Comparative features of newly acquired left and right bundle branch block in the general population: the Framingham study.

Cardiovascular abnormalities were prospectively identified in all 55 persons who acquired left bundle branch block and all 70 persons who acquired right bundle branch block during 18 years of follow-up of the Framingham Study cohort. Those with left and right bundle branch block did not differ from each other in the overall prevalence of either hypertension, clinical coronary disease or diabetes. In men, but not in women, left bundle branch block was associated with a significantly greater prevalence of cardiac enlargement and congestive failure than was right bundle branch block. A trend suggesting a higher mortality rate from cardiovascular disease in those with left than in those with right bundle branch block was more apparent in men than in women. It is concluded that in the general adult population, men who acquire left bundle branch block are more likely to have or subsequently acquire advanced cardiovascular abnormalities than are men who acquire right bundle branch block. In women, however, the clinical correlates of the two conduction abnormalities are similar.