Sinus Node Dysfunction (Sick Sinus Syndrome)


  • A disease characterised by abnormal sinus node functioning with resultant bradycardia and cardiac insufficiency.


  • May be multi-factorial in origin.
  • Causes can be considered either intrinsic or extrinsic.


  • Idiopathic Degenerative Fibrosis (commonest).
  • Ischaemia.
  • Cardiomyopathies.
  • Infiltrative Diseases e.g. sarcoidosis, haemochromatosis.
  • Congenital abnormalities.

Extrinsic Causes

ECG in Sinus Node Dysfunction

ECG abnormalities can be variable and intermittent. Multiple ECG abnormalities can be seen in sinus node dysfunction including:

  • Sinus Bradycardia.
  • Sinus Arrhythmia — associated with sinus node dysfunction in the elderly in the absence of respiratory pattern association.
  • Sinoatrial Exit Block.
  • Sinus Arrest — pause > 3 seconds.
  • Atrial fibrillation with slow ventricular response.
  • Bradycardia – tachycardia syndrome.

Bradycardia – tachycardia syndrome

  • Alternating bradycardia with paroxysmal tachycardia, often supraventricular in origin.
  • On cessation of tachyarrhythmia may be a period of delayed sinus recovery e.g. sinus pause or exit block.
  • If significant this period of delayed recovery may result in syncope. 

Clinical Manifestations

  • Commonly seen in the elderly but sinus node dysfunction can affect all age groups.
  • Symptoms are due to decreased cardiac output and end-organ hypoperfusion associated with cardiac rhythm abnormality.
  • Wide range of clinical symptoms including syncope, near-syncope, dizziness, fatigue and palpitations.


  • Correction / removal of extrinsic causes e.g. non-essential drugs.
  • Pacemaker insertion – requires correlation of both ECG abnormalities and clinical symptoms.

Recommendation for Pacing in Sinus Node Dysfunction

Class I – Evidence and/or agreement that permanent pacing is useful and effective.

  • Sinus node dysfunction with documented symptomatic bradycardia, including frequent sinus pauses that produce symptoms. In some patients, bradycardia is iatrogenic and will occur as a consequence of essential long-term drug therapy of a type and dose for which there are no acceptable alternatives.
  • Symptomatic chronotropic incompetence.

Class IIa – Conflicting evidence/ divergence of opinion but weight of evidence / opinion in favour

  • Sinus node dysfunction occurring spontaneously or as a result of necessary drug therapy, with heart rate less than 40 bpm when a clear association between significant symptoms consistent with bradycardia and the actual presence of bradycardia has not been documented.
  • Syncope of unexplained origin when major abnormalities of sinus node function are discovered or provoked in electrophysiological studies.

Class IIb – Conflicting evidence/divergence of opinion where usefulness / efficacy is less well established

  • In minimally symptomatic patients, chronic heart rate less than 40 bpm while awake.

Class III –  Permanent pacing  is not useful/effective and in some cases may be harmful.

  • Sinus node dysfunction in asymptomatic patients, including those in whom substantial sinus bradycardia (heart rate less than 40 bpm) is a consequence of long-term drug treatment.
  • Sinus node dysfunction in patients with symptoms suggestive of bradycardia that are clearly documented as not associated with a slow heart rate.
  • Sinus node dysfunction with symptomatic bradycardia due to nonessential drug therapy.


ECG Examples

Example 1: Sinus arrest

Sinus arrest:

  • Prolonged absence of sinus node activity (absent P waves) > 3 seconds.


Example 2:  Bradycardia-tachycardia syndrome

Bradycardia-tachycardia syndrome:

  • Runs of tachycardia interspersed with long sinus pauses (up to 6 seconds).
  • The sinus rate is extremely slow, varying from 40 bpm down to around 10 bpm in places.
  • Sinus beats are followed by paroxysms of junctional tachycardia at around 140 bpm.


Related Topics

Further Reading

Author Credits


  • Surawicz B, Knilans TK. Chou’s Electrocardiography in Clinical Practice. 6th Edition. Saunders Elsevier 2008.
  • Chan TC, Brady WJ, Harrigan RA, Ornato JP, Rosen P. ECG in Emergency Medicine and Acute Care. Elsevier Mosby 2005.
  • Brady WJ, Truwit JD. Critical Decisions in Emergency & Acute Care Electrocardiography. Wiley Blackwell 2009.
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