© 2008 European Society of Cardiology
The prevalence and incidence of left bundle branch block in ambulant patients with chronic heart failure
Department of Academic Cardiology, Castle Hill Hospital Castle Road, Cottingham, Hull, UK. HU16 5JQ, UK
* Corresponding author. Castle Hill Hospital, Castle Road, Cottingham, Hull, HU16 5JQ, UK. Tel.: +44 1482 624012. a.l.clark{at}hull.ac.uk (A.L. Clark).
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Abstract |
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 Top Abstract 1. Introduction2. Methods3. Results4. DiscussionReferences |
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Background: Approximately one third of patients with chronic heart failure have left bundle branch block (LBBB) on their 12-lead ECG.
Methods and results: 1418 consecutive patients (average (SD) age 70.5 (10.4) years; 74% male) first seen in a community heart failure clinic between December 2001 and June 2006 had a 12 lead electrocardiogram (ECG). 485 (34%) had a QRS duration 
120ms. Patients with a broad QRS were older (72.2 v 69.3years), had worse left ventricular systolic function, were on a higher daily dose of diuretic and were more likely to be on amiodarone (14.4 v 7.1%).
12 lead ECG was available for 734 patients (52%) at 1year follow up. The QRS interval increased from 115.1ms at baseline to 117.6 (P<0.0001). There were 52 incident cases of LBBB, an incidence of 10.9%. The only predictors of incident LBBB were QRS duration at baseline and amiodarone use at baseline. The proportion of patients with LBBB increased from 34.0% at baseline to 36.7%, 37.7% and 42.3% at 1, 2 and 3 years follow up, respectively. Baseline LBBB was associated with a worse outcome (HR 1.25 (95% CI 1.01–1.55). New LBBB was an independent adverse prognostic feature (HR 2.09 (95% CI 1.17–3.73); P=0.013).
Conclusions: The crude incidence of LBBB is 10.9% in the first year of follow up in an unselected population of ambulatory outpatients with chronic stable heart failure. Ongoing care of patients with chronic heart failure should include a regular 12 lead electrocardiogram.
Key Words: Heart failure • Conduction • Prognosis
Received January 22, 2008; Revised April 8, 2008; Accepted May 1, 2008
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1. Introduction |
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TopAbstract1. Introduction2. Methods3. Results4. DiscussionReferences |
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Left bundle branch block (LBBB) is commonly associated with chronic heart failure with around one third of chronic heart failure patients having LBBB [1-3]. The presence of LBBB has been associated with inco-ordination of left ventricular contraction, [4,5] and is also associated with a worse outcome [6]. It has become particularly important to recognise conduction abnormalities in heart failure patients with the availability of biventricular pacing [7,8]. Although many different ways of selecting patients for biventricular pacing have been suggested, the major selection criterion for entry into clinical trials has been QRS duration. QRS duration remains "the cornerstone of dyssynchrony assessment" [9].
The incidence of LBBB in the general population is low, with only 110 out of 17,361 (0.6%) subjects developing it over 40 years [10]. Whilst the prevalence of LBBB in chronic heart failure has been reported before (frequently under the title of "incidence"; see [11] for review), there are no reports of the incidence of LBBB in patients with chronic heart failure during follow up.
The aim of the present report is to describe the prevalence and incidence of LBBB in a representative sample of ambulatory patients with chronic heart failure, together with an analysis of predictors of the development of LBBB and its association with prognosis.
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2. Methods |
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TopAbstract1. Introduction2. Methods3. Results4. DiscussionReferences |
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We report on a cohort of consecutive patients referred to a community heart failure clinic between January 2002 and June 2006. Patients are included in this report if, on echocardiography, they were found to have evidence of left ventricular systolic dysfunction and if they had an available 12 lead electrocardiogram recorded within 48 h of the echocardiogram. Seventy-one patients with right ventricular pacing were excluded from analysis, but are shown in Table 1 for interest.
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2.1. Procedures
When first seen at the heart failure clinic, a history (including current medication) was taken from the patient, who was then examined. A 12-lead electrocardiogram (ECG) with automatic interval detection software (PR; QRS and QT interval) was taken. Left bundle branch block was defined as a QRS complex of
120 ms in duration coupled with loss of septal Q waves. Patients with right bundle branch block were excluded. Each subject underwent echocardiographic examination using GE Vingmed Vivid Five scanner equipped with 2.5 MHz phased array transducers. Echocardiography was carried out by one of three trained operators. Left ventricular ejection fraction was calculated, where possible, using the Simpson's biplane method (possible in 67%). Left ventricular function was also assessed by visual estimation on a scale of normal, mild, moderate, and severe impairment, and was assessed by a second operator blind to the assessment of the first; where there was disagreement on the severity of LV dysfunction the echocardiogram was reviewed jointly with the third operator and a consensus reached. Dyssynchrony was not assessed for the majority of patients in the cohort.
2.2. Follow up
Patients were seen 4 monthly for routine follow up, with the 12 lead ECG and the echocardiogram repeated annually. Follow up was censored on June 1st, 2006; the patient status on this date was known for all patients.
2.2.1. Follow up QRS duration
As well as reporting the crude QRS duration, and in order to examine the effect of regression to the mean, we also defined change in bundle branch block status as crossing the arbitrary 120 ms boundary whilst at the same time changing QRS duration by at least 10 ms. We termed this LBBB*.
2.3. Statistical methods
Data are given as mean±SE. Normality of distribution for continuous variables was tested using the Kolmogorov-Smirnov test. The unpaired Student's t-test was used to compare mean values between groups. Proportions were compared using 
2-test and Fisher's exact test. Univariate predictors of incident and resolution of LBBB were assessed using logistic regression. Cox-proportional hazards analyses were used to assess prognostic associations. The hazard ratio (HR) with 95% confidence intervals (CI) and P-values as derived from the appropriate model are given. Hazard ratios for continuous variables apply per unit of the analysed variable. Kaplan-Meier cumulative survival plots were constructed to illustrate the results (StatView 5.0, Abacus Concepts, Berkeley, USA).
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3. Results |
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TopAbstract1. Introduction2. Methods3. Results4. DiscussionReferences |
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3.1. Baseline data
Details of the 1418 patients included in the study are shown in Table 1. Patients with LBBB had significantly worse left ventricular systolic dysfunction than those without LBBB both in terms of their left ventricular ejection fraction, where measured, and in terms of the visual grading of left ventricular impairment. However, their symptoms as rated by the New York Heart Association classification system were not different. Those patients with LBBB were more likely to be on treatment with a loop diuretic, aldosterone antagonist and amiodarone, but there was no significant difference between the two groups in use of ACE inhibitor (or angiotensin receptor blocker) and beta blocker.
QRS duration was related to severity of LV dysfunction (see Fig. 1). There was a negative correlation between heart rate and QRS duration (R=–0.09; P=0.0007) and a positive correlation between age and QRS duration (R=0.09; P=0.0007). QRS duration was greater in men than women (116.5 (30.8) ms v 110.3 (32.0), respectively: P=0.001), but was not affected by aetiology of heart failure. QRS duration was significantly greater in those taking amiodarone (126.2 (29.6) v 113.6 (31.1); P<0.0001) or aldosterone antagonist (120.5 (294) v 113.4 (31.5); P=0.0008) but not associated with use of beta adrenoceptor antagonist or angiotensin receptor antagonist.
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3.2. One year data
A 12 lead ECG was available for 734 patients (52%) at 1 year follow up. Of these, 13 had had a permanent pacemaker implanted, and were thus excluded from analysis. Details of the remaining 721 are shown in Table 1. No patient developed right bundle branch block during follow up. Of the 612 patients with no 1 year ECG, 239 had died and for 373 patients there was no ECG.
In those patients with a follow up ECG, the QRS interval increased from 114.6 ms at baseline to 117.6 (P<0.0001). Changes to QRS duration that might have impact on the decision to implant a cardiac resynchronisation device are summarised in Tables 2a and 2b. In those patients who did not have LBBB at baseline (N=473), QRS interval increased from 97.7 (12.9) ms to 101.3 (14.2) ms (P<0.0001). In the 248 patients with baseline LBBB, QRS duration was not significantly altered (147.0 (19.9) ms at baseline and 145.9 (24.8) ms at 1 year; P=0.32). Few patients reached a threshold of 150 ms.
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3.3. Incidence and resolution of LBBB and LBBB*
Table 2a shows the incidence and resolution of LBBB according to both the standard definition of LBBB and our modified definition LBBB*. There were 49 (10.4%) incident cases of LBBB at 1 year in those with QRS<120 ms at baseline (N=473). In this group of patients, QRS duration increased from 106.6 (14.9) ms to 128.2 (10.1) ms (P<0.0001). 31 patients (12.5%) with baseline LBBB no longer had LBBB at 1-year follow up. In this latter group, QRS shortened from 128.5 (11.5) ms to 106.0 (11.5); P<0.0001.
Using our modified definition of incident LBBB (LBBB*), there were 33 (7.0%) new cases of LBBB* at 1 year in those with QRS<120 ms at baseline. In this group of patients, QRS duration increased from 102.2 (16.4) ms to 131.3 (11.0) ms (P<0.0001). 19 patients (7.7%) no longer had LBBB*. In this latter group, QRS shortened from 132.5 (13.2) ms to 100.2 (11.2); P<0.0001.
3.4. Predictors of incident LBBB and LBBB*
Table 3 shows the data for patients with a baseline QRS<120 ms for whom a 12 lead ECG was available at 1 year follow up divided by whether they had incident LBBB and LBBB*. The only predictors of both LBBB and LBBB* were increasing QRS duration at baseline and amiodarone use at baseline. Starting beta adrenoceptor antagonists was not associated with prolongation of the QRS interval.
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3.5. Predictors of resolution of LBBB and LBBB*
Table 3 also shows the data for patients with a baseline QRS
120 ms for whom a 12 lead ECG was available at 1 year follow up divided by whether they had resolution of LBBB and LBBB*. The only predictors of resolution were shorter QRS duration at baseline and an underlying diagnosis of ischaemic heart disease. Those with resolved LBBB had less severe left ventricular dysfunction and less severe symptoms, but these differences did not reach statistical significance. The odds of observing a 20 ms increase in QRS at 1-year follow up increased with increasing baseline QRS width (OR 1.034 per ms (C.I. 1.023-1.044, P<0.0001)). Conversely, the odds of observing a 20 ms decrease in QRS at 1-year follow up reduced with increasing baseline QRS width (OR 0.968 per ms (C.I. 0.958-0.979, P<0.0001).
3.6. Predictors of survival
During a median follow up of 26.9 months (interquartile range 14.1-39.1) 350 patients died. The presence of left bundle branch block was associated with an adverse outcome in univariate analysis (see Fig. 2). Other univariate predictors of outcome are shown in Table 4. In a multivariate analysis using those values and shown in Table 5, increasing age, NYHA symptom class, resting heart rate, the presence of diabetes, chronic lung disease and underlying diagnosis of ischaemic heart disease were the only independent predictors of mortality.
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For those patients surviving the first year from the index ECG, change in QRS was not itself related to further survival (P=0.48). Incident left bundle branch block during the first year was associated with an adverse prognosis (see Fig. 3). In a multivariate model using the same variables as seen in Table 4, new LBBB remained an independent adverse prognostic feature (HR 1.93 (95% CI 1.05-3.56); P=0.03). The incidence of LBBB* was associated with a similar HR (2.57 (95% CI 1.35-4.92); P=0.004 in the univariate analysis and 1.89 (95% CI 0.96-3.72); P=0.06 in the multivariate analysis).
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3.7. Further follow up
In 215 patients, a 12 lead electrocardiogram was available at 2 years and 3 years follow up. In this subgroup, QRS was 112.1 (29.2) ms at baseline, and 116.7 (28.4), 115.9 (28.9) and 118.6 (32.8) ms at 1, 2 and 3 years follow up, respectively. The proportion with LBBB* increased from 34.0% at baseline to 36.7%, 37.7% and 42.3% at 1, 2 and 3 years follow up, respectively.
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4. Discussion |
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TopAbstract1. Introduction2. Methods3. Results4. DiscussionReferences |
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The prevalence of left bundle branch block in patients with chronic heart failure is around a third, [1] rising to over a third in patients with more severe left ventricular impairment [2,6]. However, little is known about the incidence of left bundle branch block in those heart failure patients with a QRS complex duration of less than 120 ms at baseline. A previous study in 112 patients reported that QRS duration increased by an average of 6 ms during a mean of 17 months' follow up. Lengthening QRS duration was associated with a higher cardiac mortality, but the incidence of new left bundle branch block is not given [12]. This is of importance now that there is cardiac resynchronisation therapy available for patients with heart failure and a prolonged QRS interval.
We have found a crude incidence of LBBB of 10.4%, in patients without LBBB at baseline, in the first year of follow up in a population of ambulatory outpatients with chronic stable heart failure. Baseline LBBB was associated with worse left ventricular function and older age. Whilst it was associated with a worse prognosis, it was not an independent predictor of outcome. Indeed, we found that prognosis was more strongly related to the presence of comorbidities than to the LBBB, a finding consistent with previous work that has suggested that it is the severity of underlying cardiac disease rather than the presence of LBBB per se that mediates a worse prognosis [13].
Whether the LBBB is the cause or consequence of the worse left ventricular function it is impossible to say from this analysis. Incident LBBB was associated with a longer QRS interval at baseline and with use of amiodarone, but was not related to measures of left ventricular function, heart rate or rhythm at baseline, age or sex. Why amiodarone is related to new left bundle branch block is not clear; the association but may be a consequence of the electrophysiological properties of the drug or its use be a marker of worse cardiac function and hence pre-disposition to LBBB.
We also found that patients with wider QRS at baseline were more likely to have progressively wider QRS at follow up and those that already had wider QRS at baseline were less likely to reduce their QRS at follow up. The population of patients studied is more broadly representative of patients with chronic heart failure than those included in clinical trials, and represents a "real world" population.
A major recent advance in the management of patients with chronic heart failure has been the introduction of cardiac resynchronisation therapy (CRT). As an addition to optimal drug therapy, CRT is associated with a 37% reduction in the risk of death [14]. We have found that QRS duration is strongly related to left ventricular function, and that the worse the systolic left ventricular function, the broader the QRS. This suggests that the QRS duration may reflect left ventricular systolic function rather than necessarily indicating dyssynchrony. Our present level of knowledge is that the benefit from cardiac resynchronisation therapy is related to the presence of left bundle branch block. There is little evidence of benefit for patients with shorter QRS complexes [15]. That knowledge may certainly be refined as a result of on-going randomised controlled trials that test the validity of using echocardiographic methods to determine the presence of dyssynchrony [16]. Early presentation of these data suggest that echo is not successful in predicting "response" to CRT, [17] and for the present at least, the decision to implant a biventricular pacing device has to be based upon QRS duration.
The fact that QRS duration changes with time and that the incidence of new left bundle branch block is as high as around 10% in the first year emphasises the importance of continuing care programmes for patients with chronic heart failure. An ECG demonstrating QRS duration of less than 120 ms should not be accepted as a "one-off" determination. Even though baseline LBBB was not an independent predictor of mortality, incident LBBB was associated with a particularly poor prognosis. We suggest that ECGs should be performed in heart failure patients at least yearly to detect QRS broadening and to prompt assessment for suitability for biventricular pacing.
4.1. Limitations
Left ventricular ejection fraction was not calculated in 30% of patients due to sub-optimal images. This is comparable with other similar series [18]. The semi-quantitative scoring method is usually applicable to all patients, although losing precision. It might be thought that there are relatively few women in the studied cohort and that the average population age is rather younger than in some epidemiological studies. However, we have excluded those patients with heart failure and normal ejection fraction, a condition affecting predominantly older women. We were concerned that our findings might represent regression to the mean; we have therefore reported the incidence of a more stringent definition of new LBBB requiring both the 120 ms threshold to be crossed and an increase in QRS duration of at least 10 ms. That we are not simply reporting regression to the mean is borne out by (1) the overall increase in QRS duration during the first year; (2) the number developing new LBBB is greater than the number with resolved LBBB; (3) those with QRS prolongation at baseline were more likely to develop further prolongation and less likely to have QRS shortening than those with shorter baseline QRS complexes; and (4) the observation of worse outcome in the new LBBB group.
4.2. Conclusion
We have studied a large cohort of patients with chronic heart failure and found a prevalence of left bundle branch block of 36%, associated with worse left ventricular function and increasing age. We found a crude incidence of left bundle branch block of 10.4%, associated with longer baseline QRS duration and the use of amiodarone.
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