What is an Implantable Cardioverter Defibrillator and who needs it?
Some patients are at high risk for dangerous heart rhythms that come from either of the bottom two chambers of the heart called the ventricles. The dangerous rhythms are fast and may cause palpitations, chest pains, breathlessness, dizzy spells or blackouts. In the worst case scenario, the heart may stop completely, which is called a Cardiac Arrest and maybe fatal. Most patients will have some form of heart failure caused by a previous heart attack or a heart muscle problem called a Cardiomyopathy e.g. Hypertrophic Cardiomyopathy. Other patients however, have defects in the proteins that give rise to the heart’s electrical activity causing problems like the Brugada and Long QT Syndromes.
In these conditions, an Implantable Cardioverter Defibrillator or ICD gives the best protection together with drug therapy. If the heart goes into cardiac arrest, the ICD immediately delivers a lifesaving shock to the heart that restores the normal rhythm. ICDs have repeatedly been shown to significantly improve lifespan in such situations.
ICD insertion is a minor surgical procedure that is performed under local anaesthetic with heavy sedation. It takes about 60 to 90 minutes to do and most patients go home on the same day. There is a 1% risk of infection for which intravenous antibiotics are given.
A 5-cm cut is made under the collar bone (usually the left side). The ICD consists of one or two wires called “leads” that are positioned inside the chambers on the right side of the heart. They are introduced through the veins that run under the collar bone and guided into the heart using X-rays. The leads are connected to a generator that sits under the skin below the collar bone and is the size of a business card. The generator is a small computer with a battery, electrical circuits and a memory chip. The battery lasts 7 to 10 years during which the ICD is constantly monitoring the heart’s electrical activity. Whenever the heart goes into a fast, dangerous rhythm the ICD switches on immediately and stimulates the heart muscle through the leads or delivers a shock to restore the normal rhythm again. The ICD also works like a pacemaker to treat slow heart rates if necessary.
The ICD is checked at least once a year in a special clinic to make sure it is working properly and to check the remaining battery life. This is done by either placing a sensor on the skin overlying the generator or by a wireless connection much like a mobile phone. A special computer called a programmer then checks the ICD and can adjust the settings if necessary. When the battery starts to run down the old generator is removed and the leads reconnected to a new one.