Implantable defibrillators (ICD)

Implantable defibrillators (ICD)

As we have seen above, a large number of patient with heart failure die suddenly. In fact, those with the poorest cardiac function tend to die of pump failure, but those with better heart function tend to die suddenly (Figure 23). These are the result of developing malignant arrhythmias that stop the heart from pumping (cardiac arrest). Those patients resuscitated from ventricular tachycardia or cardiac arrest, are at highest risk of developing further arrhythmic events.

A number of clinical trials have now shown that anti-arrhythmic drugs have little effect in reducing mortality in heart failure patients. The implantable defibrillator (Figure 24 and 25), a device like a pacemaker (but larger) that can be fully implanted within the body under local anaesthetic taking approximately an hour, can protect heart failure patients from risk of sudden death. They can terminate rapid heart rhythms by use of the pacemaker function of the device, which is painless and is successful in 80% of cases. But when the heart is so rapid or irregular that it has stopped pumping, the device will deliver a shock to reset and restore normal rhythm (Figure 26). A number of clinical trials have shown that the ICD is highly effective in reducing the risk of sudden death in patients who have had arrhythmias by 30-50% in 5 years (Figure 27).

More recently the indications for use of ICDs have also expanded to include certain patients with impaired heart function whom have never had an abnormal rhythm event but considered at significant risk (primary prevention). Trials of patients with a previous heart attack or cardiomyopathy (heart muscle disorder but normal coronary circulation) with severely impaired cardiac function have shown mortality reduction of over 20-31% (Figure 28 and 29). On the strength of these powerful studies, the National Institute of Clinical Excellence, European and American Cardiac Societies have now made clear guidelines for patient selection and device implantation to prevent sudden cardiac death. A cardiac rhythm specialist should be consulted to assess for suitability and benefit from these devices.