Sick Sinus Syndrome

Synonym: sinoatrial disease, tachy-brady syndrome

Sick sinus syndrome is a collection of conditions in which the ECG indicates sinus node dysfunction.¹ It is characterized 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. Causes include:¹

• An intrinsic disease of the sinus node:
  • Idiopathic degeneration of the sinus node is the commonest 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, beta blockers, sympatholytic agents, antiarrhythmic drugs
  • Toxins, e.g. sepsis

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

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

• 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 non-specific 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, beta blockers, sympatholytic agents such as clonidine and methyldopa, and antiarrhythmic agents.

• 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: tachycardia-bradycardia syndrome
• Ambulatory ECG to associate arrhythmias with symptoms.
• Echocardiogram: associated structural and functional heart abnormalities.

• The treatment of choice for symptomatic bradyarrhythmias in patients with sick sinus syndrome is the placement of a pacemaker.
• 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 to ventricular pacemakers.^2,3,4
• Beta-blockers, calcium channel blockers, and digoxin may be used in conjunction with a pacemaker for tachyarrhythmias.
• Anticoagulation will be needed for patients with atrial fibrillation.

• Patients with sick sinus syndrome who have tachycardia-bradycardia syndrome or chronic atrial fibrillation are at risk for embolic stroke.
• Myocardial infarction or sudden cardiac death.
• Congestive heart failure.