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

Decreased Left Ventricular Systolic Function during the Late Phase after Response to Cardiac Resynchronization Therapy

BACKGROUND

Cardiac resynchronization therapy (CRT) improves cardiac function in patients with heart failure (HF) and dyssynchrony. However, a subset of responders develops a delayed decline in left ventricular (LV) systolic function, referred to as "delayed negative reverse remodeling (DNRR)."

OBJECTIVE

This study aimed to investigate the characteristics and prognosis of DNRR in CRT responders.

METHODS

A total of 203 patients undergoing CRT device implantation were analyzed. Among them, 100 responders were identified based on a ≥5% absolute LV ejection fraction (LVEF) increase and a ≥15% relative LV end-systolic volume (LVESV) reduction at 6 months post-CRT. DNRR was defined as a ≥5% absolute decrease in LVEF at 1 year after treatment response determination.

RESULTS

Of the responders, 22 (22.0%) exhibited DNRR, while 78 (78.0%) were classified as non-DNRR. The DNRR group showed a decline in LVEF from 41.2±8.3% to 32.7±9.6% (p<0.001), while the non-DNRR group showed improvement from 42.8±9.5% to 46.2±10.5% (p<0.001). Multivariate analysis identified LVESV ≥100 mL (odds ratio [OR]: 3.575, p=0.041), paced QRS duration ≥150 ms (OR: 4.427, p=0.023), synchronized LV pacing <85% (OR: 5.753, p=0.043) at 6 months post-CRT, and intraventricular conduction disturbance (OR: 5.593, p=0.018) as independent predictors of DNRR. The DNRR group had significantly worse outcomes, including cardiac death and HF-related hospitalization, compared to the non-DNRR group.

CONCLUSION

Despite an initial response to CRT, a subset of HF patients developed DNRR, which correlated with worse clinical outcomes. Identifying risk factors associated with DNRR may help optimize CRT management and improve long-term patient care.

Impact of Intraventricular Blocks on Cardiac Cycle Dynamics: An Echocardiographic and Vectorcardiographic Analysis

BACKGROUND

Left bundle branch block (LBBB) causes delays that alter the mechanics of the ventricular cycle. The effect of other intraventricular blocks (IVB) remains little explored.

OBJECTIVES

To study the phases of the cardiac cycle (CC) and ventricular synchrony in different ventricular activation patterns.

METHODS

Cross-sectional study with 328 consecutive individuals without structural heart disease, normal electrocardiogram or IVB, conducted in the period between August/2020 and January/2022. Echocardiogram and Vectorcardiogram were performed simultaneously to analyze the electromechanics of the CC. A one-way Analysis of Variance (ANOVA) with Bonferroni's multiple comparison test was used, with a significance level of 5%.

RESULTS

The age of the participants was 64.8±15.3 years, with 57.9% male and an ejection fraction of 67.0±6.8%. The electrocardiogram was normal for 32.3%, 18.6% had right bundle branch block (RBBB), 17.7% had left anterior fascicular block (LAFB), 15.6% had RBBB+LAFB, and 15.9% had LBBB. The echocardiogram showed an increased left ventricular pre-ejection by 18.7% (p<0.001) and 56.8% (p<0.001) in RBBB+LAFB and LBBB, respectively. There was a post-systolic myocardial contraction in all types of IVB and ventricular dyssynchrony in LBBB. Using the vectorcardiogram, initial activation of the R wave was increased by 17.4% in LAFB (p<0.001), 43.5% in RBBB+LAFB (p<0.001) and 47.4% in LBBB (p<0.001) and delayed final activation by 69.4% in LBBB (p<0.001), 73.6% in RBBB+LAFB (p<0.001) and 95.3% in RBBB (p<0.001).

CONCLUSION

All IVBs modified the CC; however, only LBBB and RBBB+LAFB significantly changed the left ventricular cycle, thereby evidencing the greater complexity of these disorders.

Cardiac Resynchronization Therapy and Left Atrial Remodeling: A Novel Insight?

Cardiac resynchronization therapy (CRT) restores ventricular dyssynchrony, improving left ventricle (LV) systolic function, symptoms, and outcome in patients with heart failure, systolic dysfunction, and prolonged QRS interval. The left atrium (LA) plays tremendous roles in maintaining cardiac function, being often inflicted in various cardiovascular diseases. LA remodeling implies structural-dilation, functional-altered phasic functions, and strain and electrical-atrial fibrillation remodeling. Until now, several important studies have approached the relationship between LA and CRT. LA volumes can predict responsiveness to CRT, being also associated with improved outcome in these patients. LA function and strain parameters have been shown to improve after CRT, especially in those who were positive responders to it. Further studies still need to be conducted to comprehensively characterize the impact of CRT on LA phasic function and strain, and, also, in conjunction with its impact on functional mitral regurgitation and LV diastolic dysfunction. The aim of this review was to provide an overview of current available data regarding the relation between CRT and LA remodeling.

Comparison between conduction system pacing and cardiac resynchronization therapy in right bundle branch block patients

A significant number of right bundle branch block (RBBB) patients receive cardiac resynchronization therapy (CRT), despite lack of evidence for benefit in this patient group. His bundle (HBP) and left bundle pacing (LBP) are novel CRT delivery methods, but their effect on RBBB remains understudied. We aim to compare pacing-induced electrical synchrony during conventional CRT, HBP, and LBP in RBBB patients with different conduction disturbances, and to investigate whether alternative ways of delivering LBP improve response to pacing. We simulated ventricular activation on twenty-four four-chamber heart geometries each including a His-Purkinje system with proximal right bundle branch block (RBBB). We simulated RBBB combined with left anterior and posterior fascicular blocks (LAFB and LPFB). Additionally, RBBB was simulated in the presence of slow conduction velocity (CV) in the myocardium, left ventricular (LV) or right ventricular (RV) His-Purkinje system, and whole His-Purkinje system. Electrical synchrony was measured by the shortest interval to activate 90% of the ventricles (BIVAT-90). Compared to baseline, HBP significantly improved activation times for RBBB alone (BIVAT-90: 66.9 ± 5.5 ms vs. 42.6 ± 3.8 ms, p < 0.01), with LAFB (69.5 ± 5.0 ms vs. 58.1 ± 6.2 ms, p < 0.01), with LPFB (81.8 ± 6.6 ms vs. 62.9 ± 6.2 ms, p < 0.01), with slow myocardial CV (119.4 ± 11.4 ms vs. 97.2 ± 10.0 ms, p < 0.01) or slow CV in the whole His-Purkinje system (102.3 ± 7.0 ms vs. 75.5 ± 5.2 ms, p < 0.01). LBP was only effective in RBBB cases if combined with anodal capture of the RV septum myocardium (BIVAT-90: 66.9 ± 5.5 ms vs. 48.2 ± 5.2 ms, p < 0.01). CRT significantly reduced activation times in RBBB in the presence of severely slow RV His-Purkinje CV (95.1 ± 7.9 ms vs. 84.3 ± 9.3 ms, p < 0.01) and LPFB (81.8 ± 6.6 ms vs. CRT: 72.9 ± 8.6 ms, p < 0.01). Both CRT and HBP were ineffective with severely slow CV in the LV His-Purkinje system. HBP is effective in RBBB patients with otherwise healthy myocardium and Purkinje system, while CRT and LBP are ineffective. Response to LBP improves when LBP is combined with RV septum anodal capture. CRT is better than HBP only in patients with severely slow CV in the RV His-Purkinje system, while CV slowing of the whole His-Purkinje system and the myocardium favor HBP over CRT.

Acute Hemodynamic Effects of Simultaneous and Sequential Multi-Point Pacing in Heart Failure Patients With an Expected Higher Rate of Sub-response to Cardiac Resynchronization Therapy: Results of Multicenter SYNSEQ Study

The aim of the SYNSEQ (Left Ventricular Synchronous vs. Sequential MultiSpot Pacing for CRT) study was to evaluate the acute hemodynamic response (AHR) of simultaneous (3P-MPP syn) or sequential (3P-MPP seq) multi-3-point-left-ventricular (LV) pacing vs. single point pacing (SPP) in a group of patients at risk of a suboptimal response to cardiac resynchronization therapy (CRT). Twenty five patients with myocardial scar or QRS ≤ 150 or the absence of LBBB (age: 66 ± 12 years, QRS: 159 ± 12 ms, NYHA class II/III, LVEF ≤ 35%) underwent acute hemodynamic assessment by LV + dP/dtmax with a variety of LV pacing configurations at an optimized AV delay. The change in LV + dP/dt max (%ΔLV + dP/dt max) with 3P-MPP syn (15.6%, 95% CI: 8.8%-22.5%) was neither statistically significantly different to 3P-MPP seq (11.8%, 95% CI: 7.6-16.0%) nor to SPP basal (11.5%, 95% CI:7.1-15.9%) or SPP mid (12.2%, 95% CI:7.9-16.5%), but higher than SPP apical (10.6%, 95% CI:5.3-15.9%, p = 0.03). AHR (defined as a %ΔLV + dP/dt max ≥ 10%) varied between pacing configurations: 36% (9/25) for SPP apical, 44% (11/25) for SPP basal, 54% (13/24) for SPP mid, 56% (14/25) for 3P-MPP syn and 48% (11/23) for 3P-MPP seq.Fifteen patients (15/25, 60%) had an AHR in at least one pacing configuration. AHR was observed in 10/13 (77%) patients with a LBBB but only in 5/12 (42%) patients with a non-LBBB (p = 0.11). To conclude, simultaneous or sequential multipoint pacing compared to single point pacing did not improve the acute hemodynamic effect in a suboptimal CRT response population.

Clinical Trial Registration

ClinicalTrials.gov, identifier: NCT02914457.

Preimplantation interlead ECG heterogeneity is superior to QRS complex duration in predicting mechanical super-response in patients with non-left bundle branch block receiving cardiac resynchronization therapy

BACKGROUND

Reliable quantitative preimplantation predictors of response to cardiac resynchronization therapy (CRT) are needed.

OBJECTIVE

We tested the utility of preimplantation R-wave and T-wave heterogeneity (RWH and TWH, respectively) compared to standard QRS complex duration in identifying mechanical super-responders to CRT and mortality risk.

METHODS

We analyzed resting 12-lead electrocardiographic recordings from all 155 patients who received CRT devices between 2006 and 2018 at our institution and met class I and IIA American College of Cardiology/American Heart Association/Heart Rhythm Society guidelines with echocardiograms before and after implantation. Super-responders (n=35, 23%) had ≥20% increase in left ventricular ejection fraction and/or ≥20% decrease in left ventricular end-systolic diameter and were compared with non-super-responders (n=120, 77%), who did not meet these criteria. RWH and TWH were measured using second central moment analysis.

RESULTS

Among patients with non-left bundle branch block (LBBB), preimplantation RWH was significantly lower in super-responders than in non-super-responders in 3 of 4 lead sets (P=.001 to P=.038) and TWH in 2 lead sets (both, P=.05), with the corresponding areas under the curve (RWH: 0.810-0.891, P<.001; TWH: 0.759-0.810, P≤.005). No differences were observed in the LBBB group. Preimplantation QRS complex duration also did not differ between super-responders and non-super-responders among patients with (P=.856) or without (P=.724) LBBB; the areas under the curve were nonsignificant (both, P=.69). RWH_V1-3LILII ≥ 420 μV predicted 3-year all-cause mortality in the entire cohort (P=.037), with a hazard ratio of 7.440 (95% confidence interval 1.015-54.527; P=.048); QRS complex duration ≥ 150 ms did not predict mortality (P=.27).

CONCLUSION

Preimplantation interlead electrocardiographic heterogeneity but not QRS complex duration predicts mechanical super-response to CRT in patients with non-LBBB.