How does an ICD work?

What does an ICD do?

An implantable cardioverter defibrillator (ICD) monitors the heart rhythm, and if it suddenly becomes dangerously fast and potentially life-threatening (which can lead to a cardiac arrest), it delivers a small burst of electrical current to reset the heart’s electrical system.

A standard (transvenous) ICD can also act as a pacemaker by sending regular electrical impulses to help speed up a slow heart. In some patients with heart failure, it can be used to help synchronise the heart (this is called a CRT-D).

How is an ICD fitted?

An ICD has a generator that is inserted below the collarbone, usually on the left side just underneath the skin. It is connected to leads, which are passed through the blood vessel to the heart. 

This is done in hospital, usually under local anaesthetic.

What is the recovery like?

The recovery period is generally only a few days. You will be advised not to raise your arm above shoulder height for two weeks, or to lift heavy weights or do strenuous activity for six weeks.

After that you should be able to live a normal life, but it will depend on the underlying condition that led to the need for an ICD. It often causes a slight bulge of the skin that may be noticeable, especially in slimmer people.

What is an ICD made of?

The outer layer of the generator is made of titanium and other metals, with complex circuitry and a high-capacity battery inside. The wires have inner conductors with outer silicone and polyurethane insulation. The tips of the leads are usually coated with platinum or another similar metal.

What is a subcutaneous ICD?

A subcutaneous ICD (S-ICD) has the same parts as a normal ICD, but is larger. It is inserted just below the left armpit and a single lead sits in front of the heart, beneath the skin but without entering the blood vessels or the heart itself. The advantage is a lower risk of complications such as leads being dislodged or infections in the heart. They do not have a pacemaker function.

What are the risks of an ICD?

ICD insertion has a small risk of complications, including ICD bleeding, serious infection and lead movement, and damage to blood vessels, lungs or heart. These affect two to three out of every 100 patients.

Inappropriate shock is where the device delivers the same burst of electrical current it would use for life-threatening rhythms, but when the heart rhythm isn’t actually life-threatening. This happens to about five people in every 100 over the lifetime of the device. BHF researchers are working to reduce this number.

Will an ICD definitely go off if I have a cardiac arrest?

ICDs save many lives, but it’s not a guarantee. As not all cardiac arrests are caused by a shockable heart rhythm, the ICD would not deliver a shock in those situations.

What will a shock feel like?

It may feel uncomfortable or painful, but it is potentially life-saving. Patients are often briefly unconscious, so are not aware of the shock.

How long will it last?

Usually the battery lasts between eight and 15 years. When the battery nears the end of its life, the generator can be replaced. 

How can I cope with my worries about having an ICD?

Some people feel sad about the fact that they need an ICD, or anxious about living with one. This is normal.

Try talking to your device clinic, to others with an ICD on the BHF HealthUnlocked community or to our Heart Helpline./p>

• Visit our page on implantable cardioverter defibrillators for more on ICDs, or order our free booklet, Implantable Cardioverter Defibrillators (HIS19), on 0300 200 2222.