The precordial electrocardiogram in incomplete right bundle branch block.

I N 1917 Rothberger and Winterberg’ published an electrocardiographic record which depicts the gradual clearing of a defect in conduction affecting the right branch of the bundle of His. An attempt to cut this structure in the course of an experiment on a dog blocked it only temporarily. Fortunately, one of the tracings taken spanned the period during which the injured bundle gradually recovered its conductivity. The investigators recognized that the central complexes of this record represent incomplete right bundle branch block. They are transitional in form between the preceding complexes, which are characteristic of complete block, and the subsequent complexes, which are of normal outline. Some years later, W&on and Herrmann, without being aware of this earlier work, carried out an extensive experimental investigation in which the canine dextrocardiogram and levocardiogram were superimposed in varying time relations by a number of different methods. By producing right bundle branch block and then stimulating the anterior wall of the right ventricle just after the normal excitation wave had reached the left, they were able to produce at will complexes representing a delay in right ventricular activation of any magnitude less than that which occurs in complete right bundle branch block. Such complexes are identical with those of complete right bundle branch block with regard to the parts of the QRS wave written before excitation of the right ventricle begins; that is to say, before the excitation wave spreads to muscle normally excited via the right Purkinje plexus. They are transitional between bundle branch block complexes and normal complexes with regard to the length of the QRS interval and the form of the T wave. The present report deals with the description, classification, and interpretation of clinical electrocardiograms which are intermediate, with regard to the form of the ventricular complex, between normal tracings and those which represent complete right bundle branch block, and which display a QRS interval measuring less than 0.12 second in the limb leads. We have attempted to establish criteria for the diagnosis of incomplete right bundle branch block and to