Electrocardiographic and hemodynamic correlation in atrial septal defect

Abstract

The electrocardiographic changes and hemodynamic factors have been correlated in ninety-five cases of atrial septal defect. The electrocardiograms of 66.3 per cent revealed the pattern of right bundle branch block, 25.3 per cent showed right ventricular hypertrophy, and 8.4 per cent were considered normal. The majority of patients had a significant shift of the QRS axis to the right; only five had left axis shift of the frontal QRS axis. In spite of the marked right atrial dilatation that is known to occur in this entity, P-wave abnormalities were uncommon in Leads II and III. Approximately one-half of the patients demonstrated diphasic P waves in Lead V 1. Atrioventricular block and cardiac arrhythmias were rare in this series and no instance of atrial fibrillation was encountered. As right ventricular systolic pressure increased, the pattern of right bundle branch block decreased and was replaced by that of right ventricular hypertrophy. There was an associated shift in the frontal QRS vector to the right. The pulmonary flow diminished as elevation in right ventricular pressure occurred. ECG signs of increased pressure also included an R S ratio in V 6 of less than one. Following successful closure of interatrial septal defects the right ventricular systolic pressure fell, the electrical axis of the frontal QRS vector shifted toward the left, and the R S ratio in V 1 decreased. In patients showing the pattern of right bundle branch block the R′ in V 1 often showed a striking decrease in amplitude and duration. The pattern of incomplete right bundle branch block has been observed to emerge from that of right ventricular hypertrophy after closure of the atrial defect. It is suggested that the pattern of right bundle branch block encountered in atrial septal defect represents the normal cardiac vectors, not bundle branch block. It is believed the characteristic electrocardiographic pattern represents selective hypertrophy of the basal portion of the right ventricle secondary to increased right ventricular stroke volume. As pulmonary hypertension develops, the electrocardiographic pattern of hypertrophy of the free wall of the right ventricle is superimposed on this picture. This occurs relatively early in the QRS complex.