Digoxin toxicity

Introduction

Digoxin is a medication used to treat various heart conditions. Digoxin is derived from the species Digitalis lanata and was first described by William Withering in 1785.

Nowadays, the only clinical indication for digoxin use is atrial fibrillation with rapid ventricular response. Very rarely might be used as an inotropic agent in patients with heart failure as a third-line therapy.

Effects

  • negative chronotropic  → slows down the heart rate

  • negative dromotropic → slows conduction over the AV node

  • positive inotropic → enhance myocardial contraction (increases the amount of calcium in the heart’s cells)

Digoxin therapeutic window

  • level > 2ng/ml is toxic and increases the likelihood of arrhythmias

Digoxin toxicity effects

  • CVS: Palpitations, syncope, dyspnoea
  • GIT: Nausea, vomiting, anorexia, diarrhoea
  • Visual: Blurred vision, yellow/green discolouration, haloes
  • CNS: Confusion, dizziness, delirium, fatigue

ECG changes 

1) Therapeutic 

  • ST segment depression resembling “reverse tick”, “scoop appearance”, “Salvador Dali sign”
  • flattened, inverted, or biphasic T wave
  • shortened QT interval 
  • mild PR interval prolongation (due to increased vagal tone)
  • increased U wave amplitude

Picture 1 Typical digitalis related ST depression + biphasic T wave

2) Toxic 

       The classic digoxin toxic dysrhythmia combines:

  • supraventricular arrhythmia (increased automaticity)
  • slow ventricular rate (decreased AV conduction) 

       Typically occurs: 

  • bradycardia due to AV block or significant decrease in heart rate 
  • atrial tachycardia with a 2:1 conduction, bidirectional ventricular tachycardia and atrial fibrillation with a slow ventricular response
  • digoxin intoxication can also cause ventricular tachycardia or ventricular fibrillation resulting in death

 

ECG 1  Digoxin effect (slow atrial fibrillation and typical ST depressions seen in lateral leads)

References 

  1. https://www.healio.com/cardiology/learn-the-heart/ecg-review/ecg-topic-reviews-and-criteria/digoxin-effect
  2. https://ecgwaves.com/topic/digoxin-ecg-changes-arrhythmias-digoxin-digitalis/
  3. https://bjcardio.co.uk/2015/08/digoxin-and-the-heart/
  4. https://litfl.com/digoxin-toxicity-ecg-library/
  5. https://litfl.com/digoxin-effect-ecg-library/