Randomized Study of Integrated Evaluation of Conventional Biventricular and Left Bundle Branch Pacing Therapy Effect on Left Ventricular Remodeling and Clinical Outcomes in Patients With Chronic Heart Failure With Reduced Ejection Fraction

The heart failure (HF) is a rapidly growing public health issue with an estimated prevalence of more than 37.7 million individuals globally. In the developed world, this disease affects approximately 2.0% of the adult population. In the United States the total percentage of the population with HF is projected to rise from 2.4% in 2012 to 3.0% in 2030. In Russian Federation the prevalence of chronic HF (CHF) is 10.2%. The main cause of CHF is a coronary heart disease, which accounts for about 70.0%, and the remaining 30.0% are non-ischemic heart diseases. More than 2 decades of research has established the role of cardiac resynchronization therapy (CRT) in medically refractory, mild to severe systolic HF with abnormal QRS duration and morphology. The prolongation of QRS (120 ms or more) occurs in 14.0% to 47.0% of HF patients and the ventricular conduction disturbance, most commonly left bundle branch block (LBBB), is present in approximately one-third of HF, leading to mechanical dyssynchrony of ventricles. Prospective randomized studies of patients with both ischemic HF (IHF) and non-ischemic HF (NIHF) have shown that CRT translates into long-term clinical benefits, such as improved quality of life, increased functional capacity, reduction in hospitalization for HF, and overall mortality. These patients qualified as responders to CRT. However, CRT is effective in 70.0% of patients, and the remaining 30.0% do not respond to the device therapy. In fact, biventricular CRT leads to the fusion of two fronts of non-physiological excitation waves and leaves a significant residual dyssynchrony.

His bundle pacing (HBP) is possible alternative to biventricular CRT. During HBP there is a physiological electromechanical synchrony by facilitating conduction through the native His-Purkinje system. HBP promotes higher electrical ventricular resynchronization than biventricular CRT. Studies have shown that HBP, as well as conventional biventricular CRT, improves cardiac function, which leads to a decrease in the number of HF hospitalizations. The main unsolved problems that limit the use of HBP are the low amplitude of the intracardiac signal, high pacing thresholds and troubles associated with lead implantation in the area of the His bundle, which ultimately increases the risk of re-implantation.

In 2017, W. Huang et al. pioneered left bundle branch pacing (LBBP) and demonstrated that it provided clinical benefits in patients with HF and LBBB, aiming to pacing the proximal left bundle branch (LBB) along with LV myocardial capture. During selective pacing, only LBB is captured without the nearby myocardium, while with non-selective LBBP the septal myocardium is captured. LBBP with lead implanted slightly distal to the His bundle and screwed deep into the left ventricular (LV) septum is ideal for the LBB capture. LBBP has emerged as an alternative to HBP due to pacing of LBB outside the blocking site, a stable pacing threshold, and a narrow QRS in patients with bradycardia. In clinical cases of W. Huang et al. was demonstrated for the first time that LBBP could lead to complete correction of LBBB and improvement in cardiac function in patients with LBBB and HF. In another observational study, W. Zhang et al. showed that LBBP could be a new method of CRT. Subsequently, several case reports and observational studies have demonstrated the efficacy and safety of LBBP in patients with indications for CRT device implantation.

The above studies demonstrate that LBBP is clinically feasible in patients with HF and LBBB. However, there are still few data about CRT using LBBP in patients with HF and reduced LVEF. There are also few studies on direct comparison of changes in clinical, speckle tracking echocardiography and other laboratory and instrumental parameters between patients with conventional biventricular CRT and CRT using LBBP.

CRT induces reverse remodeling of the affected heart, improves LV systolic and diastolic function and left heart filling pressure. The measurement of fibrosis and remodeling biomarkers representing the pattern of active processes in HF be useful.