What is the most common cause of sudden death in a previously healthy young adult (aged 15–35 years)?

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Sudden Death in Young Adults: Most Common Cause

Hypertrophic cardiomyopathy is the single most common cause of sudden cardiac death in previously healthy young adults aged 15-35 years, accounting for approximately one-third of all cases in this population. 1, 2

Primary Etiology

  • Hypertrophic cardiomyopathy (HCM) represents the leading cause, responsible for at least 33% of sudden cardiac deaths in young people under 30-35 years of age, according to the American College of Cardiology and American Heart Association. 1, 2

  • The disease affects approximately 1 in 500 individuals in the general population, making it relatively common despite being historically considered rare. 1

  • HCM is particularly lethal in young competitive athletes, where it accounts for the majority of sports-related sudden deaths, especially in basketball and football players. 1

Mechanism of Death

  • Ventricular tachyarrhythmias (ventricular fibrillation and ventricular tachycardia) are the terminal rhythm in 75-80% of sudden deaths from HCM, emanating from an electrically unstable myocardial substrate characterized by myocyte disarray and fibrosis. 1, 3

  • Death typically occurs during mild exertion, sedentary activities, or sleep, though vigorous physical exertion is a recognized trigger. 1

  • Most deaths occur without reliable warning signs or symptoms, often presenting as the initial manifestation of disease in asymptomatic or mildly symptomatic individuals. 1

Secondary Causes (Ranked by Frequency)

Congenital Coronary Artery Anomalies

  • Second most common cause, accounting for 15-20% of cases, with anomalous origin of the left main coronary artery from the right sinus of Valsalva being the most lethal variant. 1, 2, 4

  • These anomalies frequently remain clinically silent with no premonitory symptoms until the fatal event. 2

Other Genetic Cardiomyopathies and Channelopathies

  • Each accounts for approximately 5% or fewer of deaths, including arrhythmogenic right ventricular cardiomyopathy (more common in Italy), dilated cardiomyopathy, long QT syndrome, Brugada syndrome, and catecholaminergic polymorphic ventricular tachycardia. 1, 2, 4

Myocarditis

  • Responsible for approximately 5% of sudden deaths in young adults and may be clinically silent until the fatal event. 1, 2

Aortic Pathology

  • Aortic valve stenosis and aortic dissection/rupture (including Marfan syndrome) each account for approximately 5% of cases. 1

Critical Demographic Patterns

  • Males predominate by approximately 9:1 in athletic populations and 2:1 in general young populations. 1, 2

  • African-Americans face elevated risk, though the underlying etiologies in this population require further study. 1, 2

  • Risk extends through mid-life and beyond, though most frequent in adolescents and young adults under 30-35 years; achieving any particular age does not confer immunity. 1

Diagnostic Approach for Risk Stratification

When HCM is Suspected

  • Echocardiography is the primary screening tool and readily identifies HCM, showing characteristic asymmetric septal hypertrophy (unlike the symmetric, proportional increases seen in physiologic athlete's heart). 2

  • Look for left ventricular wall thickness ≥15 mm, systolic anterior motion of the mitral valve, and left ventricular outflow tract obstruction. 1

When Coronary Anomalies are Suspected

  • Transesophageal echocardiography, cardiac MRI, or CT coronary angiography may be required for definitive diagnosis. 2, 4

Genetic Testing Considerations

  • Certain genetic defects (cardiac troponin T mutations, specific beta myosin heavy chain mutations like Arg403Gln) are associated with higher sudden death risk. 1

  • Family history of HCM-related sudden death is present in 10-20% of probands, with less than 5% having multiple premature deaths. 1

Critical Pitfalls to Avoid

  • Do not dismiss all athletic bradycardia as benign physiologic adaptation—in athletes over 35 years, coronary artery disease becomes the predominant cause of sudden death. 2, 3

  • Do not assume negative family history excludes genetic disease—up to 40% of dilated cardiomyopathy cases are familial, and many genetic conditions have incomplete penetrance. 2, 3

  • Do not confuse physiologic athlete's heart with pathologic hypertrophy—HCM shows asymmetric septal hypertrophy with small left ventricular cavity, while athlete's heart demonstrates symmetric increases with proportional cavity enlargement. 2

  • Do not overlook myocarditis, which may be clinically silent and accounts for 5% of sudden deaths in the young. 2

Age-Specific Context

While HCM dominates in the 15-35 year age group, atherosclerotic coronary artery disease becomes the overwhelming cause (50-60% of cases) in adults over 35 years, making age a critical factor in differential diagnosis. 3

References

1
Guideline

Guideline Directed Topic Overview

Dr.Oracle Medical Advisory Board & Editors, 2025

2
Guideline

Sudden Cardiac Death in Young Patients

Praxis Medical Insights: Practical Summaries of Clinical Guidelines, 2026

3
Guideline

Sudden Cardiac Death Causes and Mechanisms

Praxis Medical Insights: Practical Summaries of Clinical Guidelines, 2026

4
Research

Congenital and hereditary causes of sudden cardiac death in young adults: diagnosis, differential diagnosis, and risk stratification.

Radiographics : a review publication of the Radiological Society of North America, Inc, 2013

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Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.

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