This topic was brought to our attention today by Dr. Glassman.
5 Facts about Digoxin:
1) It is a cardiac glycoside that increases inotropy and automaticity
2) Treats tachyarrhythmias and CHF
3) Mechanism of action: inhibits the Na/K ATPase pump
4) Renally cleared (look out for pts with new renal failure on digoxin)
5) It's one of those tricky drugs with a narrow therapeutic index!
Net effect: increased intracellular Na+ and Ca2+ levels; increased extracellular K+ levels
Dig Tox by Systems:
GI: nausea, vomiting, diarrhea, abd pain
Cardiovascular: palpitations, syncope, dyspnea
CNS: confusion/delirium, dizziness, altered color perception
Metabolic: hyperkalemia (early sign!)
Time Course of Toxicity:
GI effects seen @ 2-4 hr
Life-threatening cardiovascular complications @ 8-12 hr
Peak serum levels @ 6 hr
More on the Cardiac Effects...
Digoxin can cause a multitude of dysrhythmias!
- Frequent PVCs (most common) including ventricular bigeminy and trigeminy
- Sinus bradycardia
- Slow atrial fibrillation
- Any degree of AV block (due to increased vagal effects at the AV node)
- SVT (due to the enhanced automaticity) with SLOW ventricular response (again due to increased vagal effects at the AV node)
- VT
Confused? Yet this makes some sense. If you've watched any lectures by Amal Mattu, he calls hyperkalemia the Syphilis of EKGs, referring to its status as the "Great Imitator" of many diverse pathologies. Gross, right? And what does digoxin cause? Hyperkalemia!
Some Possible EKG Findings in Dig Tox:
This unique "scooped" or "swooping" depression of the ST segment memorably resembles the shape of Salvador Dali's mustache.
Paroxysmal atrial tachycardia with 2nd degree AV block AND frequenct PVCs
Atrial flutter with a slow ventricular rate due to AV nodal blockade by digoxin
Treatment:
You'll find that digoxin-induced arrhythmias are usually refractory to standard therapies.
Ex: bradycardia resistant to atropine and pacing
The solution? Digibind (digoxin Fab fragments)! There are dosing formulas (ask your pharmacist for help!) but if in doubt, start with 5 vials for stable acute toxicity and 10 vials for unstable acute toxicity (ex: accidental ingestion by a child). For chronic toxicity, start with 2 vials empirically and titrate up.
References:
Life In the Fast Lane
UpToDate
