the procedure
  • Swelling, bleeding or bruising where your ICD was implanted
  • Damage to the vein where your ICD leads are placed
  • Bleeding around your heart, which can be life-threatening
  • Blood leaking through the heart valve where the ICD lead is placed
  • Collapsed lung (pneumothorax)

There is also the possibility that the device stops working properly or can malfunction. If the ICD missenses a heart rhythm, it can deliver a shock to the heart when a shock isn't necessary. This is called an inappropriate shock. An inappropriate shock can also happen if a lead breaks in the heart. There are ways to turn off an ICD if there is a malfunction until the ICD can be repaired or replaced.

Does an implantable cardioverter-defibrillator (ICD) battery run out?

Yes. An ICD uses a lithium battery. Depending on how often the ICD is activated, the battery can last up to seven years. Patients with ICDs generally have six-month checkups where their battery level is checked. Once the battery runs low, the old generator is replaced with a new one during a minor procedure.

Who needs an implantable cardioverter-defibrillator (ICD)?

This is a hard question to answer and varies greatly depending on who you speak to. Generally, patients who have an ICD have survived a cardiac arrest or have fainted due to a confirmed, dangerous arrhythmia. For more information about who should and shouldn't get an ICD, you can view these videos by Dr. Ackerman.

Cardiac Channelopathies and ICDs

"Most patients with a cardiac channelopathy do not need an ICD."

Avoiding ICD Implantation in Primary Electrical Disease

Meet other people talking about genetic heart disorders and ICDs on Mayo Clinic Connect. Join the Heart Rhythm Conditions group to join the conversation, share experiences, ask questions, and discover your support network.

For up-to-date information, please follow Dr. Ackerman and the Windland Smith Rice Genetic Heart Rhythm Clinic on Twitter by clicking the links below.


Interested in more newsfeed posts like this? Go to the Genetic Heart Rhythm Diseases blog.

Is A-Fib a primary electrical disease ?


Is A-Fib a primary electrical disease ?

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Hi @phillipdobrien, welcome to Mayo Clinic Connect. Arrhythmias are due to electrical signal disturbances of the heart. You can find out more here:
– Atrial fibrillation https://www.mayoclinic.org/diseases-conditions/atrial-fibrillation/symptoms-causes/syc-20350624

You may also be interested in connecting with other people who live with afib in the Heart Rhythm Conditions group: https://connect.mayoclinic.org/group/heart-rhythm-conditions/

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