Conduction and block in the right bundle branch, real and imagined.

ELECTROCARDIOGRAPHY is a subject now sufficiently old that it should contain more science than art, partiQularly in view of the sophisticated methods currently available to study the electrical activity of the heart. That many quaint terms have persisted in electrocardiographic nomenclature may be more attributable to their charming lilt than their scientific accuracy. We have long suspected that "incomplete right bundle-branch block" was one of these, and in the October issue of CIRCULATION Moore and his colleagues presented firm evidence to support that suspicion.' If the electrocardiographic pattern of QRS prolongation up to 0.11 sec (in adults), with a terminal r' in V, and S wave in leads V5 and V6 or standard lead I, were often the sole consequence of delayed conduction within the right bundle branch, then the term incomplete right bundle-branch block to describe this pattern might be appropriate. Conversely, if delay in conduction in the right bundle branch is only inconsistently present in this electrocardiographic constellation, then the diagnosis of incomplete right bundle-branch block would be at best imprecise and often incorrect. What Moore and his colleagues have now demonstrated electrophysiologically is the absence of a conduction delay in the right bundle branch, and a histologically normal right bundle branch in dogs with a heritable electrocardiographic pattern of incomplete right bundle-branch block. Their conclusion that the electrocardiographic findings in these dogs were caused by a heritable focal hypertrophy of the right ventricle, and not a delay in conduction in the right bundle branch, is elegantly documented. The study proves the inaccuracy of the electrocardio-graphic diagnosis of incomplete right bundle-branch block in these dogs, and invites an analysis of the possible alterations in the electrical activation of the heart that may produce the identical electrocardiographic pattern in man. All explanations for incomplete right bundle-branch block are likely to share the requirement that some portion of the right ventricle continue to depolarize after the completion of left ventricular depolarization.