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).

Table 1: Drugs causing Bradycardia

AV blocking agents Beta-blockers
  Calcium channel blockers
Cardiac glycosides Digoxin
Cholinergic agents Organophosphates (including nerve agents)
Antihypertensive agents Clonidine
Antiarrythmics Quinidine
Antipsychotic agents such as lithium Amitriptyline
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