Risk factor implications of incidentally discovered uncomplicated bundle branch block

To evaluate the long-term outcome of a community-based patient population with incidentally discovered asymptomatic and uncomplicated bundle branch block (BBB).

A retrospective observational cohort study was undertaken of patients in Olmsted County, Minnesota, who were evaluated between 1975 and 1999 and were incidentally diagnosed as having BBB. We performed Kaplan-Meier analyses of all-cause mortality and development of first cardiac morbidity after the diagnosis of BBB, along with matched control group comparisons.

A total of 723 patients with left BBB (LBBB) (58.1%) and right BBB (41.9%) met criteria. Mortality was higher in patients with BBB compared with controls (absolute difference of approximately 10% over 20 years; hazard ratio = 1.27; confidence interval, 1.02-1.58; P=.03) as was the development of first cardiac-related morbidity (hazard ratio = 1.32; confidence interval, 1.14-1.54; P<.001). Patients with BBB and without the risk factors of diabetes, hypertension, and/or hypercholesterolemia showed increased long-term mortality compared with matched controls (no BBB) also without risk factors (P=.02). However, comparable mortality was shown between patients with BBB who did not have these risk factors and matched control patients who had these risk factors. The risk of developing cardiac-related morbidity also was increased in the presence of BBB, particularly LBBB.

Uncomplicated asymptomatic BBB (notably LBBB) with normal left ventricular ejection fraction is not benign. Our findings indicate that the presence of isolated BBB denotes a high-risk patient subgroup that has a compromised long-term outcome comparable to patients with conventional cardiovascular risk factors.