Defibrillators (ICDs)
Why you may need a defibrillator
When to see a cardiologist
How a defibrillator works
The defibrillator implant procedure
Living with a defibrillator
Complications of a defibrillator
Why You May Need a Defibrillator
Defibrillators (ICDs) are common medical devices used to protect against potentially fatal heart rhythm disorders. Around 5,000 people in the UK are fitted with a defibrillator every year.
Defibrillators are offered to patients who are either at high risk of having a potentially fatal heart rhythm problem (generally this means either ventricular tachycardia or ventricular fibrillation), or have survived an attack of these arrhythmias in the past.
Making a decision to have a defibrillator fitted is a matter of weighing up the risks of having a device, versus the risks of potentially suffering a fatal or disabling heart rhythm disturbance. A cardiac electrophysiologist - or heart rhythm specialist - is ideally placed to help patients navigate these decisions.
When to See a Cardiologist
Many different groups of patients are at risk of tachyarrhythmias (ventricular tachycardia and ventricular fibrillation). Some heart attack survivors as well as patients with inherited muscle or electrical diseases of the heart may reach the threshold where defibrillator implantation is recommended.
Patients with advanced heart failure are commonly offered defibrillators as a preventative measure.
How a Defibrillator Works
Most defibrillators consist of a number of insulated wires (“leads”) that pass down veins into the heart and fix to the internal surface of one of more heart chambers. The leads are wired into a small computer and battery pack (“generator”) that sits under the skin or muscle near to the left or right shoulder. Many different variations on this basic setup exist, including different numbers of leads and different positions for the generator, depending on what problem is being treated.
More recent developments include the use of “subcutaneous” defibrillators whose leads sit outside the heart, over the breastbone, and “extravascular” defibrillators that sit below the breastbone but outside the heart and lungs. For some patients, these newer technologies have advantages over traditional defibrillators that sit inside the veins and the heart, particularly for young patients who are going to live with these devices for many decades.
The fundamental job of all defibrillators is to detect when the heart enters a dangerous fast rhythm, and to deliver treatment to return the heart to a normal rhythm. This treatment can either be “overdrive pacing” where the defibrillator attempts to simply overtake the dangerous rhythm with a faster paced rhythm, or - if all else fails - a high energy shock delivered across the chest. Either treatment is capable of returning the heart to a safe and normal rhythm.
Traditional defibrillators that sit within the veins and heart can also function as pacemakers to guarantee a minimum heart rate. You can read more about pacemakers here.
The Defibrillator Implant Procedure
Defibrillators are generally fitted as an elective procedure but may also be carried out for patients already in hospital, typically after admission with a cardiac arrest. Most defibrillator implant procedures will be done with the patient awake but sedated.
As one of the main risks of defibrillator implantation is infection, a lot of care is paid to cleaning the skin and maintaining sterility of the surgical area using surgical drapes. The drapes will be arranged to prevent the patient from viewing the procedure.
Although Dr Idris Harding is expert in the implantation and management of subcutaneous defibrillators, the majority of defibrillators implanted in the UK are traditional transvenous devices. For a traditional implant procedure, an injection is used to numb an area high on the chest, near to one or other shoulder. Once the area is numb a 3-4cm cut is made to the skin through which the rest of the procedure is carried out. Most of the procedure should be entirely painless but the stage where a space is made for the generator to sit under the skin can be uncomfortable. This is usually very brief, however (over in well under a minute).
A basic defibrillator implant procedure will usually take around an hour. Antibiotics are given beforehand and a dressing applied at the end of the procedure. Checks are done on the device both during and after the procedure, and waiting for these checks is a common reason why discharge from hospital may be later than anticipated: it is important to give time for any problems to become obvious.
Living With A Defibrillator
Early after a defibrillator implant there are a short list of restrictions on activity to help minimise the risk of the leads becoming displaced. These are mostly common sense measures such as avoiding lifting the arm on the affected side above horizontal, avoiding carrying heavy items on that side, and so forth. Generally these restrictions last a few weeks at most.
The DVLA stipulates that patients undergoing defibrillator implantation cannot drive for a period afterwards. The precise duration of the driving band and the need to inform the DVLA about the procedure depends on whether the patient has a Group 1 or Group 2 driving licence.
Golfers may be asked to take an extended break from playing because the golf swing involves extreme movements of the arm, clavicle and shoulder joint, all of which can impact on the leads and generator, and cause them to displace.
Until the cut used to implant the defibrillator has healed, patients are asked not to get moisture on or near the wound.
Overall around 1/20 patients with a defibrillator will need a second procedure early on after the implant to fix a problem. The majority of these are to fix leads that have become displaced.
Over the longer term, once the leads and generator have scarred firmly into place and the cut has healed fully, there are relatively few restrictions on living with a defibrillator but there may be restrictions related to the condition that led to the device being implanted. Most of the concerns regarding the device relate to magnets and magnetic fields that can interfere with the programming and function of the generator.
Due to shifts in technology the precise advice changes frequently. The British Heart Foundation maintains a useful list of dos and don’ts aimed at patients with pacemakers here. However most of the items on the list also apply to defibrillators. The BHF also has specific pages on living with a defibrillator here.
Unlike living with a pacemaker, patients with a defibrillator must live with the knowledge that the device may deliver treatments that they will be aware of, and that these can be unpleasant to experience. There is also the small chance that the defibrillator will deliver treatment when it is not needed. This is, for some people, a troubling thought.
Complications of Defibrillators
Most of the complications of having a defibrillator to the implant procedure. Global figures show that one in 20 people will require a second procedure to fix a problem related to the first implant procedure; the majority of those will be to reposition leads that have moved in the heart. More serious complications also occur but tend to be much rarer.
Long term, the main complications of defibrillators are mainly related to the leads, which can malfunction or degrade over time. Battery change operations, as well as the original implant procedure, carry a small risk of infection but this climbs with the number of battery change procedures.
The newer subcutaneous and extravascular defibrillator devices do not carry such a high risk associated with the leads in the long term and many patients prefer the thought of having these devices. However S-ICD and EV-ICD devices cannot deliver the same range of treatments as traditional ICDs and may not be suitable for all patients.