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QTc Above 500ms Management — MRCPsych Paper B MCQ

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HardSchizophrenia & PsychosisQTc Above 500ms ManagementMRCPsych Paper B

A 42-year-old man with schizophrenia has been stable on olanzapine, recently increased from 10 mg to 20 mg nightly. His QTc before the increase was 438 ms. Ten days later, an automated ECG reports a QTc of 506 ms at a heart rate of 112 beats/minute. After resting, a repeat 12-lead ECG is manually checked and confirms a QTcF of 510 ms. He has no syncope or presyncope. Serum potassium is 3.3 mmol/L, magnesium is normal, and he takes no other QT-prolonging medicines. Which is the most appropriate management?

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

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Correct answer: A — Stop olanzapine, correct reversible factors and obtain immediate cardiology review while planning a lower-QT-effect antipsychotic

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

B is correct. A manually confirmed QTc above 500 ms is a major risk threshold for torsade de pointes. UK specialist guidance recommends stopping the suspected causative antipsychotic, correcting reversible factors such as hypokalaemia, reviewing other QT-prolonging agents and obtaining immediate cardiology review. Ongoing antipsychotic treatment should be reconsidered using an agent with lower QT effect. Dose reduction with repeat ECG, as in C, is appropriate to consider when QTc is prolonged but remains below 500 ms; it is insufficient here. A and E inappropriately continue the suspected drug, while D adds unnecessary antipsychotic exposure. The absence of syncope means immediate rhythm monitoring is not automatically required, but it does not remove the need for urgent action and cardiology assessment.

Reference: Lambiase PD et al. British Heart Rhythm Society Clinical Practice Guidelines on the Management of Patients Developing QT Prolongation on Antipsychotic Medication, section 'Action to be Taken According to QTc', 2019. https://pubmed.ncbi.nlm.nih.gov/31463053/