CHAPTER 7 The abnormal heart shadow
7.1 Atrial septal defect (ASD)
Always remember to study the heart and the pulmonary arteries. If the heart is enlarged or pulmonary hypertension is present then one possible cause is an ASD. If you suspect an ASD then look for the following:
1. The heart may be enlarged. Determine the cardiothoracic ratio by measuring the width of the thorax and the width of the heart. If the heart is more than half the diameter of the thorax it is enlarged.
2. Look at the shape of the heart. Look first at the apex which is often rounded due to enlargement of the right ventricle and is sometimes lifted clear of the diaphragm. Next look at the right heart border. Because the right atrium enlarges, the right heart border looks much fuller than normal.
3. Look at the position of the heart by comparing it to the position of the vertebrae. With an ASD the heart is sometimes shifted to the left and so the right edge of the vertebral column is revealed.
4. Look at the aortic knuckle and arch of the aorta. It is often smaller if an ASD is present since blood is diverted to the right atrium rather than passing through the aorta.
