Accessory pathways and supraventricular tachycardia

Accessory pathways represent abnormalities of atrioventricular conduction. According to the course and the site of insertion they can be divided into atrioventricular (AV), atrio-His, atriofascicular, nodoventricular, nodofascicular and fasciculoventricular. AV accessory pathways are the most common form. An anterior, lateral and posterior localisation of AV accessory pathways can be distinguished in the left and right free wall. Atriofascicular accessory pathways usually exhibit antegrade conduction with AV node-like decremental properties. Right atriofascicular accessory pathways are involved in most cases of Mahaim-type tachycardias. AV re-entrant tachycardia based on the presence of AV accessory pathway is mostly orthodromic, less commonly antidromic. The orthodromic AV re-entrant tachycardia based on the pathway exhibiting decremental retrograde conduction is known as permanent junctional reciprocating tachycardia. Patients with Wolff-Parkinson-White syndrome often demonstrate an atrial fibrillation. As conduction over an accessory pathway during atrial fibrillation can be rapid, some of them are at a high risk of ventricular fibrillation and sudden cardiac death. (Ref. 26.)