Characteristics of atrio-His conduction in the short PR interval, normal QRS complex syndrome. Evidence for enhanced slow-pathway conduction.

This study confirms the existence of accelerated conduction via a fast atrio-His pathway in patients with the so-called Lown-Ganong-Levine (LGL) syndrome. Additional slow AH pathway conduction was detected in about 50% of patients. Comparison of slow pathway conduction characteristics in the LGL syndrome with AH conduction in age-matched normals and patients with dual AV nodal pathways revealed that the 'slower' of dual AH pathways in LGL patients also exhibits relatively enhanced conduction. This finding cannot be explained by the presence of an anomalous AH pathway ('James' fibre') bypassing a normal AV node. It is suggested that a non-specific and as yet unknown effect causes enhanced conduction throughout the AV junction in patients with the LGL syndrome.