Abstract 1085: Bypassing the Compact Atrioventricular Node in the Normal Rabbit Heart: Implications for Synchronized Ventricular Pacing
Direct His bundle pacing (DHBP) is a pacing strategy recently explored to combat asynchronous ventricular contraction due to right ventricular pacing. The compact atrioventricular node (cAVN) is thought to be the sole gatekeeper to the His-Purkinje system. Thus, DHBP strategies pace distal to the AVN close to His. In this study, we identified a relatively large right atrial pacing region that bypasses the cAVN, and can be used to excite the His.
Methods: New Zealand rabbit triangle of Koch preparations (n=7) were electrically and optically mapped for: activation pattern, bipolar electrogram morphology, unipolar stimulation thresholds, and stimulus-His (S-H) intervals. Electrode was mounted on a force transducer to control contact force.
Results: Pacing stimuli ≥2mm above the tricuspid valve (TV) caused fast pathway activation of the AVN and His (see atrial excitation area in Fig. A⇓; threshold: 2.1±1.5mA). An area directly below the coronary sinus (CS) had high thresholds (8.7±1.5mA) that still resulted in atrial excitation (P<0.0001). S-H intervals for atrial activation did not depend on the distance from the His electrode (Fig. B⇓). Stimuli applied <2mm from the TV resulted in inferior nodal extension (INE) or direct His excitation (4.3 ± 2mA threshold, P<0.0001 compared to atrial threshold). With INE or His excitation, S-H intervals showed a strong dependence on the distance from the His electrode (Fig. C⇓). Connexin immunolabeling of the pathways supports their differential conduction properties.
Conclusions: The S-H intervals for INE/His activation suggest that INE excitation bypasses the cAVN, which can be exploited to achieve long term synchronized ventricular pacing.