This study presents longitudinal data on RBBB in a highly selected cohort of North American men. Thus, caution should be exercised when extrapolating these data to the general population. However, the relatively young age at entry of the majority of this cohort permits more accurate estimation both of the age at onset of RBBB and freedom from preexisting disease than is possible in studies commencing with older age groups. It also provides longitudinal data on this conduction disturbance from a young age. Other cautions include the problem of measuring A QRS in the right bundle. The exact time during the QRS that activation of the right ventricle occurs is not always apparent or predictable for each individual case. Although much of the interest is centered on extremes of axis deviation, the small number of cases in some subgroups of A QRS is also a concern. Another precaution in the extrapolation of these results is the different lengths of follow-up within each age group. Those 30 years of age and younger at detection of RBBB have been under observation for almost 30 years, but the length of follow-up is decreased in older age groups.
The present study demonstrated that the ominous prognosis attributed to RBBB and marked right or left axis deviation in patients with heart disease should not be applied to persons without heart disease who have the same ECG finding recorded on a routine examination.