What is the pathophysiology of the murmur in atrial septal defect?
The murmur heard in a patient with an atrial septal defect is a systolic ejection murmur originating from the pulmonary valve. It is a flow murmur caused by the increased blood volume passing from the left atrium to the right atrium, and so through the right ventricle and pulmonary valve. The passage of blood through the atrial septal defect itself does not cause a murmur because the pressure differential between the two atria is low. What are the signs of an atrial septal defect? The two major signs of an atrial septal defect are a systolic ejection murmur best heard with the diaphragm over the second or third left interspaces, and fixed splitting of S2. How do you determine whether or not there is fixed splitting of S2? Determine whether you can hear splitting during expiration as well as during inspiration. If you can, and the patient is supine, reassess splitting with the patient in the sitting position. If you can still hear splitting in the expiratory phase of respiration, the pa