Sudden Cardiac Death in Children, Adolescents, and Young Adults

Introduction

  • Sudden cardiac death (SCD) in children, adolescents, and young adults is rare but poses challenges for medical examiners.
  • These deaths are often unexpected, leaving families emotionally unprepared.
  • There's a common perception that young individuals are inherently healthy and invulnerable.
  • Such cases often attract significant media attention.
  • Accusations of foul play are frequently associated with these deaths.

Outline of Topics

  • Definitions used in this context
  • Epidemiology of SCD
  • Structural Causes:
    • Hypertrophic cardiomyopathy
    • Dilated cardiomyopathy
    • Arrhythmogenic right ventricular dysplasia
    • Aortic stenosis/coarctation
    • Valve disorders
    • Congenital Coronary Artery Anomalies
    • Aortic rupture
  • Infectious Causes:
    • Myocarditis
    • Infectious Endocarditis
  • Conduction System Dysrhythmias:
    • Long QT syndrome
    • Wolff-Parkinson-White syndrome
  • Other Causes:
    • Commotio Cordis
    • Cocaine intoxication
    • Anabolic steroids
    • Dietary and nutritional supplements
    • Anorexia and bulimia
  • Conclusion/Summary

Definitions

  • Sudden Cardiac Death: An unexpected, natural death occurring within one hour of the onset of symptoms.
  • Child: Defined as birth to 12 years.
  • Adolescent: Defined as 12-18 years.
  • Young Adulthood: Defined as 18-35 years.

Epidemiology

  • SCD in young individuals often occurs during play or competitive sports.
  • Intense physical activity can expose previously undiagnosed cardiovascular illnesses under pro-arrhythmic conditions.
  • This involves:
    • Increased demands on the myocardium
    • Increased oxygen requirements
    • Altered electrolyte and catecholamine levels
  • Most SCD cases in young people occur in high school-aged individuals, with a median age of 17 years.
  • Most deaths happen from August through January, during afterschool sports (3-9 pm).
  • Common sports associated with SCD:
    • In the U.S.: Basketball and Football (65%)
    • In Europe: Soccer
  • Gender ratio: 9:1 Male/Female.
    • This may reflect less female participation in high-risk sports.
  • African American males are at the highest risk (44% of cases) due to a statistically increased prevalence of hypertrophic cardiomyopathy.
    • May also reflect less access to specialized care and diagnostic testing.

Case 1

  • A 33-year-old female with no prior medical history but a family history of sudden cardiac death at a young age.
  • She collapsed while jogging in the park.
  • EMS found her pulseless with fixed, dilated pupils.
  • Autopsy revealed a 720 gm heart (normal heart weight for her body weight would be approximately 300 gm).

Structural Causes: Hypertrophic Cardiomyopathy (HCM)

  • Definition: Idiopathic hypertrophied and non-dilated left ventricle.
  • Asymmetric hypertrophy: Septum (most prominent in the subaortic septum) > Ventricle free wall.
  • Often leads to left ventricular outflow tract obstruction.
  • Mitral valve thickening and enlarged left atrium are often observed.
  • 50% of cases are familial (autosomal dominant), involving a myosin heavy chain defect.
  • Linked to HLA on chromosome 6.
  • Relatively common genetic disease (1 in 500 of the general population).
  • One of the most common causes of sudden, unexplained death in young athletes.
  • Sudden death due to HCM often affects young, asymptomatic individuals engaged in frequent physical activity.
  • Physical exertion can lead to an electrically unstable myocardial substrate with reentrant ventricular tachyarrhythmias.
  • Histologically:
    • Disorganized myocardial architecture.
    • Replacement scarring due to microvascular abnormalities and myocardial ischemia.
    • Thickened walls of interstitial vessels.
  • Physiologic abnormality: Reduced chamber size and poor compliance with reduced stroke volume, resulting from impaired diastolic filling of the massively hypertrophied left ventricle.
  • Approximately 25% of patients with HCM have dynamic obstruction of the left ventricular outflow.
  • Limited cardiac output and increased pulmonary venous pressure cause exertional dyspnea.
  • Auscultation reveals a harsh systolic ejection murmur caused by ventricular outflow obstruction as the anterior mitral leaflet moves toward the ventricular septum during systole.
    • Endocardial fibrosis can sometimes be seen from the impact of the leaflet on the septum.
  • Due to the massive hypertrophy, high left ventricular chamber pressure, and potentially abnormal intramural arteries, focal myocardial ischemia commonly results even without coronary artery disease (CAD).
  • Major clinical problems:
    • Anginal pain
    • Atrial fibrillation with mural thrombus formation and possible embolization
    • Infective endocarditis of the mitral valve
    • Intractable cardiac failure
    • Ventricular arrhythmias
    • Sudden death

Case 2

  • A 35-year-old male with a history of severe, chronic alcohol abuse and increasing cardiac failure (last documented EF ~25%).
  • Presented with shortness of breath and leg swelling.
  • Found dead at home.
  • Autopsy revealed a large, soft, and dilated heart.

Structural Causes: Dilated Cardiomyopathy (DCM)

  • Definition: A form of cardiomyopathy characterized by progressive cardiac dilatation and contractile (systolic) dysfunction, usually with concomitant hypertrophy.
  • Also known as “Congestive cardiomyopathy”.
  • In DCM, the heart is usually heavy (often weighing 2-3x normal size) and flabby, with dilatation of all four chambers.
  • Ventricular thickness may be less than, equal to, or greater than normal due to wall thinning that accompanies dilation.
  • Mural thrombi are common and may be a source of thromboemboli.
  • There are no primary valve alterations, and mitral or tricuspid regurgitation, when present, is due to left ventricular chamber dilation (functional regurgitation).
  • Histologic features are nonspecific and usually do not reflect a specific causative agent.
  • Most muscle cells are hypertrophied with enlarged nuclei, but you can also have attenuated, stretched, and irregular myocytes.
  • Interstitial and endocardial fibrosis of variable degree.
  • Small subendocardial scars replacing cells, likely reflecting healing of old ischemic necrosis caused by hypertrophy-induced imbalance between perfusion, supply, and demand.
  • Causes:
    • Approximately 25% to 35% have a familial (genetic) component. Autosomal dominant is usually the predominant pattern. Genetic abnormalities largely affect the cytoskeleton (but mitochondrial defects most commonly cause DCM in children).
    • Toxicities (especially chronic alcoholism, but consider also chemotherapeutic agents like doxorubicin/adriamycin), myocarditis (especially from viral nucleic acids from coxsackievirus B and other enteroviruses), pregnancy-associated nutritional deficiency, or immunologic reaction.
    • When the cause is unknown, such cases are called idiopathic dilated cardiomyopathy.
  • DCM can occur at any age (including childhood) but commonly affects individuals between ages 20-50.
  • Presents with slowly progressive signs and symptoms of CHF (dyspnea/easy fatigability/poor exertional capacity), but patients can slip precipitously from a compensated to a decompensated state.
  • Death is usually attributable to progressive cardiac failure or an arrhythmia and can occur suddenly.
  • Embolism from dislodgement of an intracardiac thrombus may occur.

Case 3

  • A 29-year-old Italian male with no prior medical history, in NYC for a soccer tournament.
  • Collapsed while playing, clutching his chest.
  • Autopsy revealed a thin right ventricle almost entirely composed of fat.

Structural Causes: Arrhythmogenic Right Ventricular Dysplasia (ARVD)

  • Definition: ARVD is associated with marked thinning of the right ventricular wall due to loss of myocytes, with extensive fatty infiltration and replacement fibrosis.
  • Most commonly associated with right-sided heart failure and various rhythm disturbances, particularly ventricular tachycardia.
  • Left-sided involvement with left-sided heart failure can also occur.
  • Grossly, there is marked dilatation and thinning of the right ventricle.
  • Histologically, there is near-transmural replacement of the right ventricle free wall myocardium by fat and fibrosis.
  • Cause: Most cases have no family history, but familial forms do occur.
  • Although a gene defect has been localized on chromosome 14, the pathogenesis remains obscure.
  • Pedigree analyses of large kindreds indicate autosomal dominant inheritance with variable penetrance.

Case 4

  • A 33-year-old Electrician with no prior medical history.
  • Complained of chest pain while helping a colleague move heavy furniture, then collapsed and became unresponsive.
  • Autopsy revealed a ruptured aorta just proximal to an area of stenosis of the ascending aortic arch, with hemopericardium (cardiac tamponade).

Structural Causes: Aortic Coarctation/Stenosis

  • Definition: Narrowing or constriction of the aorta. Ranks high in frequency among the common structural anomalies.
  • M:F frequency 2:1.
  • Two classic forms:
    • Infantile: Diffuse, tubular hypoplasia of the aortic arch proximal to a PDA that is often symptomatic in early childhood.
    • Adult form: Discrete, localized, ridge-like infolding of the aorta, just opposite the closed ductus arteriosus (ligamentum arteriosum). Most common type.
  • Clinical manifestations depend almost entirely on the severity of the aortic narrowing and the patency of the ductus arteriosus.
  • Usually manifests early in life, if not immediately after birth. In infants, the delivery of unsaturated blood through the DA produces cyanosis localized to the lower half of the body.
  • Coarctation of the aorta without a PDA are often asymptomatic:
    • There is hypertension in the upper extremities, but weak pulses and a lower blood pressure in the lower extremities.
    • There are manifestations of arterial insufficiency (i.e., claudication and coldness).
    • In adults, there is characteristic development of collateral circulation between the precoarctation arterial branches and the postcoractation arteries through enlarged intercostal and internal mammary arteries. This manifests itself radiologically as visible erosions (“notching”) of the undersurface of the ribs.
    • Murmurs are present throughout systole. Sometimes a thrill may be present, and there is cardiomegaly owing to left ventricular hypertrophy.
  • Without surgical repair, 60% of patients die before 40 years of age due to:
    • Aortic rupture
    • Endocarditis
    • Hypertension
    • Congestive heart failure

Case 5

  • A 27-year-old woman whose only past medical history was a recent fracture of her left ankle.
  • Heard a loud