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.