NATURAL-HISTORY OF ISOLATED BUNDLE-BRANCH BLOCK

The purpose of this study was to determine the longterm outcome of pat ients with bundle branch block (BBB) who have no clinical evidence of cardiovascular disease. Among 110,000 participants in a screening prog ram, 310 subjects with BBB without apparent or suspected heart disease were identified. Their outcome after a mean follow-up of 9.5 years wa s compared with that of 310 similarly screened age- and sex-matched co ntrols. Among the screened population, isolated right BBB was more pre valent than isolated left BBB (0.18% vs 0.1%, respectively; p < 0.001) , and the prevalence of each abnormality increased with age (p < 0.001 ). Total actuarial survival was no different for those with left BBB o r right BBB and their respective controls. Cardiac mortality, however, was increased in the left BBB group when compared with their controls (p=0.01, log rank test). Left BBB, but not right BBB, was associated with an increased prevalence of cardiovascular disease at follow-up (2 1% vs 11%; p=0.04). In the absence of clinically overt cardiac disease , the presence of left BBB or right BBB is not associated with increas ed overall mortality. Isolated left BBB is associated with an increase d risk of developing overt cardiovascular disease and increased cardia c mortality.