**Abstract**

Cardiac pacing is an established treatment option for patients with bradycardia and heart failure. In the recent decade, there is an increasing scientific and clinical interest in the topic of direct His bundle pacing (HBP) and left bundle branch pacing (LBBP) as options for cardiac conduction system pacing (CSP). The concept of CSP started evolving from the late 1970s, passing several historical landmarks. HBP and LBBP used in CSP proved to be successful in small cohorts of patients with various clinical conditions, including binodal disease, atrioventricular blocks, and in patients with bundle branch blocks with indications for cardiac resynchronization therapy. The scope of this chapter is synthesis and analysis of works devoted to this subject, as well as representation of the author's experience in this topic. The chapter includes historical background, technical, anatomical, and clinical considerations of CSP, covers evidence base, discusses patient outcomes in line with the pros and cons of the abovementioned methods. The separate part describes practical aspects of different pacing modalities, including stages of the operation and pacemaker programming. The textual content of the chapter is accompanied by illustrations, ECGs, and intracardiac electrograms.

**Keywords:** His bundle pacing, left bundle branch pacing, cardiac pacing, conduction system pacing, interventricular septum, electrophysiology, cardiac resynchronization therapy

### **1. Introduction**

Cardiac pacing from the right ventricular apical (RVA) site results in nonphysiological ventricular activation, which leads to ventricular function impairment in a long-term perspective. Alternative pacing sites include right ventricular septal pacing (RVSP) and right ventricular (RV) outflow tract pacing; they are thought to be more beneficial to patients because of possibly better activation patterns than the RVA pacing. However, studies on pacing sites that are alternative to RVA are still contradictory as activation still relies on myocardial cell-to-cell conduction, thus does not prevent the development of pacing-induced cardiomyopathy [1]. Biventricular pacing (BVP) is a more favorable option than RVA pacing but still produces non-physiological activation patterns. The ideal physiological cardiac pacing requires sustained proximity to the intrinsic cardiac conduction system that preserves normal QRS complexes or even narrows QRS pattern in the bundle branch block (BBB) presence.

Direct conduction system pacing (CSP) becomes a frontier in the field of cardiac pacing, collecting evidence both from follow-up data and clinical case reports

resulting in favor of His bundle (HB) pacing (HBP) and left bundle branch pacing (LBBP) as targets for His-Purkinje CSP. Although, it is necessary to mention that randomized clinical trials or meta-analyses that compare conventional pacing techniques to CSP are currently absent.
