Mechanisms of QRS complex prolongation in man: Left ventricular conduction disturbances

Abstract

Abstract 1.1. Eighty cases of QRS prolongation to .12 second or more due to right ventricular conduction disturbances have been collected. In each case one or more tracings with normal ventricular conduction was also available. This is the first controlled study of the electrical effects of right bundle branch block in man. 2.2. In all cases the initial electrical forces of the QRS interval were unchanged by the development of right bundle branch block. This is in contrast with the findings in experimental right bundle branch block. Evidence is presented which suggests that the difference is due to the fact that the lesion lies more distally along right ventricular conduction pathways in clinical right bundle branch block than in experimental right bundle branch block. The studies suggest that there is no period when right ventricular excitation is arrested or delayed in clinical right bundle branch block as is commonly believed, but that excitation instantly leaks out into the right ventricular myocardium when it reaches the site of the block. 3.3. These findings confirm the observation made by other investigators that the deformity of the initial QRS forces due to myocardial infarction is not altered by the development of right bundle branch block. Thus Q wave criteria for the diagnosis of infarction are valid in the presence of right bundle branch block. The only exception to this is found with strictly posterior infarction, and the reasons for this are discussed. 4.4. The electrocardiographic syndrome of diaphragmatic peri-infarction block is described and criteria for differentiating it from right bundle branch block, which it closely resembles, are suggested. In addition two cases of diaphragmatic peri-infarction block without deformity of initial QRS forces are described. This is a previously unrecognized electrocardiographic manifestation of infarction.