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Rhythm

Sinus bradycardia

Not medically reviewed · Content last updated · 1 min read ·

This is the date the draft was written, not a medical review date.

Sinus bradycardia is a sinus rhythm with a rate below 60 beats/min. It is often physiological, for example in athletes and during sleep, but may reflect drugs, raised vagal tone or sinus node disease.

ECG criteria

  • Rate below 60 beats/min (a threshold of 50 is often used for clinical significance).
  • Regular rhythm.
  • Normal P wave before every QRS, with normal axis.
  • Normal PR interval, constant.
  • Narrow QRS with normal ST and T waves.

Mechanism

The sinoatrial node fires more slowly because of increased parasympathetic tone, reduced sympathetic drive, drugs or intrinsic node dysfunction. Conduction itself is normal, so each beat keeps the normal sequence of P wave, PR interval and QRS.

Common causes

  • Physiological: athletic training, sleep, young age.
  • Drugs: beta-blockers, some calcium channel blockers, digoxin, amiodarone and others.
  • Raised vagal tone (vasovagal episodes, pain, vomiting) or raised intracranial pressure.
  • Hypothyroidism, hypothermia, inferior myocardial infarction, sick sinus syndrome.

Management principles

Asymptomatic sinus bradycardia usually needs no treatment beyond finding and correcting reversible causes such as drugs or hypothyroidism. Symptomatic or unstable patients are managed by the local advanced life support and bradycardia protocols; follow local guidelines on pacing indications.

High-level principles for study. Treatment decisions follow local guidelines and the clinical situation.

Pitfalls and mimics

  • A slow ventricular rate with a regular pattern may be complete AV block or 2:1 block; check that each QRS is preceded by a P wave with a constant PR.
  • Non-conducted premature atrial beats in bigeminy can produce a slow pulse that mimics sinus bradycardia.
  • Rate alone does not define significance: judge symptoms, perfusion and context.

Practise in the ECG trainer — Recognise this pattern on generated tracings.

References

  1. 2018 ACC/AHA/HRS Guideline on the Evaluation and Management of Patients With Bradycardia and Cardiac Conduction Delay. American College of Cardiology / American Heart Association / Heart Rhythm Society (2018) — Tier 2 (guidelines / primary literature)
  2. 2021 ESC Guidelines on cardiac pacing and cardiac resynchronization therapy. European Society of Cardiology (2021) — Tier 2 (guidelines / primary literature)
  3. Wagner GS, Strauss DG. Marriott's Practical Electrocardiography. Wolters Kluwer, 12th edition (2013) — Tier 3 (textbook)

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