Synonyms: sinoatrial disease, tachy-brady syndrome

Definition

Sick sinus syndrome is a collection of conditions in which the ECG indicates sinus node dysfunction.¹ It is characterised by sinus node dysfunction with an atrial rate inappropriate for normal requirements. Sick sinus syndrome is usually caused by idiopathic fibrosis of the sinus node.

Aetiology

Causes include:¹

• An intrinsic disease of the sinus node:
  • Idiopathic degeneration of the sinus node is the most common cause of sick sinus syndrome
  • Collagen vascular disease; amyloidosis, haemochromatosis, fatty replacement, sarcoidosis
  • Familial sinoatrial node disorders; Friedreich's ataxia, muscular dystrophy
  • Cardiomyopathies; ischaemia, myocardial infarction, myocarditis, pericarditis, rheumatic heart disease, surgical injury, arteritis
  • Surgical injury
• Extrinsic causes:
  • Hyperkalaemia, hypoxia, hypothermia, hypothyroidism, hyperthyroidism
  • Drugs, e.g. digoxin, calcium-channel blockers, betablockers, sympatholytic agents, antiarrhythmic drugs
  • Toxins, e.g. result of sepsis

Sleep apnoea may be a contributing factor by causing reduced cardiac oxygenation. Paediatric causes include congenital abnormalities and sinoatrial nodal artery deficiency.

Epidemiology

Sick sinus syndrome is most common in the elderly, but can occur in all ages.

Presentation

• Abnormalities in sick sinus syndrome include episodes of sinus bradycardia, sinus arrest or exit block, combinations of sinoatrial and atrioventricular nodal conduction disturbances, and atrial tachyarrhythmias (tachycardia-bradycardia syndrome or 'tachy-brady syndrome').
• Patients are often asymptomatic, or have subtle or nonspecific symptoms, such as fatigue.
• Presentation may be with syncope, palpitations or dizziness.
• Central nervous system: dementia, irritability, lethargy, lightheadedness, confusion, memory loss, nocturnal wakefulness, syncope.
• Cardiovascular system: angina, arterial thromboemboli, cerebrovascular accident, congestive heart failure (dyspnoea), palpitations.
• Other: digestive disturbances, dizziness, errors in judgment, facial flushing, fatigue, oliguria.
• Symptoms associated with sick sinus syndrome may be aggravated by digoxin, verapamil, betablockers, sympatholytic agents such as clonidine and methyldopa, and antiarrhythmic agents.

Investigations

• Blood tests include renal function, electrolytes, thyroid function tests and drug levels (e.g. digoxin).
• ECG: arrhythmias associated with sick sinus syndrome include:
  • Atrial bradyarrhythmias: sinus bradycardia, sinus arrest (with or without junctional escape), sinoatrial exit block (Mobitz type I or Mobitz type II block), ectopic atrial bradycardia, atrial fibrillation with slow ventricular response greater than 3-second pause following carotid massage, long pause following cardioversion of atrial tachyarrhythmias
  • Atrial tachyarrhythmias: atrial fibrillation, atrial flutter, atrial tachycardia, paroxysmal supraventricular tachycardia
  • Ventricular (escape) tachyarrhythmia
  • Alternating bradycardias and tachycardias: tachy-brady syndrome
• Ambulatory ECG to associate arrhythmias with symptoms.
• Echocardiogram: associated structural and functional heart abnormalities.

Management

• The treatment of choice for symptomatic bradyarrhythmias in patients with sick sinus syndrome is the placement of a pacemaker.²
• Atrial or dual-chamber pacemakers usually provide effective relief of symptoms and lower the incidence of atrial fibrillation, thromboembolic events, heart failure and mortality, when compared with ventricular pacemakers.^3,4,5
• Betablockers, calcium-channel blockers and digoxin may be used in conjunction with a pacemaker for tachyarrhythmias.
• Anticoagulation will be needed for patients with atrial fibrillation.⁶

Complications

• Patients with sick sinus syndrome who have tachy-brady syndrome or chronic atrial fibrillation are at risk for embolic cerebrovascular event.
• Myocardial infarction or sudden cardiac death.
• Congestive heart failure.

Document references

1. Adan V, Crown LA; Diagnosis and Treatment of Sick Sinus Syndrome. American Family Physician; Volume 67, Number 8; April 15 2003.
2. Dual-chamber pacemakers for the treatment of symptomatic bradycardia, NICE Technology Appraisal (February 2005)
3. Dretzke J, Toff WD, Lip GY, et al; Dual chamber versus single chamber ventricular pacemakers for sick sinus syndrome and atrioventricular block. Cochrane Database Syst Rev. 2004;(2):CD003710. [abstract]
4. Alboni P, Menozzi C, Brignole M, et al; Effects of permanent pacemaker and oral theophylline in sick sinus syndrome the THEOPACE study: a randomized controlled trial. Circulation. 1997 Jul 1;96(1):260-6. [abstract]
5. Andersen HR, Nielsen JC, Thomsen PE, et al; Long-term follow-up of patients from a randomised trial of atrial versus ventricular pacing for sick-sinus syndrome. Lancet. 1997 Oct 25;350(9086):1210-6. [abstract]
6. Anticoagulation - oral, Clinical Knowledge Summaries (April 2009)

Internet and further reading

• Masserli AW; Sinus Node Dysfunction; eMedicine; August 2009
• ECG Library; © Stephen Gerred (Medical Registrar Auckland, New Zealand) Dean Jenkins (Specialist Registrar, Llandough Hospital, Cardiff, Wales)
• Cobbe SM and Rankin AC in Oxford Textbook of Medicine, 4th Edition. Eds; Warrell DA et al. OUP 2003.

Acknowledgements