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ICD stands for implantable cardioverter defibrillator. If your doctor has suggested that you need an ICD you may have experienced or may be at risk of experiencing an abnormal, fast heart rhythm. An ICD constantly monitors your heart rhythm and can deliver various electrical impulses to correct potential problems. It is made up of a small pulse generator, contains a battery and electronic circuits, and sophisticated leads that connect the generator to the heart. An ICD, like a pacemaker, is usually placed under the skin below your collarbone.

S-ICD system

A traditional implantable cardioverter defibrillator (ICD), has one or more leads that enter the heart allowing the device to provide pacemaker functions as well as defibrillation. Conversely, an S-lCD has no leads connected to the heart, presenting a less invasive option for patients not in need of any cardiac pacing. For example, if your doctor has told you that you have, or are at risk of, a slow heartbeat, an S-ICD would not be an appropriate option. The implanting doctor will be able to advise whether or not a traditional ICD or an S-ICD is suitable.

Visit S-ICD dedicated website | Download Arrhythmia Alliance ICD/S-ICD patient information booklet



Most modern ICDs have three main functions:

  1. If your heart rhythm is too slow, the device can give your heart extra support by working as a normal pacemaker (anti-bradycardia pacing).
  2. If your heart beats too fast, the ICD can return your heart back to a normal rhythm (anti-tachycardia pacing or ATP).
  3. If the anti-tachycardia pacing doesn’t bring your heart back to a normal rhythm, or if the ICD senses a faster, dangerous rhythm called ventricular fibrillation, the ICD can then give a shock (defibrillation) to the heart to restore normal rhythm.

Some modern ICDs only provide defibrillation.  These are suitable for patients not in need of cardiac pacing, and are particularly of interest to patients not wishing to bear the risks associated with having leads threaded through the veins to the heart.

This procedure is performed undICDs help to restart the heart following sudden cardiac arrester either a general anaesthetic or a local anaesthetic with sedation. The pulse generator is connected to either one or two leads that, for most models, pass through a vein into the heart. The doctor may test the device during the procedure to ensure it is working correctly. The implant should take between one and two hours and any stitches that may need to be removed will be done at your GP surgery.

You will probably be allowed to go home the next day provided your ICD is checked and there are no complications. You will be given an ICD identity card, emergency information and instructions at this point. You will also be given a helpline number should you have any queries later on.

Normally an ICD battery lasts between six and nine years and the replacement procedure will usually involve changing the ICD generator, not having new leads implanted.

Some patients have reported that having shocks can feel like they have been suddenly kicked or punched in the chest. These shocks can be quite painful but the pain will only last for a few seconds, others may not feel anything.

If you do feel unwell after a shock, or if your device has given you several shocks, please dial 999 for an ambulance. Show the paramedics your identity card along with any emergency instructions; this will inform them of exactly which type of device you have and what the best course of action will be.

You should always contact your ICD centre if you think you have had a shock.

There may be some restrictions on driving; you can access DVLA guidelines on:




Current rules (2013) place a six month ban on driving following implant of secondary prevention ICD or delivery of an appropriate shock. For primary prevention ICDs the rules are a one month restriction. lt is very important that you discuss this with your nurse, physiologist or doctor at your lCD centre who will explain this in more detail and let you know what is specific to your circumstances.

It is strongly recommended that you inform your insurance company.

For specific and detailed information please see the DVLA website

Many ICDs are fitted to prevent arrhythmias from deaths from sudden cardiac arrest (SCA).  For information on SCA please click here for the A-A SCA web or download the booklet below on SCA. 

A recent alternative to ICDs that require leads attached to the heart is available in some countries.  Called subcutaneous ICDs (S-ICD), the new devices are able to defibrillate the heart with only a lead that is placed just beneath the skin instead of into the heart.  The are not suibable for all patients.

For more information please click below to download an Arrhythmia Alliance leaflet on S-ICDs.


SCA booklet
S-ICD leaflet