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ECG Disease Patterns
ECG Disease Patterns

Digoxin Toxicity

February 15th, 2021


Digoxin is a cardiac glycoside which can be associated with significant toxicity. Certain ECG findings are characteristic.
Digoxin inhibits the Na+/K+ ATPase pump, which results in sodium influx and potassium efflux. This subsequently increases the activity of the Na+/Ca2+ exchange pump, resulting in calcium influx which increases automaticity and has a positive inotropic effect (increases contractility). Digoxin also increases parasympathetic (vagal) tone, causing reduced conduction through the AV node.
  • Effects of Digoxin

  • Increased automaticity - due to an increase in intracellular calcium
  • Reduced conduction via the AV node - due to an increase in parasympathetic (vagal) tone
Certain ECG changes with digoxin may purely indicate a therapeutic effect (such as the ST depression and T wave flattening), while other changes (such as T wave inversion and arrhythmias) indicate toxicity.
  • ECG Findings in Digoxin Toxicity

  • ST depression - down-sloping or scooped
  • T wave changes - flattening, inversion or biphasic T waves
  • Due to Increased Automaticity

  • QT shortening (due to reduced ventricular repolarisation time)
  • Premature beats - atrial, junctional or ventricular
  • Tachyarrhythmias - atrial tachycardia, accelerated junctional tachycardia
  • Due to Reduced Conduction

  • Prolonged PR interval
  • Bradyarrhythmias - sinus bradycardia, bundle branch block, AV block
The ST depression of digoxin toxicity is characteristically scooped - this is often referred to as a reverse tick or Salvador Dali's moustache ST depression.
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