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Idnetifying The Right Patients 455
Who Benefits From AICD Implantation

Primary prevention: of 35% or less and are in heart failure (NYHA class II
or III) are recommended AICD implantation.
Patients with a prior cardiac arrest, although at very
high risk of a recurrent event, form only a small
proportion of patients who die suddenly. Often Nonischemic Cardiomyopathy:
sudden death happens as the first event in patients In patients with left ventricular dysfunction, but
without prior warning. In order to prevent these without a previous MI, recommendation to implant
deaths, the concept of primary prevention evolved. an AICD for primary prevention is based on the
SCDHeFT trial referred to above and the DEFINITE
This involves identifying patients who are at risk of
experiencing a lethal arrhythmia, but who have not trial (5) which both showed survival benefit in this
yet experienced a cardiac arrest. Structural heart subgroup of patients. However, the benefit from AICD
disease is one of the most important markers of implantation in patients with ventricular dysfunction
risk and primary prevention is most often applied to and heart failure in the absence of coronary artery
patients with structural heart disease. disease has always been less robust than that in
patients with coronary
However, since not all these patients would require
device implantation, other markers have to be used to artery disease. The more recent DANISH trial (6) which
identify those most at risk. Despite various markers specifically studied this in a large group of patients
like frequent premature ventricular complexes, found no survival benefit from AICD implantation.
non-sustained VT, signal averaged ECG, Heart rate
variability, T wave alternans, etc having been studied, Hypertrophic Cardiomyopathy:
ejection fraction remains the one robust measurement Another form of cardiomyopathy that is relatively
that has been repeatedly shown in various studies common and carries a risk of sudden death in some
to predict future risk of sudden death. Therefore, patients is hypertrophic cardiomyopathy (HCM).
despite its known various limitations, it remains the With a population prevalence of about 1 in 500, it
most clinically useful marker of risk. The important is benign in most patients, but is also one of the
group of heart diseases where primary prevention is most important causes of sudden death in the young
considered are discussed below. and in athletes. Current guidelines suggest that all
patients with HCM should be evaluated for their risk
Ischemic Cardiomyopathy: of sudden death at initial presentation. Presence of
Coronary artery disease is the most important one of the established risk markers
underlying substrate for lethal ventricular arrhythmias. unexplained syncope, maximal left ventricular wall
Patients with significant left ventricular dysfunction thickness more than 30 mm, non sustained ventricular
following an acute myocardial infarction (MI) are at tachycardia, abnormal blood pressure response to
risk. exercise and a history of sudden death in a first
degree relative should prompt AICD implantation.
The pivotal study was MADIT II (3) in which patients
with a previous MI and left ventricular dysfunction
with ejection fraction (EF) of 30 or less were When not to implant an AICD:
randomized to conventional medical therapy alone or As important as, or maybe more important than
implantation of a defibrillator in addition. Implantation knowing when to implant an AICD is knowing
of defibrillators was found to provide a survival benefit when not to implant an AICD. Idiopathic ventricular
with a mortality of 14.2% compared to 19.8% in the tachycardia is always amenable to ablation and
conventional medical treatment group over a follow does not warrant AICD implantation. Patients with
up of 20 months. Based on this study, patients with incessant or recurrent ventricular tachycardia are
EF of less than or equal to 30% at least 40 days after often advised emergency AICD implantation. The
an acute MI are recommended AICD implantation. emphasis should be on control of the arrhythmias
with drugs or ablation in these patients. Only after
Another major study was the SCDHeFT trial (4), where control of the arrhythmia should AICD implantation
patients with ischemic and non-ischemic causes of be considered. The overall clinical status of the patient
cardiomyopathy with EF less than 35% and heart should be taken into consideration when deciding on
failure were randomized to placebo, Amiodarone the need for device implant. Any coexistent condition
or AICD implantation. Over a follow up period of that results in an expected longevity of less than a
45 months, mortality was 29%, 28% and 22% in the year should be a contraindication for AICD implant.
placebo, amiodarone and AICD implantation groups. Significant comorbidities like renal dysfunction
Based on this patients with prior MI who have an EF

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