Sick Sinus Syndrome

Basics

Description

  • Collective term used to describe dysfunction in the sinus node’s automaticity and impulse generation
  • Mechanism:
    • Caused by progressive degeneration of the intrinsic functions of the sinoatrial (SA) node
    • Characterized by periods of unexplained sinus node dysfunction leading to bradyarrhythmias, often without compensatory atrial or junctional escape beats
  • Syndrome includes:
    • Sinus Arrhythymia
    • Sinus Bradycardia
    • Sinus Pause or Arrest
    • SA Exit Block
    • Atrial Fibrillation (AFib) with slow ventricular response
    • Tachy-Brady Syndrome
  • Presents in all age groups (mean age >65 yr)
  • Male/female ratio is 1:1

Etiology

  • Intrinsic causes:
    • Most common cause is idiopathic degenerative fibrosis of the sinus node
    • Coronary artery or SA nodal artery disease
    • Congenital heart disease
    • Ion-channel mutations/familial SSS
    • Leukemia and metastatic disease
    • Infiltrative disorders including amyloidosis, sarcoidosis, and hemachromatosis
    • Surgical trauma
  • Inflammatory diseases:
    • Rheumatic heart disease
    • Chagas disease
    • Pericarditis and myocarditis
  • COVID-19:
    • Novel mechanism with ongoing investigation
    • possibly direct invasion of virus into cardiac conduction system
  • Extrinsic causes (not true SSS but similar presentation):
    • Drugs:
      • β-Blockers, calcium-channel blockers, clonidine
      • Digoxin, amiodarone
      • Lithium, phenytoin
    • Autonomically mediated syndromes (cholinesterase deficiency)
    • Hyperkalemia/hypokalemia
    • Hypothyroidism
    • Hypothermia
    • Hypoglycemia
    • Sepsis/infection

Pediatric Considerations

Associated with congenital abnormalities and subsequent surgical repair, as well as with congenital SA nodal artery deficiency

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