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©2013 UpToDate ® Print Email Accessory pathways with preexcitation syndromes A number of atrioventricular (AV) accessory pathways resulting in preexcitation syndromes have been identified. The muscular AV fiber (AVF), which is also called the Kent bundle, traverses the AV annulus and is responsible for most cases of Wolff-Parkinson-White syndrome. Proposed pathways responsible for the Lown-Ganong-Levine syndrome or enhanced AV nodal conduction include an intranodal bypass tract (INBT) and atrionodal tracts (ANT), also known as James fibers. Traditionally, the etiology for a Mahaim fiber tachycardia was thought to result from a nodoventricular (NVF) and fasciculoventricular (FVF) fiber. However, the true etiology is likely an atriofascicular fiber (AFF) that arises from the right atrium close to the annulus, inserting into the apical part of the right ventricle close to a fascicular branch of the right bundle branch.