Right and Left Ventricular Activation Sequence in Patients with Heart Failure and Right Bundle Branch Block: A Detailed Analysis Using Three-Dimensional Non-Fluoroscopic Electroanatomic Mapping System

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.

Early effects of left bundle branch area pacing on ventricular activation by speckle tracking echocardiography

BACKGROUND

Left bundle branch area pacing (LBBAP) is an emerging cardiac pacing modality that preserves fast electrical activation of the ventricles and provides very good electrical measures. Little is known on mechanical ventricular activation during this pacing modality.

METHODS

We prospectively enrolled patients receiving LBBAP. Electrocardiographic and electrical parameters were evaluated at implantation, < 24 h and 3 months. Transthoracic echocardiography with strain analysis was performed at baseline and after 3 months, when ventricular mechanical activation and synchrony were analyzed by time-to-peak standard deviation (TPSD) of strain curves for both ventricles. Intraventricular left ventricular (LV) dyssynchrony was investigated by LV TPSD and interventricular dyssynchrony by left ventricle-right ventricle TPSD (LV-RV TPSD).

RESULTS

We screened 58 patients with permanent pacing indication who attempted LBBAP. Procedural success was obtained in 56 patients (97%). Strain data were available in 50 patients. QRS duration was 124.1 ± 30.7 ms at baseline, while paced QRS duration was 107.7 ± 13.6 ms (p < 0.001). At 3 months after LBBAP, left ventricular ejection fraction (LVEF) increased from 52.9 ± 10.6% at baseline to 56.9 ± 8.4% (p = 0.004) and both intraventricular LV dyssynchrony and interventricular dyssynchrony significantly improved (LV TPSD reduction from 38.2 (13.6-53.9) to 15.1 (8.3-31.5), p < 0.001; LV-RV TPSD from 27.9 (10.2-41.5) to 13.9 (4.3-28.7), p = 0.001). Ameliorations with LBBAP were consistent in all subgroups, irrespective of baseline QRS duration, types of intraventricular conduction abnormalities, and LVEF.

CONCLUSIONS

Echocardiographic strain analysis shows that LBBAP determines a fast and synchronous biventricular contraction with a stereotype mechanical activation, regardless of baseline QRS duration, pattern, and LV function.

Long-Term Outcomes of Cardiac Resynchronization Therapy in Patients With Repaired Tetralogy of Fallot: A Multicenter Study

BACKGROUND

A growing number of patients with tetralogy of Fallot develop left ventricular systolic dysfunction and heart failure, in addition to right ventricular dysfunction. Although cardiac resynchronization therapy (CRT) is an established treatment option, the effect of CRT in this population is still not well defined. This study aimed to investigate the early and late efficacy, survival, and safety of CRT in patients with tetralogy of Fallot.

METHODS

Data were analyzed from an observational, retrospective, multicenter cohort, initiated jointly by the Pediatric and Congenital Electrophysiology Society and the International Society of Adult Congenital Heart Disease. Twelve centers contributed baseline and longitudinal data, including vital status, left ventricular ejection fraction (LVEF), QRS duration, and NYHA functional class. Outcomes were analyzed at early (3 months), intermediate (1 year), and late follow-up (≥2 years) after CRT implantation.

RESULTS

A total of 44 patients (40.3±19.2 years) with tetralogy of Fallot and CRT were enrolled. Twenty-nine (65.9%) patients had right ventricular pacing before CRT upgrade. The left ventricular ejection fraction improved from 32% [24%-44%] at baseline to 42% [32%-50%] at early follow-up (P<0.001) and remained improved from baseline thereafter (P≤0.002). The QRS duration decreased from 180 [160-205] ms at baseline to 152 [133-182] ms at early follow-up (P<0.001) and remained decreased at intermediate and late follow-up (P≤0.001). Patients with upgraded CRT had consistent improvement in left ventricular ejection fraction and QRS duration at each time point (P≤0.004). Patients had a significantly improved New York Heart Association functional class after CRT implantation at each time point compared with baseline (P≤0.002). The transplant-free survival rates at 3, 5, and 8 years after CRT implantation were 85%, 79%, and 73%.

CONCLUSIONS

In patients with tetralogy of Fallot treated with CRT consistent improvement in QRS duration, left ventricular ejection fraction, New York Heart Association functional class, and reasonable long-term survival were observed. The findings from this multicenter study support the consideration of CRT in this unique population.

Bilateral Bundle Branch Block

Left bundle branch block (LBBB) and right bundle branch block (RBBB) are classic manifestations of bundle branch conduction disorders. However, a third form that is uncommon and underrecognized may exist that has features and pathophysiology of both: bilateral bundle branch block (BBBB). This unusual form of bundle branch block exhibits an RBBB pattern in lead V1 (terminal R wave) and an LBBB pattern in leads I and aVL (absence of S wave). This unique conduction disorder may confer an increased risk of adverse cardiovascular events. BBBB patients may be a subset of patients that respond well to cardiac resynchronization therapy.

Cardiac Resynchronization Therapy Improves Outcomes in Patients With Intraventricular Conduction Delay But Not Right Bundle Branch Block: A Patient-Level Meta-Analysis of Randomized Controlled Trials

BACKGROUND

Benefit from cardiac resynchronization therapy (CRT) varies by QRS characteristics; individual randomized trials are underpowered to assess benefit for relatively small subgroups.

METHODS

The authors analyzed patient-level data from pivotal CRT trials (MIRACLE [Multicenter InSync Randomized Clinical Evaluation], MIRACLE-ICD [Multicenter InSync ICD Randomized Clinical Evaluation], MIRACLE-ICD II [Multicenter InSync ICD Randomized Clinical Evaluation II], REVERSE [Resynchronization Reverses Remodeling in Systolic Left Ventricular Dysfunction], RAFT [Resynchronization-Defibrillation for Ambulatory Heart Failure], BLOCK-HF [Biventricular Versus Right Ventricular Pacing in Heart Failure Patients with Atrioventricular Block], COMPANION [Comparison of Medical Therapy, Pacing and Defibrillation in Heart Failure], and MADIT-CRT [Multicenter Automatic Defibrillator Implantation Trial - Cardiac Resynchronization Therapy]) using Bayesian Hierarchical Weibull survival regression models to assess CRT benefit by QRS morphology (left bundle branch block [LBBB], n=4549; right bundle branch block [RBBB], n=691; and intraventricular conduction delay [IVCD], n=1024) and duration (with 150-ms partition). The continuous relationship between QRS duration and CRT benefit was also examined within subgroups defined by QRS morphology. The primary end point was time to heart failure hospitalization (HFH) or death; a secondary end point was time to all-cause death.

RESULTS

Of 6264 patients included, 25% were women, the median age was 66 [interquartile range, 58 to 73] years, and 61% received CRT (with or without an implantable cardioverter defibrillator). CRT was associated with an overall lower risk of HFH or death (hazard ratio [HR], 0.73 [credible interval (CrI), 0.65 to 0.84]), and in subgroups of patients with QRS ≥150 ms and either LBBB (HR, 0.56 [CrI, 0.48 to 0.66]) or IVCD (HR, 0.59 [CrI, 0.39 to 0.89]), but not RBBB (HR 0.97 [CrI, 0.68 to 1.34]; Pinteraction <0.001). No significant association for CRT with HFH or death was observed when QRS was <150 ms (regardless of QRS morphology) or in the presence of RBBB. Similar relationships were observed for all-cause death.

CONCLUSIONS

CRT is associated with reduced HFH or death in patients with QRS ≥150 ms and LBBB or IVCD, but not for those with RBBB. Aggregating RBBB and IVCD into a single "non-LBBB" category when selecting patients for CRT should be reconsidered.

REGISTRATION

URL: https://www.

CLINICALTRIALS

gov; Unique identifiers: NCT00271154, NCT00251251, NCT00267098, and NCT00180271.

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.

The effect of cardiac resynchronization without a defibrillator on morbidity and mortality: an individual patient data meta-analysis of COMPANION and CARE-HF

AIMS

Cardiac resynchronization therapy (CRT) reduces morbidity and mortality for patients with heart failure, reduced left ventricular ejection fraction, QRS duration >130 ms and in sinus rhythm. The aim of this study was to identify patient characteristics that predict the effect, specifically, of CRT pacemakers (CRT-P) on all-cause mortality or the composite of hospitalization for heart failure or all-cause mortality.

METHODS AND RESULTS

We conducted an individual patient data meta-analysis of the Comparison of Medical Therapy, Pacing, and Defibrillation in Heart Failure (COMPANION) and Cardiac Resynchronization-Heart Failure (CARE-HF) trials. Only patients assigned to CRT-P or control (n = 1738) were included in order to avoid confounding from concomitant defibrillator therapy. The influence of baseline characteristics on treatment effects was investigated. Median age was 67 (59-73) years, most patients were men (70%), 68% had a QRS duration of 150-199 ms and 80% had left bundle branch block. Patients assigned to CRT-P had lower rates for all-cause mortality (hazard ratio [HR] 0.68, 95% confidence interval [CI] 0.56-0.81; p < 0.0001) and the composite outcome (HR 0.67, 95% CI 0.58-0.78; p < 0.0001). No pre-specified characteristic, including sex, aetiology of ventricular dysfunction, QRS duration (within the studied range) or morphology or PR interval significantly influenced the effect of CRT-P on all-cause mortality or the composite outcome. However, CRT-P had a greater effect on the composite outcome for patients with lower body surface area and those prescribed beta-blockers.

CONCLUSIONS

Cardiac resynchronization therapy-pacemaker reduces morbidity and mortality in appropriately selected patients with heart failure. Benefits may be greater in smaller patients and in those receiving beta-blockers. Neither QRS duration nor morphology independently predicted the benefit of CRT-P.

CLINICAL TRIAL REGISTRATION

COMPANION, NCT00180258; CARE-HF, NCT00170300.

Bilateral Bundle Branch Block

Left bundle branch block (LBBB) and right bundle branch block (RBBB) are classic manifestations of bundle branch conduction disorders. However, a third form that is uncommon and underrecognized may exist that has features and pathophysiology of both: bilateral bundle branch block (BBBB). This unusual form of bundle branch block exhibits an RBBB pattern in lead V1 (terminal R wave) and an LBBB pattern in leads I and aVL (absence of S wave). This unique conduction disorder may confer an increased risk of adverse cardiovascular events. BBBB patients may be a subset of patients that respond well to cardiac resynchronization therapy.

Right bundle branch block and risk of cardiovascular mortality: the Ibaraki Prefectural Health Study

Historically, a right bundle branch block has been considered a benign finding in asymptomatic individuals. However, this conclusion is based on a few old studies with small sample sizes. We examined the association between a complete right bundle branch block (CRBBB) and subsequent cardiovascular mortality in the general population in Japan. In this large community-based cohort study, data of 90,022 individuals (mean age, 58.5 ± 10.2 years; 66.2% women) who participated in annual community-based health check-ups were assessed. Subjects were followed up from 1993 to the end of 2016. Cox proportional hazards' models and log-rank tests were used for the data analysis. CRBBB was documented in 1,344 participants (1.5%). Among all included participants, CRBBB was associated with an increased risk of cardiovascular mortality after adjustment for all potential confounders (hazard ratio [HR] 1.21; 95% confidence interval [CI] 1.06-1.38). The increased risk of cardiovascular mortality was particularly evident in women aged < 65 years (HR 2.00; 95% CI 1.34-2.98) and men aged ≥ 65 years (HR 1.28; 95% CI 1.06-1.55). CRBBB is associated with an increased risk of cardiovascular mortality in women aged < 65 years and men aged ≥ 65 years. Clinicians should be aware of the presence of CRBBB in young women and elderly men, even if they exhibit no symptoms.

Right ventricular dilatation and systolic dysfunction and relationship to QRS duration in patients with left bundle branch block and cardiomyopathy

BACKGROUND

Marked QRS widening in patients with left bundle branch block (LBBB) may reduce efficacy of cardiac resynchronization therapy (CRT). We hypothesized that extreme QRS prolongation may accompany right ventricular (RV) dilatation/systolic dysfunction (RVD/RVsD) as well as left ventricular dilatation/systolic dysfunction (LVD/LVsD).

METHODS

We assessed rates of both ventricular dilatation and systolic dysfunction according to widening of QRS duration (QRSd) in 100 consecutive cardiomyopathy patients with true LBBB (QRSd ≥ 130 ms in female or ≥140 ms in male, QS or rS in leads V1/V2, and mid-QRS notching/slurring in ≥2 contiguous leads of I, aVL, and V1/V2/V5/V6). Ventricular dimensions and function were measured by cardiac magnetic resonance imaging.

RESULTS

There was a trend toward an increase in the prevalence of LVD (13%, 20%, and 90%), LVsD (67%, 77%, and 90%), RVD (23%, 27%, and 50%), RVsD (27%, 27%, and 40%), RVD plus RVsD (13%, 17%, and 40%), or RVD/RVsD (37%, 37%, and 50%) according to the degree of QRS prolongation (<150 ms, n = 30; 150-180 ms, n = 60; and ≥180 ms, n = 10). Similarly, patients in the highest quartile of QRSd (QRSd ≥ 168 ms, n = 26) showed greater rates of RVD (23% vs. 44%, p = .069), RVsD (22% vs. 48%, p = .032), RVD plus RVsD (10% vs. 30%, p = .040), or RVD/RVsD (33% vs. 57%, p = .050) compared to those in the remaining quartiles (n = 74). QRSd ≥ 180 ms was identified as an independent predictor for the presence of RVD plus RVsD.

CONCLUSION

The rates of RVD and/or RVsD increased with QRS widening, particularly when QRSd exceeded 180 ms. This may diminish anticipated CRT response rates in cardiomyopathy patients with LBBB.

Current Role of Echocardiography in Cardiac Resynchronization Therapy: from Cardiac Mechanics to Flow Dynamics Analysis

PURPOSE OF REVIEW

The aim of this review is to summarily explain what LV synchrony, coordination, myocardial work, and flow dynamics are, trying to clarify their advantages and limitations in the treatment of heart failure patients undergoing or with implanted cardiac resynchronization therapy (CRT).

RECENT FINDINGS

CRT is an established treatment for patients with heart failure and left ventricular systolic dysfunction. In the current guidelines, CRT implant indications rely only on electrical dyssynchrony, but in the last years, many aspects of cardiac mechanics (including contractile synchrony, coordination, propagation, and myocardial work) and flow dynamics have been studied using echocardiographic techniques to better characterize patients undergoing or with implanted CRT. However, the concepts, limits, and potential applications of all these echocardiographic evaluations are unclear to most clinicians. The use of left ventricular dyssynchrony and discoordination indices may help to identify those significant mechanical alterations whose correction may increase the probability of a favorable CRT response. Assessment of myocardial work and intracardiac flow dynamics may overcome some limitations of the conventional evaluation of cardiac mechanics but more investigations are needed before extensive clinical application.

<p>Left Ventricular Contraction Sequence in a Case Where the QRS Changed from Left to Atypical Right Bundle Branch Block</p>

A subgroup of right bundle branch block (RBBB) patients may exhibit a significant left ventricular (LV) activation delay. We evaluated echocardiography in a non-ischemic heart failure patient whose QRS morphology changed from left bundle branch block (LBBB) to atypical RBBB. The septum to posterior wall motion delay (SPWMD) measured using the M-mode was 196 ms while the patient presented with LBBB but decreased to 32 ms after the morphology changed to RBBB. These changes were also associated with delayed appearance of the septal displacement peak. Speckle tracking longitudinal strain was evaluated using three standard apical views after the morphology changed to RBBB. The LV contraction initially appeared in the basal inferior wall and there was delayed anterior wall contraction. The LV contraction pattern in our patient changed when the QRS morphology changed to atypical RBBB. A specific LV contraction sequence observed in atypical RBBB may reflect a significant LV activation delay between the inferior and anterior wall.

The Emerging Role of Cardiac Conduction System Pacing as a Treatment for Heart Failure

PURPOSE OF REVIEW

The aim of cardiac resynchronization therapy (CRT) is to improve cardiac function by delivering more physiological cardiac activation to patients with heart failure and conduction abnormalities. Biventricular pacing (BVP) is the most commonly used method for delivering CRT; it has been shown in large randomized controlled trials to significantly improve morbidity and mortality in patients with heart failure. However, BVP delivers only modest reductions in ventricular activation time and is only beneficial in patients with prolonged QRS duration. In this review, we explore conduction system pacing as a method for delivering more effective ventricular resynchronization and to extend pacing therapy for heart failure to patients without left bundle branch block (LBBB).

RECENT FINDINGS

The aim of conduction system pacing is to provide physiological ventricular activation by directly stimulating the conduction system. Current modalities include His bundle and left conduction system pacing. His bundle pacing is the most established method; it has the potential to correct left bundle branch block and deliver more effective ventricular resynchronization than BVP. This translates into greater acute haemodynamic improvements and observational data suggests that His-CRT results in improvements in cardiac function and symptoms. AV-optimized His bundle pacing is being investigated in patients with heart failure and long PR interval without LBBB, to see if this improves exercise capacity. More recently, a technique for pacing the left bundle branch has been developed. Early studies show potential advantages including low and stable capture thresholds. Conduction system pacing can deliver more effective ventricular resynchronization than BVP, which has the potential to deliver greater improvements in cardiac function. It may also provide the opportunity to extend pacing therapy for heart failure to patients who do not have LBBB. Further data is required from randomized trials to assess these promising pacing techniques.

The ECG Belt for CRT response trial: Design and clinical protocol

The ECG Belt for CRT response trial is designed to test the hypothesis that in patients traditionally less likely to respond to cardiac resynchronization therapy (CRT), an individualized approach utilizing the electrocardiogram (ECG) Belt to guide lead placement, vector selection, and device programming is superior to current standard of care. The ECG Belt is a noninvasive mapping technology designed to measure beat by beat electrical activation of the left ventricle by utilizing unipolar measurements from multiple ECG electrodes on the body surface. The ECG Belt for CRT response trial is a multicenter, prospective, randomized, investigational pre-market research study conducted at 48 centers in the United States, Canada, and Europe and will randomize approximately 400 subjects. The trial has three arms (enrollment will be 2:1:1, respectively): utilization of the Belt to guide implant as well as postimplant programming, utilizing the Belt to guide postimplant programming alone, and a non-Belt control arm. AdaptivCRT will be an option in the treatment arm but not the control arms. The primary endpoint is change in left ventricular end-systolic volume between preimplant and at 6 months. This paper describes the design and analytic plan for the trial.

Sex differences in left ventricular electrical dyssynchrony and outcomes with cardiac resynchronization therapy

Background

Women seem to derive more benefit from cardiac resynchronization therapy (CRT) than men, even after accounting for the higher burden of risk factors for nonresponse often observed in men.

Objective

To assess for sex-specific differences in left ventricular (LV) electrical dyssynchrony as a contributing electrophysiological explanation for the greater degree of CRT benefit among women.

Methods

We compared the extent of baseline LV electrical dyssynchrony, as measured by the QRS area (QRSA), among men and women with left bundle branch block (LBBB) undergoing CRT at Duke University (n = 492, 35% women) overall and in relation to baseline QRS characteristics using independent sample t tests and Pearson correlation coefficients. Cox regression analyses were used to relate sex, QRSA, and QRS characteristics to the risk of cardiac transplantation, LV assist device implant, or death.

Results

Although the mean QRS duration (QRSd) did not differ by sex, QRSA was greater for women vs men (113.8 μVs vs 98.2 μVs, P < .001), owing to differences in the QRSd <150 ms subgroup (92.3 ± 28.7 μVs vs 67.6 ± 26.2 μVs, P < .001). Among those with nonstrict LBBB, mean QRSd was similar but QRSA was significantly greater among women than men (96.0 ± 25.0 μVs vs 63.6 ± 26.2 μVs, P < .001). QRSA was similar among men and women with strict LBBB (P = .533). Female sex was associated with better long-term outcomes in an unadjusted model (hazard ratio 0.623, confidence interval 0.454–0.857, P = .004) but sex no longer predicted outcomes after accounting for differences in QRSA.

Conclusions

Our study suggests that sex-specific differences in LV dyssynchrony contribute to greater CRT benefit among women. Standard QRSd and morphology assessments seem to underestimate the extent of LV electrical dyssynchrony among women with LBBB.

Interrelationships between interventricular electrical delays in cardiac resynchronization therapy

INTRODUCTION

In cardiac resynchronization therapy, pacing the left ventricle (LV) at sites of prolonged electrical delay is associated with better outcomes. We sought to characterize the interrelationships between intrinsic, right-ventricular (RV)-paced, and LV-paced interventricular delays.

METHODS AND RESULTS

The following electrical timings were measured at implantation for all electrodes of the LV quadripolar leads: QLV, interventricular delay in intrinsic rhythm (RVs-LVs), in RV-paced rhythm (RVp-LVs), and in LV-paced rhythm (LVp-RVs). We included 32 patients (78% men, age 72 years, LV ejection fraction 29%, left bundle branch block 84%). QLV and RVs-LVs were correlated (R²  = .72, p < .0001), as were RVs-LVs and RVp-LVs (R²  = .27, p = .002) and RVp-LVs and LVp-RVs (R²  = .60, p < .001). Direction of activation along the four LV lead electrodes was concordant between RVs-LVs and RVp-LVs in only 17 (53%) patients. The latest-activated electrodes in RVs-LVs and RVp-LVs were concordant in 26 (81%) patients, adjacent in 3 (9%) patients, and remote in 3 (9%) patients. Biventricular-paced QRS duration varied by more than 10 ms between the two electrodes in half of the patients with dissimilar latest electrodes. Among the seven echocardiographic nonresponders at 6 months, the programmed electrode was remote from the latest electrode in RVs-LVs in five patients and in RVp-LVs in three patients.

CONCLUSION

Intrinsic and RV-paced interventricular electrical delays are correlated, but there is substantial heterogeneity between patients. The latest-activated electrode may be different between RVs-LVs and RVp-LVs, and this might have important implications in selecting the optimal LV vector.

Electrical and mechanical dyssynchrony in patients with right bundle branch block

BACKGROUND

Though fairly benign reputation, the right bundle branch block (RBBB) can cause left ventricular mechanical dyssynchrony (LVMD). Still, the relationship between electrical disturbance and LVMD is partly unclear among these patients.

METHODS

Thirty patients with RBBB and 60 matching controls were studied with vector electrocardiography and myocardial perfusion imaging phase analysis. RBBB group was divided into those with and those without LVMD.

RESULTS

Prevalence of LVMD among RBBB patients was 50% and among controls 22%. Odds ratio (OR) for LVMD in patients with RBBB vs controls without RBBB was 3.6 (95% CI 1.4 to 9.3). Ejection fraction (EF), end-systolic volume, the angle between QRS and T vectors, and the QRS angle in the sagittal plane were significantly different between RBBB patients with and without LVMD. The QRS duration was comparable in these groups. EF associated independently with LVMD, explaining 60% of its variation. A cut-off value of EF ≤ 55% detected LVMD in 100% specificity (sensitivity of 47%).

CONCLUSION

Half of the patients with RBBB had LVMD. The OR for LVMD between RBBB and normal ECG was 3.6. It seems that EF, rather than electrical parameters, is the main determinant of LVMD. This information might be useful when evaluating indications for cardiac resynchronization therapy.

Indications of Cardiac Resynchronization in Non-Left Bundle Branch Block: Clinical Review of Available Evidence

Cardiac resynchronization therapy (CRT) benefits have been firmly established in patients with heart failure and reduced left ventricular ejection fraction (HFrEF), who remain in New York Heart Association (NYHA) functional classes II and III, despite optimal medical therapy, and have a wide QRS complex. An important and consistent finding in published systematic reviews and in subgroup analyses is that the benefits of CRT are maximum for patients with a broader QRS durations, typically described as QRS duration > 150 ms, and for patients with a typical left bundle branch block (LBBB) QRS morphology. It remains uncertain whether patients with non-LBBB QRS complex morphology clearly benefit from CRT or only modestly respond.

Understanding non-response to cardiac resynchronisation therapy: common problems and potential solutions

Heart failure is a complex clinical syndrome associated with a significant morbidity and mortality burden. Reductions in left ventricular (LV) function trigger adaptive mechanisms, leading to structural changes within the LV and the potential development of dyssynchronous ventricular activation. This is the substrate targeted during cardiac resynchronisation therapy (CRT); however, around 30-50% of patients do not experience benefit from this treatment. Non-response occurs as a result of pre-implant, peri-implant and post implant factors but the technical constraints of traditional, transvenous epicardial CRT mean they can be challenging to overcome. In an effort to improve response, novel alternative methods of CRT delivery have been developed and of these endocardial pacing, where the LV is stimulated from inside the LV cavity, appears the most promising.

Clinical Influence and Predictors of Pacing-Induced Mechanical Asynchrony in Patients with Normal Cardiac Function with Ventricular Lead Placed in Non-Apical Position

Right ventricular apical (RVA) pacing often causes left ventricular (LV) mechanical asynchrony, which is enhanced by impaired cardiac contraction and intrinsic conduction abnormality. However, data on patients with normal cardiac function and under RV non-apical (non-RVA) pacing are limited.We retrospectively investigated 97 consecutive patients with normal ejection fraction who received pacemaker implantation for atrioventricular block with the ventricular lead placed in a non-RVA position. We defined mechanical asynchrony as discoordinate contraction between opposing regions of the LV wall evaluated by echocardiography. Asynchrony was detected in 9 (9%) patients at baseline and in 38 (39%) under non-RVA pacing (P < 0.001). Asynchrony at baseline was significantly associated with complete left bundle branch block (CLBBB) [odds ratio (OR) = 20.8, P < 0.001]. Asynchrony under non-RVA pacing was significantly associated with left anterior fascicular block (LAFB) (OR = 7.14, P < 0.001) and CLBBB (OR = 13.3, P = 0.002) at baseline. New occurrence of asynchrony was significantly associated with LAFB at baseline (OR = 5.88, P = 0.001). During a median follow-up period of 4.8 years, the incidence of device-detected atrial fibrillation (AF) was more frequent in patients who developed asynchrony than in those who did not (53.3% versus 27.5%, hazard ratio = 2.17, 95% confidence interval = 1.02-4.61, P = 0.03).In patients with normal cardiac function, LAFB at baseline was significantly associated with new occurrence of mechanical asynchrony under non-RVA pacing. Abnormal contraction had a significant influence on the incidence of device-detected AF.

Rationale and design for ENHANCE CRT: QLV implant strategy for non-left bundle branch block patients

AIMS

Historically, cardiac resynchronization therapy (CRT) response in non-left bundle branch block (non-LBBB) patients has been suboptimal in comparison with that observed in left bundle branch block patients. The electrical activation pattern of the left ventricle (LV) is different between these two QRS morphologies. Small non-randomized studies have suggested that targeting the LV wall with greatest electrical delay may be superior to conventional anatomical pacing from the lateral wall in non-LBBB patients. This article outlines the design and rationale of a prospective, randomized, pilot study, which assesses the effect of a non-traditional LV lead implant strategy on the clinical composite score after 12 months of follow-up in a non-LBBB patient population.

METHODS

All patients will receive an Abbott quadripolar CRT-D system (Quartet 1458Q LV lead with Unify Quadra™, Quadra Assura™ CRT-D or any market-approved CRT-D device with quadripolar pacing capabilities). Patients will be randomized in a 2:1 ratio between a QLV-based implant strategy vs. standard of care. Up to 250 patients will be enrolled in the study.

CONCLUSIONS

If the primary endpoint is achieved, this study will provide important information about reducing the non-responder rate in non-LBBB patients and provide further evidence for the QLV-based implant strategy.

Optimizing Cardiac Resynchronization Therapy: an Update on New Insights and Advancements

PURPOSE OF REVIEW

This review focuses on the current advancements in optimizing patient response to cardiac resynchronization therapy (CRT).

RECENT FINDINGS

It has been well known that not every patient will derive benefit from CRT, and of those that do, there are varying levels of response. Optimizing CRT begins well before device implant and involves appropriate patient selection and an understanding of the underlying substrate. After implant, there are different CRT device programming options that can be enabled to help overcome barriers as to why a patient may not respond. Given the multifaceted components of optimizing CRT and the complex patient population, multi-subspecialty clinics have been developed bringing together specialists in heart failure, electrophysiology, and imaging. Data as to whether this results in better response rates and outcomes shows promise.

The electromechanical substrate for response to cardiac resynchronization therapy in patients with right bundle branch block

BACKGROUND

Some patients with RBBB may respond to cardiac resynchronization therapy (CRT). However, little is known regarding the electromechanical substrate for CRT and whether this is the optimal pacing strategy.

METHODS

This was a pilot prospective double crossover randomized controlled clinical study comparing ventricular back up pacing (VVI-40), RV fusion pacing (DDD-40, RV only), and biventricular (BIV) pacing (DDD-40 BIV) in nine patients with RBBB and depressed EF. The study compared the frequency of dyssynchrony on baseline echocardiogram in patients with RBBB (n = 4), RBBB + anterior MI (RBBB with left axis deviation + left ventricular (LV) anterior wall thinning, n = 3), and RBBB + LAFB (RBBB with left axis deviation without LV anterior wall thinning n = 2). Echocardiographic assessment of LV dyssynchrony, LV size, and LV function was repeated after 6 months in each pacing mode.

RESULTS

Patients with RBBB + LAFB demonstrated baseline echocardiographic dyssynchrony between the LV anterior and inferior wall. Both DDD-40 RV-only pacing and DDD-40 BIV pacing resulted in improved LV function and clinical status compared to VVI-40 back up pacing. Patients with RBBB alone and RBBB with anterior MI had no baseline dyssynchrony and CRT using either RV only or BIV pacing resulted in LV dilation, worsened left ventricular ejection fraction and worsened clinical status compared to VVI-40 back up pacing.

CONCLUSION

Patients with RBBB, left axis deviation, and no prior anterior MI may have LV dyssynchrony between the anterior and inferior walls that is correctable with CRT.

Non-invasive, model-based measures of ventricular electrical dyssynchrony for predicting CRT outcomes

AIMS

Left ventricular activation delay due to left bundle branch block (LBBB) is an important determinant of the severity of dyssynchronous heart failure (DHF). We investigated whether patient-specific computational models constructed from non-invasive measurements can provide measures of baseline dyssynchrony and its reduction after CRT that may explain the degree of long-term reverse ventricular remodelling.

METHODS AND RESULTS

LV end-systolic volume reduction (ΔESV_LV) measured by 2D trans-thoracic echocardiography in eight patients following 6 months of CRT was significantly (P < 0.05) greater in responders (26 ± 20%, n = 4) than non-responders (11 ± 16%, n = 4). LV reverse remodelling did not correlate with baseline QRS duration or its change after biventricular pacing, but did correlate with baseline LV endocardial activation measured by electroanatomic mapping (R²=0.71, P < 0.01). Patient-specific models of LBBB ventricular activation with parameters obtained by matching model-computed vectorcardiograms (VCG) to those derived from standard patient ECGs yielded LV endocardial activation times that correlated well with those measured from endocardial maps (R²=0.90). Model-computed 3D LV activation times correlated strongly with the reduction in LVESV (R²=0.93, P < 0.001). Computed decreases due to simulated CRT in the time delay between LV septal and lateral activation correlated strongly with ΔESV_LV (R²=0.92, P < 0.001). Models also suggested that optimizing VV delays may improve resynchronization by this measure of activation delay.

CONCLUSIONS

Patient-specific computational models constructed from non-invasive measurements can compute estimates of LV dyssynchrony and their changes after CRT that may be as good as or better than electroanatomic mapping for predicting long-term reverse remodelling.

Bridging the gap between heart failure and the device clinic

INTRODUCTION

While cardiac resynchronization therapy (CRT) is a mainstay in the management of selected patients with chronic systolic dysfunction, many patients are noted to experience less than expected or no benefit at all from the therapy. Multidisciplinary care has been shown to provide benefit in follow up for patients receiving CRT devices. Areas covered: This review will focus on the apparent reasons behind less than optimal outcomes following CRT as well as multidisciplinary approaches to treating patients with CRT devices. The literature review focused mainly on the data behind multidisciplinary care of CRT patients. Expert commentary: A multidisciplinary approach incorporating input from various cardiology backgrounds is an important strategy in ensuring optimal outcomes in patients receiving CRT devices. Breaking down the 'silo' effect amongst cardiac subspecialties is vital in achieving high level multidisciplinary care.

Association between right ventricular systolic function and electromechanical delay in patients with right bundle branch block

BACKGROUND

Elevated right ventricle (RV) pressure and/or volume can place stress on the right bundle branch block (RBBB) and its associated Purkinje network, which can affect its electrical properties, resulting in conduction delay or block. We hypothesized that prolonged R' wave duration in lead V1 would extend the later portion of the QRS complex and can act as an indicator of reduced RV function in patients with RBBB.

METHOD

Kosin University Gospel Hospital echocardiography and electrocardiography (ECG) database was reviewed to identify patients with complete RBBB between 2013 and 2015. ECGs recorded closest to the time of the echocardiography were carefully reviewed, and QRS and R' wave duration were measured. RV systolic dysfunction was defined as an RV fractional area change (FAC) less than 35%, as indicated by echocardiography guidelines.

RESULTS

Compared to patients with normal RV function (n=241), patients with RV dysfunction (n=123) showed prolonged QRS duration (145.3±19.3ms vs. 132.2±13.4ms, p<0.001), predominantly due to R' prolongation (84.8±13.0ms vs. 102.9±12.0ms, p<0.001). R' duration was significantly associated with RV FAC (r=-0.609, p<0.001), RV systolic pressure (r=0.142, p=0.008), RV dimension (r=0.193, p<0.001), and RV myocardial performance index (r=0.199, p<0.001). On receiving operator characteristic curve analysis, V1 R' duration ≥93ms was associated with RV dysfunction with 90% sensitivity and 87% specificity (area under the curve: 0.883, 95% confidence interval=0.845-0.914, p<0.001).

CONCLUSION

Prolonged R' wave duration in lead V1 is an indicator of RV dysfunction and pressure and/or volume overload in patients with RBBB.

Cardiac Resynchronization Therapy and Implantable Cardioverter Defibrillator Therapy in Advanced Heart Failure

Patients with advanced heart failure are at high risk for progression of their disease and sudden cardiac death. The role of device therapy in this patient population continues to evolve and is directed toward improving cardiac pump function and/or reducing sudden arrhythmic death.

Effects of ventricular conduction block patterns on mortality in hospitalized patients with dilated cardiomyopathy: a single-center cohort study

BACKGROUND

Ventricular conduction blocks (VCBs) are associated with poor outcomes in patients with known cardiac diseases. However, the prognostic implications of VCB patterns in dilated cardiomyopathy (DCM) patients need to be evaluated. The purpose of this study was to determine all-cause mortality in patients with DCM and VCB.

METHODS

This cohort study included 1119 DCM patients with a median follow-up of 34.3 (19.5-60.8) months, patients were then divided into left bundle branch block (LBBB), right bundle branch block (RBBB), intraventricular conduction delays (IVCD) and narrow QRS groups. The all-cause mortality was assessed using Kaplan-Meier survival curves and Cox regression.

RESULTS

Of those 1119 patients, the all-cause mortality rates were highest in patients with IVCD (47.8, n = 32), intermediate in those with RBBB (32.9, n = 27) and LBBB (27.1 %, n = 60), and lowest in those with narrow QRS (19.9 %, n = 149). The all-cause mortality risk was significantly different between the VCB and narrow QRS group (log-rank χ2 = 51.564, P < 0.001). The presence of RBBB, IVCD, PASP ≥ 40 mmHg, left atrium diameter and NYHA functional class were independent predictors of all-cause mortality in DCM patients.

CONCLUSIONS

Our findings indicate that RBBB and IVCD at admission,but not LBBB, were independent predictors of all-cause mortality in patients with DCM.

Why QRS Duration Should Be Replaced by Better Measures of Electrical Activation to Improve Patient Selection for Cardiac Resynchronization Therapy

Cardiac resynchronization therapy (CRT) is a well-known treatment modality for patients with a reduced left ventricular ejection fraction accompanied by a ventricular conduction delay. However, a large proportion of patients does not benefit from this therapy. Better patient selection may importantly reduce the number of non-responders. Here, we review the strengths and weaknesses of the electrocardiogram (ECG) markers currently being used in guidelines for patient selection, e.g., QRS duration and morphology. We shed light on the current knowledge on the underlying electrical substrate and the mechanism of action of CRT. Finally, we discuss potentially better ECG-based biomarkers for CRT candidate selection, of which the vectorcardiogram may have high potential.

Evaluation of R-wave offset in the left chest leads for estimating the left ventricular activation delay: An evaluation based on coronary sinus electrograms and the 12-lead electrocardiogram

BACKGROUND

The QRS duration does not always reflect the left ventricular (LV) activation delay in patients with ventricular conduction disturbances. The R-wave offset in left chest leads may more closely reflect the LV activation delay than the QRS offset.

METHODS

We evaluated 138 cases with left bundle branch block (LBBB, n=11), right BBB (RBBB, n=38), non-specific intraventricular conduction disturbance (n=11), narrow QRS (<120ms, n=56) and right ventricular pacing (n=22). Cases with right axis deviation (120 to 270 degrees) were excluded. The intervals from the QRS onset to the V-waves in coronary sinus bipolar electrograms (QCS) were measured, and the longest interval was defined as the QCSmax. In the 12-lead electrocardiogram, the interval from the QRS onset to the R-wave offset (QR) was measured and then averaged in leads I-aVL, II-III-aVF, V1-V2, V3-V4 and V5-V6.

RESULTS

Significant correlations (p<0.05) were found between QCSmax and QR in I-aVL (r=0.83), II-III-aVF (r=0.51) and V5-V6 (r=0.86) in cases with a normal axis (0 to 90 degrees, n=64); and I-aVL (r=0.90), II-III-aVF (r=0.31) and V5-V6 (r=0.69) in cases with left axis deviation (-45 to -89 degrees, n=52). Overall, the QRS duration was also correlated with QCSmax (r=0.72, p<0.001); however, this correlation was weaker than the correlation between QCSmax and QR in I-aVL (r=0.89, p<0.001) due to disparities in RBBB (p<0.001).

CONCLUSIONS

The interval from the QRS onset to R-wave offset in the left chest leads reflects the degree of LV activation delay regardless of differences in QRS duration and morphology.

Right Bundle Branch Block and Electromechanical Coupling of the Right Ventricle: An Echocardiographic Study

Background:

A growing body of evidence suggests that the presence of a right bundle branch block (RBBB) is a negative prognostic indicator in patients with and without preexisting heart disease. Even though electromechanical activation of the right ventricle (RV) in patients with RBBB and pulmonary hypertension (PH) has been investigated; a direct comparison of the presence of RBBB, on the duration of RV mechanical systole using echocardiography has not been studied.

Materials and Methods:

In this retrospective study, we analyzed the echocardiograms of 40 patients by measuring the magnitude and timing of tricuspid annulus plane systolic excursion (TAPSE) and tricuspid annulus systolic velocity (TA S’). Patients were selected to form four groups of ten patients based on the presence or absence of RBBB and PH to determine if RBBB has any effect on the time-to-peak of TAPSE or TA S’, which for our purposes serves as a measure of duration of RV mechanical systole.

Results:

Our results demonstrate that RBBB leads to a measurable prolongation of TAPSE and TA S’ in patients without PH. Time-to-peak of TAPSE or TA S’ was not significantly prolonged in patients with PH.

Conclusions:

The results of this pilot study show that RV mechanical systole is prolonged in patients with RBBB, and the addition of PH attenuates this change. Additional prospective studies are now required to elucidate further the electrical and mechanical dyssynchrony that occurs as a result of RBBB, and how these new echocardiographic measurements can be applied clinically to risk stratify patients with RBBB and PH.

Septal flash and septal rebound stretch have different underlying mechanisms

Abnormal left-right motion of the interventricular septum in early systole, known as septal flash (SF), is frequently observed in patients with left bundle branch block (LBBB). Transseptal pressure gradient and early active septal contraction have been proposed as explanations for SF. Similarities in timing (early systole) and location (septum) suggest that SF may be related to septal systolic rebound stretch (SRSsept). We aimed to clarify the mechanisms generating SF and SRSsept. The CircAdapt computer model was used to isolate the effects of timing of activation of the left ventricular free wall (LVFW), right ventricular free wall (RVFW), and septum on SF and SRSsept. LVFW and septal activation times were varied by ±80 ms relative to RVFW activation time. M-mode-derived wall motions and septal strains were computed and used to quantify SF and SRSsept, respectively. SF depended on early activation of the RVFW relative to the LVFW. SF and SRSsept occurred in LBBB-like simulations and against a rising transseptal pressure gradient. When the septum was activated before both LVFW and RVFW, no SF occurred despite the presence of SRSsept. Computer simulations therefore indicate that SF and SRSsept have different underlying mechanisms, even though both can occur in LBBB. The mechanism of leftward motion during SF is early RVFW contraction pulling on and straightening the septum when unopposed by the LVFW. SRSsept is caused by late LVFW contraction following early contraction of the septum. Changes in transseptal pressure gradient are not the main cause of SF in LBBB.