A 48-year-old woman with Wolff-Parkinson-White syndrome develops AF with rapid ventricular response (HR 220 bpm, irregular, wide and pre-excited complexes). BP is 90/60 mmHg. Which immediate pharmacological choice is most dangerous in this setting?
- A IV verapamil — contraindicated as it can precipitate VF by enhancing accessory pathway conduction ✓
- B Procainamide IV — safe in pre-excited AF to slow accessory pathway conduction
- C IV adenosine — safe for acute termination of the tachycardia in WPW-AF
- D Electrical cardioversion — the treatment of choice given haemodynamic compromise
Explanation
In pre-excited AF (WPW with AF), AV nodal blocking agents — verapamil, diltiazem, digoxin, and adenosine — are contraindicated because they reduce refractoriness in the accessory pathway while slowing conduction through the AV node, paradoxically increasing conduction through the accessory pathway and causing extremely rapid ventricular rates that can degenerate into ventricular fibrillation. Procainamide slows accessory pathway conduction and is the pharmacological agent of choice. However, given haemodynamic instability (BP 90/60), synchronised electrical cardioversion is the safest immediate definitive treatment.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
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Written and medically reviewed by the StethoPrep medical team.