The electrocardiographic diagnosis of bilateral bundle branch block in relation to heart block

The electrocardiographic differential diagnosis of all possible combinations of first, second or third degree bilateral bundle branch block is discussed in detail on the basis of cases observed by the author or published in the world literature. While a definite diagnosis of this condition can be made only if both left and right bundle branch block patterns appear in the same patient, accompanied by consistent changes of the P-R interval, there are many signs which made an A-V conduction disturbance due to bilateral bundle branch block, rather than to block in the A-V node or the common bundle, probable. Several types of atypical right bundle branch block patterns described by the author earlier now appear to be caused by a combination of block of the entire right bundle branch and a part of the left branch.