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Atropine-unresponsive complete heart block due to suspected digoxin toxicity — MRCEM SBA MCQ

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HardCardiovascular emergenciesAtropine-unresponsive complete heart block due to suspected digoxin toxicityMRCEM SBA

A 74-year-old woman taking digoxin for paroxysmal atrial fibrillation and furosemide for heart failure presents after three days of nausea and poor oral intake. She is drowsy and clammy, with a blood pressure of 80/46 mmHg. Her ECG shows sinus P waves unrelated to a regular ventricular escape rhythm at 30/min. Creatinine is 218 micromol/L (previously 92 micromol/L) and potassium is 3.0 mmol/L. A digoxin concentration taken 10 hours after her last dose is 2.0 nmol/L (laboratory reference interval 0.8–2.6 nmol/L). There is no evidence of acute myocardial ischaemia. Intravenous atropine 1 mg has produced no change. Digoxin has been withheld; resuscitation, cardiac monitoring and pacing pads are in place. Which treatment plan should be prioritised?

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Correct answer: E — Give digoxin-specific Fab and correct potassium, with monitored admission.

The independent atrial and ventricular rhythms establish complete heart block; the profound bradycardia is causing shock and has not responded to atropine. Acute renal impairment reduces digoxin clearance, while hypokalaemia increases myocardial sensitivity to it. A digoxin concentration within the stated laboratory interval does not exclude clinically important toxicity. This is suspected life-threatening digoxin toxicity with an atropine-unresponsive bradyarrhythmia, for which digoxin-specific antibody fragments are indicated. Seek urgent UK poisons advice on dosing, correct potassium, and continue resuscitation and monitored specialist care. ([medicines.org.uk](https://www.medicines.org.uk/emc/product/102213/smpc)) A is insufficient because withholding digoxin, potassium replacement and observation will not promptly reverse this unstable rhythm. B is attractive as atropine is a usual initial treatment for symptomatic bradycardia, but it has already failed and must not delay the antidote. C may provide an immediate bridge if perfusion remains inadequate while Fab is obtained; it does not treat the toxicity. D may be needed if bradycardia persists despite treatment, but arranging invasive pacing instead of prioritising Fab likewise leaves the cause untreated. Fab requires continued ECG and potassium monitoring after administration. ([medicines.org.uk](https://www.medicines.org.uk/emc/product/102213/smpc))

Reference: DigiFab 40 mg/vial: Summary of Product Characteristics (8 June 2026) — https://www.medicines.org.uk/emc/product/102213/smpc Digoxin 250 microgram/ml: Summary of Product Characteristics (26 May 2026) — https://www.medicines.org.uk/emc/product/5462/smpc