Definition
- Sinus rhythm with a resting heart rate of < 60 bpm in adults, or below the normal range for age in children.
Normal heart rates in children
- Newborn: 110 – 150 bpm
- 2 years: 85 – 125 bpm
- 4 years: 75 – 115 bpm
- 6 years+: 60 – 100 bpm
Causes
Non-pharmacological
- Normal during sleep
- Increased vagal tone (e.g. athletes)
- Vagal stimulation (e.g. pain)
- Inferior myocardial infarction
- Sinus node disease
- Hypothyroidism
- Hypothermia
- Anorexia nervosa
- Electrolyte abnormalities – hyperkalaemia, hypermagnesaemia
- Brainstem herniation (the Cushing reflex)
- Myocarditis
Pharmacological
- Beta-blockers
- Calcium-channel blockers (verapamil & diltiazem)
- Digoxin
- Central alpha-2 agonists (clonidine & dexmedetomidine)
- Amiodarone
- Opiates
- GABA-ergic agents (barbiturates, benzodiazepines, baclofen, GHB)
- Organophosphate poisoning
Differential Diagnosis
- Sinus bradycardia may be indistinguishable from type II sino-atrial block.
ECG Example
Sinus bradycardia secondary to anorexia nervosa
- Sinus bradycardia (35 bpm) in a 15-year old girl with anorexia nervosa.
- Note the prominent U waves in the precordial leads, a common finding in sinus bradycardia.
Related Topics
Further Reading
- ECG BASICS — Waves, Intervals, Segments and Clinical Interpretation
- ECG CLINICAL CASES — Your favourite ECG’s placed in clinical context with a challenging Q&A approach
- ECG and Cardiology Eponymous Syndromes — Cheats guide to eponymous emancipation
- ECG Exam Template — a framework for the FACEM part 2 exam.
- ECG Reference Sites on the WEB — the best of the rest
Author Credits
References
- Chan TC, Brady WJ, Harrigan RA, Ornato JP and Rosen PR. ECG in Emergency Medicine and Acute Care. Elsevier 2005
- Mattu A, Brady W. ECGs for the Emergency Physician 2, BMJ Books 2008.
- Surawicz B, Knilans T. Chou’s Electrocardiography in Clinical Practice (6th edition), Saunders 2008.
- Wagner, GS. Marriott’s Practical Electrocardiography (11th edition), Lippincott Williams & Wilkins 2007.
About Edward Burns
