Causes of Bradycardia

The causes of bradycardia can be broadly categorised as:

• Normal physiological variants as seen, for example, in athletes
• Intrinsic cardiac causes such as:
  • Idiopathic degeneration
  • Infarction and ischaemia
  • Myotonic dystrophy
  • Congenital Heart disease
  • Sick sinus syndrome
• Infections such as endocarditis
• Drugs (see next page)
• Autonomic mediated such as:
  • Situational – vasovagal syncope
  • Carotid sinus hypersensitivity
  • Cough or micturition syncope
• Systemic illness such as:
  • Hypothyroidism
  • Hypothermia
  • Sarcoid
  • Amyloidosis
• Head injury: Cushing’s response
• Electrolyte disturbance: Hyperkalaemia and hypokalaemia

Drugs Causing Bradycardias

Various drugs can also affect the electrophysiology of the heart myocytes and their nerve supply (Table 1).