Diagnosis and treatment of diseases of the aorta

Current Problems in

Cardiology Volume 22

Number 10

October 1997

Diagnosis and Treatment of Diseases of the Aorta Joseph Lindsay, Jr., MD Section of Cardiology The Washington Hospital Center The George Washington University School of Medicine Washington, DC

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Current Problems in

Cardiology Diagnosis and Treatment of Diseases of the Aorta

Foreword

488

Introduction

490

Etiologic and Pathogenetic Considerations in Aortic Disease

490 490 491 496 499 5O3 5O6

Medial Changes of Aging Atherosclerosis Abnormalities of the Aortic Media InfectiousAortitis Nonspecific Aortitis Congenital Anomalies of the Aorta

Clinical Manifestations of Aortic Disease AorticAneurysm Aortic Dissection Aortic Obstruction

References

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Foreword In the October 1997 issue of Current Problems in Cardiology, Dr. Joseph Lindsay, Jr., Director of the Section of Cardiology at The Washington Hospital Center and Professor of Medicine at The George Washington University School of Medicine, provides the reader with an up-to-date and well-referenced discussion of the diagnosis and treatment of diseases of the aorta. The text includes a complete discussion of the etiology and pathogenesis of aortic disease, includes a comprehensive presentation of the clinical manifestations of aortic disease, and elucidates the use of noninvasive and invasive techniques for obtaining an accurate diagnosis. Finally, the appropriate management of various diseases of the aorta is well delineated. The Editorial Board of Current Problems in Cardiology appreciates Dr. Lindsay's comprehensive and current review of a common clinical problem in cardiology.

Robert A. O'Rourke, MD Editor-in-Chief

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Joseph Lindsay, Jr., graduated from Clemson University and received his MD degree from the Emory University School of Medicine and his training in cardiology at Grady Hospital, both in Atlanta, Georgia. While at Grady Hospital, his career-long interest in diseases of the aorta was stimulated by Dr. J. Willis Hurst. Dr. LJndsay has served on the faculty of the medical schools of Emory University, the George Washington University, and the Louisiana State University in Shreveport. He currently is Director of the Section of Cardiology at the Washington Hospital Center and is Professor of Medicine at the George Washington University School of Medicine.

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Diagnosis and Treatment of Diseases of the Aorta tructurally and functionally an uncomplicated structure, the aorta manifests disease in a limited number of ways. When weakened by disease, the wall of this major conduit may dilate, producing an aneurysm, or may split in its long axis, producing dissection. In either case, fatal rupture may result. Moreover, like all pipes, it may become obstructed; however, its main trunk is narrowed less frequently than the origin of a main branch. In contrast to these relatively few clinical manifestations, an array of disease processes involve the aorta. Different diseases produce similar clinical findings. This review first discusses the various diseases that affect the aorta together with their pathogenetic mechanisms, characteristic pathologic features, and clinical findings unique to the disease process. A description of the clinical manifestations of aortic disease for which there may be several causes or for which the origin is unknown will follow.

Etiologic and Pathogenetic Considerations in Aortic Disease

Medial Changes of Aging Circumferential plates or lamellae of elastin fibers constitute the most conspicuous feature of the aortic media when it is examined histologically. Dispersed between the circular elastic fibers are longitudinally oriented smooth-muscle cells, collagen fibers, micro fibrils, and ground substance 1 (Fig. 1). Clinicians have long recognized dilatation and elongation of the aorta in the elderly. Characteristic alterations in the structure of the aortic wall accompany these changes. Schlatman and Becket 2 identified these as fragmentation of elastic fibers and loss of smooth-muscle cell nuclei, so-called "medionecrosis." Moreover, collagenous tissue and basophilic ground substance replace the lost structures. More recently, investigators also have identified amyloid deposits as a feature of the aging aorta? The degree to which these changes develop in any one individual may vary, but they appear to be an almost universal consequence of aging. Schlatman and Becker2 believe that these changes reflect the years of hemodynamic stress imposed on the aortic wall. 490

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FIG. 1. Microscopic section of wall of normal aorta stained for elastin. Concentric elastic lamellae are the most prominent feature. Nuclei of smooth-muscle cells are visible within collagenous matrix. This structure provides radial strength but allows cleavage along the long axis or circumferentially, as in aortic dissection and its variants.

Atherasclerosis Pathologic Anatomy. By middle life, aortic atherosclerosis is nearly universal in the western world. Although common, it varies in severity from individual to individual. Diabetes, hypercholesterolemia, smoking, and hypertension are among the factors that seem to accelerate it. Its first manifestation, "fatty streaks" are commonly present in the aortas of children, even in societies in which serum cholesterol measurements are low. These yellow, circumscribed, flat or slightly raised intimal lesions represent focal subintimal collections of intracellular lipid. They are encountered most frequently just above the aortic valve ring and in the area of the scar of the ductus arteriosus. In older children or adolescents, fatty streaks cluster near the orifices of the aortic branches. By young adulthood, some, but not all, of these fatty streaks have evolved into firm, pale, gray, elevated lesions. These "fibrous plaques," the characteristic lesions of advancing atherosclerosis, comprise lipid-laden macrophages and smooth-muscle cells surrounded by proteoglycans and by a matrix of lipid, collagen, and elastic fibers. Their central core of amorphous, yellow material consists of extracellular lipid and cell debris. With the passage of time, many of these plaques become ulcerated and calciCurr Probl Cardiol, October 1997

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fled. Overlying thrombus is common. Initially an intimal process, the larger and more complex lesions penetrate the underlying media producing scarring and atrophyY The most advanced atherosclerotic changes display a characteristic distribution in the adult aorta. Atherosclerotic involvement is most severe below the renal arteries in the abdominal aorta and is common but characteristically less severe in the descending thoracic segment. Although the process does not avoid the ascending segment, in that segment it tends to be less severe.6This characteristic distribution does not apply in a few special situations. In patients with diabetes mellitus, atherosclerosis is frequently of great severity throughout the aorta. Individuals with type II hyperlipoproteinemia are a second exception to the rule that the ascending aorta is spared. 7Finally, atherosclerosis can be of great severity overlying areas of syphilitic aortitis involving the ascending segment. At least two mechanisms have been invoked to account for the predilection of atherosclerosis for the infrarenal aorta. First, the velocity and pulsatile characteristics of blood flow in that segment differ from those found in the proximal aortic segments. These differences may alter the physics of the interface of blood with the aortic wall in a manner that favors plaque development. 8 Second, the wall of the abdominal aorta is thinner and has fewer elastic lamellae and more smooth-muscle fibers. Moreover, it lacks the rich network of vasa vasorum found in the proximal aorta? Clinical Manifestations. Aortic atherosclerosis is manifest clinically in four major ways: aneurysm, obstruction of the infrarenal aorta, embolization from atheromatous plaques to distal arterial beds, and medial dissection initiated by penetration of a plaque into the media. Aneurysm. Aneurysm of the abdominal aorta (AAA) has long been presumed to be a consequence of weakening of the media by the atherosclerotic process and as such to represent the most frequent and the most important clinical manifestation of aortic atherosclerosis. The risk factors for AAA are the same as those for atherosclerosis, and these aneurysms characteristically appear in those with the most severe aortic atherosclerosis in uninvolved segments of the aorta. 1° Recent recognition of familial clustering of patients with such lesions, 11,12 the identification of genetically determined defects in collagen in a family with multiple aneurysms, 13and the detection of abnormal collagenase and elastase in tissue from aortic aneurysms resected at operation have led some to question this assumption. They suggest that rather than producing the aneurysm, atherosclerosis represents a secondary response to dilatation of the aorta consequent to a medial weakness, a4 This debate is discussed in greater detail in the section on aneurysms. 492

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Aneurysm of the descending thoracic aorta has also traditionally been attributed to atherosclerosis. This assumption has been strengthened by the observation that such lesions are commonly accompanied by an infrarenal aneurysm. The clinical features, recognition, and management of aneurysms are covered in a later section. Obstruction of the aortoiliac bifurcation. The tendency for the atherosclerotic process to be most severe in the infrarenal aorta dictates that obstruction of the main aortic channel rarely occurs except in that segment. Often the obstruction extends into the proximal iliac arteries. The clinical features, recognition, and management of obstruction of the terminal aorta and its bifurcation are discussed in a later section. Because atherosclerotic plaques also tend to localize at the orifice of aortic branches, symptoms referable to obstruction at the origin of the coronary arteries, the brachiocephalic arteries, the renal arteries, or the splanchnic vessels are encountered far more commonly than is obstruction of the aorta itself. Atheroembolism. The luminal surface of a severely atherosclerotic aortic segment is quite often rough and covered with thrombus. Embolization of plaque material and thrombus from these "raw" surfaces now appears to be far more common than was once appreciated. 1517Emboli to the brain, the lower extremities, and to the renal or visceral circulation have been reported. 151vEven coronary embolization from the aorta has been reported? 8 Large intraluminal aortic clots also have been observed at necropsy and may be responsible for occlusion of the aortoiliac bifurcation 19 or other aortic branches. 2° Transesophageal echocardiography now provides rather startling views of pedunculated thrombus or other atherosclerotic material waving in the aortic blood flow 17(Fig. 2). Those with pedunculated, mobile thrombi are more apt to embolize than are those with flat, layered clots. A variation on the theme of atheroembolism, the clinical syndrome labeled "cholesterol embolization" is a rare spontaneous complication of severe aortic atherosclerosis. "Cholesterol emboli" have been thought of as tiny particles that obstruct small arteries or arterioles. Signs of such an event include mottled skin and "purple toes" in the lower extremities together with renal insufficiency and visceral ischemia in more severe cases. 21'= Still rare but more common than spontaneous cholesterol embolization, this syndrome appears as a consequence of intraaortic catheter manipulation. 2a,22Because eosinophilia is frequent in the initial stages of this event, an immune reaction to the free particles has been suggested. 21,22 Penetratingplaques. When an atherosclerotic plaque penetrates the internal elastic membrane, the stage is set for the formation of an intramural Curr Probl Cardiol, October 1997

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FIG. 2. Transesophageol echocardiographic views of descending thoracic aorta in four patients. The severityof atherosclerotic plaques varies from minimal (A, upper left) to severe and protruding (D, lower left). The mare severe examples are the likely sources for atheroembolism. (Reprinted with permission from Lindsay J Jr, Goldstein SA, Dolmatch BL. Diseases of the aorta. In: Schlant RC, Alexander RW, Lipton MJ, editors. Diagnostic atlas of the heart. New York: McGraw-Hill, 1996:319,)

hematoma. 23 The structure of the aortic wall provides great radial strength but allows cleavage of the elastic lamellae by the medial hematoma (Fig. 1). Extension circumferentially and in the long axis of the media may produce a limited medial dissection (Fig. 3). The wall is now less able to resist radial forces, and pseudoaneurysm or rupture may result. Usually single, these penetrating atheromatous ulcers are typically, but not invariably, located in the descending thoracic aorta. The clinical picture resembles that of aortic dissection or that of expansion/rupture of a preexisting aneurysm. The sudden onset of severe back pain in a patient with hypertension or one known to have atherosclerosis is typical. Many are identified in the course of imaging for suspected aortic dissection. Because they are located in the descending thoracic aorta, aortic regurgitation and altered pulses are not characteristic features. Surgical treatment is often indicated, although some patients are known to survive without operation. 23 494

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FIG. 3. Aortogram (A) and magnetic resonance image (B) from elderly woman with a clinical syndrome suggesting aortic dissection. A penetrating aortic plaque was demonstrated in ascending aorta, an unusual location. High signal density in right lateral wall of aorta on MRI reflects rim of hematoma. (Courtesy of Thomas A. Goldbaum, MD.)

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Abnormalities of the Aortic Media Aneurysm and medial dissection point to a defective aortic media. Both entities are encountered in readily identifiable congenital syndromes (e.g., bicuspid aortic valve or coarctation of the aorta) and in heritable disorders of connective tissue (e.g., Marfan syndrome, polycystic kidney disease, Turner's syndrome, and Ehlers-Danlos syndrome).24 More often, however, aneurysm and dissection are associated with hypertension, atherosclerosis, or an inflammatory process. Often, however, the precise origin cannot be identified. For example, infrarenal abdominal aortic aneurysms, long assumed to be atherosclerotic in origin, may in fact reflect an underlying medial defect. Cystic Medial Degeneration. Changes in the aortic media detectable by light microscopy, termed "cystic medial necrosis" by Erdheim, were long thought to be diagnostic of medial degeneration. They were identified in Marfan syndrome, in other instances of aortic aneurysm o r d i s s e c t i o n , 25'26 and in a variety of familial or congenital syndromes. 24 In its most florid form, this histologic lesion is characterized by dramatic fragmentation of elastic fibers, disappearance of the nuclei of smooth-muscle cells, increase in collagenous fibers, and most characteristically, by replacement of the degenerated tissue with interstitial collections (cysts) of basophilic-staining ground substance. Note the similarity of this description to that presented in preceding paragraphs addressing the changes of senescence. More recently the fundamental nature of this lesion has been questioned. Hirst and Gore 27 pointed out that the lesion was neither cystic nor necrotic. Recent detailed study of the histologic characteristics of the aortic media in patients with aortic dissection failed to demonstrate a close association with this marker of medial degeneration.28'29Schlatmann and Becket 2'26suggested that qualitatively similar lesions are common with aging, albeit somewhat more common and more severe in some but not all patients with Marfan syndrome, with dilatation of the aorta from any cause, or with aortic dissection. They proposed that the observed changes reflect the wear and tear of hemodynamic stress. It is noteworthy in this context that the presence of this lesion has been reported in the aortas of patients with coarctation of the aorta. 3° Most authorities now agree that although defective in many patients with aortic aneurysm or dissection, the aortic media in such instances reveals no specific lesion on conventional histologic study. Investigators are now focused on subcellular and molecular abnormalities.24 A defect in a microfibrillar constituent of the matrix, fibrillin, has been identified in the Marfan syndrome, and the responsible gene has been identified. 31 Clinical Manifestations. A characteristic aortic aneurysm testifies to the presence of a predominantly medial defect (or more likely, defects). In 496

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FIG. 4. Aortogram demonstrating typical appearance of the "onion bulb" or "Florence flask" appearance of the aneurysm produced by anuloaortic ectasia. Typical of aortic lesion in Marfan syndrome, this aneurysm is more common in those with none of the musculoskeletal or ocular manifestations of that disorder.

such cases, aneurysmal dilatation of the ascending aorta extends proximally into the aortic sinuses and ends distally just short of the innominate artery. The descriptive term "anuloaortic ectasia" has been applied. 25 Anuloaortic ectasia is the characteristic aortic lesion of Marfan syndrome. 24,25The prototypical "Florence flask" or "onion bulb" appearance reflects the severity of the medial degeneration in the aortic root (Fig. 4). Rupture of such aneurysms or the hemodynamic effects of aortic regurgitation, the consequence of the aortic root dilatation, are responsible for most of the premature deaths from this disorder. Aortic dissection is somewhat less common if we exclude the intimal tears and associated limited medial disruptions commonly encountered within the aneurysm. In the most complete presentation of Marfan syndrome, skeletal, ocular, Curr Probl Cardiol, October 1997

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and cardiovascular anomalies are present, and a family history of similar abnormalities exists. 24,25 Long extremities, particularly long, thin, hands and feet ("arachnodactyly"), and sparse muscle mass are outstanding musculoskeletal aberrations. Subluxed or frankly dislocated lenses attributable to lax supporting ligaments are characteristic. In addition to aortic aneurysm, myxomatous transformation of the aortic and mitral valves may produce valvular incompetence. Exceptionally, medial degeneration severe enough to result in aneurysm, rupture, or dissection is found in the main pulmonary arteries or in the aorta distal to the ascending segment. Medial Degeneration in Heritable Disorders or Congenital Aortic Valvular Deformity. Aortic aneurysm, often in the form of anuloaortic ectasia, and aortic dissection are reported with considerable frequency in patients with congenitally deformed aortic valves. The risk of aortic dissection has been estimated to be increased ninefold in subjects with bicuspid or unicuspid valves.32 Echocardiographic evidence for an increased prevalence of dilatation of the aortic root and ascending aorta in subjects with a biscupid aortic valve also has been presented? 3,34 Patients with coarctation of the aorta have long been known to be at risk for aortic aneurysm, dissection, and rupture. 24'34 Although there is as yet no direct evidence that a specific medial defect rather than hypertension accounts for this fact, it is reasonable to consider such a possibility as a result of numerous clinical observations .34The strong association of bicuspid aortic valve with coarctation is a foundation for this hypothesis. Turner's syndrome provides an intriguing experiment of nature in this context. Bicuspid aortic valve, coarctation of the aorta, and aortic dissection are strongly associatedY A better understanding of the genetic basis for this association might provide clues to the pathogenesis of medial degeneration. Reports linking polycystic kidney disease, 36,37 Ehlers-Danlos syndrome, 38 and osteogenesis imperfecta39 with aortic aneurysm and dissection further support the idea that medial degeneration may often have a genetic basis. Isolated Anuloaortic Ectasia. Whereas, as indicated in the preceding paragraphs, dilatation of the aortic root and ascending aorta occurs in association with a variety of congenital and hereditable disorders, it is far more often encountered in those with no other manifest disease? 5,4° Anuloaortic ectasia is the most frequently encountered origin for aortic regurgitation severe enough to require valve replacement41and is responsible for a significant number of instances of fatal rupture or dissection. The possibility of an intrinsic media weakness in these patients is emphasized by the recent report of Milewicz et al., 42 who identified mutations in the 498

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fibrillin gene in three patients with anuloaortic ectasia who did not have the complete Marfan phenotype.

Infectious Aortitis A variety of bacterial, mycobacterial, and fungal organisms have been known to infect the walls of the aorta. Microorganisms may gain a foothold in the aortic wall through several mechanisms: (1) seeding of the vasa vasorum during hematogenous spread, (2) direct invasion of the wall from the aortic lumen (usually in previously diseased segments or at prosthetic grafts), (3) septic emboli (usually from infective endocarditis) that lodge at a branch point, (4) spread of infection from contiguous structures (e.g., infected cardiac valves or tuberculous periaortic nodes), or (5) traumatic aortic injury with subsequent infection.43

Syphilitic Aortitis Epidemiologic characteristics. Alone among the infectious aortic diseases, treponemal infection produces a chronic aortitis. Clinically evident involvement of the cardiovascular system occurs in ~ 10% of patients with untreated tertiary syphilis of long duration and is the primary cause of death in about the same percentage? 4,45Autopsy evidence of the process is more frequent. About half of patients with untreated syphilis for > 10 years have autopsy evidence of cardiovascular involvement.44,45 Pathologic characteristics. During the spirochetemic phase of primary syphilis, Treponemapallidum organisms lodge in the adventitia of the vasa vasorum and initiate an inflammatory response, characteristically a perivascular lymphocytic and plasma cell infiltrate. Later, an obliterative endarteritis develops, resulting in patchy medial necrosis and elastic fiber fragmentation, leading to weakening of the aortic wall and predisposition to aneurysm formation. On gross inspection, the intima of the aorta has a characteristic wrinkled appearance. Atherosclerotic plaques are frequently superimposed on these damaged areas, obscuring this intimal wrinkling and giving rise to the so-called "tree bark" appearance. Because the infection is seeded through the vaso vasorum, the process is typically most severe in the ascending aorta and the arch. These are the segments most richly supplied with these small arteries. Clinical manifestations. Syphilitic aortitis may be seen in four ways44'45: asymptomatic aortitis, aortic regurgitation, coronary ostial stenosis, and aortic aneurysm. Asymptomatic aortitis, the most common, may be unrecognized until necropsy but can be identified from chest radiograph in some patients by linear calcium deposits in the ascending aorta. Aortic regurgitation; present in ~20% to 30% of patients with syphilitic aortitis, 44'45 results primarily from dilatation of the aortic root. Coronary arterial ostial Curr Probl Cardiol, October 1997

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stenosis occurs in 25% to 30% of patients with syphilitic aortitis. 44'45 In as many as 85% of these patients, there is associated aortic regurgitation. 44,45 Interestingly, whereas angina is common in patients with syphilitic ostial stenosis, myocardial infarction is rare. Aneurysm, the least common manifestation of syphilitic aortitis, is present in 5% to 10% of affected patients. 44,45About 75% are saccular and 25% are fusiform. Half are located in the ascending aorta, 30% to 40% in the transverse arch, 10% to 15% in the proximal descending thoracic aorta, and <5% in the abdominal aorta. Rarely syphilis causes aneurysm of a sinus of Valsalva. 46When not treated surgically, syphilitic aortic aneurysms are associated with a 2-year mortality of 80%. 44,45Thus operative intervention appears warranted in patients with large syphilitic aortic aneurysms. Although antibiotic therapy is indicated for all patients with cardiovascular syphilis, it is unclear what impact, if any, such treatment has on the progression of syphilitic aortic disease. Diagnosis. The clinical diagnosis of cardiovascular syphilis may be difficult to establish, especially in patients older than 50 years. In this age group, many of the effects of syphilis are mimicked by hypertensive and atherosclerotic disease. Serology can be helpful. Of patients with cardiovascular syphilis, 40% to 95% have an elevated venereal disease research laboratory (VDRL) titer, and nearly all have a positive fluorescent treponemal antibody absorption (FTA-ABS) test. 44,45 Rare patients with untreated cardiovascular syphilis have no serologic evidence of the disease. Thus the diagnosis of cardiovascular syphilis must be considered in patients with aortic regurgitation and dilatation of the aortic root, aneurysms of the thoracic aorta, and ostial coronary arterial narrowing (especially when accompanied by aortic regurgitation). Fortunately, the frequency of syphilis has decreased dramatically over the past several decades because of the identification and treatment of syphilis in its early stages. Bacterial Aortitis Complicating Blood-Borne Infections. Because damaged aortic segments are more susceptible to invasion, bacterial aortitis most often is seen as an infection of a preexisting aneurysm. Less frequently, the infectious process seems to be responsible for initiating an aneurysm or a false aneurysm (Fig. 5). Salmonella species and Staphylococcus aureus are the most frequent invading organisms, 4v,48but the spectrum of agents is wide. Infections involving prosthetic graft material result from agents similar to those causing infective endocarditis. Salmonella organisms have an unusually strong proclivity for invading vascular endothelium. Cohen et al.49 found a 25% prevalence of endothelial infection (arteritis or endocarditis) in 105 patients older than 50 years 500

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FIG. 5. Bacterial infection of aortic wall as complication of staphylococcal endocarditis. The growth of a "mycotic" aneurysm is demonstrated in these sequential transesophageal echocardiographic views. TEE on admission demonstrated area of localized thickening in the wall (AN) with "texture" suggestive of abscess. Middle panel obtained during intraoperative TEE during aortic valve replacement depicts definite aneurysm and led to second operation to remove aneurysm. TEE at that time (bottom) showed further increase in size of infectious aneurysm. (Reprintedwith permission from Goldstein SA, LindsayJ Jr. Thoracic aortic aneurysms: role of echocardiography. Echocardiography 1996;13:213-32.) Curr Probl Cardiol, October 1997

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with nontyphoidal Salmonella bacteremia. They found no such endothelial invasion in patients younger than 50 years, probably because of a lower prevalence of atherosclerosis to serve as a nidus for infection. Because of the high incidence of endothelial infection in older patients, Cohen et al. 49 recommended antibiotic treatment for acute salmonella gastroenteritis in patients older than 50 years. Clinical manifestations and diagnosis. The diagnosis of infectious aortitis or of an infected aneurysm can be elusive and relies heavily on Clinical suspicion prompting further diagnostic evaluation. 5° Unfortunately, symptoms are nonspecific. Abdominal aortic infections may include abdominal, back, or flank pain, whereas chest or shoulder pain are more characteristic of thoracic aortic infections: Oskoui et al. 51found that half of 98 previously reported cases of Salmonella infections of the aorta had such localized pain. Physical findings include fever in nearlyall patients 52and a pulsatile abdominal mass in nearly half. Leukocytosis is very common, s2 as are positive blood cultures. In the series Of patients with Salmonella aortic infection, 83% had positive blood cultures and 74% had positive stool cultures, even though only a third had gastroenteritisY Unfortunately, there are no specific diagnostic studies for aortic infection. Abdominal ultrasound and computed tomography are useful to identify an aneurysm and occasionally to show periaortic inflammation or mass. Noncalcified aneurysms and aneurysms with smooth walls, seen on aortography or computed tomographic scanning, are characteristic of an infectious process.43Often the diagnosis of infection of the aorta cannot be made -withcertainty without surgery, and even at operation, the diagnosis may be questionable. Thus the diagnosis of aortic infection is made most often on the basis of a compatible clinical picture and supporting, if not conclusive, diagnostic tests. Unexplained fever, leukocytosis, and bacteremia (especially Salmonella sp.) in a patient with a high likelihood of having underlying atherosclerotic disease should prompt a thorough search for further evidence of aortic infection and may be sufficient reason for operative exploration. Treatment. Infections of the aorta almost always lead to fatal aortic rupture unless treated surgically. Antibiotics alone are not sufficient. The specific surgical approach is dictated primarily by the extent o f involvement of periaortic tissue. If the aortic bed is relatively clean, excision and simple interposition grafting is acceptable. If periaortic infection is widespread, then extraanatomic grafting (e.g., axillobifemoral, thoracic aortobifemoral) is n e c e s s a r y 9 Some have recommended that essentially all patients with aortic infection be treated, at least initially, with extraanatomic grafting. 43

Infectious Aortitis as a Result of Spread from Contiguous Tissue. 502

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Tuberculous aortitis most often results from spread of the organism from infected periaortic nodes. False aneurysm, perforation, or aortoenteric fistula s3,54may result. An infection of the aortic valve may invade the valve ring and adjacent structures, producing a perivalvular abscess (sometimes called a "valve ring abscess"). This complication of aortic valvular endocarditis is frequent, especially when infecting organisms are virulent or when patients with prosthetic valves are affected, ss-59 Perivalvular abscesses may compress adjacent structures or rupture into the pericardial space. Should the abscess drain into the aortic lumen, a false aneurysm of a sinus of Valsalva may result. 6°'61Moreover, abscesses may disrupt the attachment of the aortic media to the fibrous skeleton of the heart, producing fistulous communicationsfi 6-62

Nonspecific Aortitis Narrowing of an aortic segment or of one of its branches, aneurysm formation, or aortic regurgitation may be produced by an arteritis for which no specific origin can be found. It may occur as an isolated abnormality or be associated with noninfectious inflammatory involvement of other organs, as in, for example, lupus erythematosus or rheumatoid arthritis. Takayasu's Arteritis. Takayasu's arteritis, named for the Japanese ophthalmologist who first called attention to the fundoscopic findings in the disease, is the prototype. 63 Because of its predilection for the brachiocephalic vessels, this arteritis has been labeled "pulseless disease" and "aortic arch syndrome." The classic form occurs with the greatest frequency inAsia; however, patients with nonspecific aortitis quite similar to this prototype are encountered worldwide. 64,65Whether they represent similar or identical disease processes is uncertain. The description to follow focuses on the prototypical illness described in Asia. Variations on the theme may be encountered elsewhere. 66 Origin. The cause ofTakayasu's arteritis is unknown. No infectious agent has been identified. Clinical and serologic data suggest an "autoimmune" process, and antiendothelial antibodies were recently identified in 18 of 19 patients.67 A genetic predisposition has been postulated because of clustering of the disorder in certain families and because of the frequency of similar histocompatibility antigens in these kindred. 68 Pathologic characteristics. Histologic e x a m i n a t i o n discloses a granulomatous arteritis during active stages of the disease. The microscopic appearance is remarkably similar to that in giant-cell arteritis and in the aortitis associated with seronegative spondylitis. In later stages, medial degeneration, fibrous scarring, intimal proliferation, and thrombosis result Curr Probl Cardiol, October 1997

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in narrowing of the affected vessel. Aneurysm formation is observed rather less commonly than are stenosis and aortic rupture or dissection. Detailed angiographic examination has provided a great deal of information about the distribution of the stenotic lesions. 66The left subclavian artery, particularly in its midportion, is narrowed in ~90% of instances. The right subclavian, the left carotid, and the brachiocephalic trunk follow closely with regard to frequency of stenosis. Ishikawa 66detected lesions in the thoracic aorta by angiography in two thirds of his series. Involvement of the abdominal aorta was identified in half, but in only ~ 12% was there aortoiliac involvement. He found angiographic evidence of pulmonary arteritis in about half. Pulmonary hypertension may be found at catheterization. In patients studied at the Mayo Clinic, 64 involvement of the abdominal aorta, renal, and superior mesenteric arteries was more frequent than in the Japanese series. Clinical features. Manifestations of the illness appear during the second or third decade in 70% to 80% of instances, but it has been reported in childhood and in middle life. Women are 8 or9 times more often affected than are men.6366 During the early or "prepulseless" period of the illness, constitutional manifestations, such as fever, night sweats, malaise, nausea and vomiting, weight loss, arthralgia, and skin rash, are frequently encountered. The patient may have Raynaud's phenomenon, and splenomegaly may be found on examination. Laboratory study may disclose an elevated erythrocyte sedimentation rate, anemia, and serum protein abnormalities. 63-66 Claudication or numbness of an upper extremity resulting from subclavian artery narrowing and evidence of ischemia of the central nervous system occur with great frequency. Postural dizziness or frank syncope usually reflects cerebral ischemia caused by narrowing of the brachiocephalic arteries.63-66,69.7° Narrowing of the aorta proximal to the renal arteries or of those branches proper accounts for some, if not all, of the hypertension observed in more than half of patients with aortitis. It must be remembered that difficulty may be encountered in accurately measuring arterial pressure because of arch vessel stenosis. Cardiac manifestations may result from aortic regurgitation, coronary artery narrowing, or severe hypertension. Dilatation of the aortic root commonly accompanies the aortic valve incompetence. Angina pectoris, heart failure, and myocardial infarction are reported. Pericarditis has been observed clinically, but more commonly, healed pericarditis is noted at necropsy. The retinopathy to which Takayasu first directed attention is believed to result from ischemia of the retina. Ocular ischemia may also be manifested by transient loss of vision, cataracts, corneal opacity, and iridial atrophy. Blindness is a common complication. 504

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Involvement of the visceral arteries occasionally results in splanchnic ischemia, and intermittent claudication caused by aortoiliac obstruction may occur. Recently attention was directed toward the special problems that may arise during pregnancy in patients with this disorder. 7~,72Hypertension is a frequent and troublesome problem, but outcome for mother and child is acceptable when meticulous obstetrical care is provided. Diagnosis. The American College of Rheumatology identified six major criteria for the diagnosis of Takayasu's arteritis. 73 Onset of illness by age 40 years was recommended as an obligatory criterion to avoid overlap with patients having giant-cell arteritis. Others include upper-extremity claudication, diminished brachial pulses, a 10 m m Hg difference between the systolic blood pressure in the two arms, a subclavian or aortic bruit, and identification of narrowing of the aorta or a major branch. Identification in a patient of three of these six criteria is associated with high diagnostic sensitivity and specificity. Prognosis. Disability and death intrude on the lives of patients in whom severe aortitis exists at the time of diagnosis. One third to one quarter will have a significant event or will die within 5 years. Those with few or no ischemic complications at the time of diagnosis fare rather better. These patients appear to have a good 5- and 10-year outlook. In addition to the presence of complications at diagnosis, the presence of severe hypertension or of cardiac involvement predict a shortened life expectancy. 69,7° Cerebrovascular accidents and blindness are the most common major events. Congestive heart failure and aortic rupture or dissection are less frequent. Management. The benefits of any specific therapy have been difficult to assess because the disease typically runs a chronic course. Adrenocorticoids appear to be effective in suppressing the inflammation of the active phase. 74,75 Immunosuppressive therapy also has been used. Operative treatment may relieve symptoms from arterial obstruction, and percutaneous angioplasty has been used with favorable initial results. 76'77 Giant-Cell Arteritis. Giant-cell arteritis (temporal arteritis or polymyalgia rheumatica) involves extracranial arteries, including the aorta in 10% to 13% of cases. 78 Its peak incidence in late life seems to set it apart from other varieties of nonspecific arteritis. Like those, it may produce narrowing of the brachiocephalic arteries, aneurysm of the ascending aorta, aortic regurgitation, and aortic dissection. 79,8° Unlike Takayasu's arteritis, giant-cell arteritis rarely involves the descending thoracic or abdominal aorta. A ortitis in HLA-B2 7-Associated Spondyloarthropathies. Although the origin of neither ankylosing spondylitis nor Reiter's syndrome is known, Curr Prob[ Cardiol, October 1997

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> 9 0 % o f t h o s e a f f l i c t e d w i t h one o f t h e s e d i s o r d e r s have the histocompatibility antigen HLA-B27, an antigen quite infrequent in the general population. This observation may provide a clue to a common pathogenetic mechanism? 1 Aortitis has been demonstrated to occur in a sizeable minority of patients with these disorders. 8~Moreover, it may in fact be present in some patients with the H L A - B 2 7 antigen who are not a f f l i c t e d with spondyloarthropathy. Patients with the antigen can be identified with considerable frequency among subjects with lone aortic regurgitation or conduction abnormalities. 81 On histologic examination, the inflammatory aortic lesion found in association with these disorders resembles that of syphilis. Focal destruction of the medial elastic tissue is seen, but that layer is not thickened as are the intima and adventitia. An obliterative arteritis of the vasa vasorum may be present. 82Aortitis is more frequent in patients with spondylitis of long duration, in those with peripheral joint complaints in addition to spondylitis, and in patients with associated iritis. Unlike syphilis, the process is largely limited to the sinuses of Valsalva and immediately above those structures. The thickening of the adventitia and the intimal proliferation extend below the aortic valve to involve the membranous ventricular septum and the base of the anterior leaflet of the mitral valve.82The aortic valve cusps are thickened and retracted, and their edges rolled. As is the case with syphilis, aortic regurgitation is the most frequent clinical manifestation of these forms of aortitis. Extension of the aortitis onto the interventricular septum occasionally results in atrioventricular conduction abnormalities. Either of these clinical manifestations may be severe and life threatening.

Congenital Anomalies of the Aorta A discussion of the aortic arch anomalies and the complex congenital conditions manifest in infancy or early childhood are beyond the scope of this review. The recent review by Hougen 83 covers these topics for interested readers. Coarctation of the aorta is discussed in the portion of this review discussing conditions producing obstruction of the aorta, and sinus of Valsalva aneurysms are discussed in the section on aneurysm.

Clinical Manifestations of Aortic Disease

Aortic Aneurysm Aneurysms, areas of focal or diffuse dilatation of the aorta, develop at sites of congenital or acquired medial weakness. Hypertension, frequently present 506

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in patients with aneurysm, exposes weakness that might otherwise not be manifest. Once begun, aneurysm formation is promoted by physical laws, particularly that of LaPlace, which hold that for any level of intraluminal pressure, tangential wall tension increases with the square of the radius. Thus expansion and rupture are nearly inevitable unless the patient dies of intercurrent disease before this can occur. 84 "Fusiform" and "saccular" aneurysms are described. In the former, circumferential dilatation, the result of a diffuse area of weakness, produces a spindle-shaped deformity. In the latter, balloon-like dilatation occurs, beginning at a relatively narrow neck. Many aneurysms are not pure examples of either. In either variety, by the time the aortic wall has been stretched to aneurysmal size, little or no recognizable medial tissue remains; the wall of the aneurysmal sack is composed almost entirely of fibrous tissue. 85,86 The lumen of an aneurysm virtually always contains laminated thrombus. Such clots may be extensive enough to fill a saccular aneurysm or to cover the circumference of a fusiform aneurysm. For this reason, angiographic opacification of the aortic lumen often does not clearly delineate the size or extent of an aneurysm. Aneurysms may result from a variety of causes. Heritable medial weakness as a basis for aortic dilatation was discussed in the previous section. With the declining incidence of syphilis, aneurysms resulting from aortitis, either infectious or nonspecific, are uncommon. Saccular aneurysms are often encountered in regions of the aorta weakened by aortic dissection. 87 In spite of this variety of possibilities, the great majority of aortic aneurysms, particularly those of the descending thoracic or abdominal aorta, have been labeled "atherosclerotic. ''84 A series of clinical observations supports such an assumption. First, severe atherosclerosis nearly always accompanies an aneurysm. Second, aortic aneurysms are most commonly located in the infrarenal segment, the site of the most severe involvement of the aorta by atherosclerosis. Third, the usual risk factors for atherosclerosis also are risk factors for abdominal aortic aneurysm. 88Finally, there is strong association between abdominal aortic aneurysm and coronary, cerebral, and peripheral atherosclerosis. Challenging this assumption is a series of recent clinical and experimental observations indicating that aneurysm formation is a complex process 85,86 and that to consider atherosclerosis to be solely responsible may be too simplistic. First, it was suggested that atherosclerosis may be an epiphenomenon inevitably accompanying the altered hemodynamics produced by aortic dilatation of any cause. In fact atherosclerosis predictably forms on the intimal surface of any aneurysm, regardless of the origin. For exCurr Probl Cardiol, October 1997

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ample, atherosclerosis is characteristically seen in the false channel of a chronic aortic dissection or on the luminal surface of a luetic aneurysm. Second, the clinical features of patients with atherosclerotic obstruction of the infrarenal aorta differ from those of patients with infrarenal aneurysm. 85,86 Third, strong family clustering of abdominal aneurysms and their association with aneurysmal dilatation of other arteries provide reasons to suspect that an underlying heritable medial defect may play an important role in this process. 89'9° Fourth, it has been difficult to produce abdominal aneurysms in experimental animals by feeding an atherogenic dietY '86 Finally, several investigators have produced evidence of increased metabolic activity in the walls of aneurysms as compared with normal segments or those from patients with occlusive disease in the abdominal aorta. Accelerated protease activity, increased thrombolytic capacity, increased inflammatory cell presence, and increased vascularity have been demonstrated. 85,86,91 In their recent review of the issue, Halloran and Baxter 85concluded, "Abdominal aortic aneurysms result not from Passive dilatation, but from a complex remodeling process involving the synthesis and degradation of matrix proteins." Suffice it to say that the final word on the role of atherosclerosis or of a genetically determined abnormality of the media has not been heard. Sinus ofValsalva Aneurysm. Congenital failure of fusion of the aortic media with the fibrous skeleton of the heart at the aortic valve ring provides a point of weakness through which a sinus of Valsalva aneurysm may d e v e l o p . 92'93Aneurysm of the fight coronary sinus is most frequent. Most of the rest protrude from the noncoronary sinus. Congenital aneurysms of the left coronary sinus are rare. In that location, infectious endocarditis is a more frequent cause. Because the root of the aorta is surrounded by cardiac chambers, aneurysms of the right coronary sinus protrude into the right ventricular outflow tract. When they rupture, a fistulous connection between the aorta and right ventricle results. Similarly, an aneurysm of the noncoronary sinus, located posteriorly and to the right of the anterior sinus, typically protrudes into the fight atrium and usually ruptures into that structure. The rare aneurysms of the left coronary sinus protrude into the pericardial space from beneath the left main coronary artery. Some defects in the fight coronary sinus are extensive enough to produce undermining of the aortic valve and incompetence of that valve, and some are associated with incomplete closure of the membranous ventricular septum and an interventricular shunt results. Rarely recognized before rupture, they may be detected on imaging of a patient for some other purpose. Rarely the mass of the unruptured aneu508

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rysm may obstruct the right ventricular outflow tract or the left coronary artery. 94 Heart block or other conduction abnormalities may be produced from protrusion into the interventricular septum.

P.M. Shah: In the current era of widespread availability and use of echocardiography, asymptomatic disease of the aortic sinuses may be readily demonstrated by use of multiple imaging planes. The short-axis cross section of the aortic root readily shows abnormalities in pathogenesis of aortic regurgitation originating at center of stretched cusps. The severity of regurgitation also may be gauged from color-flow imaging,

Rupture of the sinus ofValsalva aneurysm usually results in a large shunt from the aorta to the right heart chambers. 94 The patient is seen with a continuous murmur and bounding arterial pulses. Often severe heart failure is present. The diagnosis is readily made from the clinical picture and echocardiography, Surgical correction may be expected to be effective.

Thoracic Aneurysm Origin and pathologic anatomy. Anuloaortic ectasia, the typical aneurysm resulting from medial degeneration, has been described as having the appearance of a "Florence flask" or an "onion bulb." These are apt descriptors because the dilatation is greatest in the proximal ascending aorta, including the aortic sinuses. The diameter quickly tapers, approaching a normal dimension before the takeoff of the innominate artery. Anuloaortic ectasia, the hallmark aortic manifestation of Marfan syndrome, is often encountered in those with no musculoskeletal or ocular manifestations of that disorder. Limited or extensive medial dissection may complicate this lesion.24,25,95 Syphilitic aneurysms are still occasionally encountered. They are typically saccular. The ascending aorta and arch are most often affected, but the aortic dilatation often extends into the aortic sinuses and into the descending aortic segment. The abdominal aorta is rarely affected. Saccular aneurysms of the thoracic aorta frequently follow aortic dissection when operative repair is not carried out. Moreover, they may develop in the descending thoracic aorta even after successful operative repair of a dissection involving the ascending a o r t a s Such aneurysms may gradually expand over time and require operative treatment months or years after the acute dissection. In frequency about equal to that of thoracic aneurysms after dissection are those that have in the past been assumed to be atherosclerotic in origin for the reasons noted previously. They are, however, far less common than Curt Probl Cardiol, October1997

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FIG. 6. Chest radiograph from patient with large aneurysm of descending thoracic aorta. Aneurysm had leaked into parenchyma of adherent left lung, producing recurrent hemoplysis and ultimately fatal hemorrhage.

infrarenal abdominal aneurysms. Unlike anuloaortic ectasia, these are typically located in the descending thoracic segment and are usually, but not invariably, fusiform. When they extend proximally into the arch or distally into the abdomen, they present a particularly difficult surgical problem. An aneurysm of the abdominal aorta is quite frequently associated and should be sought whenever a thoracic aneurysm is encountered. 96,97 Clinicalfeatures. Aneurysms limited to the ascending aorta rarely produce symptoms directly, unless they are undergoing active expansion or rupture. They are commonly recognized in the course of evaluation of a patient with the murmur of aortic regurgitation. Because the aortic root is located within the cardiac silhouette and the entire ascending aorta within the pericardial space, dilatation may not be readily appreciated on a chest radiograph. Like aneurysms of the ascending aorta, those of the arch and descending segments are often asymptomatic and detected fortuitously in the course of an incidental chest radiograph. They are, however, more likely than are those confined to the ascending aorta to produce symptoms. These segments are fixed by the brachiocephalic arteries and lie in a position to com510

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press a variety of mediastinal structures, as well as the thoracic spine. Compression of the tracheobronchial tree may be attended by cough or dyspnea. Tracheal deviation or "tug" may be detected on physical examination. Pressure on the esophagus may result in dysphagia, rarely quite severe. Hoarseness may result from the compression of the recurrent laryngeal nerve. Adjacent vascular structures may be compressed, resulting in pulmonary arterial stenosis or superior vena caval obstruction. Chest pain, described as deep and aching or throbbing, is the most frequent symptom reported in patients with thoracic aneurysm. Pain may be associated with erosion of the rib cage or vertebrae. The appearance of pain clearly related to an aneurysm must be regarded as a signal of expansion and threatened rupture. 97It is not unusual for expansion or rupture to be the initial manifestation of a thoracic aneurysm. Massive, usually fatal, hemorrhage into the mediastinum, pleural space, esophagus, or tracheobronchial tree ensues. Rupture of aneurysm of the ascending aorta, because of the intrapericardial location of that structure, results in acute hemopericardium and cardiac tamponade. Hemoptysis may precede by days or weeks fatal hemorrhage in descending thoracic aneurysms that have become adherent to adjacent lung (Fig. 6). Rarely aneurysms may rupture into adjacent vascular structures, producing aortovenous or aortopulmonary fistulas. Diagnostic studies. The aorta may now be imaged by a variety of modalities. Of these, chest radiograph and transthoracic echocardiography are the most readily available and thus most useful for screening purposes. Aortography, computerized tomography, magnetic resonance imaging, and transesophageal echocardiography all provide detailed information regarding the anatomy of the aorta. 98 Natural history and prognosis. Most of the data concerning the natural history of thoracic aortic aneurysms come from retrospective somewhat dated reports of hospital experience, 96,97but some more recent epidemiologic studies have appeared. 99 If anuloaortic ectasia and aortic dissection are excluded, the vast majority of cases studied have involved the descending aortic segment. Joyce's classic review 96 suggests a 50% 5-year and a 70% 10-year mortality. More recent studies suggested that the 5-year mortality may approach 75%. 99 One third to half of deaths result from rupture of the aneurysm; most of the remainder are a consequence of other vascular diseases. The location of the aneurysm does not influence the mortality rate, but advanced age, an aneurysm >6 cm in size, the presence of hypertension, and the association of other cardiovascular disease all increase the risk of death. The presence of symptoms (a reflection of a large aneurysm or one threatening to rupture) was associated with a reduced rate of survival. Insofar as the mortality data collected by Murdoch et al. ~°° in patients Curr Probl Cardiol, October 1997

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with Marfan syndrome apply to all patients with anuloaortic ectasia, their outlook may be even more grim than for those with aneurysm of the descending aorta. In that series, 52 of 56 patients with Marfan syndrome died as a consequence of aortic disease at an average age of 32 years. In a more recent study, the mean age of death in patients with Marfan syndrome was 41 years. 1°1 This improvement may be attributable to advances in cardiovascular surgery or to improved medical therapy (including the use of I]receptor blocking drugs), but different methods of collecting and analyzing data make the comparison debatable. It is of interest that the echocardiographic features of the aortic root (its shape, 1°2 its size, and its rate of expansion ~°3) in patients with Marfan syndrome appear useful in assessing the risk of rupture.

P.M, Shah- Serial echocardiographic evaluations of patients with Marfan disease and of those relatives with some evidence of the disease are indicated to diagnose asymptomatic progressive dilatation of proximal aorta. The chest radiograph is less sensitive and less diagnostic for proximal aortic disease as compared with echocardiography.

Management. Surgical repair constitutes the only known effective treatment for thoracic aneurysms. It is urgently indicated in patients if symptoms suggest expansion or compression of an adjacent structure. Cardiac failure from aortic regurgitation or aortocameral fistula may also necessitate early operative treatment. Available data suggest that, in asymptomatic patients, the larger the aneurysm and the more rapid its increase in size, the more likely rupture will occur. 1°4,1°5Resection is less urgent in small, asymptomatic aneurysms. At what point the size of the aneurysm dictates elective operation continues to be debated, but most agree that a diameter of 6 cm represents a point at which operative repair should be considered. Consideration of the severity of associated diseases is also important in selection of patients for surgery. Compared with the patient who has no other disease, the patient with associated coronary or cerebrovascular disease has a greater operative risk and a smaller risk of dying from rupture of the aneurysm before dying of the associated vascular disease. Surgical treatment consists of replacing the resected aneurysmal segment with a graft attached to relatively normal aorta proximally and distally. Specific surgical procedures vary with the site of the aneurysm and 512

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the need for maintaining circulation to distal parts of the body during the necessary period of aortic occlusion. Accordingly, the surgeon divides thoracic aneurysms into (1) those affecting the ascending aorta, (2) those affecting the arch of the aorta containing origins of the brachiocephalic vessels, (3) those affecting the descending thoracic aorta arising just distal to the origin of the left subclavian artery, and (4) thoracoabdominal aneurysms (i.e., those arising in the descending thoracic aorta and extending into the abdominal aorta). 1°6 For aneurysms of the ascending aorta, total cardiopulmonary bypass is required. The myocardium is protected by cold cardioplegia during the period that the coronary ostia are exposed. The aneurysm is opened, and a graft is sutured in place from within the aneurysm. Finally, the aneurysm is trimmed and sutured around the graft. If the aneurysm is associated with aortic valve incompetency, the leaflets are excised, and a composite graft including a prosthetic valve is sutured in place. The coronary ostia are sutured to an appropriate opening made in the composite graft or to a smaller Dacron graft, which is sutured side-to-side to the composite graft. For aneurysms of the transverse arch of the aorta, total cardiopulmonary bypass also is required. Additionally, profound hypothermia is used to protect the brain during temporary absence of circulation to the brachiocephalic vessels. Recent evidence suggests that retrograde perfusion of the brain through the superior vena cava adds further cerebral protection. A graft is sutured to relatively normal aorta proximally and distally from within the aneurysm, and the brachiocephalic, left common carotid, and left subclavian arteries are attached individually to appropriate openings in the graft. It is often possible to preserve the relatively normal aortic wall segment from which these vessels arise. This segment can be attached to an appropriate opening made in the graft for this purpose. The walls of the aneurysm are trimmed and sutured together around the grafts. For aneurysms arising distal to the left common carotid artery, it is usually desirable to use atrial/femoral bypass, femoral/femoral partial cardiopulmonary bypass, or various types of shunts during the period of aortic occlusion. 1°7 Although many techniques to prevent spinal cord ischemia are being studied for this purpose, there is not, as yet, sufficient evidence that any of them reduces the incidence of paralysis associfited with these procedures. Although the evidence is not conclusive, there is some reason to believe that some type of shunt is useful. Results of these methods of surgical treatment have been most encouraging. The surgical mortality rate for all aneurysms of the ascending or descending thoracic aorta ranges between 10% and 15%, although it is somewhat higher for those affecting the transverse arch and origins of the Curr Probl Cardiol, October 1997

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brachiocephalic vessels. Follow-up studies of these patients for >40 years provide evidence of maintenance of good results with long-term survival.l°7 Deaths during this period have usually been the result of associated diseases or other causes, although aneurysms occasionally develop in later years in other parts of the aorta and require surgical treatment. Thoracoabdominal aneurysms arise in the descending thoracic aorta and extend distally for varying distances into the abdominal aorta as far as the bifurcation, and occasionally into the common iliac arteries. They present a particular challenge to the surgeon because the arteries supplying blood to the abdominal organs arise from this portion of the aorta. The surgeon must expose the aorta in both the thorax and the abdomen. A left intercostal incision is made and extended down the midline of the abdomen, after which the diaphragm is incised, and the abdominal structures are mobilized retroperitoneally to expose the entire aneurysm. In most cases, it is possible to attach an opening in the interposed graft to the segment of the aorta from which arise the celiac, superior mesenteric, and renal arteries, and thus avoid the need to use individual grafts to each artery. Occasionally, however, because of the pathologic features of the aneurysm, it may be necessary to use a separate graft for one or more of these arteries. Results of this operation have been highly satisfactory, with an operative mortality rate of 5% to 10%. As in aneurysms of the descending thoracic aorta, paresis or paraplegia is a potential complication, occurring with about the same or perhaps somewhat higher frequency. Abdominal Aneurysm. Responsible for nearly 15,000 deaths annually in the United States, rupture of an abdominal aortic aneurysm is the tenth leading cause of death for men aged 55 years and older. Moreover, 40,000 aneurysmectomies are undertaken each year to prevent such catastrophes. Indeed, recent evidence indicates that the incidence of abdominal aneurysms is increasing, 1°8 in spite of the well-known decline in age-adjusted deaths from coronary atherosclerosis. This lesion is particularly treacherous because it is often clinically silent until rupture occurs. Origin. Until recently virtually all abdominal aneurysms were attributed to atherosclerosis34"1°8 As discussed previously, recent evidence compels a reconsideration of this assumptionY '86 Rarely a traumatic, congenital, or mycotic abdominal aneurysm is encountered, and one is occasionally found as a residual of aortic dissection or in patients with Marfan syndrome. Pathologic anatomy. Abdominal aneurysms are, as a rule, fusiform but may be saccular. Located, in almost all instances, distal to the renal arteries, they may extend to the aortic bifurcation and involve the iliac arteries. Exceptionally, they extend above the renal arteries. In that case, the origins 514

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of not only the renal arteries but also the major visceral arteries may be involved. As previously noted, such involvement complicates operative management.84.108 Five percent to 10% of abdominal aneurysms are accompanied by an intense inflammatory and fibrotic reaction in the anterior and lateral periaortic tissue, 1°9-m a process histologically similar to retroperitoneal fibrosis. It has been suggested that these "inflammatory aneurysms" result from a hypersensitivity reaction to an antigen or antigens in the atherosclerotic plaque. Systemic manifestations, such as weight loss, abdominal pain, and an elevated erythrocyte sedimentation rate, may reflect such a reaction. The difficulty of operative repair is increased. Clinical features. Men are 3 or 4 times more likely to have an abdominal aortic aneurysm than are women. The typical patient is in the seventh or eighth decade. Most aneurysms are asymptomatic and are detected in the course of an examination directed at unrelated symptoms. 84'1°8 Pain that can definitely be attributed to the aneurysm, especially when it is of recent onset, should be viewed as threatened rupture. Characteristically constant and located in the midabdomen, lumbar region, or pelvis, the pain:may be severe and may be described as having a boring quality. Detection of an aneurysm that is tender to palpation carries much the same threat of rupture, re,H3 Because they are seen with abdominal pain and often a tender abdominal mass, inflammatory aneurysms may mimic threatened rupture, 1°9-11I Unless the patient is obese, physical examination almost always discloses an abdominal mass in the epigastrium, slightly to the left of the midline. If definite expansile movement can be detected, the diagnosis of abdominal aneurysm is reasonably secure. Bruits may be audible, and femoral pulses are reduced in some patients. Rupture may be the initial manifestation. Rapid exsanguination may result from free rupture into the peritoneal cavity. Fortunately, more often the rupture is directed into the retroperitoneal space, where hemorrhage may be retarded. Abdominal pain and evidence of occult blood loss may persist for hours or days, allowing time for diagnosis and operative treatment. Rarely the rupture is confined for several days to a few weeks. In such instances, the patient may present a puzzling diagnostic picture consisting of abdominal pain, fever, and slight to moderate blood lOSS. 112-114 Recognition of the nature of the illness can be lifesaving because secondary rupture always ensues. Rarely rupture occurs into an adjacent retroperitoneal structure. When a communication develops with the vena cavae or other large veins, a loud continuous murmur in the abdomen and high-output congestive heart failCurr Probl Cardiol, October 1997

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FIG. 7. Computed tomographic scans from two patients. One (A} had large infrarenal aneurysm. "Egg-shell" calcium in wall is easily seen. For comparison, B is tomographic section of abdominal aorta from patient with aortic dissection. True channel is filled with contrast material and lies medially and anterior to Larger false channel.

ure may e n s u e . 114 Rupture into the duodenum results in gastrointestinal bleeding, H4 but aortoduodenal fistulas are more common after graft replacement of the infrarenal aorta. An unruptured aneurysm also may produce serious complications.Acute thrombosis may mimic saddle embolism. Furthermore, embolization of thrombus or atherosclerotic debris from aneurysms (and indeed from severely atherosclerotic but nonaneurysmal segments) to the lower extremities is far more frequent than is generally appreciated. 114,115Secondary bacterial infection of an aortic aneurysm gives rise to fever, leukocytosis, and abdominal pain. Such infections lead to rupture of the aneurysm. Diagnostic studies. Anteroposterior or cross-table lateral radiographs of 516

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the abdomen often confirm the presence of aneurysm by demonstrating the characteristic "egg-shell" calcification of its wall (Fig. 7). Imaging with ultrasound provides reproducible measurements of the dimensions of the aneurysm, and computed radiographic tomography or magnetic resonance imaging provides m o r e definitive confirmation of the diagnosis. Aortography can be reserved for instances in which additional information regarding the extent of the aneurysm or the degree of involvement of branch arteries is required. The aortogram, a depiction of the luminal contour, may be misleading because the aneurysm is characteristically filled or lined with thrombus. 116 Management. Because the threat of fatal rupture looms over every patient with an abdominal aneurysm and because rupture frequently appears in a previously asymptomatic patient, screening of at-risk populations by means of abdominal ultrasound has been considered. When this was undertaken in 8944 subjects aged at least 65 years, <5% were found to have abdominal aneurysm, and in <1% did it exceed 4 cm in diameter. 117 The costeffectiveness of such an approach has therefore been questioned. 118 The cost-effectiveness of screening could be enhanced by limiting the screening to high-risk populations, such as patients with a family history of aneurysmal disease or patients with atherosclerotic disease in other arteries. Abdominal aneurysms detected in asymptomatic patients during screening or the course of incidental examinations present a sometimes difficult management choice. 119The risk of fatal rupture must be balanced against the risk of aneurysmectomy. Considerable effort has been directed toward identifying the baseline characteristics of the patient and of the aneurysm that predict a high risk of rupture. 84'1°8'12°-123It has repeatedly been shown that the larger the aneurysm, the greater the risk of rupture. There is, therefore, general agreement that when discovered in a patient who is a reasonable operative risk, aneurysms 5 cm in size should be resected, whereas those <4 cm may safely be monitored pending an increase in size. Those whose diameter is >4 cm but <5 cm are in a gray zone in which there is disagreement regarding the desirability of operation. Cronewett et al. 12° carefully investigated other baseline factors in patients that might indicate an increased risk of rupture. They found that in addition to aneurysm size, systemic hypertension and chronic obstructive lung disease were independent predictors of increased risk. Commonly associated with abdominal aneurysms are coronary and cerebrovascular disease.119 Two characteristics of patients with these comorbid conditions are noteworthy. They are both less likely to die of rupture because of the lethality of their "organ-fixed" atherosclerosis, and they incur a greater operative risk in aneurysmectomy. It is important to recognize Curr Probl Cardiol, October 1997

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that, given appropriate preoperative screening for coronary disease with noninvasive imaging or coronary arteriography and appropriate treatment of the coronary disease, the risk of aneurysmectomy is acceptable in such patients.124-127 Because operative repair of abdominal aneurysms can now be accomplished with a mortality rate well <5 %,84 surgery can be recommended for all patients except those with advanced associated disease. Symptomatic aneurysms require urgent surgical treatment because early rupture can be confidently predicted. A ruptured abdominal aneurysm is a surgical emergency. Prompt surgical treatment can save most of these patients. Death is otherwise inevitable. Surgery for an abdominal aortic aneurysm does not require maintenance of the distal circulation. 128 The aorta is clamped proximally between the aneurysm and the renal arteries, the iliac arteries are clamped distally, and the aneurysm is opened. From within the aneurysm, the graft is sutured proximally to normal aorta and distally to the aortic bifurcation or individually to the iliac arteries. Finally, the aneurysmal walls are trimmed and sutured over the graft. The surgical risk depends primarily on the presence or absence of rupture, associated heart disease or hypertension, and patient's age. Experience has shown that the 5- to 10-year survival rate for patients operated on for aneurysms of the abdominal aorta closely parallels that for comparable age groups in the normal population.

Aortic Dissection Aortic dissection is believed to be the most common potentially fatal aortic disease, an even more frequent cause of aortic rupture than abdominal aneurysm. 129-132Every busy general hospital will encounter several each year. Because fundamental differences exist between the pathogenesis, clinical presentation, and treatment of dissections and those of aneurysms, the confusing term, "dissecting aneurysm," should be discarded. Pathologic Anatomy. Cleavage of the aortic media in its long axis by a dissecting column of blood characterizes aortic dissection. The split in the media, not usually circumferential, typically occupies about half of the circumference of the aorta and may extend through the entire length of the vessel. The plane of dissection often follows the greater curvature of the ascending aorta and the arch. In the descending aorta, the path of the dissection is most often located lateral to the true lumen, but it may be medial and may spiral "barber pole" fashion about the long a x i s . 133 In classic aortic dissection, the "false channel" created by this medial hematoma communicates with the "true lumen" through an intimal tear 518

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FIG. 8. Two frames from aortogram in patient with dissection involving ascending aorta. A, Contrast material in true lumen lying medial to false channel. Severeaortic regurgitation is present. Right coronary artery is visible coming off true channel. Clearly its patency was jeopardized by dissection process. 13,True and false channels have been equally opacified. Radiolucent line represents flap of media and intima separating true and false channels. Curr Probl Cardiol, October 1997

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Intimal ear

True

Jmen

False

lumen

Type I or Type A or Proximal

Type III or Type B or Distal

Variation

FIG. 9. Artist's depiction of three major anatomic patterns of aortic dissection. Left, most common variety, most frequently labeled type I of DeBakey but has also been called type A. Center, second most frequent variation, type III of DeBakey, alternately called type B. Lack of involvement of ascending aorta is its hallmark. Right, one of many variations from typical types. Note that intimal tear is located distal to arch vessels but ascending aorta is involved "retrogradely." (Reproduced with permission from Lindsay J Jr. Aortic dissection. Heart Dis Stroke 1992;1:69. Copyright 1992 American Heart Association.)

located near its proximal end. Such tears are typically single and transverse in orientation, but exceptions are frequent. Multiple secondary ("reentry") tears, located more distally along the false channel, also are quite common. Two patterns of involvement predominate. In about two thirds of instances, the false channel originates in the ascending aorta and the proximal ("entry") tear is located a few centimeters above the aortic valve (Fig. 8). The false channel frequently extends to the aortoiliac bifurcation. Dissections that do not involve the ascending aorta account for about a quarter of all cases. In the latter, the proximal tear lies in the descending thoracic aorta. The medial hematoma begins in proximity to the origin of the left subclavian artery and extends distally for varying distances. 129-a33 Many medial dissections do not follow these classic patterns. In some, the medial hematoma is short and limited to the arch or to the descending thoracic or abdominal segments. In another rather frequently encountered variation, an entry tear is located just beyond the left subclavian artery, but the dissection extends proximally into the ascending aorta. The most widely applied nomenclature is that of DeBakey. 129-m In this classification, dissection involving the ascending aorta belongs in type I, 520

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FIG. 10. Computed tomographic scan of thorax in patient with clinical picture of aortic dissection. Medial hematoma is present in posterior and lateral wall of descending aorta.

whereas those originating beyond the arch are included in type III. Type II is composed of those limited to the ascending aorta. Apart from length, many in type II are indistinguishable from those in type I, but others originate within chronic fusiform dilatation of the ascending aorta (Fig. 9). Reviews describing large numbers of patients with the clinical syndrome of aortic dissection have usually included a small number of patients with a medial hematoma but no intimal tear. 134 In recent years, imaging with computed tomography, transesophageal echocardiography, or magnetic resonance has conclusively demonstrated the existence of such a subset 135-137 (Fig. 10). These are now included under the rubric "intramural hematoma." Among 195 patients with medial hemorrhage documented with one of the tomographic imaging techniques cited, Nienaber et al. 137found 25 with no demonstrable communicating tear. In the reported experience, the aortic segments involved with intramural hematoma and the presenting clinical picture of the process do not substantially differ from those of typical dissection.135-137Aortography does not identify these abnormalities because contrast material injected into the aortic lumen fails to enter the medial hematoma.138 At present the therapeutic strategy for these lesions is the same as that for typical dissection. T o m o g r a p h i c i m a g i n g of the aorta with m a g n e t i c r e s o n a n c e , transesophageal echocardiography, or computerized x-ray also has allowed Curr Probl Cardiol, October 1997

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identification of another basis for medial hematoma formation, the penetrating atherosclerotic ulcer. 23In these patients, a large, ulcerated atherosclerotic plaque disrupts the aortic media, creating a potential for rupture, false aneurysm formation, or dissection by hematoma. These lesions appear almost exclusively in the mid and distal descending thoracic aorta. Exceptionally, major branch vessels are threatened. The initial presentation of a complication of a penetrating plaque (whether partial rupture or medial dissection) may mimic typical aortic dissection. Surgery will be indicated in selected cases because external rupture is a hazardY Death caused by aortic dissection most often occurs from disruption of the outer wall of the false channel opposite the entrance tear. ~29-134Rupture of proximal dissection therefore produces hemopericardium and cardiac tamponade. Hemorrhage into the mediastinum or either pleural space may occur. Typically external rupture of distal dissection results in a left hemothorax. Death caused by external rupture, often abrupt, may be delayed by temporary cessation of hemorrhage attributable to decreasing arterial pressure and increasing tension in the periaortic tissue. Dramatic clinical syndromes result in those rare instances in which the false channel ruptures into the right heart chambers, producing a large left-to-fight shunt. 139 In approximately half of patients with proximal dissection, medial hematoma undermines the aortic valve, rendering it incompetent. Fortunately, very serious hemodynamic consequences of aortic regurgitation appear infrequently during the acute phase. 129-132 One or more branch vessels of the aorta become obstructed by dissection in about half of patients with type I and in fewer with type III dissection. 129"132 The results may be catastrophic, particularly in patients with type I, because in them, the coronary and cerebral circulations are jeopardized. Fortunately rare, obstruction by the dissection of the orifice of one of the coronary arteries may produce an acute myocardial infarction. Failure to recognize the underlying process may result in thrombolytic therapy, with disastrous results. ~4° Obstruction of renal or splanchnic arteries may produce life-threatening complications. Severe hypertension and acute renal failure may attend renal artery involvement. The iliac arteries are the branch arteries most frequently compromised. Potentially disabling but usually not immediately life threatening, narrowing of these arteries may produce dramatic, painful ischemia of the lower extremities. TM The aortic wall that has been weakened by aortic dissection but that does not rupture during the acute phase is often the site of subsequent aneurysm formation. Rupture of these constitutes a major threat to the survivor of the i n i t i a l i l l n e s s . 82'142'143

Pathogenesis. Arterial hypertension seems clearly to be a factor in the 522

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genesis of aortic dissection. An elevated blood pressure, or evidence of its existence, can be found in 80% of patients. 129-134In most patients, no conclusive evidence of a medial defect can be identified, and no heritable or congenital basis for suspecting such a defect is apparent. Increased arterial pressure must certainly expose any existing weakness of the aortic wall and may, in addition, accentuate medial degeneration. The frequency with which dissecting hematoma is noted in Marfan syndrome, 24'25 in certain other congenital and heritable conditions, 24'25 and in experimental lathyrism provides a strong argument for the importance of an underlying medial defect in at least some persons with this disorder. Indeed histologic evidence of degeneration of elastin or of smooth-muscle cells in the aortic media of such patients has long been noted. As noted earlier, recent authors have thrown considerable doubt on the specificity of the classic histologic findings. These newer studies indicate that such findings are frequently absent in patients with dissection and are remarkably similar to changes encountered in older patients without dissection. 28'29'144 It seems likely that any fundamental medial defect or defects may be unrecognizable by light microscopy. The role of the intimal (entry) tear in the genesis of medial dissection is debated. Many investigators believe that it exposes the media to blood under luminal pressure and that the resulting shear forces initiate and propagate the medial cleavage. Others propose that medial weakness leads to hemorrhage from the vasa vasorurn. The resulting intramural hematoma splits the medial layers. 129-134In this hypothesis, the intimal tears are secondary. The instances of medial hematoma in which no intimal tear can be identified support the existence of this mechanism. 981°° Clinical Features. Most common in the fifth through the seventh decades of life, aortic dissection has been reported in children as well as in the very old. Men are affected at least twice as commonly as are women. 129-132 Predisposing conditions. Certain congenital lesions of the aorta (e.g., coarctation and bicuspid aortic valve) are associated with increased frequency of dissection. 32A greater-than-expected incidence is encountered in patients with aortic stenosis, even after aortic valve replacement. The same is true with certain heritable disorders such as Marfan and Turner's syndromes. 24 Iatrogenic vascular trauma, a complication of cardiac catheterization, coronary bypass surgery, cardiopulmonary bypass, or intraaortic balloon counterpulsation, may produce extensive aortic dissection. Many writers have concluded that pregnancy, either because of its effects on the aortic wall or because of attendant hemodynamic stress, predisposes to medial dissection. 145 This conclusion has been based on the Curr Probl Cardiol, October 1997

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fact that half or more of the reports of aortic dissection in women younger than 40 years have occurred during pregnancy. Because the total number reported is relatively small (certainly in relation to the frequency of pregnancy) and because most reports concern one or a few cases, it is possible that selective reporting accounts for this association. 146 History. Sudden, excruciating pain, presumably attributable to the progress of the medial cleavage, announces the onset of dissection in 90% of instances. Patients may describe the pain as "cutting," "ripping," or "tearing," but such vivid descriptors cannot always be e l i c i t e d . 129-132 They will most commonly locate the discomfort in the anterior chest, somewhat less frequently in the interscapular area in the epigastrium, or in the lumbar region. Because these locations often are the site of pain from more common processes (e.g., myocardial infarction or cholecystitis), the examiner must be alert to the possibility of aortic dissection in any patient with pain in these sites in whom the more common diagnoses are not immediately obvious. Two features of the pain of dissection help to separate it from that of other conditions. The discomfort of dissection typically is at its most intense from its inception and does not build in intensity, as is the case with other disorders producing severe pain in the trunk. Moreover, it often is located either simultaneously or sequentially in more than one of the four sites mentioned previously. Suspicion should be aroused particularly by pain occurring both above and below the diaphragm. 129-132 When pain is not a prominent feature of the presentation, it is usually because a sudden neurologic episode has diminished the patient's ability to perceive or report pain. Syncope is the most frequent neurologic event and is a particularly ominous sign. It seems always to reflect external rupture, almost always of the ascending aorta into the pericardial space. Less frequently, focal neurologic signs reflect arterial occlusion of the cerebral or spinal circulation. When pain is not prominent, occlusion by the dissection of the femoral or the subclavian artery may be the predominant clinical feature. Arterial embolism may be simulated. 129-132 Rarely the acute episode goes entirely unrecognized by the patient. In such instances, diagnostic study of patients who have an abnormal chest radiograph, aortic regurgitation, or obstruction of an arterial branch of the aorta uncovers chronic dissection. Physical examination. Although none is diagnostic of dissection, physical findings that greatly increase the probability of its presence can often be detected on examination. The murmur of aortic regurgitation can be heard in about half of all patients with acute type I dissection. Loss or diminution of 524

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an arterial pulse also may be detected in half. One or both of these cardinal findings is present in all but a small minority of that subgroup. In contrast, patients with dissection limited to the descending aorta less frequently have pulse deficits and uncommonly have a murmur of aortic regurgitation. Thus these patients often have none of these confirmatory findings, a29132 The frequency with which hypertension underlies aortic dissection has been mentioned, and a majority of patients with dissection will have high arterial pressure, but the elevation is modest in many. Some who are not hypertensive will be able to provide a history of high blood pressure, and even those with neither a history of hypertension nor a measurable blood pressure elevation will on examination have left ventricular hypertrophy or vascular changes in the optic fundi. Extraordinarily high readings can be encountered, particularly in those with type III dissection. Renal ischemia, a consequence of renal artery involvement, has been invoked to explain diastolic blood pressures that may reach 140 to 160 mm Hg. 129-I32 Of patients with dissection involving the ascending aorta, 20% have hypotension. Such a presentation requires immediate consideration of operative treatment because external rupture almost always is responsible.129-132 Diagnostic studies. Of the routine diagnostics studies, only the chest radiograph provides diagnostic information of much value. The aortic shadow is abnormal in 80% to 90% of cases but may also be abnormal in many instances in patients who do not have dissection. Dilatation of the ascending aorta, reflected by protrusion of its shadow from the right side of the mediastinum, is a characteristic finding in proximal dissection. Dilatation of the aortic knob and descending thoracic aorta is typical of distal disease. Certain other findings (e.g., progressive widening of the aortic silhouette on serial films, a lobulated or serrated margin of the aortic shadow, or a "double-lumen" effect created by a less radiopaque false channel) are less frequent but more specific. The same may be said for detection of intimal calcification >6 mm inside the margin of the aorta. 116 For confirmation of the diagnosis, either computed tomography after intravenous administration of contrast material or transesophageal echocardiography may be used with confidence. Both have high sensitivity and specificity. Some believe that magnetic resonance imaging is even more accurate; however, its value is limited in acutely ill patients because of the longer imaging time and the relative inaccessibility of patients during the imaging process. 116.147.149 P.M. Shah: The aortic dissection involving the ascending aorta has a high incidence of rupture in the first minutes and hours of presentation. Hence, a prompt diagnosis is paramount to outcome. It is a practice in our institution, as in several Curr Probl Cardiol, October 1997

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others, to perform TEE in the emergency department. The patient may be taken directly to the operating room. The diagnostic accuracy of TEE has been validated in several centers, and early report of low specificity was based on failure to recognize artifacts by use of single-plane TEE. More recent studies have shown approximately 95% sensitivity and 95% specificity. When TEE is unavailable, contrast computed tomography would be the modality of choice. Aortography is rarely, if ever, needed and is a poor substitute for more diagnostic methods.

An aortogram, accomplished by means of contrast injection through a catheter placed in the aorta, is occasionally required to provide details of branch vessel involvement. The findings on aortography are often quite dramatic. Two aortic channels can usually be identified because of the variation in intensity and timing of their opacification. Moreover, the aortogram may identify a linear lucency representing the aortic intima and media separating the two channels. At times the false channel is not opacified because of thrombosis or because it does not communicate with the true lumen. In such cases, the true lumen may appear to be compressed and to lie at a distance from the margins of the aortic shadow. The resulting appearance of a thickened aortic wall also can be produced by thrombosis within an aneurysm, aortitis, or mediastinal hematoma or tumor. These can usually, but not invariably, be distinguished from dissection because in these, the aortic lumen is not significantly compressed. 136-138 Natural History and Prognosis. We must look to older reports of aortic dissection for information about its natural history. Since the mid 1960s, virtually all patients have received either operative intervention or aggressive antihypertensive treatment. From the classic work of Hirst et al.134 and others, 15°,151it can be estimated that 35% of patients die within the initial 24 hours and that the mortality rate continues high during the first and second weeks, Fifty percent die within 48 hours, 70% by 1 week, and 80% by 2 weeks. Certain subgroups with widely differing natural histories can be identified, Hypotension (blood pressure <100 mm Hg) usually indicates aortic rupture and nearly certain early death. Almost all such patients have involvement of the ascending aorta; one quarter of those with such involvement are first seen in this way. Those with type III dissection are at the other end of the spectrum with regard to their natural history. Older reports indicate that about half survive the acute phase without aggressive treatment. Absent modern therapeutic intervention, the mortality rate of patients with type i or II dissection with hypertension or normotension is intermediate between these extremes. Patients who survive the first 2 weeks continue to have a high mortality 526

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rate in the first year. About half of the survivors die within 3 months and an additional 10% within a year of the onset of their illness. The lucky few who pass the first anniversary apparently may expect reasonable longevity. Late deaths may be caused by cerebrovascular complications of hypertension, heart failure from severe aortic regurgitation, or rupture of a saccular aneurysm of the residual false channel. 152,153 Management. Sudden life-threatening complications, such as very severe hypertension, cardiac tamponade, massive hemorrhage, severe aortic regurgitation, or ischemic injury to the myocardium, the central nervous system, and kidneys, threaten the patient with aortic dissection. Optimal management requires close surveillance of vascular pressures, urine flow, mental status, and neurologic signs in an intensive care unit. Pain relief can be difficult, even with potent narcotics, but can usually be obtained with drug therapy to reduce arterial pressure. 129132 A successful outcome in patients with aortic dissection requires that progression of the medial cleavage be halted and that external rupture of the weakened aortic wall be prevented. Inasmuch as the aortic defect is structural, operative treatment provides the most effective long-term remedy for many patients.Aggressive antihypertensive treatment lessens the stress on the aortic wall and thus the likelihood of progression of the dissection and of rupture of the weakened wall. Such therapy is widely used before and, in selected instances, as an alternative to surgical management. 92-95 In the acute phase, one of several drug regimens may be used to reduce arterial pressure and its rate of increase. Aggressive use of a [3-blocking agent may be adequate in patients who present with relatively modest levels of hypertension. In others with more severe hypertension, intravenous nitroprusside combined with a [3-blocking agent may be required. Drug therapy should aim to reduce systolic arterial pressure to 100 to 120 mm Hg. Optimal blood pressure reduction may not be possible if oliguria (<25 ml/hour) or mental confusion appears. Our intensivists currently prefer intravenous esmolol as the [3-blocking agent for acute dissection because its effects can be readily titrated. Before infusion this agent must be diluted to a concentration of no more than 10 mg per ml because more concentrated solutions are very irritating to veins. An initial loading dose of 0.5 mg/kg administered over a 1-minute period is followed by an infusion of 0.05 mg/kg/minute. The infusion rate can be increased at 4-minute intervals by 0.05 mg/kg/minute. Rates >0.3 mg/kg/ minute have not been shown to provide added therapeutic benefit. The substantial amounts of fluid required to maintain this infusion limit the usefulness of this agent in some patients. Alternately, propranolol can be administered intravenously in 0,5 mg Curr Probl Cardiol, October 1997

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increments at 1- to 5-minute intervals until the target blood pressure is achieved, the pulse rate slows, or a total dose of 1.5 rag/10 kg of body weight has been given. This scheme can be repeated at 4- to 6-hour intervals. Appropriate oral doses of this agent or comparable [3-blocking agents can be given for long-term maintenance after the need for short-term [3blockade has passed. The ability of intravenous nitroprusside to reduce arterial pressure promptly and consistently and the ease with which its hypotensive effects can be titrated recommend it as the current drug of choice for the patient whose blood pressure does not respond to [3-blockade. As little as 0.5 gg/ kg/minute may produce the desired result. Occasionally as much as 10 gg! kg/minute is necessary. This dose, however, should not be exceeded and should be reduced as soon as is practical. A 13-blocking agent should nearly always be used in conjunction with nitroprusside because animal data suggest that when used alone it does not reduce and may, through reflex mechanisms, enhance the rate of rise of arterial pressure. Intravenous labetalol is another alternative to the combination of nitroprusside and a [3-adrenergic blocking agent. Hydralazine, minoxidil, and diazoxide cannot be recommended because they produce reflex stimulation of the left ventricle and consequently an increase in the rate of rise in aortic pressure. Not all patients with acute aortic dissection have elevated blood pressure. Hypotension, it has been noted, reflects aortic rupture and dictates emergency operation. Some individuals have pressures only slightly higher than the 100 to 120 mm Hg target level for antihypertensive treatment. Pharmacologic treatment is of dubious value in such patients, although 13adrenergic blockade may be tried as a means of reducing the rate of rise of aortic pressure. As has been stated, operative treatment must be considered in all patients, but certain subgroups can be recognized whose clinical presentation dictates the timing of the surgery. At one extreme are those who are hypotensive on admission. The need for emergency operation has already been noted. On the other hand, operative treatment may never be an option in those with severe comorbid illness. Further, it may not be justified in those with severe neurologic injury from the dissection. In these inoperable patients, antihypertensive therapy is continued indefinitely by converting the drug regimen to an oral one that avoids vasodilators. The appropriateness and urgency of surgery for aortic dissection depends on its location and the clinical picture presented. For patients whose dissection involves the ascending aorta, operative repair should be undertaken as soon as the patient can be stabilized and appropriate diagnostic informa528

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FIG. 11. Chest radiograph of adult patient with coarctation of aorta. Lack of prominence (actually absence) of aortic knob is typical, as are notches in lower margins of ribs (arrows). (Reprinted with permission from Lindsay J Jr, Goldstein SA, Dolmatch BL. Diseasesof the aorta. In: Schlant RC, Alexander RW, Lipton MJ, editors. Diagnostic atlas of the heart. New York: McGraw-Hill, 1996:328.)

tion compiled. Such patients are in grave danger of a fatal complication in spite of effective antihypertensive therapy. By contrast, for those with uncomplicated type III dissection, it is now believed that operation during the acute phase does not improve survival beyond that achieved with drug treatm e n t . 129'132'153Younger patients and those who are relatively good operative risks may benefit from operation in the subacute phase to protect them from eventual rupture of a residual saccular aneurysm.142 The surgical technique for aortic dissection varies with the origin of the Curr Probl Cardiol, October 1997

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dissecting process and its extent. The surgeon's primary goal is always to remove the proximal (i.e., entry) tear and to close the false channel at that site. For dissection involving the ascending aorta, the procedure consists of transection of the ascending aorta with use of cardiopulmonary bypass, obliteration of the false lumen by approximation of the inner and outer walls of the false channel, and end-to-end anastomosis of the transected aorta. It may be necessary to restore vascular continuity by means of a patch or tube graft. Aortic-valve incompetence resulting from loss of commissural support of the valve leaflets may be corrected when this repair effectively resuspends the valve. Other patients may require prosthetic valve replacement or the use of a composite graft. Surgical treatment for dissection beginning beyond the arch vessels consists of resection of the descending thoracic aorta proximal to the origin of the dissecting process (usually at, or just below, the origin of the left subclavian artery), obliteration of the distal false passage by suture closure of the inner and outer layers, and replacement of the excised segment with an aortic graft. The surgical mortality rate has been steadily reduced and varies with the type and stage of the disease. In general it approaches 15%.

Aortic Obstruction Coarctation of the Aorta. In its most common form, aortic coarctation consists of hemodynamically significant narrowing of the aortic isthmus, that segment lying between the left subclavian artery and the insertion of the ductus arteriosus. A common congenital abnormality, it accounts for ~9% of all congenital heart disease in children and is the fourth leading cause of symptomatic congenital heart disease in infancy. 83,154,155The appearance of heart failure in an infant typically announces its presence. Associated, complex cardiac anomalies are frequent and contribute to this phenomenon.A less complex and often asymptomatic abnormality, bicuspid aortic valve, is by far the most frequent of the associated anomalies. It is present in half or more of patients. Absent the appearance of heart failure in infancy, coarctation may be detected as upper-extremity hypertension in an older child or young adult. Large, tortuous collateral arteries develop in response to the aortic obstruction. These connections between branches of the subclavian and the intercostal arteries deliver blood to the distal aorta. They enlarge, often to near aneurysmal proportions, gradually eroding the undersides of the ribs, producing the characteristic"rib notching" found on chest radiograph (Fig. 1 1). Flow through these collaterals often produces recognizable bruits over the rib cage. The natural history of this lesion is grim. Untreated, many patients die in childhood, and 80% die by age 50 y e a r s . 83'154455 In the older patients, death 530

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is precipitated by cerebral hemorrhage (at least in part the result of an association with berry aneurysm), aortic dissection or rupture, and infectious endocarditis). 83,154,155 Management. Relief of the obstruction offers the only possibility for improving this threatening natural history. Operative repair was first performed in 1945.156 Currently resection and end-to-end anastomosis, patch angioplasty, or subclavian flap angioplasty are used. Balloon dilatation of the narrowing is being investigated in a number of centers. 157,158 Unfortunately, resection of the coarcted segment has not been so curative as might have been hoped. Persistent hypertension has been a problem in a sizeable minority of patients, and the formation of aneurysms accompanied by dissection or rupture is well k n o w n . 156 Pseudocoarctation of the Aorta. Congenital kinking, so-called pseudocoarctation of the aorta, may be detected during the investigation of a mediastinal mass or of a systolic murmur. An abnormally elongated thoracic aorta tethered to the ligamentum arteriosum produces a silhouette shaped like an "S" or a "3" on radiographic examination. Thus it may resemble true coarctation; however, rib notching is not present. Exclusion of hemodynamically significant coarctation may require sophisticated imaging or the demonstration that no pressure difference exists between the upper and the lower aortic segments. True coarctation may coexist, and congenital cardiovascular anomalies similar to those found in true coarctation may be associated. Some authorities believe the abnormality to be a sharp downward angulation of the aorta at the attachment of the ligamentum arteriosum as a result of elongation of the fourth aortic arch. Others consider the embryologic defect to be the same as that for typical isthmic coarctation, except only that in these cases the narrowing is not severe enough to result in significant obstruction. 159.160 Abdominal Coarctation (Middle Aortic Syndrome). Although rare, hemodynamically significant narrowing of the descending thoracic or abdominal aorta deserves attention because it affects young people and because it often produces life-threatening hypertension that is surgically correctable. 161-163Although it most often appears to be a congenital lesion, at least some examples seem to result from healed aortitis. 164For this reason, some writers prefer to avoid the term "coarctation" and label it "middle aortic syndrome." Although the narrowed aortic segment is typically quite focal, diffuse hypoplasia of the abdominal aorta involving the branch arteries may be encountered. The renal arteries may be stenosed, hypoplastic, or thrombosed. As a consequence, severe hypertension is the most common cornCurr Probl Cardiol, October 1997

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plaint. Involvement of the visceral arteries may result in ischemia in their distribution. Intermittent claudication from involvement of the iliac arteries is more frequent than is the case in patients with coarctation at the aortic isthmus. On examination, similarities to the more common postductal coarctation will be noted. Upper-extremity hypertension will be present together with feeble pulses and hypotension in the legs. Attention may be directed to the unusual location of the stenosis by a bruit in the lumbar or umbilical area. Operative treatment is usually required because severe hypertension significantly shortens the life expectancy of patients with this disorder. Chronic Obstruction of the Terminal Aorta Origin and pathogenesis. The aortoiliac bifurcation is among the most common sites for atherosclerosis in the arterial tree and underlies the vast majority of instances of chronic obstruction of the infrarenal aorta. 163,~65,166 F u r t h e r m o r e , m a n y patients with s y m p t o m a t i c f e m o r o p o p l i t e a l atherosclerosis also have aortoiliac narrowing. Rarely infrarenal coarctation, aortitis, clinically silent embolism, or in situ thrombosis produce this situation. Rupture of atherosclerotic plaques sets the stage for mural thrombus and gradual progression of luminal narrowing and, in many instances, for complete occlusion of the terminal aorta. Collateral vessels develop concomitant with this progression. The lumbar and inferior mesenteric arteries are connected to branches of the internal iliac and common femoral arteries, ameliorating the effects of the aortic narrowing. Thus the symptoms of lower-extremity ischemia typically progress over months or years, and progression to complete occlusion may not be marked by a clinical event. This indolent course may, however, be punctuated by abrupt acceleration of symptoms, the result of sudden increase in the size of the obstructing thrombus or its extension to a significant collateral. ~63,~65,166 The pathogenesis of aortoiliac atherosclerosis may differ from that of atherosclerosis in more distal segments of the arterial tree.163,167Those with aortoiliac narrowing are younger and have a shorter duration of symptoms than do patients with femoropopliteal obstruction. It has been reasoned that, in the normal course of events, the narrowing in the more distal femoropopliteal arteries appears first. Only when other factors intrude, the reasoning continues, does "premature" atherosclerotic narrowing in the infrarenal aorta appear, and thus the younger age. The predilection of atherosclerosis for the terminal aorta may be enhanced in some patients because they have anatomic variations of the aortoiliac bifurcation that produce an "impedance mismatch." For example, 532

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an iliac bifurcation angle more acute than normal has been observed in some patients, 16s and in others, the aorta and iliac arteries are smaller than average. 169 Clinical features. Men are affected far more often than are women. The mean age of patients in most series is in the sixth decade, but some are much younger. The usual risk factors for atherosclerosis are found with great frequency. The original description of the clinical features of this process by Rene Leriche 17°still applies; however, variations on the theme are more frequent than is the full-blown syndrome. Pain or tiredness in the lower back, buttocks, or thighs produced by exertion and relieved by brief periods of rest are hallmarks of aortoiliac obstruction. Claudication may occur in the calf or foot in association with the more proximal distress and can be the sole complaint. Men often complain of inability to maintain a penile erection. Absence of, or reduction in, the femoral pulse is typical. More distal pulses in the legs are reduced or absent, and bruits are commonly audible over femoral arteries and in the midline of the abdomen near the umbilicus. Low skin temperature, diminished hair growth, atrophy of the skin and subcutaneous tissue, and diminished muscle bulk in the lower limbs are common but not universal signs. Frank gangrene is infrequent, and amputation for ischemia is therefore seldom required. 163,165,166 The findings in patients with aortoiliac obstruction overlap those in patients with femoropopliteal narrowing. A firm identification of involvement of the aortoiliac segment may be difficult on clinical grounds. Further to complicate matters, in many patients obstructing lesions are present at both levels. Fortunately, modem imaging techniques have made diagnosticians less dependent on clinical findings for the localization of the level of arterial obstruction. 163,165,166 Natural history and prognosis. The survival rate for patients with the Leriche syndrome appears to be lower than for those in a control population matched for age and sex, but death rarely results from aortoiliac disease. Coronary and cerebrovascular atherosclerosis are largely responsible for the higher death rate. Significant morbidity or death occasionally follows occlusion of the renal arteries by proximal extension of the thrombotic process. 163,165,166 Management. When surgical treatment is necessary, end-to-side bypass with a flexibl e, knitted, bifurcation graft is the preferred method of treatment. In the absence of femoropopliteal occlusive disease, this method has nearly always been successful in restoring normal distal circulation. Even when there is combined aortoiliac and femoropopliteal disease, bypass of the aortoiliac occlusion alone may increase lower-extremity flow sufficiently Curr Probl Cardiol, October 1997

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to relieve symptoms. Follow-up observations have provided evidence of maintenance of good long-term results with a relatively low recurrence rate. 17~ Percutaneous transluminal angioplasty is being used with increasing frequency in the treatment of iliac and femoropopliteal obstructive atherosclerotic disease. The early success rate appears to be satisfactory, but the long-term patency rate remains to be determined.

Acute Obstruction of the Terminal Aorta Origin. Sudden occlusion of the terminal aorta may result from a large ("saddle") embolus, trauma, a dissection, or in situ thrombosis of an aneurysm or a severely atherosclerotic aorta. When either dissection or trauma is responsible, the clinical picture usually leaves little doubt as to the reason for the aortic occlusion. 172-~74 Most emboli large enough to occlude the terminal aorta are thrown off from the heart. Thus embolus must be considered when acute aortoiliac occlusion occurs in patients with mitral stenosis, atrial fibrillation, or recent myocardial infarction. Rarely embolization of a vegetation from fungal endocarditis may be large enough to occlude the aortic bifurcation? 72-174 In situ thrombosis of an aneurysm or of a severely atherosclerotic aorta may develop when blood flow through these vessels is considerably reduced, as may be the case in shock or congestive heart failure. Clinical features. Unlike gradually progressive obstruction, abrupt total or near-total interruption of flow through the terminal aorta or common iliac arteries poses an immediate threat to life and limb. Although the clinical picture varies, depending on the presence of preexisting collaterals, the full-blown syndrome is characterized by the abrupt onset of pain, typically severe and located in the lumbar area, the buttocks, the perineum, the abdomen, and the legs. Numbness, paresthesia, dysesthesia, and finally paralysis of the affected limb dominate the picture. Pulses are absent in the legs, although at times faint femoral pulsations may be detected. The legs are cold and pale. Unless circulation is promptly restored, massive muscle necrosis may produce myoglobinuria, renal failure, acidosis, and hyperkalemia.

P.M. Shah: The author has written a comprehensive review of this important topic, which all practicing physicians and students will find useful. The discussions on pathogenesis, diagnosis, and management provide practical information that represents state-of-the-art understanding of diseases of the aorta.

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Management. In contrast to chronic aortoiliac occlusion, acute obstruction to blood flow does not allow for the formation of collateral circulation. Immediate operation is necessary for survival. The procedure used depends on the cause of the occlusion. Moreover, consideration must be given to treatment of the underlying disease, such as concomitant open mitral commissurotomy at the time of embolectomy, to prevent recurrent embolization to such vital organs as the brain. Although aortoiliac embolectomy may be performed directly through an incision in the distal aorta or proximal iliac arteries, this approach requires laparotomy in a severely ill patient, and it does not provide the means for removing the more distally lodged embolic material often present in these patients. The preferable approach is to expose both common femoral arteries in the groin and, through transverse arteriotomies, to remove, with balloon-tipped Fogarty catheters, the embolic material lodged proximally and distally. Even large amounts of embolic material in the distal aorta itself can be safely removed in this manner. Good circulation usually is restored after such procedures. Subsequent mortality rates, however, remain high because of the underlying disease. References 1. Wolinsky H, Glagov S. A lamellar unit of aortic medial structure and function in mammals. Circulation 1967;20:99-111. 2. Schlatmann TJM, Becker AE. Histologic changes in the normal aging aorta: implications for dissecting aortic aneurysm. Am J Cardiol 1977;39:13-20. 3. Cornwell GG HI, Westermark R Murdoch W, et al. Senile aortic amyloid: a third distinctive type of age-related cardiovascular arnyloid. Am J Pathol 1982; 108:135-40. 4. Ross R. The pathogenesis of atherosclerosis: a perspective for the 1990s. Nature 1993;362:801-9. 5. Stary HC, Chandler AB, Glagov S, et al. A definition of initial, fatty streak, and intermediate lesions of atherosclerosis: a report from the Committee on Vascular Lesions of the Council on Arteriosclerosis, American Heart Association. Circulation 1994;89:2462-78. 6. Khoury Z, Gottlieb S, Stern S, et al. Frequency and distribution of atherosclerotic plaques in the thoracic aorta as determined by transesophageal echocardiography in patients with coronary artery disease. Am J Cardiol 1997;79:23-7. 7. Roberts WC, Ferrans V J, Levy RI, et al. Cardiovascular pathology in hyperlipoproteinemia. Am J Cardiol 1973;31:557-70. 8. Zarins CK, Glagov S, Giddens DR et al. Hemodynamic factors and atherosclerotic change in the aorta. In: Bergan JJ, Yao JST, editors. Aortic surgery. Philadelphia: WB Saunders, 1989:17-25. 9. Wolinsky H, Glagov S. Comparison of abdominal and thoracic aortic medial structure in mammals: deviation of man from the usual pattern. Circ Res 1969;25:677-86. 10. Reed D, Reed C, Stemmermann G, et al. Are aortic aneurysms caused by atherosclerosis ? Circulation 1992; 85:205-11. 11. Bengtsson H, Norrgard O, Angquist KA, et al. Ultrasonographic screening of the abdominal aorta among siblings of patients with abdominal aortic aneurysms. Br J Surg 1989;76:589-91. Curr Probl Cardiol, October 1997

535

12. Darling RC III, Brewster DC, Darling RC, et al. Are familial abdominal aortic aneurysms different? J Vasc Surg 1989;10:39-43. 13. Kontusaari S, Tromp G, Kuivaniemi H, et al. A mutation in the gene for type III procollagen (COL3A1) in a family with aortic aneurysms. J Clin Invest 1990;80:146573. 14. Tilson MD. Aortic aneurysms and atherosclerosis. Circulation 1992;85:378-9. 15. Khatibzadeh M, Mitusch R, Stierle U, et al.Aortic atherosclerotic plaques as a source of systemic embolism. J Am Coil Cardiol 1996;27:664-9. 16. French Study of Aortic Plaques in Stroke Group. Atherosclerotic disease of the aortic arch as a risk factor for recurrent ischemic stroke. N Engl J Med 1996;334:1216-21. 17. Kronzon I, Tunick PA. Atheromatous disease of the thoracic aorta: pathologic and clinical implications. Ann Intern Med 1997; 126:629-37. 18. Nader RG, Barr F, Rubin R, et al.Aortic degenerative changes and thrombus formation: an unusual cause of massive myocardial infarction with normal coronary arteries. Am J Med 1989;86:718-22. 19. Bergin PJ. Aortic thrombosis and peripheral embolizationafter thoracic gunshot wound diagnosed by transesophageal echocardiography. Am Heart J 1990;119:688-90. 20. Kochar G, Kotler MN, Hartman J, et al. Thrombosed aorta resulting in spinal cord ischemia and paraplegia in ischemic cardiomyopathy. Am Heart J 1987; 113:150813. 21. Rosman HS, Davis TP, Reddy D, et al. Cholesterol embolization: clinical findings and implications. J Am Col1 Cardiol 1990; 15:1296-9. 22. OmA, Ellahham S, DiSciascio G. Cholesterol embolism: an underdiagnosed clinical entity. Am Heart J 1992;124:1321-6. 23. Movsowitz HD, Lampert C, Jacobs LE, et al. Penetrating atherosclerotic ulcers. Am Heart J 1994;128:1210-7. 24. Roman MJ, Devereux RB. Heritable aortic disease. In: Lindsay J Jr, editor. Diseases of the aorta. Philadelphia: Lea & Febiger, 1994:55-74. 25. Savunen T. Annulo-aortic ectasia: a clinical, structural and biochemical study. Scand J Thorac Cardiovasc Surg 1986;suppl 37:1-45. 26. Schlatmann TJM, Becker AE. Pathogenesis of dissecting aneurysm of the aorta: comparative histopathologic study of significance of medial changes. Am J Cardiol 1977;39:21-6. 27. Hirst AE, Gore I. Is cystic medionecrosis the cause of dissecting aortic aneurysm? Circulation 1976;53:915-6. 28. Wilson SK, Hutchins GM. Aortic dissecting aneurysms: causative factors in 204 patients. Arch Pathol Lab Med 1982;106:175-80. 29. NakashimaY, Kurozumi T, Sueishi K, et al. Dissecting aneurysm: a clinicopathologic and histopathologic study of 111 autopsied cases. Hum Pathol 1990;21:291-6. 30. Isner JM, Donaldson RF, Fulton D, et al. Cystic medial necrosis in coarctation of the aorta. Circulation 1987;75:689-95. 31. Tsipouras E De1 Mastro R, Sarfarazi M, et al. Genetic linkage of the Marfan syndrome, ectopia lentis, and congenital contractural arachnodactyly to the fibrillin genes on chromosomes 15 and 5. N Engl J Med 1992;326:905-9. 32. Roberts CS, Roberts WC. Dissection of the aorta associated with congenital malformation of the aortic valve. J Am Coll Cardiol 1991;17:712-6. 33. Hahn RT, Roman MJ, Mogtader AH, et al. Association of aortic dilatation with regurgitant, stenotic, and functionallynormal bicuspid aortic valves. JAm Coll Cardiol 1992;19:283-8. 34. Lindsay J Jr. Coarctation of the aorta, bicuspid aortic valve and abnormal ascending aortic wall. Am J Cardiol 1988;61:~182-4. 35. Subramaniam PN. Case report: Turner's syndrome and cardiovascular abnormalities: a case report and review of the literature. Am J Med Sci 1989;297:260-2. 536

Curr Probl Cardiol, October 1997

36. Nunez L, O'Connor LF, Pinto AG, et al. Annuloaortic ectasia and adult polycystic kidney: a frequent association. Chest 1986;90:299-300. 37. Biagini A, Maffei S, Baroni M, et al. Familial clustering of aortic dissection in polycystic kidney disease. Am J Cardiol 1993;72:741-2. 38. Leier CV, Call TD, Fulkerson PK, et al. The spectrum of defects in the Ehlers-Danlos syndrome, types I and III. Ann Intern Med 1980;92:171-8. 39. Hortop J, Tsiponras E Hanley JA, et al. Cardiovascular involvement in osteogenesis imperfecta. Circulation 1986;73:54-61. 40. Marsalese DL, Moodie DS, Lytle BW, et al. Cystic medial necrosis of the aorta in patients without Marfan's syndrome: surgical outcome and long-term follow-up. J Am Coll Cardiol 1990;16:68-73. 41. Roman MJ, Devereux RB, Niles NW, et al. Aortic root dilatation as a cause of isolated, severe aortic regurgitation. Ann Intern Med 1987; 106: 800-7. 42. Milewicz DM; Michael K, Fisher N, et al. Fibrillin-1 (FBN1) mutations in patients with thoracic aortic aneurysms. Circulation 1996;94:2708-11. 43. Ewart JM, Burke ML, Bunt TJ. Spontaneous abdominal aortic infections: essentials of diagnosis and management. Am Surg 1983;49:37-50. 44. Jackman JD, Radolf JD. Cardiovascular syphilis. Am J Med 1989;87:425-33. 45. Heggtveit HA. Syphilitic aortitis. Circulation 1964;29:346-55. 46. Merten CW, Finby N, Steinberg I. The antemortem diagnosis of syphilitic aneurysm of the aortic sinuses: report of nine cases. Am J Med 1956;20:345-60. 47. Atnip RG. Mycotic aneurysms of the suprarenal abdominal aorta: prolonged survival after in situ aortic and visceral reconstruction. J Vasc Surg 1989; 10:635-41. 48. Oz MC, McNicholas KW, Serra AJS, et al. Review of salmonella mycotic aneurysms of the thoracic aorta. J Cardiovasc Surg 1989;30:99-103. 49. Cohen PS, O'Brien TF, Schoenbaum SC, et al. The risk of endothelial infection in adults with salmonella bacteremia. Ann Intern Med 1978;89:931-2. 50. Johansen K, Devin J. Mycotic aortic aneurysms: a reappraisal. Arch Surg 1983;118:583-641. 51. Oskoui R, Davis WA, Gomes MN, Salmonella aortitis: a report of a successfully treated case with a comprehensive review of the literature. Arch Intern Med 1993; 153:517-25. 52. Bennett DE. Primary mycotic aneurysms of the aorta. Arch Surg 1967;94:758-65. 53. Goldbaum TS, Lindsay J Jr, Levy C, et al. Tuberculous aortitis presenting with an aortoduodenal fistula. Angiology 1986;37:519-23. 54. Colucci V, Moreo A, Passini L, et al. Successful resection of a tuberculous p s e u d o a n e u r y s m of the d e s c e n d i n g t h o r a c i c aorta. Tex H e a r t Inst J 1992;19:142-5. 55. Arnett EN, Roberts WC. Valve ring abscess in active infective endocarditis: frequency, location, and clues to clinical diagnosis from the study of 95 necropsy patients. Circulation 1976;54:140-5. 56. Miller SW, Dinsmore RE. Aortic root abscess resulting from endocarditis: spectrum of angiographic findings. Radiology 1984;153:357-61. 57. Saner HE, Asinger RW, Homans DC, et al. Two-dimensional echocardiographic identification of complicated aortic root endocarditis: implications for surgery. J Am Coll Cardiol 1987;10:859-68. 58. David TE, Komeda M, Brofman PR. Surgical treatment of aortic root abscess. Circulation 1989;80(suppl I):I269-74. 59. Daniel WG, Mugge A, Martin RP, et al. Improvement in the diagnosis of abscesses associated with endocarditis by transesophageal echocardiography. N Engl J Med 1991 ;324:795-800. 60. Bjork VO, Bjork L. Aneurysm of the sinus of Valsalva. J Thorac Cardiovasc Surg 1965;50:16-21. Curr Probl Cardiol, October 1997

537

61. Feigl D, Feigl A, Edwards JE. Mycotic aneurysms of the aortic root: a pathologic study of 20 cases. Chest 1986;90:553-7. 62. Conde CA, Meller J, Donoso E, et al. Bacterial endocarditis with ruptured sinus of Valsalva and aortocardiac fistula. Am J Cardiol 1975;35:912-5. 63. Ito I. Aortitis syndrome (Takayasu's arteritis): a historical perspective. Jpn Heart J 1995;36:273-81. 64. Hall S, Barr W, Lie JT, et al. Takayasu's arteritis: a study of 32 North American patients. Medicine 1985;64:89-99. 65. Kerr GS, Hallahan CW, Giordano J, et al. Takayasu arteritis. Ann Intern Med 1994;120:919-29. 66. Ishikawa K. Diagnostic approach and proposed criteria for the clinical diagnosis of Takayasu's arteriopathy. J Am Coil Cardiol 1988;12:964-72. 67. Eichorn J, Sima D, Thiele B, et al. Anti-endothelial cell antibodies in Takayasu's arteritis. Circulation 1996;94:2396-401. 68. TakeuchiY, Matsuki K, SaltoY, et al. HLA-D region genomic polymorphism associated with Takayasu's arteritis. Angiology 1990;41:421-6. 69. Subramanyan R, Joy J, Balakrishnan KG. Natural history of aortoarteritis (Takayasu's disease). Circulation 1989;80:429-37. 70. Ishikawa K, Maetani S. Long-term outcome for 120 Japanese patients withTakayasu's disease. Circulation 1994;90:1855-60. 71. Ishikawa K, Matsuura S. Occlusive thromboaortopathy (Takayasu's disease) and pregnancy. Am J Cardiol 1982;50:1293-300. 72. Wong VCW, Wang RYC, Tse TF. Pregnancy and Takayasu's arteritis. Am J Med 1983;75:597-601. 73. Arend WE Michel BA, Bloch DA, et al. The American College of Rheumatology 1990 criteria for the classification of Takayasu arteritis.ArthritisRheum 1990;33:112934. 74. Ishikawa K. Effects of prednisolone therapy on arterial angiographic features in Takayasu's disease. Am J Cardiol 1991;68:410-3. 75. Fraga A, Mintz G, Valle L, et al. Takayasu's arteritis: frequency of systemic manifestations (study of 22 patients) and favorable response to maintenance corticosteroid therapy with adrenocorticosteroids (12 patients). Arthritis Rheum 1972;15:617-24. 76. Tyagi S, Kaul UA, Nair M, et al. Balloon angioplasty of the aorta in Takayasu's arteritis: initial and long-term results. Am Heart J 1992;124:876-82. 77. Tyagi S, Singh B, Kaul UA, Sethi KK, Arora R, Khalilullah M. Balloon angioplasty for renovascular hypertension in Takayasu's arteritis. Am Heart J 1993; 125:1386-93. 78. Klein RG, Hunder GG, Stanson AW, et al. Large artery involvement in giant cell (temporal) arteritis. Ann Intern Med 1975;83:806-12. 79. Evans JM, Bowles CA, Bjornsson J, et al. Thoracic aortic aneurysm and rupture in giant cell arteritis. Arthritis Rheum 1994;37:1539-47. 80. Evans JM, O'Fallon WM, Hunder GG. Increased incidence of aortic aneurysm and dissection in giant cell (temporal) arteritis. Ann Intern Med 1995; 122:502-7. 81. Bergfeldt L, Insulander P, Lindblom D, et al. HLA-B27: an important genetic risk factor for lone aortic regurgitation and severe conduction system abnormalities. Am J Med 1988;85:12-8. 82. Bulkley BH, RobertsWC.Ankylosing spondylitis and aortic regurgitation: description of the characteristic cardiovascular lesion from study of eight necropsy patients. Circulation 1973;48:1014-27. 83. Hougen TJ. Congenital anomalies of the aortic arch. In: Lindsay J Jr, editor. Diseases of the aorta. Philadelphia: Lea & Febiger, 1994:19-51. 84. Kent KC, Boyce SW. Aneurysms of the aorta. In: Lindsay J Jr, editor. Diseases of the aorta. Philadelphia: Lea & Febiger, 1994:109-25. 538

Curr Probl Cardiol, October 1997

85. Halloran BG, Baxter BT. Pathogenesis of aneurysms. Semin Vasc Surg 1995;8:8592. 86. Patel MI, Hardman DTA, Fisher CM. Current views on the pathogenesis of abdominal aortic aneurysms. JAm Coll Surg 1995;181:371-82. 87. Heinemann M, Laas J, Karck M, et al. Thoracic aortic aneurysm after acute type A aortic dissection: necessity for follow-up. Ann Thorac Surg 1990;49:580-4. 88. Reed D, Reed C, Stemmermann G, et al. Are aortic aneurysms caused by atherosclerosis? Circulation 1992;85:205-11. 89. Baird PA, SadovnickAD, Yee IML, et al. Sibling risks of abdominal aortic aneurysm. Lancet 1995;346:601-4. 90. Verloes A, Sakalihasan N, Koulischer L, et al. Aneurysms of the abdominal aorta: familial and genetic aspects in three hundred thirteen pedigrees. J Vasc Surg 1995;21:646-55. 91. Newman KM, Jean-Claude J, Li H, et al. Cytokines that activate proteolysis are increased in abdominal aortic aneurysms. Circulation 1994:90(Pt 2) :II224-7. 92. Edwards JE, Burchell HB. The pathological anatomy of deficiencies between the aortic root and the heart, including aortic sinus aneurysms. Thorax 1957; 12:125-39. 93. Sakakibara S, Konno S. Congenital aneurysm of the sinus of Valsalva: anatomy and classification. Am Heart J 1962;63:405-24. 94. Lindsay J Jr. Anatomic and pathogenetic bases for some uncommon clinical syndromes from aortic disease. In: Lindsay J Jr, editor. Diseases of the aorta. Malvern (PA): Lea & Febiger, 1994:165-77. 95. Smith JA, Farm JI, Miller DC, et al. Surgical management of aortic dissection in patients with the Marfan syndrome. Circulation 1994;90(Pt 2):II235-42. 96. Joyce JW, Fairbaim JF II, Kincaid OW, et al. Aneurysms of the thoracic aorta: a clinical study with special reference to prognosis. Circulation 1964;29:176-81. 97. Pressler V, McNamara JJ. Thoracic aortic aneurysm: natural history and treatment. J Thorac Cardiovasc Surg 1980;79:489-98. 98. Goldstein SA, Lindsay J Jr. Thoracic aortic aneurysms: role of echocardiography. Echocardiography 1996; 13:213-32. 99. Bickerstaff LK, Pairolero PC, Hollier LH, et al. Thoracic aortic aneurysms: a population-based study. Surgery 1982;92:1103-8. 100. Murdoch JL, Walker BA, Halpern BL, et al. Life expectancy and causes of death in the Marfan syndrome. N Engl J Med 1972;286:804-8. 101. Silverman DI, Burton KJ, Gray J, et al. Life expectancy in the Marfan syndrome. Am J Cardiol 1995;75:157-60. 102. Roman MJ, Rosen SE, Kramer-Fox R, et al. Prognostic significance of the pattern of aortic root dilatation in the Marfan syndrome. J Am Coll Cardiol 1993;22:1470-6. 103. Legget ME, Unger TA, O'Sullivan CK, et al. Aortic root complications in Marfan's syndrome: identification of a lower risk group. Heart 1996;75:389-95. 104. MasudaY, Takanashi K, Takasu J, et al. Expansion rate of thoracic aortic aneurysms and influencing factors. Chest 1992;102:461-6. 105. Dapunt OE, Galla JD, Sadeghi AM, et al. The natural history of thoracic aortic aneurysms. J Thorac Cardiovasc Surg 1994; 107:1323-33. 106. DeBakey ME, Noon GR Aneurysms of the thoracic aorta. Med Concepts Cardiovasc Dis 1975;44:53-8. 107. DeBakey ME, McCollum CH, Graham JM. Surgical treatment of aneurysms of the descending thoracic aorta: long-term results in 500 patients. J Cardiovasc Surg 1978;19:571-6. 108. Ernst CB. Abdominal aortic aneurysm. N Engl J Med 1993;328:1167-72. 109. Pennell RC, Hollier LH, Lie JT, et al. Inflammatory abdominal aortic aneurysms: a thirty-year review. J Vasc Surg 1985;2:859-69. 110. SterpettiAV, HunterWJ, Feldhaus RJ, et al. Inflammatory aneurysms of the abdominal Curr Probl Cardiol, October 1997

539

111. 112. 113. 114. 115. 116.

117. 118. 119. 120. 121. 122. 123. 124.

125. 126. 127. 128. 129. 130. 131. 132. 133. 134.

540

aorta: incidence, pathologic, and etiologic considerations. J Vasc Surg 1989;9:64350. Leseche G, Schaetz A, Arrive L, et al. Diagnosis and management of 17 consecutive patients with inflammatory abdominal aortic aneurysms.Am J Surg 1992;164:39-44. Rutherford RB, McCroskey BL. Ruptured abdominal aortic aneurysms: special considerations. Surg Clin North Am 1989;69:859-68. Sullivan CA, Rohrer MJ, Cutler BS. Clinical management of the symptomatic but unruptured abdominal aortic aneurysm. J Vasc Surg 1990; 11:799-803. Bower TC, Cherry KJ Jr, Pairolero PC. Unusual manifestations of abdominal aortic aneurysms. Surg Clin North Am 1989;69:745-54. Keen RR, McCarthy WJ, Shireman PK, et al. Surgical management of atheroembolization. J Vasc Surg 1995;21:773-81. Dolmatch BL, Gray RJ, Horton KM, et al. Diagnostic imaging in the evaluation of aortic disease. In: Lindsay J Jr, editor. Diseases of the aorta. Philadelphia: Lea & Febiger, 1994:197-250. Scott RAP, Wilson NM, Ashton HA, et al. Is surgery necessary for abdominal aneurysm less than 6 cm in diameter? Lancet 1993;342:1395-6. Frame PS, Fryback DG, Patterson C. Screening for abdominal aortic aneurysm in men ages 60 to 80 years. Ann Intern Med 1993;119:411-6. Lederle FA. Management of small abdominal aortic aneurysms. Ann Intern Med 1990;113:731-2. Cronewett JL, Murphy TF, Zelenock GB, et al. Actuarial analysis of variables associated with rupture of small abdominal aneurysms. Surgery 1985;98:472-83. Nevitt MP, Ballard DJ, Hallett JW Jr. Prognosis of abdominal aortic aneurysm: a population-based study. N Engl J Med 1989;321:1009-14. Guirnis EM, Barber GG. The natural history of abdominal aortic aneurysms. Am J Surg 1991;162:481-3. Nehler MR, Taylor LM Jr, Moneta GL, et al. Indications for operation for infrarenal abdominal aneurysms: current guidelines. Semin Vasc Surg 1995;8:108-14. Roger VL, BaUard DJ, Hallett JW Jr, et al. Influence of coronary artery disease on morbidity and mortality after abdominal aortic aneurysmectomy: a population-based study, 1971-1987. J A m Coll Cardiol 1989;14:1245-52. Graor RA. Preoperative evaluation and management of coronary and carotid artery occlusive disease in patients with abdominal aortic aneurysms. Surg Clin North Am 1989;69:737-43. Cambria RP, Eagle K. Cardiac screening before abdominal aortic aneurysm surgery: a reassessment. Semin Vasc Surg 1995 ;8:93-102. Bayazit M, Gol MK, Battaloglu B, et al. Routine coronary arteriography before abdominal aortic aneurysm repair. Am J Surg 1995;170:246-50. DeBakey ME. Aneurysmectomy of the abdominal aorta. Surg Tech Illus 1976; 1:5-20. Spittell PC, Spittell JA Jr, Joyce JW, et al. Clinical features and differential diagnosis of aortic dissection: experience with 236 cases (1980-1990). Mayo Clin Proc 1993 ;68:642-51. Crawford ES. The diagnosis and management of aortic dissection. JAMA 1990:264:2537-41. DeSanctis RW, Doroghazi RM, Austen WG, et al. Aortic dissection. N Engl J Med 1987;317:1060-7. Lindsay J Jr. Aortic dissection. In: Lindsay J Jr, editor. Diseases of the aorta. Philadelphia: Lea & Febiger, 1994:127-43. Roberts WC. Aortic dissection: anatomy, consequences, and causes. Am Heart J 1981;101:195-214. Hirst AE Jr, Johns VJ Jr, Kime SW Jr. Dissecting aneurysms of the aorta: a review of 505 cases. Medicine 1958;37:217-79. Curr Probl Cardiol, October 1997

135. Robbins RC, McManus RP, Mitchell RS, et al. Management of patients with intramural hematoma of the aorta. Circulation 1993;88(Pt 2): 1-10. 136. Mohr-Kahaly S, Erbel R, Kearney P, et al. Aortic intramural hemorrhage visualized by transesophageal echocardiography: findings and prognostic implications. J Am Coll Cardiol 1994;23:658-64. 137. Nienaber CA, von KodolitschY, Peterson B, et al. Intramural hemorrhage of the thoracic aorta: diagnostic and therapeutic implications, Circulation 1995;92:1465-72. 138. Bansal RC, Chandrasekaran K, Ayala K, et al. Frequency and explanation of false negative diagnosis of aortic dissection by aortography and transesophageal echocardiography. J Am Coil Cardiol 1995;25:1393-401. 139. Lindsay J Jr. Aortocameral fistula: a rare complication of aortic dissection. Am Heart J 1993;126:441-3. 140. Kamp TJ, Goldschmidt-Clermont PJ, Brinker JA, et al. Myocardial infarction, aortic dissection, and thrombolytic therapy, Am Heart J 1994; 128:1234-7. 141. Hughes JD, Bacha EA, Dodson TF, et al. Peripheral vascular complications of aortic dissection. Am J Surg 1995;170:209-12. 142. Kato M, Bal H, Sato K, et al. Determining surgical indications for acute type B dissection based on enlargement of aortic diameter during the chronic phase. Circulation 1995;92 Suppl II:II107-12. 143. Moore NR, Parry A J, Trottman-Dickenson B, et al. Fate of the native aorta after repair of acute type A dissection: a magnetic resonance imaging study. Heart 1996;75:62-6. 144. Larson EW, Edwards WD. Risk factors for aortic dissection: a necropsy study of 161 cases. Am J Cardiol 1984;53:849-55. 145. Williams GM, GottVL, Brawley RK, et al. Aortic disease associated with pregnancy. J Vasc Surg 1988;8:470-5. 146. Oskoui R, Lindsay J Jr. Aortic dissection in women <40 years of age and the unimportance of pregnancy. Am J Cardiol 1994;73:821-2. 147. Keren A, Kim CB, Hu BS, et al. Accuracy of biplane and multiplane transesophageal echocardiography in diagnosis of typical acute aortic dissection and intramural hematoma. J Am Coil Cardiol 1996;28:627-36. 148. Cigarroa JE, Isselbacher EM, DeSanctis RW, et al. Diagnostic imaging in the evaluation of suspected aortic dissection. N Engl J Med 1993;328:35-43. 149. Erbel R, Oelert H, Meyer J, et al. for the European Cooperative Study Group on Echocardiography. Effect of medical and surgical therapy on aortic dissection evaluated by transesophageal echocardiography: implications for prognosis and therapy. Circulation 1993;87:1604-15. 150. Lindsay J Jr, Hurst JW. Clinical features and prognosis in dissecting aneurysm of the aorta: a reappraisal. Circulation 1967;35:880-8. 151. Slater EE, DeSanctis RW. The clinical recognition of dissecting aortic aneurysm. Am J Med 1976;60:625-33. 152. Doroghazi RM, Slater EE, DeSanctis RW, et al. Long-term survival of patients with treated aortic dissection. J Am Coll Cardiol 1984;3:1026-34. 153. Glower DD, Fann JI, Speier RH, et al. Comparison of medical and surgical therapy of uncomplicated descending aortic dissection. Circulation 1990;82 Suppl IV:IV39-46. 154. Reifenstein GH, Levine SA, Gross RE. Coarctation of the aorta. Am Heart J 1947;33:146-68. 155. Liberthson RR, Pennington DG, Jacobs ML, et al. Coarctation of the aorta: review of 234 patients and clarification of management problems. Am J Cardiol 1979;43:835-40. 156. Maron BJ, Humphries JO, Rowe RD, et al. Prognosis of surgically corrected coarctation of the aorta: a 20-year postoperative appraisal. Circulation 1973;47:119-26. 157. McCrindle BW, Jones TK, Morrow WR, et al. Acute results of balloon angioplasty of native coarctation versus recurrent aortic obstruction are equivalent. JAm Coil Cardiol 1996;28:1810-7. Curr Probl Cardiol, October 1997

541

158. Kaine SF, Smith O, Mott AR, et al. Quantitative echocardiographic analysis of the aortic arch predicts outcome of balloon angioplasty of native coarctation of the aorta. Circulation 1996;94:1056-62. 159. Hoeffel JC, Henry M, Mentre B, et al. Pseudocoarctation or congenital kinking of the aorta: radiologic considerations. Am Heart J 1975;89:428-36. 160. Smyth PT, Edwards JE. Pseudocoarctation, kinking or buckling of the aorta. Circulation 1972;46:1027-32. 161. Bergamini TM, Bernard JD, Mavroudis C, et al. Coarctation of the abdominal aorta. Ann Vasc Surg 1995;9:352-6. 162. Cohen JR, Birnbaum E. Coarctation of the abdominal aorta. J Vasc Surg 1988;8:160-4. 163. Lindsay J Jr. Acquired Obstructive disease of the aorta. In: Lindsay J Jr, editor. Diseases of the aorta. Philadelphia: Lea & Febiger, 1994:145-56. 164. Lande A. Takayasu's arteritis and congenital coarctation of the descending thoracic and abdominal aorta: a critical review. AJR Am J Roentgenol 1976; 127:227-33. 165. Brewster DC. Clinical and anatomical considerations for surgery in aortoiliac disease and results of surgical treatment. Circulation 1991;83 Suppl I:I42-52. 166. Bergan JJ. Variations of the Leriche syndrome. In: Bergan JJ, Yao JST, editors. Aortic surgery. Philadelphia: WB Saunders, 1989:149-59. 167. Stubbs DH, Kasulke RJ, Kapsch DN, et al. Populations with the Leriche syndrome. Surgery 1981;89:612-6. 168. Sharp WV, Donovan DL, Teague PC, et al. Arterial occlusive disease: a function of vessel bifurcation angle. Surgery 1982;91:680-5. 169. Palmaz JC, Carson SN, Hunter G, et al. Male hypoplastic infrarenal aorta and premature atherosclerosis. Surgery 1983;94:91-4. 170. Leriche R, MorelA. The syndrome of thrombotic obliteration of the aortic bifurcation. Ann Surg 1948;127:193-204. 171. DeBakey ME. Patterns of atherosclerosis and rates of progression. In: Paoletti R, Gotto AM Jr, editors. Atherosclerosis reviews. Vol 3. New York: Raven, 1978:1-56. 172. Schatz IJ, Stanley JC. Saddle embolus of the aorta. J A M A 1976;235:1262-3. 173. Busuttil RW, Keehn G, Milliken J, et al, Aortic saddle embolus: a twenty-year experience. Ann Surg 1983;197:698-706. 174. Webb KH, Jacocks MA. Acute aortic occlusion. Am J Surg 1988;155:405-7.

542

Curr Probl Cardiol, October 1997