Experimental right bundle branch block in the normal human heart: Electrocardiographic, vectorcardiographic and hemodynamic observations

1. 1. Right bundle branch block was experimentally produced in twenty normal subjects by applying pressure on the right ventricular septal surface with an electrode-catheter. Electrocardiographic, vectorcardiographic and hemodynamic observations were performed in varying degrees of right bundle branch block obtained in this way. 2. 2. The results of these experimental studies in man are in agreement with the current criteria for the diagnosis of right bundle branch block of advanced degree (complete right bundle branch block), but new and valuable information has been obtained concerning the minor degrees of right bundle branch block (incomplete right bundle branch block). 3. 3. Morphologic changes are more important than quantitative data for the electrocardiographic and vectorcardiographic diagnosis of incomplete right bundle branch block. A QRS duration of only 0.07 or 0.08 second can be associated with minor degrees of right bundle branch block. Slowing of the QRSsÊ loop is not always present in these cases, and the relationship between electrical and mechanical systole remains frequently within normal variations. 4. 4. Right bundle branch block of advanced and minor degrees is an experimental reality in human beings. On the other hand, the remarkable similarity between the experimental and clinical findings constitutes a valuable support of the hypothesis which explains the complete and incomplete right bundle branch block patterns, seen frequently in clinical practice, by right bundle branch involvement. However, it does not mean that a late R wave in the right precordial leads results always from this mechanism. 5. 5. A surprising similarity is noted when the electrocardiographic and vectorcardiographic changes developing during the regression from experimental right bundle branch block are compared with those observed following surgical repair of atrial septal defects with mild pulmonary hypertension or without pulmonary hypertension. It is believed that right bundle branch block in regression could be an electrogenic factor in these postoperative changes.