Internal Cardiac Defibrillator (ICD)

Glossary of terms

Atria- Top chambers of the heart

Arrhythmia- An abnormal heart rhythm 

Bradycardia – A slow heart rate, normally less than 60 beats per minute.

Cardiac Arrest- When the heart is unable to pump blood around the body due to an abnormal heart rhythm. 

Defibrillation- The use of a shock to stop fast heart rhythms.

Heart Attack – Occurs when one of the coronary arteries (pipes supplying blood to the heart) becomes blocked by a blood clot. The blood supply to part of the heart muscle is blocked, causing part of the heart muscle to die. 

Pulse Generator- The part of the ICD which contains the battery and electrical circuits.

Ventricles- The two lower chambers of the heart.

Ventricular Tachycardia (VT) – A fast potentially dangerous heart rhythm which causes the heart to pump less efficiently, and may lead to dizziness, fainting and unconsciousness. If not treated with medication, pacing or a shock, the rhythm may lead to Ventricular Fibrillation.  

Ventricular Fibrillation (VF) – A fast, dangerous heart rhythm which causes the heart to stop pumping. This rhythm needs a shock to stop it and return the heart back to a normal rhythm. A cardiac arrest can soon follow if the rhythm is not treated quickly with a shock.

Frequently Asked Questions

What is an ICD?

ICD stands for Implantable Cardioverter Defibrillator. It is made up of a small box-shaped device which contains a battery and electronic circuits. It is a mini-computer. The device is connected to your heart by one or more wires (leads). The leads are passed through a vein to your heart and the ICD box is usually implanted under the skin or muscle in your upper chest, near your collarbone. The ICD can recognise and monitor your heart rhythm and can deliver various electrical treatments if needed. It also has a memory that stores information about your heart rate and rhythm, which can be accessed when you go to the clinic for your next follow-up. It may also have a remote monitoring facility which can be automatically downloaded via a digital phone link.

What can an ICD do?

Most modern ICDs have three main functions; however you may not need to have all of them. Your cardiologist will select what settings are best for your condition.

  • If your heart rhythm is too slow, the device can give your heart extra support by working as a pacemaker. This is called anti-bradycardia pacing.
  • If your heart beats too fast (see “Ventricular Tachycardia” above), the ICD can give you a burst of extra beats at slightly faster rate which will normally return your heart back to a normal rhythm. This is called anti-tachycardia pacing (or ATP).
  • 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. This is called defibrillation.

Why do I need an ICD?

If the doctor has suggested that you need an ICD you may have experienced OR may be at risk of experiencing an abnormal, fast heart rhythm. This can cause you to become unwell, unconscious, or your heart to stop beating.  

How the heart works normally?

The heart is a muscle, whose function is to pump blood and oxygen around your body and to all of your vital organs. It has four chambers, two at the top (the right and left atrium) and two at the bottom (the right and left ventricles). The heart also has an electrical system, which sends impulses (beats) through the heart causing it to contract and pump blood around the body. Each normal heartbeat begins in the natural pacemaker of the heart (the sinoatrial or SA node) which lies at the top of the right atrium. It then travels across the two top chambers and down through a small junction box (the atrioventricular or AV node) which lies between the upper and lower chambers. It then spreads through the conduction pathways across the bottom chambers causing the heart to contract and pump.

The Heart and Normal Conduction (click here)

Sometimes the electrical system in your heart does not work as well as it should. This can cause your heart to beat too quickly. The ICD can stop fast heart rhythms that start in the ventricles. This fast heart rhythm is called Ventricular Tachycardia (VT) or Ventricular Fibrillation (VF). This may sometimes start after a heart attack or in people who have angina or coronary artery disease. There are several other reasons for having an ICD, even if you have never had an abnormal heart rhythm.

The heart and normal conduction

You may have a heart condition that puts you at risk of having an abnormal rhythm in the future, eg. you may have a family history of sudden collapse or even death. This may be the result of muscular damage or abnormalities in the heart’s natural electrical system. These conditions may put you at risk of having Ventricular Tachycardia or Ventricular Fibrillation, which can be life threatening if it is not treated quickly with an electric shock delivered to the heart. You may need to have some tests before the decision to have an ICD is made. Your cardiologist will advise you if these are needed and discuss the reasons for having an ICD implanted in detail.  

How is an ICD implanted?

The procedure will either be performed under a general anaesthetic or you will be given sedation, which will make you relaxed and sleepy. Before the procedure starts your skin will be cleaned with antiseptic solution. Then some local anaesthetic will be placed under the skin just below your collarbone (on the left side most commonly). This will numb the area and allow a small wire (lead) to be placed through a vein into your heart. You may have one, two or three leads inserted depending on what type of ICD you need. The lead(s) are then connected to the ICD box (pulse generator). This will be placed under the skin on your chest wall. The area will then be stitched with dissolvable sutures (stitches) and a dressing will be placed over the top. Your doctor may test the device during the procedure to ensure it is working correctly; this involves making heart beat very quickly whereby the ICD will give a shock to restore your heart rhythm back to normal. You will be given strong sedation before this happens, so you will not feel the shock.  

Are there any risks associated with the procedure?

There a risks associated with any heart operation. The most common risks are:

  • A small risk of infection, bleeding and bruising to the pacemaker site
  • A small risk of perforation of the lung during the procedure (a pneumothorax) – this is often detected on the chest X ray that is performed following the ICD implant and can sometimes rectify itself without treatment. Very occasionally a small drain may need to be inserted through your side into your lung (in the space between your ribs) this is a simple procedure and the drain will be removed prior to your discharge home
  • A small risk of lead displacement – the ICD lead can move and would then need to be repositioned
  • A small risk of perforation of the heart which can cause bleeding around the heart

What happens after the ICD has been implanted?

After the procedure and once all the checks have been made, you will be taken back to the cardiology ward or recovery area. You will be asked to lie in bed for a couple of hours before you can get up, eat and drink. As the wound can feel quite bruised and sore, especially for the first day or two, your nurse will give you regular painkillers. You may also be given antibiotics after the procedure to minimise the risk of infection. Your ICD will be checked before you go home by a cardiac physiologist or technician. This check will involve the use of a special programmer that can look at the device settings and make sure the ICD is working properly. It will be specially programmed for your condition and you will be given a special identity card for your ICD. You will also have a chest x-ray to check the lungs and lead position.

Arm movements

Try to avoid lifting the arm on the same side as the ICD above shoulder level for the first 6 weeks. Extra tissue will grow around the lead(s) in your heart after period, which will prevent the wire(s) moving out of place. After this time you will be able to return to normal activity.  

Wound site

You should avoid showering or bathing for the first 24 hours after the procedure. Showering after this is OK, but direct water contact on the dressing is best avoided. Your doctor will advise when the dressing should be removed. The skin sutures (stitches) will dissolve and do not require removal. Bruising at the site of the operation is not uncommon and usually settles on its own. Your wound site should take about six weeks to fully heal. Try to avoid wearing tight clothing over the wound until it has healed completely to avoid excess rubbing over the area. If you notice any redness, soreness or swelling of the area, or any signs of bleeding or oozing from the wound, report this immediately to your doctor as these may be a sign of wound infection. You will probably be able to feel the ICD box under your skin as well as other lumps close by. These are the leads that are attached to the box, curled up beside the box under the skin. It is extremely important that you don’t try to move the box or leads, but please let your doctor know if they continue to bother you.

Will I feel the treatment from the ICD?

The device will be programmed to the best settings for your condition. Your cardiologist will do this initially when the ICD is implanted, but settings can be modified during your follow up appointments in the clinic if necessary. The ICD can give the following treatments, but you may not have all of them programmed;

  • Anti-bradycardia pacing pulses

If your heart is beating too slowly, the ICD can send small impulses to the heart generating extra heartbeats when required. These are called paced beats. As these impulses are very small they are not painful and usually go un-noticed.  

  • Anti-tachycardia pacing pulses (ATP)

If your heart beats too fast, the device can send out faster pacing impulses which can help to get the heart back into a normal rhythm. This can be done so quickly by the ICD that many people do not know that this has even happened. However, it is not uncommon to experience palpitations or feel lightheaded / dizzy. If the ATP does not correct your fast heart rhythm your device will be able to deliver a shock.      

  • Defibrillation shocks

These are shocks which the device will deliver if it senses that your heart is beating so fast that it is life-threatening. These fast heart rhythms are called Ventricular Tachycardia and Ventricular Fibrillation. 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 their heart is beating so fast that they have become dizzy or unconscious. If someone is with you when you have a shock, they will probably notice you jolt. No harm will come to anyone who is touching you when they receive a shock. Indeed, it can be very comforting and reassuring to have someone put their arm around you as you experience a shock. When you come to the ICD clinic your physiologist or technician will examine your device and any treatment that you may have had will be detected.  

What should I do if the ICD gives me a shock?

You may experience warning signs that your ICD is about to deliver a shock, such as palpitations, or feeling light-headed or dizzy. However, this may happen so quickly that you have no warning at all. If you do think that you are about to receive a shock, you should sit or lie down on the ground. If possible, you should also let someone know how you are feeling. After a shock you should recover quite quickly. Even if you feel well after the shock you should still contact the implant centre as soon as you can to arrange to have your device checked. If you do feel unwell after a shock or if your device has given you several shocks, please dial 000 for an ambulance to take you to your nearest hospital. Your ICD will be checked to find out why the shocks were given. If you do call for an ambulance, make sure you tell the paramedics that you have an ICD implanted and show them your identity card along with any emergency instructions you have been given. This will inform them of exactly which type of device you have and what the best course of action will be.  


Getting back to normal

Having an ICD implanted can be seen as a rather big event in your life. However with help and support, most people adapt well over time. After a fairly short recovery period you should be able to return to previous activities however some restrictions will apply for your own safety.  


The Roads and Traffic Authority (RTA) have strict guidelines in relation to patients who require an ICD and whether or not they are safe to drive. There are some restrictions but these vary depending on why you have had your ICD fitted. It is very important that you discuss this with your technician or doctor at your ICD centre who will explain this in more detail. You will also need to inform your insurance company that you have had an ICD fitted.  

Physical activity

A certain level of exercise is needed to keep your heart healthy. It is natural to be concerned about the possibility of the ICD delivering a shock or stressing the heart. Following your initial recovery, normally about 4-6 weeks, it is recommended that you try to increase your level of activity if possible. You may be offered cardiac rehabilitation or exercise testing to restore your confidence. Once your wound has fully healed, you will be able to go swimming if you wish. However you are advised not to swim alone. Contact sports are not advised as the device or leads may become dislodged.

Sexual Activity

It is very common to be reluctant to resume sexual activity. However the device will not cause any harm to your partner, even if a shock is delivered to you during intercourse.  


You can safely use equipment (such as electric drills) as long as they are in good working order, although you should keep them away from your ICD site.  

Arc welding

This should be avoided.  

Electromagnetic Interference

Electromagnetic interference will not damage your ICD but may stop it from delivering any treatment for the period of time that you are in contact with it. Most electrical equipment that you come into contact with in day-to-day life, such as radios, fridges, cookers, computers and microwaves, will not affect your ICD as long as they are in good working order. However, should you ever feel dizzy or experience palpitations whilst using an electrical appliance, you should move away from the appliance and telephone the technician or doctor at the ICD clinic for advice. When buying electrical equipment / tools / appliances the instructions often say “do not use if you have a Pacemaker / ICD”. This is usually to protect the manufacturer from being sued and is not normally a problem. If you do come across any of these items talk to your ICD clinic who will be able to advise you.  


Do not carry magnets or place a magnet over your chest! Avoid carrying stereo or hi-fi speakers as they contain strong magnets that can interfere with your ICD. ICD therapies may be temporarily disabled by magnets.

Shop doorway security systems

There is a very small risk of interference to your ICD, so you are advised to walk through shop doorways at a normal pace and not to wait around in this area.  

Electronic ignition systems

Avoid leaning over the alternator in a car whilst the engine is running, otherwise it is generally safe to work as a mechanic.  

Medical equipment / other hospital treatments

Most equipment used by your hospital or GP surgery will not cause any problems to your ICD. However it is advised that you let medical and dental staff know that you have an ICD as technical support may be required before some treatments. Please take your ID card with you whenever you go to hospital. It may also be useful to contact your implanting centre for advice before you go into hospital for any investigations or operations that are not associated with your ICD. It is safe for you to have X-rays, CT scans and mammograms. However you must not have magnetic resonance imaging (MRI) scans unless you are sure your ICD is MRI compatible. Some electrical nerve and muscle stimulators (TENS units) may cause interference with ICDs but this depends on where they are being applied. If this form of treatment is suggested to you then your ICD clinic should be contacted for advice.  


If you require an operation, you must tell your surgeon and anaesthetist that you have an ICD implanted. It may be necessary to temporarily switch off (deactivate) the shocks on your ICD for the duration of the operation. This can be done through a programmer, but equally using a magnet taped over your ICD.

Deactivating ICD shocks

As well as being able to temporarily switch off your ICD shocks during operations, there may be certain circumstances which would cause you to consider having your ICD ‘deactivated’. For example, if you are diagnosed with a terminal illness, you may not wish to have the added burden of worrying if you will be shocked by your ICD when this will no longer provide life-saving treatment. This will only be carried out at your request and after you have been fully informed of your choices. Should circumstances change, the ICD can be easily switched back on.  


You can safely travel abroad with your ICD, but you are advised to show security staff your identification card and ask to be searched by hand. This is because the hand held wands can temporarily interfere with your ICD. Walk through the metal detector archway if asked to do so, but the metal casing of the device may set off the airport security alarm. The detector will not cause any harm to your ICD provided you walk briskly through the arch. You will need to make sure that your travel insurance company is aware that you have an ICD.  

Mobile phones / iPods / MP3 players

Some studies have shown that mobile phones and MP3 players can affect the ICD if held within six inches (15cm) of the device. It is therefore recommended that you do not keep them in a coat or shirt pocket over the ICD. Keep the handset more than six inches away from the ICD; ideally hold your phone over the ear on the opposite side to the device.  

ICD Clinic Visits

Your ICD should be checked regularly and visits may be necessary more often just after the ICD is fitted. During each clinic visit, the physiologist or technician will examine your ICD using a special programmer. This machine allows the settings and the battery life of your device to be examined. All the information is stored in your records. Depending on your ICD model, you may not always physically need to attend an out-patient appointment at the hospital. Some checks can be carried out remotely and your ICD centre will inform you if this is possible with your particular device.

Changing the ICD

Normally an ICD battery lasts between five and seven years. Your battery will be checked at every visit to the ICD clinic and staff at the clinic will be able to predict when you need a new ICD box. It will not be allowed to completely run down. In order to have the box changed, you will need to be admitted to hospital. The procedure is similar to having your first ICD fitted, but it will not usually involve having new leads put in so is usually a shorter procedure.

Have you been advised that an ICD may be required? Perhaps you have questions about the procedure? If you would like a consultation with Dr Gomes please refer to our Contact page for available locations close to you, and phone or email for your appointment.