Bradycardia

This article discusses sinus bradycardia i.e. a heart rate of less than 60 beats/minute, the rhythm of which is initiated by the sinoatrial node.

Causes

• Physiological: Athletes/during sleep
• Cardiac:
  • Following a myocardial infarction
  • Atrioventricular block
  • Sick sinus syndrome: A condition where the sinoatrial node becomes fibrosed and degenerates, resulting in various symptoms including palpitations and syncope.
• Drugs:
  • Beta-blockers
  • Amiodarone
  • Non-dihydropyridine calcium channel blockers i.e. verapamil and diltiazem
  • Digoxin
• Non-Cardiac:
  • Hypothyroidism
  • Vasovagal syncope
  • Hyperkalaemia
  • Hypothermia

Management

The following management is based on the UK Resus Council 2021 guidelines.

Patients should be assessed using the A-E approach (airways, breathing, circulation, disability and exposure), and IV access needs to be obtained. Blood pressure, oxygen saturations and ECG need to be monitored, and the patient should be given oxygen if there is hypoxia. If there is a reversible cause to the bradycardia, it should be treated e.g. hyperkalaemia or beta-blocker overdose.

If serious clinical features such as chest pain, shock, syncope, heart failure, hypotension, altered mental status etc occur, the patient requires intervention with one of the following options:

• First line: Atropine (500mcg IV which can be repeated every 3-5 minutes up to a maximum dose of 3mg)
• Second line: If the initial dose of atropine fails to provide a satisfactory response, one of the following can be used:
  • Repeat atropine (up to 3mg)
  • Other drugs: Adrenaline, isoprenaline, aminophylline, glucagon 
  • Alternatively, transcutaneous pacing can be used.

If there are no signs or symptoms indicating lack of perfusion secondary to the bradycardia, the patient can be observed and monitored provided they do not have a risk of asystole. The following factors indicate this risk:

• Mobitz II heart block
• Third-degree heart block with broad QRS
• Recent asystole
• Ventricular pause of >3 seconds

If there is risk of asystole, they require the same management as those with adverse signs i.e. atropine etc.

References

https://www.resus.org.uk/library/2015-resuscitation-guidelines/peri-arrest-arrhythmias

https://www.resus.org.uk/sites/default/files/2021-04/Bradycardia%20Algorithm%202021.pdf 

https://www.ncbi.nlm.nih.gov/books/NBK493201/

Davidson’s Principles and Practice of Medicine, 23rd Edition

https://www.nhsinform.scot/illnesses-and-conditions/heart-and-blood-vessels/conditions/heart-block