skip to main content

Haemodynamically stable pre-excited atrial fibrillation — MRCEM SBA MCQ

Instant feedback + full explanation. One question, done properly.

HardCardiovascular emergenciesHaemodynamically stable pre-excited atrial fibrillationMRCEM SBA

A 32-year-old woman attends the emergency department 70 minutes after the sudden onset of palpitations. She is alert, with a blood pressure of 124/76 mmHg, no chest pain and no signs of heart failure. The ECG shows an irregular tachycardia at 200–230/min, with marked beat-to-beat variation in QRS width and morphology. An ECG from a previous assessment in sinus rhythm shows a short PR interval and delta waves. Her previous echocardiogram showed a structurally normal heart, and she has no history of ischaemic heart disease. Continuous monitoring, intravenous access and defibrillator pads are in place. Which immediate treatment and disposition plan is most appropriate?

Educational content. Not a substitute for clinical judgement or local policy.

Reveal the answer and explanation

Correct answer: E — Give intravenous flecainide and admit for electrophysiology assessment.

The very rapid, irregular rhythm with changing QRS morphology, together with documented ventricular pre-excitation in sinus rhythm, indicates atrial fibrillation conducting through an accessory pathway. This is not an ordinary broad-complex tachycardia for which atrioventricular nodal blockade is appropriate: pre-excited atrial fibrillation can deteriorate into ventricular fibrillation. She has no haemodynamic features requiring immediate electrical cardioversion, so monitored intravenous flecainide is a suitable option. Her structurally normal heart and absence of known ischaemic disease matter because flecainide should be avoided in patients with structural or ischaemic heart disease. ([slcn.nhs.uk](https://slcn.nhs.uk/wp-content/uploads/2021/10/sl-arrhythmia-nf-102021.pdf)) Adenosine (A) may terminate a regular atrioventricular node-dependent tachycardia, but must not be used to treat this irregular pre-excited rhythm. Metoprolol (B) and verapamil (C) are plausible rate-control drugs in atrial fibrillation without pre-excitation; here, blocking the atrioventricular node can favour conduction through the accessory pathway. Option D chooses the appropriate acute drug but an inappropriate disposition. The risk posed by the pathway remains if she converts to sinus rhythm, so inpatient electrophysiology assessment is indicated. If haemodynamic instability develops, electrical cardioversion takes priority. ([slcn.nhs.uk](https://slcn.nhs.uk/wp-content/uploads/2021/10/sl-arrhythmia-nf-102021.pdf))

Reference: Patient Cases – ECG’s & Scenarios: Pre-excited atrial fibrillation (2021) — https://slcn.nhs.uk/wp-content/uploads/2021/10/sl-arrhythmia-nf-102021.pdf Atrial fibrillation: diagnosis and management, recommendations 1.7.9 and 1.8.5 (2021) — https://www.nice.org.uk/guidance/NG196/chapter/recommendations Flecainide Acetate 100 mg tablets: Summary of Product Characteristics (18 June 2026) — https://www.medicines.org.uk/emc/product/3086/smpc