Prognostic impact of bundle branch block after acute coronary syndrome. Does it matter if it is left of right?

Background: In previous guidelines, acute coronary syndromes (ACS) with new or presumably new left bundle branch block (LBBB) were an indication for reperfusion treatment, preferably with primary angioplasty. Recent guidelines also included the presence of right bundle branch block (RBBB) in this recommendation. It was our objective to evaluate in a population of patients with ACS the differential impact of RBBB and LBBB in prognosis. Methods: Consecutive patients included prospectively in a single-centre registry of ACS were included in the study. Patients were analyzed according to baseline ECG characteristics (normal QRS, LBBB or RBBB). Primary outcome was all-cause mortality at one-year follow-up. We used Cox-proportional hazards models to assess the predictive value for the primary outcome. Results: A total of 3990 patients were included in, with a mean age of 64 (13) years, 72% males, 3.4% with LBBB and 4.3% with RBBB. Patients with BBB were older, with more previous history of myocardial infarction and coronary revascularization and higher prevalence of cardiovascular risk factors (except smoking). Medical treatment was similar but they were less often submitted to angioplasty. In univariate analysis, BBB patients had worst outcome (Log-rank, p < 0.001), but similar in LBBB and RBBB (Log-rank, p = 0.597). In multivariate analysis, only RBBB (HR 1.66, 95%CI 1.14–2.40, p = 0.007) is an independent predictor of all-cause mortality. Conclusions: Patients with BBB have worst outcome after an ACS, particularly with RBBB. For that reason, we should pay special attention and treat these patients as aggressively as patients with normal QRS duration or LBBB. Keywords: Acute coronary syndromes, Bundle branch block, Prognosi