Simultaneous His Bundle and Left Ventricular Pacing for Optimal Cardiac Resynchronization Therapy Delivery

Is Conduction System Pacing a Valuable Alternative to Biventricular Pacing for Cardiac Resynchronization Therapy?

Cardiac resynchronization therapy (CRT) significantly improves clinical outcomes in patients with ventricular systolic dysfunction and dyssynchrony. Biventricular pacing (BVP) has a class IA recommendation for patients with symptomatic heart failure with reduced ejection fraction (HFrEF) and left bundle branch block (LBBB). However, approximately 30% of patients have a poor therapeutic response and do not achieve real clinical benefit. Pre-implant imaging, together with tailored programming and dedicated device algorithms, have been proposed as possible tools to improve success rate but have shown inconsistent results. Over the last few years, conduction system pacing (CSP) is becoming a real and attractive alternative to standard BVP as it can restore narrow QRS in patients with bundle branch block (BBB) by stimulating and recruiting the cardiac conduction system, thus ensuring true resynchronization. It includes His bundle pacing (HBP) and left bundle branch area pacing (LBBAP). Preliminary data coming from small single-center experiences are very promising and have laid the basis for currently ongoing randomized controlled trials comparing CSP with BVP. The purpose of this review is to delve into the emerging role of CSP as an alternative method of achieving CRT. After framing CSP in a historical perspective, the pathophysiological rationale and available clinical evidence will be examined, and crucial technical aspects will be discussed. Finally, evidence gaps and future perspectives on CSP as a technique of choice to deliver CRT will be summarized.

Effect of scar and His-Purkinje and myocardium conduction on response to conduction system pacing

INTRODUCTION

Conduction system pacing (CSP), in the form of His bundle pacing (HBP) or left bundle branch pacing (LBBP), is emerging as a valuable cardiac resynchronization therapy (CRT) delivery method. However, patient selection and therapy personalization for CSP delivery remain poorly characterized. We aim to compare pacing-induced electrical synchrony during CRT, HBP, LBBP, HBP with left ventricular (LV) epicardial lead (His-optimized CRT [HOT-CRT]), and LBBP with LV epicardial lead (LBBP-optimized CRT [LOT-CRT]) in patients with different conduction disease presentations using computational modeling.

METHODS

We simulated ventricular activation on 24 four-chamber heart geometries, including His-Purkinje systems with proximal left bundle branch block (LBBB). We simulated septal scar, LV lateral wall scar, and mild and severe myocardium and LV His-Purkinje system conduction disease by decreasing the conduction velocity (CV) down to 70% and 35% of the healthy CV. Electrical synchrony was measured by the shortest interval to activate 90% of the ventricles (90% of biventricular activation time [BIVAT-90]).

RESULTS

Severe LV His-Purkinje conduction disease favored CRT (BIVAT-90: HBP 101.5 ± 7.8 ms vs. CRT 93.0 ± 8.9 ms, p < .05), with additional electrical synchrony induced by HOT-CRT (87.6 ± 6.7 ms, p < .05) and LOT-CRT (73.9 ± 7.6 ms, p < .05). Patients with slow myocardium CV benefit more from CSP compared to CRT (BIVAT-90: CRT 134.5 ± 24.1 ms; HBP 97.1 ± 9.9 ms, p < .01; LBBP: 101.5 ± 10.7 ms, p < .01). Septal but not lateral wall scar made CSP ineffective, while CRT was able to resynchronize the ventricles in the presence of septal scar (BIVAT-90: baseline 119.1 ± 10.8 ms vs. CRT 85.1 ± 14.9 ms, p < .01).

CONCLUSION

Severe LV His-Purkinje conduction disease attenuates the benefits of CSP, with additional improvements achieved with HOT-CRT and LOT-CRT. Septal but not lateral wall scars make CSP ineffective.

Pacing interventions in non-responders to cardiac resynchronization therapy

Non-responders to Cardiac Resynchronization Therapy (CRT) represent a high-risk, and difficult to treat population of heart failure patients. Studies have shown that these patients have a lower quality of life and reduced life expectancy compared to those who respond to CRT. Whilst the first-line treatment for dyssynchronous heart failure is "conventional" biventricular epicardial CRT, a range of novel pacing interventions have emerged as potential alternatives. This has raised the question whether these new treatments may be useful as a second-line pacing intervention for treating non-responders, or indeed, whether some patients may benefit from these as a first-line option. In this review, we will examine the current evidence for four pacing interventions in the context of treatment of conventional CRT non-responders: CRT optimization; multisite left ventricular pacing; left ventricular endocardial pacing and conduction system pacing.

Leadless biventricular left bundle and endocardial lateral wall pacing versus left bundle only pacing in left bundle branch block patients

Biventricular endocardial (BIV-endo) pacing and left bundle pacing (LBP) are novel delivery methods for cardiac resynchronization therapy (CRT). Both pacing methods can be delivered through leadless pacing, to avoid risks associated with endocardial or transvenous leads. We used computational modelling to quantify synchrony induced by BIV-endo pacing and LBP through a leadless pacing system, and to investigate how the right-left ventricle (RV-LV) delay, RV lead location and type of left bundle capture affect response. We simulated ventricular activation on twenty-four four-chamber heart meshes inclusive of His-Purkinje networks with left bundle branch block (LBBB). Leadless biventricular (BIV) pacing was simulated by adding an RV apical stimulus and an LV lateral wall stimulus (BIV-endo lateral) or targeting the left bundle (BIV-LBP), with an RV-LV delay set to 5 ms. To test effect of prolonged RV-LV delays and RV pacing location, the RV-LV delay was increased to 35 ms and/or the RV stimulus was moved to the RV septum. BIV-endo lateral pacing was less sensitive to increased RV-LV delays, while RV septal pacing worsened response compared to RV apical pacing, especially for long RV-LV delays. To investigate how left bundle capture affects response, we computed 90% BIV activation times (BIVAT-90) during BIV-LBP with selective and non-selective capture, and left bundle branch area pacing (LBBAP), simulated by pacing 1 cm below the left bundle. Non-selective LBP was comparable to selective LBP. LBBAP was worse than selective LBP (BIVAT-90: 54.2 ± 5.7 ms vs. 62.7 ± 6.5, p < 0.01), but it still significantly reduced activation times from baseline. Finally, we compared leadless LBP with RV pacing against optimal LBP delivery through a standard lead system by simulating BIV-LBP and selective LBP alone with and without optimized atrioventricular delay (AVD). Although LBP alone with optimized AVD was better than BIV-LBP, when AVD optimization was not possible BIV-LBP outperformed LBP alone, because the RV pacing stimulus shortened RV activation (BIVAT-90: 54.2 ± 5.7 ms vs. 66.9 ± 5.1 ms, p < 0.01). BIV-endo lateral pacing or LBP delivered through a leadless system could potentially become an alternative to standard CRT. RV-LV delay, RV lead location and type of left bundle capture affect leadless pacing efficacy and should be considered in future trial designs.

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.

Leadless Left Bundle Branch Area Pacing in Cardiac Resynchronisation Therapy: Advances, Challenges and Future Directions

Leadless left bundle branch area pacing (LBBAP) represents the merger of two rapidly progressing areas in the field of cardiac resynchronisation therapy (CRT). It combines the attractive concepts of pacing the native conduction system to allow more physiological activation of the myocardium than conventional biventricular pacing, with the potential added benefits of avoiding long-term complications associated with transvenous leads via leadless left ventricular endocardial pacing. This perspective article will first review the evidence for the efficacy of leadless pacing in CRT. We then summarise the procedural steps and pilot data for leadless LBBAP, followed by a discussion of the safety and efficacy of this novel technique. Finally, we will examine how further mechanistic evidence may shed light to which patients may benefit most from leadless LBBAP, and how improvements in current experience and technology could promote widespread uptake and expand current clinical indications.

ECG optimisation for CRT systems in the era of automatic algorithms: a comprehensive review

Cardiac resynchronisation therapy (CRT) may fail in up to one third of patients, mainly due to anatomical and procedural issues. In the daily practice, ECG optimisation is largely used to address CRT delivery. Ineffective CRT can be related to non-optimal pacing timing as well as inadequate pacing-capture. A rate-competitive atrial fibrillation (AF) or a high daily burden of premature ventricular contractions (PVC) may also affect CRT by means of fusion or pseudo-fusion captures. Growing observations suggest that in a subset of patients with typical left bundle branch block (LBBB), selected LV pacing may be more effective, producing a complete fusion between the left pacing and the intrinsic right bundle activation. The His-ventricular (HV) interval is an invasive measurement (derived from electrophysiological study), which mainly reflects the RV activation (and its contribution to QRS timing) and has been proposed by some authors when addressing LV-paced–RV-sensed fusion. In sinus rhythm CRT patients, with baseline typical LBBB criteria and preserved AV conduction, the “dromotropic” management to achieve RV intrinsic activation with LV fusion is also “AV delay dependent”. In this regard, the RV intrinsic activation (detected by RV sensing) and the A (paced/sensed)-RV (sensed) interval are also influenced by the RV lead position within the RV. The current families of CRT devices have implemented automatic algorithms to optimise AV and VV timing intervals. The proof of principle is again the evidence that fusion of an LV-paced beat with intrinsic rhythm may be more beneficial than standard biventricular pacing, provided a preserved AV conduction. In the present review, all the above issues are discussed.

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).

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.

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).

Device Programming for His Bundle Pacing

Although permanent His bundle pacing was first reported almost 2 decades ago, it is only recently gaining wider adoption, following facilitation of the implant procedure by dedicated tools. An additional challenge is programming the system, as His bundle pacing may have specific configurations and require special considerations which current implantable pulse generators are not designed for. The aim of this article is to provide practical recommendations for programming His bundle pacing, to deliver optimal therapy and ensure patient safety.

His-Optimized Cardiac Resynchronization Therapy to Maximize Electrical Resynchronization: A Feasibility Study

Background Cardiac resynchronization therapy (CRT) is an established therapy for patients with cardiomyopathy, left bundle branch block, and heart failure. His bundle pacing (HBP) may also improve clinical outcomes by narrowing QRS duration. The QRS narrowing by HBP may not always be optimal. The aim of the study was to determine if CRT could be optimized by sequential HBP followed by left ventricular (LV) pacing (His-Optimized CRT [HOT-CRT]) to maximize electrical resynchronization. Methods We attempted permanent HBP in 27 patients (left bundle branch block 17, intraventricular conduction defect 5, and right ventricular pacing 5) referred for CRT in addition to LV lead. HBP was followed by LV pacing at a delay equal to His-ventricular interval. QRS duration at baseline, during HBP, biventricular pacing, and HOT-CRT was measured. Echocardiographic parameters and New York Heart Association functional class were assessed at baseline and during follow-up. Results HOT-CRT was successful in 25 of 27 patients (age 72±15 years, men 23, ischemic 21). QRS duration at baseline was 183±27 ms and significantly narrowed to 162±17 ms with biventricular pacing ( P=0.003), to 151±24 ms during HBP ( P<0.0001), and further to 120±16 ms during HOT-CRT ( P<0.0001). During a mean follow-up of 14±10 months, LV ejection fraction improved from 24±7% to 38±10% ( P<0.0001), and New York Heart Association functional class changed from 3.3 to 2.04. Twenty-one of 25 patients (84%) were clinical responders while 23 of 25 (92%) showed echocardiographic response. Conclusions In this feasibility cohort, HOT-CRT resulted in improved electrical resynchronization. HOT-CRT may improve clinical and echocardiographic outcomes in advanced heart failure patients requiring CRT.

Should His Bundle Pacing Be Preferred over Cardiac Resynchronization Therapy Following Atrioventricular Junction Ablation?

Atrial fibrillation (AF) and heart failure (HF) are associated with high morbidity and mortality, which is particularly detrimental when patients develop rapid ventricular rates (RVR). Atrioventricular junction (AVJ) ablation with pacemaker implantation has been used as a method of achieving rate control in patients with incessant AF with RVR. Right ventricular only pacing is known to be harmful in the setting of HF. His bundle pacing (HBP) and biventricular (BiV) pacing both offer durable pacing solutions that offer more physiologic activation. This review describes the benefits and drawbacks of HBP and BiV pacing in HF patients after AVJ ablation.

Ejection fraction in left bundle branch block is disproportionately reduced in relation to amount of myocardial scar

INTRODUCTION

The relationship between left ventricular (LV) ejection fraction (EF) and LV myocardial scar can identify potentially reversible causes of LV dysfunction. Left bundle branch block (LBBB) alters the electrical and mechanical activation of the LV. We hypothesized that the relationship between LVEF and scar extent is different in LBBB compared to controls.

METHODS

We compared the relationship between LVEF and scar burden between patients with LBBB and scar (n = 83), and patients with chronic ischemic heart disease and scar but no electrocardiographic conduction abnormality (controls, n = 90), who had undergone cardiovascular magnetic resonance (CMR) imaging at one of three centers. LVEF (%) was measured in CMR cine images. Scar burden was quantified by CMR late gadolinium enhancement (LGE) and expressed as % of LV mass (%LVM). Maximum possible LVEF (LVEFmax) was defined as the function describing the hypotenuse in the LVEF versus myocardial scar extent scatter plot. Dysfunction index was defined as LVEFmax derived from the control cohort minus the measured LVEF.

RESULTS

Compared to controls with scar, LBBB with scar had a lower LVEF (median [interquartile range] 27 [19-38] vs 36 [25-50] %, p < 0.001), smaller scar (4 [1-9] vs 11 [6-20] %LVM, p < 0.001), and greater dysfunction index (39 [30-52] vs 21 [12-35] % points, p < 0.001).

CONCLUSIONS

Among LBBB patients referred for CMR, LVEF is disproportionately reduced in relation to the amount of scar. Dyssynchrony in LBBB may thus impair compensation for loss of contractile myocardium.

His bundle pacing

His bundle pacing (HBP) has recently emerged as a technique to avoid the negative effects of long-term right ventricular apical pacing. In addition to providing physiologic ventricular activation, HBP has been shown to correct underlying conduction abnormalities in certain patients. Although large prospective, randomized clinical trials have not yet been completed, the available observational clinical data support the safety and efficacy of this technique. Here, we review the physiology of the his bundle (HB) as it relates to HBP, describe the current clinical experience, and discuss future directions of this emerging therapy.

Acute torrential mitral regurgitation during transcatheter aortic valve replacement: a case report

Background

Transcatheter aortic valve replacement (TAVR) is a minimally invasive approach to aortic valve replacement. However, critical cardiovascular collapse can occur during the procedure for various reasons.

Case presentation

A 90-year-old man with severe aortic stenosis and left circumflex artery stenosis developed acute torrential mitral regurgitation (MR) during TAVR. The valve deployment process induced left ventricular dyssynchrony due to left bundle-branch block and myocardial ischemia in the left circumflex artery region with torrential MR. Transesophageal echocardiography clearly demonstrated the mechanisms of MR, which was successfully bailed out by left ventricular pacing and intra-aortic balloon pumping.

Conclusions

MR can be seriously exaggerated by various and complicated mechanisms during TAVR and should be rapidly assessed and appropriately managed depending on its mechanisms.

Electronic supplementary material

The online version of this article (10.1186/s40792-018-0446-z) contains supplementary material, which is available to authorized users.

Magnetic Resonance Imaging Correlates of Left Bundle Branch Disease in Patients With Nonischemic Cardiomyopathy

The pathologic correlates of intraventricular conduction delays in patients with nonischemic cardiomyopathy (NIC) have been scarcely investigated. We assessed left ventricular (LV) structural, functional, and tissue abnormalities associated with intraventricular conduction left bundle disease (LBD), including left anterior hemiblock or complete left bundle branch block, in a cohort of patients with NIC submitted to cardiovascular magnetic resonance. Twelve-lead electrocardiogram and cardiovascular magnetic resonance were performed in 196 consecutive patients with NIC. The presence and extent of myocardial fibrosis was evaluated with late gadolinium enhancement (LGE) technique. Compared with normal intraventricular conduction patients, those with LBD were older (66 vs 59 years, p = 0.001), had greater LV volumes (p = 0.035 for end-diastolic and p = 0.009 for end-systolic volume) and mass (p = 0.034), and showed lower LV ejection fraction (33% vs 40%, p = 0.008). LGE was observed more commonly in LBD than in normal intraventricular conduction patients and was more often located in the ventricular septum (p < 0.001). On multivariate analysis, septal LGE was independently associated with a higher likelihood of LBD (odds ratio 6.1, 95% confidence interval 2.9 to 12.7, p < 0.001), even after correction for LV volumes, mass, and ejection fraction. In conclusion, in NIC, the presence of LBD is associated with worse LV remodeling and dysfunction than normal intraventricular conduction. Septal fibrosis yielded a 6-fold greater likelihood of LBD, independently of the degree of LV dilatation and systolic dysfunction.

His bundle pacing: Initial experience and lessons learned

Direct His bundle pacing provides the most physiologic means of artificial pacing of the ventricles with a preserved His-Purkinje system and may play a role in patients with a diseased intrinsic conduction system. We describe our initial motivations and experience with permanent direct His bundle pacing and important lessons learned since that time.