having a dig…

the case.

87 year old female presents to your ED following an intentional overdose. She tells you that approximately 4 hours ago she ingested ‘most of [her] digoxin tablets’ that she bought earlier in the afternoon.

After speaking to family and paramedic staff, in reality, she has systematically dissolved and swallowed close to 150 tablets of 62.5mcg digoxin; ~ 9.4 milligrams !!

[DDET Outline your risk assessment…]

Acute intoxication  occurs with >10x the normal daily dose ingested.
Typically 75mcg/kg in children is safe.

Potentially lethal digoxin toxicity can be predicted by:

1. Dose ingested >10mg in adults [>4mg in children]
2. Serum digoxin level > 15 nmol/L at anytime
3. Serum potassium > 5.5 mmol/L

[/DDET]

[DDET Her bedside investigations return…]

• VBG.
  • pH 7.31 / pCO2 54 / HCO3 26 / BE 1 / Lactate 2.8
• BSL.
  • 6.1 mmol/L
• Potassium [from blood gas].
  • 4.7 mmol/L
• 12-lead ECG.

[/DDET]

[DDET Describe & interpret her ECG…]

• Rate.
  • ~54 /min
• Rhythm.
  • Irregular
  • No discernible P-waves
• Axis.
  • Normal [+90*]
• Intervals.
  • PR – n/a
  • QRS ~ 80-90msec
  • QTc ~ 380 msec
• Segments.
  • Down-sloping ST depression in leads V5-V6.
• Other.
  • Incomplete LBBB pattern
  • Movement artefact [most pronounced in lead I & III]

Interpretation.
Slow atrial fibrillation with lateral ST changes consistent with digoxin-effect.

[/DDET]

[DDET What other ECG changes can you expect in this scenario?]

The ECG manifestations of digoxin toxicity centre around two electrocardiographic effects;
(1) increased automaticity & (2) AV-blockade.

• Increased automaticity
  • Ventricular ectopy, bigeminy or trigeminy.
  • SVTs with AV-block [atrial flutter or atrial tachycardia]
• AV blockade
  • 1st, 2nd or 3rd degree AV-block
  • Atrial fibrillation with ventricular response < 60 bpm

The other ‘classic’ ECG for dig-toxicty is bidirectional ventricular tachycardia [often found on exams…]

• Hallmark is beat-to-beat alternation of the frontal QRS axis.
  • This may manifest with alternating left & right bundle-branch blocks…

For more ECG examples check out LITFL’s ECG Features of Digoxin Toxicity.

[/DDET]

[DDET What about a DIGOXIN level ?!?]

Her level comes back at 14.5 nmol/L [Normal = 0.6-1.2 nmol/L]

[/DDET]

[DDET Outline your management]

Acute Digoxin Toxicity

This is a potentially life-threatening toxicology emergency & requires full cardiorespiratory monitoring and 1:1 nursing in a resuscitation area.

RESUSCITATION. 

Predict & prepare for potential life-threats;

1. Hypotension
   • IV access x2
   • Crystalloid boluses
   • Vasopressors
2. Cardiac dysrhythmias
   • Lignocaine 1mg/kg  [up to 100mg] IV
   • Phenytoin  15-20mg/kg [up to 1g] IV → may enhance AV-conduction
   • MgSO4 → 2-4 grams IV
3. Cardiac arrest
   • ACLS
   • Empiric  20 ampoules of Digoxin-immune Fab [Digibind]
   • Continue resuscitative efforts for at least 30mins post-Digibind administration

Other complications & considerations;

• Hyperkalaemia
  • NaHCO3 100mmol IV bolus [1mmol/kg in children]
  • Insulin + Dextrose
  • Calcium is still controversial !!
    • Theoretical concern regarding “Stone Heart” – calcium tetany produced by increasing the already elevated intracellular calcium levels produced by digoxin.
    • Levine M et al (2011) – 23 patients with acute digoxin toxicity received IV calcium. No increase in mortality or dysrhythmias.
• AV-blockade
  • Atropine 600mcg IV x3 doses
  • Pacing: external or transvenous – rarely effective

DECONTAMINATION.

• Consider activated charcoal in cooperative adults within the first hour of ingestion.
• Caution in those with vomiting & potential co-ingestion that will lead to altered level of consciousness.

THE ANTIDOTE.

Digoxin-immune Fab [aka. Digibind]
The definitive treatment for acute digoxin poisoning !!

Indications.

• ACUTE:
  • Cardiac arrest
  • Life-threatening cardiac dysrhythmia
  • Dose ingested >10mg in adults [>4mg in children]
  • Serum digoxin level > 15 nmol/L at anytime
  • Serum potassium > 5.5 mmol/L

THE DOSE in ACUTE DIGOXIN OVERDOSE.
No. of Ampoules = Ingested dose (mg) x 0.8 (bioavail) x 2

What if the dose is unknown ??
5 amps if patient is stable, or 10 amps if unstable.
a further 5 amp boluse can be given until stability is achieved !!

The end-point.
Restoration of normal cardiac rhythm / conduction.

[/DDET]

[DDET The case continues….]

Given the patients age & rapid onset of a bradydysrhythmia with associated hypotension; we decide to administer the Digibind.

At the end of 12 ampoules, her haemodynamics improve & she is taken off to Intensive Care. It is here that someone repeats her Digoxin level…

23.3 nmol/L !!!

But why ?!?! How ?!?! Didn’t we treat this ?!?!
Remember: Digoxin-assays measure both free & Fab-bound digoxin !!

[/DDET]

[DDET References]

1. Murray L, Daly F, Little M & Cadogan M. Toxicology Handbook. 2nd Edition. Elsevier 2011.
2. Rosenʼs Emergency Medicine. Concepts and Clinical Approach. 7th Edition
3. Tintinalli’s Emergency Medicine: A Comprehensive Study Guide. 7th Edition.
4. Heart of Stone?: calcium and digoxin toxicity by ThePoisonReview
5. Levine M et al. The effects of intravenous calcium in patients with digoxin toxicity. J Emerg Med. 2011 Jan;40(1):41-6.

[/DDET]