- 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).
- Infiltrative Diseases e.g. sarcoidosis, haemochromatosis.
- Congenital abnormalities.
ECG in Sinus Node Dysfunction
- 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.
- 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
- 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.
Example 1: Sinus arrest
Example 2: 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.
- Da Costa D, Brady WJ, Edhouse J. Bradycardias and atrioventricular conduction block. BMJ. 2002 Mar 2;324(7336):535-8. Review. PMID: 11872557
- Hampton, JR. The ECG In Practice, 6e
- Surawicz B, Knilans T. Chou’s Electrocardiography in Clinical Practice: Adult and Pediatric, 6e
- Wagner, GS. Marriott’s Practical Electrocardiography 12e
- Chan, TC. ECG in Emergency Medicine and Acute Care
- Mattu, A. ECG’s for the Emergency Physician
LITFL Further Reading
- ECG BASICS — Waves, Intervals, Segments and Clinical Interpretation
- ECG A to Z by diagnosis –alphabetical diagnostic approach to the ECG
- ECG CLINICAL CASES — ECG’s placed in clinical context with a challenging Q&A approach
- 100 ECG Quiz — Self-assessment tool for examination practice
- ECG Reference SITES and BOOKS — the best of the rest
- LITFL ECG IMAGE Database — Searchable database of LITFL ECG’s
- ECG and Cardiology Eponymous Syndromes — Cheats guide to eponymous emancipation
- ECG Exam Template — a framework for answering ECG exam questions.