A latent atrioventricular decrementally conducting accessory pathway mimicking a bystander nodoventricular fiber.

A 41-year-old woman with recurrent wide-QRS tachycardia is reported. Electrophysiologic findings were consistent with the diagnosis of a preexcited atrioventricular nodal reentrant tachycardia due to a bystander nodo-ventricular fiber. However, slow pathway ablation did not preclude tachycardia recurrence. A second electrophysiology study shed light on the correct mechanism and eventually a successful ablation was achieved.