Implications of left bundle branch block in patient treatment

Beyond conduction impairment: Unveiling the profound myocardial injury in left bundle branch block

BACKGROUND

Left bundle branch block (LBBB) represents a frequently encountered conduction system disorder. Despite its widespread occurrence, a continual dilemma persists regarding its intricate association with underlying cardiomyopathy and its pivotal role in the initiation of dilated cardiomyopathy. The pathologic alterations linked to LBBB-induced cardiomyopathy (LBBB-CM) have remained elusive.

OBJECTIVE

This study sought to investigate the chronologic dynamics of LBBB to left ventricular dysfunction and the pathologic mechanism of LBBB-CM.

METHODS

LBBB model was established through main left bundle branch trunk ablation in 14 canines. All LBBB dogs underwent transesophageal echocardiography and electrocardiography before ablation and at 1 month, 3 months, 6 months, and 12 months after LBBB induction. Single-photon emission computed tomography imaging was performed at 12 months. We then harvested the heart from all LBBB dogs and 14 healthy adult dogs as normal controls for anatomic observation, Purkinje fiber staining, histologic staining, and connexin43 protein expression quantitation.

RESULTS

LBBB induction caused significant fibrotic changes in the endocardium and mid-myocardium. Purkinje fibers exhibited fatty degeneration, vacuolization, and fibrosis along with downregulated connexin43 protein expression. During a 12-month follow-up, left ventricular dysfunction progressively worsened, peaking at the end of the observation period. The association between myocardial dysfunction, hypoperfusion, and fibrosis was observed in the LBBB-afflicted canines.

CONCLUSION

LBBB may lead to profound myocardial injury beyond its conduction impairment effects. The temporal progression of left ventricular dysfunction and the pathologic alterations observed shed light on the complex relationship between LBBB and cardiomyopathy. These findings offer insights into potential mechanisms and clinical implications of LBBB-CM.

Predicting cardiovascular events in out-of-hospital patients presenting with atypical chest pain and complete left bundle branch block: role of CTA and echocardiographic Global Longitudinal Strain

Background

Out-of-hospital patients presenting with atypical chest pain and complete left bundle branch block (LBBB) have to be stratified for the presence of coronary artery disease and the risk of developing heart failure (HF). We investigated the prognostic role of coronary CT-angiography (CTA) and echocardiographic global longitudinal strain (GLS) in those patients in a mid-term follow-up.

Methods

Out-of-hospital patients with LBBB underwent echocardiography and a 64-slice CT angiography were evaluated retrospectively. Development of HF or a cardiovascular death were the events scheduled.

Results

Seventy-eight patients (32 female; mean age: 66.0 ± 10.4 years were enrolled. During a follow-up of 33 months (IQR: 17-77), one patient (1.5%) experienced a cardiovascular death, 14 patients (17.9%) required urgent outpatient visits due to acute decompensated HF (12 hospitalizations). Echocardiography showed a slightly reduced left ventricular ejection fraction (LVEF) (50.0% ± 9.8%) and GLS within the normal range (-16.2% ± 4.1%). CTA analysis showed coronary stenosis > 50% in 28 patients (35.9%). A high Agatston score (> 100) was observed in 29.5%. Notably, 25 patients (32.1%) were diagnosed with left main coronary artery disease and 15 patients (16.7%) underwent revascularization during the follow up. Significant associations were observed between events and LVEF (P = 0.001), diastolic dysfunction grade ≥ 2 (P = 0.02), GLS (P < 0.001), multiple coronary stenosis (P = 0.04) and Agatston score (P = 0.05). Multivariate analysis confirmed the relationships with LVEF (R2 = 0.89, P < 0.001), diastolic dysfunction (R2 = 3.30, P = 0.04), GLS (R2 = 1.43, P < 0.001), and Agatston score (R2 = 1.01, P = 0.05).

Conclusions

In patients with complete LBBB, CTA and GLS identified those at a high risk of development HF.

Assessment of myocardial strain patterns in patients with left bundle branch block using cardiac magnetic resonance

Recently, a classification with four types of septal longitudinal strain patterns was described using echocardiography, suggesting a pathophysiological continuum of left bundle branch block (LBBB)-induced left ventricle (LV) remodeling. The aim of this study was to assess the feasibility of classifying these strain patterns using cardiovascular magnetic resonance (CMR), and to evaluate their association with LV remodeling and myocardial scar. Single center registry included LBBB patients with septal flash (SF) referred to CMR to assess the cause of LV systolic dysfunction. Semi-automated feature-tracking cardiac resonance (FT-CMR) was used to quantify myocardial strain and detect the four strain patterns. A total of 115 patients were studied (age 66 ± 11 years, 57% men, 28% with ischemic heart disease). In longitudinal strain analysis, 23 patients (20%) were classified in stage LBBB-1, 37 (32.1%) in LBBB-2, 25 (21.7%) in LBBB-3, and 30 (26%) in LBBB-4. Patients at higher stages had more prominent septal flash, higher LV volumes, lower LV ejection fraction, and lower absolute strain values (p < 0.05 for all). Late gadolinium enhancement (LGE) was found in 55% of the patients (n = 63). No differences were found between the strain patterns regarding the presence, distribution or location of LGE. Among patients with LBBB, there was a good association between strain patterns assessed by FT-CMR analysis and the degree of LV remodeling and LV dysfunction. This association seems to be independent from the presence and distribution of LGE.

Left Bundle Branch Block: Characterization, Definitions, and Recent Insights into Conduction System Physiology

Left bundle branch block (LBBB) is not just a simple electrocardiogram alteration. The intricacies of this general terminology go beyond simple conduction block. This review puts together current knowledge on the historical concept of LBBB, clinical significance, and recent insights into the pathophysiology of human LBBB. LBBB is an entity that affects patient diagnosis (primary conduction disease, secondary to underlying pathology or iatrogenic), treatment (cardiac resynchronization therapy or conduction system pacing for heart failure), and prognosis. Recruiting the left bundle branch with conduction system pacing depends on the complex interaction between anatomy, site of pathophysiology, and delivery tools.

[Left bundle branch block - dilated cardiomyopathy - heart failure: common links in the closed pathogenetic chain]

This review summarizes the available information on the epidemiology and prognosis of patients with left bundle branch block (LBBB), morphological alterations of the myocardium both resulting in and ensuing LBBB, cardiac biomechanics in LBBB, and possibilities of its correction.

Prevalence and incidence of intraventricular conduction disturbances among Chinese adults: Results from the Kailuan study

Objectives

Epidemiological data on intraventricular conduction disturbances (IVCDs) are limited in the Chinese population. We aimed to investigate the prevalence and incidence of different types of IVCDs among Chinese adults.

Methods

From June 2006 to October 2007, a total of 100,250 individuals from the Kailuan Study underwent electrocardiogram examinations. Follow-up visits were performed biennially. The prevalence and incidence of right bundle branch block (RBBB), incomplete RBBB (IRBBB), left bundle branch block (LBBB), incomplete LBBB, left anterior fascicular block (LAFB), left posterior fascicular block (LPFB) and non-specific IVCD (NIVCD) were calculated. Their association with risk factors and cardiovascular diseases was also investigated.

Results

The prevalence and incidence of all IVCDs were 3.19 and 1.70%, respectively. RBBB, IRBBB, and LAFB were the IVCD types that had the highest prevalence and incidence. The prevalence (3.67% vs. 1.29%; P &lt; 0.001) and incidence (1.93% vs. 0.84%; P &lt; 0.001) of IVCDs were higher among males than among females. The prevalence and incidence of most IVCD types increased with age. IRBBB, LBBB, and LAFB were significantly associated with hypertension. LBBB and NIVCD were associated with diabetes mellitus. In addition, LBBB and LAFB were related to prior myocardial infarction.

Conclusion

IVCDs differ in prevalence and incidence according to sex and age group. They also show disparate associations with other cardiovascular comorbidities. These differences need to be considered in daily clinical practice.

Left Bundle Branch Block: Characterization, Definitions, and Recent Insights into Conduction System Physiology

Left bundle branch block (LBBB) is not just a simple electrocardiogram alteration. The intricacies of this general terminology go beyond simple conduction block. This review puts together current knowledge on the historical concept of LBBB, clinical significance, and recent insights into the pathophysiology of human LBBB. LBBB is an entity that affects patient diagnosis (primary conduction disease, secondary to underlying pathology or iatrogenic), treatment (cardiac resynchronization therapy or conduction system pacing for heart failure), and prognosis. Recruiting the left bundle branch with conduction system pacing depends on the complex interaction between anatomy, site of pathophysiology, and delivery tools.

Severe myocardial ischemia in a patient with diabetes mellitus and left bundle branch block

We present the case of a 69-year-old woman with diabetes mellitus, left bundle branch block, and obesity who develops cardiogenic shock after undergoing myocardial perfusion imaging and diagnostic left heart catheterization, but prior to coronary revascularization. This case highlights the risk of cardiac decompensation awaiting surgery in patients with multivessel coronary artery disease. It also emphasizes the subtleties involved in imaging patients with diabetes mellitus and left bundle branch block, as well as the risk of developing complete heart block in the setting of ischemia with underlying conduction disease.

Cardiac Resynchronisation Therapy and Cellular Bioenergetics: Effects Beyond Chamber Mechanics

Cardiac resynchronisation therapy is a cornerstone in the treatment of advanced dyssynchronous heart failure. However, despite its widespread clinical application, precise mechanisms through which it exerts its beneficial effects remain elusive. Several studies have pointed to a metabolic component suggesting that, both in concert with alterations in chamber mechanics and independently of them, resynchronisation reverses detrimental changes to cellular metabolism, increasing energy efficiency and metabolic reserve. These actions could partially account for the existence of responders that improve functionally but not echocardiographically. This article will attempt to summarise key components of cardiomyocyte metabolism in health and heart failure, with a focus on the dyssynchronous variant. Both chamber mechanics-related and -unrelated pathways of resynchronisation effects on bioenergetics – stemming from the ultramicroscopic level – and a possible common underlying mechanism relating mechanosensing to metabolism through the cytoskeleton will be presented. Improved insights regarding the cellular and molecular effects of resynchronisation on bioenergetics will promote our understanding of non-response, optimal device programming and lead to better patient care.

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.

Adverse effects of left ventricular electrical dyssynchrony on cardiac reverse remodeling and prognosis after aortic valve surgery

BACKGROUND

Electrical dyssynchrony (ED) is one of the important contributing mechanisms in the progression of heart failure. We hypothesized that ED would interfere with cardiac reverse remodeling and affect prognosis after aortic valve surgery.

METHODS

A total of 411 consecutive patients (233 males, mean age 65±11 years) who underwent aortic valve surgery were retrospectively analyzed. The patients were divided into two groups according to the presence of ED [Group 1: no ED (n=382, 93%), Group 2: ED (n=29, 7%)]. ED was defined as either left ventricular bundle branch block, or electrical pacing rhythm. Cardiac reverse remodeling was assessed at 1 year after surgery by the changes in left ventricular ejection fraction (LVEF), LV end-systolic volume (LVESV), and left atrial volume index (LAVI). The primary endpoint was a composite of hospitalization for heart failure, and all-cause mortality.

RESULTS

At 1 year after surgery, group 2 showed lower LVEF (58±15% vs. 64±9%, p=0.044), and higher LAVI (42±18ml/m² vs. 33±13ml/m², p=0.018) than group 1. However, LVESV values (55±38ml vs. 42±24ml, p=0.076) were not significantly different. In particular, in patients with reduced preoperative LVEF, the LVEF was markedly increased in group 1 but not in group 2 after 1 year. During a median follow-up of 39 months, group 2 showed a worse clinical outcome than group 1 (20.7% vs. 7.6%, p=0.031). After adjusting for confounding factors in the multivariate analyses, age [hazard ratio (HR) 1.11, 95% confidence interval (CI) 1.06-1.16, p<0.001] and the presence of ED (HR 2.43, 95% CI 1.01-5.89, p=0.046) were found to be independent predictors of clinical outcomes.

CONCLUSIONS

ED after aortic valve surgery negatively affected cardiac remodeling and prognosis.

Contemporary Review of Left Bundle Branch Block in the Failing Heart - Pathogenesis, Prognosis, and Therapy

Cardiac resynchronisation therapy (CRT) is a cornerstone in the contemporary management of heart failure. The most effective way of predicting response to this therapy remains electrocardiographic (ECG) criteria of electromechanical dyssynchrony. The left bundle branch block (LBBB) pattern is currently the most robust ECG criterion in predicting improvement in symptoms and reduction in mortality. However, recent studies using three-dimensional (3D) mapping and cardiac magnetic resonance imaging (CMR) have demonstrated heterogeneous left ventricular activation patterns in patients with LBBB. This has led to intense debate on the activation pattern of "true LBBB" and resulted in the proposal of stricter criteria for defining LBBB. This review will focus on the definitions and implications of LBBB in the CRT era. At a minimum, the use of stricter ECG criteria appears warranted, and adjunctive pre-implant imaging or mapping may further identify patient-specific electrophysiological patterns that determine response to CRT.

Association of left bundle branch block with obstructive coronary artery disease on coronary CT angiography: a case-control study

AIMS

Left bundle branch block (LBBB) is considered an unfavourable prognostic marker in patients with underlying heart disease. Testing for coronary artery disease (CAD) is often prompted by incidental LBBB finding, but published studies disagree about a significant association between LBBB and CAD. We therefore assessed the association of LBBB with previously unknown CAD in patients undergoing coronary computed tomography angiography (CCTA).

METHODS AND RESULTS

We enrolled 818 patients (mean age 57.2 ± 11.1 years, 106 patients with presumably new LBBB and 712 controls) without known CAD who underwent 64-slice CCTA. Image quality was assessed for each coronary segment. Comparison of obstructive CAD prevalence (defined as ≥50% stenosis) was performed using triple case-matching for pre-test probability (based on age, gender, and symptom typicality) in 101 LBBB patients and 303 matched controls with diagnostic quality in all segments. We found no difference in obstructive CAD prevalence between LBBB patients and matched controls (15 vs. 16%, P = 0.88). Similarly, there were no significant differences in cardiovascular risk factors (CVRF), stenosis severity, CAD extent, non-obstructive CAD, and vessel-based analysis between patient groups. Image quality was very high in LBBB patients and comparable to controls. On multivariate analysis, age, gender, typical angina, and CVRF, but not LBBB (P = 0.94), emerged as significant and independent predictors of obstructive CAD.

CONCLUSION

CAD prevalence is similar in LBBB patients at low-to-moderate pre-test probability compared with controls with similar CVRF matched for age, gender, and symptom typicality. CCTA is a useful imaging modality in LBBB patients, providing comparable image quality to non-LBBB controls.

Modificación de los criterios de Sgarbossa para el diagnostico de infarto agudo de miocardio en presencia de bloqueo de rama izquierda

El bloqueo de rama izquierda dificulta el diagnostico de infarto agudo de miocardio.  Los criterios de Sgarbossa,  mencionados en las guías de manejo de las diferentes sociedades científicas, son útiles pero con limitaciones bien reconocidas.  Recientemente se ha publicado una modificación a estos  criterios que puede mejorar su rendimiento diagnostico  y así ser parte de un algoritmo de manejo de estos pacientes, aunque hasta el momento hagan falta estudios para validar lo anteriori

Genetic variation at the human connexin 43 locus but not at the connexin 40 locus is associated with left bundle branch block

Background

Bundle branch block (BBB) has been regarded as a disease of the conduction system, but occurs in mice lacking connexin 40 (expressed in atria, proximal conduction system) or connexin 43 (expressed in Purkinje cells, cardiomyocytes).

Objective

The aim of this paper is to explore whether BBB is heritable, and whether polymorphisms at connexin 40 and connexin 43 loci are associated with BBB.

Methods

To assess BBB heritability, we screened descendants of men with BBB in the population cohort ‘The Study of Men Born 1913’. DNA samples from 80-year-old men with extreme QRS-duration phenotypes were used to search for polymorphisms at connexin 40 and 43 loci. Associations between identified polymorphisms and BBB were evaluated in an independent cohort (INTERGENE).

Results

Seventy-seven men from ‘The Study of Men Born 1913’ with BBB had 116 descendants. Among the 76 participating descendants, 2 sons (6.4%) had BBB at 54 years of age. At the same age, 0.9% of men born in 1913 had BBB. We identified 6 single nucleotide polymorphisms (SNPs) in connexin 40 and 1 polymorphism in connexin 43. In the INTERGENE cohort, the connexin 43 polymorphism was associated with left BBB (LBBB) (4 of 35 LBBB vs 16 of 232 without BBB, χ²=7.4, p=0.03), but not with right BBB (RBBB) or overall BBB. None of the connexin 40 SNPs or haplotypes were associated with LBBB or RBBB.

Conclusions

These findings indicate that conduction by connexin 43 within the ventricular muscle distal to the specialised conduction system may be important for LBBB development.

The prognostic value of left ventricular mechanical dyssynchrony using gated myocardial perfusion imaging in patients with end-stage renal disease

BACKGROUND

Prior studies show that left ventricular mechanical dyssynchrony (LVD), measured by gated SPECT myocardial perfusion imaging (MPI), identifies patients with end-stage renal disease (ESRD) at higher risk for all-cause mortality but these were in small number of patients. We sought to assess the interaction between LVD and LV perfusion pattern in risk-stratification of a large sample size of patients with ESRD.

METHODS

From the renal transplantation database maintained at the University of Alabama at Birmingham, we identified consecutive patients with ESRD who had gated SPECT MPI between 2003 and 2007. MPIs were reprocessed to derive LV ejection fraction (EF), perfusion defect size, and LVD [phase bandwidth (BW) and phase standard deviation (SD)]. The primary end-point was all-cause mortality, which was prospectively collected and verified against the social security death index database.

RESULTS

There were 828 patients aged 52.6 ± 0.36 years (45% were women and 60% had diabetes mellitus). The LVEF was 54.8 ± 0.4% and the perfusion pattern was abnormal in 334 patients (41%). During a follow-up period of 61 ± 0.9 months, 230 patients (28%) received renal transplants and 290 patients (35%) died. The phase BW (73.1 ± 2.6° vs 66.3 ± 1.8°, P = .02) and SD (25.2 ± 0.8° vs 23.4 ± 0.5°, P = .06) were greater in patients who died than those who survived indicating greater dyssynchrony. Patients with phase BW >56° or SD ≥21° (median values) had worse 5-year survival (64% vs 72%, and 66% vs 71%, log-rank P = .005 and P = .07, respectively). After adjusting for demographics, co-morbidities, LVEF, and perfusion pattern, phase BW was associated with worse outcome (hazard ratio 1.289 95% CI 1.010-1.644, P = .04).

CONCLUSIONS

LVD by phase analysis of gated SPECT MPI provides prognostic value in ESRD beyond myocardial perfusion and EF.

Risk factors and outcomes associated with the development of myocardial ischemic events in patients who receive cardiac resynchronization therapy

There are limited data regarding risk factors for the development of ischemic events (IEs) among patients with ischemic cardiomyopathy (IC) who receive cardiac resynchronization therapy with a defibrillator (CRT-D) and their effect on the efficacy of the device. The present study population comprised 1,045 patients with IC enrolled in the Multicenter Automatic Defibrillator Implantation Trial-Cardiac Resynchronization Therapy. We used multivariate Cox proportional hazards regression modeling to identify risk factors for the development of IE (comprising hospitalization for acute coronary syndromes and/or coronary interventions during the trial) among study patients. Time-dependent analysis was performed to identify the effect of IE on the risk for subsequent heart failure (HF) or death in CRT-D recipients. Independent predictors for the development of IE among study patients included previous revascularization (coronary artery bypass surgery: hazard ratio [HR] 1.88, p = 0.003; percutaneous coronary intervention: HR 3.21, p <0.001) and increased systolic blood pressure (HR 1.67, p = 0.02), whereas a left bundle branch block pattern on the baseline electrocardiogram was associated with reduced risk for IE (HR 0.62, p = 0.02). Treatment with CRT-D did not have a significant effect on IE risk compared with defibrillator-only therapy (HR 0.87, p = 0.51). Time-dependent analysis showed that the development of IEs among CRT-D recipients was associated with more than twofold (p = 0.01) increased risk for subsequent heart failure or death. In conclusion, our data suggest that treatment with CRT-D does not reduce the risk of IE in patients with IC and that the benefit of CRT-D is attenuated after the development of IEs in this population.

The left bundle-branch block puzzle in the 2013 ST-elevation myocardial infarction guideline: from falsely declaring emergency to denying reperfusion in a high-risk population. Are the Sgarbossa Criteria ready for prime time?

Prompt and accurate identification of ST-elevation myocardial infarction (STEMI) in the presence of left bundle-branch block (LBBB) remains difficult. The 2004 STEMI guideline recommended emergent reperfusion therapy to patients with suspected ischemia and new or presumably new LBBB. These recommendations have led to frequent false catheterization laboratory activation and inappropriate fibrinolytic therapy because most patients with suspected ischemia and new or presumably new LBBB do not have acute coronary artery occlusion on angiography. The new 2013 STEMI guideline makes a drastic change by removing previous recommendations. Therefore, patients with suspected ischemia and new or presumably new LBBB would no longer be treated as STEMI equivalent. The new guideline fails to recognize that some patients with suspected ischemia and LBBB do have STEMI, and denying reperfusion therapy could be fatal. The Sgarbossa electrocardiography criteria are the most validated tool to aid in the diagnosis of STEMI in the presence of LBBB. A Sgarbossa score of ≥3 has a superb specificity (98%) and positive predictive value for acute myocardial infarction and angiography-confirmed acute coronary occlusion. Thus, we propose a diagnosis and triage algorithm incorporating the Sgarbossa criteria to quickly and accurately identify, among patients presenting with chest pain and new or presumably new LBBB, those with acute coronary artery occlusion. This is a high-risk population in which reperfusion therapy would be denied by the 2013 STEMI guideline. Our algorithm will also significantly reduce false catheterization laboratory activation and inappropriate fibrinolytic therapy, the inevitable consequence of the 2004 STEMI guideline.