Bradycardia, Hyperkalemia and Visual Halos in a Patient on Digoxin
A 58-year-old man with heart failure with reduced ejection fraction (LVEF 30%) and permanent atrial fibrillation attends the emergency department with 3 days of nausea, vomiting, anorexia and "yellow-green halos" around lights. He is drowsy but rousable. Medications are sacubitril/valsartan 97/103 mg twice daily, carvedilol 6.25 mg twice daily, furosemide 40 mg daily, spironolactone 25 mg daily and digoxin 0.25 mg daily; baseline creatinine is 1.6 mg/dL (eGFR 38 mL/min/1.73 m²). Heart rate is 44/min, BP 92/54 mmHg, respiratory rate 18/min and SpO2 94% on air. Jugular venous pressure is not raised and the lungs are clear. The ECG shows a junctional bradycardia at 42/min with downsloping ST depression. Point-of-care potassium is 6.4 mmol/L; laboratory creatinine is 2.9 mg/dL. A serum digoxin level drawn 10 hours after the last dose is 3.8 ng/mL.
1. Which findings establish digoxin toxicity, and how do the potassium and creatinine results alter your interpretation?
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Toxicity is a clinical diagnosis supported by the level, not defined by it alone. This man has the classic triad of gastrointestinal symptoms, neuropsychiatric/visual symptoms (halos) and a bradyarrhythmia, with a concentration of 3.8 ng/mL - far above the 0.5–0.9 ng/mL target used in heart failure. The level was drawn 10 hours after the dose and in evolving renal failure, but at this height with symptoms it is diagnostic rather than incidental.
Hyperkalemia is the most important severity marker. Digoxin inhibits Na+/K+-ATPase, so potassium shifts out of cells; renal impairment amplifies the rise. A potassium of 6.4 mmol/L with bradycardia predicts ventricular arrhythmia or asystole and is itself an indication for digoxin-specific antibody fragments. The creatinine rise from 1.6 to 2.9 mg/dL explains accumulation of a renally cleared drug. Do not dismiss the potassium as ordinary renal-failure hyperkalemia: it reflects toxicity, and calcium is traditionally avoided in this setting.
2. Set out your immediate management in the first two hours, including drugs, doses and thresholds.
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- Stop digoxin and attach continuous ECG monitoring; secure IV access and treat hypoxia.
- Digoxin-specific Fab fragments urgently. For life-threatening bradyarrhythmia plus hyperkalemia >5.5 mmol/L, give empiric 10–20 vials (or calculate from the level and weight) without waiting for the laboratory. Do not delay for dialysis, which removes little digoxin.
- Lower potassium with IV insulin 10 units and 25 g glucose; consider sodium bicarbonate if acidotic. Avoid IV calcium. Recheck potassium hourly.
- Bradycardia: atropine 0.5 mg IV may be tried but often fails in digoxin-induced junctional rhythms. Use temporary transcutaneous or transvenous pacing if there is hemodynamic compromise; capture may be difficult until Fab fragments take effect.
- Monitor potassium, creatinine, magnesium and the digoxin level, and look for a precipitant such as dehydration or a new interacting drug. Rebound hypokalemia can follow Fab fragment administration, so continue frequent checks.
3. What should be avoided, and how should his long-term antiarrhythmic and heart-failure therapy be adjusted?
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Avoid IV calcium, electrical cardioversion (which can provoke refractory ventricular arrhythmia) and drugs that raise digoxin concentrations or reduce clearance - amiodarone, verapamil, spironolactone, NSAIDs and trimethoprim. Note that spironolactone is already on his list and can increase digoxin levels.
After recovery, do not simply restart 0.25 mg daily. Either stop digoxin or reduce to 0.0625–0.125 mg daily, with a target trough of 0.5–0.9 ng/mL, and review renal function and electrolytes at each visit. Reassess rate control using a beta-blocker, and consider whether digoxin is adding anything to his heart-failure regimen. Educate him about sick-day rules during vomiting or diarrhea, and document the interaction risk so future prescribers check the level and renal function before continuing the drug.