skip to main content

Haemodynamically unstable new-onset atrial fibrillation — MRCEM SBA MCQ

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

EasyResuscitation and critical illnessHaemodynamically unstable new-onset atrial fibrillationMRCEM SBA

A 72-year-old man develops sudden palpitations and breathlessness. Three hours later, in the emergency department, a 12-lead ECG shows new-onset atrial fibrillation with a ventricular rate of 170/min and no pre-excitation. He is pale and clammy, with a blood pressure of 76/44 mmHg, SpO₂ of 89% on air and bilateral inspiratory crackles. There is no evidence of bleeding or infection. Oxygen, cardiac monitoring and intravenous access are in place, and the resuscitation team is present. What is the most appropriate immediate treatment?

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

Reveal the answer and explanation

Correct answer: A — Perform emergency synchronised electrical cardioversion

The ECG establishes new-onset atrial fibrillation, while the profound hypotension, poor perfusion and pulmonary oedema indicate life-threatening haemodynamic instability. With no competing cause of shock apparent, the rapid arrhythmia requires immediate treatment. NICE recommends emergency electrical cardioversion in this situation, without delaying it to achieve anticoagulation. Appropriate procedural preparation should proceed alongside resuscitation. ([nice.org.uk](https://www.nice.org.uk/guidance/NG196/chapter/recommendations)) Intravenous amiodarone (B) can be considered for a rhythm-control strategy in selected patients without life-threatening instability, but it is not the priority here. Intravenous metoprolol (C) addresses ventricular rate rather than providing the recommended immediate cardioversion; suspected acute decompensated heart failure also calls for senior specialist input before beta-blocker use. Diltiazem (D) may be a rate-control option in a stable patient, but NICE advises against calcium-channel blockers when acute decompensated heart failure is suspected. Anticoagulation (E) matters in new-onset atrial fibrillation, but giving heparin must not postpone emergency cardioversion in this shocked patient. ([nice.org.uk](https://www.nice.org.uk/guidance/NG196/chapter/recommendations))

Reference: NICE NG196: Atrial fibrillation: diagnosis and management — recommendations 1.8.1–1.8.8 (Last updated 30 June 2021) — https://www.nice.org.uk/guidance/NG196/chapter/recommendations