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Adult Bradycardia

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Overview

Bradycardia is described as a pulse rate <60 bpm, however, for some individuals, they may not be symptomatic until their heart rate is below 50 bpm.

Bradycardia can be classified according to which site is disturbed. Some forms of bradycardia (Mobitz type I (Wenckebach) atrioventricular (AV) block and sinus bradycardia) can be normal in young, athletic people.

Causes

Some causes include:

  • Sinus problems:
    • Sinus bradycardia:
      • May be normal in young, athletic people)
    • Sick sinus syndrome:
      • Conditions that lead to dysfunction of the sinoatrial node (SAN). This includes degenerative fibrosis of the SAN
  • Atrioventricular (AV) conduction disorders:
    • First-degree heart block
    • Second-degree heart block:
      • Mobitz I (Wenckebach)
      • Mobitz II
      • 2:1 block
    • Third-degree heart block

Presentation

The hallmark feature is a heart rate of <60 bpm. Associated features include:

Management

Initial management

Management is based on the Resuscitation Council UK bradycardia algorithm:

  • Assess with an ABCDE approach
  • Give oxygen if needed and obtain IV access
  • Monitor ECG, blood pressure, and oxygen saturations, and record a 12-lead ECG
  • Identify and treat reversible causes (e.g. electrolyte abnormalities)
  • Assess for evidence of life-threatening signs – this guides management and includes:
    • Shock – may be characterised by tachycardia with or without hypotension
    • Syncope
    • Myocardial ischaemia
    • Heart failure

Evidence of life-threatening signs present

  • Give IV atropine 500 micrograms
  • If unsuccessful, try one of:
    • Repeating atropine up to a maximum total dose of 3 mg (6 times) or
    • Transcutaneous pacing or
    • Consider alternative drugs such as an isoprenaline, adrenaline, aminophylline, dopamine, glucagon (if beta-blocker or calcium channel overdose), or glycopyrrolate (may be used instead of atropine)
  • If these measures fail, seek specialist help for transvenous pacing 

No evidence of life-threatening signs present

  • First assess for the risk of asystole. A high risk of asystole is present if any of the following apply:
    • Recent asystole
    • Mobitz II AV block
    • Complete heart block with a broad QRS complex
    • Ventricular pause >3 seconds
  • If any of the above are present, manage with the same protocol as if there is evidence of life-threatening signs present (i.e. starting with atropine as mentioned above)
    • Even if these respond to initial measures, specialist advice must be sought to consider transvenous pacing

If no risk factors for asystole are present: observe 

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