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| EDITORIAL |
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| Year : 2019 | Volume
: 4
| Issue : 1 | Page : 1-3 |
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His-purkinje conduction system pacing: State of the art
Keping Chen, Shu Zhang
Arrhythmia Center, Fuwai Hospital, State Key Laboratory of Cardiovascular Disease, National Center for Cardiovascular Diseases, Peking Union Medical College, Chinese Academy of Medical Sciences, Beijing, China
| Date of Web Publication | 25-Nov-2019 |
Correspondence Address:
Dr. Shu Zhang
Center of Arrhythmia, Fuwai Hospital, Chinese Academy of Medical Sciences, Peking Union Medical College, Beijing 100037
China
 Source of Support: None, Conflict of Interest: None  | Check |
DOI: 10.4103/IJHR.IJHR_5_19
How to cite this article:
Chen K, Zhang S. His-purkinje conduction system pacing: State of the art. Int J Heart Rhythm 2019;4:1-3 |
His bundle pacing (HBP) acts as an ideal physiological pacing modality and has recently become a hot topic in the field of pacing, as it can maintain the relatively normal ventricular activation sequence and synchronous contraction owing to the electrical activation being delivered through the intracardiac conduction system.[1] With the improvement of implantation tools and tremendous research interest and enthusiasm, HBP has rapidly been adapted into clinical practice. The current recommendation of HBP is mainly inclusive of three parts as follows:[2] (1) patients with heart failure (HF) and atrial fibrillation indicated for atrioventricular node ablation; (2) atrioventricular block patients with preserved conduction function below the level of His bundle; and (3) in left bundle branch block (LBBB) patients with indications for cardiac resynchronization therapy (CRT), HBP can help in recruiting the LBBB, normalizing the QRS morphology, and eventually achieving cardiac resynchronization, according to the longitudinal dissociation hypothesis and voltage theory.[3],[4] As per the 2018 ACC/AHA/HRS Guideline for the Evaluation and Management of Patients with Bradycardia and Cardiac Conduction Delay, HBP was recommended for the first time: In atrioventricular block patients with indications for permanent cardiac pacing, under the circumstance of left ventricular ejection fraction ranging from 36% to 50% and ventricular pacing percentage being >40%, CRT or HBP could preserve physiological ventricular activation sequence, which is overall superior to traditional right ventricular pacing (IIa, B-NR); in pacing-indicated patients with atrioventricular block at the level of atrioventricular node, HBP could restore physiological ventricular activation (IIb, B-NR).[5]
Despite the fact that HBP serves as a physiological pacing modality, several limitations still exist:[6],[7] (1) The procedure of HBP could be technically challenging for implanters, especially for those at the early learning stage of HBP. Although the improvement of implantation tools has significantly streamlined the procedure, dramatically increasing the success rate, for patients with atrial enlargement, structural heart disease, and previous tricuspid valve repair, HBP could be challenging and painstaking; (2) given the anatomical characteristics of His bundle, HBP features a lower R-wave amplitude with the potential of atrial cross-talk sensing and high pacing threshold, especially in patients with bundle branch block (BBB). Usually, the threshold of HBP with BBB correction is high. The underlying assumption is that HBP entails greater energy consumption due to the higher pacing threshold, resulting in a shortened battery life. Besides, the fibrosis of the local tissue may lead to an increase in threshold and even loss of capture; (3) for patients with progressive conduction system disease, especially for those whose blockage site is in the distal portion of the His bundle, a backup right ventricular lead should be considered; (4) HBP is not suitable in patients with diffuse intraventricular conduction block caused by nonproximal block or myocardial disease; and (5) due to the lack of appropriate pulse generator for HBP, the programming of HBP is complicated. Thus, left bundle branch pacing (LBBP) has emerged as an alternative physiological pacing.
In 2003, Peschar et al.[8] for the first time implemented left ventricular septal pacing (LVSP) using an open-chest model in canine hearts. Taking consideration of the short-term experimental results, LVSP could achieve favorable ventricular synchronized contraction in comparison with traditional right ventricular pacing. In 2009, Mills et al.[9] performed LVSP in dogs undergoing atrioventricular nodal ablation. In light of the long-term experimental outcome, LVSP was superior to traditional right ventricular pacing in terms of left ventricular electrical and mechanical synchrony, myocardial contraction and hemodynamic effects, etc. In 2016, Mafi-Rad et al.[10] for the first time put LVSP into clinical practice, and the results indicated that the acute hemodynamic parameters had an advantage over that of right ventricular apical/septal pacing. According to the outcomes from 6-month follow-up, the pacing parameters were stable and satisfactory, and no procedure-related complications (e.g., lead dislodgment) were observed.
A case regarding LBBP as a novel pacing strategy first described by Huang et al.[11] in 2017 suggested that LBBP was successfully performed in an LBBB patient with HF, and normalized QRS morphology could be achieved by adjusting atrioventricular delay with LBBB correction. More importantly, significant clinical improvement was observed in this patient at the 12-month follow-up. In November 2018, Chen et al.[12] first evaluated the clinical feasibility and electrocardiogram characteristics of LBBP in comparison with right ventricular pacing. The results showed the procedural and clinical feasibility and safety of LBBP that produced a pattern of right bundle branch delay, shortened QRS duration (QRSd), and ideal pacing parameters. Hence, LBBP could be considered as one of the physiological pacing techniques for patients requiring ventricular pacing. Since then, the advent of LBBP has raised a revolution of physiological pacing and LBBP has been under wide investigation. Li et al.[13] showed that LBBP could be successfully and safely performed in most patients with a success rate of 80.5%, achieving narrower electrocardiographic QRSd and favorable pacing parameters compared with right ventricular septal pacing. Then, the research by Vijayaraman et al.[14] further demonstrated the feasibility and the electrophysiologic and echocardiographic characteristics of LBBP. According to their results, the LBBP threshold at implant was 0.6 ± 0.4 V/0.5 ms and R-waves were 10 ± 6 mV, which remained stable during the follow-up. Importantly, Li et al.[15] reported their experience of LBBP in 33 atrioventricular block patients that LBBP was performed with a high success rate of 90.9% and yielded a stable threshold and a narrow QRSd and preserved left ventricular synchrony with few complications. Besides, Hou et al.[16] proved that LBBP preserved better cardiac electrical and left ventricular mechanical synchrony compared with right ventricular septal pacing. Recently, a study by Zhang et al.[17] evaluated the feasibility of LBBP in patients with systolic HF and LBBB, of which LBBP, as a new CRT to recruit LBBB, could provide ventricular synchrony and improve clinical symptom with LV reverse remodeling.
After penetrating through the membranous atrioventricular septum, conductive fibers of the left bundle branches spread beneath the endocardium of the ventricular septum in a relatively large dimension, which offers an opportunity for pacing left bundle branch in an easier manner.[18] Left bundle branch pacing is achieved by a transventricular septal approach, which demonstrates a low and stable pacing threshold, large R-wave amplitude, and shorter paced QRSd compared to right ventricular pacing. For patients with LBBB, right bundle branch conduction delay during LBBP can be offset by sequential atrioventricular delay optimization to fuse activations deriving from LBBP and intrinsic right bundle branch, leading to a normal electrocardiogram QRS complex.[19] Compared with HBP, there are several advantages of LBBP over HBP.[12],[13] First, LBBP is easier to perform with less fluoroscopic exposure time. Second, pacing parameters are better than that of HBP likely because of the anatomical characteristic. The pacing threshold is low and stable, and the R-wave amplitude is high. Finally, since the pacing tip is fixed at or nearby the left bundle branch with neighboring myocardial tissue and the myocardium can be captured at the pacing output, there is no need to implant a backup lead in case of loss of LBB capture. In clinical practice, LBBP is more suitable for the following patients:[11],[20],[21],[22] (1) patients who are not eligible for HBP, such as patients with infra-Hisian atrioventricular block, failure of HBP, and high threshold of BBB correction; (2) HF patients with reduced ejection fraction who have an indication for ventricular pacing and high-degree atrioventricular block; and (3) patients who failed to CRT implantation or had no response to CRT.
Despite recent advances and broad interest in LBBP, there still remain several unsolved issues in LBBP: (1) unreached consensus on the definition and criteria of LBBP; (2) no researches pertinent to long-term clinical outcomes and benefits; (3) potential risks including interventricular septal hematoma and septal perforation; and (4) lead problems by mechanical septal contraction and difficulties in lead extraction due to the lead being partly positioned in septum.[23] Left bundle branch pacing is a novel pacing strategy, although with several unanswered questions and concerns, the criteria and procedures are not standardized, and no long-term efficacy and safety results have been reported. More data deriving from large multicenter clinical trials or registries are needed to evaluate its feasibility and safety.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
| References | |  |
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