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: Cushings 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 |