Syncope and preexcitation: a case of a Kent and fasciculoventricular Mahaim fibers.

A case involving an 8-year-old girl with syncope and preexcitation on a surface electrocardiogram (ECG) that was suggestive of Wolff-Parkinson-White syndrome is presented. An intracardiac electrophysiologic study revealed a posteroseptal bidirectionally conducting Kent fiber. Radiofrequency ablation of the Kent fiber was successful, but the patient had a residual short His-ventricular (HV) interval and a new preexcitation pattern. Atrial extra stimuli and ventricular pacing revealed a fixed, preexcited QRS. Nodal block and loss of preexcitation was provoked with adenosine. The surface QRS and electrophysiologic features are consistent with a left septal fasciculoventricular Mahaim fiber.