Sudden cardiac death is defined as an event that is non-traumatic, non-violent, unexpected, and resulting from sudden cardiac arrest within six hours of previously witnessed normal health.¹

Epidemiology

• The incidence of sudden cardiac death is approximately 1 in 1,000 per year.²
• The incidence of sudden cardiac death parallels the incidence of ischaemic heart disease, with the peak incidence occurring in people aged 45-75 years.³
• Sudden cardiac death in those aged 35 years or less is more common in males than females.⁴
• Sports activity in adolescents and young adults is associated with an increased risk of sudden cardiac death.⁵ Sudden cardiac death is predominantly caused by pre-existing congenital cardiac abnormalities rather than the sporting activity.⁶
• The combined disease prevalence of all cardiovascular disorders that predispose young athletes to sudden cardiac death is approximately 0.3%.⁷
• Premature atherosclerotic disease is an important cause in young adults.⁶
• There is an increased risk of sudden cardiac death associated with cocaine abuse.⁸

Causes⁹

In 4% of sudden deaths in the 16-64 age group, post-mortem examination fails to identify a cause; these cases are diagnosed as having sudden arrhythmic death syndrome (SADS).^2,10

• Coronary artery disease: acute myocardial infarction, congenital anomaly of coronary arteries, coronary artery embolism, coronary arteritis
• Hypertrophic obstructive cardiomyopathy (HOCM)
• Dilated cardiomyopathy
• Arrhythmogenic right ventricular cardiomyopathy (ARVC)
• Cardiac ion channelopathies, e.g. congenital long QT syndrome (LQTS), Brugada syndrome
• Valvular heart disease (with or without infective endocarditis), e.g. aortic stenosis, mitral valve prolapse
• Cyanotic heart disease, e.g. Fallot's tetralogy, transposition
• Acyanotic heart disease, e.g. ventricular septal defect, patent ductus arteriosus
• Cardiac arrhythmias, e.g. Wolff-Parkinson-White syndrome
• Myocarditis
• Myotonic dystrophy

Differential diagnosis

Other causes of sudden death in young people include:¹¹

• Serious infection, e.g. meningitis, encephalitis
• Epilepsy
• Asthma
• Pulmonary embolism
• Intracranial haemorrhage

Investigations

• The background history of the victim of sudden death should be elicited including preceding symptoms, previous medical history and circumstances of death.
• The family history must be established, including any histories of unexplained syncope, sudden death or muscle weakness.
• Laboratory investigations include: cardiac enzymes, electrolytes, calcium, and magnesium, drug levels (e.g. procainamide, tricyclic antidepressants, digoxin), toxicology screen (e.g. cocaine), thyroid function tests (hyperthyroidism can lead to tachycardia and tachyarrhythmias) and brain natriuretic peptide (BNP).³
• Sometimes the underlying diagnosis may only be identified by detecting abnormalities in relatives (e.g. cardiac ion channelopathies). The investigations of first degree relatives include:
  • 12-lead ECG
  • Echocardiogram
  • Holter monitor (24 hours or longer)
  • Exercise ECG
• Depending on these results, further specialist tests can be undertaken, e.g. contrast ventriculography in the diagnosis of arrhythmogenic right ventricular dysplasia.¹²
• Genetic testing: current knowledge of specific genetic associations with various causes of sudden cardiac death, e.g. LQTS, Brugada syndrome and HOCM, helps in confirming diagnosis and following up family members. Increasing knowledge is likely to give genetic testing a greater role in diagnosis and management in the future.

Prevention

• If a diagnosis has been made then advice on testing of other relatives is appropriate.
• Pre-participation cardiovascular screening of young competitive athletes by 12-lead ECG (in addition to history and physical examination) has been recommended both in Europe and the United States.¹³
• The detection of cardiac abnormalities, such as hypertrophic cardiomyopathy, dilated cardiomyopathy, or arrhythmogenic right ventricular dysplasia offers the prospect of treatment that will improve symptoms and greatly reduce the risk of sudden death.¹⁴