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Lyme carditis with complete heart block — MSRA MCQ

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HardInfectious DiseasesLyme carditis with complete heart blockMSRA

A 34-year-old woman who is 17 weeks pregnant presents to her GP with episodic dizziness and two near-syncopal episodes today. Three weeks earlier, after hillwalking in the Scottish Highlands, she removed an attached tick from her left thigh. Seven days later she developed an enlarging, non-itchy, painless erythematous rash at that site, now measuring 14 cm with partial central clearing. She has since had fatigue, myalgia and intermittent palpitations. Her BP is 92/58 mmHg, pulse 38 beats/minute and temperature 37.4°C. She is alert and has no focal neurological deficit. An ECG performed in the practice shows complete heart block. She has no cardiac history and takes only folic acid and an iron supplement. She has no known drug allergies. Which is the most appropriate management now?

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

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Correct answer: D — Arrange immediate hospital transfer for cardiac monitoring and intravenous ceftriaxone 2 g once daily

Explanation lettering: D = shown as A · A = shown as B · B = shown as C · C = shown as D

This is clinically diagnosed Lyme disease with cardiac involvement. The enlarging, painless, non-pruritic rash developing one week after a tick bite is erythema migrans; NICE advises diagnosis and treatment without laboratory testing when erythema migrans is present. Complete heart block, symptomatic bradycardia and hypotension indicate a cardiac complication requiring emergency referral rather than community management. In haemodynamically unstable Lyme carditis, NICE recommends intravenous ceftriaxone 2 g once daily for 21 days; cardiac monitoring and specialist management are required. A is inappropriate because serology must not delay treatment or emergency management when erythema migrans is present. B uses an antibiotic regimen appropriate as an alternative for uncomplicated erythema migrans, but not for complete heart block. D would be the standard oral regimen for haemodynamically stable Lyme carditis, but this patient requires emergency inpatient management and doxycycline is contraindicated in pregnancy. E is unsuitable because azithromycin should not be used in Lyme disease with cardiac abnormalities because of QT-related risk, and outpatient investigation is unsafe in complete heart block.

Reference: NICE NG95: Lyme disease — Recommendations (2018; checked 16 August 2026) — https://www.nice.org.uk/guidance/ng95/chapter/Recommendations Doxycycline 100 mg Capsules — Summary of Product Characteristics (24 March 2026) — https://www.medicines.org.uk/emc/product/13082/smpc