Multiple accessory pathways in patients with the pre-excitation syndrome.

We have studied 135 patients with the pre-excitation syndrome and have demonstrated evidence of multiple accessory pathways in 20 patients. Five patients had two distinct accessory atrioventricular (A-V) connections, associated with enhanced A-V node conduction in one patient. Twelve patients had a single accessory A-V connection associated with enhanced A-V conduction. In one of these there was an additional fasciculo-ventricular connection. One patient had an accessory A-V connection associated with a nodoventricular bundle. Two patients had fasciculo-ventricular connections combined with enhanced A-V conduction. The latter two patients had electrocardiograms suggestive of a complete accessory A-V connection. Patients with enhanced A-V conduction had shorter cycle lengths during reciprocating tachycardia, primarily because of a short A-H during the dysrhythmia, than those without such conduction. In addition, patients with enhanced A-V conduction demonstrated more rapid conduction from atrium to His bundle during induced atrial fibrillation and two developed life-threatening ventricular responses during atrial fibrillation. A nodo-ventricular pathway was documented to participate in reciprocating tachycardia in one patient. Surgery was undertaken in 13 patients. In 11, the intraoperative mapping studies confirmed the preoperative predictions. In two patients, the presence of a second accessory A-V connection was documented after ablation of one.