The<unk><unk><unk> s of 12 young American<unk>  (under age 35) were analyzed in a 2003 medical review: Cause Incidence Hypertrophic cardiomyopathy 26% Genetically determined Commotio cordis 20% Structurally normal heart, disrupted electrically by a blow to the chest Coronary artery anomalies 14% Exact mechanisms unknown; some association with other congenital CVS abnormalities Left ventricular hypertrophy of undetermined origin 7% Probable variant of hypertrophic cardiomyopathy Myocarditis 5% Acute inflammation Ruptured aortic aneurysm (Marfan syndrome) 3% Genetically determined; also associated with unusual height Arrhythmogenic right ventricular cardiomyopathy 3% Genetically determined Tunneled coronary artery 3% Congenital abnormality Aortic valve stenosis 3% Multiple causes Atherosclerotic coronary artery disease 3% Mainly acquired; dominant cause in older adults Other diagnosis 13% While most causes of<unk><unk><unk>  relate to congenital or acquired cardiovascular disease, an exception is commotio cordis, in which the heart is structurally normal but a potentially fatal loss of rhythm occurs because of the accident of timing of a blow to the chest. Its fatality rate is about 65% even with prompt CPR and defibrillation, and more than 80% without. Age 35 serves as an approximate borderline for the likely cause of<unk><unk><unk> . Before age 35, congenital abnormalities of the heart and blood vessels predominate. These are usually asymptomatic prior to the fatal event, although not invariably so. Congenital cardiovascular<unk> s are reported to occur disproportionately in African-American<unk> . After age 35, acquired coronary artery disease predominates (80%), and this is true regardless of the<unk> s former level of fitness. Various performance-enhancing drugs can increase<unk>  risk, though evidence has been inconclusive about their involvement in<unk><unk><unk> s.
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