The National Institute for Clinical Excellence (NICE) has
recommended that implantable cardioverter defibrillators should be routinely
considered for patients who have survived ventricular fibrillation or
ventricular tachycardia with haemodynamic compromise for secondary prevention of
arrhythmic death. It also recommends it in certain patients who have not yet had
a serious arrhythmic event but who are at high risk of sudden cardiac death as
primary prevention. This second group comprises mainly patients who have
survived a myocardial infarction. Only a tiny minority of these patients is
currently being investigated and treated with implantable defibrillators.
After an infarction,
-
impaired ventricular function with an ejection fraction
of 35% or less
-
non-sustained ventricular tachycardia (three beats or
more) on ambulatory 24 hour monitoring
-
inducible ventricular tachycardia at electrophysiological
testing
-
identify a subgroup of patients at high risk of sudden
death.
Paradoxically, antiarrhythmic drugs increase the risk of
death and should be avoided in patients with significantly impaired ventricular
function.
Two prospective randomised controlled trials of preventive
strategies have shown the benefit of the implantable cardioverter defibrillator
in this high risk group. The multicentre automatic defibrillator trial, or MADIT,
compared the implantable cardioverter defibrillator with best medical treatment,
which included amiodarone in 74% of the control group. It was a relatively small
study, justified by its sequential trial design.
The multi-centre unsustained tachycardia, or MUSIT, compared
an electrophysiology guided strategy with no antiarrhythmic therapy. The
strategy involved serial drug testing - antiarrhythmic drugs were given, and the
electrophysiology study repeated to determine if ventricular tachycardia could
still be induced.
Both these trials have shown that implantable cardioverter
defibrillators confer a relative risk reduction of 54%-60% in all-cause
mortality. Using this evidence the American College of Cardiology, American
Heart Association, National Institute of Clinical Excellence, and European
Society of Cardiology have all recommended using an implantable cardioverter
defibrillator as a primary prevention strategy in such high risk patients. In
addition, NICE recommends that screening programmes should be put in place so
that these patients can be identified.
Best guesses suggest that after an infarction about 1% of
screened patients should be considered for cardioverter defibrillator
implantation. There are 300 000 myocardial infarctions each year in the United
Kingdom; over half the patients survive. Using these assumptions, over 1500
patients each year should be considered for an implantable cardioverter
defibrillator as a primary prevention strategy if
