Tasty Morsels of EM 126 – #FRCEM Digoxin Toxicity

24 Aug

I’m entering a few months prep for the UK and Ireland exit exam in Emergency Medicine: the FRCEM. I’ll be adding lots of little notes on pearls I’ve learned along the way. A lot of my revision is based around the Handbook of EM as a curriculum guide and review of contemporary, mainly UK guidelines. I also focus on the areas that I’m a bit sketchy on. With that in mind I hope they’re useful.

You can find more things on the FRCEM on this site here.

I’ve never used digibind since i was an intern (and that was literally me attaching it as someone else ordered it). It’s one of the ones that is very testable that I don’t know much about.

From Toxbase, OHEM 4th and Rosen’s 8th

How does digoxin work?

  • increases myocardial contratility by blocking N-K-ATPase, increasing extracellular potassium and ultimately increasing the amount of calcium put into the sarcoplasmic reticulum causing increased contraction
  • slows rate by blocking AV node (can also increase vagal output and reduce SA activity)
  • half life is 30-40 hours and can be severely prolonged in renal impairment

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What types of toxicity are there and how do they present?

  • acute
    • either in someone naive to the medication or on it long term
    • nausea, anorexia, fatigue, visual disturbance (all very vague)
    • new arrhythmias is the big thing to look for
  • chronic
    • this is much more insidious with a higher mortality possibly related to the underlying comorbidities
  • dig levels
    • steady state concentrations predict toxicity rather than peak (usually around 6-8 hours post acute OD)
    • levels are particularly tricky in chronic toxicity were lowish levels of 2-6 can still be associated with mortality

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What are the ECG changes?

  • legion!
  • classically a supraventricular tachy like an atrial tachy with a slow ventricular response

LITFL, Click for source

  • the other famous one is bidirectional VT

LITFL, Click for source

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How is it managed?

  • there are 2 antidotes
  • DigiBind/DigiFab (different brands as far as i can work out, DigiBind has been discontinued)
    • Digoxin Fragment antigen-binding antibodies
  • Indications (as per Toxbase)
    • severe brady or ventricular arrhythmias
    • hyperkalaemia
  • Dosing
    • this is complex but well  described on Toxbase with some subtleties regarding full and partial neutralisation. I’m never gonna remember that for the exam so I’m not putting it here.
    • Rosen’s has empiric 10 vials in an acute severe OD, with 20 in cardiac arrest.
  • Traditionally people have talked about avoiding calcium for the hyper K given the mysterious “stone heart syndrome”. This is probably not a big risk and Toxbase agrees saying it’s fine to give the calcium
  • there is some enterorhepatic recirculation so this is one of the times to “consider” multi dose charcoal

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