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Plain-film evaluation of valvular heart disease
P l a i n - F i l m E v a l u a t i o n of V a l v u l a r H e a r t D i s e a s e Richard C. Romero and Lawrence M. Boxt
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OSTEROANTERIOR (PA) and lateral (LAT) chest radiographs yield qualitative and quantitative information concerning cardiac chamber size and myocardial mass, pulmonary blood flow, pulmonary venous pressure, and intracardiac calcification in patients with cardiac murmurs. Changes seen in patients with acute and chronic valvular heart disease represent the ability of the heart to adapt to acute changes as well as the chronic adaptations made to alterations in atrial and ventricular volume and pressure loads. Appreciating the homeostatic mechanisms of maintaining wall stress within a normal range and maintenance of systemic cardiac output provides a means of understanding the changes in chamber volume and myocardial mass producing the radiographic changes that form the basis of diagnosis. Although there may be many different diseases that cause a particular valve to perform abnormally, the radiographic changes are characteristic of that valve dysfunction. Close attention to other radiographic abnormalities will help limiting the differential diagnosis. MITRAL STENOSIS
Chronic rheumatic carditis is the most common cause of mitral stenosis. Congenital mitral stenosis is rare and is observed mainly in infants and children. 1 Isolated mitral stenosis occurs in about 40% of all patients presenting with rheumatic heart disease. Nearly 60% of patients with pure mitral stenosis report a history of rheumatic fever.2,3 Rheumatic fever initially presents acutely with pancarditis in which the inflammatory reaction induces mitral papillary muscle dysfunction or acute mitral annular dilation. The end result of these processes is inadequate opposition of the edges of the mitral valve cusps and regurgitant systolic blood flow from the left ventricle. The
From the Department of Radiology, Columbia University College of Physicians and Surgeons, New York,"and the Division of Cardiovascular MRI, Department of Radiology, Beth Israel Medical Cente~ New York, NY Address reprint requests to Lawrence M. Boxt, MD, Division of Cardiovascular MRL Department of Radiology, Beth Israel Medical Center, First Ave and 16th St, New York, NY 10003. Copyright © 1999 by W.B. Saunders Company 0037-198X/99/3403-0008510. 00/0 216
characteristic valvular lesion of acute rheumatic heart disease is thus mitral regurgitation. On the other hand, rheumatic mitral stenosis results from a chronic and progressive fibrotic process instigated by the initial rheumatic fever inflammatory reaction. Because of the slowly progressive nature of the reactive fibrosis, a 20- to 40-year latent period may ensue before a patient with a history of acute rheumatic fever develops signs or symptoms of rheumatic mitral stenosis. Once symptoms occur, another decade may pass before symptoms become disabling. 2 The fibrotic process results in diffuse thickening, calcification and adherence of the mitral cusp margins, and decreased mitral leaflet compliance such that the mitral orifice becomes smaller and the leaflet motility is reduced. In addition, the chordae tendineae become thickened, fused, and nonpliable, further impeding an individual leaflet's opening excursion during diastole. This restriction imposes a functional narrowing of the mitral orifice.l,4 Decreasing the mitral orifice size from a normal area of 4.0 to 5.0 to <2.5 cm 2 increases the left atrial outflow resistance. With this reduction in valve area blood can flow from the left atrium to left ventricle only if propelled by a pressure gradient. The diastolic transmitral gradient is the fundimental expression of mitral stenosis, 5 resulting in left atrial hypertension. The left atrium dilates and hypertrophies in response to this volume and pressure load. Because the pulmonary veins are valveless, the elevated left atrial pressure is transmitted into the pulmonary venous system. The transmittal gradient is a function of the square of the transvalvular flow rate and dependent on the length of the diastolic filling period. 6 Thus, heart rate is the significant factor in inducing symptoms. As pulmonary venous and pulmonary capillary pressure increases, the pulmonary endothelia become permeable and alveolar wall edema develops. As pulmonary venous and pulmonary capillary pressure increases, the interstices of the pulmonary venules are stretched, and the space among the cells increases, allowing water to seep from the vascular compartment into the perivascular sheaths of the pulmonary veins. Continued or progressive elevation in left atrial pressure will cause continued fluid transudation. This progresses to cause interstitial Seminars in Roentgenology, Vol XXXIV, No 3 (July), 1999: pp 216-227
DIAGNOSIS OF VALVULAR HEART DISEASE
pulmonary edema. Eventually fluid will make its way proximally in the venous tree, to increase alveolar-capillary distance, thus decreasing oxygenation of capillary blood. Chronic elevation in pulmonary venous pressure stretches the venule interstices to allow whole blood products (red and white cells) into the pulmonary parenchyma, essentially causing parenchymal pulmonary hemorrhage. The pulmonary phagocytic system attacks this blood, and the red and white cells are phagocytosed. The phagocytosing white blood cells (dust cells) convert the hemoglobin to hemosiderin. The initial increase in left atrial pressure may not be recognizible on plain chest film examination. However, with continued elevation in pressure and progressive interstitial pulmonary edema, radiographic changes begin to appear. The earliest sign of left atrial hypertension is straightening of the left atrial appendage segment on the left heart border. Usually concave, this segment straightens and eventually becomes convex. Radiographic changes in the lungs mirror change in left atrial pressure as well as changes resulting from interstitial edema formation. Normally, in the upright PA chest examination, the lower lobe vessels are greater in caliber than the upper lobe vessels. There is more lung parenchyma in the lower lung zones and therefore more pulmonary blood flow. The decreased flow to the upper lobes results in decreased pulmonary venous return from the lungs to the heart. Thus, upper lobe alveolar pressure is greater than pulmonary venous pressure and the upper lobe veins appear smaller in caliber than the lower lobe vessels. However, both upper and lower lobe vessels are sharply defined by the interface between the fluid-filled blood vessels surrounded by the air-filled lungs. The interstitial edema caused by left atrial hypertension initially affects the lower lobes, mainly by causing unsharpening of the edges of the lower lobe vessels. Early radiographic findings in patients with left atrial hypertension and chronic mitral stenosis include difficulty in defining the edges of the lower lobe vessels, in face of normal-appearing, sharp upper lobe vessels. Progressive increase in left atrial pressure results in further unsharpening of the lower lobe vessels and progressive opacification of the lower lobe pulmonary parenchyma. The lungs appear "busy." The normally dark spaces among the lower lobe vessels now appear grey, and the vessels are difficult to identify within the noise
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of the parenchymal background. Progressive lower lobe interstitial edema decreases parenchymal compliance, and thus increases resistance to lower lobe pulmonary blood flow. As increased pressure is maintained and edema fluid tracks back toward the alveolar-capillary interface, blood oxygenation may decrease. Hypoxia is a potent arteriolar vasoconstrictive stimulus, causing increased lower lobe pulmonary resistance. Thus, decreased lower lobe parenchymal compliance in addition to local arteriolar vasoconstriction increases resistance to lower lobe pulmonary blood flow. Blood flow is directed toward the lower resistance upper lobe pulmonary arteries. This is reflected by the next stage in the radiographic appearance of left atrial hypertension, called cephalization or redistribution. In this circumstance the increased upper lobe pulmonary blood flow is reflected by an increase in the caliber of the upper lobe pulmonary arteries and veins. If an upper lobe vessels is identified, then a lower lobe vessel, measured the same distance from the pulmonary hilum, appears less distinct, and smaller than the upper lobe vessel. Continuous progression of this process will eventually result in development of perivascular and interstitial edema of the upper lobes as well, causing upper lobe vessel unsharpness. Interstitial edema is drained by the pulmonary lymphatics. Progressive interstitial edema is reflected by engorgement of the interlobar septa and lymphatics, causing the appearance of Kerley A, B, and C lines. A and C lines appear as nearly randomly distributed sharply defined curvilinear densities across the lung parenchyma. Kerley B lines are found as linear densities extending from the pleural edges of the lungs, nearly parallel and horizontal in orientation. When left atrial pressure rises above 22 mm Hg, plasma oncotic pressure is overcome, and frank alveolar pulmonary edema results. Radiographically, this appears as diffuse, usually bilateral fluffy infiltrates. However, the infiltrates do not appear as dense as those of bacterial pneumonia. Early in the course of mitral stenosis, pulmonary arterial hypertension is caused by transmission of the elevated pulmonary venous pressure across the capillary bed. However, pulmonary arteriolar resistance subsequently rises in these patients, 7,8 causing precapillary pulmonary hypertension. Chronic
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elevation in pulmonary resistance elicits increased right ventricular work against the afterload, resulting in right ventricular hypertension and myocardial hypertrophy. The hypertrophic response changes the geometry of the right ventricular cavity, and thus the function of the tricuspid valvular papillary muscles, inducing tricuspid regurgitation. The added volume load onto the already pressure-loaded right ventricle hastens right ventricular failure. The plain-film appearance of mitral stenosis is characterized by the sequelae of chronic left atrial hypertension and near-normal left ventricular filling. That is, left atrial enlargement, pulmonary venous hypertension, and varying evidence of pulmonary hypertension but a normal left ventricle (Fig 1). The earliest signs of left atrial enlargement are caused by change in the appearance of the left atrial appendage along the left heart border. Straightening and eventually convex curvature will be identified. An early sign of left atrial enlargement on lateral examination is posterior displacement of the left bronchus. Subsequently, on PA examina-
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don, identification of the dilated left atrium as a double density within the contours of the heart, elevation of the left bronchus, and eventually enlargement of the double density so that the right heart border is formed by the enlarged left atrium. In addition to left atrial enlargement, chronic mitral stenosis may be associated with left atrial endocardial and subendocardial calcification and left atrial appendage calcification (Fig 2). The pulmonary changes in mitral stenosis reflect transmission of the transmittal gradient to the pulmonary veins. These first include evidence of pulmonary venous hypertension and mild to moderate pulmonary hypertension. As described earlier, the pulmonary venous changes are bilateral and progressive, beginning in the lower lobes and eventually involving both the lung bases and apices. Pulmonary hypertension is identified by the disparity between the caliber of the enlarged main pulmonary artery segment and central pulmonary arteries and the parenchymal branches. Depending on the severity of the interstitial edema, this
Fig 1, A 44-year-old woman with exertional dyspnea is shown. (A) Posteroanterior view. Left atrial dilatation is indicated by convexity of the left atrial appendage segment (arrows) of the left heart border and extension of the density of the left atrial margin (arrowheads) to the right heart border. Mild pulmonary hypertension is reflected in the main (PA) and hilar right pulmonary artery (RP) dilatation with vasoconstriction of the parenchymal branches. Cephalization of the pulmonary blood flow indicates left atrial hypertension. The left ventricle is normal. (B) In lateral view, left atrial enlargement fills the superior retrocardiac space (large arrow) and right ventricular and pulmonary artery enlargement fills the retrosternal space (small arrows).
DIAGNOSIS OF VALVULAR HEART DISEASE
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Fig 2. Two patients with rheumatic mitral stenosis treated by mitral valve replacement are shown. (A) Calcification of the organized mural left atrial thrombus outlines the shape and defines the increased size (arrows) of the left atrium in this 58-year-old woman. (B) Curvilinear calcification along the convex left atrial appendage section of the left heart border (arrows) indicates chronic left atrial hypertension, and previous rheumatic involvement.
observation may be difficult. That is, the interstitial edema obscures the parenchymal vessel edges, making comparison of caliber with the larger vessels less reliable. However, careful examination of the parenchymal vessels will reveal that they are, in fact, decreased in caliber, and that they do not extend beyond the middle third of the lung fields, thus allowing differentiation between pulmonary hypertension caused by a shunt lesion from pulmonary hypertension caused by left heart disease. In cases of long-standing mitral stenosis, chronic left atrial and pulmonary venous hypertension results in marked left atrial enlargement and transudation of red and white cells into the pulmonary parenchyma. Erythrocytes that leak from dilated veins and congested capillaries are phagocytosed and hemoglobin is converted to hemosiderin, which is subsequently calcified. Alveolar and interstitial edema leads to fibrosis. Pulmonary artery hypertension is passive at first. Subsequent (reactive) pulmonary arteriolar changes, namely muscular hypertrophy and hyperplasia, result in progressive, irreversible hypertension (Fig 3).
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Fig 3. A 56-year-old woman with chronic mitral stenosis. There is marked cardiac enlargement with left atrial dilatation manifesting as increased right heart border convexity. In addition, the hilar pulmonary arteries are dilated and indistinct. A pseudotumor of pleural fluid is within the minor fissure. Punctate calcifications of hemosiderosis (small arrows) are throughout the lower lung fields.
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MITRAL REGURGITATION
Common causes of mitral regurgitation include mitral valve prolapse syndrome, acute or chronic rheumatic heart disease, coronary artery disease, infective endocarditis, and collagen vascular disease. An uncommon, but recently reported cause of mitral regurgitation is ingestion of anorectic agents. 9 Mitral regurgitation can develop acutely or chronically. Acute severe mitral regurgitation imposes a sudden volume load on an unprepared left ventricle. Although total left ventricular stroke volume increases somewhat because of the Frank-Starling principle, 1° foward stroke volume and total cardiac output are reduced; adequate time for development of compensatory eccentric left ventricular hypertrophy has not transpired. Similarly, the left atrium has not had adequate time to accommodate the increased volume, resulting in left atrial hypertension and pulmonary vascular congestion. Patients with acute mitral regurgitation thus often present with both low cardiac output and pulmonary congestion. Acute mitral regurgitation results from acute changes in the structures anchoring the valvular leaflets or from damage of the cusps themselves, including acute papillary muscle dysfunction or rupture resulting from myocardial infarction and chordae tendineae rupture or leaflet perforation resulting from infective endocarditis. In patients with acute mitral regurgitation, focal right upper lobe pulmonary edema may be observed. This finding is caused by a jet of regurgitant blood directed toward the right upper lobe pulmonary vein that locally accentuates the pulmonary venous pressure and thus the driving force for interstitial edema formation.t1 In cases of chronic mitral regurgitation, the initial insult is not sufficient to produce the signs and symptoms of low cardiac output and pulmonary congestion; adequate time for the formation of eccentric left ventricular hypertrophy and lengthening of individual myocardial fibers has transpired. 1°,12This compensatory increase in left ventricular end-diastolic volume permits increased total stroke volume and restoration of foward cardiac output. 14 Again, in an analogous manner, left atrial dilatation allows accommodation of the additional regurgitant volume at a lower left atrial pressure. With time, signs and symptoms of pulmonary vascular congestion abate. Chronic causes of mitral regurgitation include dilation of the mitral orifice and loss of opposition of the mitral cusp
edges, This can result from ventricular dilation stemming from cardiomyopathy, ischemic heart disease, hypertensive heart disease, or myxomatous degeneration of the mitral leaflets. The chest radiograph in chronic mitral regurgitation differs from that in the acute circumstance in terms of both pulmonary vascular signs and left atrial and ventricular size. In chronic mitral regurgitation both left atrial and left ventricular volume are increased, but pulmonary vascular congestion is only mild, or nearly normal in appearance (Fig 4). Left atrial enlargement is pronounced, with convexity of the left atrial appendage portion of the left heart border, as well as elevation of the left bronchus, and fight heart border-forming left atrium. Patients with mitral regurgitation have the largest left atria. 13The left ventricular contour is markedly increased in contour as well as displaced toward the left chest wall. On lateral examination, filling of the superior posterior retrocardiac space by the left atrium and inferior posterior retrocardiac space by the left ventricle are both evident. Posterior displacement of the left bronchus is virtually the rule. As described earlier, pulmonary vascular congestion is mild or nearly absent. Thus, there is a significant disparity between the appearance of left atrial and heart size with the appearance of the pulmonary vascular markings. Furthermore, in contrast to the appearance of the chest film in patients with mitral stenosis, there are no signs of pulmonary hypertension. Progressive left atrial enlargement decompresses atrial hypertension, resulting in nearnormal atrial and pulmonary venous pressure, no increase in pulmonary resistance or pulmonary artery pressure, and therefore no evidence of right heart failure. Aortic Stenosis
Aortic valvular stenosis represents one element of a spectrum of left ventricular outflow obstruction. Obstruction can occur at, below, or above the aortic valve; for example, valvular, subvalvular, or supravalvular stenosis. Plain-film examination is sensitive to changes caused by left ventricular hypertrophy, but limited in its specificity in differentiating among the different levels of obstruction. The most common causes of aortic stenosis are congenital, calcific degenerative, and rheumatic, i5.17 Subvalvular and supravalvular aortic stenosis are usually congenital in origin. 18 An important exception is subvalvular obstruction in hypertrophic
DIAGNOSIS OF VALVULAR HEART DISEASE
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Fig 4. A 52-year-old man with chronic mitral regurgitation is shown. (A) Posteroanterior view shows mild convexity of the left atrial appendage (short arrows) and increased convexity of the left ventricular contour (curved arrow). There is evidence of mild pulmonary vascular congestion, but the central pulmonary arteries are normal, indicating no pulmonary hypertension. (B) Lateral view shows posterior displacement of the left bronchus (short arrow) and extension of the posterior border of the left ventricle (open arrows), indicating left atrial and left ventricular dilatation, respectively.
obstructive cardiomyopathy19; however, this may, in fact, be congenital in origin as well. 2° In congenital aortic stenosis, the valve may be unicuspid or bicuspid. Newborn and infant patients with critical aortic stenosis, who present early in life, usually have a unicuspid valve. 16 Congenitally bicuspid aortic valves are malformed at birth but are not the cause of a significant gradient in early life. That is, the valve may consist of two enlarged cusps or one small cusp and one dominant cusp formed from commissural fusion of two smaller cusps. Because of the distorted architecture, blood flow across the valve is turbulent rather than laminar. The turbulent blood flow traumatizes the leaflet edges, resulting in collagenous generation, lipid deposition, fibrosis, and calcification, similar to that found much later in life in individuals with tricuspid aortic valves. Gradually increasing leaflet rigidity and orificial narrowing result in a gradient. The abnormal structure also makes the valve more susceptible to inflammatory damage resulting from infective endocarditis and may result in aortic regurgitation. As a result, patients with this lesion
tend to present later in life after variable stenotic progression. Degenerative aortic stenosis describes the narrowing of normal tricuspid aortic valves found in patients older than 65 years of age. This calcific disease progresses from the base of the valve cusps to the leaflets, eventually reducing effective valve area. Commissural fusion is not usually found. Because other degenerative changes can be found in these patients' hearts (such as calcified coronary arteries, calcified mitral annuli, and fibrous thickening of other valves), this abnormality is thought to be the result of normal wear on the valve. Diabetes and hypercholesterolemia are the two predominant predisposing factors for degenerative aortic stenosis. Aortic stenosis in patients with rheumatic heart disease results from commissural adhesion and fusion, hallmarks of the chronic rheumatic cycle of injury and healing. The valve is frequently both regurgitant and stenotic, fixed in an open configuration. In long-standing cases of rheumatic aortic stenosis, aortic valvular calcification develops, and
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further narrows the valvular orifice. Concomitant mitral valvular disease is often present but may not be recognized clinically. Thus, in the newborn or infant with unicuspid congenital aortic stenosis, there is a critical valve obstruction, and the child presents in acute heart failure. In other forms of aortic stenosis, the left ventricular obstruction develops gradually. Adaptation of the left ventricle to the progressive obstruction and systolic pressure overload is by a hypertrophic process that increases wall thickness while maintaining normal chamber volume. 21,22The development of concentric hypertrophy appears to be appropriate and provides a beneficial adaptation to compensate for high intracavitary pressure. However, hypertrophy leads to decreased left ventricular compliance and elevated left ventricular enddiastolic pressure, necessitating left atrial hypertension for left ventricular filling. Furthermore, left ventricular hypertrophy may have reduced coronary blood flow (per gram of ventricular myocardium) and exhibits increased sensitivity to ischemic injury.23 All forms of left ventricular outflow obstruction
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result in left ventricular hypertrophy. The effect of left ventricular hypertrophy on the plain-film appearance of the heart is to change the appearance of the left ventricular contour of the left heart border (Fig 5). That is, the left ventricular hypertrophy of aortic stenosis does not increase the size of the ventricle; the left ventricle is not dilated. However, it changes the "roundness" of the lower portion of the left heart border, producing the so-called "left ventricular configuration. ''24 The increased curvature of the left ventricular contour is exaggerated by the normal, concave-appearing left atrial border and normal pulmonary artery segment. Thus, the left heart border in a left ventricular configuration consists of a convex aortic arch segment and left ventricular contour, between which the relatively concave left atrial appendage and main pulmonary artery segments are sandwiched. Because aortic stenosis causes left ventricular hypertrophy and not dilation, the left ventricle appears normal on lateral examination. The inferior retrocardiac space is clear. In cases of valvular aortic stenosis, poststenotic dilatation of the ascending aorta causes increased
Fig 5. A 50-year-old man with shortness of breath is shown. (A) Posteroanterior view shows the typical convex-concave-convex appearance of the left heart border (arrows), and increased curvature of the ascending aorta (open arrows) along the right heart border, The pulmonary vascularity is normal. (B) In lateral view, the left ventricle is normal in size, and the retrosternal space is filling from behind by the dilated ascending aorta (small arrows). Aortic valvular calcification in the center of the heart (arrowheads) marks the calcified, stenotic aortic valve.
DIAGNOSIS OF VALVULAR HEART DISEASE
curvature of the mid-right heart border. The lateral border of the ascending aorta often extends beyond the right hilum, superimposed over the proximal right pulmonary artery. However, in many patients, the dilatation of the ascending aorta seems to be eccentric. That is, no change in the mid-right heart border is identified. On lateral examination, the retrosternal clear space appears to be filled in from behind, by the anterior-ward dilatation of the ascending aorta. If left ventricular outflow obstruction is below the level of the aortic valve, such as in hypertrophic obstructive cardiomyopathy, then there is no poststenotic dilatation, and the ascending aorta appears normal in configuration. Aortic valvular calcification is almost always found on plain-film examination of patients with clinically significant degenerative calcific aortic stenosis. 25 Because the fibrocalcific process begins at birth in patients with congenital aortic stenosis, calcification may be identified in younger individuals with bicuspid aortic valve stenosis. Aortic valve calcification in a young individual characterizes congenital aortic stenosis, but calcification in an older individual cannot be used to differentiate between congenital and acquired disease. Visualization of aortic valve calcification may be difficult on plain-film examination for a number of reasons. First, plain-film examination technique is optimized for evaluation of the lungs and pulmonary vascularity. Thus, bony (ie, calcified) structures may not be well appreciated. Furthermore, the aortic valve lies in nearly the center of the heart, usually projected over, or just to the left of the spine, limiting its identification. Aortic valvular calcification is best appreciated on lateral chest examination. It appears as clunky, irregular calcification at or near the center of the cardiac silhouette.
Aortic Regurgitation Aortic regurgitation can be caused by many conditions that affect the aortic valve, the aorta, or both. Valvular causes include rheumatic heart disease, infective endocarditis, congenital bicuspid aortic valve, and Marfan's syndrome affecting the aortic valve leaflets. Aortic causes include trauma, aortic dissection, and idiopathic dilation of the aortic annulus. Less commonly, inflammatory and connective tissue disease involve the aorta, such as anklyosing spondylitis, syphlitic aortitis, rheumatoid arthritis, giant call aaortitis, Ehlers-Danlos syndrome, and Reiter's syndrome. Most of these
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diseases cause chronic aortic regurgitation, which produces slow, insidious left ventricular dilation and a prolonged asymptomatic phase. Other diseases, in particular infective endocarditis, aortic dissection, and trauma, produce acute severe aortic regurgitation, which results in rapid elevation of left ventricular filling pressures and reduced cardiac output. The left ventricular response to aortic regurgitation depends on the rate at which the insufficiency develops. Aortic regurgitation imposes a volume overload on the left ventricle. In cases of acute severe aortic regurgitation, the left ventricle has not had enough time to adapt to the sudden volume load. The abrupt increase in end-diastolic left ventricular volume increases left ventricular enddiastolic and left atrial pressure dramatically. Although the Frank-Starling mechanism is used, the inability of the ventricle to develop compensatory dilatation acutely results in decreased foward cardiac output. Hence, elevated left atrial pressure and decreased forward cardiac output produces pulmonary edema and shock. In chronic aortic regurgitation, the left ventricle compensates for the volume load by increasing end-diastolic volume, increasing ventricular compliance so that the increased volume can be accommodated without increasing left atrial pressure, and acquiring a combination of concentric and eccentric ventricular myocardial hypertrophy. Thus, left ventricular performance remains normal, with normal ejection fraction. Most patients remain asymptomatic during this compensated phase, which may last for decades. Patients with chronic aortic regurgitation have a volume-loaded left ventricle and aorta. Left ventricular dilatation becomes pronounced and progressive. 13 Therefore, they present on frontal chest examinations with a left heart configuration and a pronounced mid-right heart border from the distended ascending aorta (Fig 6). The left ventricular portion of the left heart border is not only increased in curvature, but since dilated, it appears to extend farther torward the left chest wall as well. In addition, since dilated, the cardiothoracic ratio in these patients will be increased. Because chronic aortic regurgitation does not effect the left atrium until the left ventricle fails, the frontal chest radiograph will reveal a normal left atrium and pulmonary vasculature. However, once the left ventricle fails, the frontal radiograph will display
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A
Fig 6. An asymptomatic 22-year-old man is shown. (A) In posteroanterior view, the increased curvature of the lower left heart border appears similar to the man in Figure 5. However, the superior aspect of the left ventricular contour (arrows) is fuller. Pulmonary vascular markings are normal. (B) In lateral view, the left atrium is normal, but the contour of the left ventricle extends beyond the spine, indicating left ventricular dilatation. The dilated ascending aorta (small arrows) fills the retrosternal space from behind.
evidence of left atrial hypertension: a flattening of the left atrial appendage segment with prominent, unsharp, and cephalized congested pulmonary vessels. Similar to patients with aortic stenosis, the ascending aorta may not distend torward the right, and an increase in the corvature of the mid-right heart border may not be found. In lateral radiographs, the left ventricular dilation is characterized by filling of the inferior retrocardiac space. Using the Hoffman and Rigler sign, 26 the posterior border of the left ventricle extends more than 1.8 cm posteriorly to the border of the inferior vena cava when measured at 2 cm cephalad to the crossing of the right hemidiaphragm and inferior vena cava. The dilated ascending aorta fills the retrosternal airspace from the middle mediastinum toward the sternum. Because the left ventricle cannot rapidly compensate for the sudden regurgitant volume, plain-film examinations of patients with acute aortic regurgitation display signs of left atrial and pulmonary venous hypertension without left ventricular or aortic enlargement.
Tricuspid Regurgitation Tricuspid regurgitation in patients with a normal valve may be present in cases with elevated right ventricular systolic or diastolic pressure, fight ventricular dilatation, and tricuspid annular dilatation. 27,% Right ventricular systolic hypertension occurs in patients with chronic mitral stenosis, valvular pulmonic stenosis, and the various causes of pulmonary hypertension. Right ventricular diastolic hypertension is found in patients with dilated cardiomyopathy and right heart failure. Valvular abnormalities leading to tricuspid regurgitation may be acquired or congenital. Acute rheumatic valvulitis, infective endocarditis, carcinoid, rheumatoid arthritis, trauma, and Marfan's syndrome all may cause valvular regurgitation. Ebstein's malformation 29,3° is a congenital downward displacement of the tricuspid leaflet attachments into the right ventricle, resulting in an associated abnormality of the valvular apparatus causing tricuspid regurgitation and an alteration in the architecture of the right ventricle ("atrializa-
DIAGNOSIS OF VALVULAR HEART DISEASE
tion" of the right ventricle); decreased functional right ventricular myocardium limits fight ventricular cardiac output. Tricuspid regurgitation volume loads the compliant right atrium and right ventricle such that they dilate. Right atrial dilation increases the convex curvature of the lower fight heart border on frontal chest radiographs (Fig 7). Right ventricular dilatation increases the curvature of the lower third of the left heart border. Both right atrial and right ventricular dilatation cause rotation of the heart into the left chest such that the superior vena cava comes to be projected over the spine, narrowing the superior mediastinum on frontal radiographs. The increased curvature of the left heart border is seen to parallel the course of the left bronchus. Radiological differential diagnosis of tricuspid regurgitation depends on observation of other findings, which may help elucidating the underlying cause or sequelae of the regurgitant valve. The most common cause of tricuspid regurgitation is pulmonary hypertension. Thus, in addition to right heart dilatation, dilatation of the main pulmonary artery segment and central hilar pulmonary arteries and abrupt change in caliber of the parenchymal pulmonary branches, will be present in these cases. Left atrial enlargement with a normal left ventricle,
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i;;!iiill Fig 7. A 62-year-old man with chronic mitral stenosis, pulmonary hypertension, and tricuspid regurgitation is shown. Left atrial hypertension is indicated by cephalization of the pulmonary blood flow. The dilated main pulmonary artery and dilated left atrial appendage segments of the left heart border blend to form a generalized convexity superior to the left ventricular contour. The marked increase in convexity of the right heart border caused by right atrial dilatation is the result of tricuspid regurgitation mediated by pulmonary hypertension.
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and evidence of pulmonary hypertension point to mitral stenosis as a cause of the pulmonary hypertension and subsequent tricuspid regurgitation. Hyperaerated lungs and a normal left atrium indicate a pulmonary cause of the pulmonary hypertension. Pulmonary blood flow should be expected to be normal in patients with tricuspid regurgitation. Thus, fight heart enlargement with a small or diminuitive pulmonary artery segment with or without decreased caliber of parenchymal pulmonary artery segments indicates the decreased fight ventricular output found in patients with Ebstein's anomaly. Multivalvular Heart Disease
Multivalvular heart disease is usually of rheumatic origin. The most common combinations are mitral stenosis with aortic regurgitation, mitral stenosis with tricuspid regurgitation, combined mitral and aortic regurgitation, combined mitral and aortic stenosis, and combined aortic stenosis and mitral regurgitation. In combined valvular disease, the hemodynamic physiology, and therefore clinical and radiological picture, is determined by the proximal lesion. However, the appearance will vary depending on the relative severity as well as the physiological sequelae of each particular valve lesion. When both mitral stenosis and aortic regurgitation coexist, the pathophysiology is similar to that of severe mitral stenosis. Thus, left ventricular filling from the left atrium is impaired, and left ventricular size, despite the presence of aortic regurgitation, may not appear to be greatly enlarged. Nevertheless, the signs of mitral stenosis are present, including left atrial enlargement, moderate to severe left atrial hypertension with interstitial edema, and mild to moderate pulmonary hypertension. The association of tricuspid regurgitation with mitral stenosis is usually mediated by pulmonary hypertension caused by the mitral stenosis (Fig 7). As described previously, these patients have the plain-film appearance of mitral stenosis with right heart dilatation. Combined mitral and aortic regurgitation produces significant left heart dilatation, with enlargement of the left atrium, left ventricle, and ascending aorta (Fig 8). Depending on the chronicity of the disease, left atrial pressure may be near normal, and evidence of left atrial hyperten-
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Fig 8. This 58-year-old man with mixed mitral stenosis and regurgitation with secondary tricuspid regurgitation presents with marked dilatation of both the left and right heart borders. The pronounced enlargement of the left atrium associated with left ventricular dilatation results from the mitral regurgitation component of his disease. The mitral stenosis component is reflected in the pulmonary venous hypertensive changes and marked dilation of the right atrium secondary to pulmonary hypertension.
sion lacking, or only mild in appearance. The pulmonary artery segment, central pulmonary arteries, and fight heart will appear normal. In mixed mitral and aortic stenosis, radiological picture is dictated by the mitral stenosis (Fig 9). Left atrial outflow obstruction limits aortic valve flow. The radiological appearance in these patients may mimic mitral stenosis, but careful evaluation will more often than not reveal calcification of the aortic valve, indicating the second lesion. Mixed aortic stenosis with mitral regurgitation is usually caused by rheumatic heart disease. However, in young people, coexisting congenital aortic stenosis with
Fig 9. Rheumatic mixed mitral and aortic stenosis in a 57-year-old woman is shown, increased curvature of the left ventricular portion of the lower left heart border caused by left ventricular hypertrophy is superimposed on the left atrial and pulmonary artery enlargement and pulmonary venous hypertension due to mitral stenosis.
mitral valve prolapse and mitral regurgitation may produce similar symptoms and radiological findings. Left atrial and left ventricular enlargement with poststenotic dilatation of the ascending aorta, in the absence of evidence of chronic left atrial hypertension, may be helpful for considering this disease. If aortic stenosis is severe, it will worsen the mitral regurgitation and produce progressive left atrial and ventricular enlargement.
REFERENCES
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Particular reference to mitral stenosis. Circulation 12:69-81, 1955 6. GorlinR, Gorlin SG: Hydraulicformulafor calculationof the area of stenotic mitralvalve,other cardiac valvesand central circulatory shunts.Am Heart J 41:1-29, 1951 7. Wood P: An appreciationof mitral stenosis: part II. BMJ 1:1113-1124, 1954 8. GorlinR: The mechanismof the signs and symptoms of mitralvalve disease. Br Heart J 16:375-380, 1954 9. Connolly HM, Crary JL, McGoon MD, et al: Valvular heart disease associated with fenfluramine-phenteramine.N Engl J Med 337:581-588, 1997 10, Carabello BA: Mitral regurgitation: Basic pathophysiologic principles.Part 1. Mod Concepts Cardiovasc Dis 57:5358, 1988
DIAGNOSIS OF VALVULAR HEART DISEASE
11. Gurney JW, Goodman LR: Pulmonary edema localized in the right upper lobe accompanying mitral regurgitation. Radiology 171:397-399, 1989 12. Grossman W, Jones D, McLaurin LP: Wall stress and patterns of hypertrophy in the human left ventricle. J Clin Invest 56:56-64, 1975 13. Carlsson E, Gross R, Hold RG: The radiologic diagnosis of cardiac valvular insufficiencies. Circulation 55:921-933, 1977 14. Zile MR, Gaasch WH, Carroll JD, et al: Chronic mitral regurgitation: Predictive value of preoperative echocardiographic indexes of left ventricular function and wall stress. J Am Coll Cardiol 3:235-242, 1984 15. Braunwald E, Goldblatt A, Aygen MM, et al: Congenital aortic stenosis: I. Clinical and hemodynamic findings in 100 patients. II. Surgical treatment and results of operation. Circulation 27:426-462, 1963 16. Moller JH, Nakib A, Elliot RS, et al: Symptomatic congenital aortic stenosis in the first year of life. J Peadiatr 69:728-734, 1966 17. Passik CS, Ackerman DM, Piuth JR, et al: Temporal changes in the causes of aortic stenosis: A surgical pathological study of 646 cases. Mayo Clin Proc 62:119-123, 1987 18. Roberts WC: Valvular, subvalvular and supravalvular aortic stenosis: Morphologic features. Cardiovasc Clin 5:97124, 1973 19. Maron BJ, Epstein SE: Hypertrophic cardiomyopathy. Recent observations regarding the specificity of three hallmarks of the disease: Asymmetric septal hypertrophy, septal disorganization, and systolic anterior motion of the anterior mitral leaflet. Am J Cardio145:141-154, 1980 20. Perryman MB, et al: Expression of a missense mutation
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in the mRNA for [3-myosic heavy chain in myocardial tissue in hypertrophic cardiomyopathy. J Clin Invest 90:271-287, 1990 21. Sasayama S, Ross J Jr, Franklin D, et al: Adaptations of the left ventricle to chronic pressure overload. Circ Res 38:172178, 1976 22. Spann JF, Bove AA, Natarajan G, et al: Ventricular performance, pump function and compensatory mechanisms in patients with aortic stenosis. Circulation 62:576-582, 1980 23. Koyanagi S, Eastham CL, Harrison DG, et al: Increased size of myocardial infarction in dogs with chronic hypertension and left ventricular hypertrophy. Circ Res 50:55-62, 1982 24. Elliot LP, Schiebler GL: The normal cardiovascular silhouette, in Elliot LR Schiebler GL (eds): The X-Ray Diagnosis of Congenital Heart Disease in Infants, Children, and Adults. Springfield, IL, Charles C. Thomas, 1979 25. Lehman JS, Florence H, Schimert AR et al: Acquired aortic valvular stenosis. Radiology 81:24-37, 1963 26. Hoffman RB, Rigler LG: Evaluation of left ventricular enlargement in the lateral projection of the chest. Radiology 85:93-100, 1965 27. Waller BF, Howard J, Fess S: Pathology of tricuspid valve stenosis and pure tricuspid regurgitation: Part III. Clin Cardiol 18:225-230, 1995 28. Waller BE Moriarty AT, Eble JN, et al: Etiology of pure tricuspid regurgitation based on annular circumference and leaflet area: Analysis of 45 necropsy patients with clinical and morphologic evidence of pure tricuspid regurgitation. J Am Coll Cardiol 18:97-102, 1986 29. Zuberbuhler JR, Allwork SR Anderson RH: The spectrum of Ebstein's anomaly of the tricuspid valve. J Thorac Cardiovasc Surg 77:202-211, 1979 30. Lev M, Liberthson RR, Joseph RH, et al: The pathologic anatomy of Ebstein's disease. Arch Patho190:334-343, 1970
p
OSTEROANTERIOR (PA) and lateral (LAT) chest radiographs yield qualitative and quantitative information concerning cardiac chamber size and myocardial mass, pulmonary blood flow, pulmonary venous pressure, and intracardiac calcification in patients with cardiac murmurs. Changes seen in patients with acute and chronic valvular heart disease represent the ability of the heart to adapt to acute changes as well as the chronic adaptations made to alterations in atrial and ventricular volume and pressure loads. Appreciating the homeostatic mechanisms of maintaining wall stress within a normal range and maintenance of systemic cardiac output provides a means of understanding the changes in chamber volume and myocardial mass producing the radiographic changes that form the basis of diagnosis. Although there may be many different diseases that cause a particular valve to perform abnormally, the radiographic changes are characteristic of that valve dysfunction. Close attention to other radiographic abnormalities will help limiting the differential diagnosis. MITRAL STENOSIS
Chronic rheumatic carditis is the most common cause of mitral stenosis. Congenital mitral stenosis is rare and is observed mainly in infants and children. 1 Isolated mitral stenosis occurs in about 40% of all patients presenting with rheumatic heart disease. Nearly 60% of patients with pure mitral stenosis report a history of rheumatic fever.2,3 Rheumatic fever initially presents acutely with pancarditis in which the inflammatory reaction induces mitral papillary muscle dysfunction or acute mitral annular dilation. The end result of these processes is inadequate opposition of the edges of the mitral valve cusps and regurgitant systolic blood flow from the left ventricle. The
From the Department of Radiology, Columbia University College of Physicians and Surgeons, New York,"and the Division of Cardiovascular MRI, Department of Radiology, Beth Israel Medical Cente~ New York, NY Address reprint requests to Lawrence M. Boxt, MD, Division of Cardiovascular MRL Department of Radiology, Beth Israel Medical Center, First Ave and 16th St, New York, NY 10003. Copyright © 1999 by W.B. Saunders Company 0037-198X/99/3403-0008510. 00/0 216
characteristic valvular lesion of acute rheumatic heart disease is thus mitral regurgitation. On the other hand, rheumatic mitral stenosis results from a chronic and progressive fibrotic process instigated by the initial rheumatic fever inflammatory reaction. Because of the slowly progressive nature of the reactive fibrosis, a 20- to 40-year latent period may ensue before a patient with a history of acute rheumatic fever develops signs or symptoms of rheumatic mitral stenosis. Once symptoms occur, another decade may pass before symptoms become disabling. 2 The fibrotic process results in diffuse thickening, calcification and adherence of the mitral cusp margins, and decreased mitral leaflet compliance such that the mitral orifice becomes smaller and the leaflet motility is reduced. In addition, the chordae tendineae become thickened, fused, and nonpliable, further impeding an individual leaflet's opening excursion during diastole. This restriction imposes a functional narrowing of the mitral orifice.l,4 Decreasing the mitral orifice size from a normal area of 4.0 to 5.0 to <2.5 cm 2 increases the left atrial outflow resistance. With this reduction in valve area blood can flow from the left atrium to left ventricle only if propelled by a pressure gradient. The diastolic transmitral gradient is the fundimental expression of mitral stenosis, 5 resulting in left atrial hypertension. The left atrium dilates and hypertrophies in response to this volume and pressure load. Because the pulmonary veins are valveless, the elevated left atrial pressure is transmitted into the pulmonary venous system. The transmittal gradient is a function of the square of the transvalvular flow rate and dependent on the length of the diastolic filling period. 6 Thus, heart rate is the significant factor in inducing symptoms. As pulmonary venous and pulmonary capillary pressure increases, the pulmonary endothelia become permeable and alveolar wall edema develops. As pulmonary venous and pulmonary capillary pressure increases, the interstices of the pulmonary venules are stretched, and the space among the cells increases, allowing water to seep from the vascular compartment into the perivascular sheaths of the pulmonary veins. Continued or progressive elevation in left atrial pressure will cause continued fluid transudation. This progresses to cause interstitial Seminars in Roentgenology, Vol XXXIV, No 3 (July), 1999: pp 216-227
DIAGNOSIS OF VALVULAR HEART DISEASE
pulmonary edema. Eventually fluid will make its way proximally in the venous tree, to increase alveolar-capillary distance, thus decreasing oxygenation of capillary blood. Chronic elevation in pulmonary venous pressure stretches the venule interstices to allow whole blood products (red and white cells) into the pulmonary parenchyma, essentially causing parenchymal pulmonary hemorrhage. The pulmonary phagocytic system attacks this blood, and the red and white cells are phagocytosed. The phagocytosing white blood cells (dust cells) convert the hemoglobin to hemosiderin. The initial increase in left atrial pressure may not be recognizible on plain chest film examination. However, with continued elevation in pressure and progressive interstitial pulmonary edema, radiographic changes begin to appear. The earliest sign of left atrial hypertension is straightening of the left atrial appendage segment on the left heart border. Usually concave, this segment straightens and eventually becomes convex. Radiographic changes in the lungs mirror change in left atrial pressure as well as changes resulting from interstitial edema formation. Normally, in the upright PA chest examination, the lower lobe vessels are greater in caliber than the upper lobe vessels. There is more lung parenchyma in the lower lung zones and therefore more pulmonary blood flow. The decreased flow to the upper lobes results in decreased pulmonary venous return from the lungs to the heart. Thus, upper lobe alveolar pressure is greater than pulmonary venous pressure and the upper lobe veins appear smaller in caliber than the lower lobe vessels. However, both upper and lower lobe vessels are sharply defined by the interface between the fluid-filled blood vessels surrounded by the air-filled lungs. The interstitial edema caused by left atrial hypertension initially affects the lower lobes, mainly by causing unsharpening of the edges of the lower lobe vessels. Early radiographic findings in patients with left atrial hypertension and chronic mitral stenosis include difficulty in defining the edges of the lower lobe vessels, in face of normal-appearing, sharp upper lobe vessels. Progressive increase in left atrial pressure results in further unsharpening of the lower lobe vessels and progressive opacification of the lower lobe pulmonary parenchyma. The lungs appear "busy." The normally dark spaces among the lower lobe vessels now appear grey, and the vessels are difficult to identify within the noise
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of the parenchymal background. Progressive lower lobe interstitial edema decreases parenchymal compliance, and thus increases resistance to lower lobe pulmonary blood flow. As increased pressure is maintained and edema fluid tracks back toward the alveolar-capillary interface, blood oxygenation may decrease. Hypoxia is a potent arteriolar vasoconstrictive stimulus, causing increased lower lobe pulmonary resistance. Thus, decreased lower lobe parenchymal compliance in addition to local arteriolar vasoconstriction increases resistance to lower lobe pulmonary blood flow. Blood flow is directed toward the lower resistance upper lobe pulmonary arteries. This is reflected by the next stage in the radiographic appearance of left atrial hypertension, called cephalization or redistribution. In this circumstance the increased upper lobe pulmonary blood flow is reflected by an increase in the caliber of the upper lobe pulmonary arteries and veins. If an upper lobe vessels is identified, then a lower lobe vessel, measured the same distance from the pulmonary hilum, appears less distinct, and smaller than the upper lobe vessel. Continuous progression of this process will eventually result in development of perivascular and interstitial edema of the upper lobes as well, causing upper lobe vessel unsharpness. Interstitial edema is drained by the pulmonary lymphatics. Progressive interstitial edema is reflected by engorgement of the interlobar septa and lymphatics, causing the appearance of Kerley A, B, and C lines. A and C lines appear as nearly randomly distributed sharply defined curvilinear densities across the lung parenchyma. Kerley B lines are found as linear densities extending from the pleural edges of the lungs, nearly parallel and horizontal in orientation. When left atrial pressure rises above 22 mm Hg, plasma oncotic pressure is overcome, and frank alveolar pulmonary edema results. Radiographically, this appears as diffuse, usually bilateral fluffy infiltrates. However, the infiltrates do not appear as dense as those of bacterial pneumonia. Early in the course of mitral stenosis, pulmonary arterial hypertension is caused by transmission of the elevated pulmonary venous pressure across the capillary bed. However, pulmonary arteriolar resistance subsequently rises in these patients, 7,8 causing precapillary pulmonary hypertension. Chronic
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elevation in pulmonary resistance elicits increased right ventricular work against the afterload, resulting in right ventricular hypertension and myocardial hypertrophy. The hypertrophic response changes the geometry of the right ventricular cavity, and thus the function of the tricuspid valvular papillary muscles, inducing tricuspid regurgitation. The added volume load onto the already pressure-loaded right ventricle hastens right ventricular failure. The plain-film appearance of mitral stenosis is characterized by the sequelae of chronic left atrial hypertension and near-normal left ventricular filling. That is, left atrial enlargement, pulmonary venous hypertension, and varying evidence of pulmonary hypertension but a normal left ventricle (Fig 1). The earliest signs of left atrial enlargement are caused by change in the appearance of the left atrial appendage along the left heart border. Straightening and eventually convex curvature will be identified. An early sign of left atrial enlargement on lateral examination is posterior displacement of the left bronchus. Subsequently, on PA examina-
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don, identification of the dilated left atrium as a double density within the contours of the heart, elevation of the left bronchus, and eventually enlargement of the double density so that the right heart border is formed by the enlarged left atrium. In addition to left atrial enlargement, chronic mitral stenosis may be associated with left atrial endocardial and subendocardial calcification and left atrial appendage calcification (Fig 2). The pulmonary changes in mitral stenosis reflect transmission of the transmittal gradient to the pulmonary veins. These first include evidence of pulmonary venous hypertension and mild to moderate pulmonary hypertension. As described earlier, the pulmonary venous changes are bilateral and progressive, beginning in the lower lobes and eventually involving both the lung bases and apices. Pulmonary hypertension is identified by the disparity between the caliber of the enlarged main pulmonary artery segment and central pulmonary arteries and the parenchymal branches. Depending on the severity of the interstitial edema, this
Fig 1, A 44-year-old woman with exertional dyspnea is shown. (A) Posteroanterior view. Left atrial dilatation is indicated by convexity of the left atrial appendage segment (arrows) of the left heart border and extension of the density of the left atrial margin (arrowheads) to the right heart border. Mild pulmonary hypertension is reflected in the main (PA) and hilar right pulmonary artery (RP) dilatation with vasoconstriction of the parenchymal branches. Cephalization of the pulmonary blood flow indicates left atrial hypertension. The left ventricle is normal. (B) In lateral view, left atrial enlargement fills the superior retrocardiac space (large arrow) and right ventricular and pulmonary artery enlargement fills the retrosternal space (small arrows).
DIAGNOSIS OF VALVULAR HEART DISEASE
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Fig 2. Two patients with rheumatic mitral stenosis treated by mitral valve replacement are shown. (A) Calcification of the organized mural left atrial thrombus outlines the shape and defines the increased size (arrows) of the left atrium in this 58-year-old woman. (B) Curvilinear calcification along the convex left atrial appendage section of the left heart border (arrows) indicates chronic left atrial hypertension, and previous rheumatic involvement.
observation may be difficult. That is, the interstitial edema obscures the parenchymal vessel edges, making comparison of caliber with the larger vessels less reliable. However, careful examination of the parenchymal vessels will reveal that they are, in fact, decreased in caliber, and that they do not extend beyond the middle third of the lung fields, thus allowing differentiation between pulmonary hypertension caused by a shunt lesion from pulmonary hypertension caused by left heart disease. In cases of long-standing mitral stenosis, chronic left atrial and pulmonary venous hypertension results in marked left atrial enlargement and transudation of red and white cells into the pulmonary parenchyma. Erythrocytes that leak from dilated veins and congested capillaries are phagocytosed and hemoglobin is converted to hemosiderin, which is subsequently calcified. Alveolar and interstitial edema leads to fibrosis. Pulmonary artery hypertension is passive at first. Subsequent (reactive) pulmonary arteriolar changes, namely muscular hypertrophy and hyperplasia, result in progressive, irreversible hypertension (Fig 3).
~i~':I~' !
Fig 3. A 56-year-old woman with chronic mitral stenosis. There is marked cardiac enlargement with left atrial dilatation manifesting as increased right heart border convexity. In addition, the hilar pulmonary arteries are dilated and indistinct. A pseudotumor of pleural fluid is within the minor fissure. Punctate calcifications of hemosiderosis (small arrows) are throughout the lower lung fields.
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MITRAL REGURGITATION
Common causes of mitral regurgitation include mitral valve prolapse syndrome, acute or chronic rheumatic heart disease, coronary artery disease, infective endocarditis, and collagen vascular disease. An uncommon, but recently reported cause of mitral regurgitation is ingestion of anorectic agents. 9 Mitral regurgitation can develop acutely or chronically. Acute severe mitral regurgitation imposes a sudden volume load on an unprepared left ventricle. Although total left ventricular stroke volume increases somewhat because of the Frank-Starling principle, 1° foward stroke volume and total cardiac output are reduced; adequate time for development of compensatory eccentric left ventricular hypertrophy has not transpired. Similarly, the left atrium has not had adequate time to accommodate the increased volume, resulting in left atrial hypertension and pulmonary vascular congestion. Patients with acute mitral regurgitation thus often present with both low cardiac output and pulmonary congestion. Acute mitral regurgitation results from acute changes in the structures anchoring the valvular leaflets or from damage of the cusps themselves, including acute papillary muscle dysfunction or rupture resulting from myocardial infarction and chordae tendineae rupture or leaflet perforation resulting from infective endocarditis. In patients with acute mitral regurgitation, focal right upper lobe pulmonary edema may be observed. This finding is caused by a jet of regurgitant blood directed toward the right upper lobe pulmonary vein that locally accentuates the pulmonary venous pressure and thus the driving force for interstitial edema formation.t1 In cases of chronic mitral regurgitation, the initial insult is not sufficient to produce the signs and symptoms of low cardiac output and pulmonary congestion; adequate time for the formation of eccentric left ventricular hypertrophy and lengthening of individual myocardial fibers has transpired. 1°,12This compensatory increase in left ventricular end-diastolic volume permits increased total stroke volume and restoration of foward cardiac output. 14 Again, in an analogous manner, left atrial dilatation allows accommodation of the additional regurgitant volume at a lower left atrial pressure. With time, signs and symptoms of pulmonary vascular congestion abate. Chronic causes of mitral regurgitation include dilation of the mitral orifice and loss of opposition of the mitral cusp
edges, This can result from ventricular dilation stemming from cardiomyopathy, ischemic heart disease, hypertensive heart disease, or myxomatous degeneration of the mitral leaflets. The chest radiograph in chronic mitral regurgitation differs from that in the acute circumstance in terms of both pulmonary vascular signs and left atrial and ventricular size. In chronic mitral regurgitation both left atrial and left ventricular volume are increased, but pulmonary vascular congestion is only mild, or nearly normal in appearance (Fig 4). Left atrial enlargement is pronounced, with convexity of the left atrial appendage portion of the left heart border, as well as elevation of the left bronchus, and fight heart border-forming left atrium. Patients with mitral regurgitation have the largest left atria. 13The left ventricular contour is markedly increased in contour as well as displaced toward the left chest wall. On lateral examination, filling of the superior posterior retrocardiac space by the left atrium and inferior posterior retrocardiac space by the left ventricle are both evident. Posterior displacement of the left bronchus is virtually the rule. As described earlier, pulmonary vascular congestion is mild or nearly absent. Thus, there is a significant disparity between the appearance of left atrial and heart size with the appearance of the pulmonary vascular markings. Furthermore, in contrast to the appearance of the chest film in patients with mitral stenosis, there are no signs of pulmonary hypertension. Progressive left atrial enlargement decompresses atrial hypertension, resulting in nearnormal atrial and pulmonary venous pressure, no increase in pulmonary resistance or pulmonary artery pressure, and therefore no evidence of right heart failure. Aortic Stenosis
Aortic valvular stenosis represents one element of a spectrum of left ventricular outflow obstruction. Obstruction can occur at, below, or above the aortic valve; for example, valvular, subvalvular, or supravalvular stenosis. Plain-film examination is sensitive to changes caused by left ventricular hypertrophy, but limited in its specificity in differentiating among the different levels of obstruction. The most common causes of aortic stenosis are congenital, calcific degenerative, and rheumatic, i5.17 Subvalvular and supravalvular aortic stenosis are usually congenital in origin. 18 An important exception is subvalvular obstruction in hypertrophic
DIAGNOSIS OF VALVULAR HEART DISEASE
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Fig 4. A 52-year-old man with chronic mitral regurgitation is shown. (A) Posteroanterior view shows mild convexity of the left atrial appendage (short arrows) and increased convexity of the left ventricular contour (curved arrow). There is evidence of mild pulmonary vascular congestion, but the central pulmonary arteries are normal, indicating no pulmonary hypertension. (B) Lateral view shows posterior displacement of the left bronchus (short arrow) and extension of the posterior border of the left ventricle (open arrows), indicating left atrial and left ventricular dilatation, respectively.
obstructive cardiomyopathy19; however, this may, in fact, be congenital in origin as well. 2° In congenital aortic stenosis, the valve may be unicuspid or bicuspid. Newborn and infant patients with critical aortic stenosis, who present early in life, usually have a unicuspid valve. 16 Congenitally bicuspid aortic valves are malformed at birth but are not the cause of a significant gradient in early life. That is, the valve may consist of two enlarged cusps or one small cusp and one dominant cusp formed from commissural fusion of two smaller cusps. Because of the distorted architecture, blood flow across the valve is turbulent rather than laminar. The turbulent blood flow traumatizes the leaflet edges, resulting in collagenous generation, lipid deposition, fibrosis, and calcification, similar to that found much later in life in individuals with tricuspid aortic valves. Gradually increasing leaflet rigidity and orificial narrowing result in a gradient. The abnormal structure also makes the valve more susceptible to inflammatory damage resulting from infective endocarditis and may result in aortic regurgitation. As a result, patients with this lesion
tend to present later in life after variable stenotic progression. Degenerative aortic stenosis describes the narrowing of normal tricuspid aortic valves found in patients older than 65 years of age. This calcific disease progresses from the base of the valve cusps to the leaflets, eventually reducing effective valve area. Commissural fusion is not usually found. Because other degenerative changes can be found in these patients' hearts (such as calcified coronary arteries, calcified mitral annuli, and fibrous thickening of other valves), this abnormality is thought to be the result of normal wear on the valve. Diabetes and hypercholesterolemia are the two predominant predisposing factors for degenerative aortic stenosis. Aortic stenosis in patients with rheumatic heart disease results from commissural adhesion and fusion, hallmarks of the chronic rheumatic cycle of injury and healing. The valve is frequently both regurgitant and stenotic, fixed in an open configuration. In long-standing cases of rheumatic aortic stenosis, aortic valvular calcification develops, and
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further narrows the valvular orifice. Concomitant mitral valvular disease is often present but may not be recognized clinically. Thus, in the newborn or infant with unicuspid congenital aortic stenosis, there is a critical valve obstruction, and the child presents in acute heart failure. In other forms of aortic stenosis, the left ventricular obstruction develops gradually. Adaptation of the left ventricle to the progressive obstruction and systolic pressure overload is by a hypertrophic process that increases wall thickness while maintaining normal chamber volume. 21,22The development of concentric hypertrophy appears to be appropriate and provides a beneficial adaptation to compensate for high intracavitary pressure. However, hypertrophy leads to decreased left ventricular compliance and elevated left ventricular enddiastolic pressure, necessitating left atrial hypertension for left ventricular filling. Furthermore, left ventricular hypertrophy may have reduced coronary blood flow (per gram of ventricular myocardium) and exhibits increased sensitivity to ischemic injury.23 All forms of left ventricular outflow obstruction
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result in left ventricular hypertrophy. The effect of left ventricular hypertrophy on the plain-film appearance of the heart is to change the appearance of the left ventricular contour of the left heart border (Fig 5). That is, the left ventricular hypertrophy of aortic stenosis does not increase the size of the ventricle; the left ventricle is not dilated. However, it changes the "roundness" of the lower portion of the left heart border, producing the so-called "left ventricular configuration. ''24 The increased curvature of the left ventricular contour is exaggerated by the normal, concave-appearing left atrial border and normal pulmonary artery segment. Thus, the left heart border in a left ventricular configuration consists of a convex aortic arch segment and left ventricular contour, between which the relatively concave left atrial appendage and main pulmonary artery segments are sandwiched. Because aortic stenosis causes left ventricular hypertrophy and not dilation, the left ventricle appears normal on lateral examination. The inferior retrocardiac space is clear. In cases of valvular aortic stenosis, poststenotic dilatation of the ascending aorta causes increased
Fig 5. A 50-year-old man with shortness of breath is shown. (A) Posteroanterior view shows the typical convex-concave-convex appearance of the left heart border (arrows), and increased curvature of the ascending aorta (open arrows) along the right heart border, The pulmonary vascularity is normal. (B) In lateral view, the left ventricle is normal in size, and the retrosternal space is filling from behind by the dilated ascending aorta (small arrows). Aortic valvular calcification in the center of the heart (arrowheads) marks the calcified, stenotic aortic valve.
DIAGNOSIS OF VALVULAR HEART DISEASE
curvature of the mid-right heart border. The lateral border of the ascending aorta often extends beyond the right hilum, superimposed over the proximal right pulmonary artery. However, in many patients, the dilatation of the ascending aorta seems to be eccentric. That is, no change in the mid-right heart border is identified. On lateral examination, the retrosternal clear space appears to be filled in from behind, by the anterior-ward dilatation of the ascending aorta. If left ventricular outflow obstruction is below the level of the aortic valve, such as in hypertrophic obstructive cardiomyopathy, then there is no poststenotic dilatation, and the ascending aorta appears normal in configuration. Aortic valvular calcification is almost always found on plain-film examination of patients with clinically significant degenerative calcific aortic stenosis. 25 Because the fibrocalcific process begins at birth in patients with congenital aortic stenosis, calcification may be identified in younger individuals with bicuspid aortic valve stenosis. Aortic valve calcification in a young individual characterizes congenital aortic stenosis, but calcification in an older individual cannot be used to differentiate between congenital and acquired disease. Visualization of aortic valve calcification may be difficult on plain-film examination for a number of reasons. First, plain-film examination technique is optimized for evaluation of the lungs and pulmonary vascularity. Thus, bony (ie, calcified) structures may not be well appreciated. Furthermore, the aortic valve lies in nearly the center of the heart, usually projected over, or just to the left of the spine, limiting its identification. Aortic valvular calcification is best appreciated on lateral chest examination. It appears as clunky, irregular calcification at or near the center of the cardiac silhouette.
Aortic Regurgitation Aortic regurgitation can be caused by many conditions that affect the aortic valve, the aorta, or both. Valvular causes include rheumatic heart disease, infective endocarditis, congenital bicuspid aortic valve, and Marfan's syndrome affecting the aortic valve leaflets. Aortic causes include trauma, aortic dissection, and idiopathic dilation of the aortic annulus. Less commonly, inflammatory and connective tissue disease involve the aorta, such as anklyosing spondylitis, syphlitic aortitis, rheumatoid arthritis, giant call aaortitis, Ehlers-Danlos syndrome, and Reiter's syndrome. Most of these
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diseases cause chronic aortic regurgitation, which produces slow, insidious left ventricular dilation and a prolonged asymptomatic phase. Other diseases, in particular infective endocarditis, aortic dissection, and trauma, produce acute severe aortic regurgitation, which results in rapid elevation of left ventricular filling pressures and reduced cardiac output. The left ventricular response to aortic regurgitation depends on the rate at which the insufficiency develops. Aortic regurgitation imposes a volume overload on the left ventricle. In cases of acute severe aortic regurgitation, the left ventricle has not had enough time to adapt to the sudden volume load. The abrupt increase in end-diastolic left ventricular volume increases left ventricular enddiastolic and left atrial pressure dramatically. Although the Frank-Starling mechanism is used, the inability of the ventricle to develop compensatory dilatation acutely results in decreased foward cardiac output. Hence, elevated left atrial pressure and decreased forward cardiac output produces pulmonary edema and shock. In chronic aortic regurgitation, the left ventricle compensates for the volume load by increasing end-diastolic volume, increasing ventricular compliance so that the increased volume can be accommodated without increasing left atrial pressure, and acquiring a combination of concentric and eccentric ventricular myocardial hypertrophy. Thus, left ventricular performance remains normal, with normal ejection fraction. Most patients remain asymptomatic during this compensated phase, which may last for decades. Patients with chronic aortic regurgitation have a volume-loaded left ventricle and aorta. Left ventricular dilatation becomes pronounced and progressive. 13 Therefore, they present on frontal chest examinations with a left heart configuration and a pronounced mid-right heart border from the distended ascending aorta (Fig 6). The left ventricular portion of the left heart border is not only increased in curvature, but since dilated, it appears to extend farther torward the left chest wall as well. In addition, since dilated, the cardiothoracic ratio in these patients will be increased. Because chronic aortic regurgitation does not effect the left atrium until the left ventricle fails, the frontal chest radiograph will reveal a normal left atrium and pulmonary vasculature. However, once the left ventricle fails, the frontal radiograph will display
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A
Fig 6. An asymptomatic 22-year-old man is shown. (A) In posteroanterior view, the increased curvature of the lower left heart border appears similar to the man in Figure 5. However, the superior aspect of the left ventricular contour (arrows) is fuller. Pulmonary vascular markings are normal. (B) In lateral view, the left atrium is normal, but the contour of the left ventricle extends beyond the spine, indicating left ventricular dilatation. The dilated ascending aorta (small arrows) fills the retrosternal space from behind.
evidence of left atrial hypertension: a flattening of the left atrial appendage segment with prominent, unsharp, and cephalized congested pulmonary vessels. Similar to patients with aortic stenosis, the ascending aorta may not distend torward the right, and an increase in the corvature of the mid-right heart border may not be found. In lateral radiographs, the left ventricular dilation is characterized by filling of the inferior retrocardiac space. Using the Hoffman and Rigler sign, 26 the posterior border of the left ventricle extends more than 1.8 cm posteriorly to the border of the inferior vena cava when measured at 2 cm cephalad to the crossing of the right hemidiaphragm and inferior vena cava. The dilated ascending aorta fills the retrosternal airspace from the middle mediastinum toward the sternum. Because the left ventricle cannot rapidly compensate for the sudden regurgitant volume, plain-film examinations of patients with acute aortic regurgitation display signs of left atrial and pulmonary venous hypertension without left ventricular or aortic enlargement.
Tricuspid Regurgitation Tricuspid regurgitation in patients with a normal valve may be present in cases with elevated right ventricular systolic or diastolic pressure, fight ventricular dilatation, and tricuspid annular dilatation. 27,% Right ventricular systolic hypertension occurs in patients with chronic mitral stenosis, valvular pulmonic stenosis, and the various causes of pulmonary hypertension. Right ventricular diastolic hypertension is found in patients with dilated cardiomyopathy and right heart failure. Valvular abnormalities leading to tricuspid regurgitation may be acquired or congenital. Acute rheumatic valvulitis, infective endocarditis, carcinoid, rheumatoid arthritis, trauma, and Marfan's syndrome all may cause valvular regurgitation. Ebstein's malformation 29,3° is a congenital downward displacement of the tricuspid leaflet attachments into the right ventricle, resulting in an associated abnormality of the valvular apparatus causing tricuspid regurgitation and an alteration in the architecture of the right ventricle ("atrializa-
DIAGNOSIS OF VALVULAR HEART DISEASE
tion" of the right ventricle); decreased functional right ventricular myocardium limits fight ventricular cardiac output. Tricuspid regurgitation volume loads the compliant right atrium and right ventricle such that they dilate. Right atrial dilation increases the convex curvature of the lower fight heart border on frontal chest radiographs (Fig 7). Right ventricular dilatation increases the curvature of the lower third of the left heart border. Both right atrial and right ventricular dilatation cause rotation of the heart into the left chest such that the superior vena cava comes to be projected over the spine, narrowing the superior mediastinum on frontal radiographs. The increased curvature of the left heart border is seen to parallel the course of the left bronchus. Radiological differential diagnosis of tricuspid regurgitation depends on observation of other findings, which may help elucidating the underlying cause or sequelae of the regurgitant valve. The most common cause of tricuspid regurgitation is pulmonary hypertension. Thus, in addition to right heart dilatation, dilatation of the main pulmonary artery segment and central hilar pulmonary arteries and abrupt change in caliber of the parenchymal pulmonary branches, will be present in these cases. Left atrial enlargement with a normal left ventricle,
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ill! ¸
i;;!iiill Fig 7. A 62-year-old man with chronic mitral stenosis, pulmonary hypertension, and tricuspid regurgitation is shown. Left atrial hypertension is indicated by cephalization of the pulmonary blood flow. The dilated main pulmonary artery and dilated left atrial appendage segments of the left heart border blend to form a generalized convexity superior to the left ventricular contour. The marked increase in convexity of the right heart border caused by right atrial dilatation is the result of tricuspid regurgitation mediated by pulmonary hypertension.
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and evidence of pulmonary hypertension point to mitral stenosis as a cause of the pulmonary hypertension and subsequent tricuspid regurgitation. Hyperaerated lungs and a normal left atrium indicate a pulmonary cause of the pulmonary hypertension. Pulmonary blood flow should be expected to be normal in patients with tricuspid regurgitation. Thus, fight heart enlargement with a small or diminuitive pulmonary artery segment with or without decreased caliber of parenchymal pulmonary artery segments indicates the decreased fight ventricular output found in patients with Ebstein's anomaly. Multivalvular Heart Disease
Multivalvular heart disease is usually of rheumatic origin. The most common combinations are mitral stenosis with aortic regurgitation, mitral stenosis with tricuspid regurgitation, combined mitral and aortic regurgitation, combined mitral and aortic stenosis, and combined aortic stenosis and mitral regurgitation. In combined valvular disease, the hemodynamic physiology, and therefore clinical and radiological picture, is determined by the proximal lesion. However, the appearance will vary depending on the relative severity as well as the physiological sequelae of each particular valve lesion. When both mitral stenosis and aortic regurgitation coexist, the pathophysiology is similar to that of severe mitral stenosis. Thus, left ventricular filling from the left atrium is impaired, and left ventricular size, despite the presence of aortic regurgitation, may not appear to be greatly enlarged. Nevertheless, the signs of mitral stenosis are present, including left atrial enlargement, moderate to severe left atrial hypertension with interstitial edema, and mild to moderate pulmonary hypertension. The association of tricuspid regurgitation with mitral stenosis is usually mediated by pulmonary hypertension caused by the mitral stenosis (Fig 7). As described previously, these patients have the plain-film appearance of mitral stenosis with right heart dilatation. Combined mitral and aortic regurgitation produces significant left heart dilatation, with enlargement of the left atrium, left ventricle, and ascending aorta (Fig 8). Depending on the chronicity of the disease, left atrial pressure may be near normal, and evidence of left atrial hyperten-
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Fig 8. This 58-year-old man with mixed mitral stenosis and regurgitation with secondary tricuspid regurgitation presents with marked dilatation of both the left and right heart borders. The pronounced enlargement of the left atrium associated with left ventricular dilatation results from the mitral regurgitation component of his disease. The mitral stenosis component is reflected in the pulmonary venous hypertensive changes and marked dilation of the right atrium secondary to pulmonary hypertension.
sion lacking, or only mild in appearance. The pulmonary artery segment, central pulmonary arteries, and fight heart will appear normal. In mixed mitral and aortic stenosis, radiological picture is dictated by the mitral stenosis (Fig 9). Left atrial outflow obstruction limits aortic valve flow. The radiological appearance in these patients may mimic mitral stenosis, but careful evaluation will more often than not reveal calcification of the aortic valve, indicating the second lesion. Mixed aortic stenosis with mitral regurgitation is usually caused by rheumatic heart disease. However, in young people, coexisting congenital aortic stenosis with
Fig 9. Rheumatic mixed mitral and aortic stenosis in a 57-year-old woman is shown, increased curvature of the left ventricular portion of the lower left heart border caused by left ventricular hypertrophy is superimposed on the left atrial and pulmonary artery enlargement and pulmonary venous hypertension due to mitral stenosis.
mitral valve prolapse and mitral regurgitation may produce similar symptoms and radiological findings. Left atrial and left ventricular enlargement with poststenotic dilatation of the ascending aorta, in the absence of evidence of chronic left atrial hypertension, may be helpful for considering this disease. If aortic stenosis is severe, it will worsen the mitral regurgitation and produce progressive left atrial and ventricular enlargement.
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