What fraction of patients develop atrial fibrillation associated with a bypass tract that has antegrade conduction?

• A. One third
• B. One half
• C. One quarter
• D. Two thirds

Answer: (A)

In Wolff-Parkinson-White physiology, an accessory pathway that conducts antegradely provides a route for impulses from the atria to reach the ventricles bypassing the AV node. If atrial fibrillation occurs in this setting, those rapid atrial impulses can be conducted to the ventricles through the bypass tract, producing very fast ventricular rates and risking hemodynamic instability or degeneration to ventricular fibrillation. Approximately one third of patients with a bypass tract capable of antegrade conduction develop atrial fibrillation. This makes AF with pre-excitation a notable concern in WPW. The other percentage options are not the typical estimate for this scenario.