Introduction: Conventional right ventricular pacing can cause left ventricular systolic dysfunction, heart failure symptoms and atrial fibrillation in the long run. Early upgrade to biventricular stimulation or physiological stimulation may be able to prevent these adverse outcomes. His bundle pacing (HBP) has several pitfalls which include lack of capture at acceptable thresholds, incremental threshold values over time, premature battery depletion, poor lead stability with an increased risk for lead dislodgement, inability to identify the perfect pacing position, presence of intranodal block or disease in the distal His bundle, complex procedure with increased fluoroscopy exposition time, oversensing of the atrial electrogram and other technical issues. Deep septal, distal HBP has the potential to overcome some of these issues. There are two ways to perform distal HBP: a primary fluoroscopic approach or the zero fluoroscopic approach by way of 3D high density electroanatomic mapping (EAM).
Methods: Ensite X (Abbott) was used to locate the distal His bundle for pacemaker lead placement with a zero (low) fluoroscopy approach in all patients with right bundle branch block from 7/2022 through 12/2022. A multipolar steerable mapping catheter (Inquiry™ Abbott) was used to create a 3D map of the right heart. Regions of interest were mapped fashioning a venous approach only. During mapping, the His-ventricle intervals were recorded. The C315 catheter (Medtronic) was first placed in the area of interest, and the Select Secure 3830 lead was advanced only to expose the helix. Unipolar mapping was performed to identify the His bundle electrogram. The lead was then advanced into the septum and fixed. Contrast injection was performed through the deflectable C304His sheath in left anterior oblique 30° fluoroscopic view once. The pacing leads were displayed in the 3D mapping system in unipolar configuration during mapping and in bipolar configuration once the leads were placed. The procedure could include ‘ablate and pace’ strategy in patients where indicated. Follow-up was 6 months per patient. Primary endpoint was change of threshold during 6 months follow-up. Secondary endpoints included adverse events of all grades.
Results: Thirteen consecutive patients underwent 3D map guided distal His-bundle pacing lead placement with a 92.3% (n=12 patients) success rate at 6-months follow-up. In one case, severe fibrosis led a lead placement in a caudo-lateral position from optimal placement according to 3D map. During follow-up, no lead or procedure-related adverse events could be observed.
Discussion and conclusion: Unlike proximal His bundle pacing, the excitation in the distal His bundle area has been proposed as a viable alternative providing for lead stability, low and stable pacing thresholds, and ability to correct of distal conduction system deterioration. Therefore, distal His bundle pacing has the advantages of stable local ventricular capture and less risk for ventricular pause because of oversensing. The procedure comes with some procedural obstacles, which might be overcome by high density maps of the area of interest. Proper identification of the distal His bundle electrogram during his lead placement by 3D mapping led to successful lead placement with a stable pacing threshold for a 6-months follow-up period in our cohort. ❑
Figure 1
Figure 2: Maps of proximal, mid and distal His bundle
