Dual anterograde His bundle pathways in man

Multiple gap phenomena associated with dual His bundle pathways having a lower common tract

We report a case showing 4 types of aberrant conduction and 2 types of gap phenomena produced by single atrial extrastimulus during sinus rhythm. One of the gap phenomena was associated with dual His bundle pathways, demonstrating a fast-to-slow jump-up phenomenon. Of note, a sharp potential considered as retrograde His bundle activations was recorded, which indicated that the activation wave front descended the slow His bundle pathway and turned up the fast His bundle pathway.

Longitudinal dissociation in the his bundle: a possible mechanism of two distinct cycle lengths in atrioventricular reentrant tachycardia

Two wide QRS tachycardias with identical morphology but different cycle lengths (CLs) developed in a 63-year-old man. Electrophysiological study demonstrated inducible atrioventricular reentrant tachycardia (AVRT) due to a concealed left posterior accessory pathway (AP), which was successfully ablated by radiofrequency application. Neither dual AV nodal pathways nor other APs were documented. Splitting of the His-bundle electrogram was shown, and programmed stimulation induced sudden prolongation of intra-hisian conduction time. These results suggest longitudinal dissociation in the His bundle may be responsible for two distinct CLs in AVRT without dual AV nodal physiology.

Electrophysiologic demonstration of anterograde fast and slow pathways within the His bundle in patients with normal intraventricular conduction

Electrophysiological evidence of functional longitudinal dissociation has been shown in different structures of the normal conduction system of the heart and in anomalous atrioventricular (AV) pathways. The typical sudden fast-to-slow jump phenomenon, which is commonly observed in patients with dual AV nodal pathways, has not been demonstrated so far within the normal His bundle. Herein we report unusual electrophysiological properties of the His bundle in two patients with normal intraventricular conduction. Of 86 patients with discontinuous anterograde AV function curves, programmed atrial stimulation revealed dual anterograde His bundle pathways in only 2 (2.3%) patients. Extrastimuli introduced at critically timed coupling intervals produced a sudden marked increase in H2-V2 interval suggesting failure of fast pathway with conduction proceeding through a slower pathway with shorter refractory period. With further decreasing coupling intervals, the second H2-V2 curve showed decremental conduction which allowed a type II gap phenomenon in the right bundle branch to occur in one of the patients. No echo beats were observed. These results provide the first electrophysiological demonstration, in patients with normal intraventricular conduction, of anterograde failure of a fast His bundle pathway with subsequent conduction through a slow His bundle pathway. His bundle duality was manifested by dual conduction times and refractory periods. These observations further expand our knowledge on the electrophysiologic properties of the His bundle.

Effects of autonomic blockade on dual atrioventricular nodal pathways pattern

Fifteen patients (age: 57.6 +/- 14 years) showing dual A-V nodal pathways pattern during basal electrophysiological testing were studied following pharmacological autonomic blockade (iv propranolol 0.2 mg/Kg and iv atropine 0.04 mg/Kg). After induction of the autonomic blockade, the dual A-V nodal pathways pattern was not present in four patients due to disappearance of the slow pathway; the pattern remained in 11 (73%). The longest A2-H2 interval, the effective and functional refractory periods of the fast pathway did not change significantly following autonomic blockade. Even the electrophysiological measures of the slow pathway, in the 11 patients in whom they were comparable, did not change significantly after autonomic blockade. These data suggest that: the dual A-V nodal pathways pattern is mainly related to the intrinsic structure of the A-V node; the autonomic nervous system only affects in a variable way the refractoriness and the conduction velocity in the two pathways.