Intra His Purkinje gap phenomenon during retrograde conduction in man.

Ventricular refractory period studies were performed in 24 patients using the ventricular extrastimulus (V2) method at a basic ventricular drive (V1V1). Gap phenomenon confined to the His-Purkinje system (V-H gap) during retrograde conduction was observed in six of 24 patients. In this form of gap, the premature impulse (V2) is initially blocked in the His-Purkinje system (HPS) as recognized by the absence of retrograde His bundle deflection (H2) and atrial depolarization (A2) following V2. At closer V1V2 intervals, V2 resumed conduction to the bundle of His (H2) but not to the atria. The mechanism of this form of gap is similar to the one proposed for the previously described gap phenomena in ventriculoatrial (V-A) conduction and involves proximal delay allowing more time for distal recovery. At shorter V1V2 intervals, V2 resumes conduction to the bundle of His because it encounters sufficient delay in some region below the His bundle. However, this delay may be insufficient to allow recovery of excitability at the A-V node and hence resumption of conduction to the atria is not an integral part of V-H gap. The relation of V-H gaps to the occurrence of reentry within the HPS (V2 phenomenon) is discussed. V-H gaps also explain the failure of some ventricular premature beats (VPBs) to show the effects of concealed conduction in the A-V node. The similarities and differences between V-A and V-H gaps during retrograde conduction are discussed.