The heart

Pathology

 

The diagnosis of congenital heart disease is usually established during infancy or early childhood. The congenital heart diseases are therefore described in the chapter on Pediatric Radiology.

The enlarged heart

Enlargement of the heart may be generalized or involve only one or two chambers. Enlargement may also involve predominantly one chamber initially with secondary effects on other chambers. Several methods of measuring the volume of the heart exist.

The simplest and most usual method is to measure the greatest transverse diameter of the heart in a frontal picture, and relate this to the greatest internal width of the thorax (Fig. 19). When the size of the heart is normal, the heart's greatest transverse diameter is less than half the maximal internal diameter of the thorax. In Scandinavia, it has also been usual to calculate the volume of the heart in millilitres. For this purpose, frontal and lateral views of the chest are required. A normal heart resembles an ellipsoid, and the volume of the ellipsoid can be calculated when the axes are measured. The definition of the axes is shown in Fig. 20 a, b. The axes are multiplied by each other and by a constant to determine the total volume of the heart. The constant (usually 0.40) compensates for radiographic magnification. In order to relate the heart's total volume to the size of the body, the total volume is divided by the body surface expressed in square metres, calculated from height and weight. The normal upper limit for women is 450 ml/m2, while a volume of over 500 ml/m2 should be regarded as enlarged. A relative heart volume between
500 and 550 ml/m2 body surface is regarded as borderline in men.

However, there are considerable sources of error connected with the method, and differences in measurement of 15 % must be accepted as within the margin of error. Because 2D echocardiography and MRI display the individual chambers, these methods provide accurate measurements of chamber volume and myocardial mass. Assessment of cardiac volumes is most frequently done using 2D echocardiography.

General enlargement of the heart

General enlargement of the heart (enlargement affecting all cardiac chambers) is seen in a number of different diseases of the heart and lungs - see description of these in appropriate sections.

Figure 20 a + b. Drawing - calculation of heart volume Volume (rel) = a x b x c x 0.4/surface

Figure 21. Slight to moderate left ventricular enlargement with rounded and low-lying heart apex.

 

Left ventricular enlargement

Enlargement of the left ventricle is due either to hypertrophy or dilatation. If the enlargement of the left ventricle or silhouette is considerable, it is invariably due to dilatation. The most common sign of enlargement of the left ventricle is an elongation of the longest axis of the left ventricle. The apex is also seen to be rounded and low-Iying. These changes are se en in a frontal view (Fig. 21). In the lateral view, left ventricular enlargement is indicated by the posterior border of the left ventricle lying behind the barium- filled oesophagus. The lower posterior part of the left ventricle is also frequently seen projected behind the outline of the inferior vena cava, where this crosses the right diaphragm.

The ejection fraction of the left ventricle (expressed by the relationship between the stroke volume and the end diastolic volume) is a reliable index of left ventricular function. The ejection fraction is normally between 60 and 75%. In diseases affecting the left ventricle, the ejection fraction is reduced either by reduction of stroke volume or by an increase in end-diastolic volume. The ejection fraction and the end-diastolic volume can be estimated using angiocardiography, by calculating the volumes at end diastole and end systole. However, it is becoming increasingly more common to calculate the se values using echocardiography. The most accurate and reproducible measurement of ventricular volume can be provide d by cine MRI. The most frequent causes of left ventricular enlargement are mitral and/or aortic valvular insufficiency, dilated cardiomyopathy, ischemic cardiomyopathy, and decompensated aortic

 

a  b

Figure 22. a) Generally enlarged heart with large left atrium. The left atrium is projected over the right atrium and makes the outline (black arrow). b) Lateral view - generally enlarged heart with large left atrium, which bulges backwards considerably (black arrow).

stenosis and hypertension.

The most common signs of enlargement of the left atrium (Fig. 22 a, b) are backwards displacement of the contrast filled esophagus, elevation of the left main bronchus, dislocation of the right margin of the left atrium posterior to the right atrium (double contour sign), or dilatation of the left auricle. The left atrium is the
heart chamber where isolated enlargement of the heart is easiest to detect. The size of the left atrium can be more precisely determined by 20 echocardiography.
The most common cause of enlargement of the left atrium is mitral valve disease. Another frequent cause is resistance to left ventricle filling caused by disease which reduces compliance, such as aortic stenosis and hypertrophic cardiomyopathy. Enlargement of the left atrium may occur secondary to hypertrophy and/or dilatation of the left ventricle.

Right ventricular enlargement

The most common radiological sign of enlargement of the right ventricle is filling of the retrosternal clear space with increased contact of the right ventricle with the posterior border of the sternum. Normally, less than one-third of the posterior border of the sternum should be in contact with the right ventricle. Assuming a normal position of the sternal border, enlargement of the right ventricle increases the area of contact between the sternum and the right ventricle. On the frontal view, right ventricular enlargement displaces the left border of the heart directly laterally in contradistinction to the left ventricular enlargement, which causes the border to extend both laterally and caudally.

Two-dimensional echocardiography can provide a qualitative assessment of right ventricular size but is not reliable for measuring volumes of the right ventricle. Cine MRI, and ultra fast CT can provide accurate measurement of right ventricular volumes. The most frequent causes of enlargement of the right ventricle are rheumatic heart disease affecting the tricuspid valve, advanced mitral stenosis (due to pulmonary arterial hypertension), and long-lasting pulmonary hypertension, frequently accompanied by simultaneous pulmonary or tricuspid insufficiency.

Right atrial enlargement

Enlargement of the right atrium seldom occurs as an isolated phenomenon. The most common radiological sign is that the right outline of the heart is projected far rightward, over the right lung. With substantial enlargement there is elongation of the right atrial margin so that this margin comprises more than 60% of the length of the mediastinal cardiovascular silhouette. Right atrial enlargement can also obliterate the retrosternal clear space as depicted on the lateral film.

Enlargement of the right atrium is readily demonstrated by echocardiography, ultra fast CT and MRI. The most common cause of enlargement of the right atrium is tricuspid insufficiency, usually caused by rheumatic heart disease. Acquired tricuspid stenosis seldom occurs.

Acquired valvular diseases

Mitral valve disease
Mitral stenosis is usually caused by rheumatic heart disease and rarely by congenital defects or left atrial myxoma. Mitral regurgitation has

 

a b

Figure 23. a) Mitral insufficiency - enlargement of the left atrium with backwards dislocation of the contrast filled esophagus. b) Mitral defect with enlargement of the left atrium (oblique view). The enlarged left atrium dislocates the contrast filled esophagus backwards.

many etiologies, including mitral valve prolapse, spontaneous chordal rupture, bacterial eondocarditis, post infarctional papillary muscle rupture or dysfunction and rheumatic heart disease.

In the acute phase of rheumatic fever, the chest radiograph is normal. If cardiomegaly occurs, it is usually due to pericardial fluid as a result of pericarditis. Enlargement of the heart not due to pericarditis is, at this stage, most often caused by an acute involvement of the mitral valves, resulting in mitral insufficiency.

When chronic changes develop, there is scar formation and retraction of the cusps, which become thickened. At the same time, fibrosis develops in the surrounding papillary muscles. A combination of stenosis and insufficiency is usually seen. In late stages, calcification of the cusps may occur.

Stenosis of the mitral valve causes increased mean pressure in the left atrium, which is transmitted retrogradely to the pulmonary veins (pulmonary venous hypertension), eventually resulting in interstitial and later alveolar edema. At a later stage, as a result of the development of pulmonary hypertension, pulmonary insufficiency, dilatation of the right ventricle, and tricuspid insufficiency develop.

 

Figure 24. Considerably enlarged heart with "mitral configuration ". All parts of the heart are enlarged. Special accentiIation of upper left heart outline, considerably dilated vascular structures in the right hilar region.

The initial radiological finding is enlargement of the left atrium (Fig. 23 a, b). The left auricle is frequently dilated and is seen as a lateral evagination in the segment of the left cardiac margin between the pulmonary artery and the left ventricle on the frontal radiograph. At the same time, there is elevation of the left main bronchus. The esophagus is dislocated posteriorly and to the left. There may be signs of pulmonary hypertension or edema and subsequently, right ventricular enlargement (Fig. 24).

Calcification of the valves may be difficult to detect in frontal and lateral views, but are readily identified if present, on fluoroscopy and on CT scans. In some cases, calcification on the wall of the left atrium may occur. This is usually found in the posterior part of the atrial wall.

On the basis of frontal and lateral views of the heart, it is sometimes possible to determine whether the dominant abnormality is mitral stenosis or insufficiency. If there is enlargement of both the left atrium and left ventricle, mitral insufficiency is likely to be the most important component, if it is possible to exclude the simultaneous presence of an aortic valve disease.

The definitive diagnosis of mitral valve disease is established by left ventricular angiography and echocardiography. In the left ventricular angiography, the left ventricle is catheterized, and contrast medium is injected. When normal mitral valves open, non-opacified blood flows from the left atrium into the left ventricle and causes a void (wash-in defect) in the contrast pool of the left ventricular chamber. In mitral stenosis there is restriction of the wave front of unopaficied blood flow into the left ventricle. In mitral insufficiency, there is regurgitation of contrast medium from the left ventricle to the left atrium during systole.

Echocardiography is ideal for evaluation of the mitral valve morphology and motion. M-mode echocardiography allows the study of reduction in DCR (diastolic closure rate), and also permits demonstration of thickening of both the anterior and posterior cusps of the mitral valve. Echocardiography also provides a visual demonstration of the left atrium, making it possible to calculate its volume. The existence of thrombi in the left atrium can also be visualized by the same technique. Echocardiography is the most important modality in the diagnosis of mitral defects of non-rheumatic etiology.

Tricuspid valvular defects

Tricuspid valvular defects arise either as a consequence of a purely rheumatic process involving the valvular apparatus, or by the tricuspid valve becoming insufficient because of dilatation of the right ventricle.

The most important radiological sign is an enlarged right atrium. As tricuspid defects are seldom seen as isolated phenomena, the diagnosis is difficult to make on the basis of conventional radiography with frontal and lateral views of the heart. Calcification of the tricuspid valve is extremely rare.

It is easiest to examine the tricuspid valve by echocardiography. In the presence of a tricuspid defect, cardiac catheterization with insertion of a catheter through the tricuspid orifice to the right ventricle is difficult. An enlarged right atrium makes it difficult to insert the tip of the catheter through the tricuspid valves, especially if stenosis is also present.

Aortic valvular disease

Aortic stenosis
Aortic stenosis can occur either on a rheumatic basis or as a result of calcification in adult life of congenitally abnormal valves, usually bicuspid valves. Aortic stenosis on a rheumatic basis is frequently accompanied by aortic insufficiency. In rheumatic aortic valvular disease, however, concomitant abnormalities of the mitral valves are always present and frequently dominate the clinical features and the radiographic findings.

Figure 25. Lateral view of the heart with calcification of the aortic valve cusps (black arrows).

The aortic valves are frequently calcified (Fig. 25). During the compensated phase, there is hypertrophy of the left ventricle but usually radiographic signs of enlargement of the left ventricle. In the decompensated phase, moderate enlargement of the heart may be present, but the left ventricle size may be increased considerably in the presence of simultaneous aortic insufficiency. In aortic stenosis, the ascending aorta is dilated (post-stenotic dilatation). Echocardiography provides a good view of the aortic valves, and the degree of restriction of motion can be assessed. The pressure gradient between the valves can be estimated by measuring the peak velocity of blood flow using Doppler echocardiography. Echocardiography has reduced the necessity of catheterization of the left ventricle, which is beneficial, as this may be difficult to perform through a stenotic aortic orifice.

Aortic insufficiency
The radiographic features are different for acute and chronic aortic insufficiency. Acute aortic insufficiency is usually caused by bacterial endocarditis, and produces a rapid increase in the left ventricle end-diastolic pressure, with development of pulmonary edema. In the acute phase, the size of the heart will be normal in most patients, but if heart failure develops there will be pulmonary edema and redistribution of flow to the pulmonary vessels in the upper part of the lungs. Acute aortic insufficiency

Figure 26. Aortic insufficiency - injection of contrast medium into the ascending aorta immediately above the aortic valve with regurgitation of contrast into the whole left ventricle (black arrows). Aortic insufficiency grade III.

is one of the causes of pulmonary edema in a patient with a heart of normal size.

Chronic aortic insufficiency is most often a result of congenital valvular defect or rheumatic heart disease. Bicuspid valves are the most common form of congenital anomaly. Rheumatic heart disease usually leads to destruction of the valvular apparatus, often with adhesion of the commisures, resulting in combined aortic stenosis and insufficiency. The mitral valves are frequently also involved.

The diagnosis and the amount of regurgitation from the ascending aorta to the left ventricle in diastole can be estimated by Doppler echocardiography. The thickening and limitation of the aortic leaflets can also be established by echocardiography. Two-dimensional echocardiography is used to determine the size of the left ventricle and left ventricular function. Cine MRI has been used to identify valvular regurgitation due to the signal void caused by the regurgitant jet (Fig. 12).

Right-sided cardiac catheterization is usually performed in addition to left ventricular angiography in order to evaluate the right-sided valve and pulmonary arterial pressure. Left ventricular angiography is used to assess the function of the left ventricle. Preoperatively, coronary angiography will nearly always also be done to exclude significant stenoses. Aortic insufficiency is graded angiographically (grades I-IV), according to the amount of contrast medium refluxing into the left ventricle after injection of contrast medium into the ascending aorta (Fig. 26).

Ischemic heart disease

 

Angina pectoris
Angina pectoris is a clinical syndrome, characterized by retrosternal chest pain with typical radiation to the left arm. When surgery is considered in these patients, coronary angiography is carried out in order to identify the sites and severities of stenoses in the coronary arteries. In the presence of severe stenosis (> 85% reduction in luminal diameter) or occlusion, collateral vessels are frequently present originating from the ipsilateral or contralateral coronary artery.

Evaluation of regional and global function of the left ventricle is an integral part of angiography in the assessment of a patient with angina pectoris. The global function of the left ventricle is provided by measurements of the ejection fraction and the end-diastolic pressure and regional function defined by wall motion. Assessment of left ventricular function can also be made by echocardiography. Ventricular function can also be studied using scintigraphy techniques and/or isotope ventriculography (Fig. 16 a, b). At present, neither echocardiography nor scintigraphy can provide the necessary morphological information on the condition of the coronary arteries.

Infarct
Myocardial infarction is ischemic necrosis of the heart muscle leaving fibrotic scar tissue. Currently, many infarcts are treated with thrombolytic therapy, which may attenuate the severity and extent of the infarction.

Uncomplicated infarction causes no changes in the chest radiograph. If an earlier infarct has led to the development of an aneurysm, this may appear as a bulging of the outline of the heart (Fig. 27). Calcification rarely marks the site of prior infarctions or aneurysms. In some cases acute infarction causes pulmonary venous hypertension or edema, usually with a normal heart size.

In left ventricular angiography, the infarcted region usually shows no wall motion (akinesis), paradoxical motion (dyskinesis) or severe reduction in wall motion (hypokinesis). Multiple or large infarcts reduce the ejection fraction of the left ventricle and increase end-diastolic pres
sure. Dilatation of the ventricle may develop, producing the features of ischemic cardiomyopathy. Coronary angiography usually demonstrates

Figure 27. PA view of the heart with large left ventricular aneurysm with massive bulging of the left outline of the heart.

high degrees of stenosis, or possible occlusion, of the arteries that supply the infarcted area.

Complications of infarction
A number of complications may occur secondary to myocardial infarction, including cardiac rupture. This leads to cardiac tamponade, and these patients die so quickly that angiography and echocardiography are seldom carried out.

Aneurysms of the left ventricle may develop after large transmural infarcts. The diagnosis can be evident on the radiograph, where there is a focal bulging (evagination) of the normal contour of the heart, most frequently in the apical region (Fig. 27). During fluoroscopy, reduced, possibly paradoxical, movement of the aneurysmal area is seen. The diagnosis is otherwise made by left ventricular angiography, 2D echocardiography, or MRI (Fig. 10).

Large infarctions that include the ventricular septum may lead to rupture of the ventricular septum. This is a complication with high mortality if the rupture occurs in the lower posterior part, but a slightly better prognosis if the rupture occurs in the anterior part of the ventricular septum. The chest radiographs show an enlarged heart with pulmonary edema. Right-sided cardiac catheterization demonstrates signs of left-to right shunt with highly oxygenated blood in the right half of the heart. The diagnosis is easily made by left ventricular angiography, where a leak of contrast from the left to the right ventricle is seen, and by echocardiography.

Thrombi in the left ventricle, usually at the apex, are also seen as a complication of infarction. This diagnosis can be made by left ventricular angiography, 2D echocardiography and MRI.

Other heart diseases

There are a number of other diseases that are confined to the myocardium, including different types of cardiomyopathy. The major types of cardiomyopathies are: dilated (congestive), hypertrophic, restrictive, and obliterated forms.

Cardiomyopathy may be caused by infection, collagen vascular diseases, atherosclerosis, or metabolic diseases. Use of alcohol and drugs may produce dilated (congestive) cardiomyopathy. Endomyocardial fibrosis also causes a form of cardiomyopathy. However, most cases of dilated cardiomyopathy are idiopathic.
In the dilated form of cardiomyopathy, the heart is considerably enlarged, and there is also pulmonary venous congestion and/or edema. Echocardiography, angiography, and isotope ventriculography can be used to assess ventricular function and thereby document the severity of dilated cardiomyopathy.
Two dimensional echocardiography and MRI are used to evaluate the severity and distribution of hypertrophy throughout the left ventricle in hypertrophic cardiomyopathy. Most patients have asymmetric thickening of the ventricular septum with or without obstruction of the subaortic region. MRI has been useful for quantifying myocardial mass in this disease.

Tumors in the heart are rare and are usually benign. The most common types are myxoma of the left atrium and lipoma of the right atrium. In a chest radiograph the heart is either normal in size, or there is slight enlargement of the left atrium. On echocardiography, it may be difficult to differentiate between an intra-atrial myxoma and a thrombus. MRI has recently been shown to be a very effective method for demonstrating the presence and extent of intracardiac and paracardiac tumors (Figs. 7, 8). The diagnosis can also be made by angiography, but here too, it may be difficult to distinguish between a thrombus and a tumor. On MRI the signal intensity of thrombus is usually lower than that of most, but not all, cardiac tumors.

Pericardial diseases

 

Pericardial cysts
Pericardial cysts are congenital and filled by clear serous fluid. They may communicate with the pericardial space. About 2/3 of all pericardial cysts are found caudally and anteriorly on the right side. On the chest radiograph, it is impossible to differentiate between cysts and pericardial fat pads, but the differential diagnosis is readily established by 2D echocardiography, computed tomography, or MRI. Pericardial diverticula are less common than pericardial cysts. These are true diverticula, containing all the layers of the pericardium.

Pericardial tumors
Pericardial tumors are very unusual. Mesothelioma is the most frequently se en malignant tumor. Dermoid is a benign tumor of the pericardium. Metastases are seen more often. In most respects, the clinical and radiological picture resembles that seen with an ordinary pericardial effusion. A pericardial tumor is suggested by a hemorrhagic pericardial effusion. The hemorrhagic effusion can be defined as such by MRI, when it causes bright signal on T1-weighted spin echo images. Pericardial tumors are best demonstrated by MRI.

Pericardial fluid
Pericardial effusion may be caused by a number of conditions, the most common being cardiovascular, infectious, malignant, metabolic, or iatrogenic in origin. Common causes are congestive heart failure, uremia, acute viral pericarditis, and myocardial infarction. When investigating a patient suspected of having a dissecting aneurysm in the ascending aorta, echocardiogra