Sequential His bundle and left ventricular pacing for cardiac resynchronization

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.

Conduction System Pacing for Cardiac Resynchronization Therapy

Cardiac resynchronization therapy (CRT) via biventricular pacing (BiVP-CRT) is considered a mainstay treatment for symptomatic heart failure patients with reduced ejection fraction and wide QRS. However, up to one-third of patients receiving BiVP-CRT are considered non-responders to the therapy. Multiple strategies have been proposed to maximize the percentage of CRT responders including two new physiological pacing modalities that have emerged in recent years: His bundle pacing (HBP) and left bundle branch area pacing (LBBAP). Both pacing techniques aim at restoring the normal electrical activation of the ventricles through the native conduction system in opposition to the cell-to-cell activation of conventional right ventricular myocardial pacing. Conduction system pacing (CSP), including both HBP and LBBAP, appears to be a promising pacing modality for delivering CRT and has proven to be safe and feasible in this particular setting. This article will review the current state of the art of CSP-based CRT, its limitations, and future directions.

2023 HRS/APHRS/LAHRS guideline on cardiac physiologic pacing for the avoidance and mitigation of heart failure

Cardiac physiologic pacing (CPP), encompassing cardiac resynchronization therapy (CRT) and conduction system pacing (CSP), has emerged as a pacing therapy strategy that may mitigate or prevent the development of heart failure (HF) in patients with ventricular dyssynchrony or pacing-induced cardiomyopathy. This clinical practice guideline is intended to provide guidance on indications for CRT for HF therapy and CPP in patients with pacemaker indications or HF, patient selection, pre-procedure evaluation and preparation, implant procedure management, follow-up evaluation and optimization of CPP response, and use in pediatric populations. Gaps in knowledge, pointing to new directions for future research, are also identified.

2023 HRS/APHRS/LAHRS guideline on cardiac physiologic pacing for the avoidance and mitigation of heart failure

Cardiac physiologic pacing (CPP), encompassing cardiac resynchronization therapy (CRT) and conduction system pacing (CSP), has emerged as a pacing therapy strategy that may mitigate or prevent the development of heart failure (HF) in patients with ventricular dyssynchrony or pacing-induced cardiomyopathy. This clinical practice guideline is intended to provide guidance on indications for CRT for HF therapy and CPP in patients with pacemaker indications or HF, patient selection, pre-procedure evaluation and preparation, implant procedure management, follow-up evaluation and optimization of CPP response, and use in pediatric populations. Gaps in knowledge, pointing to new directions for future research, are also identified.

Outcomes of conduction system pacing for cardiac resynchronization therapy in patients with heart failure: A multicenter experience

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

The purpose of this study was to assess the echocardiographic and clinical outcomes of CSP compared to biventricular pacing (BiVP).

METHODS

This multicenter 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

A total of 238 patients were included. Mean age was 69.8 ± 12.5 years, and 66 (27.7%) were female. Sixty-nine patients (29%) had His-bundle pacing, 50 (21%) had left bundle branch area pacing, and 119 (50%) had BiVP. Mean follow-up duration in the CSP and BiVP groups was 269 ± 202 days and 304 ± 262 days, respectively (P = .293). The proportion of CRT responders was greater in the CSP group than in the BiVP group (74% vs 60%, respectively; P = .042). On Kaplan-Meier analysis, there was no statistically significant difference in the time to first heart failure hospitalization (log-rank P = .78) and overall survival (log-rank P = .68) between the CSP and BiVP groups.

CONCLUSION

In patients with heart failure and reduced ejection fraction, CSP resulted in 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.

Electrophysiological demonstration of nonselective His-Purkinje system capture with para-Hisian pacing

BACKGROUND

The adverse effects of conventional right ventricular (RV) apical pacing prompted the search for more physiological pacing sites, such as selective and nonselective His bundle pacing (HBP), a variant of nonselective HBP (para-Hisian pacing), and mid-septal pacing. However, knowledge of their true benefit on the physiology of ventricular activation, lead stability, and pacing thresholds is limited.

METHODS AND RESULTS

We included 152 consecutive patients (mean age 61 ± 24, 63% men) in this retrospective study. Of these, 137 patients with different bradyarrhythmias underwent active fixation lead implantation at the RV apex (n = 54), para-Hisian region (n = 66), or mid interventricular septum (n = 17). Fifteen patients with ventricular preexcitation due to an accessory pathway not undergoing pacing were included as controls. A 12‑lead ECG was recorded in all patients, and cardiac electrical synchrony was assessed using the Synchromax® cross-correlation cardiac synchrony index (CSI).

RESULTS

QRS duration was prolonged in all pacing sites: from 114 ± 28 to 160 ± 29 (RV apex), from 110 ± 28 to 122 ± 29 (para-Hisian), and from 121 ± 24 to 154 ± 30 (mid interventricular septum). The CSI was significantly improved only in patients undergoing para-Hisian pacing, despite a slight widening of the QRS interval. There was no difference in pacing thresholds and sensed R-wave voltage between pacing sites. Only 1 lead, implanted at the para-Hisian region (1.5%), was dislodged towards the mid septum 48 h after implantation but did not require repositioning.

CONCLUSIONS

QRS duration was not associated with changes in CSI, meaning that QRS width does not significantly affect electrical synchrony.

Bilateral septal pacing in combination with coronary venous pacing for cardiac resynchronization therapy

BACKGROUND

Conventional right ventricular pacing combined with coronary venous pacing (CVP) is a mainstay for cardiac resynchronization therapy (CRT). However, QRS duration of conventional CRT may be frequently more than 130 ms. This study aimed to evaluate the effectiveness of QRS narrowing by bilateral septal pacing (BSP) in combination with CVP for CRT (BSP-CRT).

METHODS

Fourteen patients with QRS > 130 ms of conventional CRT after failure of physiological conduction system pacing were enrolled. Electrophysiologic characteristics were compared among different modes of CRT during procedure. BSP which was defined as capture of both sides of interventricular septum manifested as shortened R wave peak time without a right bundle branch block QRS pattern.

RESULTS

BSP-CRT were successfully achieved in 85.7% (12/14) patients. QRS duration at baseline was 185 ± 13 ms and significantly narrowed to 156 ± 9 ms during conventional CRT (n = 14, P < .001), to 143 ± 7 ms during left ventricular septal pacing (LVSP) in combination with CVP for CRT (LVSP-CRT) (n = 9, P < .001), and further to 122 ± 10 ms during BSP-CRT (n = 12, P < .001). Notably, among 7 patients in whom both LVSP and BSP were achieved, BSP-CRT outperformed LVSP-CRT at QRS narrowing by 16% (P < .001). At 3-month follow-up, left ventricular ejection fraction improved from 29 ± 6% to 41 ± 8% (P < .001).

CONCLUSIONS

BSP-CRT resulted in superior acute electrical synchronization to conventional CRT and might be considered as an alternative to conventional CRT with QRS more than 130 ms.

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.

Alternative pacing strategies for optimal cardiac resynchronization therapy

Cardiac resynchronization therapy (CRT) via biventricular pacing (BVP) improves morbidity, mortality, and quality of life, especially in subsets of patients with impaired cardiac function and wide QRS. However, the rate of unsuccessful or complicated left ventricular (LV) lead placement through coronary sinus is 5–7%, and the rate of “CRT non-response” is approximately 30%. These reasons have pushed physicians and engineers to collaborate to overcome the challenges of LV lead implantation. Thus, various alternatives to BVP have been proposed to improve CRT effectiveness. His bundle pacing (HBP) has been increasingly used by activating the His–Purkinje system but is constrained by challenging implantation, low success rates, high and often unstable thresholds, and low perception. Therefore, the concept of pacing a specialized conduction system distal to the His bundle to bypass the block region was proposed. Multiple clinical studies have demonstrated that left bundle branch area pacing (LBBAP) has comparable electrical resynchronization with HBP but is superior in terms of simpler operation, higher success rates, lower and stable capture thresholds, and higher perception. Despite their well-demonstrated effectiveness, the transvenous lead-related complications remain major limitations. Recently, leadless LV pacing has been developed and demonstrated effective for these challenging patient cohorts. This article focuses on the current state and latest progress in HBP, LBBAP, and leadless LV pacing as alternatives for failed or non-responsive conventional CRT as well as their limits and prospects.

Physiologic Pacing Targeting the His Bundle and Left Bundle Branch: a Review of the Literature

PURPOSE OF REVIEW

Conduction system pacing (CSP) has emerged as a means to preserve or restore physiological ventricular activation via pacing at the His bundle or at more distal targets in the conduction system, including the left bundle branch area. This review examines strengths, weaknesses, and clinical applications of CSP performed via these approaches.

RECENT FINDINGS

His bundle pacing (HBP) has been successfully utilized for standard bradyarrhythmia indications and for QRS correction among patients receiving devices for cardiac resynchronization therapy (CRT). Limitations of HBP pacing have included implant complexity and rising pacing thresholds over time. Left bundle branch area pacing (LBBAP) appears to deliver similar physiological benefits with shorter implant times and more stable thresholds. More recently, hybrid systems utilizing HBP or LBBAP in combination with left ventricular leads have been used to treat heart failure (HF) patients, and may be useful in multilevel or mixed conduction blocks. There is growing interest in CSP for bradycardia and HF indications, although high quality data with randomized controlled trials are needed to help guide future treatment paradigms.

Conduction System Pacing for Cardiac Resynchronization Therapy

Although conventional biventricular pacing has been shown to benefit patients with heart failure and conduction system disease, there are limitations to its therapeutic success, resulting in widely variable clinical response. Limitations of conventional biventricular pacing evolve around myocardial scar, fibrosis, and inability to effectively stimulate diseased tissue. Several observational and acute hemodynamic studies have demonstrated improved electrical resynchronization and echocardiographic response with conduction system pacing. This article provides a systematic review of conduction system pacing as a physiologic alternative to conventional CRT, which is currently undergoing rigorous investigation.

His-Optimized and Left Bundle Branch-Optimized Cardiac Resynchronization Therapy: In Control of Fusion Pacing

Fusion pacing, which exploits conduction via the intrinsic His-Purkinje system, forms the basis of recent cardiac resynchronization therapy (CRT) optimization algorithms. However, settings need to be constantly adjusted to accommodate for changes in AV conduction, and the algorithms are not always available (eg, depending on the device, in case of AV block or with atrial fibrillation). His-optimized cardiac resynchronization therapy (HOT-CRT), and left-bundle branch optimized cardiac resynchronization therapy (LOT-CRT) which combines conduction system pacing with ventricular fusion pacing, provide constant fusion with ventricular activation (irrespective of intrinsic AV conduction). These modalities provide promising treatment strategies for patients with heart failure, especially in those with chronic atrial fibrillation who require CRT (in whom the atrial port is usually plugged and can be used to connect the conduction system pacing lead).

The clinical utility of direct His-bundle pacing in patients with heart failure and permanent atrial fibrillation

In patients with significantly impaired left ventricle function permanent atrial fibrillation (AF) often coexists with symptoms of heart failure. Based on various studies, it is assumed that in patients with heart failure in functional class III and IV AF occurs in 40-50% of patients. AF adversely affects cardiac hemodynamics, and its harmfulness increases particularly in the failing heart. The lack of mechanical function of the left atrium, the usually fast ventricular rate and the irregular sequence of ventricular contraction constitute the spectrum of harmful effects of this arrhythmia. Therefore, the only way to address the underlying problem of AF, which is irregular ventricular rhythm, is to pace the ventricles and to slow or block the AV conduction. Classic, right ventricular pacing is contraindicated in this population as it promotes the abovementioned disorders by initiating additional dyssynchrony of left ventricular contraction with reduction of its contractility and aggravation of AF-related mitral regurgitation. The possibility of direct His bundle pacing (DHBP) significantly extended the clinical armamentarium of cardiac pacing. The restoration of the physiological electrical activation could significantly contribute to echocardiographic and clinical improvement. With time and the development of dedicated tools for direct His bundle pacing the success rate of implantations became more than 90% and the acceptable pacing thresholds under 2.0 V (1 ms) could be achieved in most patients. This contributed to the broader clinical application of DHBP in different patient' groups with various pacing indications. The authors of the paper discuss different electrocardiographic and clinical indications for DHBP.

Is His-optimized superior to conventional cardiac resynchronization therapy in improving heart failure? Results from a propensity-matched study

BACKGROUND

His bundle pacing (HBP), alone or optimized in association with coronary sinus pacing (HBP+LV) has recently been proposed as an alternative to conventional cardiac resynchronization therapy (CRT). However, there is lack of controlled studies that assessed clinical outcome.

METHODS

We did a single-center, propensity-score matched, case-control study of comparison of HBP and HBP+LV versus conventional CRT in patients with heart failure (HF) and standard indications for CRT. The study group patients were consecutively enrolled in the year 2019. The control group patients were selected, by propensity score matching, among those CRT implantations performed in the years 2015-2018.

RESULTS

There were 27 patients in each group. In the active group, 12 (44%) patients received HBP alone and 12 (44%) patients HBP+LV pacing. HBP failed in three (11%) patients. In the control group, conventional CRT was achieved in 26 (96%) patients and failed in one. Paced QRS width was shorter in the active than in the control group (128 ± 18 vs. 148 ± 27 ms, p = .004). During a mean of 9.6 months of follow-up, a composite clinical outcome of death, hospitalization for HF or worsening HF occurred in three (11%) in the active group and in four (15%) in the control group, p = .58. No difference was also observed with softer endpoints: NYHA class (1.9 ± 0.7 vs. 2.1 ± 0.7), subjective improvement (74% vs. 74%) and LV ejection fraction (40.7% vs. 40.7%).

CONCLUSION

Compared with conventional CRT, a shorter QRS width can be obtained with HBP alone or in association with coronary sinus pacing but we were unable to show a better clinical outcome. There is urgent need for large, randomized trials.

Left bundle branch-optimized cardiac resynchronization therapy (LOT-CRT): Results from an international LBBAP collaborative study group

BACKGROUND

Cardiac resynchronization therapy (CRT) based on the conventional biventricular pacing (BiV-CRT) technique sometimes results in broad QRS complex and suboptimal response.

OBJECTIVE

We aimed to assess the feasibility and outcomes of CRT based on left bundle branch area pacing (LBBAP, in lieu of the right ventricular lead) combined with coronary venous left ventricular pacing in an international multicenter study.

METHODS

LBBAP-optimized CRT (LOT-CRT) was attempted in nonconsecutive patients with CRT indications. Addition of the LBBA (or coronary venous) lead was at the discretion of the implanting physician, who was guided by suboptimal paced QRS complex, and/or on clinical grounds.

RESULTS

LOT-CRT was successful in 91 of 112 patients (81%). The baseline characteristics were as follows: mean age 70 ± 11 years, female 22 (20%), left ventricular ejection fraction 28.7% ± 9.8%, left ventricular end-diastolic diameter 62 ± 9 mm, N-terminal pro-B-type natriuretic peptide level 5821 ± 8193 pg/mL, left bundle branch block 47 (42%), nonspecific intraventricular conduction delay 25 (22%), right ventricular pacing 26 (23%), and right bundle branch block 14 (12%). The procedure characteristics were as follows: mean fluoroscopy time 27.3 ± 22 minutes, LBBAP capture threshold 0.8 ± 0.5 V @ 0.5 ms, and R-wave amplitude 10 mV. LOT-CRT resulted in significantly greater narrowing of QRS complex from 182 ± 25 ms at baseline to 144 ± 22 ms (P < .0001) than did BiV-CRT (170 ± 30 ms; P < .0001) and LBBAP (162 ± 23 ms; P < .0001). At follow-up of ≥3 months, the ejection fraction improved to 37% ± 12%, left ventricular end-diastolic diameter decreased to 59 ± 9 mm, N-terminal pro-B-type natriuretic peptide level decreased to 2514 ± 3537 pg/mL, pacing parameters were stable, and clinical improvement was noted in 76% of patients (New York Heart Association class 2.9 vs 1.9).

CONCLUSION

LOT-CRT is feasible and safe and provides greater electrical resynchronization as compared with BiV-CRT and could be an alternative, especially when only suboptimal electrical resynchronization is obtained with BiV-CRT. Randomized controlled trials comparing LOT-CRT and BiV-CRT are needed.

The electrocardiogram characteristics and pacing parameters of permanent left bundle branch pacing: a systematic review and meta-analysis

PURPOSE

Recent advances in conduction system pacing have led to the use of left bundle branch pacing (LBBP), which has potential advantages over His bundle pacing (HBP). For example, LBBP engages the electrical activation through the left bundle branch, produces ventricular electrical synchrony, and avoids the weakness of HBP such as lead instability, higher threshold, and early battery depletion. This pacing modality has been considered an attractive mode to achieve normal physiological pacing. However, as a new technology, LBBP is still in the stage of clinical exploration and lacks adequate evaluation. This study aims to investigate the electrocardiogram characteristics, pacing parameters, the safety, and the effectiveness of LBBP.

METHODS

A computerized search of PubMed, Embase, and The Cochrane Library for the effects of LBBP was done. The baseline characteristics of patients, successful rate of implantation, capture threshold, R-wave amplitude, pacing impedance, QRS duration, and follow-up date were extracted and summarized.

RESULTS

Thirteen studies including 712 patients were included in this analysis. The overall successful rate for implantation was 92.9%. The main indications for LBBP were atrioventricular block (AVB), sinus node dysfunction (SND), atrial fibrillation (AF) with slow ventricular rate, and cardiac resynchronization therapy (CRT) candidates. For patients with QRS duration>120 ms, permanent LBBP resulted in narrower QRS duration compared to that before implantation (P = 0.05). QRS duration and capture threshold of LBBP remained stable during follow-up. Moreover, there was higher R-wave amplitude and lower pacing impedance at follow-up compared to those at implantation (P = 0.01 and P < 0.00001, respectively).

CONCLUSIONS

Permanent LBBP has shown promising results for pacemaker-indicated patients in small observational studies. Good electrical synchronization, high success rates, and stable pacemaker lead parameters suggested significant advantages of LBBP in physiological pacing. Randomized controlled trials are needed to assess the efficacy of LBBP in patients.

Conduction System Pacing for Cardiac Resynchronisation

Conduction system pacing (CSP) is a technique of pacing that involves implantation of permanent pacing leads along different sites of the cardiac conduction system and includes His bundle pacing and left bundle branch pacing. There is an emerging role for CSP to achieve cardiac resynchronisation in patients with heart failure with reduced ejection fraction and inter-ventricular dyssynchrony. In this article, the authors review these strategies for resynchronisation and the available data on the use of CSP in overcoming dyssynchrony.

His Bundle Pacing – Stand-alone or adjunctive physiological pacing: a systematic review

His-bundle pacing (HBP) appears to be a viable stand-alone or adjunctive physiological pacing therapy in pacemaker dependent patients. It could also serve as an effective adjunct or alternative pacing therapy for heart failure patients who require cardiac resynchronization therapy or pacemaker upgrade. His-bundle pacing has demonstrated improvement of His-Purkinje conduction, left ventricular electrical / mechanical synchronization, and left ventricular ejection fraction (LVEF) compared with right ventricle pacing. Patients who have high pacing dependence and/or LVEF impairment would benefit most from HBP in terms of heart failure hospitalization and LVEF improvement. Mortality benefit has not been consistently demonstrated in latest meta-analysis. The long-term clinical benefit and safety profile of HBP remains to be explored in future studies.  Key words: His bundle pacing, physiologic pacing, upgrade pacing

His-Optimized Cardiac Resynchronization Therapy With Ventricular Fusion Pacing for Electrical Resynchronization in Heart Failure

OBJECTIVES

This study sought to evaluate the effectiveness of His-optimized cardiac resynchronization therapy (HOT-CRT) for reducing left ventricular activation time (LVAT) compared to His bundle pacing (HBP) and biventricular (BiV) pacing (including multipoint pacing [MPP]), using electrocardiographic (ECG) imaging.

BACKGROUND

HBP may correct bundle branch block (BBB) and has shown encouraging results for providing CRT. However, HBP does not correct BBB in all patients and may be combined with univentricular or BiV fusion pacing to deliver HOT-CRT to maximize resynchronization.

METHODS

Nineteen patients with a standard indication for CRT, implanted with HBP without correction of BBB and BiV (n = 14) or right ventricular (n = 5) leads, were prospectively enrolled. Patients underwent ECG imaging while pacing in different configurations using different LV electrodes and at different HBP ventricular pacing (VP) delays. The primary endpoint was reduction in LVAT with HOT-CRT, and the secondary endpoints included various other dys-synchrony measurements including right ventricular activation time (RVAT).

RESULTS

Compared to HBP, HOT-CRT reduced LVAT by 21% (-17 ms [95% confidence interval [CI]: -25 to -9 ms]; p < 0.001) and outperformed BiV by 24% (-22 ms [95% CI: -33 to -10 ms]; p = 0.002) and MPP by 13% (-11 ms [95% CI: -21 to -1 ms]; p = 0.035). Relative to HBP, HOT-CRT also reduced RVAT by 7% (-5 ms [95% CI: -9 to -1 ms; p = 0.035) in patients with right BBB, whereas RVAT was increased by BiV. The other electrical dyssynchrony measurements also improved with HOT-CRT.

CONCLUSIONS

HOT-CRT acutely improves ventricular electrical synchrony beyond BiV and MPP. The impact of this finding needs to be evaluated further in studies with clinical follow-up. (Electrical Resynchronization and Acute Hemodynamic Effects of Direct His Bundle Pacing Compared to Biventricular Pacing; NCT03452462).

Clinical outcomes of His-Purkinje conduction system pacing

His-Purkinje conduction system pacing (HPCSP) in the form of His bundle pacing (HBP) and left bundle branch pacing (LBBP) allows normal left ventricular activation, thereby preventing the adverse consequences of right ventricular pacing. HBP has been established for several years with centers from China, Europe, and North America reporting their experience. There is international guidance as to how to implant such systems with the differing patterns of His bundle capture clearly described. LBBP is a more recent innovation with potential advantages including improved pacing parameters. HPCSP has been extensively studied in a variety of indications including cardiac resynchronization therapy, atrioventricular node ablation, and bradycardia pacing. This review will focus on the clinical outcomes of HPCSP including mortality and morbidity of heart failure hospitalization and symptoms.