Digoxin

Digoxin is a cardiac glycoside that inhibits the Na⁺-K⁺-ATPase pump. Toxicity may be:

• Cardiac
  Typically tachyarrhythmias with ↓ AV nodal conduction, and may be life-threatening.
• Non-cardiac
  May cause hyperkalaemia and yellow vision, in addition to more general symptoms such as confusion and GI upset.
• Chronic
  Due to progressive accumulation. Most common presentation, and has high mortality (15-30%). Due to:
  • Too high a daily dose
  • ↓ Renal function with unchanged dose
  • Drug interactions
• Acute
  From a large single ingestion:
  • Toxicity: 2mg
  • Fatal:
    • Adult: >10mg
    • Children: ~4mg

Adverse effects may be delayed by several hours.

Epidemiology and Risk Factors

Pathophysiology

Aetiology

Drug interactions:

• ↓ Clearance
  • Amiodarone
  • Non-dihydropyridine calcium channel blockers
• ↑ Absorption
  • Macrolides
    Kill gut bacteria which may digest some of the absorbed dose.
  • PPI
    ↑ Permeability.

Clinical Features

Cardiac:

The tachyarrhythmias are essentially any that don’t rely on AV conduction.

• ↓ HR and heart block due to slowing of AV nodal conduction
• ↑ Automaticity
  General ↑ in rate of discharge of pacemaker cells, causing a variety of tachyarrhythmias:
  • AF
  • Flutter
    With low ventricular rate due to AV block.
  • Ventricular ectopics
  • VF
  • VT

Non-cardiac:

• Xanthopsia
  Yellow bias of colour perception.
• Hyperkalaemia
  Due to inhibition of the Na⁺-K⁺-ATPase in cardiac and skeletal muscle.
• GI symptoms
  Nausea, vomiting, diarrhoea, abdominal pain.
• Confusion

Xanthopsia vs. Normal Vision

Diagnostic Approach and DDx

Investigations

Bedside:

• ABG/VBG
  • Potassium level
• ECG

Laboratory:

• Blood
  • Serum digoxin level
  • UEC
    • Glucose

Imaging:

Other:

Management

• Manage arrhythmia
• Correct electrolytes and acidosis
  Toxicity is exacerbated by hypokalaemia, hypomagnesaemia, hypocalcaemia, and acidosis.
• Give digoxin-specific antibody
• Multi-dose activated charcoal

Resuscitation:

• C
  • ↓ HR
    • Atropine
    • Adrenaline
    • Pacing
      Rarely effective.
  • ↑ HR
    • Magnesium
    • Lignocaine
• F
  • Electrolytes
    • Hyperkalaemia
      • Insulin-dextrose as first line
      • Correct to high-normal
    • Hypomagnesaemia
    • Hypocalcaemia
  • Acidosis

Specific therapy:

Serum digoxin levels cannot be accurately measured for ~3 weeks after digoxin antibody as the assay will measure bound digoxin.

• Pharmacological
  • Digoxin-specific antibody fragments
    Indicated for:
    • Cardiac arrest
    • Life-threatening arrhythmia
    • Lethal dose ingestion
    • Persistent hyperkalaemia or arrhythmia
    • Serum level >12ng/mL
  • Activated charcoal
    Multiple doses to interrupt enterohepatic recirculation.
• Procedural
• Physical

Supportive care:

Disposition:

Preventative:

Marginal and Ineffective Therapies

Anaesthetic Considerations

Complications

Prognosis

Key Studies

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References

1. Bersten, A. D., & Handy, J. M. (2018). Oh’s Intensive Care Manual. Elsevier Gezondheidszorg.
2. Wagner, BT. Kline, D. The Basis of Colour Vision. Vision and Aging Lab: University of Calgary. 2007. Accessed via the Wayback Machine.