ICDs and EF

	AVID was a randomized trial of ICD vs amiodarone
in patients with VF or VT. It showed a benefit for ICD.
	The first substudy tried to identify a group of
AVID patients who were at very low risk of death and who
therefore would not benefit from an ICD. Such a group 
was found. They have these characteristics:

an index arrhythmia of ventricular fibrillation
absence of cerebral vascular disease
absence of prior arrhythmia
either a history of revascularization or an EF higher 
than 27%.
	
	The second substudy had a similar result. This
examined whether patients with low EF got more benefit
from an ICD than patients with higher EF. The AVID 
study showed that when EF was less than 35%, the
benefit of an ICD was much more than if EF was higher
than 35%.
	This suggests there is a low-risk patient group,
with well-preserved ejection fraction, who may not 
benefit much from ICD therapy.