Spatial vectorcardiography: Right bundle branch block. VIII

The vectorcardiographic patterns and characteristics of right bundle branch block may be summarized as follows: 1. 1. "Classical" right bundle branch block is associated with a QRS SÊ loop inscribed in the right, lower, anterior octant. The progress of the wave of accession is slow, and the time markers are closely spaced throughout the QRS SÊ loop. There is a positive ST vector directed upward, posterior, and to the left. The T SÊ loop is discordant. It points upward, backward, and to the left. Instances of this type of right bundle branch block are rare. 2. 2. Atypical right bundle branch block is characterized by alteration chiefly of the terminal portion of the QRS SÊ loop. This terminal portion is increased in duration, slow and irregular in contour, and invariably directed to the right and anteriorly, to a greater or lesser extent. This terminal portion of the QRS SÊ loop produces the slow, widened S wave of Lead I and the R′ or late R wave of Lead V₁. This terminal abnormality may coexist with any normal or pathological variety of the QRS SÊ loop. The study of a case of transient, atypical complete right bundle branch block revealed that the major portion of the QRS SÊ loop is also affected by the presence of the abnormal conduction, though only to a minor extent. However, the fact that some change is produced in the initial portion of the QRS SÊ loop indicates that the lack of contribution of right ventricular electromotor force to the entire QRS cycle is detectable although of small quantity. This might be considered as evidence that this type of block is true bundle branch block and not merely a "focal block" of the Purkinje system or a local abnormality of muscular conduction in the crista terminalis. It was further observed that the long axis of the T SÊ loop shifted to the left and posteriorly by more than 100 degrees. The significance of the T SÊ loop shift was shown clearly in the patients with marked left ventricular hypertrophy or myocardial damage. The electrocardiographic diagnosis of both of these conditions depends greatly upon evidence of an altered gradient producing inverted T waves in Leads I and V₅ or V₆. That the T-wave change due to right bundle branch block alone would obscure such a diagnostic criterion was suspected from the alteration seen in the patient with transient block and was confirmed in the patients with left ventricular hypertrophy and myocardial damage associated with right bundle branch block. In all of them, T waves were upright in Leads I and V₅ and V₆. The diagnosis of myocardial damage, myocardial infarction, and left ventricular hypertrophy, however, could be made from the configuration of the QRS SÊ loop alone.