Atrial Fibrillation with Ventricular Pre-Excitation: A Diagnosis That Must Not Be Missed

Wolff-Parkinson-White (WPW) syndrome is caused by an accessory pathway that communicates between the atria and ventricles known as the Bundle of Kent. The development of atrial fibrillation, can result in the atrial impulses all being conducted via the accessory pathway and result in a sinister, board complex, irregular tachycardia, with varying QRS morphology (known as pre-excited atrial fibrillation) Adenosine is a potent atrioventricular node blocker, which can be used in the treatment of supraventricular tachycardias, but also has diagnostic utility, particularly in differentiating between supraventricular tachycardia with aberrant conduction (which would often terminate) and a ventricular tachycardia (which would not respond to adenosine). However, the administration of adenosine in pre-excited atrial fibrillation can precipitate 1:1 atrial to ventricular conduction, which can degenerate into life-threatening ventricular arrythmias. This case describes a patient who presented with pre-excited atrial fibrillation and received intravenous adenosine that resulted in development of broad complex tachycardia with haemodynamic compromise. In patients with pre-exited atrial fibrillation, AV nodal blocking agents should be avoided and direct current cardioversion should be utilised.