Physiology of Left Ventricular Septal Pacing and Left Bundle Branch Pacing

Left bundle area pacing in hypertrophied hearts: An ex vivo ovine model to study deployment of pacing leads in thick septum

BACKGROUND

Knowledge of lead biomechanics in a hypertrophied interventricular septum (IVS) may improve the success rate of left bundle branch area pacing (LBBAP) in these patients.

OBJECTIVES

We sought to investigate the biomechanics of lead penetration in an ex vivo ovine model of a hypertrophied IVS and compare the behavior of lumenless leads (LLL) vs stylet-driven leads (SDL) in terms of torque transfer and penetrating capacity.

METHODS

Twenty fresh ex vivo ovine interventricular septae were excised to create a virtual hypertrophied IVS model by having 2 septae sandwiched together and placed in a custom-made clamp. Five different leads were driven into the hypertrophied IVS model with sheath support via a custom-engineered tool which allowed control of input rotation, forward movement, and measurement of torque transfer curves.

RESULTS

A total of 100 lead runs were completed which revealed the following 5 distinct patterns of lead behavior: (1) endocardial entanglement, (2) endocardial barrier, (3) drill, (4) myocardial barrier (only observed using LLL, P<.001), and (5) screwdriver (only observed using SDL, P<.001). The maximum torque during successful and deep penetration trended lower compared with when the lead failed to penetrate 2.78 ± 1.21 mN vs 3.6 mN ± 1.62 mN (P = .085). SDL was able to achieve a greater depth of penetration compared with the LLL (20.89 ± 6.46 mm vs 14.8 ± 2.39 mm; P<.001).

CONCLUSION

Lead deployment patterns in hypertrophied septae vary between leads. SDL achieves deeper septal penetration at lower torque and faster forward motion than LLL.

Pacing of the specialized His Purkinje conduction system: 'HOW and FOR WHOM'

The human heart's conduction system consists of specialized cardiomyocytes that generate and transmit electrical impulses, leading to the rhythmic and synchronized contraction of the atria and ventricles, which is crucial for the normal cardiac cycle. In conduction system pacing (CSP), pacing leads are placed in the His bundle region and the left bundle branch area to achieve physiological cardiac activation. This method offers a more natural alternative to the myocardial stimulation provided by conventional right ventricular pacing and biventricular pacing. In this review, we describe the implantation techniques for CSP and discuss the current recommendations for their use.

Impact of leadless pacemaker implantation site on cardiac synchronization and tricuspid regurgitation

BACKGROUND

To investigate the optimization of leadless pacemaker placement and to assess its impact on heart synchronization and tricuspid regurgitation.

RESULTS

A clinical trial was conducted involving 53 patients who underwent leadless pacemaker implantation at the Second Affiliated Hospital of Zhejiang University School of Medicine and Hangzhou First People's Hospital between March 2022 and February 2023. Implantation site localization was determined using the 18-segment method under RAO 30° imaging. Intraoperative and 1-month post-operative echocardiography was performed to assess cardiac electromechanical synchronization and tricuspid regurgitation; parameters of interest included interventricular mechanical delay (IVMD), pre-ejection period of the aorta (L-PEI), and septal-to-posterior wall motion delay (SPWMD). Pacing thresholds, sensing, and impedance exhibited no significant differences between the 8/9 zone and other sites (P > 0.05). In contrast, the 8/9 zone group manifested a significant reduction in L-PEI (128.24 ± 12.27 vs. 146.50 ± 18.17 ms, P < 0.001), IVMD (17.92 ± 8.47 vs. 28.56 ± 15.16 ms, P < 0.001), and SPWMD (72.84 ± 19.57 vs. 156.56 ± 81.54 ms, P < 0.001), compared to the non-8/9 group. Post-pacing QRS duration showed no significant difference between the two groups (139.21 ± 11.36 vs. 143.83 ± 16.35 ms P = 0.310). Notably, for patients with atrial fibrillation, the 8/9 zone placement significantly reduced tricuspid regurgitation. During the 1-month follow-up, neither group reported major complications such as bleeding, cardiac tamponade, pacemaker detachment, or malignant arrhythmias.

CONCLUSION

Implantation of the leadless pacemaker in the right ventricular 8/9 zone provides superior electromechanical synchronization compared to other sites.

Assessment of ventricular electrical heterogeneity in left bundle branch pacing and left ventricular septal pacing by using various electrophysiological methods

INTRODUCTION

Left bundle branch area pacing (LBBAP) comprises pacing at the left ventricular septum (LVSP) or left bundle branch (LBBP). The aim of the present study was to investigate the differences in ventricular electrical heterogeneity between LVSP, LBBP, right ventricular pacing (RVP) and intrinsic conduction with different dyssynchrony measures using the ECG, vectorcardiograpy, ECG belt, and Ultrahigh frequency (UHF-)ECG.

METHODS

Thirty-seven patients with a pacemaker indication for bradycardia or cardiac resynchronization therapy underwent LBBAP implantation. ECG, vectorcardiogram, ECG belt and UHF-ECG signals were recorded during RVP, LVSP and LBBP, and intrinsic activation. QRS duration (QRSd) was measured from the ECG, QRS area was calculated from the vectorcardiogram, LV activation time (LVAT) and standard deviation of activation time (SDAT) from ECG belt and electrical dyssynchrony (e-DYS16) from UHF-ECG.

RESULTS

Both LVSP and LBBP significantly reduced ventricular electrical heterogeneity as compared to underlying LBBB and RV pacing in terms of QRS area (p < .001), SDAT (p < .001), LVAT (p < .001) and e-DYS16 (p < .001). QRSd was only reduced as compared to RV pacing(p < .001). QRS area was similar during LBBP and normal intrinsic conduction, e-DYS16 was similar during LVSP and normal intrinsic conduction, whereas SDAT was similar for LVSP, LBBP and normal intrinsic conduction. For all these variables there was no significant difference between LVSP and LBBP.

CONCLUSION

Both LVSP and LBBP resulted in a more synchronous LV activation than LBBB and RVP. Especially LBBP resulted in levels of LV synchrony comparable to normal intrinsic conduction.

Left bundle branch pacing vs ventricular septal pacing for cardiac resynchronization therapy

Background

The outcomes of left bundle branch pacing (LBBP) and left ventricular septal pacing (LVSP) in patients with heart failure remain to be learned.

Objective

The objective of this study was to assess the echocardiographic and clinical outcomes of LBBP, LVSP, and deep septal pacing (DSP).

Methods

This retrospective study included patients who met the criteria for cardiac resynchronization therapy (CRT) and underwent attempted LBBP in 5 Mayo centers. Clinical, electrocardiographic, and echocardiographic data were collected at baseline and follow-up.

Results

A total of 91 consecutive patients were included in the study. A total of 52 patients had LBBP, 25 had LVSP, and 14 had DSP. The median follow-up duration was 307 (interquartile range 208, 508) days. There was significant left ventricular ejection fraction (LVEF) improvement in the LBBP and LVSP groups (from 35.9 ± 8.5% to 46.9 ± 10.0%, P < .001 in the LBBP group; from 33.1 ± 7.5% to 41.8 ± 10.8%, P < .001 in the LVSP group) but not in the DSP group. A unipolar paced right bundle branch block morphology during the procedure in lead V1 was associated with higher odds of CRT response. There was no significant difference in heart failure hospitalization and all-cause deaths between the LBBP and LVSP groups. The rate of heart failure hospitalization and all-cause deaths were increased in the DSP group compared with the LBBP group (hazard ratio 5.10, 95% confidence interval 1.14-22.78, P = .033; and hazard ratio 7.83, 95% confidence interval 1.38-44.32, P = .020, respectively).

Conclusion

In patients undergoing CRT, LVSP had comparable CRT outcomes compared with LBBP.

Left Bundle Branch Area Pacing and Atrioventricular Node Ablation in a Single-Procedure Approach for Elderly Patients with Symptomatic Atrial Fibrillation

BACKGROUND

Implantation of a permanent pacemaker and atrioventricular (AV) node ablation (pace-and-ablate) is an established approach for rate and symptom control in elderly patients with symptomatic atrial fibrillation (AF). Left bundle branch area pacing (LBBAP) is a physiological pacing strategy that might overcome right ventricular pacing-induced dyssynchrony. In this study, the feasibility and safety of performing LBBAP and AV node ablation in a single procedure in the elderly was investigated.

METHODS

Consecutive patients with symptomatic AF referred for pace-and-ablate underwent the treatment in a single procedure. Data on procedure-related complications and lead stability were collected at regular follow-up at one day, ten days and six weeks after the procedure and continued every six months thereafter.

RESULTS

25 patients (mean age 79.2 ± 4.2 years) were included and underwent successful LBBAP. In 22 (88%) patients, AV node ablation and LBBAP were performed in the same procedure. AV node ablation was postponed in two patients due to lead-stability concerns and in one patient on their own request. No complications related to the single-procedure approach were observed with no lead-stability issues at follow-up.

CONCLUSIONS

LBBAP combined with AV node ablation in a single procedure is feasible and safe in elderly patients with symptomatic AF.

Cardiac resynchronization therapy: present and future

Cardiac resynchronization therapy (CRT) via biventricular pacing (BVP) is a well-established therapy for patients with heart failure with reduced ejection fraction and left bundle branch block, who remain symptomatic despite optimal medical therapy. Despite the long-standing clinical evidence, as well as the familiarity of cardiac electrophysiologists with the implantation technique, CRT via BVP cannot be achieved or may result ineffective in up to one-third of the patients. Therefore, new alternative techniques, such as conduction system pacing and left ventricular pacing, are emerging as potential alternatives to this technique, not only in case of BVP failure, but also as a stand-alone first choice due to several potential advantages over traditional CRT. Specifically, due to its procedural characteristics, left bundle branch area pacing appears to be the most convincing technique, showing comparable efficacy outcomes when compared with traditional CRT, not increasing short-term device-related complications, as well as improving procedural times. However, transvenous leads remain a major limitation of all these pacing modalities. To overcome this limit, a leadless left ventricular endocardial pacing has been developed as an additional tool to achieve a left endocardial activation, although being still associated with non-negligible pitfalls, limiting its current use in clinical practice. This article focuses on the current state and latest progresses in cardiac resynchronization therapy.

Pacing of the specialized His-Purkinje conduction system: 'back to the future'

The conduction system of the human heart is composed of specialized cardiomyocytes that initiate and propagate the electric impulse with consequent rhythmic and synchronized contraction of the atria and ventricles, resulting in the normal cardiac cycle. Although the His-Purkinje system (HPS) was already described more than a century ago, there has been a recent resurgence of conduction system pacing (CSP), where pacing leads are positioned in the His bundle region and left bundle branch area to provide physiological cardiac activation as alternatives to the unnatural myocardial stimulation obtained with conventional right ventricular and biventricular pacing. In this review, we describe the fundamental anatomical and pathophysiological aspects of the specialized HPS along with the CSP technique's nuts and bolts to highlight its potential benefits in everyday clinical practice.

Conduction system pacing for cardiac resynchronization therapy: State of the art, current controversies, and future perspectives

Biventricular pacing (BVP) is the established treatment to perform cardiac resynchronization therapy (CRT) in patients with heart failure (HF) and left bundle branch block (LBBB). However, BVP is an unnatural pacing modality still conditioned by the high percentage of non-responders and coronary sinus anatomy. Conduction system pacing (CSP)-His bundle pacing (HBP) and Left bundle branch area pacing (LBBAP)- upcomes as the physiological alternative to BVP in the quest for the optimal CRT. CSP showed promising results in terms of better electro-mechanical ventricular synchronization compared to BVP. However, only a few randomized control trials are currently available, and technical challenges, along with the lack of information on long-term clinical outcomes, limit the establishment of a primary role for CSP over conventional BVP in CRT candidates. This review provides a comprehensive literature revision of potential applications of CSP for CRT in diverse clinical scenarios, underlining the current controversies and prospects of this technique.