**2. Historical landmarks**

#### **2.1 Predispositions for development**

Permanent right ventricular pacing was firstly performed in humans on October 8th, 1958 by Swedish Surgeon Ake Senning. It was a breakthrough of that time, allowing to cope with Adams–Stokes syndrome to a 43-year-old man. Overall, this patient required 26 pacemakers to extend his life for 40 years and to live asymptomatically up to the age of 83 [2].

After 10 years from that date, in 1969, Narula, Sherlag proposed HBP using the electrophysiological catheter for HB stimulation. Authors also supposed a possibility of HB longitudinal dissociation.

More than 30 years passed since that time before Deshmukh et al. firstly implied this method in a group of patients of 12 with atrial fibrillation and indications for permanent cardiac pacing, "narrow" QRS complex, decreased left ventricular ejection fraction (LVEF) of 40% or less and NYHA III-IV [3]. For these purposes, the authors used standard electrodes with active fixation and modified stylet.

HBP was technically possible only in 66% of cases. The authors admitted a statistically significant increase in LVEF from 20 ± 9% to 31 ± 11% (p < 0.01). They supposed that the development of dedicated delivery systems for His-electrodes may turn an idea of more physiological cardiac pacing into reality, thus improving conventional RV pacing. However, this article reached the public at the time of BVP prosperity. BVP was proposed as a solution to tackle interventricular asynchronicity that progressively developed in scientific and practical aspects while being supported by the manufactures of cardiac pacemakers.

Numerous randomized clinical trials of cardiac resynchronization therapy (CRT) with the use of biventricular pacemakers and left ventricular epicardial pacing left HBP behind for more than 10 years. It was the first historical curiosity in HBP development.

#### **2.2 Modern stage**

At the same time, there was a rise in articles that analyzed predominantly retrospective data regarding HBP [4, 5]. The number of publications devoted to the HBP increases significantly since 2015. Among them are publications that analyze HBP in patients with atrioventricular (AV) block and sick sinus syndrome (SSS) [6]. Separate studies were dedicated to the comparison of HBP and RV pacing [7, 8], as well as to the evaluation of short-term and long-term outcomes of HBP [9].

A significant contribution to the topic was added by Vijayaraman et al. [6, 10] from Geisinger Heart Institute, USA, who demonstrated a technical possibility of HBP with the use of the 4.1 Fr Select Secure 3830 (Medtronic, USA) leads, which boosted the technical efficiency of HBP and expanded indications for it. It was the second curiosity in the HBP history because the abovementioned stylet-less pacing lead was initially developed about 20 years ago for permanent pacing in children with AV blocks, but not for the dedicated HBP.
