Abnormal Motion of the Interventricular Septum in Right Ventricular Volume Overload

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Abstract
Abnormal systolic motion of the interventricular septum has previously been noted using echocardiography in patients with atrial septal defect and has been ascribed to right ventricular volume overload. To evaluate the mechanism responsible for this abnormality, right ventricular volume overload was created in open-chest dogs by pumping blood from the left atrium to the right atrium. In seven of eight dogs changes in interventricular septum motion were produced acutely at shunt flow as low as 500 cc/min. When the shunt was decreased or stopped, interventricular septum motion returned to normal. Shunts producing left ventricular volume overload (aorta to left atrium and right atrium to left atrium) caused no change in interventricular septum motion. Clinical observations showed that six of seven patients with partial anomalous pulmonary venous connection and no atrial septal defect displayed abnormal interventricular septum motion on echocardiography. Twenty-one patients undergoing surgery for atrial septal defect were studied before and after operation. Sixteen of the 21 had abnormal interventricular septum motion preoperatively; the abnormal interventricular septum motion returned to normal in only one of the 16 patients during a postoperative follow-up period of up to one year. Three patients were studied only postoperatively up to six years after closure of atrial septal defect; all three retained abnormal interventricular septum motion. Since the abnornal motion of the interventricular septum seen in patients with atrial septal defect can be produced and reversed acutely by creating a left-to-right atrial shunt in an experimental model, this abnormality must indeed be related to right ventricular volume overload. However, failure of interventricular septum motion to revert to normal following surgical correction in patients with atrial septal defect suggests that additional factors are involved in the persistence of this abnormal motion.