100 QUESTIONS IN CARDIOLOGY

that the ICD should be reserved for those with the worst LV

function. Unfortunately, such patients have competing causes for

mortality such as pump failure and electromechanical

dissociation that are responsible for 50% of deaths. On the other

hand, patients with little or no impairment of LV function and a

single tachyarrhythmic event usually have late and rare recur-

rence leading to sudden death. An ICD can potentially restore

them to near normal life expectancy in the absence of ongoing

myopathic process. The long term studies requiring more than

one life span of an ICD are not available to define the true value of

ICD therapy in such patients.

Although the ability of the implantable cardioverter de-

fibrillator (ICD) to terminate potentially lethal ventricular

arrhythmias is well acknowledged there is less consensus as to

whom should receive an ICD. A good place to start is the

American College of Cardiology/American Heart Association

Practice Guidelines for Arrhythmia Devices.^1 There are three

classes of indications: class one, where there is evidence and/or

general agreement that the treatment is beneficial, useful and

effective; class two, where there is conflicting evidence or a diver-

gence of opinion; and class three, where there is evidence and

general agreement that a treatment is not useful or effective.

The class one indications for ICD implantation are:

11 Cardiac arrest due to VF or VT not due to a transient or reversible

cause.

22 Spontaneous sustained VT.

33 Syncope of undetermined origin with clinically relevant,

haemodynamically significant sustained VT or VF induced at

electrophysiological study when drug therapy is ineffective,

not tolerated or not preferred.

44 Non-sustained VT with coronary disease, prior MI, LV

dysfunction, and inducible VF or sustained VT at electro-

physiological study that is not suppressible by a class I anti-

arrhythmic drug.

The class two indications for ICD implantation are:

11 Cardiac arrest presumed to be due to VF when electro-

physiological testing is precluded by other medical conditions.

22 Severe symptoms attributable to sustained ventricular

arrhythmias while awaiting cardiac transplantation.