What causes bradycardia?

Causes of Bradycardia

Bradycardia is caused by a wide range of physiological and pathological conditions including sinus node dysfunction, atrioventricular conduction disorders, medication effects, and various systemic conditions that affect cardiac conduction. 1

Sinus Node Dysfunction Causes

• Intrinsic causes:

  • Age-related degenerative changes (most common)
  • Ischemic heart disease and myocardial infarction
  • Cardiomyopathies
  • Infiltrative diseases (amyloidosis, sarcoidosis)
  • Congenital heart defects
  • Surgical trauma (cardiac surgery, valve replacement, maze procedure)
  • Heart transplantation (acute or chronic rejection)

• Extrinsic/Reversible causes:

  • Medications:

    • Beta-blockers
    • Non-dihydropyridine calcium channel blockers (verapamil, diltiazem) 2
    • Antiarrhythmic drugs (amiodarone, sotalol)
    • Digoxin
    • Lithium
    • Methyldopa
    • Risperidone
    • Cisplatin
    • Interferon

  • Electrolyte abnormalities:

    • Hyperkalemia
    • Hypokalemia
    • Hypoglycemia

  • Increased vagal tone:

    • Athletic training
    • Sleep
    • Vasovagal episodes
    • During defecation, urination, or vomiting

  • Endocrine disorders:

    • Hypothyroidism
    • Hypopituitarism

  • Neurological conditions:

    • Increased intracranial pressure
    • Central nervous system abnormalities 3
    • Stroke

  • Infectious causes:

    • Meningitis 3
    • Lyme disease
    • Legionella
    • Typhoid fever
    • Viral myocarditis
    • HIV infection 3

  • Other systemic conditions:

    • Hypothermia 4
    • Hypoxemia
    • Hypercarbia
    • Acidosis
    • Sleep apnea
    • Obstructive jaundice 3
    • Hypovolemic shock

Atrioventricular Block Causes

• First-degree, second-degree, and third-degree AV block:
  • Age-related degenerative changes
  • Ischemic heart disease
  • Medications (same as those causing sinus bradycardia)
  • Increased vagal tone
  • Congenital heart defects
  • Infiltrative diseases
  • Infectious causes (myocarditis)
  • Autoimmune disorders (maternal lupus with anti-Ro/SSA antibodies) 3
  • Tumors (rare) 3

Special Considerations

• Tachy-brady syndrome: A form of sick sinus syndrome characterized by alternating episodes of bradycardia and tachycardia (often atrial fibrillation) 5

• Pediatric bradycardia: Normal ranges differ by age; causes include congenital heart disease, genetic variants, and post-surgical complications 6

• Neonatal bradycardia: May be associated with maternal conditions (lupus with anti-Ro/SSA antibodies) or congenital heart malformations 3

Diagnostic Approach

When evaluating bradycardia, consider:

1. Is it symptomatic? Symptoms include fatigue, reduced exercise capacity, dizziness, pre-syncope, syncope, and heart failure symptoms 3

2. Is it persistent or intermittent? Intermittent bradycardia may have variable contributions from intrinsic and extrinsic mechanisms 3

3. Are there reversible causes? Always check for medication effects, electrolyte abnormalities, hypothyroidism, and increased vagal tone before considering permanent interventions 3

4. Is there evidence of structural heart disease? Echocardiography may be indicated when clinically appropriate 3

Management Considerations

Treatment depends on:

• Presence and severity of symptoms
• Underlying cause (reversible vs. irreversible)
• Risk of progression to more severe conduction disorders
• Associated conditions (heart failure, structural heart disease)

For symptomatic bradycardia with hemodynamic compromise, atropine is first-line therapy, followed by temporary pacing if necessary. Permanent pacing may be indicated for persistent symptomatic bradycardia not due to reversible causes 1.

Remember that bradycardia can sometimes be physiologic (as in athletes) or even beneficial in certain cardiac conditions, so treatment should be guided by symptoms and hemodynamic effects rather than heart rate alone 7.