Digoxin Toxicity

Digoxin toxicity is not a laboratory diagnosis. It is a clinical syndrome in which excessive cardiac glycoside effect produces both abnormal impulse generation and impaired impulse conduction. That combination explains why a patient may have frequent ventricular ectopy and profound bradycardia, or atrial tachycardia with block, in the same episode. The serum concentration supports the diagnosis but does not define it. A patient with renal failure, hypokalemia, hypomagnesemia, hypercalcemia, advanced age or cardiac amyloidosis may become seriously toxic at a concentration that appears acceptable. Conversely, a high concentration drawn too soon after a dose may be falsely reassuring or falsely alarming depending on how it is interpreted. The experienced clinician notices the change from baseline first: new anorexia or vomiting, confusion, visual alteration, a slow or irregular pulse, or an unexpected ECG rhythm in a person taking digoxin. The next question is not simply What is the level? It is whether the patient has acute, acute-on-chronic or chronic exposure, whether renal function or electrolytes have changed, and whether the heart is becoming electrically or haemodynamically unstable.