michael s
(Michael S)
#1
87 What are the indications for implantable
cardioverter defibrillator (ICD) implantation and
what are the survival benefits?
Roy M John and Mark Squirrell
Studies in the early 1980s showed that recurrence rates were high
for patients presenting with a malignant arrhythmia unrelated to
myocardial ischaemia or infarction. Survivors of cardiac arrest,
those presenting with sustained monomorphic VT and un-
explained syncope in the presence of heart disease clearly are
patients at high risk for sudden cardiac death. A series of clinical
trials completed in the recent past have confirmed the uniform
survival benefit from ICD therapy in such patients (AVID, CASH,
CIDS) when compared to therapy with amiodarone or sotalol. In
the largest prospective randomised trial (Antiarrhythmics versus
Implantable Defibrillators Trial – AVID trial), the ICD reduced
mortality by 39% at 1 year and 31% at 3 years. Most patients
randomised to the antiarrhythmic arm of the trial were treated
with amiodarone.
With remarkable improvements in ICD technology allowing
easier implantation, the ICD is being embraced increasingly and
earlier in the course of cardiac disease. Attention has now
turned to primary prevention of sudden death. For patients with
asymptomatic non-sustained VT, there appears to be a clear
survival benefit from ICD in the presence of a remote myocardial
infarction, LVEF <40%, and inducible VT at electro-
physiological study (MADIT, MUSTT). Interestingly, this
benefit cannot be extrapolated to patients without non-
sustained VT or inducible VT. The CABG patch trial that
randomised patients with LVEF <36% and positive signal
averaged ECG to ICD or not during elective bypass surgery
failed to show a survival benefit. The role of the ICD in primary
prevention of sudden death in non-ischaemic dilated cardiomy-
opathy is also unclear at this time. Clinical trials are in progress.
The benefit from an ICD appears to be greatest for patients with
severe LV function and additive to conventional therapy with
ACE inhibitors and beta adrenergic blockers. In the AVID trial for
example, survival benefit with ICD was observed only when
LVEF was less than 35%. Similarly, in the primary prevention
trials, the mean LVEF was 30%. One could advance the argument
