RADIOLOGICAL EXAMINATION OF THE CARDIOVASCULAR SYSTEM

1. RADIOLOGICAL EXAMINATION OF THE CARDIOVASCULAR SYSTEM DEPARTMENT OF ONCOLOGY AND RADIOLOGY PREPARED BY I.M.LESKIV

2. METODS OF EXAMINATION • Echocardiography, radionuclide examinations and plain films are the standard non-invasive imaging investigations used in cardiac disease. Echocardiography has now become a particularly important imaging technique that provides morphological as well as functional information. It is excellent for looking at the heart valves, assessing chamber morphology and volume, determining the thickness of the ventricular wall and diagnosing intraluminal masses. Doppler ultrasound is an extremely useful tool for determining the velocity and direction of blood flow through the heart valves and within cardiac chambers. Radionuclide examinations reflect physiological parameters such as myocardial blood flow and ventricular contractility but provide little anatomical detail, whereas plain radiographs are useful for looking at the effects of cardiac disease on the lungs and pleural cavities, but provide only limited information about the heart itself. MRI provides both functional and anatomical information but is only available in specialized centres and is used only for specific reasons.

4. ROENTGENOGRAPHY • A complete roentgen study of the heart usually requires a minimum of four projections: posteroanterior, left anterior oblique at approximately 60°, right anterior oblique at approximately 45°, and lateral. The films are exposed at a 6-foot distance, with the patient in the upright position and in moderately deep inspiration. Magnification resulting from divergent distortion is minimized by obtaining posteroanterior and anterior oblique views to place the heart closer to the film (the anterior chest is adjacent to film). A left lateral view (with the left side adjacent to film) also tends to minimize magnification. To outline the esophagus, we use a barium suspension as an aid in determining position and size of the aortic arch. In addition, alteration inesophageal contour may reflect changes in the left-sided chambers. The use of ultrasound in determining cardiac chamber size has decreased the use of the oblique projections, so that frequently the cardiac examination is restricted to PA and lateral projections, usually without barium in the esophagus.

5. FLUOROSCOPY • Cardiovascular fluoroscopy no longer has widespread use and in our institution is largely limited to the evaluation of specific questions: i.e., the presence of large pericardial effusions and the evaluation of aortic arch anomalies. Generally, calcium is better seen on fluoroscopy then on plain films and these observations may be made at the time of cardiac catheterization. Minor amounts of calcification are best seen on CT. The use of fluoroscopy has virtually disappeared in the study of congenital heart disease because in general the patients require more definitive studies such as cardiac catheterization, angiocardiography, ultrasonography, and MRI. • There are several disadvantages in cardiac fluoroscopy, one of the most important of which is the amount of radiation to which the patient is exposed. • The second disadvantage is distortion. Because the distance between the target of the x-ray tube and the patient is short, there is considerable enlargement of the cardiac silhouette and distortion of other thoracic structures. This can be decreased by using longer distances between target and the patient, and by using a small shutter opening, producing the central beam effect. The third disadvantage is lack of permanent record. This is obviated to a certain extent by the use of cine or videotape recording and by roentgenograms obtained before the procedure.

6. ANGIOCARDIOGRAPHY • This method of contrast cardiac visualization has been used widely for examination of patients with all types of cardiac and pulmonary diseases. The method is used in the diagnosis of congenital and acquired cardiac disease. Selective angiocardiography in which a small amount of opaque medium (an organic iodide) is injected into a specific chamber or vessel during cardiac catheterization is used almost exclusively.

7. CORONARY ARTERIOGRAPHYAORTOGRAPHY • CORONARY ARTERIOGRAPHY • Selective catheterization of the coronary arteries followed by injection of a contrast medium (one of the organic iodides) is used in combination with cineradiography rapid serial filming or videotaping to study the coronary arteries. Details of technique are beyond the scope of this discussion. • AORTOGRAPHY • This examination consists of the injection of one of the organic iodides into the aorta through a catheter introduced into one of its major branches and placed into a desired position in the aorta. The examination has a place in the investigation of patients with congenital and acquired problems of the aortic arch. It is used in infants with congestive heart failure in whom there is evidence of a left to right shunt and in whom patent ductus arteriosus is suspected. Coarctation of the aorta in infants may also cause congestive heart failure. The lesion can be defined by aortography. In adults, aortography is used to define anomalies of the aortic arch and its branches as well as in the study of the aortic valve and the coronary arteries. It is also useful in patients with masses adjacent to the aorta in whom aneurysm is a possibility and in patients suspected of having dissecting hematoma, and traumatic or other aneurysms.

8. ULTRASONIC INVESTIGATION OF THE HEART • The use of ultrasound in examination of the heart has increased greatly in the past 20 years, and it is now well established and a widely used diagnostic tool. Ultrasonic investigation is a noninvasive, safe, and comfortable study that will demonstrate valve and chamber motion wall thickness and size. Doppler examination allows determination of the cross sectional area of a valve as well as quantification of gradients that may be present. It is of value in the study of the hypertrophic cardiomyopathies both with and without associated subaortic stenosis and in the study of the congestive type in which there is chamber dilatation. With ultrasound, left ventricular diameter and outflow configuration can be determined; qualitative assessment of right and left ventricular size is possible, also. The size of the left atrium can be measured accurately and left atrial myxomas or other intraatrial tumors can be detected. Ultrasound is also useful in the investigation of congenital heart disease, particularly in patients with hypoplastic left-heart syndrome, double-outlet right ventricle, and right ventricular volume overload. In addition, it is the most sensitive method for determining the presence of pericardial effusion.

9. DETERMINATION OF CARDIAC SIZE • The most commonly used are (1) measurement of transverse diameters; (2) measurement of surface area; and (3) cardio-thoracic ratio. The transverse diameter of the heart is the sum of the maximum projections of the heart to the right and to the left of the midline; the measurement should be made so as not to include epicardial fat or other noncardiac structures. The diameter can then be compared with the theoretic transverse diameter of the heart for various and weights. Surface area estimations based on artificial construction of the base of the heart and of the diaphragmatic contour of the heart. The cardiothoracic ratio is the ratio between the transverse cardiac diameter and the greatest internal diameter of the thorax, measured on the frontal teleroentgenogram. This is the easiest and quickest method of measurement of cardiac size; an adult heart that measures more than one half of the internal diameter of the chest is considered enlarged. The method is gross, because the cardiothoracic ratio varies widely with variations in body habitus. It can be useful, however, as a rough estimate of cardiac size. The cardiothoracic ratio is most useful in assessing changes in heart size or monitoring progression of disease, or as a response to therapy.

10. Measurement of heart size. The transverse diameter of the heart is the distance between the two vertical tangents to the heart outline. When the cardiothoracic ratio (CTR) is calculated, the transverse diameter of the heart (B) is divided by the maximum internal diameter of the chest (A)

11. THE ADULT HEART

12. Left ventricular enlargment in a patient with aortic incompetence. The cardiac apex is displaced downwards and to the left. Note also that the ascending aorta causes a bulge of the right mediastinal border - a feature that is almost always seen in significant aortic valve disease.

13. Right ventricular enlargement in an adult with primary pulmonary hypertension. The heart is enlarged with the apex of the heart somewhat lifted off the diaphragm. Note also the features of pulmonary arterial hypertension - enlargement of the main pulmonary artery and hilar arteries with normal vessels within the lungs.

14. Left atrial enlargement in a patient with mitral valve disease showing the 'double contour sign' (the left atrial border has been drawn in) and dilatation of the left atrial appendage (LAA) (arrow). The enlarged LAA should not be confused with dilatation of the main pulmonary artery. The main pulmonary artery is the segment immediately below the aortic knuckle. The LAA is separated from the aortic knuckle by the main pulmonary artery

15. Pericardial disease • Echocardiography is ideally suited to detect pericardial fluid. Since patients are examined supine, fluid in the pericardial space tends to flow behind the left ventricle and is recognized as an echo-free space between the wall of the left ventricle and the pericardium. A smaller amount of fluid can usually be seen anterior to the right ventricle. Even quantities as small as 20-50 ml of pericardial fluid can be diagnosed by ultrasound. The nature of the fluid cannot usually be ascertained, and needle aspiration of the fluid may be necessary; such aspiration is best performed under ultrasound control. Pericardial effusion can also be recognized at CT and MRI, although they are rarely performed primarily for this purpose. Computed tomography and MRI are particularly useful for assessing thickening of the pericardium, whereas echocardiography is poor in this regard. • It is unusual to be able to diagnose a pericardial effusion from the plain chest radiograph. Indeed, a patient may have sufficient pericardial fluid to cause life-threatening tamponade, but only have mild cardiac enlargement with an otherwise normal contour. A marked increase or decrease in the transverse cardiac diameter within a week or two, particularly if no pulmonary oedema occurs, is virtually diagnostic of the condition. Pericardial effusion should also be considered when the heart is greatly enlarged and there are no features to suggest specific chamber enlargement. Pericardial calcification is seen in up to 50 % of patients with constrictive pericarditis. Calcific constrictive pericarditis is usually postinfective in aetiology, tuberculosis and Coxsackie infections being the common known causes. In many cases no infecting agent can be identified. The calcification occurs patchily in the pericardium, even though the pericardium is thickened and rigid all over the heart. It may be difficult or even impossible to see the calcification on the frontal view. On the lateral film, it is usually maximal along the anterior and inferior pericardial borders. Widespread pericardial calcification is an important sign, because it makes the diagnosis of constrictive pericarditis certain.

16. Large pericardial effusion on an apical four-chamber view echocardiogram. (b). CT scan showing fluid density (arrows) in pericardium. LA, left atrium; LV, left ventricle; RA, right atrium; RV, right ventricle.

17. Pericardial effusion. The heart is greatly enlarged. (Three weeks before, the heart had been normal in shape and size.) The outline is well defined and the shape globular. The lungs are normal. The cause in this case was a viral pericarditis. This appearance of the heart, though highly suggestive of, is not specific to pericardial effusion. (Compare with (b).) (b) Congestive cardiomyopathy causing generalized cardiac dilatation. This appearance can easily be confused radiologically with a pericardial effusion. A B Pericardial calcification in a patient with severe constrictive pericarditis. The distribution of the calcification is typical. It follows the contour of the heart and is maximal anteriorly and inferiorly. As always, it is more difficult to see the calcification on the PA film. (This patient also had pneumonia in the right lower lobe.)

18. Pulmonary vessels • The plain chest film provides a simple method of assessing the pulmonary vasculature. Even though it is not possible to measure the true diameter of the main pulmonary artery on plain film, there are degrees of bulging that permit one to say that it is indeed enlarged. Conversely, the pulmonary artery may be recognizably small. The assessment of the hilar vessels can be more objective since the diameter of the right lower lobe artery can be measured: the diameter at its midpoint is normally between 9 and 16 mm. The size of the vessels within the lungs reflects pulmonary blood flow.There are no generally accepted measurements of normality, so the diagnosis is based on experience with normal films. By observing the size of these various vessels it may be possible to diagnose one of the following haemodynamic patterns. • Increased pulmonary blood flow:Atrial septal defect, ventricular septal defect and patent ductus arteriosus are the common anomalies in which there is shunting of blood from the systemic to the pulmonary circuits (so-called left to right shunts), thereby increasing pulmonary blood flow. The severity of the shunt varies greatly. In patients with a haemodynamically significant left to right shunt (2:1 or more), all the vessels from the main pulmonary artery to the periphery of the lungs are large. This radiographic appearance is sometimes called pulmonary plethora. There is reasonably good correlation between the size of the vessels on the chest film and the degree of shunting.

19. Decreased pulmonary blood flow: To be recognizable radiologically, the reduction in pulmonary blood flow must be substantial. The pulmonary vessels are all small, an appearance known as pulmonary oligaemia. The commonest cause is the tetralogy of Fallot, where there is obstruction to the right ventricular outflow and a ventricular septal defect which allows right to left shunting of the blood. Pulmonary valve stenosis only causes oligaemia in extremely severe cases in babies and very young children. • Pulmonary arterial hypertension: The pressure in the pulmonary artery is dependent on cardiac output and pulmonary vascular resistance. The con ditions that cause significant pulmonary arterial hypertension all increase the resistance of blood flow through the lungs. There are many such conditions including: • various lung diseases (cor pulmonale); • pulmonary emboli; • pulmonary arterial narrowing in response to mitral valve disease or left to right shunts; • idiopathic pulmonary hypertension. • Pulmonary arterial hypertension has to be severe before it can be diagnosed on plain films and it is difficult to quantify in most cases. The plain chest film features are enlargement of the pulmonary artery and hilar arteries, the vessels within the lung being normal or small. When the pulmonary hypertension is part of Eisenmenger's syndrome (greatly raised pulmonary arterial resistance in association with atrial septal defect, ventricular septal defect or patentductus arteriosus, leading to reversal of the shunt so that it becomes right to left), the vessels within the lungs may also be large, but there is still disproportionate enlargement of the central vessels.The reason for pulmonary arterial hypertension may be visible on the chest film; in cor pulmonale the lung disease is often radiologically obvious, and in mitral valve disease and other.

20. Interstitial oedema: There are many septa in the lungs which are invisible on the normal chest film because they consist of little more than a sheet of connective tissue containing very small blood and lymph vessels. When thickened by oedema, the peripherally located septa may be seen as line shadows. These lines, known as Kerley В lines, named after the radiologist who first described them, are horizontal lines never more than 2 cm long seen laterally in the lower zones. They reach the lung edge and are therefore readily distinguished from blood vessels, which never extend into the outer centimetre of the lung. Other septa radiate towards the hila in the mid and upper zones (Kerley A lines). These are much thinner than the adjacent blood vessels and are 3-1 cm in length. Another sign of interstitial oedema is that the outline of the blood vessels may become indistinct owing to oedema collecting around them. This loss of clarity is a difficult sign to evaluate and it may only be recognized by looking at follow-up films after the oedema has cleared. Fissures may appear thickened because oedema may collect against them. Alveolar oedema: Alveolar oedema is a more severe form of oedema in which the fluid collects in the alveoli. It is almost always bilateral, involving all the lobes. The pulmonary shadowing is usually maximal close to the hila and fades out peripherally leaving a relatively clear zone that may contain septal lines, around the edge of the lobes. This pattern of oedema is sometimes referred to as the 'butterfly' or 'bat's wing' pattern. Pulmonary oedema: The common cardiac conditions causing pulmonary oedema are left ventricular failure and mitral stenosis. Cardiogenic pulmonary oedema occurs when the pulmonary venous pressure rises above 24-25 mmHg (the osmoticpressure of plasma). Initially, the oedema is confined to the interstitial tissues of the lung, but if it becomes more severe fluid will also collect in the alveoli. Both interstitial and alveolar pulmonary oedema are recognizable on plain chest films.

21. B Septal lines in interstitial pulmonary oedema, (a) Left upper zone showing the septal lines known as Kerley A lines (arrowed) in a patient with acute left ventricular failure following a myocardial infarction. Note that these lines are narrower and sharper than the adjacent blood vessels, (b) Right costophrenic angle showing the septal lines known as Kerley В lines in a patient with mitral stenosis. Note that these oedematous septa are horizontal non-branching lines which reach the pleura. One such line is arrowed.

22. Alveolar oedema in a patient with acute left ventricular failure following a myocardial infarction. The oedema fluid is concentrated in the more central portion of the lungs leaving a relatively clear zone peripherally. Note that all the lobes are fairly equally involved.

23. Aorta • With increasing age the aorta elongates. Elongation necessarily involves unfolding, because the aorta is fixed at the aortic valve and at the diaphragm. This unfolding results in the ascending aorta deviating to the right and the descending aorta to the left. Aortic unfolding can easily be confused with aortic dilatation. • True dilatation of the ascending aorta may be due to aneurysm formation or secondary to aortic regurgitation,aortic stenosis or systemic hypertension. • The two common causes of aneurysm of the descending aorta are atheroma and aortic dissection. A rarer cause is previous trauma, usually following a severe deceleration injury. The diagnosis of aortic aneurysm may be obvious on plain film but substantial dilatation is needed before a bulge of the right mediastinal border can be recognized. Atheromatous aneurysms invariably show calcification in their walls and this calcification is usually recognizable on plain film. Computed tomography with intravenous contrast enhancement is very useful when aortic aneurysms are assessed. It is important to know the extent of aortic dissections as those involving the ascending aorta are treated surgically while those confined to the descending aorta are usually treated conservatively with hypotensive drugs. Standard echocardiography shows dissection of the aortic root but transoesophageal echocardiography showsdissections distal to the aortic root and in the descending aorta as well. Dissecting aneurysms can also be shown with CT and MRI and these non-invasive techniques have largely replaced aortography, which is only performed in selected cases. • Two congenital anomalies of the aorta may be visible on plain films of the chest: coarctation and right-sided aortic arch, a condition that is sometimes seen in association with intracardiac malformations, notably tetralogy of Fallot, pulmonary atresia and truncus arteriosus. It can also be an isolated and clinically insignificant abnormality. In right aortic arch, the soft tissue shadow of the arch is seen to the right, instead of to the left, of the lower trachea.

24. Aortic dissection, (a) Transoesophageal echocardiogram showing the true (T) and false (F) lumina in the descending aorta. CT scan showing the displaced intima (arrows) separating the true and false lumina in the ascending and descending aorta. MRI scan showing the displaced intima in the ascending and descending aorta (arrows). AAo, ascending aorta; DAo, descending aorta; PA, pulmonary artery.