Sinus Bradycardia
February 15th, 2021
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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