Hypertrophic cardiomyopathy (HCM) is the most common cause of death in the 
young, particularly in young competitive athletes. Death often occurs suddenly 
in asymptomatic, apparently healthy individuals. Several clinical parameters as 
well as genetic factors have been characterized that can identify those HCM 
patients who are at high risk for sudden cardiac death (SCD). The clinical 
parameters that have some predictive values for SCD in HCM patients are the 
following: a prior history of SCD, a family history of SCD, history of syncope, 
symptomatic ventricular tachycardia on Holter monitoring, inducible ventricular 
tachycardia during electrophysiologic studies, and myocardial ischemia in 
children with HCM. Recent identification of mutations in the beta myosin heavy 
chain gene and genotype-phenotype correlation in HCM patients have shown that 
the beta myosin heavy chain mutations are also prognosticators in HCM families. 
Several mutations such as Arg403Gln and Arg719Gln are associated with a high 
incidence of SCD, while Leu908Val mutation is associated with a benign course 
and a low incidence of SCD in HCM families. Additional genetic factors such as a 
polymorphism in angiotensin-converting enzyme I gene may also contribute to a 
high incidence of SCD in HCM families. Identification and characterization of 
HCM patients at high risk for SCD provide the opportunity to render prophylactic 
therapeutic interventions, such as implantation of defibrillators, in these 
individuals.