ICD - Implantable Cardioverter Defibrillators

Background
Implantation of ICD and follow-up
ICD complications
Clinical trials of ICD
Quality of life
Indications for ICD
Conclusions
CRY's myheart Support Network

Background

Sudden cardiac death is a common problem, and increasing numbers of patients are surviving a first episode of a life threatening ventricular arrhythmia. Patients who survive either ventricular fibrillation or sustained ventricular tachycardia have a high risk of further episodes, which may be fatal. For some time, anti-arrhythmic drugs were the standard treatment for patients with malignant ventricular arrhythmias, but despite using the best appropriate medical treatment, arrhythmia recurrence rates were still 40-50% at five years.

Since the turn of the century, there has been growing evidence to support the wider use of implantable cardioverter defibrillators - ICDs - as primary treatment in certain patients with serious ventricular arrhythmias. These devices were developed in the 1970s, with the first human implant in 1980. Original devices had a single therapy option of defibrillation only; the generator was implanted in the abdomen, and thoracotomy was required. With advances in technology the units have become smaller (modern ICDs are about the size of a matchbox) and can be implanted pectorally. Furthermore, anti-tachycardia pacing, low energy synchronised cardioversion, and high-energy defibrillation shocks can be given via a single transvenous lead.
 

Implantation and follow-up

Nowadays, ICD implantation is technically straightforward and only slightly more complicated than pacemaker implantation. Strict attention to asepsis is necessary, and prophylactic antibiotics are generally used. In the past, ICD implants were performed under general anaesthetic; however, many centres now implant these devices using a combination of local anaesthesia and intravenous sedation. Most patients can be discharged home 24-48 hours after implantation following post-implantation device function checks. Patients are usually followed up 4-6 weeks post-implant, then at 3-6 monthly intervals. At each follow up visit, the device and its memory are interrogated and standard pacing and sensing tests are performed. Details of any stored arrhythmic events are downloaded and printed, and correlated with symptoms. If indicated, appropriate programming changes can be made or the patient's medication can be altered.
 

Complications of ICDs

ICD nowadays are much simpler to implant than was previously the case and the complication rate is decreasing. Nevertheless, all complications which apply to pacemakers, can occur with the ICD (e.g. infection, lead fracture, etc) and some of these complications may require revision or even replacement of the system, which can be a major undertaking. Additional problems may occur, the most common being inappropriate shocks. Such complications can usually be treated or circumvented either by additional medication or by further programming of the device.

Clinical trials of ICDs

ICDs are effective at treating ventricular arrhythmias but until recently there has not been clear evidence that they reduce mortality. However, the results of large randomised controlled trials of ICD treatment have been published - including the AVID, CIDS and CASH studies - which compared ICD therapy with medication in patients who had sustained VT or VF. They showed a superior beneficial outcome with ICD. In the three studies, 934 patients were treated with an ICD and 932 with amiodarone. In over 2000 patient years of follow up in each group, there were 200 deaths in patients treated with an ICD and 255 deaths in patients treated with amiodarone. This equates to a 28% reduction in mortality in the ICD group (p = 0.0006). Importantly, the meta-analysis showed that patients who presented with ventricular tachycardia had as much to gain from an ICD as those whose index arrhythmia was ventricular fibrillation.

Several studies have also assessed the efficacy of ICD treatment for "primary prevention" in patients at high risk for sudden death who have not yet had a clinical event. The MADIT study studied high-risk survivors of myocardial infarction with impaired left ventricular function and non-sustained ventricular tachycardia on ECG monitoring. Patients recruited to this trial had to have an inducible sustained ventricular arrhythmia at electrophysiological study, which could not be suppressed by medication. These patients were randomly allocated to treatment with an ICD or an anti-arrhythmic drug (amiodarone in 80% of the cases). The trial was terminated in 1996 after demonstrating a 54% reduction in mortality with defibrillator therapy compared to anti-arrhythmic drug treatment.

The MUSTT study recruited patients similar to those in the MADIT study. Patients were randomly allocated to a "control" group, who received no specific treatment; and an electrophysiologically guided treatment group, who received anti-arrhythmic drugs if the tachycardia could be suppressed by drugs, or an ICD if drugs were ineffective at electrophysiological study. The five year mortality in this study was 48% in those not treated with anti-arrhythmic medication; patients on anti-arrhythmic drugs fared marginally worse, but those treated with an ICD had a five year mortality rate of 24% (p < 0.001). These results show that patients with prior myocardial infarction, impaired left ventricular function, and non-sustained ventricular tachycardia can be stratified by electrophysiological study. Patients with inducible sustained ventricular arrhythmias are highly likely to benefit from prophylactic ICD implantation, even though they have not yet had a major spontaneous arrhythmic event.

ICDs have also been shown to be beneficial in terms of preventing sudden cardiac death and/or terminating potentially fatal ventricular arrhythmias among patients with hypertrophic cardiomyopathy (HCM). HCM is the commonest cause of non-traumatic sudden death in individuals below the age of 35 years and among athletes. ICD therapy is also the treatment of choice in high-risk patients with other forms of cardiomyopathy such as dilated cardiomyopathy or arrhythmogenic right ventricular cardiomyopathy.

There are several other ongoing trials, which are comparing the efficacy of ICD therapy with other treatments in high-risk patients with heart failure or with poor left ventricular function post-myocardial infarction. 

Quality of life with ICDs

An ICD is not a cure. Patients are still considered to be at risk of an arrhythmia, which might cause unconsciousness or cardiac arrest - if only for a few seconds before treatment is delivered. Inevitably^, many patients face significant lifestyle restrictions, and a minority of patients have psychological problems. Although the implant procedure is similar to pacemaker implantation, follow up of patients with ICDs tends to be more complex. Many of the patients have coronary artery disease and poor left ventricular function, and are likely to require ongoing medical treatment.

Although some patients may develop an adverse psychological reaction to ICD implantation, it is important to be aware that these patients often improve with the passage of time as they become accustomed to having the device and adapt to their physical limitations. There is no doubt, however, that many patients tolerate defibrillation shocks very poorly, particularly if they experience multiple shocks. For this reason, anti-arrhythmic drugs may have a role in reducing the incidence of arrhythmias in patients with ICDs.

The issue of fitness to drive in patients with ICDs is a contentious one. Until recently, patients with ICDs in the UK faced a lifetime ban from driving. Since then the regulations in the UK have been relaxed. ICD recipients may be allowed to drive between 1 and 6 months after implantation, depending on individual circumstances.  ICD recipients must also refrain from driving for 6 months following any shock from their device.  The DVLA may also impose certain other restrictions, but these can change over time - contact the DVLA for more details (www.dvla.gov.uk). 

Issues relating to quality of life with an ICD are often discussed by members of CRY's myheart Support Network.

Indications for ICDs

In the UK, the National Institute for Clinical Excellence (NICE) published guidance on the use of ICDs. This stated that ICDs should be routinely considered for both primary and secondary prevention of life threatening arrhythmias. The guidance is summarised below.

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