Implantable Cardioverter Defibrillator (ICD)

What Is an Implantable Cardioverter Defibrillator (ICD) ?

An ICD is a small device which can treat people with dangerously abnormal heart rhythms.

It sends electrical pulses to regulate abnormal heart rhythms, especially those that could be dangerous and cause a cardiac arrest.

The heart has it’s own electrical system that regulates the heartbeat. With every heartbeat, there’s an electrical signal that follows through your heart, causing it to contract and pump blood. If this doesn’t happen properly, you could have an abnormal heart rhythm (or arrhythmia) and you may need an ICD fitted.


An ICD is placed under the skin, usually in the space just below the collar bone (clavicle) to monitor your heart rate. Thin wires connect the ICD to the heart, where its always checking your heart rate and rhythm. It monitors your heart rhythm through the electrodes.

If an ICD notices a dangerous heart rhythm it can deliver one or more of the following treatments:

  • Pacing – a series of low-voltage electrical impulses (paced beats) at a fast rate to try and correct the heart rhythm.
  • Cardioversion – one or more small electric shocks to try and restore the heart to a normal rhythm.
  • Defibrillation – one or more larger electric shocks to try and restore the heart to a normal rhythm.

ICDs are inserted under local anaesthetic, but with sedation, so you will feel very sleepy. It can take anything from one hour to three or more hours to implant an ICD, and the time it takes will depend on the type of device you’re having. You will often (but not always) need to stay overnight in hospital and your ICD will be checked thoroughly before you leave.

The ICD is inserted just under your collar bone. It looks similar to a pacemaker and is a little bigger than a matchbox. 

An ICD is made up of:
  • a pulse generator – a battery powered electronic circuit
  • one or more electrode leads, which are placed into your heart through a vein.

A different type of ICD is suitable for some people. It’s called a subcutaneous (under the skin) ICD – or SICD for short. An SICD works in the same way as an ICD, but it’s inserted under the skin of the chest (outside of the ribcage) and there are no leads placed into the heart. Your doctor will talk to you about this option if it’s right for you.


You might need an ICD if:

  • you have already had a life-threatening abnormal heart rhythm and are at risk of having it again
  • you haven’t had a life-threatening heart rhythm, but tests show you are at risk of one in the future. This is usually because you have inherited faulty genes and may have a condition such as Cardiomyopathy, Long QT syndrome or Brugada syndrome
  • you have heart failure and are at risk of developing a life-threatening heart rhythm. This is called cardiac resynchronisation therapy with a defibrillator, or CRT-D. This single device combines a pacemaker with an ICD. The leads and the CRT-D work together to make sure that the ventricles beat in time. 

It’s important to have regular follow-up appointments at your ICD clinic, so you can have your ICD checked. Your appointments may be every 3 to 12 months, depending on the type of ICD you have and if it has delivered any treatment. You’ll need to have follow-up appointments for the rest of your life.

Some ICD checks may be done remotely with the information from your ICD sent via a signal on the device or a home docking station to your health care professional, so there is sometimes no need to attend hospital.

You may have to make some changes to your lifestyle, for instance, if you drive or take part in contact sports. You also need to be aware of how some electronic devices, such as TENS machines or airport security systems, can affect your ICD.


It’s ok to have a smartphone when you have an ICD, though care should be taken in case they contain magnetic material. It’s recommended that smartphones are kept at least 6 inches away from where your device is. 

Apple iPhone 12 models, including other products like iPads, contain extra magnets in their charging functions that could turn off ICD’s. Apple advise that you keep these products and their charging accessories more than 6 inches away from your device, or more 12 inches away if charging wirelessly (when the magnets are in use). 

Don’t worry too much if your phone gets too close to your ICD, as they’re designed to return to their normal settings once the magnet is moved away.

If you’re unsure about your phone for any reason, we recommend you check it’s handbook/instructions or talk to the manufacturer. You could also contact your doctor or pacing clinic if you have concerns about your device.