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  Implantable Cardioverter Defibrillator (ICD)

What is an ICD?

An ICD (Implantable Cardioverter Defibrillator) is an implanted device (rather like a big pacemaker) that monitors the heart’s electrical rhythm in order to detect and treat dangerous fast heart rhythms, ventricular tachycardia (VT) and ventricular fibrillation (VF). It is important to remember that they do not prevent these abnormal heart rhythms from occurring in the first place.

What are ventricular tachycardia (VT) and ventricular fibrillation (VF)?

VT and VF are fast abnormal heart rhythms coming from the main pumping chambers of the heart – the ventricles. There are many causes of VT and VF but most cases are due to restriction of the blood supply to the heart muscle due to narrowings in the coronary arteries, or to scarring of the heart muscle.

During ventricular tachycardia the electricity that makes the heart beat goes around in a continuous circle, usually faster than the normal heart beat. The most common symptom is palpitation but VT may also cause chest pain, breathlessness, dizziness or even a blackout. During ventricular fibrillation the electricity in the ventricles becomes very rapid and chaotic and the heart cannot pump blood around the body resulting in cardiac arrest.

How does an ICD work?

The ICD consists of a ‘pulse generator’ and one or more leads. The pulse generator contains a battery, a capacitor and a clever electronic ‘brain’. The pulse generator is usually implanted just below the collar bone, usually on the left but occasionally on the right. The lead or leads pass inside the large veins of the chest to the heart. The leads detect the heart’s electrical rhythm and transmit that information back to the pulse generator. The leads also deliver treatment from the pulse generator to the heart.

How does the ICD treat VT and VF?

If the VT is not too rapid it can be treated by ‘anti-tachycardia pacing’. The ICD sends out a short train of impulses to stimulate the heart slightly faster than the VT. Anti-tachycardia pacing can be very successful in stopping VT and you may not even be aware that it had occurred. VF and very fast VT cannot be treated by anti-tachycardia pacing and are treated by an electric shock. The shock is delivered between the lead in the right ventricle of the heart and the pulse generator. A shock, although very brief, can be painful.

Is the ICD like a pacemaker?

In many respects an ICD is very similar to a pacemaker and all ICDs act as pacemakers; that is, they will stop the heart from going too slowly. The main difference is that pacemakers do no treat VT and VF. Because of the extra technology to treat VT and VF ICDs are significantly larger than pacemakers.

How is an ICD implanted?

An ICD is usually implanted under local anaesthetic; you can also have some sedation to make you feel sleepy and more relaxed. The procedure generally takes about an hour or two and is performed in a ‘cardiac catheterisation laboratory’. Your heart rhythm, blood pressure and the oxygen level in your blood are monitored continuously. The doctor puts local anaesthetic under the skin below your collar bone. The anaesthetic stings for a few seconds as it gets to work but the area rapidly goes numb. An incision about 5 cms long is made below the collarbone. The next stage of the procedure is for the doctor to find a vein through which the leads are passed to the heart. Once the leads are in the veins they can be positioned in the heart. This is not in any way uncomfortable although you may feel a few extra heart beats for a short period. Care is taken to find the ideal position for the lead or leads and you will hear numbers being called out, referring to measurements made through the leads. When the doctor is happy that the leads are in the best position, they are stitched in and a pocket is created to house the pulse generator. This pocket may be underneath the skin or deeper, under the muscle of the chest wall. In most, but not all cases the ICD is then tested further by putting the heart into VF to ensure that the ICD can detect and treat it with a good safety margin. You will be well sedated and comfortable as this is done. Finally the incision is closed up with stitches. For the skin stitch some doctors use a dissolvable suture while others prefer a suture that is taken out at your doctor’s surgery after 7 days. You will be told which you have.

Can comlications occur?

This procedure cannot be performed without some element of risk; you need to understand the risks before you sign the consent form.  It is important that you understand that these risks are potential and unpredictable.  The majority of patients, however, have no problems.  The potential risks are listed below for your information:

Pneumothorax  (air leak around the lungs): this occurs in approximately 1 in 100 patients. The veins used to get the pacemaker wires to your heart lie very near to the lung. It is possible to nick the lung on the way past causing an air leak. Sometimes this resolves on its own. Occasionally a chest drain is needed; if so your stay in hospital may be delayed by several days.

Pericardial effusion (blood leak around the heart): this occurs in approximately 1 in 500 patients. When the wire is positioned in the heart it can cause a fluid collection around the outside of the heart. Sometimes this resolves on its own but occasionally a drain is needed; very rarely an operation is needed. If so your stay in hospital may be delayed by several days.

Infection: this occurs in approximately 2 in 100 patients. Antibiotics are given routinely to help prevent this. In the unlikely event that the ICD does become infected, it will probably need to be removed and a new ICD implanted.

Haematoma (severe bruising): this occurs in approximately 4 in 100 patients. Rarely this bruising may need drainage.  Patients taking blood thinning drugs are more prone to haematoma formation.

Wire displacement: this occurs in approximately 5 in 100 patients. This causes the pacemaker to pace inappropriately.  In most cases the wires need to be repositioned requiring further surgery.

Failure to shock your heart back to a normal rhythm: this is rare but can occur in certain circumstances. Shocks from a rescue defibrillator are given to get your heart back to a normal rhythm. Often programming changes or alterations to the system can resolve the problem. Occasionally new medicines are needed or others are stopped. Very rarely special extra leads are needed.

Death: this is fortunately an extremely rare complication

What to expect after the ICD is implanted

It is normal to experience some discomfort and bruising at the site of the wound for a few days. There is usually some slight redness of the skin at the edges of the wound. This occurs straight away and should go away within a few days. In many cases you will be able to go home the morning after the ICD is implanted.

Follow-up

It is important that your ICD is checked at regular intervals. The first check is usually performed about four weeks after implantation and approximately six monthly thereafter. The ICD is ‘interrogated’ by placing a ‘wand’ over it. The wand is connected to a ‘programmer’ – essentially a dedicated computer. The ICD is checked to make sure that it is working well and programmed correctly. If VT or VF has occurred the ICD stores a lot of information about each episode that can be downloaded by the programmer. Routine follow up does not involve shocks from the ICD.
An important function of follow up is to measure the battery status of the ICD. As the battery approaches the end of its life the ICD continues to work normally, but follow up may be performed more frequently until the pulse generator requires replacement. Battery depletion occurs in a predictable fashion such that generator replacement can be planned with several weeks notice.

How long can I expect my ICD to last?

This is one of the most difficult questions to answer as the life of the battery is determined by many different factors. In general the current generation of ICDs lasts four to six years before requiring generator replacement.

Are there any restrictions if I have an ICD?

In general your life with an ICD should be near-normal. As ICDs treat VT and VF but do not prevent them, you should avoid putting yourself in situations where you might be in danger if you became dizzy or received a shock, for example, swimming unaccompanied.

a) Driving
The DVLA rules are revised periodically and the current rules can be viewed at http://www.dvla.gov.uk/drivers/dmed1.htm. However in brief:

  • Implantation of an ICD means that you cannot hold a vocational (group 2) driving licence.
  • If you have an ordinary driving licence then you must not drive for:
    • six months if your ICD was implanted following an episode (or presumed episode) or VT or VF and you should inform the DVLA.
    • one month if the ICD was implanted for purely prophylactic reasons i.e. your doctor thinks you may be at risk of VT or VF but have not had an event yet. In this case you do not need to inform the DVLA.
  • NOTE: IF YOU RECEIVESHOCKS FROM YOUR DEVICE THE DVLA MAY IMPOSE A LONGER DRIVING BAN

b) Interference from machinery
Patients with ICDs are often concerned that machinery may cause interference that may cause their ICD to malfunction. Modern ICDs are very well protected against electromagnetic interference and it is rarely a problem. It is recommended that mobile phones are not over the ICD and that you use the ear opposite the ICD. Microwaves do not cause a problem. You should walk through the security gates at shop entrances at a normal speed but not stand leaning against them. You can usually bypass the security gates at airports by showing your ICD identification card but walking through at a normal pace should not cause a problem. If you are concerned about interference from a particular piece of equipment at home or at work, ask your consultant or the cardiac physiologists in the pacemaker clinic.

c) Medical procedures
Medical MRI scans can only be performed on patients with ICDs with extreme caution and you should inform the doctor proposing an MRI scan that you have an ICD. Many surgical operations involve the use of diathermy (an electrical method of stopping bleeding), which can interfere with ICDs. You should inform the surgeon and anaesthetist, who can then arrange for you ICD to be reprogrammed for the duration of the operation to prevent interference.

What happens if I get a shock while someone is touching me?

They might feel a slight tingling sensation briefly but they are in no danger whatsoever.

 


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