A man eats a homeopathic herbal preparation containing Aconitum napellus. Within 30 minutes he develops perioral tingling and numbness spreading to the limbs, profuse vomiting, hypotension, and runs of broad-complex tachycardia. The arrhythmia arises because aconitine:
- A Binds to voltage-gated sodium channels and holds them in the open state ✓
- B Blocks cardiac sodium channels in a use-dependent fashion, similar to class Ib agents
- C Antagonises beta-adrenergic receptors in the SA node
- D Blocks potassium channels, prolonging repolarisation uniformly
Correct answer: A. Binds to voltage-gated sodium channels and holds them in the open state
Explanation
Aconitine binds site 2 of the voltage-gated sodium channel and shifts activation, keeping channels persistently open. This causes sustained sodium influx, membrane depolarisation, and increased automaticity, producing the characteristic ventricular ectopy, bidirectional ventricular tachycardia, and refractory arrhythmias of aconite poisoning. Channel blockade would suppress excitability, the opposite of what is observed clinically.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
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