Sudden cardiac death is the most devastating manifestation of hypertrophic 
cardiomyopathy (HCM) and often occurs in young and previously asymptomatic 
patients. Therefore, risk stratification for sudden death has a major role in 
the management of HCM and has acquired even greater relevance since the 
implantable cardioverter-defibrillator (ICD) has proved to be highly effective 
in preventing sudden death in this disease. The ICD is definitely indicated for 
secondary prevention of sudden death in patients with HCM who have survived a 
cardiac arrest with documented ventricular fibrillation, or experienced one or 
more episodes of sustained ventricular tachycardia. However, uncertainties 
persist regarding the precise selection of patients for primary prophylactic ICD 
implantation. A number of risk markers are used to assess the magnitude of risk, 
including family history of premature sudden death; extreme left ventricular 
(LV) hypertrophy (> 30 mm) in young patients; nonsustained ventricular 
tachycardia on Holter electrocardiographic recording; unexplained (not neurally 
mediated) syncope, particularly in young patients; and blood pressure decrease 
or inadequate increase during upright exercise. Multiple risk factors convey a 
definite increase in risk. However, a single risk factor such as family history 
of multiple sudden deaths, massive LV hypertrophy in a young patient, or 
frequent and/or prolonged runs of nonsustained ventricular tachycardia on 
Holter, may also justify consideration of a prophylactic ICD.