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AChEI Cardiac Effects — MRCPsych Paper B MCQ

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ModerateOld Age PsychiatryAChEI Cardiac EffectsMRCPsych Paper B

A 76-year-old woman with Alzheimer's disease has two episodes of abrupt syncope 2 weeks after her donepezil dose was increased from 5 mg to 10 mg daily. Before the dose increase, her pulse was 72 beats/min and her ECG was normal. Her pulse is now 42 beats/min, and ECG shows new second-degree atrioventricular block. Thyroid function and serum electrolytes are normal, and she takes no other medication that slows cardiac conduction. What is the most likely explanation?

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Correct answer: A — Donepezil-induced bradycardia and heart block

Donepezil-induced bradycardia and heart block is the best explanation. Acetylcholinesterase inhibitors can exert vagotonic cardiac effects, slowing the sinus rate and atrioventricular conduction, and the UK SmPC advises considering heart block or long sinus pauses when such patients present with syncope. The close relationship to dose escalation, previously normal pulse and ECG, persistent marked bradycardia and new atrioventricular block strongly support this adverse drug effect; donepezil should be stopped and cardiology review arranged. Age-related conduction disease remains possible in an older person but is less likely given the timing and previously normal findings. Hypothyroidism is excluded by normal thyroid function. Non-adherence would reduce rather than produce cholinergic effects. Vasovagal syncope can cause transient reflex bradycardia but does not explain persistent bradycardia with documented second-degree atrioventricular block.

Reference: electronic Medicines Compendium. Donepezil Hydrochloride 10 mg Film-coated Tablets, Summary of Product Characteristics, sections 4.4 and 4.8 (current UK SmPC). https://www.medicines.org.uk/emc/product/4427/smpc