Retrograde activation of the his bundle in the human heart

The catheter technique of His bundle (HBE) recordings proved to be useful in the analysis of retrograde conduction in the human heart. Retrograde activation of the His bundle was more easily detected in bipolar HBE leads with interelectrode distances of 1 mm (or less) than in leads with an interelectrode distance of 10 mm. A high bipolar atrial electrogram (BAE) simultaneously recorded with the HBE was essential to differentiate between superoinferior (sinoventricular) or inferosuperior (retrograde) activation of the atria. V-A delays occurred both above (nodal region) and below (Purkinjebundle branch specialized tissues) the His bundle. The greatest area of delay was seen in the A-H (nodal) region. Ventricular echoes were observed during continuous and intermittent paired ventricular pacing. The atria appeared to be a necessary link in the production of echoes. The echoes, which passed through the His bundle during their forward and retrograde propagation, were best explained by a functional (longitudinal) intranodal dissociation. The reciprocating circuit was represented as follows: V → H → FCP → α → A → β → FCP → H → V. The study of His bundle recordings has enhanced our knowledge of cardiac electrophysiology.