Effect vs toxicity — the key distinction
"Digoxin effect" is an expected ECG change at therapeutic levels and is not dangerous. Digoxin toxicity is a clinical/biochemical diagnosis with a wide range of arrhythmias. Don't call the reverse-tick sign "toxicity".
Digoxin effect (therapeutic)
- Downsloping "reverse-tick" ST depression (likened to a Salvador Dalí moustache)
- T-wave flattening or inversion
- Short QT interval
- Prominent U waves
Digoxin toxicity
Digoxin increases automaticity while slowing AV conduction, so the hallmark is increased ectopy with block:
- Atrial tachycardia with AV block
- Bidirectional VT (near-pathognomonic)
- Frequent ventricular ectopics, ventricular bigeminy
- Bradyarrhythmias: sinus bradycardia, any degree of AV block
Systemic clues: nausea/vomiting, confusion, xanthopsia (yellow-green visual haloes).
Precipitants
- Hypokalaemia (commonly diuretic-induced), hypomagnesaemia, hypercalcaemia
- Renal impairment (digoxin is renally cleared)
- Drug interactions: amiodarone, verapamil, quinidine
Management
- Digoxin-specific antibody fragments (DigiFab) for life-threatening toxicity
- Correct K⁺ and Mg²⁺; treat arrhythmias
- In the hyperkalaemia of digoxin toxicity, IV calcium is traditionally avoided (the "stone heart" concern) — prioritise DigiFab
See a real 12-lead example
For an annotated tracing of this pattern, see the Digoxin Toxicity page in the LITFL ECG Library:
ECG image examples are hosted by Life in the Fast Lane (LITFL), whose ECG library is published under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 licence. We link to LITFL rather than reproducing their tracings. The teaching notes above are original and written independently for MedNotes Hub.