Tripartite Left Bundle Branch Area Pacing.

Abstract

P ermanent His bundle pacing (HBP) brings us the most physiologic contraction in ventricular pacing. It reduces the risk for pacing-induced cardiomyopathy, heart failure hospitalization, and mortality compared to RV apical or septal pacing. The AHA/ACC/HRS guideline on management of bradycardia recommends HBP as a class IIa indication for patients with atrioventricular (AV) block whose left ventricular (LV) ejection fraction is between 36% and 50%. The guideline also considers HBP as a class IIb indication in patients with AV block at the AV node level who require ventricular pacing. While additional potential benefits of HBP such as applications even for infra-nodal block, correction of left bundle branch block, and alternative treatment to biventricular pacing, HBP may have some technical concerns with respect to being a routine clinical strategy. For example, the higher the capture threshold at implant, the greater the risk for a late rise in HBP thresholds, which need lead revisions. The success rates of HBP lead implantation by trainees are limited due to a long learning curve, higher capture thresholds at implant, and increased risk for late lead trouble. The implantation technique of HBP requires outstanding expertise because target sites are a small area. Moreover, in a dilated heart, the target lesion access becomes challenging with the current delivery system, resulting in long procedural and fluoroscopic duration. The HBP success rate varies from 56% to 95%. It depends on the severity of conduction system impairment and the experience of the center. Thus, some of the patients might have resulted in the loss of His capture during follow-up. To overcome these issues, Huang, et al. first demonstrated a new strategy to directly capture the left ventricle conduction system called left bundle branch area pacing (LBBAP). The LBBAP is achieved by deeply inserting a pacing lead from the right ventricular basal septum to the left side. The newly emerging pacing features are 1) LBBAP can contract the left ventricle through the conduction system 2) the target area is much broader than that of HBP, and 3) the pacing threshold is lower than that of HBP. Left bundle branch block correction is a benefit of HBP compared to traditional pacing. LBBAP has a further advantage for the correction because the left bundle beyond the blocked site can often be stimulated by placing the lead at a more distal location within the conduction system. Currently, LBBAP might be an alternative method for failed HBP cases such as high pacing threshold of the His bundle, infranodal atrioventricular block to show the exit block, or failed correction of left bundle branch block by HBP. Huang, et al. proposed success criteria for LBBAP. Successful LBBAP could be confirmed when the following criteria 1 and 2, and at least 1 of the other 3 criteria are met: 1) paced morphology of right bundle branch block pattern, 2) presence of left bundle branch potential, 3) left ventricular activation time (LVAT), defined as the interval from the pacing stimulus to the R wave peak in V 5/6, is shortened at high output pacing, 4) availability of determination of selective and non-selective left bundle branch capture, and 5) evidence for direct left bundle branch capture. In selective left bundle branch pacing, pacing latency: stimulus-QRS complex, and discrete local endocardial activation wave separated from stimulus can be seen. This indicates capturing only the left bundle branch as a direct left bundle branch capture. In non-selective left bundle branch pacing, no stimulus-QRS latency is detected due to the result of capturing both the left bundle branch and the adjacent local left ventricular septal myocardium.