Outcomes of Conduction System Pacing for Cardiac Resynchronization Therapy in Patients with Heart Failure: A Multicenter Experience

Abstract

Background:

Whether conduction system pacing (CSP) is an alternative option for cardiac resynchronization therapy (CRT) in patients with heart failure remains an area of active investigation.

Objective:

To assess the echocardiographic and clinical outcomes of CSP compared to biventricular pacing (BiVP).

Methods:

This multi-center retrospective study included patients who fulfilled CRT indications and received CSP. Patients with CSP were matched using propensity score matching and compared in a 1:1 ratio to patients who received BiVP. Echocardiographic and clinical outcomes were assessed. Response to CRT was defined as an absolute increase of ≥5% in left ventricular ejection fraction (LVEF) at 6 months post-CRT.

Results:

238 patients were included. The mean age was 69.8±12.5 years, and 66 (27.7%) were female. 69 (29%) patients had HBP, 50 (21%) patients had LBBAP, and 119 (50%) patients had BiVP. The mean follow-up duration in the CSP and BiVP groups was 269±202 days and 304±262 days, respectively (P=0.293). The proportion of CRT responders was greater in the CSP group as compared to the BiVP group (74% in the CSP group versus 60% in the BiVP group, P=0.042). On Kaplan Meier analysis, there was no statistically significant difference in the time to first heart failure hospitalization (log rank P=0.78) and overall survival (log rank P=0.68) between the CSP group and the BiVP group.

Conclusion:

In patients with HFrEF, CSP resulted in a greater improvement in LVEF compared to BiVP. Large-scale randomized trials are needed to validate these outcomes and further investigate the different options available for CSP.

Introduction

In patients with severely reduced left ventricular ejection fraction (LVEF) and left bundle branch block (LBBB), cardiac resynchronization therapy (CRT) is beneficial to improve cardiac function and relieve heart failure symptoms ^1–4. To date, biventricular pacing (BiVP) with right ventricular (RV) pacing most often delivered at the RV apex and left ventricular (LV) pacing epicardially through the coronary sinus, has been the standard therapeutic pacing modality for CRT ⁵. However, it is non-physiological in nature with the activation spreading between the RV endocardium and the LV epicardium. There remains up to one third of patients with HFrEF who do not derive benefits from conventional CRT via BiVP ^6–8.

Conduction system pacing (CSP), including His bundle pacing (HBP) and left bundle branch area pacing (LBBAP), provides more physiological ventricular activation by pacing within the conduction system to activate the left ventricle. With improvements in tools and techniques, CSP has emerged as a feasible pacing modality in patients requiring CRT to acheive synchronous ventricular activation ^9–14. Data from large randomized clinical trials and observational studies comparing the outcomes of CSP to BiVP in patients with HFrEF remain limited. The aim of this multicenter study is to assess the echocardiographic and clinical outcomes of CSP to achieve cardiac resynchronization in patients with HFrEF.

Methods

Study Design and Patient Selection

This multicenter retrospective cohort study included 119 patients with HFrEF who met the criteria for CRT and underwent HBP or LBBAP between 2017 and 2021 ¹⁵. This cohort was, in 1:1 ratio, compared to 119 patients who received BiVP for CRT between 2002 and 2017. Controls were chosen from the Mayo Clinic CRT database and were matched to the CSP group using propensity score matching. Matching criteria included sex, age at the time of CRT implantation, baseline LVEF, atrial fibrillation, ischemic cardiomyopathy, use of beta blocker, use of angiotensin converting enzyme (ACE) inhibitor/angiotensin receptor blocker (ARB), use of spironolactone, and baseline QRS duration. All demographic, procedural, electrocardiographic, echocardiographic, CRT device interrogation, and clinical data were manually collected from the electronic health records. The research reported in this paper adhered to the Helsinki Declaration guidelines.

Inclusion Criteria

Patients included in this study had (i) an LVEF ≤35% and a QRS complex ≥120 ms or (ii) an LVEF ≤50% and need for permanent ventricular pacing ¹⁶. Patients were on optimal medical therapy for at least 3 months before CRT implantation.

Exclusion Criteria

Patients aged 18 years and younger were excluded from the study.

Sites Included

This study included 8 sites: Mayo Clinic (Rochester, Minnesota (MN), United States of America (USA)), Hospital Clínic de Barcelona (Barcelona, Spain), Columbia University Irving Medical Center-New York Presbyterian (New York, New York, USA), University of Washington Medical Center (Seattle, Washington, USA), Houston Methodist Hospital (Houston, Texas, USA), Texas Cardiac Arrhythmia Institute (Dallas, Texas, USA), Case-Western Reserve University (Cleveland, Ohio, USA), and Dalhousie University (Halifax, Canada). The study was approved by the institutional board at each site. Only patients who had previously authorized consent to use their records for research purposes were included.

Implant Technique

CSP

CSP was performed using the SelectSecure pacing lead (model 3830 lead, Medtronic Inc., Minneapolis, MN, USA), which was delivered through either a fixed curve sheath (C315 His; Medtronic Inc., Minneapolis, MN, USA) or a deflectable sheath (C304 His, Medtronic Inc., Minneapolis, MN, USA). After obtaining venous access (cephalic, subclavian, or axillary), the delivery sheath was inserted into the RV over a guidewire. The pacing lead was then advanced through the delivery sheath. The His bundle was identified by mapping the membranous septum ¹⁷. LBBAP was achieved by advancing the sheath and placing the lead 1–2 cm distal to the His bundle while ensuring a septal position in the left anterior oblique view. The lead was then inserted and screwed into the interventricular muscular septum along the course of the left bundle ¹⁸.

BiVP

LV lead implantation was achieved by cannulating the coronary sinus and positioning the pacing lead, preferably in the lateral or posterolateral vein. The right atrial and RV leads were positioned in the right atrial appendage and RV septum or apex.

Follow-up and Definitions of Outcomes

Echocardiographic outcomes by clinical records included LVEF (Simpson method), LV linear dimensions (left ventricular end-systolic dimension (LVESD) and left ventricular end-diastolic dimension (LVEDD)), the severity of mitral regurgitation (MR), the severity of tricuspid regurgitation (TR), RV systolic dysfunction, and right ventricular systolic pressure (RVSP). A core laboratory was not used. Response to CRT was defined as an absolute increase of ≥5% in LVEF at 6 months post-CRT ^19–21. The severity of MR and TR was graded as absent (=0), mild (=1), mild-moderate (=2), moderate (=3), moderate-severe (=4), or severe (=5). RV systolic dysfunction was graded as absent (=0), mild (=1), moderate (=2), or severe (=3). RV systolic dysfunction was assessed using visual gradation in addition to at least one quantitative parameter ²². Quantitative parameters included tricuspid annular plane systolic excursion (TAPSE), tissue Doppler imaging of the basal free lateral wall of the RV (S′), and/or longitudinal strain of the free lateral wall of the right ventricle (RV-GLS) ²².

Patients were followed in the device clinic at 1–3 months and 1 year and by remote monitoring every 3 months. All capture thresholds were defined using a pulse width of 1 ms for HBP and 0.4 ms for LBBAP. Lead-related complications and lead revisions were captured. Time to first heart failure hospitalization (HFH) and overall survival were determined through review of the electronic health record. HFH was defined as an outpatient or emergency department visit or inpatient hospitalization in which the patient presented with signs and symptoms consistent with heart failure requiring intravenous diuretic therapy. The time of follow-up was estimated from the date of CRT implantation to the date of the last clinical encounter.

Statistical Analysis

The severity of MR, TR, and RV systolic dysfunction was evaluated as numeric variables. Those numeric variables were treated as continuous variables in the statistical analysis to facilitate clear and meaningful reporting and comparison between the different groups.

Continuous variables were expressed as mean ± SD if normally distributed or as the median and interquartile range (IQR) if not normally distributed. Continuous variables were compared between independent groups using the student’s t-test or the Mann-Whitney test. Comparisons of continuous variables before and after CRT implantation were performed using the paired t-test or the Wilcoxon signed-rank test as appropriate. Categorical variables were expressed as counts and percentages, and comparisons between groups were performed using the Chi-squared test or the Fisher exact test as appropriate. Multivariate logistic regression was used to create a model to compare the improvement in LVEF (an increase of ≥5%) between the CSP and control groups. Cox proportional-hazards model was used to study the association between time to first HFH and overall survival time and multiple predictor variables that are clinically or statistically relevant. All p-values were 2-sided with a level of significance <0.05. Freedom from HFH and overall survival outcomes were also compared using Kaplan-Meier analysis. A p-value <0.05 was considered statistically significant for the log-rank test. Statistical analysis was done using BlueSky Statistics software v7.4 (BlueSky Statistics LLC, Chicago, IL, USA).

Ethical Considerations

This study was approved by the Institutional Review Board at Mayo Clinic.

Results

Baseline Patient Characteristics

This study included 119 patients who underwent CSP for CRT, with a matched cohort (n=119) who underwent BiVP. In the CSP group, 69 (58%) patients had HBP, and 50 (42%) patients had LBBAP (Figure 1). 80 (67.2%) patients underwent de novo implantations and 35 (29.4%) patients underwent device upgrade. 1 (0.9%) patient had previously failed to respond to conventional BiVP and 3 (2.5%) patients had coronary sinus lead dislodgement. In the BiVP group, 78 (65.5%) patients underwent de novo implantations and 41 (34.5%) patients underwent device upgrade. The baseline characteristics of the overall study population are described in Table 1. The CSP group and the BiVP group characteristics were comparable at baseline except for use of nitrates, diuretics, and digoxin, which were more common in the BiVP group. The mean follow-up duration in the CSP and BiVP groups was 269±202 days and 304±262 days, respectively (P=0.293). The mean follow-up duration in the HBP and LBBAP groups was 298±238 and 232±137 days, respectively (P=0.104).

Figure 1: Flowchart of the patients included in the study.

Abbreviations: BiVP: biventricular pacing; CS: coronary sinus; CSP: conduction system pacing; CRT: cardiac resynchronization therapy; HBP: His bundle pacing; LBBAP: left bundle branch area pacing.

Table 1:

Baseline characteristics

	CSP (n=119)	BiVP (n=119)	P value
Age, mean (years)	69.1±13.1	70.6±11.9	0.362
Female sex (n, %)	34 (28.6%)	32 (26.9%)	0.772
Hypertension (n, %)	79 (66.4%)	89 (74.8%)	0.155
Diabetes mellitus (n, %)	40 (33.6%)	46 (38.7%)	0.418
Atrial fibrillation (n, %)	57 (47.9%)	58 (48.7%)	0.897
ICM (n, %)	27 (22.7%)	32 (26.9%)	0.453
CRT indication
LVEF≤35% + QRS≥120 ms (n, %)	62 (52.1%)	72 (60.5%)	0.191
LVEF≤50% + anticipated RV pacing≥40% (n, %)	57 (47.9%)	47 (39.5%)
QRS duration, mean (ms)	149.4±33.1	150.5±33.9	0.806
Type of conduction abnormality
LBBB (n, %)	44 (37%)	38 (31.9%)	0.413
Non-LBBB (n, %)	54 (45.4%)	49 (41.2%)	0.513
Paced (n, %)	21 (17.6%)	32 (26.9%)	0.087
LVEF, mean (%)	34.2±10.2	34.6±12.5	0.779
LVEDD, mean (mm)	56.6±8.8	58.2±8.8	0.164
LVESD, mean (mm)	46±10.5	47.7±10.7	0.302
Beta blocker (n, %)	84 (70.6%)	94 (79%)	0.135
ACE/ARB inhibitor (n, %)	73 (61.9%)	64 (53.8%)	0.238
Spironolactone (n, %)	37 (31.1%)	34 (28.6%)	0.671
Hydralazine (n, %)	6 (5%)	10 (8.4%)	0.300
Nitrate (n, %)	5 (4.2%)	21 (17.6%)	<0.001*
Diuretic (n, %)	75 (63%)	92 (77.3%)	0.016*
Digoxin (n, %)	8 (6.7%)	39 (32.8%)	<0.001*
Sacubitril-valsartan (n, %)	13 (10.9%)	12 (10.1%)	0.940

Abbreviations: ACE: angiotensin-converting enzyme; ARB: angiotensin receptor blocker; CAD: coronary artery disease; ICM: ischemic cardiomyopathy; LVEF: left ventricular ejection fraction; LVEDD: left ventricular end-diastolic diameter; LVESD: left ventricular end-systolic diameter.

Echocardiographic Outcomes

CSP versus BiVP

The QRS duration was narrowed from 150.6±32.9 ms to 128±26.5 ms (P <0.001) in the CSP group. In the BiVP group, there was no significant change in QRS duration (150.9±33.3 ms to 157.3±44 ms, P=0.152). The paced QRS duration was significantly narrower in the CSP group compared to the BiVP group (128±26.5 ms versus 157.3±44 ms, P<0.001). Figure 2 illustrates examples of electrocardiograms before and after CRT in patients with CSP and BiVP.

Figure 2: Examples of electrocardiograms before and after cardiac resynchronization therapy in patients with conduction system pacing and biventricular pacing.

LVEF improved from 33.2±9.5% to 43.6±11.5% (P<0.001) in the CSP group and from 35.3±12 to 42.7±12.8 (P<0.001) in the BiVP group (Figure 3). The mean change in LVEF after CRT was greater in the CSP group than in the BiVP group (10.4±10.9% versus 7.3±9.4%, P=0.037). The proportion of patients whose LVEF increased by ≥5% was greater in the CSP group as compared to the BiVP groups (73/99 (74%) in the CSP group versus 57/95 (60%) in the BiVP group, P=0.042). Among the CRT responders in the CSP group, 45 (62%) patients had CRT device implantation due to cardiomyopathy with a LVEF ≤35% and wide bundle branch block while 28 (38%) patients had CRT device implantation due to cardiomyopathy with a LVEF ≤50% and anticipated high RV pacing burden.

Figure 3: Echocardiographic outcomes before and after cardiac resynchronization therapy in patients with conduction system pacing and biventricular pacing.

Abbreviations: CRT: cardiac resynchronization therapy; LVEF: left ventricular ejection fraction; LVESD: left ventricular end-systolic dimension; MR: mitral regurgitation; RV: right ventricular.

LVESD decreased from 46.2±11 mm to 42.1±9.8 mm (P<0.001) in the CSP group and from 47.9±10.2 mm to 43.7±10.4 mm in the BiVP group (P<0.001) (Figure 3). The mean change in LVESD after CRT was similar between the CSP group and the BiVP group (−4.1±8.5 mm versus −4.2±7.0 mm, P=0.942). There was significant reduction in MR severity and improvement in RV function in the CSP group and the BiVP group (Figure 3).

Univariate analysis revealed that atrial fibrillation, presence of LBBB, LVEF at baseline, and pacing modality were associated with CRT response (Table 2). On multivariate analysis, only presence of LBBB and LVEF at baseline were significant predictors of CRT response. Presence of LBBB was associated with better CRT response (OR_adjusted 2.51 [1.03–6.30], P=0.013). Higher LVEF at baseline was associated with lower odds of CRT response (OR_adjusted 0.95 [0.92–0.99], P=0.044). There was no significant difference in CRT response between patients receiving CSP versus BiVP (OR_adjusted 2.05 [0.98–4.37], P=0.059) (Table 2).

Table 2.

Multivariate analysis to assess the predictors of CRT response in patients with conduction system pacing and biventricular pacing

Variable	Univariate Analysis			Multivariate Analysis
	OR	95% CI	P value	OR	95% CI	P value
Age	1.00	0.98–1.03	0.821	1.01	0.98–1.04	0.524
Female sex	1.59	0.80–3.29	0.193	2.18	0.89–5.79	0.100
AFib	0.51	0.28–0.92	0.027*	0.66	0.30–1.45	0.302
ICM	0.62	0.32–1.20	0.151	0.50	0.20–1.21	0.123
Diabetes mellitus	1.50	0.80–2.88	0.217	1.60	0.71–3.74	0.268
Baseline LVEF	0.95	0.92–0.98	<0.001*	0.95	0.92–0.99	0.044*
Baseline QRS duration	1.00	0.996–1.01	0.321	0.99	0.98–1.003	0.129
LBBB	3.00	1.50–6.22	0.002*	2.51	1.03–6.30	0.013*
Pacing modality CSP versus BiVP	1.85	1.02–3.40	0.045*	2.05	0.98–4.37	0.059

Abbreviations: AFib: atrial fibrillation; BiVP: biventricular pacing; CI: confidence interval; CRT: cardiac resynchronization therapy; CSP: conduction system pacing; ICM: ischemic cardiomyopathy; LBBB: left bundle branch block; LVEF: left ventricular ejection fraction; OR: odds ratio.

HBP versus LBBAP

The QRS duration was narrowed from 144.89±33.59 ms to 124.61±28.37 ms (P<0.001) in the HBP group and from 158.89±30.36 ms to 132.80±23.06 ms (P<0.001) in the LBBAP group. There was no significant difference in the paced QRS duration between HBP and LBBAP (124.61±28.37 ms versus 132.80±23.06 ms, P=0.108). The echocardiographic outcomes after CRT in patients with HBP and LBBAP are summarized in Table 3. LVEF improved from 34.6±9.9% to 45.4±10.9% (P<0.001) in the HBP group and from 31.4±8.9% to 41.4±12% (P<0.001) in the LBBAP group. The mean change in LVEF after CRT was similar in the HBP and LBBAP groups (10.8±9.5% versus 10±12.5%, P=0.731). The proportion of patients whose LVEF increased by ≥5% was similar in the HBP group and LBBAP group (41/55 (75%) versus 32/44 (73%), P=0.838).

Table 3.

Echocardiographic outcomes after cardiac resynchronization therapy in patients with His bundle pacing and left bundle branch area pacing

Variable	HBP (n=55)			LBBAP (n=44)
	Pre-CRT	Post-CRT	P value	Pre-CRT	Post-CRT	P value
LVEF, mean (%)	34.6±9.9	45.4±10.9	<0.001*	31.4±8.9	41.4±12	<0.001
LVEDD, mean (mm)	55.5±9.3	51.1±9.3	<0.001*	59.3±7.9	54.8±8.7	<0.001
LVESD, mean (mm)	43.4±11	40.8±9.3	0.055	50.7±9.5	44.1±10.5	0.003
MR severity	1.4±1.2	0.9±0.9	0.004*	1.5±1.1	1.2±1.1	0.042
TR severity	1.3±1.0	1.2±1.2	0.405	1.3±1.2	1.1±1.1	0.342
RV dysfunction	0.5±0.7	0.2±0.5	0.002*	0.6±0.8	0.5±0.8	0.128
RVSP, mean (mmHg)	39.5±12.1	37.0±11.9	0.128	40.7±15.3	39.3±14.6	0.578

Abbreviations: BiVP: biventricular pacing; CSP: conduction system pacing; CRT: cardiac resynchronization therapy; LVEF: left ventricular ejection fraction; LVEDD: left ventricular end-diastolic dysfunction; LVESD: left ventricular end-systolic dysfunction; RV: right ventricular; RVSP: right ventricular systolic pressure.

Heart Failure Hospitalizations

The overall unadjusted incidence rate of HFH was similar between the CSP group and the BiVP group at the end of follow-up (16/113 (14%) in the CSP group versus 10/109 (9%) in the BiVP group, P=0.248). On Kaplan Meier analysis, there was no statistically significant difference in the time to first HFH between the CSP group and the BiVP group (log rank P=0.78) (Figure 4). The multivariate Cox proportional hazards model analysis revealed that age at the time of CRT implantation (HR=1.04, [1.00 – 1.08], P=0.044), diabetes mellitus (HR=4.21, [1.67–10.58], P=0.002), and use of diuretics (HR=5.63, [1.44–22.06], P=0.013) were associated with a higher risk of HFH.

Figure 4: Kaplan-Meier curves demonstrating comparison of time to first heart failure hospitalization between patients with conduction system pacing and biventricular pacing.

Survival Outcomes

The overall unadjusted mortality rate was similar between the CSP group and the BiVP group at the end of follow-up (17/113 (15%) in the CSP group versus 22/109 (20%) in the BiVP group, P=0.314). On Kaplan Meier analysis, there was no statistically significant difference in the overall survival between the CSP group and the BiVP group (log rank P= 0.68) (Figure 5). The multivariate Cox proportional hazards model analysis revealed that age at the time of CRT implantation (HR=1.04, [1.02 – 1.07], P=0.003), and diabetes mellitus (HR=2.63, [1.41–4.92], P=0.002) were associated with an increased risk of mortality, while female sex (HR=0.24, [0.11–0.57], P=0.001) was associated with a decreased risk of mortality.

Figure 5: Kaplan-Meier curves demonstrating survival comparison between patients with conduction system pacing and biventricular pacing.

Pacing Thresholds and Lead Revision

In patients with HBP, the average capture threshold was 1.29±1.00 V at baseline and 1.46±1.14 V at follow-up (P=0.269). The incidence of His lead revision was 7/63 (11.1%). The His lead was abandoned in 4 patients (2 patients after lead revision and 2 patients without lead revision). Reasons for lead revision included lead dislodgement (5 patients) and high capture threshold (2 patients). None of the patients had atrial lead revision.

In patients with LBBAP, the average capture threshold was 0.92±0.54 V at baseline and 0.86±0.50 V at follow-up (P=0.326). The incidence of lead revision was 1/47 (2.1%) and was lower than the lead revision rate in patients with HBP (P=0.041) The reason for the lead revision was lead dislodgement.

In patients with BiVP, 11/119 (9.2%) patients had a lead revision. 7 patients needed lead revision due to lead malfunction (atrial lead in 2 patients, RV lead in 4 patients, and LV lead in 1 patient). 4 patients needed lead revision due to lead dislodgement (atrial lead in 2 patients, RV lead in 1 patient, and LV lead in 2 patients).

Center Differences in CSP Outcomes

Supplemental Table 1 summarizes the differences in CSP outcomes among the centers included in the study. The study group is heterogenous including patients from medical centers in the USA and Europe. Most patients included in the study were from Mayo Clinic (Rochester, Minnesota, USA) and Hospital Clinic de Barcelona (Barcelona, Spain).

Discussion

The main findings of this retrospective study can be summarized as follows:

1. CSP resulted in a greater rate of CRT response as compared to BiVP.

2. HBP and LBBAP resulted in similar rates of CRT response.

3. The incidence of HFH and overall survival were similar between the CSP and BiVP groups.

4. The incidence of lead revision was lower with LBBAP as compared to HBP.

CSP versus BiVP outcomes

BiVP has been the conventional pacing modality for CRT with more than 20 years of track record. However, the lack of CRT response in a third of patients receiving BiVP, in addition to anatomical limitations such as lack of suitable venous branches and unavoidable phrenic nerve stimulation, leave a subset of CRT candidates unserved by BiVP ^6–8. CSP has lately gained attention as a promising alternative option for CRT. Despite the growing excitement about CSP, data from randomized controlled trials comparing its outcomes to those of BiVP are still limited ^23,24. The mounting evidence supporting the benefits of CSP has been mainly derived from observational studies ^{9–14,25–37}.

In a meta-analysis conducted by Gui et al, 18 studies (1517 patients) comparing the outcomes of CSP to BiVP in patients with heart failure were included. Patients in the LBBAP subgroup demonstrated greater improvement in LVEF, LVEDD, and New York Heart Association functional class than patients with BiVP ³⁸. No significant difference in outcomes was noted between patients with HBP and BiVP ³⁸. Similar findings were shown in a meta-analysis conducted by Tan et al to compare the outcomes of LBBAP to BiVP ³⁹. Patients with LBBAP had a greater reduction in paced QRS, and a greater improvement in New York Heart Association Class and LVEF ³⁹. Recently, Vijayaraman et al. demonstrated better clinical outcomes with CSP compared to BiVP in a retrospective study comparing 258 patients with CSP and 219 patients with BiVP. CSP was associated with a lower risk of death or HFH compared to BiVP ⁴⁰. These favorable outcomes were mainly driven by a lower rate of HFHs ⁴⁰.

Similar to the study by Vijayaraman et al, the rate of CRT response was higher in the CSP group compared to the BiVP group in our study, but the clinical outcomes of HFH and all-cause mortality were comparable between the two groups. Paced QRS duration was significantly narrower in the CSP group as compared to the BiVP group which might translate into improved ventricular resynchronization and CRT response in the CSP group as compared to the BiVP group. Even though all-cause mortality rates were similar between the two groups, there may have been lack of power, and the follow-up duration may have been too short to detect a significant difference in the clinical outcomes between the two groups.

HBP versus LBBAP outcomes

When compared to HBP, LBBAP had a similar mean change in LVEF and rate of CRT response. Incidence of lead revision was lower in patients with LBBAP as compared to patients with HBP. These findings are in line with the findings of a recent meta-analysis by Zhuo et al comparing the pacing characteristics of HBP to those of LBBAP ⁴¹. In this metanalysis, which included seven studies (n=867), LBBAP had higher implant success rates, lower capture thresholds at implantation and follow-up, and similar LVEF improvement as compared to HBP ⁴¹. Our rate of lead revision with LBBAP was similar to the one reported by De Pooter et al ⁴². Reasons for the higher rate of lead revision with HBP included high capture thresholds, lead dislodgement, and concern for pacing failure ^43,44. LBBAP has the advantage of being easier to implant and is associated with stable and lower pacing threshold than HBP ^45–47, which mitigates the incidence of reoperation and provides a longer battery life.

Study Limitations

This is an observational, retrospective study, and the results should be interpreted with caution. The number of patients in the HBP and LBBAP groups is small limiting comparisons between the two groups. Additionally, follow-up was incomplete in some patients. The decision to pursue CSP versus BiVP and HBP versus LBBAP was operator dependent and may have introduced some bias, although this was accounted for by doing a multivariate logistic regression analysis. Programming was not standardized and left to the operator discretion. The degree of atrioventricular (AV) and ventriculo-ventricular (VV) optimization may have been variable among patients and may have affected the study results. Echocardiographic studies were not performed in a core laboratory. Despite these limitations, the findings of our study represent a multicenter experience with CSP and are crucial to advancing our knowledge about the outcomes of CSP.

Conclusion

In patients with HFrEF, CSP may result in better ventricular resynchronization as compared to BiVP. Incidence of heart failure hospitalizations and overall survival were similar between the two groups. Large-scale randomized trials are needed to validate these outcomes and further investigate the different options available for CSP.

Abbreviations:

BiVP

biventricular pacing

CRT

cardiac resynchronization therapy

CSP

conduction system pacing

HBP

His bundle pacing

HFH

heart failure hospitalization

HFrEF

heart failure with a reduced ejection fraction

LBBB

left bundle branch block

LBBAP

left bundle branch area pacing

LV

left ventricle

LVEF

left ventricular ejection fraction

RV

right ventricle