Discussion
To the best of our knowledge, this was the largest study to explore the
long-term outcome in patients with CLBBB underwent catheter ablation of
AF. This study found that CLBBB was associated with a higher risk of a
composite endpoint of stroke, all-cause mortality, and cardiovascular
hospitalization in the patients underwent catheter ablation of AF. CLBBB
was also an independent risk factor for recurrence of catheter ablation
of AF.
AF was the most common tachyarrhythmias, which was an important
contributor to population morbidity and mortality. CLBBB and QRS
prolongation were also known risk factors for poor cardiovascular
prognosis. AF combined with CLBBB was an important clinical situation
and was not rarely coexisted. There were several studies exploring the
relationship between CLBBB and AF. In the National Inpatient Sample
database, 1,420,585 hospitalizations (0.7% of the total sample size)
had LBBB. The patients in the LBBB group had a significantly higher
prevalence of AF than the Non-LBBB group (30.5% vs. 11.9%). In
multiple regression analysis, AF was independently associated with LBBB
(odds ratio 1.17, 95%CI 1.16-1.18).3 In another
study, 25,268 patients from 106 centers in the United States with LV
dysfunction were enrolled. After adjusting for potential AF risk
factors, QRS duration remained independently associated with AF
(odds ratio: 1.20, 95% CI:
1.14-1.25).11 In a large population-based study, QRS
duration was an independent predictor of incident AF among
women.12 It was also found that AF was an independent
risk factor for bundle branch block (odds ratio: 1.15, 95% CI
1.01-1.31, P = 0.036) in Candesartan in Heart failure Assessment of
Reduction in Mortality and morbidity (CHARM)
program.13 However, the study did not classify the
subtype of bundle branch block.
Whether AF and CLBBB had a synergistic effect on cardiovascular
prognosis remained controversial. In Italian Network on congestive heart
failure (IN-CHF) Registry, 185 of 5,517 (3.3%) patients with heart
failure had CLBBB and AF. The patients with CLBBB and AF had
significantly higher all-cause mortality (HR 1.88, 95%CI 1.37-2.57) and
1-year hospitalization (HR 1.83, 95% CI 1.26-2.67) than the patients
without CLBBB and AF, and those with CLBBB or AF
alone.14 In a case report, it was also shown that AF
alone (lasting for 6 years) or isolated CLBBB (lasting for 18 months
after AF ablation) did not induce cardiomyopathy. However, a combination
of AF and CLBBB induced heart failure within 6 months was
observed.15 In order to exclude the influence of LBBB
on heart failure which leads to poor outcomes, Rodríguez-Mañero M et al
found that the mortality rate of LBBB without cardiac dysfunction
population was similar to that of without LBBB group in the Atrial
Fibrillation in the BARbanza area (AFBAR) study. In multivariate
analysis, LBBB had no significant correlation with all-cause death,
all-cause hospitalization, and cardiovascular
hospitalization.16
The effect of catheter ablation of AF on prognosis remained
controversial. To our knowledge, there were no published data on the
long-term outcome of the patients with CLBBB and AF who underwent
catheter ablation of AF. This study found that CLBBB was an independent
risk factor of the composite primary endpoint of stroke, all-cause
mortality, and cardiovascular hospitalization. With regard to the
component of the primary endpoint, CLBBB significantly increased
cardiovascular hospitalization. This finding emphasized the poor
prognosis of CLBBB even in those underwent catheter ablation of AF. We
all knew that maintenance of sinus rhythm after AF ablation improved
prognosis. Catheter ablation still had positive significance for the
prevention of heart failure in AF patients combined with
CLBBB.15 However, this study failed to find an
association between sinus rhythm and the endpoint events. It suggested
that the presence of CLBBB caused an adverse effect on long-term
prognosis, which might alleviate the benefits of sinus rhythm.
There were only a few studies discussed the impact of CLBBB on AF
recurrence after catheter ablation. In Mujovic’s study, bundle branch
block was a predictor of very late recurrence after catheter ablation of
AF. However, only 5 patients with bundle branch block (3 LBBB and 2
RBBB) were enrolled. Whether LBBB was a predictor of very late
recurrence could not be determined for the small sample
size.17 In a retrospective analysis of 674 patients
who underwent cryoballoon ablation, the prevalence of LBBB was
significantly higher in the very late recurrence group than in those
without very late recurrence. That study revealed that CLBBB was an
independent predictor of recurrence after long term follow-up. However,
only 13 patients with LBBB were enrolled in the study. Whether LBBB was
an independent predictor of very late recurrence in multivariate
analysis was not shown in the study.6 This study found
that CLBBB was an independent risk factor for recurrence of AF. The
baseline characteristics and the ablation strategy of the CLBBB group
and the Non-CLBBB group were comparable. However, the mechanism of how
CLBBB increased the recurrence of catheter ablation of AF was not well
depicted in this study. Pulmonary vein reconnection was a key mechanism
of recurrence. In redo procedures, the rate of pulmonary vein
reconnection was comparable between the two groups in this study.
Previous studies showed that conduction abnormalities such as BBB may
develop degeneration/fibrosis of the myocardium, adverse ventricular
remodeling, or ischemia.18-19 Ventricular and atrial
fibrosis share some common mechanisms. Diffuse ventricular fibrosis
indexed by ventricular T1 relaxation time was independently associated
with a higher recurrence rate of catheter ablation of
AF.20
This study had several limitations. Firstly, this was a retrospective
analysis based on a prospective cohort. There may be selection bias due
to the inherent deficiency of retrospective study. We tried to reduce
bias by propensity-score match and adjusting for possible confounders by
multivariate analysis. Secondly, there were only 42 cases of AF combined
with CLBBB. However, the natural incidence of CLBBB was low. This study
was already the largest study of patients with AF and CLBBB who
underwent catheter ablation of AF up to now. Thirdly, the recurrence of
AF was detected by symptom and intermittent 12-lead ECG or 24-hour
Holter. The recurrence rate may be underestimated, especially with
asymptomatic attacks. Finally, the patients with AF and CLBBB who did
not undergo catheter ablation were not enrolled in this study. This
study was unable to evaluate whether catheter ablation could improve the
prognosis of the patients with AF and CLBBB.