Defibrillators

Defibrillators (AICD, single and biventricular) and Cardiac Resynchronisation devices

These devices treat serious and life-threatening arrhythmias and are the most effective way of doing so. They are used either to prevent sudden death in patients at risk of it because of structural heart diseases such as coronary disease or cardiomyopathy (‘Primary Prevention’) or after a near miss clinical event (‘Secondary Prevention’). All AICDs also function as pacemakers if needed ie if the heart slows down excessively.

Defibrillators treat arrhythmias in 2 ways: in the first instance the device tries to stop the abnormal rhythm with a burst of high speed pacing (cardioversion). If that fails, the device will give the heart a shock via the right ventricular lead to reset its rhythm (defibrillation). Patients are usually not aware of cardioversion & nearly always aware of defibrillation.

Since these are life-saving devices we do need to monitor them closely. In particular, we need to ensure that the system (AICD device & leads) is working normally and that inappropriate shocks are minimised.

Some patients with heart failure have a problem with the coordination of the heart’s contraction (dyssynchrony) which makes the left ventricle contract less efficiently. Standard single chamber AICDs only have a lead in the right ventricle which can actually worsen heart failure if the device is needed to pace the heart frequently. Placing  a lead in the left ventricle and pacing using both right and left ventricular leads can lead to improvement in the heart’s pumping function. We only use biventricular devices which are also Defibrillators – BiV AICDs.

X-Ray showing the atrial lead (on the upper left) and the left ventricular and right ventricular leads in a patient with a BiV AICD

The devices often record other important information such as atrial arrhythmias (atrial fibrillation) and some devices can detect fluid accumulation in the chest which can be an early indicator of heart failure.

Remote monitoring transmits important information on device function between clinic visits and this supplementary information can be very valuable to the treating cardiologist, family doctor and of course, patient.