Recent Approaches to His-Purkinje System Pacing

Recent Approaches to His-Purkinje System Pacing

Physiologic cardiac pacing has emerged as a novel technique that has gained significant attention in recent decades. Among the various methods, His bundle pacing (HBP) has long been regarded as the most physiologic approach. However, as HBP has been widely implemented, its limitations have become increasingly apparent. In this context, left bundle branch pacing (LBBP), which directly engages the His-Purkinje system, has been proposed as a superior method to mimic physiologic activation patterns. This review aims to summarize recent advancements in physiologic cardiac pacing, focusing on the strengths and weaknesses of HBP and the emerging potential of LBBP.

The concept of artificial pacemakers dates back to 1932 when Hyman first introduced the idea by implanting a needle into the right atrium to create a heartbeat. Over the decades, pacemaker technology has evolved significantly, with the introduction of endocardial pacing in 1959 marking a foundational milestone. Today, pacemakers are a standard therapeutic option for patients with conditions such as syncope, sick sinus syndrome, atrioventricular block (AVB), neuromuscular diseases, and even heart failure. The primary goal of pacemaker techniques is to restore cardiac electrical conduction and improve cardiac function, with the optimal implantation site for electrodes being a subject of ongoing debate.

The cardiac conduction system plays a critical role in maintaining normal heart function. Electrical activation begins in the sinoatrial node, spreads through the atria, and then passes through the atrioventricular node (AVN) to the ventricles. The His bundle (HB) is a specialized fibered bundle that transmits electrical impulses to the left and right bundle branches, which then activate the Purkinje network, ensuring synchronous ventricular contraction. This sequential activation pattern is essential for efficient cardiac function, and any disruption can lead to significant hemodynamic consequences.

Conventional right ventricular apex pacing (RVAP) has been the most commonly used approach for permanent cardiac pacing due to its ease of implantation and stable fixation. However, long-term studies have revealed that RVAP can lead to adverse effects, including pacing-induced cardiomyopathy. This condition is characterized by structural and functional changes in the heart, often resulting in new-onset heart failure. The desynchronized contraction patterns caused by RVAP, as evidenced by prolonged QRS duration, have been identified as a key factor in the development of pacing-induced cardiomyopathy.

In contrast to RVAP, His bundle pacing (HBP) has been promoted as a more physiologic method. HBP directly engages the His-Purkinje system, resulting in narrow QRS complexes that closely mimic normal cardiac activation. The concept of HBP was first introduced by Deshmukh et al. in 2000, and since then, it has been widely adopted. HBP can be categorized into selective HBP (S-HBP) and non-selective HBP (NS-HBP). S-HBP involves direct activation of the His-Purkinje system, while NS-HBP may cause pseudo-excitation patterns and prolonged QRS intervals. Despite its advantages, HBP has several limitations, including high pacing thresholds, difficult implantation due to the anatomic size of the His bundle, and the risk of acute trauma to the bundle branch.

One of the significant advantages of HBP is its ability to manage intra-His bundle block and sick sinus syndrome. Studies have shown that HBP can improve left ventricular ejection fraction (LVEF) and reduce paced QRS duration, leading to better clinical outcomes. For example, Ye et al. reported a reduction in paced QRS duration from 157.8 ± 13.3 ms to 109.3 ± 16.9 ms after switching from RVAP to HBP. Additionally, long-term follow-up studies have demonstrated that HBP is associated with lower rates of all-cause mortality and heart failure hospitalization compared to RVAP.

HBP has also shown promise in the management of atrial fibrillation, particularly in patients who undergo AVN ablation. Vijayaraman et al. reported significant improvements in LVEF and New York Heart Association (NYHA) functional classification in patients treated with AVN ablation plus HBP compared to those treated with AVN ablation plus RVAP. Furthermore, HBP has been explored as an alternative to cardiac resynchronization therapy (CRT) for patients with heart failure and left bundle branch block (LBBB). While CRT involves pacing the right ventricle and the left ventricle epicardium, HBP offers a more physiologic approach by directly engaging the His-Purkinje system. Studies have shown that HBP can achieve similar or even superior outcomes to CRT, particularly in patients who fail left ventricular lead implantation.

Despite its potential, HBP is not without challenges. The procedure is technically demanding, with a high failure rate due to the anatomic complexity of the His bundle. Additionally, HBP requires higher pacing thresholds, which can limit its applicability in certain patients. Abnormal sensing is another issue, as the low amplitude of HBP electrograms can reduce the sensing ability of the pacemaker.

In light of these limitations, left bundle branch pacing (LBBP) has emerged as a promising alternative. LBBP involves pacing the left bundle branch directly, resulting in narrow QRS complexes and more physiologic activation patterns. Huang et al. first reported successful LBBP implantation in 2017, and since then, several studies have demonstrated its feasibility and advantages over HBP. LBBP offers lower pacing thresholds, higher R wave amplitude, and easier fixation compared to HBP. Additionally, LBBP may be a viable option for patients with infra-His bundle block, a condition where HBP is less effective.

Our center has successfully treated 15 patients with LBBP, with 13 achieving low-threshold pacing. However, implantation failed in two patients due to technical challenges, highlighting the need for further refinement of the technique. LBBP is particularly beneficial for patients with indications for RVAP, as it provides a more physiologic pacing option. However, in patients with severe fibrosis of the right ventricular septum or dilated cardiomyopathy, LBBP may not be as effective as CRT.

In conclusion, while HBP remains the most physiologic pacing method, its limitations have spurred the development of alternative approaches such as LBBP. The clinical significance of LBBP is still under investigation, and large randomized trials are needed to validate its efficacy. As the field of cardiac pacing continues to evolve, the future holds promise for more advanced and physiologic pacing techniques that can improve outcomes for patients with cardiac conduction disorders.

doi.org/10.1097/CM9.0000000000000038

Was this helpful?

YesNo

0 / 0