Left bundle branch pacing compared to left ventricular septal myocardial pacing increases interventricular dyssynchrony but accelerates left ventricular lateral wall depolarization

Ventricular activation pattern of left ventricular septal pacing in a canine model

BACKGROUND

Left bundle branch pacing (LBBP) is a feasible and effective physiological pacing technique. The QRS morphology of left ventricular septal pacing (LVSP) is similar to that of LBBP. The ventricular activation pattern of LBBP is well-known, whereas the pattern of LVSP still needs further investigation. The present study aimed to determine ventricular activation pattern difference between LVSP and LBBP in a canine model.

METHOD

All six canines underwent successful LBBP and LVSP through trans-ventricular septum using intracardiac echocardiography and intracardiac electrogram. Their hearts were isolated and stained with Lugol's iodine to determine the position of the pacing lead. The activation sequences of the left ventricular myocardium and His-Purkinje system were recorded by placing multiple electrode catheters.

RESULTS

First, the left His-Purkinje system in LVSP was activated simultaneously from apical and basal regions to the left ventricular middle septal region, whereas the left ventricular septal myocardium was activated from the apical to basal region. The left His-Purkinje system activation in LBBP occurred in the direction of the apex from the pacing lead, but the left ventricular septal myocardium was activated in the apical to basal direction. Furthermore, the left intraventricular electrical synchrony was similar between LVSP and LBBP as determined by mapping the left ventricular septal to free wall activation time (46.7 ± 1.8 ms vs. 45.0 ± 1.4 ms, p = 0.11).

CONCLUSION

The ventricular activation sequence of LVSP was similar to LBBP. LVSP can capture LBB due to the wide distribution of LBB. These findings suggest a rationale for clinical application of LVSP.

Comparisons of long-term clinical outcomes with left bundle branch pacing, left ventricular septal pacing, and biventricular pacing for cardiac resynchronization therapy

BACKGROUND

Left bundle branch pacing (LBBP) and left ventricular septal pacing (LVSP) are referred to as left bundle branch area pacing.

OBJECTIVE

This study investigated whether long-term clinical outcomes differ in patients undergoing LBBP, LVSP, and biventricular pacing (BiVP) for cardiac resynchronization therapy (CRT).

METHODS

Consecutive patients with reduced left ventricular ejection fraction (LVEF <50%) undergoing CRT were prospectively enrolled if they underwent successful LBBP, LVSP, or BiVP. The primary composite end point was all-cause mortality or heart failure hospitalization. Secondary end points included all-cause mortality, heart failure hospitalization, and echocardiographic measures of reverse remodeling.

RESULTS

A total of 259 patients (68 LBBP, 38 LVSP, and 153 BiVP) were observed for a mean duration of 28.8 ± 15.8 months. LBBP was associated with a significantly reduced risk of the primary end point by 78% compared with both BiVP (7.4% vs 41.2%; adjusted hazard ratio [aHR], 0.22 [0.08-0.57]; P = .002) and LVSP (7.4% vs 47.4%; aHR, 0.22 [0.08-0.63]; P = .004]. The adjusted risk of all-cause mortality was significantly higher in LVSP than in BiVP (31.6% vs 7.2%; aHR, 3.19 [1.38-7.39]; P = .007) but comparable between LBBP and BiVP (2.9% vs 7.2%; aHR, 0.33 [0.07-1.52], P = .155). Propensity score adjustment also obtained similar results. LBBP showed a higher rate of echocardiographic response (ΔLVEF ≥10%: 60.0% vs 36.2% vs 16.1%; P < .001) than BiVP or LVSP.

CONCLUSION

LBBP yielded long-term clinical outcomes superior to those of BiVP and LVSP. The role of LVSP for CRT needs to be reevaluated because of its high mortality risk.

LVSP and LBBP Result in Similar or Improved LV Synchrony and Hemodynamics Compared to BVP

BACKGROUND

The effect of left ventricular septal myocardial pacing (LVSP) and left bundle branch pacing (LBBP) on ventricular synchrony and left ventricular (LV) hemodynamic status is poorly understood.

OBJECTIVES

The aim of this study was to investigate the impact of LVSP and LBBP vs biventricular pacing (BVP) on ventricular electrical synchrony and hemodynamic status in cardiac resynchronization therapy patients.

METHODS

In cardiac resynchronization therapy candidates with LV conduction disease, ventricular synchrony was assessed by measuring QRS duration (QRSd) and using ultra-high-frequency electrocardiography. LV electrical dyssynchrony was assessed as the difference between the first activation in leads V1 to V8 to the last from leads V4 to V8. LV hemodynamic status was estimated using invasive systolic blood pressure measurement during multiple transitions between LBBP, LVSP, and BVP.

RESULTS

A total of 35 patients with a mean LV ejection fraction of 29% and a mean QRSd of 168 ± 24 ms were included. Thirteen had ischemic cardiomyopathy. QRSd during BVP, LVSP, and LBBP was the same, but LBBP provided shorter LV electrical dyssynchrony than BVP (-10 ms; 95% CI: -16 to -4 ms; P = 0.001); the difference between LVSP and BVP was not significant (-5 ms; 95% CI: -12 to 1 ms; P = 0.10). LBBP was associated with higher systolic blood pressure than BVP (4%; 95% CI: 2%-5%; P < 0.001), whereas LVSP was not (1%; 95% CI: 0%-2%; P = 0.10). Hemodynamic differences during LBBP and LVSP vs BVP were more pronounced in nonischemic than ischemic patients.

CONCLUSIONS

Ultra-high-frequency electrocardiography allowed the documentation of differences in LV synchrony between LBBP, LVSP, and BVP, which were not observed by measuring QRSd. LVSP provided the same LV synchrony and hemodynamic status as BVP, while LBBP was better than BVP in both.

Left Bundle Branch Area Pacing With or Without Conduction System Capture in Heart Failure Models

BACKGROUND

Left bundle branch area pacing includes left bundle branch pacing (LBBP) and left ventricular septal pacing (LVSP), which is effective in patients with dyssynchronous heart failure (DHF). However, the basic mechanisms are unknown.

OBJECTIVES

This study aimed to compare LBBP with LVSP and explore potential mechanisms underlying the better clinical outcomes of LBBP.

METHODS

A total of 24 beagles were assigned to the following groups: 1) control group; 2) DHF group, left bundle branch ablation followed by 6 weeks of AOO pacing at 200 ppm; 3) LBBP group, DHF for 3 weeks followed by 3 weeks of DOO pacing at 200 ppm; and 4) LVSP with the same interventions in the LBBP group. Metrics of electrocardiogram, echocardiography, hemodynamics, and expression of left ventricular proteins were evaluated.

RESULTS

Compared with LVSP, LBBP had better peak strain dispersion (44.67 ± 1.75 ms vs 55.50 ± 4.85 ms; P < 0.001) and hemodynamic effect (dP/dtmax improvement: 27.16% ± 7.79% vs 11.37% ± 4.73%; P < 0.001), whereas no significant differences in cardiac function were shown. The altered expressions of proteins in the lateral wall vs septum in the DHF group were partially reversed by LBBP and LVSP, which was associated with the contraction and adhesion process, separately.

CONCLUSIONS

The animal study demonstrated that LBBP offered better mechanical synchrony and improved hemodynamics than LVSP, which might be explained by the reversed expression of contraction proteins. These results supported the potential superiority of left bundle branch area pacing with the capture of the conduction system in DHF model.

Success and complication rates of conduction system pacing: a meta-analytical observational comparison of left bundle branch area pacing and His bundle pacing

BACKGROUND

Left bundle branch area pacing (LBBAP) and His bundle pacing (HBP) are the main strategies to achieve conduction system pacing (CSP), but only observational studies with few patients have compared the two pacing strategies, sometimes with unclear results given the different definitions of the feasibility and safety outcomes. Therefore, we conducted a meta-analysis aiming to compare the success and complications of LBBAP versus HBP.

METHODS

We systematically searched the electronic databases for studies published from inception to March 22, 2023, and focusing on LBBAP versus HBP. The study endpoints were CSP success rate, device-related complications, CSP lead-related complications and non-CSP lead-related complications.

RESULTS

Fifteen observational studies enrolling 2491 patients met the inclusion criteria. LBBAP led to a significant increase in procedural success [91.1% vs 80.9%; RR: 1.15 (95% CI: 1.08-1.22); p < 0.00001] with a significantly lower complication rate [1.8% vs 5.2%; RR: 0.48 (95% CI: 0.29-0.78); p = 0.003], lead-related complications [1.1% vs 4.3%; RR: 0.38 (95% CI: 0.21-0.72); p = 0.003] and lead failure/deactivation [0.2% vs 3.9%; RR: 0.16 (95% CI: 0.07-0.35); p < 0.00001] than HBP. No significant differences were found between CSP lead dislodgement and non-CSP lead-related complications.

CONCLUSION

This meta-analysis of observational studies showed a higher success rate of LBBAP compared to HBP with a lower incidence of complications.

Strength-duration curves for left bundle branch area pacing

BACKGROUND

Despite growing clinical use of left bundle branch pacing (LBBP), data regarding the fundamentals of this pacing modality, including chronaxie and rheobase, are scarce.

OBJECTIVE

The purpose of this study was to calculate strength-duration curves with chronaxie and rheobase values for LBBP and left ventricular septal pacing (LVSP), and to analyze battery current drain and presence of selective LBBP at very short pulse duration (PD).

METHODS

A group of 141 patients with permanent LBBP were studied. LBBP and LVSP capture thresholds were assessed at 6 different PDs to calculate the strength-duration curves. Battery current drain at these PDs and presence of selective LBBP were determined. For comparison of strength-duration curves between His-bundle pacing (HBP) and LBBP, source data from our previous work based on 127 patients with HBP were obtained.

RESULTS

The chronaxies for LBBP and LVSP were very similar (0.38 vs 0.39 ms), and the rheobases were identical (0.27 V). The chronaxie for LBBP was lower than for HBP (0.38 vs 0.53 ms; P <.001), whereas rheobases were similar (0.27 vs 0.26 V). A narrow zone of selective capture was present in 19% and 41% of patients at PD of 0.06 and 0.03 ms, respectively. When pacing with the safety margin of +1 V, the lowest battery current drain was achieved with PD of 0.2 ms.

CONCLUSION

The obtained strength-duration curves for LBBP and LVSP provide insights to optimal programming of left bundle branch area pacing devices with regard to PD, voltage amplitude, battery longevity, and selective capture.

Prognostic benefits of His-Purkinje capture in physiological pacemakers for bradycardia

INTRODUCTION

Clinical outcomes of long-term ventricular septal pacing (VSP) without His-Purkinje capture remain unknown. This study evaluated the differences in clinical outcomes between conduction system pacing (CSP), VSP, and right ventricular pacing (RVP).

METHODS

Consecutive patients with bradycardia indicated for pacing from 2016 to 2022 were prospectively followed for the clinical endpoints of heart failure (HF)-hospitalizations and all-cause mortality at 2 years. VSP was defined as septal pacing due to unsuccessful CSP implant or successful CSP followed by loss of His-Purkinje capture within 90 days.

RESULTS

Among 1016 patients (age 73.9 ± 11.2 years, 47% female, 48% atrioventricular block), 612 received RVP, 335 received CSP and 69 received VSP. Paced QRS duration was similar between VSP and RVP, but both significantly longer than CSP (p < .05). HF-hospitalizations occurred in 130 (13%) patients (CSP 7% vs. RVP 16% vs. VSP 13%, p = .001), and all-cause mortality in 143 (14%) patients (CSP 7% vs. RVP 19% vs. VSP 9%, p < .001). The association of pacing modality with clinical events was limited to those with ventricular pacing (Vp) > 20% (pinteraction < .05). Adjusting for clinical risk factors among patients with Vp > 20%, VSP (adjusted hazard ratio [AHR]: 4.74, 95% confidence interval [CI]: 1.57-14.36) and RVP (AHR: 3.08, 95% CI: 1.44-6.60) were associated with increased hazard of HF-hospitalizations, and RVP (2.52, 95% CI: 1.19-5.35) with increased mortality, compared to CSP. Clinical endpoints did not differ between VSP and RVP with Vp > 20%, or amongst groups with Vp < 20%.

CONCLUSION

Conduction system capture is associated with improved clinical outcomes. CSP should be preferred over VSP or RVP during pacing for bradycardia.

Ultra-high-frequency ECG volumetric and negative derivative epicardial ventricular electrical activation pattern

From precordial ECG leads, the conventional determination of the negative derivative of the QRS complex (ND-ECG) assesses epicardial activation. Recently we showed that ultra-high-frequency electrocardiography (UHF-ECG) determines the activation of a larger volume of the ventricular wall. We aimed to combine these two methods to investigate the potential of volumetric and epicardial ventricular activation assessment and thereby determine the transmural activation sequence. We retrospectively analyzed 390 ECG records divided into three groups-healthy subjects with normal ECG, left bundle branch block (LBBB), and right bundle branch block (RBBB) patients. Then we created UHF-ECG and ND-ECG-derived depolarization maps and computed interventricular electrical dyssynchrony. Characteristic spatio-temporal differences were found between the volumetric UHF-ECG activation patterns and epicardial ND-ECG in the Normal, LBBB, and RBBB groups, despite the overall high correlations between both methods. Interventricular electrical dyssynchrony values assessed by the ND-ECG were consistently larger than values computed by the UHF-ECG method. Noninvasively obtained UHF-ECG and ND-ECG analyses describe different ventricular dyssynchrony and the general course of ventricular depolarization. Combining both methods based on standard 12-lead ECG electrode positions allows for a more detailed analysis of volumetric and epicardial ventricular electrical activation, including the assessment of the depolarization wave direction propagation in ventricles.

An individualized criterion for left bundle branch capture in patients with a narrow QRS complex

BACKGROUND

Left bundle branch (LBB) pacing (LBBP) is a physiological pacing; however, the accuracy of current electrocardiographic criteria for LBBP remains inadequate.

OBJECTIVE

The purpose of this study was to establish a novel individualized criterion to improve the accuracy of LBBP determination in patients with a narrow QRS complex.

METHODS

Patients in whom both LBBP and left ventricular septal pacing (LVSP) were acquired during operation were enrolled. LBB conduction time (LBBCT) was measured from LBB potential (LBBpo) to intrinsic QRS onset. LBBpo-V6RWPT, Native-V6RWPT, and Paced-V6RWPT were respectively measured from LBBpo, intrinsic QRS onset, and stimulus to R-wave peak in V6. ΔV6RWPT was the difference value between Paced-V6RWPT and Native-V6RWPT. The accuracy of ΔV6RWPT criterion for determining LBBP was evaluated.

RESULTS

In all 71 enrolled patients, ΔV6RWPT was <30 ms during LBBP (21.3 ± 4.6 ms; range 9.3-28.3 ms) but was >30 ms during LVSP (38.5 ± 4.6 ms; range 31.1-47.0 ms). The probability distribution of ΔV6RWPT was well separated between LBBP and LVSP. Sensitivity and specificity of the novel criterion of "ΔV6RWPT <30 ms" for determining LBBP both were 100%. However, the optimal cutoff value of Paced-V6RWPT for validation of LBBP was 64.2 ms, and sensitivity and specificity were 84.5% and 97.2%, respectively. Paced-V6RWPT during LBBP was equivalent to LBBpo-V6RWPT in all patients. There was a strong linear correlation between Native-V6RWPT and LBBpo-V6RWPT (r = 0.796; P <.001).

CONCLUSION

ΔV6RWPT could be an accurate individualized criterion for determining LBB capture with high sensitivity and specificity and was superior over the fixed Paced-V6RWPT criterion.

Left Bundle Branch Pacing vs Left Ventricular Septal Pacing vs Biventricular Pacing for Cardiac Resynchronization Therapy

BACKGROUND

Left bundle branch pacing (LBBP) and left ventricular septal pacing (LVSP) are considered to be acceptable as LBBAP strategies. Differences in clinical outcomes between LBBP and LVSP are yet to be determined.

OBJECTIVES

The purpose of this study was to compare the outcomes of LBBP vs LVSP vs BIVP for CRT.

METHODS

In this prospective multicenter observational study, LBBP was compared with LVSP and BIVP in patients undergoing CRT. The primary composite outcome was freedom from heart failure (HF)-related hospitalization and all-cause mortality. Secondary outcomes included individual components of the primary outcome, postprocedural NYHA functional class, and electrocardiographic and echocardiographic parameters.

RESULTS

A total of 415 patients were included (LBBP: n = 141; LVSP: n = 31; BIVP: n = 243), with a median follow-up of 399 days (Q1-Q3: 249.5-554.8 days). Freedom from the primary composite outcomes was 76.6% in the LBBP group and 48.4% in the LVSP group (HR: 1.37; 95% CI: 1.143-1.649; P = 0.001), driven by a 31.4% absolute increase in freedom from HF-related hospitalizations (83% vs 51.6%; HR: 3.55; 95% CI: 1.856-6.791; P < 0.001) without differences in all-cause mortality. LBBP was also associated with a higher freedom from the primary composite outcome compared with BIVP (HR: 1.43; 95% CI: 1.175-1.730; P < 0.001), with no difference between LVSP and BIVP.

CONCLUSIONS

In patients undergoing CRT, LBBP was associated with improved outcomes compared with LVSP and BIVP, while outcomes between BIVP and LVSP are similar.

Left bundle branch pacing versus left ventricular septal pacing as a primary procedural endpoint during left bundle branch area pacing: Evaluation of two different implant strategies

INTRODUCTION

Implant procedure features and clinical implications of left bundle branch pacing (LBBP) and left ventricular septal pacing (LVSP) have not been yet fully described. We sought to compare two different left bundle branch area pacing (LBBAP) implant strategies: the first one accepting LVSP as a procedural endpoint and the second one aiming at achieving LBBP in every patient in spite of evidence of previous LVSP criteria.

METHODS

LVSP was accepted as a procedural endpoint in 162 consecutive patients (LVSP strategy group). In a second phase, LBBP was attempted in every patient in spite of achieving previous LVSP criteria (n = 161, LBBP strategy group). Baseline patient characteristics, implant procedure, and follow-up data were compared.

RESULTS

The final capture pattern was LBBP in 71.4% and LVSP in 24.2% in the LBBP strategy group compared to 42.7% and 50%, respectively, in the LVSP strategy group. One hundred and eighty-four patients (57%) had proven LBB capture criteria with a significantly shorter paced QRS duration than the 120 patients (37%) with LVSP criteria (115 ± 9 vs. 121 ± 13 ms, p < .001). Implant parameters were comparable between the two strategies but the LBBP strategy resulted in a higher rate of acute septal perforation (11.8% vs. 4.9%, p = .026) without any clinical sequelae. Patients with CRT indications significantly improved left ventricular ejection fraction (LVEF) during follow-up irrespective of the capture pattern (from 35 ± 11% to 45 ± 14% in proven LBBP, p = .024; and from 39 ± 13% to 47 ± 12% for LVSP, p = .003). The presence of structural heart disease and baseline LBBB independently predicted unsuccessful LBB capture.

CONCLUSION

The LBBP strategy was associated with comparable implant parameters than the LVSP strategy but resulted in higher rates of septal perforation. Proven LBB capture and LVSP showed comparable effects on LVEF during follow-up.

Clinical outcomes of left bundle branch area pacing: Prognosis and specific applications

Cardiac pacing has become a widely accepted treatment strategy for bradyarrhythmia and heart failure. However, conventional right ventricular pacing (RVP) has been associated with electrical dyssynchrony, which may result in atrial fibrillation and heart failure. To achieve physiological pacing, Deshmukh et al. reported the first case of His bundle pacing (HBP) in 2000. This strategy was reported to have preserved ventricular synchronization by activating the conventional conduction system. Nonetheless, due to the anatomical location of the His bundle (HB), several issues such as high pacing thresholds, lead fixation, and early battery depletion may pose a challenge. Recently, left bundle branch area pacing (LBBAP) has emerged as a novel physiological pacing strategy to achieve conduction system pacing by capturing the left bundle branch through the deep septum. Additionally, several studies have investigated the clinical outcomes of LBBAP. In this paper, we describe the pacing parameters, QRS duration (QRSd), cardiac function, complications, and specific applications of LBBAP in recent years.

The Emerging Role of Left Bundle Branch Area Pacing for Cardiac Resynchronisation Therapy

Cardiac resynchronisation therapy (CRT) reduces the risk of heart failure-related hospitalisations and all-cause mortality, as well as improving quality of life and functional status in patients with persistent heart failure symptoms despite optimal medical treatment and left bundle branch block. CRT has traditionally been delivered by implanting a lead through the coronary sinus to capture the left ventricular epicardium; however, this approach is associated with significant drawbacks, including a high rate of procedural failure, phrenic nerve stimulation, high pacing thresholds and lead dislodgement. Moreover, a significant proportion of patients fail to derive any significant benefit. Left bundle branch area pacing (LBBAP) has recently emerged as a suitable alternative to traditional CRT. By stimulating the cardiac conduction system physiologically, LBBAP can result in a more homogeneous left ventricular contraction and relaxation, thus having the potential to improve outcomes compared with conventional CRT strategies. In this article, the evidence supporting the use of LBBAP in patients with heart failure is reviewed.

QRS axis and polarity in the inferior leads during left bundle branch pacing: Novel criteria in the search for better results

BACKGROUND

Left bundle branch pacing (LBBP) may be achieved in various anatomical sites within the interventricular septum (IVS), thus influencing paced QRS duration (QRSd).The purpose of this study was to determine whether paced QRS axis (QRSâ) and predominant polarity in inferior leads could be associated with a shorter paced QRSd.

METHODS

We analyzed paced QRSd, QRSâ, polarity in inferior leads, and IVS thickness in patients referred for LBBP. Three paced morphology patterns in the inferior leads were considered: All positive (P), all negative (N) and intermediate (combination of isoelectric, positive, and negative complexes, (I). Patients were divided into two groups according to a paced QRSd < 120 or ≥ 120 ms.

RESULTS

A total of 125 patients were included (age 76 ± 10 years, 46% female). Mean baseline QRSâ was 8 ± 37°. Paced QRSd was significantly shorter as compared to baseline (120 ± 10 vs. 127 ± 33 ms; p = .017) and significantly different according to paced QRS morphology pattern in the inferior leads (P 49%, 119 ± 9; N 30%, 126 ± 12; I 21%; 113 ± 10 ms; p < .001) or paced QRSâ (Normal 59%, 116 ± 1; Right 6%, 129 ± 1; Left 35%, 124 ± 11 ms; p < .001). On multivariate analysis, a QRSâ > -30°(OR 5.79 [2.40-13.93; 95% CI] p = .001), an Intermediate pattern in inferior leads (OR 3.00 [1.67-8.43; 95% CI] p = .037), and an IVS thickness ≤ 10 mm (OR 2.59 [1.10-6.10; 95% CI]; p = .029) were significantly associated with a paced QRSd < 120 ms.

CONCLUSIONS

During LBBP, a QRSâ > -30° and intermediate final polarity in inferior leads are associated with a shorter paced QRSd.

Implant, assessment, and management of conduction system pacing

His bundle pacing and left bundle branch pacing, together referred to as conduction system pacing, have (re)gained considerable interest over the past years as it has the potential to preserve and/or restore a more physiological ventricular activation when compared with right ventricular pacing and may serve as an alternative for cardiac resynchronization therapy. This review manuscript dives deeper into the implantation techniques and the relevant anatomy of the conduction system for both pacing strategies. Furthermore, the manuscript elaborates on better understanding of conduction system capture with its various capture patterns, its potential complications as well as appropriate follow-up care. Finally, the limitations and its impact on clinical care for both His bundle pacing and left bundle branch pacing are being discussed.

Cardiac Conduction System Pacing: A Comprehensive Update

The field of cardiac pacing has changed rapidly in the last several years. Since the initial description of His bundle pacing targeting the conduction system, recent advances in pacing the left bundle branch and its fascicles have evolved. The field and investigators' knowledge of conduction system pacing including relevant anatomy and physiology has advanced significantly. The aim of this review is to provide a comprehensive update on recent advances in conduction system pacing.

Electrical Synchrony Optimization for Left Bundle Branch Area Pacing in Patients With Bradycardia and Heart Failure

Left bundle branch area pacing (LBBAP) has emerged as a promising physiological pacing modality. This study was designed to investigate the acute impact of the atrioventricular delay (AVD) on cardiac electrical characteristics and identify an optimal range of AVDs for LBBAP to achieve electrical atrioventricular and interventricular synchrony. Patients indicated for ventricular or biventricular pacing were studied during routine follow-ups at least 3 months after LBBAP implantation. Patients were excluded if they had a complete AV block or persistent atrial fibrillation. AVD was programed from 40 to 240 ms or until intrinsic conduction occurred. Optimal AVD was determined by the electrocardiography criteria, including QRS duration, reduced R-wave in lead V1, reduced notching or slurring in lateral leads, and more desirable precordial QRS transition. A total of 38 patients (age 68.7 ± 10.3 years; 16 male (42%); 18 dual-chamber pacemakers and 20 cardiac resynchronization therapy devices; average follow-up period 15.1 ± 10.2 months) were included. The fusion of LBBAP and intrinsic right ventricular conduction occurred in 21 patients with corresponding optimal AVD determined. A great proportion (∼85%) of the optimal AVDs ranged from 50% to 80% of the observed atrium-to-left bundle branch-sensing (A-LBBS) intervals. The linear correlation between the optimal AVD and corresponding A-LBBS interval (optimal AVD = 0.84 × [A-LBSs interval] - 36 ms) produced R = 0.86 and p <0.0001. In conclusion, AVD selection during LBBAP greatly impacted the ventricular electrical characteristics and the optimal AVD was linearly correlated with the corresponding A-LBBS interval.

Left ventricular septal pacing - can we trust the ECG?

In contrast to left bundle branch pacing, the criteria for left ventricular septal pacing (LVSP) were never validated. LVSP is usually defined as deep septal deployment of the pacing lead with a pseudo-right bundle branch morphology in V1. The case report describes an implant procedure during which this definition of LVSP was fulfilled in four of five pacing locations within the septum, with the shallowest of them present in less than 50% of the septal thickness. The case highlights the need for a more precise definition of LVSP.

Comparison of novel ventricular pacing strategies using an electro-mechanical simulation platform

AIMS

Focus of pacemaker therapy is shifting from right ventricular (RV) apex pacing (RVAP) and biventricular pacing (BiVP) to conduction system pacing. Direct comparison between the different pacing modalities and their consequences to cardiac pump function is difficult, due to the practical implications and confounding variables. Computational modelling and simulation provide the opportunity to compare electrical, mechanical, and haemodynamic consequences in the same virtual heart.

METHODS AND RESULTS

Using the same single cardiac geometry, electrical activation maps following the different pacing strategies were calculated using an Eikonal model on a three-dimensional geometry, which were then used as input for a lumped mechanical and haemodynamic model (CircAdapt). We then compared simulated strain, regional myocardial work, and haemodynamic function for each pacing strategy. Selective His-bundle pacing (HBP) best replicated physiological electrical activation and led to the most homogeneous mechanical behaviour. Selective left bundle branch (LBB) pacing led to good left ventricular (LV) function but significantly increased RV load. RV activation times were reduced in non-selective LBB pacing (nsLBBP), reducing RV load but increasing heterogeneity in LV contraction. LV septal pacing led to a slower LV and more heterogeneous LV activation than nsLBBP, while RV activation was similar. BiVP led to a synchronous LV-RV, but resulted in a heterogeneous contraction. RVAP led to the slowest and most heterogeneous contraction. Haemodynamic differences were small compared to differences in local wall behaviour.

CONCLUSION

Using a computational modelling framework, we investigated the mechanical and haemodynamic outcome of the prevailing pacing strategies in hearts with normal electrical and mechanical function. For this class of patients, nsLBBP was the best compromise between LV and RV function if HBP is not possible.

Quantitative analysis reveals influencing factors to facilitate successful anodal-ring capture in left bundle branch pacing

AIMS

Left bundle branch pacing (LBBP) maintains left ventricular synchrony but induces right ventricular conduction delay (RVCD). Although anodal-ring capture (ARC) during bipolar LBBP improves RVCD, it is not achieved in all patients receiving LBBP. This study aimed to analyze the factors influencing ARC implementation.

METHODS AND RESULTS

Patients receiving LBBP with intraoperative ARC testing were enrolled. Electrocardiographic parameters were measured, including stimulus-to-QRS duration (stim-QRSd), stimulus-to-left/right ventricular activation time (stim-LVAT/RVAT), and V6-V1 interpeak interval. The distribution of lead-tip sites was described as the corrected longitudinal and lateral distance (longit-/lat-dist). Relative angles of the LBBP lead were measured. Echocardiography in short-axis view was used to measure the intraseptal lead length. Intergroup comparisons, correlation analysis, and stepwise logistic regression were performed. In total, 105 patients were included, among which 65 (62%) patients achieved ARC at a pacing output ≤ 5.0 V/0.5 ms (average 3.1 V/0.5 ms). Anodal-ring capture further shortened the stim-QRSd by 13.1 ± 7.5 ms. Better unipolar-ring (cathodal) threshold and R-wave sensing in LBBP-ARC group indicated the critical role of ring-septum contact in ARC. Longer corrected longit-dist and shorter corrected lat-dist of lead-tip sites were positively correlated with higher success likelihood of ARC, likely due to the greater relative angle in which the lead enters the septum and consequently the longer intraseptal lead length and better ring-septum contact.

CONCLUSION

This study elucidated the factors affecting the success likelihood of LBBP-ARC. These findings improve the understanding of LBBP-ARC, providing references for future research and clinical practice.

Left bundle branch area pacing results in more physiological ventricular activation than biventricular pacing in patients with left bundle branch block heart failure

Biventricular pacing (Biv) and left bundle branch area pacing (LBBAP) are methods of cardiac resynchronization therapy (CRT). Currently, little is known about how they differ in terms of ventricular activation. This study compared ventricular activation patterns in left bundle branch block (LBBB) heart failure patients using an ultra-high-frequency electrocardiography (UHF-ECG). This was a retrospective analysis including 80 CRT patients from two centres. UHF-ECG data were obtained during LBBB, LBBAP, and Biv. Left bundle branch area pacing patients were divided into non-selective left bundle branch pacing (NSLBBP) or left ventricular septal pacing (LVSP) and into groups with V6 R-wave peak times (V6RWPT) < 90 ms and ≥ 90 ms. Calculated parameters were: e-DYS (time difference between the first and last activation in V1-V8 leads) and Vdmean (average of V1-V8 local depolarization durations). In LBBB patients (n = 80) indicated for CRT, spontaneous rhythms were compared with Biv (39) and LBBAP rhythms (64). Although both Biv and LBBAP significantly reduced QRS duration (QRSd) compared with LBBB (from 172 to 148 and 152 ms, respectively, both P < 0.001), the difference between them was not significant (P = 0.2). Left bundle branch area pacing led to shorter e-DYS (24 ms) than Biv (33 ms; P = 0.008) and shorter Vdmean (53 vs. 59 ms; P = 0.003). No differences in QRSd, e-DYS, or Vdmean were found between NSLBBP, LVSP, and LBBAP with paced V6RWPTs < 90 and ≥ 90 ms. Both Biv CRT and LBBAP significantly reduce ventricular dyssynchrony in CRT patients with LBBB. Left bundle branch area pacing is associated with more physiological ventricular activation.

The role of conduction system pacing in patients with atrial fibrillation

Conduction system pacing (CSP) has emerged as a promising novel delivery method for Cardiac Resynchronisation Therapy (CRT), providing an alternative to conventional biventricular epicardial (BiV) pacing in indicated patients. Despite increasing popularity and widespread uptake, CSP has rarely been specifically examined in patients with atrial fibrillation (AF), a cohort which forms a significant proportion of the heart failure (HF) population. In this review, we first examine the mechanistic evidence for the importance of sinus rhythm (SR) in CSP by allowing adjustment of atrioventricular delays (AVD) to achieve the optimal electrical response, and thus, whether the efficacy of CSP may be significantly attenuated compared to conventional BiV pacing in the presence of AF. We next evaluate the largest clinical body of evidence in this field, related to patients receiving CSP following atrioventricular nodal ablation (AVNA) for AF. Finally, we discuss how future research may be designed to address the vital question of how effective CSP in AF patients is, and the potential hurdles we may face in delivering such studies.

Left bundle branch area pacing prevents pacing induced cardiomyopathy in long-term observation

BACKGROUND

Left bundle branch area pacing (LBBAP) is one of the methods to deliver conduction system pacing which potentially avoids the negative impact of conventional right ventricular pacing.

OBJECTIVE

To assess echocardiographic outcomes in a long-term observation in patients with LBBAP implemented for bradyarrhythmia indications.

METHODS AND RESULTS

A total of 151 patients with symptomatic bradycardia and LBBAP pacemaker implanted, were prospectively included in the study. Subjects with left bundle branch block and CRT indications (n = 29), ventricular pacing burden <40% (n = 11), and loss of LBBAP (n = 10) were excluded from further analysis. At baseline and the last follow-up visit, echocardiography with global longitudinal strain (GLS) assessment, 12-lead ECG, pacemaker interrogation, and blood level of NT-proBNP were performed. The median follow-up period was 23 months (15.5-28). None of the analyzed patients fulfilled the criteria for pacing induced cardiomyopathy (PICM). Improvement in left ventricular ejection fraction (LVEF) and GLS was observed in patients with LVEF <50% at baseline (n = 39): 41.4 ± 9.2% versus 45.6 ± 9.9%, and 12.9 ± 3.6% versus 15.5 ± 3.7%, respectively. In the subgroup with preserved EF (n = 62), LVEF and GLS remained stable at follow-up: 59.3 ± 5.5% versus 60 ± 5.5%, and 19 ± 3.9% versus 19.4 ± 3.8%, respectively.

CONCLUSION

LBBAP prevents PICM in patients with preserved LVEF and improves left ventricle function in subjects with depressed LVEF. LBBAP might be the preferred pacing modality for bradyarrhythmia indications.

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.

Initial experience with stylet-driven versus lumenless lead delivery systems for left bundle branch area pacing

INTRODUCTION

Left bundle branch area pacing (LBBP) has emerged as an alternative method for conduction system pacing. While initial experience with delivery systems for stylet-driven and lumenless lead implantation for LBBP has been described, data comparing outcomes of stylet-driven versus lumenless lead implantation for LBBP are limited. In this study, we compare success rates and outcomes of LBBP with stylet-driven versus lumenless lead delivery systems.

METHODS

Eighty-three consecutive patients (mean age 74.1 ± 11.2 years; 56 [68%] male) undergoing attempted LBBP at a single institution were identified. Cases were grouped by lead delivery systems used: stylet-driven (n = 53) or lumenless (n = 30). Baseline characteristics and procedural findings were recorded and compared between the cohorts. Intermediate term follow-up data on ventricular lead parameters were also compared.

RESULTS

Baseline characteristics were similar between groups. Successful LBBP was achieved in 77% of patients, with similar success rates between groups (76% in stylet-driven, 80% in lumenless, p = 0.79), and rates of adjudicated LBB capture and other paced QRS parameters were also similar. Compared with the lumenless group, the stylet-driven group had significantly shorter procedure times (90 ± 4 vs. 112 ± 31 min, p = 0.004) and fluoroscopy times (10 ± 5 vs. 15 ± 6 min, p = 0.003). Ventricular lead parameters at follow-up were similar, and rates of procedural complications and need for lead revision were low in both groups.

CONCLUSION

Delivery systems for stylet-driven and for lumenless leads for LBBP have comparable acute success rates. Long-term follow-up of lead performance following use of the various delivery systems is warranted.

A conversion CRT strategy combined with AVJA may be a perspective alternative for heart failure patients with persistent atrial fibrillation

Heart failure (HF) combined with persistent atrial fibrillation (AF) often coexist and may promote the pathological conditions of cardiac dysfunction, leading to poor prognosis. Cardiac resynchronization therapy (CRT) combined with atrioventricular junction ablation (AVJA) is a highly effective treatment for HF patients with underlying AF who either have failed or are not suitable for catheter ablation. The CRT-AVJA combination therapy can improve clinical outcomes in HF patients. Currently, clinical CRT methods are categorized into biventricular pacing (BVP) - based and conduction system pacing (CSP) - based methods. These procedures have inherent advantages and disadvantages, in addition to their considerable differences in clinical applications. This article aims to review the clinical progress of AVJA combined with different CRT strategies for treating HF patients with persistent AF and propose that conversion CRT strategy (BVP/CSP-CRT) combined with AVJA may be a perspective alternative. Meanwhile, we generalize that 7 categories of HF patients with persistent AF may need to consider the CRT-AVJA combination therapy.

Left bundle branch pacing on mechanical synchrony and myocardial work in bradycardia patients

Left bundle branch pacing (LBBP) has emerged as a novel physiological pacing method to produce narrower QRS duration, but whether it could restore mechanical synchrony and improve myocardial work still lacks sufficient evidence. Therefore, the goal of this study was to evaluate mechanical synchrony and myocardial work in LBBP. We collected 20 patients with LBBP due to symptomatic bradycardia and another 29 age-matched patients with right ventricular pacing (RVP). For LBBP patients, cardiac electro-mechanical synchrony and myocardial work were measured at baseline and 7 days after implantation and compared with the RVP patients. In the LBBP group, paced QRS duration and mechanical synchrony were not significantly different from baseline(all P > 0.05), but significantly smaller than that in the RVP group (all P<0.05). Meanwhile, global longitudinal strain (GLS) in LBBP was greater than that in the RVP group (17.7 ± 3.5% vs. 14.8 ± 3.1%, P < 0.05). Global myocardial work index and global constructive work were also better than that in the RVP group(all P<0.05). Global work efficiency was 91.9 ± 3.1%, which was greater when compared with RVP (P < 0.05). LBBP provides better cardiac electro-mechanical synchrony and more effective myocardial work than that in RVP, thus improving global heart function.

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.

Bipolar anodal septal pacing with direct LBB capture preserves physiological ventricular activation better than unipolar left bundle branch pacing

Background

Left bundle branch pacing (LBBP) produces delayed, unphysiological activation of the right ventricle. Using ultra-high-frequency electrocardiography (UHF-ECG), we explored how bipolar anodal septal pacing with direct LBB capture (aLBBP) affects the resultant ventricular depolarization pattern.

Methods

In patients with bradycardia, His bundle pacing (HBP), unipolar nonselective LBBP (nsLBBP), aLBBP, and right ventricular septal pacing (RVSP) were performed. Timing of local ventricular activation, in leads V1-V8, was displayed using UHF-ECG, and electrical dyssynchrony (e-DYS) was calculated as the difference between the first and last activation. Durations of local depolarizations were determined as the width of the UHF-QRS complex at 50% of its amplitude.

Results

aLBBP was feasible in 63 of 75 consecutive patients with successful nsLBBP. aLBBP significantly improved ventricular dyssynchrony (mean -9 ms; 95% CI (-12;-6) vs. -24 ms (-27;-21), ), p < 0.001) and shortened local depolarization durations in V1-V4 (mean differences -7 ms to -5 ms (-11;-1), p < 0.05) compared to nsLBBP. aLBBP resulted in e-DYS -9 ms (-12; -6) vs. e-DYS 10 ms (7;14), p < 0.001 during HBP. Local depolarization durations in V1-V2 during aLBBP were longer than HBP (differences 5-9 ms (1;14), p < 0.05, with local depolarization duration in V1 during aLBBP being the same as during RVSP (difference 2 ms (-2;6), p = 0.52).

Conclusion

Although aLBBP improved ventricular synchrony and depolarization duration of the septum and RV compared to unipolar nsLBBP, the resultant ventricular depolarization was still less physiological than during HBP.

A Continuous Pacing and Recording Technique for Differentiating Left Bundle Branch Pacing From Left Ventricular Septal Pacing: Electrophysiologic Evidence From an Intrapatient-Controlled Study

BACKGROUND

Left bundle branch pacing (LBBP) is a promising approach for achieving near-physiologic pacing. However, differentiating LBBP from left ventricular septal endocardial pacing (LVS(e)P) remains a challenge. This study aimed to establish a simple and effective method for differentiating LBBP from LVS(e)P and to evaluate their electrophysiologic characteristics.

METHODS

LBBP, using continuous uninterrupted pacing and real-time monitoring of electrocardiograms along with intracardiac electrograms, was performed in 97 consecutive patients. We evaluated the electrophysiologic characteristics observed during LBBP using 6 modalities: right ventricular septal pacing (RVSP), intraventricular septal pacing (IVSP 1 and 2), LVS(e)P, nonselective LBBP (NSLBBP), and selective LBBP (SLBBP).

RESULTS

Of the 97 patients, 87 (89.7%) met the criteria (abrupt change in paced QRS morphology with a transition from Qr to QR/qR in lead V1 and shortening of stimulus to V6 R-wave peak time [Stim-V6RWPT] of ≥ 10 ms with constant output while rather than after lead screwing) for nonselective left bundle branch (LBB) capture. Selective LBB capture was observed in 82 patients (84.5%). The Stim-V6RWPT of NSLBBP and SLBBP were significantly shorter than LVS(e)P (respectively, 67.1 ± 8.7 ms, 67.0 ± 9.3 ms, and 82.1 ± 10.9 ms). Stim-QRSend was the narrowest in IVSP2 (136.6 ± 15.2 ms) instead of NSLBBP (140.0 ± 17.1 ms).

CONCLUSIONS

The uninterrupted pacing technique for differentiating LBBP from LVS(e)P in the same group of patients is feasible. Electrophysiologic evidence from our intrapatient-controlled study shows that LBBP and LVS(e)P differ in ventricular electrical synchronization.

Recruitment of the cardiac conduction system for optimal resynchronization therapy in failing heart

Heart failure (HF) is a leading health burden around the world. Although pharmacological development has dramatically advanced medication therapy in the field, hemodynamic disorders or mechanical desynchrony deteriorated by intra or interventricular conduction abnormalities remains a critical target beyond the scope of pharmacotherapy. In the past 2 decades, nonpharmacologic treatment for heart failure, such as cardiac resynchronization therapy (CRT) via biventricular pacing (BVP), has been playing an important role in improving the prognosis of heart failure. However, the response rate of BVP-CRT is variable, leaving one-third of patients not benefiting from the therapy as expected. Considering the non-physiological activation pattern of BVP-CRT, more efforts have been made to optimize resynchronization. The most extensively investigated approach is by stimulating the native conduction system, e.g., His-Purkinje conduction system pacing (CSP), including His bundle pacing (HBP) and left bundle branch area pacing (LBBAP). These emerging CRT approaches provide an alternative to traditional BVP-CRT, with multiple proof-of-concept studies indicating the safety and efficacy of its utilization in dyssynchronous heart failure. In this review, we summarize the mechanisms of dyssynchronous HF mediated by conduction disturbance, the rationale and acute effect of CSP for CRT, the recent advancement in clinical research, and possible future directions of CSP.

Left bundle branch area pacing in patients with baseline narrow, left, or right bundle branch block QRS patterns: insights into electrocardiographic and echocardiographic features

AIMS

Left bundle branch area pacing (LBBAP) is a recent technique aiming at preservation of physiological ventricular electrical activation. Our goal was to assess mechanical synchrony parameters in relation to electrocardiographic features during LBBAP performed in routine practice.

METHODS AND RESULTS

From June 2020 to August 2021, all patients of our institution with permanent pacemaker implantation indication were eligible for LBBAP. A 'qR' pattern in V1 and a delay from pacing spike to the peak of the R-wave in V6 < 80 ms defined a successful LBBAP. Electrocardiogram and echocardiography were performed during spontaneous rhythm and LBBAP: left ventricular mechanical synchrony (LVMS) parameters using 2D Speckle tracking and interventricular mechanical delay (IVMD) were collected. LBBAP was attempted with success in 134/163 patients (82.2%). During LBBAP, the mean QRS width was 104 ± 12 ms. In patients with left bundle branch block (n = 47), LBBAP provided a significant decrease of QRS width from 139 ± 16 to 105 ± 12 ms (P < 0.001) with reduction of LVMS (53 ± 21 vs. 90 ± 46 ms, P = 0.009), and IVMD (14 ± 13 vs. 49 ± 18 ms, P < 0.001). In patients with right bundle branch block (n = 38), LBBAP led to a significant decrease of QRS width from 134 ± 14 to 106 ± 13 ms (P < 0.001) with no effect on LVMS and a reduction of IVMD (17 ± 14 vs. 50 ± 16 ms, P < 0.001).

CONCLUSION

LBBAP in routine practice preserved intra-ventricular mechanical synchrony in patients with narrow and RBBB QRS and improved asynchrony parameters in patients with LBBB.

New criterion to determine left bundle branch capture on the basis of individualized His bundle or right ventricular septal pacing

BACKGROUND

Left bundle branch pacing (LBBP) is an emerging physiological pacing modality. How to differentiate LBBP from left ventricular septal pacing (LVSP) remains challenging.

OBJECTIVE

We aimed to develop a new personalized intraoperative criterion to confirm left bundle branch (LBB) capture in patients with or without heart failure (HF).

METHODS

Patients were enrolled if 12-lead surface electrocardiograms of LBBP, LVSP, temporary His bundle pacing (HBP), and right ventricular septal pacing (RVSP) were recorded during the procedure, with the leads placed in the basal midseptal region. Left ventricular activation time (LVAT) was measured during different pacing modalities. ΔLVAT1 was defined as the difference in LVAT between HBP and LBBP/LVSP. ΔLVAT2 was estimated by the difference in LVAT between RVSP and LBBP/LVSP. ΔLVAT1% and ΔLVAT2% were calculated as the percent reduction of ΔLVAT1 and ΔLVAT2, respectively.

RESULTS

A total of 105 consecutive patients were included, of whom 80 (76.2%) had normal cardiac function (65 LBBP and 15 LVSP) and 25 had HF. Patients with LBBP showed significantly shorter LVAT than did those with LVSP. In patients with normal cardiac function, a cutoff value of ΔLVAT1 > 12.5 ms showed 73.9% sensitivity and 93.3% specificity to confirm LBB capture. In patients with HF, a cutoff value of ΔLVAT1% > 9.8% exhibited great accuracy for LBB capture (sensitivity 92.0%; specificity 92.3%). The optimal value of ΔLVAT2% for differentiating LBBP from LVSP was 21.2%.

CONCLUSION

Temporary HBP and RVSP can serve as references to confirm LBB capture in an individualized fashion in patients with or without HF.

Feasibility of leadless left ventricular septal pacing with the WiSE-CRT system to target the left bundle branch area: A porcine model and multicenter patient experience

BACKGROUND

The WiSE-CRT system delivers leadless endocardial left ventricular (LV) pacing to achieve cardiac resynchronization therapy. The electrode is conventionally placed on the lateral wall, but implanting on the LV septum may have advantages, including capture of the left bundle branch, and improved battery longevity owing to reduced distance from the transmitter.

OBJECTIVE

The purpose of this study was to assess the feasibility of leadless LV septal pacing via the WiSE-CRT system.

METHODS

Two pigs underwent electrode implantation on the LV septum with subsequent anatomical and histological examination. Eight patients underwent implantation of the WiSE-CRT system with deployment of the electrode on the LV septum via an interatrial transseptal approach.

RESULTS

Deployment of the electrode on the LV septum was successful in both animals. Histological examination demonstrated electrode tines in close proximity to Purkinje tissue. WiSE-CRT implantation with an LV septal electrode was successful in all patients. Biventricular capture was confirmed, with a significant reduction in QRS duration (187.1 ± 33.8 ms vs 149.5 ± 15.7 ms; P = .009). Temporary LV pacing achieved further QRS reduction (139.8 ± 12.4 ms), and in 4 patients the peak LV activation time in lead V5/V6 was <90 ms, suggesting left bundle branch capture. At early follow-up, the median LV pacing percentage was 98.5% and 5 patients (62.5%) improved symptomatically. The transmitter-to-electrode distance was lower than the distance to the lateral wall during acoustic window screening (8.8 ± 1.6 cm vs 11.9 ± 1.5 cm; P = .002).

CONCLUSION

Leadless LV septal pacing with the WiSE-CRT system to target the left bundle branch appears feasible. Further study is required to assess the efficacy and safety of this technique.

Left bundle branch area pacing: A promising modality for cardiac resynchronization therapy

Cardiac resynchronization therapy (CRT) is recognized as the first-line management for patients with heart failure (HF) and conduction disorders. As a conventional mode for delivering CRT, biventricular pacing (BVP) improves cardiac function and reduces HF hospitalizations and mortality, but there are still limitations given the high incidence of a lack of response rates. Alternative pacing methods are needed either for primary or rescue therapy. In recent years, conduction system pacing (CSP) has emerged as a more physiological pacing modality for simultaneous stimulation of the ventricles, including His bundle pacing (HBP) and left bundle branch pacing (LBBP). CSP activates the His-Purkinje system, allowing normal ventricular stimulation. However, HBP is technically challenging with a relatively low success rate, high pacing threshold, and failure to correct distal conduction abnormalities. Therefore, LBBP stands out as a novel ideal physiological pacing modality for CRT. Several non-randomized studies compared the feasibility and safety of LBBP with BVP and concluded that LBBP is superior to BVP for delivering CRT with a narrower QRS and greater improvements in left ventricular ejection fraction (LVEF) and New York Heart Association (NYHA) functional class. Concurrently, some studies showed lower and stable pacing thresholds and greater improvement of B-type natriuretic peptide (BNP) levels, as well as better mechanical synchronization and efficiency. LBBP ensures better ventricular electromechanical resynchronization than BVP. In this review, we discuss current knowledge of LBBP, compare LBBP with BVP, and explore the potential of LBBP to serve as an alternative primary therapy to realize cardiac resynchronization.

Left bundle branch area pacing in congenital heart disease

AIMS

Left bundle branch area pacing (LBBAP) has been shown to be effective and safe. Limited data are available on LBBAP in the congenital heart disease (CHD) population. This study aims to describe the feasibility and safety of LBBAP in CHD patients compared with non-CHD patients.

METHODS AND RESULTS

This is a single-centre, non-randomized observational study recruiting consecutive patients with bradycardia indication. Demographic data, ECGs, imaging, and procedural data including lead parameters were recorded. A total of 39 patients were included: CHD group (n = 13) and non-CHD group (n = 26). Congenital heart disease patients were younger (55 ± 14.5 years vs. 73.2 ± 13.1, P < 0.001). Acute success was achieved in all CHD patients and 96% (25/26) of non-CHD patients. No complications were encountered in either group. The procedural time for CHD patients was comparable (96.4 ± 54 vs. 82.1 ± 37.9 min, P = 0.356). Sheath reshaping was required in 7 of 13 CHD patients but only in 1 of 26 non-CHD patients, reflecting the complex and distorted anatomy of the patients in this group. Lead parameters were similar in both groups; R wave (11 ± 7 mV vs. 11.5 ± 7.5, P = 0.881) and pacing threshold (0.6 ± 0.3 V vs. 0.7 ± 0.3, P = 0.392). Baseline QRS duration was longer in the CHD group (150 ± 28.2 vs. 118.6 ± 26.6 ms, P = 0.002). Despite a numerically greater reduction in QRS and a similar left ventricular activation time (65.9 ± 6.2 vs. 67 ± 16.8 ms, P = 0.840), the QRS remained longer in the CHD group (135.5 ± 22.4 vs. 106.9 ± 24.7 ms, P = 0.005).

CONCLUSION

Left bundle branch area pacing is feasible and safe in CHD patients as compared to that in non-CHD patients. Procedural and fluoroscopy times did not differ between both groups. Lead parameters were satisfactory and stable over a short-term follow-up.

A systematic review and Bayesian network meta-analysis comparing left bundle branch pacing, his bundle branch pacing, and right ventricular pacing for atrioventricular block

Background

Although right ventricular pacing (RVP) is recommended by most of the guidelines for atrioventricular block, it can cause electrical and mechanical desynchrony, impair left ventricular function, and increase the risk of atrial fibrillation. Recently, the His-Purkinje system pacing, including His bundle pacing (HBP) and left bundle branch pacing (LBBP), has emerged as a physiological pacing modality. However, few studies have compared their efficacy and safety in atrioventricular block (AVB).

Methods and results

The PubMed, Web of Science, Cochrane Library, and ScienceDirect databases were searched for observational studies and randomized trials of patients with atrioventricular block requiring permanent pacing, from database inception until 10 January 2022. The primary outcomes were complications and heart failure hospitalization. The secondary outcomes included changes in left ventricular ejection fraction (LVEF) and left ventricular end-diastolic diameter (LVEDD), pacing parameters, procedure duration, and success rate. After extracting the data at baseline and the longest follow-up duration available, a pairwise meta-analysis and a Bayesian random-effects network meta-analysis were performed. Odds ratios (ORs) with 95% confidence intervals (CIs) or 95% credible intervals (CrIs) were calculated for dichotomous outcomes, whereas mean differences (MDs) with 95% CIs or 95% CrIs were calculated for continuous outcomes. Seven studies and 1,069 patients were included. Overall, 43.4% underwent LBBP, 33.5% HBP, and 23.1% RVP. Compared with RVP, LBBP and HBP were associated with a shorter paced QRS duration and a more preserved LVEF. HBP significantly increased the pacing threshold and reduced the R-wave amplitude. There was no difference in the risk of complications or the implant success rate. The pacing threshold remained stable during follow-up for the three pacing modalities. The pacing impedance was significantly reduced in HBP, while a numerical but non-significant pacing impedance decrease was observed in both LBBP and RVP. LBBP was associated with an increased R-wave amplitude during follow-up.

Conclusion

In this systematic review and network meta-analysis, HBP and LBBP were superior to RVP in paced QRS duration and preservation of LVEF for patients with atrioventricular block. LBBP was associated with a lower pacing threshold and a greater R-wave amplitude than HBP. However, the stability of the pacing output of LBBP may be a concern. Further investigation of the long-term efficacy in left ventricular function and the risk of heart failure hospitalization is needed.

Systematic review registration

[https://www.crd.york.ac.uk/prospero/display_record.php?RecordID=315046], identifier [CRD42022315046].

Criteria for differentiating left bundle branch pacing and left ventricular septal pacing: A systematic review

Background

As a novel physiological pacing technique, left bundle branch pacing (LBBP) can preserve the left ventricular (LV) electrical and mechanical synchronization by directly capturing left bundle branch (LBB). Approximately 60-90% of LBBP were confirmed to have captured LBB during implantation, implying that up to one-third of LBBP is actually left ventricular septal pacing (LVSP). LBB capture is critical for distinguishing LBBP from LVSP.

Methods and results

A total of 15 articles were included in the analysis by searching PubMed, EMBASE, Web of Science, and the Cochrane Library database till August 2022. Comparisons of paced QRS duration between LVSP and LBBP have not been uniformly concluded, but the stimulus artifact to LV activation time in lead V5 or V6 (Stim-LVAT) was shorter in LBBP than LVSP in all studies. Stim-LVAT was used to determine LBB capture with a sensitivity of 76-95.2% and specificity of 78.8-100%, which varied across patient populations.

Conclusion

The output-dependent QRS transition from non-selective LBBP to selective LBBP or LVSP is direct evidence of LBB capture. LBB potential combined with short Stim-LVAT can predict LBB capture better. Personalized criteria rather than a fixed value of Stim-LVAT are necessary to confirm LBB capture in different populations, especially in patients with LBB block or heart failure.

Ventricular Dyssynchrony and Pacing-induced Cardiomyopathy in Patients with Pacemakers, the Utility of Ultra-high-frequency ECG and Other Dyssynchrony Assessment Tools

The majority of patients tolerate right ventricular pacing well; however, some patients manifest signs of heart failure after pacemaker implantation and develop pacing-induced cardiomyopathy. This is a consequence of non-physiological ventricular activation bypassing the conduction system. Ventricular dyssynchrony was identified as one of the main factors responsible for pacing-induced cardiomyopathy development. Currently, methods that would allow rapid and reliable ventricular dyssynchrony assessment, ideally during the implant procedure, are lacking. Paced QRS duration is an imperfect marker of dyssynchrony, and methods based on body surface mapping, electrocardiographic imaging or echocardiography are laborious and time-consuming, and can be difficult to use during the implantation procedure. However, the ventricular activation sequence can be readily displayed from the chest leads using an ultra-high-frequency ECG. It can be performed during the implantation procedure to visualise ventricular depolarisation and resultant ventricular dyssynchrony during pacing. This information can assist the electrophysiologist in selecting a pacing location that avoids dyssynchronous ventricular activation.

An Electrocardiographic Characterization of Left Bundle Branch Area Pacing-Induced Right Ventricular Activation Delay: A Comparison With Native Right Bundle Branch Block

Background

Left bundle branch area pacing (LBBAP) induces delayed RV activation and is thought to be harmless, since the electrocardiographic signature is reminiscent to native RBBB. However, to what extent the delayed RV activation during LBBAP truly resembles that of native RBBB remains unexplored.

Methods

This study included patients with incomplete RBBB (iRBBB), complete RBBB (cRBBB) and patients who underwent LBBAP. Global and right ventricular activation times were estimated by QRS duration and R wave peak time in lead V1 (V1RWPT) respectively. Delayed RV activation was further characterized by duration, amplitude and area of the terminal R wave in V1.

Results

In patients with LBBAP (n = 86), QRS duration [120 ms (116, 132)] was longer compared to iRBBB patients (n = 422): 104 ms (98, 110), p < 0.001, but shorter compared to cRBBB (n = 223): 138 ms (130, 152), p < 0.001. V1RWPT during LBBAP [84 ms (72, 92)] was longer compared to iRBBB [74 ms (68, 80), p < 0.001], but shorter than cRBBB [96 ms (86, 108), p < 0.001]. LBBAP resulted in V1 R' durations [42 ms (28, 55)] comparable to iRBBB [42 ms (35, 49), p = 0.49] but shorter than in cRBBB [81 ms (68, 91), p < 0.001]. During LBBAP, the amplitude and area of the V1 R' wave were more comparable with iRBBB than cRBBB. V1RWPT during LBBAP was determined by baseline conduction disease, but not by LBBAP capture type.

Conclusion

LBBAP-induced delayed RV activation electrocardiographically most closely mirrors the delayed RV activation as seen with incomplete rather than complete RBBB.

Physiology of Left Ventricular Septal Pacing and Left Bundle Branch Pacing

Following the recognition of the adverse effects of right ventricular pacing, alternative permanent pacing strategies aiming to maintain a synchronous ventricular contraction have been sought. The quest for the optimal pacing site has recently led to several promising and rapidly emerging new pacing strategies, such as left ventricular septal pacing and left bundle branch pacing. In both animal and human studies, these pacing strategies seem to maintain electrical and mechanical activation of the left ventricle to a (near)physiologic level. However, more studies on the long-term effects of both strategies are needed.

Evaluation of Criteria for Left Bundle Branch Capture

Left bundle branch pacing (LBBP) provides electrical and mechanical synchrony at low and stable pacing output and effectively corrects distal conduction system disease. The criteria for differentiating LBBP from LV septal pacing has not been validated in large trials. There are several electrocardiography-based and intracardiac electrogram-based criteria to confirm LBB capture. In this section, the authors review these criteria and their overall accuracy.

Initial Experience with Left Bundle Branch Area Pacing with Conventional Stylet-Driven Extendable Screw-In Leads and New Pre-Shaped Delivery Sheaths

Until recently, left bundle branch area pacing (LBBAp) has mostly been performed using lumen-less fixed screw leads. There are limited data on LBBAp with conventional style-driven extendable screw-in (SDES) leads, particularly data performed by operators with no previous experience with LBBAp procedures. In total, 42 consecutive patients undergoing LBBAp using SDES leads and newly designed delivery sheaths (LBBAp group) were compared with those treated with conventional right ventricular pacing (RVp) for atrioventricular block (RVp group, n = 84) using propensity score matching (1:2 ratio). The LBBAp was successful in 83% (35/42) of patients, with satisfactory pacing thresholds (0.8 ± 0.2 V at 0.4 ms). In the LBBAp group, the mean paced-QRS duration obtained during RV apical pacing (173 ± 18 ms) was significantly reduced by LBBAp (116 ± 14 ms, p < 0.001). Compared with the RVp group, the LBBAp group showed more physiological pacing, suggested by a much narrower paced-QRS duration (116 ± 14 vs. 151 ± 21 ms, p < 0.001). The pacing threshold was comparable in both groups. The LBBAp group revealed stable pacing thresholds for 6.8 ± 4.8 months post-implant and no serious complications including lead dislodgement or septal perforation. The novel approach of LBBAp using SDES leads and the new dedicated pre-shaped delivery sheaths was effectively and safely performed, even by inexperienced operators with LBBAp procedures.