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.
7.2 Mitral stenosis
Mitral stenosis can cause changes in both the shape and size of the heart. It is a cause of pulmonary oedema. If you suspect mitral stenosis:
1. Look at the left heart border. Look just below the left hilum where the border of the heart is made up of the left atrium (Chapter 2.2). This area is usually concave in shape but in mitral stenosis the left atrium is enlarged causing a loss of this concavity and a straightening of the left heart border. Sometimes atrial enlargement is so great that this part of the heart bulges outwards.
2. Look at the right heart border. Look carefully for a double shadow which you sometimes see in a well-penetrated film and is due to left atrial dilatation.
3. Identify the trachea and follow it down until you see it split into right and left bronchi. This is the carina, and the angle between the bronchi should be less than 90°. Measure this angle. If it is more than 90° this may indicate left atrial enlargement, a feature of mitral stenosis. However, there is wide normal variation.
7.3 Left ventricular aneurysm
A left ventricular aneurysm is a cause of cardiac enlargement on the chest X-ray. It can often cause generalized enlargement of the left ventricle and be indistinguishable from left ventricular dilatation. If you suspect an aneurysm then look for:
1. A bulge in the left ventricle. Follow the left border of the heart. If a part bulges out then this is suggestive of an aneurysm.
2. Look for calcification. If the aneurysm is longstanding then it may have become calcified and you will see a rim of calcification along the heart border.
7.4 Pericardial effusion
A pericardial effusion is another cause of an enlarged heart shadow. If you suspect it then:
1. Confirm that the heart shadow is enlarged. Check that it is a PA film and that the largest diameter of the heart shadow is more than half the largest diameter of the thorax.
2. Look carefully at the shape of the heart shadow. Enlargement due to an effusion is generalized, so if the enlargement appears to be due to a specific chamber enlarging then the cause is unlikely to be an effusion. The heart shadow is globular in shape if an effusion is present, though do not be put off by a bulge that you can sometimes see on the left heart border.
3. Look at the lung fields. If cardiac enlargement is due to left ventricular failure then the vascular markings should be increased making the lung fields whiter than usual. In a pericardial effusion the vascular markings are usually normal.
5. Look at the hilum. In a pericardial effusion the heart shadow may cover both hila. This will not occur with other forms of cardiac shadow enlargement.
6. Look at the white line on the edge of the right side of the trachea (the paratracheal density). This should be less than 2–3 mm wide on an erect chest X-ray. If it is wider, one cause is enlargement of the superior vena cava. This would be consistent with a pericardial effusion (see also p. 141).
