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 bradydysrhythmias, often without appropriate atrial or junctional escape rhythms
  • Syndrome includes:
    • Chronic SA nodal dysfunction
    • Frequently depressed pacemakers
    • Atrioventricular nodal conduction disturbances
    • Sluggish return of SA nodal activity after DC cardioversion
  • Presents in all age groups (mean age >65 yr)
  • Male/female ratio is 1:1

Etiology

  • Intrinsic causes:
    • Most common cause: Idiopathic degenerative fibrosis of sinus node
    • Coronary artery or SA nodal artery disease
    • Cardiomyopathy
    • Ion-channel mutations/familial SSS
    • Leukemia and metastatic disease
    • Infiltrative cardiac or collagen vascular disease, including amyloidosis
    • Surgical trauma
  • Inflammatory diseases:
    • Rheumatic heart disease
    • Chagas disease
    • Pericarditis and myocarditis
  • 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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