Sick sinus syndrome

Background

• Also known as sinus dysfunction, sinoatrial node disease, and tachycardia-bradycardia syndrome (a specific variant)
• Collection of signs or symptoms that indicate sinus node dysfunction
• May present as bradycardia, tachycardia, or alternating bradycardia and tachycardia
  • 50% have alternating bradycardia and tachycardia (i.e. tachycardia-bradycardia syndrome)

Causes

• Intrinsic:
  • Degenerative fibrosis
  • Infiltrative disease process (e.g. amyloidosis)
  • Ion channel dysfunction
  • SA node remodeling
  • Myocardial ischemia
• Extrinsic:
  • Pharmacologic
  • Metabolic/electrolyte disturbance
  • Autonomic dysfunction
  • Obstructive sleep apnea

Clinical Features

• Syncope or presyncope (50%)
• Palpitations
• Fatigue
• Generalized weakness
• Dyspnea
• Angina
• Disturbed sleep
• Confusion

Differential Diagnosis

Narrow-complex tachycardia

• Regular
  • AV Node Independent
    • Sinus tachycardia
    • Atrial tachycardia (uni-focal or multi-focal)
    • Atrial fibrillation
    • Atrial flutter
    • Idiopathic fascicular left ventricular tachycardia
  • AV Node Dependent
    • Paroxysmal supraventricular tachycardia (PSVT)
      • AV node re-entry tachycardia (AVNRT)
      • AV re-entry tachycardia (AVRT)
        • Lown-Ganong-Levine syndrome
        • Wolff–Parkinson–White syndrome
    • Junctional tachycardia
• Irregular
  • Multifocal atrial tachycardia (MAT)
  • Sinus tachycardia with frequent PACs, PJCs, PVCs
  • Atrial fibrillation
    • Atrial fibrillation with RVR
  • Atrial flutter with variable conduction
  • Digoxin Toxicity

Symptomatic bradycardia

• Cardiac
  • Inferior MI (involving RCA)
  • Sick sinus syndrome
• Neurocardiogenic/reflex-mediated
  • Increased ICP
  • Vasovagal reflex
  • Hypersensitive carotid sinus syndrome
  • Intra-abdominal hemorrhage (i.e. ruptured ectopic)
• Metabolic/endocrine/environmental
  • Hyperkalemia
  • Hypothermia (Osborn waves on ECG)
  • Hypothyroidism
    • Myxedema coma
  • Hypoglycemia (neonates)
• Toxicologic
  • B-blocker
  • Ca-channel blocker
  • Clonidine
  • Digoxin toxicity
  • Ethanol
  • Opioids
  • Organophosphates
  • Xylazine toxicity
• Infectious/Postinfectious
  • Chagas disease
  • Lyme disease
  • Syphilis
• Other
  • Brash syndrome

Evaluation

• ECG identification, inpatient telemetry, outpatient Holter monitoring, event monitoring, loop monitoring
  • ECG frequently negative for findings early in disease course

Management

• Remove extrinsic factors and/or pacemakers
  • Pacemakers do not reduce mortality, only decrease symptoms
• Consider reversible causes e.g. treat hyperkalemia or hypokalemia
• Atropine for bradycardia, progress to catecholamine or pacing
• consider aminophylline, which inhibits suppressive effects of adenosine on the SA node in:
  • Acute inferior MI with 2nd or 3rd degree AV block; 250mv IV bolus
  • Heart transplant: 6mg/kg in 100-200mL of IV fluid over 20-30 minutes
  • Spinal cord injury: 6mg/kg in 100-200mL of IV fluid over 20-30 minutes

Disposition

• Admit

Complications

• (50%) Tachy-brady syndrome with atrial fibrillation or atrial flutter
• (50%) AV block

See Also

• Symptomatic Bradycardia