The Natural History of Isolated Bundle Branch Block: Results from Population Screened Over Quarter Century

Background and Methods. The prognostic implications of the incidental discovery of LBBB or RBBB in people without clinically apparent heart disease remain uncertain. We compared the outcome of 310 such people identified during screening carried out by The Irish Heart Foundation between 1968 and 1993, and 310 similarly screened age- and sex-matched controls with similar cardiovascular risk factor profiles. Results. Persons with isolated LBBB and RBBB constituted 0.1% and 0.18% respectively, of the screened population. After similar follow-up periods, total actuarial survival (Kaplan-Meier method) was no different for those with RBBB, LBBB and their respective controls (see table). Cardiac mortality, however, was increased in the LBBB, but not RBBB, group when compared to their respective controls (p = 0.01, log-rank test). At follow-up, overt cardiac disease was evident in 21% of those with LBBB compared to 11% of their controls (p = 0.04). No such difference was observed for those with RBBB. Conclusions. 1. Isolated LBBB, but not RBBB is associated with an increased long-term cardiac, but not total mortality. 2. Isolated LBBB is marker for the subsequent development of clinically overt cardiac disease