Pre-excitation of the ventricle associated with total intra His bundle block

A case with total intra-His bundle block and intermittent pre-excitation syndrome is presented. During A-V conduction there was a P-delta interval of 130 msec. with a P-A interval of 20 msec., an A-H interval of 60 msec. and an H-V interval of 50 msec. During rapid atrial pacing the P-delta interval increased primarily due to an A-H1 prolongation and a Mobitz type 2 block and total A-V block occured at increasing rates showing H1 following every A spike. The escape beats showed a normal width of the QRS complexes with preceding H2 spikes. After administration of Ajmaline the bypass tract was blocked and constant total A-V block occurred. It was concluded that there was a constant total intra-His bundle block and a nodoventricular or fasciculoventricular bypass tract with prolonged conduction to the ventricle. This bypass tract blocked sometimes spontaneously and could also be blocked by rapid atrial pacing and administration of drugs. The close anatomic proximity of the His bundle and Mahaim fibers is responsible for the simultaneous block resulting in total atrioventricular block.