Digoxin Toxicity – A Practical Review

CLINICAL FEATURES

  • Acute digoxin toxicity
    • Time course: initial toxic effects of nausea and vomiting occur at 2-4 hours, peak serum levels at 6 hours and life-threatening cardiovascular complications  at 8-12h
    • GI: anorexia, nausea, vomiting, diarrhoea, abdominal pain
    • Metabolic: hyperkalaemia (early sign of significant toxicity)
    • CVS: enhanced automaticity (atrial tachycardias (e.g. flutter, AF) with AV block, VF, VT, ventricular ectopic beats), bradyarrhythmias (Conduction delays / blocks, slow or regularised AF), hypotension, shock
    • CNS: lethargy, confusion
  • Chronic digoxin toxicity
    • Typically occurs  in the context of intercurrent illness, especially with impaired renal function
    • Clinical features are a combination of toxicity and the intercurrent illness
    • Symptoms may have an insidious onset over days to weeks
    • Features include those of acute digoxin toxicity as well as visual disturbances (e.g. reduced acuity, yellow halos (xanthopsia) and altered color perception (chromatopsia))

DIAGNOSIS

  • Urgent K level, creatinine
  • Serum digoxin level –  a steady state level 6 or more hours after the last dose; levels can be misleading as levels near the therapeutic range (0.6-1.3 nmol/L) correlate poorly with severity of intoxication
  • ECG

MANAGEMENT

  • ACUTE DIGOXIN TOXICITY
    • Digoxin-induced cardiotoxicity is refractory to standard measures
      • Bradyarrhythmias
        • Digibind is the definitive treatment
        • Atropine
        • Epinephrine (but may aggravate cardiac irritability)
        • Pacing (rarely effective)
      • Tachyarrhythmias
        • Digibind is the definitive treatment
        • MgSO4as an adjunctive measure
        • Often refractory to cardioversion
    • Hyperkalemia: Insulin and glucose, bicarbonate Calciumis traditionally contra-indicated due to the risk of precipitating a ‘stone heart’.
    • Activated charcoal if the patient presents <1h post-ingestion and not vomiting (unlikely to prevent severe toxicity in large ingestions)
  • CHRONIC DIGOXIN TOXICITY
    • Resuscitation as for acute digoxin toxicity
    • Renal replacement therapy may be indicated in the context of renal failure and hyperkalemia
    • Digibind!