Pre-excited atrial fibrillation

Atrial fibrillation (or atrial flutter, or other atrial tachycardias) in the setting of Wolff-Parkinson-White syndrome is dangerous as the accessory pathway allows atrial impulses to be conducted to the ventricles in a 1:1 ratio without the AV-node’s delay, causing a ventricular rate of 300 bpm or more, which can degenerate into ventricular fibrillation. This is called pre-excited atrial fibrillation. The patient is usually haemodynamically unstable.

AV-nodal blocking agents like adenosine are strictly contraindicated in wide-complex tachycardias if one cannot rule out the presence of an accessory pathway for this exact reason. Treatment is by cardioversion or non-AV-blocking antiarrhythmics.