10 Radiology of Cardiac Disease

Posteroanterior (PA) and lateral chest radiographs taken in inspiration are standard for evaluation of cardiac size and contour. On the PA chest radiograph, the right cardiomediastinal border is formed by the superior vena cava (SVC) and the right atrium; the left cardiomediastinal border is formed by the aortic arch, main pulmonary artery, left atrial appendage, and left ventricle (LV) (see Figs. 1.8, 10.1a).

On the lateral projection, the right ventricle is in contact with the lower sternum. More superiorly, the anterior cardiac silhouette is formed by the right ventricular outflow tract and pulmonary conus. The left atrium and left ventricle form the posterior cardiac contour (see Figs. 1.9, 10.1b).

Cardiac Size

While there is some variation in normal values, transverse cardiac diameter usually should not exceed the transverse diameter of one hemithorax or 50% of the widest transverse thoracic diameter. A more accurate determination of cardiac volume may be made from the lateral radiograph (Fig. 10.2) although today this has been superseded by echocardiographic assessment.

Cardiac Contour

Both congenital and acquired cardiac disease are frequently associated with specific chamber hypertrophy or enlargement resulting in alteration in the shape of the cardiac silhouette (Table 10.1).

Radiographic features in:

• Left ventricular enlargement (e.g. secondary to systemic arterial hypertension or aortic stenosis) include:
  
  
  
  1. – On the PA view transverse cardiac diameter is increased, the cardiac apex is rounded, and there is lateral convexity of the left heart border (aortic configuration.
     
  2. – On the lateral view, there is partial obliteration of the retrocardiac space as the heart extends up to 2 cm posterior to the inferior vena caval (IVC) shadow (Figs. 10.3, 10.4c,d).
  
  
• Right ventricular enlargement (e. g., due to pulmonary arterial hypertension) include:
  
  
  
  1. – Right ventricular change may be quite marked before radiographic abnormalities become apparent. Right ventricular hypertrophy results in cardiac rotation with posterior displacement of the left ventricle. The right ventricle then forms part of the left heart border and there is characteristically some “elevation” of the cardiac apex on the PA view (Fig. 10.4e, f).
     
  2. – Right ventricular hypertrophy and dilatation are frequently associated with dilatation of the main and central pulmonary arteries.
  
  
• Left atrial enlargement (due to mitral stenosis) include:
  
  
  
  1. – On the PA radiograph, left atrial dilatation is associated with prominence or “fullness” of the left cardiac border and obliteration of the normal cardiac waist.
     
  2. – The left atrium extends posteriorly as enlargement becomes more marked and then its right border may be projected within the cardiac silhouette (double “right heart border” sign).
     
  3. – There may also be splaying of the carina to an angle of greater than 90° as the left atrium extends superiorly.
     
  4. – On the lateral view, there is narrowing of the retrocardiac space as the left atrium enlarges posteriorly (Figs. 10.4a, b, 10.31).
  
  
• Right atrial enlargement (e. g., due to tricuspid insufficiency) include:
  
  
  
  1. – Prominence of the right cardiac border.
     
  2. – The height of the atrial shadow exceeds 50 % of the distance between the diaphragm and aortic arch (Higgins 1992, Fig. 10.4g).

Fig. 10.1a, b Normal cardiac anatomy on PA and lateral chest radiographs (from Klose et al. 1991) Ao = Aorta

Table 10.1 Conditions which may alter heart size (modified from Higgins 1992)

Small cardiac silhouette: Asthenic body habitus Cachexia Emphysema (narrow, elongated heart) Restrictive cardiomyopathy Constrictive pericarditis

Normal-size cardiac silhouette despite the presence of significant lesions Aortic stenosis Arterial hypertension Mitral stenosis Hypertrophic cardiomyopathy Acute myocardial infarction Some congenital heart lesions

Large cardiac silhouette: Normal variant (e. g., physiologic LV hypertrophy in athletes) Biventricular decompensation Dilated cardiomyopathy Aortic insufficiency Mitral insufficiency Decompensated valvular stenoses Congenital cardiac anomalies Pericardial effusion (globular or triangular silhouette)

Fig. 10.3 Chest radiograph in aortic stenosis. Note the rounded cardiac apex, the left ventricular enlargement, and the poststenotic dilatation of the ascending aorta.

Congenital Heart Disease

Cardiac Anomalies without a Shunt

Pulmonary Stenosis

The chest radiograph may show characteristic poststenotic dilatation of the main pulmonary artery extending to involve the left pulmonary artery and resulting in enlargement of the left hilum (Fig. 10.5). The heart is of “right ventricular” configuration with elevation, rounding, and flattening of the cardiac apex. Pulmonary vascularity is normal in most cases except in high-grade stenoses.

Echocardiography: In moderate to severe stenosis, pulmonary valve leaflets are thickened with evidence of “doming” during systole. Poststenotic dilatation of the main pulmonary artery is seen with significant degrees of obstruction. Right ventricular anterior wall thickness may be measured. Pulsed (PW) and continuous wave (CW) Doppler allow estimation of the systolic gradient across the valve. The right ventricular anterior wall thickness and the systolic gradient determine the need for surgical intervention (Grainger 1992).

Congenital Aortic Stenosis

Coarctation of the Aorta

• Infantile (preductal) COA: In this form, the stenosis lies proximal to the ductus arteriosus which usually is patent. This may result in a right-to-left shunt with cyanosis in the lower half of the body (Fig. 10.6).
  
• Adult (postductal) COA: In postductal or adult coarctation, systolic blood pressure in the upper limbs exceeds that in the lower limbs by at least 20 mmHg. The lower body is supplied by collateral vessels which usually have developed by late childhood. Associated anomalies including bicuspid aortic valve and aberrant subclavian artery occur in up to 75% of cases.

Fig. 10.6a-k Schematic representation of congenital cardiac anomalies (from Schinz et al. 1983).

Fig. 10.7 Coarctation of the aorta. Note the left ventricular enlargement, the focal “notch” in the aorta giving a “reversed 3” configuration (1) and the rib notching (2).

Fig. 10.8 Aortic coarctation: “Reversed 3” configuration of the aorta is seen.

Radiologic Findings

Chest radiograph: Radiographic findings in coarctation include a high aortic arch with pre- and poststenotic dilatation (Figs. 10.7, 10.8). In the postductal type, rib notching involving the 3rd to 8th ribs is due to pressure erosion by dilated intercostal collateral vessels. In the infantile type, dilatation of the pulmonary vessels may indicate the presence of a left-to-right shunt.

Magnetic resonance imaging and aortography demonstrate the length and level of the coarctation segment and the degree of arterial collateralization present (Figs. 10.9, 10.10). The relationship of the origin of the subclavian arteries to the stenotic segment is important to demonstrate given the association with the aberrant subclavian artery (Boxt et al. 2003). MRI also plays a role in imaging follow-up of patients after balloon dilatation and repair of the coarctation.

Congenital Cardiac Anomalies Associated with a Left-to-Right Shunt

The most common causes of a left-to-right shunt are ventricular septal defects (VSD: 20–28 % of all congenital cardiac anomalies, Fig. 10.11), atrial septal defects (ASD: 10–15%), and patent ductus arteriosus (PDA: 10–15%). Less common anomalies include Lutembacher syndrome (ASD combined with mitral stenosis) and anomalous pulmonary venous drainage (APVD).

The shunt may be at the atrial (ASD), ventricular (VSD), or arterial (PDA) level. Oxygenated blood may also be shunted from the pulmonary veins back into the right atrium (APVD). Recirculating blood volume may greatly exceed the circulating systemic volume; this leads to overload of the pulmonary circulation with resulting pulmonary arteriolar sclerosis and increased pulmonary vascular resistance. This in turn induces right ventricular hypertrophy causing further increases in pulmonary arterial pressure. Eventually right heart pressure may exceed that in the left heart chambers leading to shunt reversal (Eisenmenger reaction; see Chapter 7, p. 194).

Individuals with congenital left-to-right shunts may remain asymptomatic for many years but are at increased risk of endocarditis. Large shunts may be associated with marked symptomatology including impaired physical development in children. Characteristic auscultatory findings include a pansystolic murmur in VSD and a continuous murmur in PDA. In advanced untreated cases, signs of right heart failure (dilated neck veins, peripheral edema, and hepatomegaly) may supervene. Cyanosis develops with reversal of the shunt.

Fig. 10.10 MRI demonstrates aortic coarctation and dilated intercostal vessels inferior to the level of the aortic narrowing.

Chest radiograph: When the pulmonary to systemic shunt ratio is greater than 2:1, there is cardiomegaly (Grainger and Donner 1992) and pulmonary plethora (Higgins 1992). Other characteristic features include increased pulsation of dilated central pulmonary arteries (hilar dance) visible at fluoroscopy. The level of the shunt cannot be determined from standard radiographs although certain characteristics of the cardiac silhouette may give diagnostic clues (Fig. 10.12).

Atrial Septal Defect

Atrial septal defects are classified according to the site of the communication (see Fig. 10.6b, c):

• An ostium secundum or fossa ovalis defect is situated in the upper part of the septum posterior to the coronary sinus and superior to the tricuspid valve. The size of the defect is variable, the mildest form being a slit-like patency of the foramen ovale that normally closes soon after birth. Significant shunts are usually greater than 2 cm in diameter, are not valvular, and will transmit blood from the left to the right atrium. Ostium secundum defects account for 80 to 90% of all ASDs (Grainger and Donner 1992).
  
• An ostium primum defect involves the inferior part of the septum and is the mildest form of endocardial cushion defect. An ostium primum defect together with cleft leaflets of malformed tricuspid and mitral valves represent incomplete persistence of the arterioventricular canal. If a high VSD is also present, the combination constitutes complete persistence of the arterioventricular canal. There is mitral regurgitation with left-to-right shunting of blood. The elevation of right heart pressures results in gradual development of pulmonary hypertension.
  
• A sinus venosus defect is situated in the most superior part of the septum just inferior to the termination of the superior vena cava. This almost invariably is associated with aberrant drainage of the right upper lobe pulmonary vein into the inferior part of the SVC. Sinus venosus defects account for 5% of all ASDs.

Radiologic Findings

Chest radiograph: If the shunt ratio is greater than 2:1, there is usually cardiomegaly. There is dilatation of the central pulmonary arteries and a variable degree of pulmonary plethora is present. The aortic arch may appear small, probably due to a degree of aortic rotation (Figs. 10.13, 10.14).

Echocardiography will demonstrate nearly all defects. When a significant shunt is present, there is evidence of right ventricular dilatation with systolic anterior motion of the interventricular septum. The four-chamber subcostal view will differentiate ostium secundum from primum defects (Grainger and Donner 1992).

Fig. 10.12a, b Atrial septal defect with a left-to-right shunt. Note the central pulmonary artery dilatation (1 and 2) and the pulmonary plethora (3).

Fig. 10.13a, b Ostium secundum defect. (a) Chest radiograph shows cardiomegaly, dilatation of the main pulmonary artery, and pulmonary edema. Radiograph 4 years after operative closure of the defect is almost normal (b).

Magnetic resonance imaging: MRI in the axial plane has 97% sensitivity and 90 % specificity for detection of ASDs (Diethelm et al. 1987). Intravenous administration of gadolinium may help to demonstrate smaller and less apparent shunts (Manning et al. 1992). GRE sequences allow determination of the direction of the shunt and velocity-encoded cine (VEC) images allow some estimation of the volume of the shunt.

Ventricular Septal Defect

The magnitude of the shunt is roughly proportional to the area of the defect. With defects smaller than 0.5 cm², systolic muscle contractions are sufficient to maintain the interventricular pressure gradient. With larger defects, the right ventricle is subjected to systemic pressures with resulting right ventricular hypertrophy. Right ventricular hypertrophy and increasing pulmonary vascular resistance lead to a reduction in the volume of the left-to-right shunt and if untreated will in time lead to its reversal (Eisenmenger reaction, see Fig. 10.6d).

Radiologic Findings

The chest radiograph may be normal when just a small defect is present. Larger defects are associated with the characteristic features of a left-to-right shunt including cardiomegaly, dilated central pulmonary arteries, and pulmonary plethora.

Two-dimensional echocardiography will identify the site of the defect. Left atrial and left ventricular dilatation will be evident in moderate to large shunts. PW Doppler will confirm the presence of a shunt and Doppler color flow mapping will identify the site, extent, and direction of the shunt (Grainger and Donner 1992, Ludomirsky et al. 1986, Ortiz et al. 1985).

Magnetic resonance imaging allows diagnosis of and determination of the size of a VSD. Large defects may be readily identified on spin echo sequences as signal voids to the left of the atrioventricular rings. Smaller more distal and muscular VSDs may be difficult to demonstrate on spin echo sequences but the signal void jet of the shunted blood on GRE sequences may allow their detection.

Patent Ductus Arteriosus

This communication between the concavity of the aortic arch and the superior aspect of the main pulmonary artery constitutes an essential part of the fetal circulation and usually closes soon after birth. Persistence of this tubular connection (patent ductus arteriosus) permits passage of blood from the higher-pressure aorta into the pulmonary artery and through the pulmonary circulation thus creating a left-to-right shunt. The defect is variable in size but is seldom greater than 1 cm² in cross-sectional area. An aortopulmonary pressure gradient is maintained in the majority of cases.

Only the left heart chambers are enlarged initially as the shunt does not involve the right ventricle. Eventually, pulmonary vascular resistance increases as a result of increased pulmonary blood flow and this in turn leads to pressure overload on the right heart (see Fig. 10.6e). Eisenmenger reaction with shunt reversal occurs when pulmonary arterial pressure exceeds that of the systemic arterial circulation.

Radiologic Findings

The chest radiograph shows features of a left-to-right shunt. There is associated enlargement of structures proximal to the shunt including the left atrium, left ventricle, ascending aorta, and aortic arch (Fig. 10.15). If shunt reversal occurs (Eisenmenger reaction) then the central pulmonary arteries become more dilated and peripheral oligemia develops (Fig. 10.15). In cases of long-standing severe pulmonary hypertension with Eisenmenger reaction, calcification (Fig. 10.16) of the dilated pulmonary arteries and ductus may be seen.

Two-dimensional echocardiography will show left atrial and left ventricular dilatation. PW Doppler evaluation of the pulmonary artery confirms the diagnosis showing normal forward flow from the pulmonary valve during systole with reversed flow from the bifurcation in diastole. Doppler color flow mapping allows assessment of the overall size of the shunt (Grainger and Donner 1992, see Fig. 10.17).

Magnetic resonance imaging: Imaging in the coronal or in the parasagittal right anterior oblique (RAO) plane may demonstrate the ductal communication. However, no data are available on the sensitivity and specificity of MRI in diagnosis of PDA (Boxt et al. 2003). Furthermore, magnetic resonance (MR) evaluation of this anomaly may be limited in infants by the small size of the ductus and limited MR spatial resolution.

Aortography: Contrast medium injected into the aortic arch will demonstrate the patent ductus and opacify the pulmonary arteries (Fig. 10.17).

Total Anomalous Pulmonary Venous Drainage (TAPVD)

In TAPVD, pulmonary venous drainage is to almost any element of the sinus venosus system. This is a relatively rare anomaly accounting for approximately 2% of all cardiac malformations and is compatible with life only when a coexisting atrial septal defect is present.

TAPVD may be classified into:

• Type I: Supracardiac return is most common (55%) with pulmonary venous drainage (PVD) to the vertical vein which then drains to the brachiocephalic vein and superior vena cava or with PVD to the azygos vein and then to the SVC.
  
• Type II: Anomalous return at cardiac level with drainage to the coronary sinus or right atrium.
  
• Type III: Infradiaphragmatic return with drainage to the portal system or inferior vena cava.
  
• Type IV: Drainage at multiple levels (Pearson et al. 1987).

Fig. 10.15a, b Patent ductus arteriosus. Radiographs show cardiomegaly, marked central pulmonary artery dilatation, and a dilated aortic arch.

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