A 22-year-old athlete collapses during a football match. ECG shows a short PR interval (0.10 s), a delta wave, and a widened QRS. He has no family history. Which tachyarrhythmia is he at risk of, and why is digoxin contraindicated?
- A AV nodal reentrant tachycardia (AVNRT); digoxin slows the AV node causing sinus bradycardia
- B Ventricular tachycardia from myocarditis; digoxin is proarrhythmic in cardiomyopathy
- C Pre-excited atrial fibrillation with rapid ventricular response; digoxin enhances conduction through the accessory pathway, increasing the risk of ventricular fibrillation ✓
- D Atrial flutter with 2:1 block; digoxin causes paradoxical 1:1 conduction
Explanation
Wolff-Parkinson-White (WPW) syndrome with pre-excitation (short PR, delta wave, wide QRS) places patients at risk of AF with pre-excited rapid conduction through the accessory pathway (Kent bundle), which lacks AV nodal decremental properties. If AF occurs, impulses can conduct at 250-350 bpm through the accessory pathway, potentially degenerating into ventricular fibrillation (the main cause of SCD in WPW). Digoxin, verapamil, and beta-blockers are contraindicated as they slow AV nodal conduction without blocking the accessory pathway, potentially increasing antegrade accessory pathway conduction and ventricular rate. Procainamide or cardioversion is used for pre-excited AF.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
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Written and medically reviewed by the StethoPrep medical team.