Bilateral Bundle-Branch Block

The electrocardiograms and salient clinical features of seven patients with electrocardiographic evidence of various types of bilateral bundle-branch block (BBBB) have been presented. When the complexes change in form and the P-R interval varies, the mechanisms are usually best interpreted by using the concepts of first degree, second degree, and third degree bundle-branch block with or without block in the higher conduction system. The etiology of BBBB in many cases is idiopathic fibrosis of both bundles. The diagnosis of BBBB by ECG is important because of its relation to the subsequent development of complete heart block or Adams-Stokes syndrome, or both. In this series five of seven patients with BBBB had Adams-Stokes syndrome and three of seven had complete heart block.