His Electrogram Alternans Reveal Dual-Wavefront Inputs Into and Longitudinal Dissociation Within the Bundle of His

Abstract

Background-His electrogram (HE) amplitude and morphology changes were observed in our previous studies during transition from "fast" to "slow" atrioventricular nodal (AVN) conduction. This phenomenon and its significance for the dual-AVN electrophysiology are not well recognized and have not been studied. Methods and Results-Experiments were performed on 17 healthy rabbit atrial-AVN preparations during standard programmed electrical pacing. HEs were mapped along the His bundle with roving surface electrodes, along with recording of cellular action potentials (APs). HEs recorded from the superior margin of the His bundle were of greater amplitude during basic beats and decreased substantially, by 42Ϯ19% (PϽ0.01), when premature A 1 A 2 shortened to 178Ϯ20 ms. In contrast, the HEs from the inferior margin increased dramatically, 2.9Ϯ1.7 times (PϽ0.01), during short A 1 A 2 and remained high until AVN block occurred. In addition, during long A 1 A 2 , the superior HEs consistently preceded the inferior by 1.9Ϯ0.7 ms. In contrast, at short A 1 A 2 , the superior HEs occurred 2.7Ϯ0.8 ms after the inferior. Cellular AP recordings demonstrated clearly the presence of and the transition between early (fast) and late (slow) excitation wavefronts that accompanied HE alternans. Conclusions-The

Characterization and Modeling of Atrioventricular Conduction during Atrial Fibrillation

“…In figure 2.6 an example of high-low IHE alternans recorded during experimental AF in rabbit heart preparation [44,45,46]. Successful SP modification prolonged the AV node ERP without changing the basic AV node conduction time, which is consistent with clinical SP ablation [3].…”

“…In rabbit heart experiments it was shown that this index could be used to determine on a beat-by-beat basis during AF the AV node conduction pattern (i.e. though FP or SP) [44,45,46]. Specifically, a low amplitude inferior bundle of His electrogram (IHE) was associated with FP conduction, while high-amplitude IHE indicates SP conduction.…”

“…This index was validated during programmed electrical stimulation (e.g. generation of AV node conduction curve), as well as during atrial arrhythmia [44,45,46].…”

“…However, the study of RR interval series with the Poincaré analysis does not provide direct evidence of the dual pathways [60,41]. It is unclear whether the two pathway properties can be evaluated from the two distributions of the Poincaré plot and the role of the second pathway in the conduction curve needs to be clarified [3,47,44,45,46]. In fact, during the development of the current thesis we have attempted to clarify which are the mechanisms producing the existence of more than one RR interval distribution and the relation between the dual AV nodal pathway physiology and the ventricular response pattern during AF.…”

“…In fact, the evaluation of their individual impact on the AV nodal conduction was ambiguous since the pathway responsible for the conduction of a particular beat could not be identified. Recently Zhang et al have introduced the His Electrogram Alternance (HEA) [44,45,46], a recording technique which allows the identification of the dominant pathway and consequently the evaluation of the role of each pathway during AV nodal conduction.…”