Digoxin Toxicity

An older adult taking digoxin and furosemide develops anorexia, nausea, yellow-green visual changes, and a new irregular pulse. The digoxin concentration is 1.6 ng/mL, but the potassium is 2.8 mEq/L and creatinine has risen from baseline. This is digoxin toxicity until proven otherwise; the concentration does not make the diagnosis or exclude it. A different patient presents after an acute ingestion with a potassium of 6.2 mEq/L. That apparent contradiction is a high-yield distinction: acute pump blockade drives potassium out of cells and can produce hyperkalemia, whereas chronic toxicity commonly occurs with diuretic-associated hypokalemia, which makes the myocardium more sensitive to digoxin. The bedside model is simple but powerful: toxicity increases myocardial automaticity while slowing or blocking conduction. That combination explains ectopic beats, ventricular tachyarrhythmias, bradycardia, AV block, and the unusual rhythm of atrial fibrillation with a deceptively regular or slow ventricular response. Treat the patient’s rhythm, perfusion, and electrolytes—not an isolated laboratory number.