Sinus Bradycardia
Overview
Sinus bradycardia is initiated by the sinus node, and occurs in the setting of reduced automaticity due to either intrinsic or extrinsic causes.
Look For
- Decreased heart rate - <60bpm (or 50bpm when asleep)
- Regular rhythm - normal PR interval with P waves preceding each QRS complex
- Normal axis - positive P waves in leads I and II
Causes of Sinus Bradycardia
Intrinsic
- Idiopathic degeneration
- Myocardial infarction
- Infiltrative disease - sarcoidosis, amyloidosis, haemochromatosis
- Connective tissue disease - SLE, scleroderma, RA
- Cardiac surgery - valvular surgery, correction of congenital heart disease
- Infections - Lyme disease, endocarditis
Extrinsic
- Physiologic - sleep, athletes
- Autonomic - neurocardiogenic syncope, carotid sinus hypersensitivity
- Drugs - beta blockers, calcium channel blockers, digoxin, adenosine, flecainide, ivabradine, clonidine, acetylcholinesterase inhibitors
- Hypothyroidism
- Hypothermia
- Hyperkalaemia
- Obstructive sleep apnoea
- Raised intracranial pressure
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