Assessment of Clinical Outcomes and Electrophysiological Parameters of Left Bundle Branch Area Pacing: A Single-center Prospective Study with 12-month Follow-up

Abstract

Background:

Left bundle branch pacing (LBBP) is developing as an effective technique for cardiac pacing, offering potential advantages over traditional right ventricular pacing methods. However, comprehensive assessment of LBBP outcomes across various indications and over extended follow-up periods is limited. This single-center prospective study aims to address this gap by evaluating the electrophysiological, echocardiographic, and clinical outcomes of LBBP over a 12-month follow-up period.

Methods:

This was a single-center prospective cohort study with repeated follow-up assessments performed at 3, 6, and 12 months following left bundle branch area pacing (LBBAP) implantation. This study enrolled 63 patients aged 18–80 with symptomatic bradyarrhythmia and left ventricular dysfunction undergoing LBBAP using Select Secure pacing leads. Outcomes were compared pre- and post-implantation at 3-, 6-, and 12-month follow-up, assessing electrophysiological parameters, cardiac function, and adverse events.

Results:

In this study, successful implantation was achieved in all patients, with selective LBB capture demonstrated in 78.9%. Lead parameters such as capture threshold, paced QRS duration, pacing impedance, and R wave amplitude at 3, 6, and 12 months when compared with the baseline, remained stable with no significant changes over time. Individuals with lower baseline ejection fraction EF improved significantly from baseline between 3 and 6 months, 6 and 12 months, and 3 and 12 months, respectively. Procedural and late complications were minimal.

Conclusion:

With improvements observed in electrophysiological parameters, cardiac function, and minimal adverse events over a 12-month follow-up period, LBBP demonstrates both efficacy and safety in this patient population. These results advocate for further exploration and utilization of LBBP as a preferred pacing strategy in clinical practice.

Introduction

The modern pacemaker stands as a remarkable testament to technological advancement and our deepening understanding of cardiac electrophysiology (EP). From as early as 1958, when the first pacemaker was implanted, there has been progressive advancement.[1,2] Over the past 50 years, conventional right ventricular apical pacing (RVAP) has been a widely used technique in cardiac pacing.[3] Nevertheless, as with all methods, RVAP has certain disadvantages to its application despite its extensive use. One major concern is the occurrence of pacemaker-induced cardiomyopathy, a complication especially prevalent with long-term and high pacing burdens, with reported incidence rates ranging from 6% to 25%.[4] Despite the fact that RVAP is intended to increase the protection against pacemaker tachycardia and to provide better atrial sensing, its effectiveness in some conditions, such as first-degree atrioventricular (AV) block, is rather doubtful.[5] Furthermore, the impact of RVAP on ventricular synchrony and overall cardiac mechanics may be suboptimal for some patients, particularly those with certain comorbidities or underlying heart conditions.

As a result, left bundle branch area pacing (LBBAP), a promising new method of pacing, has received increasing attention recently.[6] This technique aims to provide more physiological pacing by targeting the left bundle branch or its vicinity. In particular, literature has documented that LBBAP results in enhancement of the cardiac mechanics and hemodynamic better compared to biventricular pacing (BiVP). Specifically, LBBAP has been found to restore mechanical homogeneity in left ventricular (LV) contraction, improve workload homogeneity, and enhance hemodynamic parameters like LV end-systolic volume, ejection fraction (EF), mean left atrial pressure, and maximum rate of LV pressure rise.[7] Based on these observations, LBBAP appears to be capable of overcoming some of the inherent limitations of RVAP to offer a viable solution for patients in need of permanent pacing.

This prospective study was undertaken to evaluate the electrophysiological, echocardiographic, and clinical results of LBBAP in various indications initially, before, and 12 months after the procedure. This study seeks to make an evaluation of how LBBAP has impacted cardiac function, rhythm control, and the patients, in a bid to bring out the understanding of the safety and efficacy of this approach. Furthermore, it examines whether LBBAP tends to impact quality of life and functional health status differently than conventional pacing interventions. These observations of the current study may yield a significant impact on the field of cardiac EP to embrace the use of LBBAP and may institute new directions in pacing therapy.

Study design

This was a single-center prospective cohort study with repeated follow-up assessments performed at 3, 6, and 12 months following LBBAP implantation. The study population consisted of 63 patients, aged 18–80 years, with symptomatic bradyarrhythmia, some with LV dysfunction enrolled at a single tertiary care center. This diverse cohort included both genders, enabling a comprehensive analysis of the intervention’s effects across various demographic groups. By accounting for gender and age diversity, the study aimed to ensure the generalizability of its findings to a broader patient population. Patients lost to follow-up or with incomplete follow-up data were excluded from time-point-specific analyses using a complete-case analysis approach. No imputation method was applied due to the modest sample size and observational nature of the study.

The intervention employed was LBBAP. This method utilized Select Secure pacing leads (model 3830, 69 cm, Medtronic Inc., Minneapolis, MN, USA), a fixed-curve sheath (C315HIS, Medtronic Inc.), and an EP recording system (St. Jude Medical/Abott). This carefully selected combination of tools and techniques was designed to optimize the precision and efficacy of the pacing procedure, ensuring accurate lead placement and effective pacing performance.

This study was designed as an exploratory feasibility study conducted over a predefined recruitment period. Formal a priori sample size calculation was not performed; however, the study aimed to evaluate procedural feasibility, pacing characteristics, and short-term clinical outcomes of LBBAP in a real-world cohort. Comparative analysis was conducted to evaluate outcomes before and after implantation, focusing on lead parameters and clinical outcomes at follow-up intervals of 3, 6, and 12 months. This comparison was crucial in determining the intervention’s impact over time and its potential long-term benefits for patients. The outcomes measured included changes in electrophysiological parameters, such as pacing thresholds and impedance, improvement in cardiac function, evidenced by metrics like EF and LV dimensions, and a reduction in adverse events, including lead dislodgment and device-related complications. The timeframe for follow-up assessments was set at 3, 6, and 12 months postimplantation, allowing for a thorough evaluation of the intervention’s short-term and mid-term effects. This comprehensive follow-up schedule ensured that any significant changes or trends in patient outcomes could be accurately captured and analyzed. Continuous variables were expressed as mean ± standard deviation. Normality of distribution was assessed using the Shapiro–Wilk test. Repeated measures comparisons were performed using paired t-tests/repeated measures ANOVA for normally distributed data. Nonparametric alternatives were considered when assumptions for parametric testing were not satisfied. P <0.05 was considered statistically significant.

Results

Patient demographics and comorbidities distribution

The demographic and clinical characteristic of the study population is summarized in Table 1. The mean age of the participants was 61.84 years, 73.0% of the study population was male, while 27.0% were female. Patients with normal LVEF were 52 (66.7%), and 11 (33.3%) had LV dysfunction. Regarding comorbidities, coronary artery disease was the most common, affecting 36.5% of the participants, followed by hypertension at 30.2%, diabetes mellitus at 25.4%, and dilated cardiomyopathy at 7.9%, and other miscellaneous group was 20.6%. In this dataset, New York Heart Association (NYHA) Class III is the most prevalent, comprising 38.4% of patients, indicating a significant proportion experiencing marked limitations in physical activity. NYHA Class I and Class II followed with 28.3% and 18.3%, respectively. NYHA Class IV comprised 15% of the patients.

Table 1.

Patient demographics and comorbidities distribution (n=63)

Category		Frequency (%)
Age (Mean)		61.84±9.722 years
Gender
Male		46 (73.0)
Female		17 (27.0)
Complaint
Presyncope		6 (9.5)
Syncope		48 (76.2)
Breathlessness		9 (14.3)
Comorbidities
CAD		23 (36.5)
Hypertension		19 (30.2)
DCMP		5 (7.9)
Diabetes mellitus		16 (25.4)
NYHA class
I		17 (28.3)
II		11 (18.3)
III		23 (38.4)
IV		9 (15)
Indications for pacing
Sick sinus syndrome		16 (26.6)
Complete heart block		36 (60)
Cardiac resynchronization therapy		8 (13.3)
LV functions
EF 50%–60%		46 (73)
EF 41%–49%		6 (10)
EF <41%		11 (17)

CAD: Coronary artery disease; DCMP: Dilated cardiomyopathy; NYHA: New York Heart Association; LV: Left ventricular; EF: Ejection fraction

Procedural characteristics

Successful implantation was achieved in all patients. The paced morphology showing right bundle branch block (RBBB) pattern (qR/Qr/rsR’ or rsr’) was the most common criteria met for LBBAP among our study population. Stimulation to LV activation time 71.8 ± 6.6 ms, which remained constant at high (10 V) and low outputs (≤2V). Selective LBB capture was demonstrated in 45 patients (78.9%). LBB potential was recorded in 9 patients (14%). At implantation, the mean pacing threshold was 0.9 ± 0.23 V/at 5 ms. Mean anodal ring capture thresholds were 1.4 ± 0.5 V. Mean sensed R-wave amplitude was 8.42 ± 8.3 mV. Mean paced QRS duration (QRSd) was 114.85 ± 11.3 ms as measured from the EP recording system [Figure 1].

Figure 1.

Electrical and pacing characteristics during left bundle branch area pacing. The figure summarizes key procedural and electrophysiological parameters, including left bundle branch potential duration, stimulus to left ventricular activation time, capture threshold, lead impedance, sensed R-wave amplitude, anodal capture threshold, paced QRS duration, and selective versus non-selective capture characteristics

Comparison of parameters at implantation and on follow-up

During the follow-up period, at 3 and 6 months, two patients passed away due to nonprocedural related diseases before reaching the 12-month mark, and 6 patients were lost to follow-up at either 3-, 6-, or 12-month time. Consequently, 55 patients completed the study at the 12-month follow-up.

Lead parameters

Figure 2 illustrates the variations in key lead parameters at different time points postimplantation. The capture threshold remains relatively stable over time, with a slight increase at 12 months, but this change is not statistically significant (P = 0.768). The paced QRSd showed minimal variation over the 12-month period (statistically nonsignificant) with no significant changes observed (P = 0.752). Pacing impedance showed a significant decrease from implantation to 3 months and continued to decrease by 6 months and 12 months (statistically). The change is statistically significant (P = 0.0005), but its significance is still unknown.

Figure 2.

Trends in electrophysiological lead parameters following left bundle branch area pacing implantation over 12 months. (a) Changes in paced QRS duration (ms) at implantation and during follow-up at 3, 6, and 12 months. (b) Changes in stimulus-to-left ventricular activation time measured at 5 V/0.4 ms during follow-up. (c) Changes in capture threshold (V at 0.5 ms) over the 12-month follow-up period. Values are presented as mean ± standard error. Statistical comparisons between time points are represented by corresponding P values. LBBAP: Left bundle branch area pacing; QRSd: QRS duration; Stim-LVAT: Stimulus-to-left ventricular activation time

Echocardiographic characteristics

The analysis of echocardiographic parameters postimplantation reveals significant changes in several key metrics over time, specifically at 3 months, 6 months, and 12 months, as depicted in Figure 3. Patients with Normal LV systolic function continued to have similar EF, and in patients with LV dysfunction, EF showed statistically improvement at baseline compared to 3, 6, and 12 months.

Figure 3.

Trends in ejection fraction (EF%) over time post LBAP in patients with left ventricular dysfunction. Temporal changes in left ventricular EF following implantation. Mean EF (%) values are presented at implantation, 3 months, 6 months, and 12 months of follow-up. Data are expressed as mean ± standard error of the mean. A progressive increase in EF was observed during follow-up, with pairwise comparisons between consecutive time points showing no statistically significant differences (P = 0.6489 for implantation vs. 3 months; P = 0.9041 for 3 vs. 6 months; P > 0.9999 for 6 vs. 12 months). LBAP: Left bundle branch area pacing

Clinical outcomes

Figure 4 details the distribution of patients across different functional classes post-implantation. Clinical improvement was seen in terms of symptom improvement, NYHA functional class, and quality of life among patients with baseline LV dysfunction and those candidates (11 patients) for cardiac resynchronization therapy (CRT). Over time, there is a noticeable improvement in the functional class of patients, with more patients moving into Class I and II and fewer remaining in Class III and IV. This suggests that the LBBAP implant has a positive effect on the patients’ heart function and quality of life, as indicated by the reduction in the severity of heart failure symptoms over the 12-month period.

Figure 4.

Distribution of New York Heart Association (NYHA) functional class over time following left bundle branch area pacing (LBBAP) implantation. Grouped bar chart demonstrating changes in NYHA functional class distribution at baseline and during follow-up at 6, 12, and 24 months. A progressive shift toward lower NYHA classes (Class I and II) is observed over time, indicating improvement in functional status and symptom burden following LBBAP

Analysis of procedural and late complications postimplantation

The procedural and late complications were low, the highest being 4.76% for micro lead dislodgment among procedural characteristics. These low rates indicate the effectiveness and safety of the implantation procedure. One patient had macro-lead dislodgment at 10 months postimplantation for which re-implantation was done using conventional RVAP. Three patients showed signs of micro-lead dislodgment at 6 months of follow-up with increased QRSd (>130 ms), and 1 patient had pocket site infection at 1 month of follow-up.

Specific study population characteristics

Patient population with left ventricular dysfunction

The dataset for 8 patients with LV dysfunction provides insights into various ECG and pacing parameters before pacing, at the time of implantation, and at subsequent follow-ups at 3 months, 6 months, and 12 months [Table 2]. The baseline QRSd ranged from 152 to 165 ms, requiring CRT, but LBBA pacing was done due to financial reasons. In these patients, Sti-LVAT was recorded, with values ranging from 68 to 95 ms. This metric is crucial for assessing the efficacy of the pacing in efficiently activating the left ventricle. Capture thresholds at implantation were low, ranging from 0.6 V to 1 V, indicating efficient pacing capture with minimal energy. Paced QRSds ranged from 110 ms to 128 ms, showing a reduction from the pre-pacing QRSds, suggesting improved electrical synchrony. Impedance values varied from 740 Ω to 940 Ω, reflecting different lead-tissue interfaces among patients. R wave amplitudes at implantation were between 6 mV and 12 mV, indicating effective sensing of intrinsic cardiac activity. Anodal Capture Threshold and Transition Zone values were stable, indicating consistent lead performance and no significant changes in pacing zones.

Table 2.

Pacing parameters of patients with left ventricular dysfunction/Bundle branch block during follow-up (range)

Parameter		Range at implantation		Range at 3 months		Range at 6 months		Range at 12 months
Sti-LVAT at 5 V/0.4 ms		68–95		68–95		68–95		65–95
Capture threshold (V/0.5 ms)		0.6–1.0		0.6–1.0		0.6–1.0		0.6–1.0
Paced QRS duration (ms)		110–128		118–130		118–130		120–130
Pacing impedance (Ω)		740–940		720–900		720–850		680–850
R wave amplitude (mV)		6–12		5–12		6–12		7–12

Sti-LVAT: Stimulation to left ventricular activation time

Discussion

LBBAP facilitates direct activation of His-Purkinje system, which provides a more physiological and well-co-ordinated ventricular activation. This is particularly so in patients who suffer from bundle branch block or other forms of conduction alteration. A higher level of electrical synchronization as a result of CRT improves ventricular function and decreases pacing-induced cardiomyopathy.[8] In the present work, LBBAP implantation was successful in all patients, with selective LBB capture in 78.9%. These conclusions agree with those of other earlier works that provide data on the efficacy of the studied treatment, varying between 80% and 97%.[9,10,11,12] Studies have shown that maintaining a narrow QRS complex can lead to improved hemodynamic outcomes and reduce the risk of heart failure progression.[13,14]

Research by Zhang et al.[15] demonstrated that LBBAP shortened interventricular mechanical delay and improved synchronization imaging across 12 LV segments compared to intrinsic LBBB. Similarly, Ponnusamy et al.[16] reported a significant reduction in QRSd from 144.38 ± 34.6 ms at baseline to 110.8 ± 12.4 ms post-LBBAP (P < 0.0001) in 99 patients, with sustained improvements over a mean follow-up period of 4.8 months. In contrast, Vijayaraman et al.[10] studied 100 patients with various pacing indications, including AV block (54%), sinus node dysfunction (23%), AV node ablation (7%), CRT (11%), and his bundle pacing lead failure (7%). They observed a baseline QRSd of 133 ± 35 ms. Mafi-Rad et al.[17] looked at the short-term outcomes of left ventricular septal (LVS) pacing and the ability to comfortably place a transvenous electrode through the interventricular septum. The study demonstrated that LVS pacing resulted in a paced QRSd of 144 ± 20 ms, which was narrower than that observed with RVAP. In addition, LVS pacing preserved acute LV pump function, indicating its potential as a hemodynamically favorable alternative for patients requiring ventricular pacing. In another study, a substantial reduction in QRSd was observed in 61 cases of LBBAP during a 1-year follow-up period, as reported by Huang et al.[18] Their findings revealed an improvement in QRSd from 169 ± 16 ms at baseline to 118 ± 12 ms. Furthermore, Liu et al.[19] demonstrated a significant reduction in QRSd within the LBBAP group compared to baseline measurements (from 177.1 ± 16.7 to 113.0 ± 18.4 ms). This reaffirmed the ability of LBBAP to induce electrical synchrony. Gupta et al.[20] reported QRSd initially at 133.18 ms; however, over a span of 6 months, this duration showed a statistically significant increase to 146.03 ms. Das and team,[21] in a comparative analysis of 60 patients undergoing LBB area pacing, revealed that LBB area pacing resulted in narrower-paced QRS complexes (34.45 ± 8.07 ms), further highlighting its efficacy in achieving superior electrical synchronization compared to other pacing techniques. These findings suggest that while LBBAP is effective in achieving acute electrical synchrony, long-term QRS widening in some cases warrants further investigation to identify contributing factors and optimize pacing strategies.

A notable finding in this study was the significant reduction in pacing impedance, indicating improved lead-tissue interfaces over time. Previous literature by Vijayaraman et al.,[10] Li et al.,[11] Zhang et al.,[15] and Ravi et al.[12] similarly reported low thresholds, with an overall consensus on achievable thresholds ≤1 V. De Mattia et al.[22] have shown that baseline R-wave amplitudes ≤2.5 mV during follow-up may pose a risk of delayed detection of ventricular fibrillation.

In our study, the significant changes in LVDV and LVSV, along with improvements in EF%, are corroborated by numerous studies on CRT. Enhanced LVEF translates to more effective blood pumping by the heart, leading to better overall cardiovascular health.[14] For instance, research by Haydock and Cowburn[23] demonstrated similar enhancements in ventricular volumes and EF, indicating effective cardiac resynchronization and improved cardiac function. The lack of significant changes in stroke volume is an interesting finding. While some studies, such as those by Smarz et al.,[24] reported improvements in stroke volume post-CRT, others, like Östenson et al.,[25] noted stable stroke volume, suggesting variability in response among different patient populations.

The analysis of procedural and late complications showed low incidence rates, with the highest being 4.76% for micro lead dislodgment among procedural complications. This low complication rate indicates the safety and effectiveness of the implantation procedure, with no significant adverse events such as transient or permanent RBB injury, pneumothorax, or pericardial effusion. Whereas, in their study, Carrión-Camacho and team[26] have found pneumothorax, occurring in 3.87% of cases, and lead dislodgment, affecting 8.39% of patients. Uncomplicated hematomas were the most frequently encountered, found in 22.58% of patients.

The stable pacing parameters, narrower QRSd, and significant improvements in cardiac function position LBBAP BiVP, particularly when conventional BiVP is not feasible or effective. By providing superior outcomes in terms of electrical synchrony and ventricular function, LBBAP has the potential to redefine pacing strategies and enhance long-term patient care.[14,27]

Compared with conventional RVAP, LBBAP provides a more physiological pattern of ventricular activation through direct engagement of the His–Purkinje conduction system, thereby minimizing electrical dyssynchrony and reducing the risk of pacing-induced cardiomyopathy.[3,4,14] Previous studies evaluating RV pacing have demonstrated wider paced QRSd and adverse ventricular remodeling during long-term follow-up, whereas LBBAP has consistently shown preservation of ventricular synchrony with narrower paced QRS complexes.[14,15,18] Similarly, compared with conventional CRT, LBBAP has demonstrated favorable electrical and echocardiographic outcomes with lower and stable pacing thresholds and effective resynchronization.[18,19,27] In the present study, the observed stability of pacing parameters, improvement in EF among patients with LV dysfunction, and low complication rates are consistent with these earlier reports and further support the clinical feasibility and safety of LBBAP in routine practice. The prospective assessment with serial follow-up at 3, 6, and 12 months additionally provides real-world longitudinal data supporting the evolving role of LBBAP as a physiological pacing strategy.

Limitations of the study

The study sample does not comprise patients of all age brackets and genders and will therefore not allow generalization of the findings to diverse and more diverse populations. The relatively modest sample size may limit statistical power for detecting smaller clinical differences and restrict subgroup analyses. Although the study includes a 12-month follow-up, longer-term outcomes and potential late complications or failures are not assessed. An extended follow-up is necessary to determine the long-term efficacy and safety of LBBAP. The intervention study was done at a single center, and how center affects patients can always be an issue of center bias. Multicenter studies are essential to ensure that the results are consistent across different clinical settings and practices. The study lacks a control group, such as patients receiving traditional CRT or alternative pacing therapies, which makes it difficult to directly compare the efficacy and safety of LBBAP with other treatments. In addition, as this was an observational feasibility study, the findings should be interpreted cautiously. Loss to follow-up in a subset of patients may have introduced attrition bias and could influence the interpretation of long-term outcomes. Larger multicenter randomized studies with extended follow-up are required to further validate the long-term efficacy and safety of LBBAP.

Conclusion

The findings of this study on LBBAP implantation are largely consistent with existing literature, reinforcing the effectiveness and safety of this approach for cardiac resynchronization and pacing. With improvements in cardiac function, stability of lead parameters, and minimal adverse events over a 12-month follow-up, LBBAP should be the preferred approach. The stability of lead parameters and improvement of ECG characteristics, and clinical outcomes, combined with low complication rates, underscore the potential of LBBAP as a preferred method for managing patients with heart failure requiring CRT. This study contributes to the growing body of evidence supporting LBBAP, highlighting its advantages over traditional CRT techniques and paving the way for broader adoption in clinical practice.

Ethical statement

The study was approved by he Research and Ethics Committee of Dayanand Medical College and Hospital. Ref no. DMCH/4/82-2020(2026).

Conflicts of interest

There are no conflicts of interest.

Funding Statement

Nil.