Left Bundle Branch Block (LBBB) is a frequently encountered electrical abnormality in patients with chronic (more than 3 months after myocardial infarction, or evidence of coronary artery disease with ischemia) coronary syndromes (CCS), but its prognostic significance remains unclear. We aimed to describe the prevalence, incidence and five-year outcomes of LBBB in outpatients with CCS using the CLARIFY registry. Main outcome was a composite of CV death, MI or stroke. Secondary outcomes included all cause death, hospitalization for heart failure (HF) and permanent pacemaker implantation. Among 23.544 patients with available information regarding LBBB status at baseline, 1.041 (4.4%) had LBBB at baseline and 1.015 (4.5%) patients developed a new LBBB during 5-year follow-up. In multivariate analysis, LBBB at baseline was not associated with the composite outcome of CV death, MI or stroke (HR 1.06, 95% CI [0.86 – 1.31], p = 0.67) or the risk of all-cause death (HR 1.07, 95% CI [0.87 – 1.32], p = 0.52) but was significantly associated with a higher risk of hospitalization for HF (HR 1.50, 95% CI [1.21 – 1.88], p < 0.001) and permanent pacemaker implantation (HR 2.11, 95% CI [1.45 – 3.07], p < 0.001). The main factors associated with new-onset LBBB were male sex (HR 0.8 [0.66-0.98], p = 0.028) history of atrial fibrillation (HR 1.29, 95% CI [1.01 – 1.64], p = 0.04), CABG (HR 1.27, [1.08 – 1.51], p = 0.004) and MI (HR 1.19, 95% CI [1.01 – 1.40], p = 0.034). In conclusion, in a contemporary registry of outpatients with CCS, the prevalence of LBBB was 4.4% and the additional 5-years incidence 6.2%. LBBB, in itself, was not associated with a higher risk of major adverse cardiovascular events or all cause mortality. It was however an independent predictor of risk of hospitalization for heart failure and permanent pacemaker implantation.
Left Bundle Branch Block (LBBB) is frequently encountered in patients with or without coronary artery disease, and its prevalence increases with age. , It is often associated with a structural cardiopathy such as left ventricular dysfunction, interventricular asynchronism or valvular heart disease, but can also be found without clinically detectable cardiopathy. The prognostic implications of LBBB have been extensively studied in various settings such as heart failure with reduced left ventricular ejection function (LVEF), and acute myocardial infarction. In those settings, LBBB was associated with worse outcomes, including all-cause mortality. However, data are scarce about LBBB in patients with chronic coronary syndromes (i.e more than 3 months after MI, or evidence of coronary artery disease with ischemia) (CCS). As LBBB is a frequently acquired and permanent condition, evaluating the association of LBBB with outcomes in CCS patients would be of interest. Using the large contemporary CLARIFY registry, we aimed to describe the prevalence and yearly incidence of LBBB, its association with baseline characteristics, management, and outcomes in outpatients with CCS.
Methods
CLARIFY (ProspeCtive observational LongitudinAl RegIstry oF patients with stable coronary artery disease) was an international, prospective, longitudinal registry of outpatients with chronic coronary syndromes which enrolled 31,593 patients from November 2009 until July 2010 in 45 countries in all geographic zones of the globe. Patients were followed annually for five years. An ECG was recorded at each visit. The rationale, design, and long-term outcomes of patients included in the CLARIFY registry have been described in detail elsewhere. To be eligible for enrolment, patients had to have any of the following: documented myocardial infarction or history of myocardial revascularization (either by percutaneous coronary intervention or coronary artery bypass grafting more than 3 months earlier) or documented coronary artery disease with coronary angiography showing at least one coronary stenosis of more than 50%, or chest pain with proven myocardial ischemia (using stress ECG, stress echocardiography, or myocardial imaging). Patients were excluded if they had been hospitalized for CV disease within the last 3 months, had a planned revascularization, or any conditions hampering the participation or the 5 year follow-up, including advanced heart failure (left ventricular ejection fraction < 30%).
In the present analysis, the CLARIFY population was stratified into two groups according to the presence or absence of LBBB at the time of enrolment. LBBB was defined as QRS duration ≥ 120 ms, rS, or QS pattern in lead V1, wide slurred R wave in V6, and T-wave inversion in leftward leads. Patients with history of previous permanent pacemaker (PPI) or internal cardiac defibrillator implantation were excluded from the present analysis. A trained physician collected LBBB at each yearly visit, by interpreting the ECG. LBBB was not adjudicated.
Outcomes definitions have been previously published. The primary outcome for the present analysis was the composite of CV death, MI or stroke. Secondary outcomes included each of the components of the primary outcome, plus new onset or worsening HF requiring hospitalization, all cause death, non-CV death, and permanent pacemaker implantation. CV death was defined as any of the following: fatal myocardial infarction, fatal stroke and other CV deaths, including sudden death.
Descriptive statistics of both groups are reported as means ± standard deviations for continuous variables and patient numbers with percentages for categorical variables. Statistical comparisons were performed between groups using Student and chi-square tests for continuous and categorical variables respectively. All outcomes at five-year follow-up were reported by baseline LBBB group as percentages with 95% confidence intervals and p-values of comparisons between groups were estimated by chi-square tests. The influence of LBBB on outcomes was estimated using odds ratios with 95% confidence intervals derived from logistic models adjusted on the following variables: age, sex, prescription of beta-blockers, atrial fibrillation, heart failure, diabetes, dyslipidemia, smoking status, treated hypertension at baseline, left ventricular ejection fraction, history of hospitalization for HF, history of coronary artery bypass grafting or percutaneous coronary intervention and MI at baseline.
The CLARIFY registry was supported by Servier. The sponsor had no role in initiating the present analysis, nor in the study design, data analysis and interpretation or in the decision to submit the manuscript for publication.
Results
Among 31,593 patients included in the CLARIFY registry, 23,544 had information regarding LBBB status at baseline. Of these, 4.4% (n = 1.041) had LBBB at baseline. Among patients without baseline LBBB (n = 22,503), 4.5% (n = 1.015) presented a new-onset LBBB during five-year follow-up ( Figure 1 ). For patients without LBBB at baseline, the yearly rate of LBBB tended to decrease between the first and last year of follow-up, and the additional 5 year incidence was 6.2%. In the first year, 286 patients developed LBBB (1.5%), 279 in the second (3.0%), 199 in the third (4.3%), 147 in the fourth (5.3%) and finally 104 (6.2%) in the last year (Table S1 in the Supplemental Data). Among those 1,015 patients, only 21 (2.1%) developed a new-LBBB in the same year as an incident MI.
Baseline characteristics of the patients according to the presence or absence of LBBB at baseline are presented in Table 1 . Briefly, compared to patients without LBBB, patients with LBBB at baseline were more likely to be older, female, with higher prevalence of risk factors, with more extensive disease, and were more symptomatic. Left ventricular ejection fraction (LVEF) was conserved in both groups, although significantly lower in patients with LBBB. Patients who developed a new LBBB during follow-up are detailed in Table S2 in the Supplemental Data.
| Variable | Left bundle branch block | p value | |
|---|---|---|---|
| Yes n = 1041 | No n = 22503 | ||
| Age, mean (SD), (years) | 67.2 (10.1) | 63.6 (10.4) | <0.001 |
| Body mass index, mean (SD), (kg/m 2 ) | )28.2 (4.4) | 28.0 (4.5) | 0.046 |
| Men | 765 (73.5 %) | 17521 (77.9%) | <0.001 |
| Treated Hypertension | 797 (76.6%) | 16176 (71.9%) | 0.001 |
| Diabetes Mellitus | 365 (35.1%) | 6390 (28.4%) | <0.001 |
| Dyslipidemia | 826 (79.3%) | 17443 (77.5%) | 0.165 |
| Current or former smoker | 573 (55.0%) | 13259 (58.9%) | 0.013 |
| No physical activity | 194 (18.7%) | 3301 (14.7%) | < 0.001 |
| Myocardial Infarction | 659 (63.3%) | 13539 (60.2%) | 0.043 |
| Percutaneous Coronary Intervention | 505 (48.5%) | 13346 (59.3%) | < 0.001 |
| Coronary Artery Bypass Grafting | 304 (29.2%) | 5324 (23.7%) | < 0.001 |
| Hospitalization for Heart Failure | 139 (13.4%) | 900 (4.0%) | < 0.001 |
| Stroke | 56 (5.4%) | 842 (3.7%) | 0.007 |
| Atrial Fibrillation / Flutter | 103 (9.9%) | 1482 (6.6%) | < 0.001 |
| Asthma / COPD | 106 (10.2%) | 1582 (7.0%) | < 0.001 |
| Peripheral Arterial Disease | 143 (13.7%) | 2304 (10.2%) | < 0.001 |
| Left Ventricular Ejection Fraction (SD), (%) | 50.3 ± 12.4 | 57.0 ± 10.3 | < 0.001 |
| Current Symptoms | |||
| Angina Pectoris | 280 (26.9%) | 5457 (24.3%) | 0.05 |
| Heart Failure | 262 (25.2%) | 3772 (16.8%) | < 0.001 |
| Baseline medications | |||
| Aspirin | 897 (86.3%) | 19857 (88.3%) | 0.05 |
| Dual Antiplatelet Therapy | 973 (24.2%) | 6398 (28.4%) | 0.003 |
| Oral Anticoagulant | 112 (10.8%) | 1684 (7.5%) | < 0.001 |
| Lipid Lowering Agent | 937 (90.2%) | 20918 (93.0%) | < 0.001 |
| Beta-blocker | 770 (74.0%) | 17248 (76.7%) | 0.05 |
| Ivabradine | 147 (14.1%) | 2601 (11.6%) | 0.011 |
| Amiodarone | 48 (4.6%) | 621 (2.8%) | 0.0004 |
| ACE inhibitor or ARB | 842 (81.0%) | 17233 (76.6%) | < 0.001 |
| Diuretics | 469 (45.1%) | 6565 (29.2%) | < 0.001 |
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