Traditional biventricular pacing (BiVP) has been shown to reduce HFH and all-cause mortality in chronic HF patients with CLBBB and LVEF ≤ 35% (1). However, more than 30% of patients have no response to CRT (2–4). The incidence of adverse events such as phrenic nerve stimulation, threshold elevation and lead dislodgement in left ventricular coronary sinus(CS) lead can reach 10%∼30%. Compared with BiVP, His- bundle pacing (HBP), as the most physiological pacing method, can better achieve cardiac resynchronization and improve cardiac function, but its development is limited by its difficult implantation technology, high threshold, low perception, early battery exhaustion. In 2017, Huang et al. (5) reported a case of LBBB combined with HF patients with failed left ventricular lead implantation in CS for the first time, and the cardiac function was significantly improved after LBBP treatment. Since then, several studies have confirmed that LBBP has become an effective physiological pacing mode, which has the advantages of easier to cross the block area, low threshold and high perception compared with HBP. Recently, small randomized controlled trials have demonstrated that LBBP has better short-term efficacy than BiVP in nonischemic cardiomyopathy (NICM) combined with CLBBB (6). At present, there is a lack of long-term follow-up data on HF patients with CLBBB.

The results showed that: (1) ΔLVEF value in LBBP group increased significantly compared with BiVP group; (2) Compared with BiVP, ΔLVEDD decreased more significantly in LBBP group; (3) The echocardiographic super response rate of LBBP group was higher than that of BiVP group; (4) There was no significant difference between LBBP and BiVP group in all-cause mortality and HFH; (5) Compared with BiVP group, the paced QRS duration in LBBP group was narrower and the electrical synchronization was better; (6) The pacemaker threshold of LBBP group was lower than that of BiVP group, and the lead parameters of both groups were stable in the near and medium term.

BiVP-CRT has been shown in randomized large-scale clinical studies to reduce hard endpoint events such as all-cause mortality and HFH in patients with HF who have failed to respond to optimal drug therapy, LBBB, QRS wave broadening, LVEF ≤ 35%, and (NYHA) II–IV functional class. However, about 30% of patients were unresponsive to CRT, which was basically consistent with the data in this study (26.7%). The location of left ventricular lead pacing, left ventricular myocardial scar, and elevated threshold affect the CRT response rate. In addition, abnormal CS anatomy, phrenic nerve stimulation, lead dislocation and other reasons may lead to operation failure. For patients with LBBB, BiVP theoretically activates the last ventricular muscle to depolarize the left ventricle ahead of time, thereby shortening the QRS wave duration, but in fact, it does not restore the conductivity of the left bundle branch, the depolarization and repolarization sequence is not corrected, and the left ventricle still has asynchronous contraction, so it is non-physiological pacing. In 2005, HBP was first applied to a patient with HF combined with complete AVB and LBBB (7). Crossing the blocked area, the paced QRS duration wave narrowed, and the cardiac function and echocardiographic results improved significantly at 6 months of follow-up. Subsequent studies have shown the effectiveness of HBP in patients with HF combined with LBBB (8–12). HBP, as the most physiological pacing mode, can cross the proximal block area of the left bundle branch (LBB) to better achieve cardiac resynchronization and improve cardiac function. However, it can not correct all LBBBS, and it is difficult to cross the distal block area of LBB, and the success rate of correction is reported to be 75.6%∼97%. Due to the difficulty of implantation technology, high threshold, low perception, early battery exhaustion and other problems, its development is limited. In 2017, Huang et al. reported for the first time a case of LBBB patients with HF who failed to receive conventional left ventricular lead implantation with LBBP treatment, and the postoperative cardiac function improved significantly. Since then, several studies have confirmed that LBBP has become an effective physiologic pacing mode, which can achieve left ventricular mechanical synchronization similar to HBP. LBB is widely distributed in a fan-shaped network in the left ventricular septum subendocardial area and is wrapped by a small number of fibers. Its anatomical structure determines that LBBP has the advantages of simple operation, easier to cross the block area, low threshold and high perception than HBP (13,14). In this study, the success rate of LBBP surgery was 95%, which was similar to the results of other studies (15). Among them, the thickness of the interventricular septum and the insufficient supporting force of the sheath made it difficult for the 3830 lead to rotate to the left interventricular septum surface were the main reasons for the unsuccessful operation. It is expected that surgical tools for LBBP can be developed in the later stage to reduce the learning curve and further improve the success rate of operation.

A prospective multicenter study enrolled 371 patients with ischemic cardiomyopathy(ICM) or NICM receiving CRT (LBBAP or BVP) with an average follow-up of 340 days (16). The LBBAP group had 39.3% fewer HFH than the BVP group (22.6% vs. 39.5%, HR = 0.607, P = 0.02), but the difference in all-cause mortality was not statistically significant. A recent multiccenter observational study of 1,778 patients with CRT indicators compared the outcomes of LBBAP and BVP in the real clinical world, and showed significantly lower mortality, HF mortality, and HFH in the former with a follow-up of (33.2 ± 15.5) months (17). In the results of this study, the all-cause mortality and HFH of HF in the LBBP group were lower than those in the BiVP group, but the difference was not statistically significant, which was considered to be related to the small number of included cases. In addition, in the above study, the LBBAP group had better echocardiographic response rate than the BVP group, especially in LBBB patients, whose ΔLVEF was higher in the LBBAP group than in the BVP group (15.3% ± 12.0% vs. 10.8% ± 12.0%; P < 0.001). In this study, LVEF values in both groups were significantly higher than before operation, and LBBP group had a higher improvement than BiVP group (14.8% ± 9.9% vs. 10.7% ± 9.0%; P < 0.001), the results of echocardiographic response rate were similar to the above study. In a prospective observational study of 41 patients with LBBB, LVEF ≤ 35% and HF treated with CRT, the LBBP group showed greater improvement in LVEF (ΔLVEF) than the BiVP group after 6 months (20.5% ± 9.6% vs. 15.4% ± 11.2%, P = 0.15). The mean LVEF of the former was close to normal (50.9% ± 10.7% vs. 44.4% ± 13.3%, P = 0.12) (18). Wang et al. (6) conducted a small-scale randomized controlled study on LBBP and BiVP, including 40 HF (LVEF ≤ 40%) patients with SR, NICM and LBBB. After 6 months, LVEF improvement (ΔLVEF) in LBBP group was significantly higher than that in BiVP group (21.08% ± 1.91% vs. 15.62% ± 1.94%, P = 0.039). It should be noted that the improvement of LVEF in the latter two studies was significantly higher than that in this study and the previous study, which may be related to the fact that the enrolled LBBB patients all met Strauss's criteria. This suggests that echocardiographic improvement is better in patients with LBBB who meet Strauss's criteria. In Vijayaraman et al. (17) study, the echocardiographic response rate of LBBB subgroup was higher, the CRT response rate of LBBAP group was better than that of BVP group, and the echocardiographic response rate (ΔLVEF ≥ 5%) was 81.7% and 68.2%, respectively. CRT overreaction rates (ΔLVEF ≥ 20% or LVEF ≥ 50%) were 42.1% and 28.5%, respectively. In this study, the LBBP group had a higher echocardiographic response rate than the BiVP group (ΔLVEF ≥ 5%), 81.7% and 73.3% (P = 0.27), respectively, and the echocardiographic super response rate (ΔLVEF ≥ 15% or LVEF ≥ 45%) in LBBP patients was significantly higher than that in the BiVP group (65% vs. 45%; P < 0.001). Different studies have different definitions of echocardiographic response rate and super response rate, and the definition of super response rate in this study was slightly looser than that in Vijayaraman et al., so the proportion of super response rate was higher. Recently, a network meta-analysis involving 4,386 patients in 33 studies compared the clinical efficacy, electrical and lead parameters of four different pacing techniques (LBBP vs. HBP vs. BVP vs. RVP). Compared with other pacing techniques, LBBP significantly improved LVEF, shortened QRS duration, reduced HFH, had a low and stable pacing threshold, good perception, and no increased lead adverse events (19).

At present, more and more studies have proved that in patients with CRT indications, especially those NICM with CLBBB, LBBP has better efficacy than BiVP, and can be used as the first-line or preferred implantation method.

There were many shortcomings in this study: (1) Single-center, retrospective, non-randomized study; (2) The number of samples was small. Therefore, the conclusions of the study may be insufficient and need to be verified by large-scale, multi-center randomized controlled clinical trials.