• Ventricular heart rate <60 beats/min:
    • Sinus bradycardia can be a normal variant
    • All other rhythms are pathologic
  • May be asymptomatic or have hypotension, altered mental status, fatigue, nausea, syncope, PEA
  • Treatment varies based on ECG findings and clinical status


  • Idiopathic:
    • Healthy athletes
  • Intrinsic cardiac disorders:
    • Sinus node dysfunction such as sick sinus syndrome (may alternate with tachycardia)
    • Atrioventricular block
    • Junctional or ventricular escape rhythm
    • Infiltrative disease:
      • Amyloidosis, sarcoidosis, hemochromatosis
    • Collagen vascular disease:
      • Systemic lupus erythematosus (SLE), scleroderma, rheumatoid arthritis
    • Anatomic abnormalities:
      • Congenital, postsurgical, posttransplant, postradiation
    • Muscular disorders:
      • Myotonic muscular dystrophy
    • Trauma with myocardial contusion
  • Extrinsic disorders:
    • Hypoxia
    • Cardiac injury and infarction:
      • RCA infarction can cause sinus bradycardia
      • LAD infarction can cause high-grade block
    • Toxic ingestion
      • Opiates, β-blockers, calcium channel blockers, digoxin, clonidine, antiarrhythmics, lithium, organophosphates
    • Electrolyte abnormalities:
      • Hypo-/hyperkalemia, hypoglycemia, hypo-/hypercalcemia, hypermagnesemia
    • Acidosis
    • Vital sign abnormalities:
      • Hypoxia, hypothermia
    • Endocrine abnormalities:
      • Hypothyroidism
    • Infectious disease:
      • Lyme disease, Chagas disease, diphtheria, endocarditis, myocarditis
    • Neurologic disorders:
      • Hemorrhagic CVA, head injury, increased intracranial pressure, increased vagal tone, carotid sinus hypersensitivity, spinal cord injury
      • Can be triggered by micturition, defecation, coughing, vomiting, ocular pressure, or other Valsalva maneuvers

Pediatric Considerations
Hypoxia is the most common etiology in children
In an infant, start compressions for HR <60 if symptomatic

Pregnancy Considerations
Maternal SLE can result in congenital complete heart block

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