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European Journal of Heart Failure 2007 9(5):510-517; doi:10.1016/j.ejheart.2006.11.006
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© 2007 European Society of Cardiology

Prevalence and prognostic impact of bundle branch block in patients with heart failure: Evidence from the CHARM programme

Nathaniel M. Hawkinsa,*, Duolao Wangb, John J.V. McMurrayc, Marc A. Pfefferd, Karl Swedberge, Christopher B. Grangerf, Salim Yusufg, Stuart J. Pocockb, Jan Östergrenh, Eric L. Michelsoni, Francis G. Dunna and CHARM Investigators and Committees

a Stobhill Hospital Glasgow, UK
b Medical Statistics Unit, London School of Hygiene and Tropical Medicine London, UK
c University of Glasgow Glasgow, UK
d Brigham and Women's Hospital Boston, MA, USA
e Sahlgrenska University Hospital/Östra Göteborg, Sweden
f Division of Cardiology, Duke University Medical Center Durham, NC, USA
g Hamilton Health Sciences and McMaster University Hamilton, ON, Canada
h Karolinska Hospital Stockholm, Sweden
i AstraZeneca LP Wilmington, DE, USA

* Corresponding author. Department of Cardiology, Stobhill Hospital, Balornock Road, Springburn, Glasgow, G21 3UW, UK. Tel.: +44 1412013064; fax: +44 1415585693.


   Abstract
Top
 Abstract
1. Introduction
 2. Methods
 3. Results
 4. Discussion
 Acknowledgments
 References
 
Background: Bundle branch block (BBB) is a powerful independent predictor of cardiovascular mortality in patients with heart failure (HF) and reduced left ventricular ejection fraction (LVEF). The prognostic implications in HF with preserved systolic function (HF–PSF) are less well understood.

Methods: The Candesartan in Heart failure: Assessment of Reduction in Mortality and morbidity (CHARM) programme randomised 7599 patients with symptomatic HF to receive candesartan or placebo. The primary outcome comprised cardiovascular death or HF hospitalisation. The relative risk conveyed by BBB relative to a normal electrocardiogram was examined.

Results: The prevalence of BBB was significantly lower in patients with preserved compared with reduced systolic function (CHARM-Preserved 14.4%, Alternative 29.6%, Added 30.5%), p<0.0001. Overall, the adjusted hazard ratio for the primary outcome was 1.48 (95% confidence interval 1.22–1.78), p<0.0001, reflecting increased risk in patients with reduced LVEF (1.72 [1.28–2.31], p=0.0003). The apparently more modest risk among patients with HF–PSF was significant in unadjusted (1.80 [1.37–2.37], p<0.0001) but not adjusted analysis (1.16 [0.88–1.54], p=0.2897). However, no formal statistical difference was observed between the two cohorts, and interpretation is limited by the unknown prevalence of left and right BBB morphologies in each. Comparing BBB presence with absence yielded qualitatively similar results.

Conclusion: The simple clinical finding of BBB is a powerful independent predictor of worse clinical outcomes in patients with HF and reduced LVEF. It is less frequent, with a more modest predictive effect, in patients with preserved systolic function.

Key Words: Heart failure • Left ventricular systolic dysfunction • Preserved systolic function • Candesartan • Electrocardiogram • Bundle branch block

Received November 11, 2005; Revised August 5, 2006; Accepted November 29, 2006


   1. Introduction
Top
 Abstract
 1. Introduction
2. Methods
 3. Results
 4. Discussion
 Acknowledgments
 References
 
Bundle branch block (BBB) on the electrocardiogram (ECG) is a powerful independent predictor of cardiovascular mortality in patients with heart failure (HF). [1] Electrical dispersion of ventricular depolarisation and conduction delay, as manifest by QRS prolongation, reflect severity of ventricular electrical, structural and mechanical dysfunction. [2] Reduced mortality in the recent Cardiac Resynchronization in Heart Failure (CARE-HF) study underscores the importance of QRS duration in selecting patients for cardiac resynchronization therapy (CRT). [3] Conflicting data exist regarding the prevalence of BBB, both in patients with left ventricular systolic dysfunction (LVSD) and in heart failure with preserved systolic function (HF-PSF). [4-6] Furthermore, independent predictors of BBB are poorly defined. While increased mortality associated with BBB is well documented in patients with LVSD, evidence regarding morbidity is limited. Furthermore, the prognostic implications of BBB in patients with HF-PSF are unknown. In the recent Candesartan in Heart failure Assessment of Reduction in Mortality and morbidity (CHARM) programme, candesartan significantly reduced cardiovascular deaths and hospital admissions for heart failure. [7] The CHARM programme provides a unique opportunity to examine BBB in a large cohort of patients with HF and wide range of left ventricular ejection fraction (LVEF). The aim of this study was to provide detailed information on the contemporary prevalence and prognostic implications of BBB in both the CHARM population as a whole and in patients with and without reduced LVEF.


   2. Methods
Top
 Abstract
 1. Introduction
 2. Methods
3. Results
 4. Discussion
 Acknowledgments
 References
 
Patients with symptomatic heart failure (New York Heart Association [NYHA] class II-IV) receiving standard therapy were enrolled into one of three parallel clinical trials according to LVEF and angiotensin converting enzyme inhibitor (ACEI) treatment: LVEF≤40% and not receiving an ACEI due to previous intolerance (CHARM-Alternative); LVEF≤40% receiving ACEI treatment (CHARM-Added); and LVEF >40% (CHARM-Preserved). There were 7599 patients randomised (with data), 3803 receiving candesartan and 3796 placebo: 2028 in CHARM-Alternative (1013 candesartan and 1015 placebo), 2548 in CHARM-Added (1276 candesartan and 1272 placebo), and 3023 in CHARM-Preserved (1514 candesartan and 1509 placebo). Details of the rationale, methods, exclusion criteria and main outcomes have been published previously. [7-12] The study was approved by local ethics committees in all participating centres and all patients provided written informed consent.

Investigators at each participating centre interpreted a baseline 12-lead ECG recorded in all patients and completed a structured report documenting electrocardiographic findings. Investigators categorised ECGs as normal or abnormal. Abnormal ECGs were further subdivided into one or more of the following categories (check "all that apply"): a) atrial fibrillation/flutter, b) BBB, c) paced rhythm, d) pathological Q waves, e) left ventricular hypertrophy and f) "other", investigator-specified, abnormalities. The definition of BBB rested with individual investigators. QRS duration and BBB morphology were not recorded.

The primary outcome was a composite of cardiovascular death or unplanned hospital admission for management of worsening HF. Secondary pre-specified endpoints and components included: cardiovascular death; hospital admission for HF; and composite of cardiovascular death, hospital admission for HF, non-fatal myocardial infarction, or non-fatal stroke. The present study focused on the associations between BBB and cardiovascular events in the cohorts with reduced (combined CHARM-Alternative/Added) and preserved (CHARM-Preserved) LV systolic function.

All data analyses were performed independently by the Medical Statistical Unit at the London School of Hygiene and Tropical Medicine, London, UK. Baseline characteristics of patients with BBB, other ECG abnormalities, and a normal ECG were summarised by mean (standard deviation) for continuous variables and by frequency (percentages) for categorical variables. Means were compared using the Student t-test and proportions compared using the chi-square test. All analyses were done by intention to treat. The prognostic significance of BBB was evaluated for predefined clinically relevant outcomes, including the primary outcome and other major cardiovascular events. In all Cox regression analyses, the ECG findings were categorised in two different ways: (1) three categories: BBB, other ECG abnormality and ECG normal; and (2) two categories: BBB presence and BBB absence. The relative risks (RR) and 95% confidence intervals (CI) associated with BBB compared to the normal ECG and the absence of BBB are therefore estimated.

The estimated hazard (risk) ratios (HR) were adjusted for all important predictors of mortality and morbidity identified in the CHARM programme, including age, sex, diabetes mellitus, NYHA class, rest dyspnoea, current cigarette smoking, previous hospitalisation for heart failure (none, within 6 months, ≥6 months), first diagnosis of heart failure over 2 years ago, previous myocardial infarction, atrial fibrillation, heart rate, diastolic blood pressure, dependent oedema, pulmonary crackles, cardiomegaly, pulmonary oedema, mitral regurgitation, and candesartan treatment, using a multivariate Cox proportional hazards model. A 2-tailed P value of less than 0.05 was considered statistically significant. Data from the two studies of patients with reduced LVEF were combined, as this group was pre-specified as clinically important. For combined analysis of the three trials, statistical heterogeneity tests were performed for each endpoint. To identify the independent predictors of BBB, a logistic regression model was employed with demographic and disease-related characteristics as potential predictors.


   3. Results
Top
 Abstract
 1. Introduction
 2. Methods
 3. Results
4. Discussion
 Acknowledgments
 References
 
3.1. Baseline characteristics
The findings from 7599 patients were analysed. The median duration of follow-up was 37.7 months. A detailed review of patients’ baseline characteristics has previously been published. [12] The baseline characteristics of patients with BBB, other ECG abnormalities, and a normal ECG are displayed in Table 1. 23.8% of study participants had BBB present on the baseline ECG. The prevalence was significantly lower in patients with preserved compared with reduced systolic function (Preserved 14.4%, Alternative 29.6%, Added 30.5%, p<0.0001). Paced rhythm was noted in 2.5% of patients with BBB and 8.6% of patients with other ECG abnormalities.


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  		Table 1 Baseline characteristics of patients with BBB

 
Dilated cardiomyopathy was more common in patients with BBB. Overall, and in the reduced and preserved systolic function groups, BBB was associated with greater disease severity when compared against other ECG abnormalities or a normal ECG. Ejection fraction was lower (33% vs 39% and 49% respectively, p<0.0001) and prevalence of cardiomegaly higher (28.3% vs 21.0% and 13.0% respectively, p<0.0001). Patients with BBB also had greater impairment of clinical status, as indicated by an increased prevalence of exertional dyspnoea, S3 gallop, pulmonary crepitations, and NYHA classification III to IV. Treatment more often included digoxin, spironolactone and diuretics. However, in all three trials patients with BBB were less likely to receive treatment with beta-blockers.

3.2. Independent predictors
Multivariate analysis for independent predictors of BBB revealed reduced LVEF to be the strongest determinant (per 10% decrease, odds ratio 1.49, p<0.0001), after adjusting for baseline variables (Table 2). The stepwise model included baseline patient demographics, aetiology of heart failure, and medical history. Black racial origin, previous MI or stroke, and atrial fibrillation were also independent predictors of BBB.


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  		Table 2 CHARM Overall: Independent predictors of BBB

 
3.3. Prognosis - overall
Bundle branch block was an independent predictor of worse prognosis in patients with heart failure (Table 3). Overall, the primary outcome of cardiovascular death or hospital admission for HF occurred more frequently in 771 of 1811 (42.6%) patients with BBB, compared with 139 of 748 (18.6%) patients with a normal ECG. The unadjusted hazard ratio (2.19 [1.82-2.64], p<0.0001) remained significant in multivariate analyses (1.48 [1.22-1.78], p<0.0001), after adjusting for additional predictors of cardiovascular risk.


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  		Table 3 Risk associated with BBB presence relative to the normal ECG

 
The adjusted hazard ratio for cardiovascular death (1.76 [1.34-2.30], p<0.0001) was somewhat greater than for HF hospitalisation (1.43 [1.15-1.78], p=0.0014). The relative hazard of sustaining a major cardiovascular event (defined as cardiovascular death, HF hospitalisation, non-fatal MI or non-fatal stroke) was 2.17 (p<0.0001), which remained significant in multivariate analyses (1.50 [1.26-1.79], p<0.0001), Fig. 1. BBB also increased the risk of both sudden death (2.14 [1.37-3.33], p=0.0008), and death due to progression of heart failure (2.17 [1.26-3.72], p=0.0049), the two major components of cardiovascular death.


Figure 01
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  		Fig. 1 CHARM Overall: covariate adjusted risk associated with BBB, BBB=bundle branch block, CV = cardiovascular, HF = heart failure, MI = myocardial infarction.

 
3.4. Prognosis - reduced vs preserved LV systolic function
In patients with reduced LV systolic function, presence of BBB increased adjusted risk of the primary (1.72 [1.28-2.31], p=0.0003) and all secondary outcomes. However, the increased risk of the primary outcome (1.16 [0.88-1.54], p=0.2897) among patients with preserved systolic function was not significant. Only the composite of major cardiovascular events (1.30 [1.00-1.68], p=0.0485) was significantly increased by presence of BBB.

Although the relative risk conferred by BBB appeared to differ between patients with reduced and preserved systolic function, this was not confirmed by formal statistical testing for an interaction (Table 3). In a similar analysis using LVEF as a continuous variable, the hazard associated with BBB was not modified by LVEF.

3.5. Prognosis — BBB present vs BBB absent
Bundle branch block was compared to the normal ECG due to the disparate nature and varying prognostic significance of the other ECG abnormalities, which included arrhythmias, pathological Q waves, paced rhythm and left ventricular hypertrophy. However, comparison of patients with and without BBB yielded similar results, though the associated risk was of lesser magnitude (Table 4). Presence of BBB increased adjusted risk of the primary (1.30 [1.17-1.43], p<0.0001) and all secondary outcomes in patients with reduced systolic function. However, the increased risk among patients with preserved systolic function was again not significant after multivariate adjustment.


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  		Table 4 Risk associated with BBB presence relative to BBB absence

 

   4. Discussion
Top
 Abstract
 1. Introduction
 2. Methods
 3. Results
 4. Discussion
Acknowledgments
 References
 
Few studies have described the prevalence of BBB in patients with heart failure, and fewer still have defined the prevalence in patients with reduced and preserved left ventricular systolic function. Furthermore, most existing data are derived from studies of patients hospitalised with decompensated heart failure, limiting applicability to the larger ambulatory HF population. No prior study has compared the prevalence of BBB in ambulatory patients with reduced and preserved systolic function.

The prevalence of BBB in CHARM-Overall was 23.8%, a rate consistent with previous studies. The Congestive Heart Failure and QRS Duration: Establishing Prognosis (CONQUEST) study found 20.8% of patients had a QRS duration ≥120 ms. [13] Prevalence was similar (20.5% BBB) in nearly three thousand intensive care unit admissions at the Henry Ford Hospital (13.2% LBBB, 7.3% RBBB). [14] Likewise, 22% of heart failure admissions to a UK hospital had BBB (15% LBBB, 7% RBBB). [15] Although selected by virtue of being enrolled in a clinical trial, the proportion of our patients with BBB was not dissimilar to the proportion with QRS prolongation in the EuroHeart Failure survey. [16] Furthermore, the prevalence in our reduced LVEF cohort of 30.1% is consistent with three studies describing a higher prevalence of BBB in patients with more severe LVSD. [1,17,18]

Our findings are also consistent with three studies dichotomising systolic function in hospitalised patients: US National Heart Failure (NHF) project (8% HF-PSF vs 24% LVSD, p<0.001);[6] Loma Linda VA Medical Centre (2% HF-PSF vs 12% LVSD, p<0.0001);[5] and a cohort of consecutive elderly admissions (3% HF-PSF vs 26% LVSD, p<0.0001).[4] We similarly found the prevalence of BBB was significantly lower in patients with HF-PSF (14.4%) compared to those with LVSD (Alternative 29.6%, Added 30.5%). The prevalence in our HF-PSF cohort appears higher, but these previous studies describe LBBB rather than all BBB. In the only study defining both conduction abnormalities, [5] 11% of patients with preserved systolic function had BBB (left or right), a finding more consistent with our own.

A number of studies have noted an inverse relationship between ejection fraction and QRS duration. [13,14,16,19,20] Only one, however, performed multivariate analysis to determine the predictors of BBB. [14] In that study of patients admitted to an intensive care unit with acute heart failure, significant independent predictors were ejection fraction (p<0.0001), renal function (p=0.04) and age (p=0.04). Our analysis is the first to characterise the magnitude of this relationship, clearly demonstrating LVEF to be the primary determinant (odds ratio 1.49 per 10% LVEF, p<0.0001). Previous MI was also a powerful independent predictor of BBB (odds ratio 1.55, p<0.0001), which is a well documented consequence of ischaemic injury, and associated with increased mortality post infarction.[21,22] The observation of black racial origin as a predictor is limited by statistical power due to the small number of these patients.

The adverse mortality implications of increased QRS duration were initially reported in a number of small studies. [23-27] Interpretation and application to clinical practice was restricted by limited patient numbers, particularly with ischaemic heart disease, variable cutoffs defining the conduction defect, and differences in multivariate analyses. Recent larger studies have demonstrated a graded increase in mortality proportional to QRS duration, with no evidence of any threshold effect at 120 ms. [28,29] In the IN-CHF registry the risk of death at 1 year was significantly greater in patients with LBBB (16.1% vs 11.9%) but not RBBB (11.9% vs 11.9%) compared to those without. [30] After multivariate adjustment, LBBB remained a powerful independent predictor of increased 1 year mortality (1.36 [1.15-1.61], p=0.0004) and sudden death (1.35 [1.05-1.73], p=0.0188). [1] A recent subgroup analysis from the German centres in Val-HeFT confirms the prognostic value of QRS duration in predicting all-cause mortality in HF patients with LVSD. [31]

The findings of CHARM corroborate existing reports of the association between BBB and mortality in patients with LVSD, while defining the impact on major cardiovascular events and also the previously unknown prognostic implications in HF-PSF. While adjusted risk associated with BBB appeared greater in patients with reduced compared to preserved systolic function, statistical testing for an interaction revealed no significant difference. Although failure to detect a difference does not imply equivalence, BBB may be important in patients with both reduced and preserved LVEF. However, further interpretation is limited by the unknown prevalence of left and right BBB morphologies in each cohort. Assuming prevalence of LBBB was similar to previous studies dichotomising systolic function, the predominant morphology may be RBBB in HF-PSF and LBBB in LVSD, with corresponding different prognostic implications. Although previous studies have focused on QRS duration rather than morphology,[13,17,28,29] the IN-CHF registry recently demonstrated that left but not right BBB was an independent predictor of 1-year mortality. [30] The Detroit study of intensive care admissions also demonstrated graded decrements in survival in patients with normal QRS, RBBB and LBBB (p=0.03). [14]

The continuous relationship between QRS duration and prognosis may also influence results. Stratification of outcomes according to QRS duration may have revealed narrower QRS complexes in patients with preserved LVEF, associated with fewer cardiovascular events. In itself, the definition of preserved systolic function may limit inclusion of patients with broad QRS complexes, who rarely have truly normal systolic contraction. However, despite including the largest cohort of preserved LVEF patients to date, further subgroup analysis would have insufficient statistical power to draw conclusions with reasonable certainty. Another limitation is the interpretation of ECGs by individual site investigators rather than a single core laboratory with standardised methods. However, we believe the simplicity of the diagnostic criteria and interpretation by individual investigators maintains applicability to clinical practice. Finally, a clinical trial population may differ from "real world" patients who are generally older, more often female and have greater co-morbidity; this may be especially true of patients with preserved systolic function.

In summary, the simple clinical finding of BBB is associated with greater disease severity and is a powerful independent predictor of worse clinical outcomes in patients with heart failure, particularly those with reduced LV systolic function. It is less frequent, with a more modest predictive effect, in patients with preserved systolic function. The ECG remains an accessible and inexpensive tool for identifying patients with ventricular conduction delay who are at particularly high cardiovascular risk, underscoring the importance of QRS duration in selecting patients for cardiac resynchronization therapy to improve prognosis in addition to providing symptomatic relief. [3]


   Acknowledgments
Top
 Abstract
 1. Introduction
 2. Methods
 3. Results
 4. Discussion
 Acknowledgments
References
 
The CHARM programme was funded by AstraZeneca, which was responsible for data collection and analysis. The Executive Committee academic leadership, consisting of Drs. Swedberg, Granger, McMurray, Yusuf and Pfeffer, supervised the management of the study and were primarily responsible for the interpretation of the data, preparation, review and approval of the manuscript. The data analysis for this manuscript was performed independently by Drs. Wang and Pocock.

Disclosures

Drs. McMurray, Pfeffer, Swedberg, Granger, Yusuf, Östergren and Dunn have received research grants, honoraria for lectures and/or consulting fees from a number of pharmaceutical companies manufacturing and selling inhibitors of the renin-angiotensin-aldosterone system, including AstraZeneca, Boehringer-Ingelheim, Bristol-Myers Squibb, Sanofi-Aventis, Merck, Novartis, Pfizer and Takeda Pharmaceutical Company. Dr. Michelson is an employee of AstraZeneca.


   References
Top
 Abstract
 1. Introduction
 2. Methods
 3. Results
 4. Discussion
 Acknowledgments
 References
 

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