Presence of underlying vulnerable substrate

• atherosclerosis
  • 80% of individuals that die with SCD have underlying atherosclerosis and risk for myocardial infarction or mild ischemia. These conditions lead to loss of cardiac muscle and scar formation, which is a cause of infarction
• structural - Cardiomyopathy)
  • Hypertrophy of the heart (heart is not functional because the walls are thick and stiff—> loses contractility) or dilated cardiomyopathy
• electrical (<5%)
  • Primary electrical and genetical abnormalities, like ion-channel abnormalities, valvular or congenital heart disease and other causes

Presence of trigger

• The trigger can be anything that causes ischemia or that makes the heart susceptible to ischemia/faster repolarization of cardiac cells
• 
• Transient ischemia: exercise is too demanding and we cannot increase blood supply as much
• Hemodynamic fluctuation: the wall of the marathon
• Neurocardiovascular influences: increases activity of sympathetic system
• Environmental factors: temperature is too high

Aetiology differs according to age

• Young patients and children
  • Electrical issues
    • Catecholaminergic VT (CPVT)
    • Brugada syndrome
    • Long QT Syndrome
• > 15-20 years old
  • Structural issues and cardiomyopathies
    • Hypertrophic Cardiomyopathy
    • Arrhythomogenic RV Cardiomyopathy
    • Dilated Cardiomyopathy
• > 35 years old
  • Structural issues and cardiomyopathies
    • Hypertrophic Cardiomyopathy
    • Arrhythomogenic RV Cardiomyopathy
    • Dilated Cardiomyopathy
• High incidence of coronary artery pathology
  • Artherosclerotic
  • Anomalous Coronary Ostia
  • Valvular heart disease
  • Coronary heart disease

Aetiology of the underlying pathology differs according to sex

• Men are extensively affected by Coronary Artery Disease
• Women is more diverse

Electrical Instability

• Results from the complex interaction between underlying a vulnerable substrate and a trigger or transient event
• The electrical instability is followed by ventricular arrythmia(85%) and asystole.
• Asystole is the cessation of heart activity - the heart can only beat so fast until it stops

Risk factors:

• Risk factors for coronary heart disease
  • smoking - MI
  • hypertension
  • diabetes
  • obesity
  • cholesterol (especially at younger age)
  • kidney disease
• Atrial fibrillation RR 2.5
  • more likely to develop ventricular fibrillation
• Genetics RR 1.8
• Psychological risk factors
  • low > high socio-economic status
  • stress/anxiety disorders/depression
• Environmental/lifestyle-related risk factors
  • nutritional risk factors (alcohol, magnesium, Mediterranean diet)
  • Time of day/week
  • Pollution
• Summary
  
• Usually a risk factor is present before a CHD/CHF, and can cause either hypertrophy, myocardial inflammation or fibrous—>result in vulnerable substrate—> and if a trigger is stimulated, it can lead to SCD.
  • Yet, there are some genes that protect against triggers + if environmental changes were applied.