Transesophageal Echocardiography in the Diagnosis of Diseases of the Thoracic Aorta

cardiology practice today Transesophageal Echocardiography in the Diagnosis of Diseases of the Thoracic Aorta* Part 1. Aortic Dissection, Aortic Intramural Hematoma, and Penetrating Atherosclerotic Ulcer of the Aorta Howard J. Willens, MD; and Kenneth M. Kessler, MD

(CHEST 1999; 116:1772–1779) Key words: acute aortic syndrome; aortic dissection; aortic intramural hematoma; penetrating aortic ulcer; thoracic aorta; transesophageal echocardiography Abbreviations: AIH 5 aortic intramural hematoma; PAU 5 penetrating atherosclerotic ulcer; TEE 5 transesophageal echocardiography; TTE 5 transthoracic echocardiography

echocardiography (TEE) has beT ransesophageal come a valuable modality for the diagnosis and management of diseases of the thoracic aorta. This procedure has also contributed greatly to our understanding of the pathogenesis of these disorders. When compared to other technologies that are used to evaluate the thoracic aorta, TEE has the unique advantages of portability and the ability to obtain high-resolution images of the normal and pathologic anatomy of the three layers of the aortic wall and the aortic lumen. In part one of this two-part article, the case-based review will focus on the use of TEE in the acute aortic syndrome (aortic dissection, aortic intramural hematoma [AIH], and penetrating atherosclerotic ulcer [PAU]) of the aorta. In part two, atherosclerotic disease of the aorta as a source of systemic emboli, and traumatic diseases of the aorta will be discussed. The two parts serve to update previous reviews in this continuously evolving field.1–5 *From the Department of Medicine, Memorial Regional Hospital (Dr. Willens), Hollywood, FL, and the University of Miami School of Medicine (Dr. Kessler), Miami, FL. Manuscript received April 23, 1999; revision accepted May 25, 1999. Correspondence to: Howard J. Willens, MD, 4925 Sheridan St, Suite 200, Hollywood, FL 33021 1772

Case Report 1 A 77-year-old hypertensive man presented with 2 h of sudden-onset severe tearing chest pain radiating to the interscapular region. On physical examination, his heart rate was 92 beats/min and regular, BP was 180/90 mm Hg bilaterally, and carotid and peripheral pulses were normal bilaterally. The lung fields were clear, and heart sounds were normal. A new grade III/VI early diastolic decrescendo aortic regurgitant murmur was heard. The mediastinum was widened on chest radiograph. A biplane TEE demonstrated a dilated ascending aorta with an intimal flap that extended from the sinotubular junction to the middescending aorta consistent with a communicating DeBakey type I aortic dissection. (The DeBakey classification of aortic dissection is as follows: type I, originating in the ascending aorta and extending into the aortic arch and beyond; type II, originating in and confined to the ascending aorta; and type III, originating in and usually limited to the descending aorta.) The intimal flap was smooth, highly echoreflective, and showed minimal mobility (Fig 1, top). An entry site was detected at the proximal origin of the dissection, and two additional communications were noted in the descending aorta. Flow was present in the false lumen. The coronary ostia (Fig 1, bottom) and left aortic arch branches were visualized and were not dissected or obstructed. The aortic valve was mildly sclerotic, and moderate aortic regurgitation caused by the significant aortic dilatation was noted. Regional and global left ventricular function were normal. There were no periaortic, pericardial, or pleural fluids. An IV b-adrenergic blocking agent and nitroprusside were immediately administered, and the patient was taken to the operating suite. The ascending aorta containing the entry site was replaced by a supracoronary interposition prosthetic graft, and the dissection layers at the distal anastomotic site of the graft were reapproximated to obliterate proximal entry into the residual false lumen. Aortic valve competence was restored by decompression of the false lumen and resuspension of the aortic valve. Intraoperative TEE documented closure of the false lumen at the distal anastomosis and aortic valve competence. Follow-up TEE has been performed at yearly intervals. Although the patient has a persistent communicating dissection of the aortic arch and descending aorta, Cardiology Practice Today

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Figure 1. Top: Biplane TEE in the longitudinal plane left ventricular outflow tract view demonstrating an aortic dissection beginning at the sinotubular junction with the intimal flap (curved arrow) separating the true and false lumens. Bottom: Biplane TEE in the horizontal plane of the aortic root demonstrating the intimal flap (curved arrow) separating the true and false lumens and a patent left main coronary artery. AO 5 aorta; AV 5 aortic valve; FL 5 false lumen; LA 5 left atrium; LM 5 left main coronary artery; MV 5 mitral valve.

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there have been no extension of the dissection or further dilatation of the aortic sinuses, aortic arch, or descending aorta.

Questions 1. The advantages of TEE compared to other diagnostic modalities include which of the following? A. High sensitivity. B. High specificity for diagnosing DeBakey type II aortic dissections (dissections originating in and not extending beyond the ascending aorta). C. Early diagnosis due to rapid acquisition of diagnostic real-time images. D. Portability that allows bedside examination with continuous monitoring.

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E. Relatively low cost. F. Comprehensive examination of the heart, the aorta, and its branches for complications of dissection relevant to clinical management. The accuracy of TEE for diagnosing type II aortic dissection and for distinguishing type II dissections from reverberation artifacts and aortic ectasia with thrombus can be improved by which of the following? A. Use of M-mode echocardiography to assess the motion of suspected intimal flaps relative to that of the posterior aortic wall and right pulmonary artery. B. Use of M-mode echocardiography to measure the distance of reverberation artifacts from their presumed source. C. Multiplane TEE. D. Observing the smoothness and echoreflectivity of the innermost echo of thickened aortic walls. E. All of the above. Complications of dissection that can be detected by TEE include which of the following? A. Dissection of the coronary ostia. B. Dissection of the left common carotid and left subclavian arteries. C. Dissection of the innominate artery. D. Aortic regurgitation. E. Pericardial and pleural effusion. F. Dissection of the mid and distal abdominal aorta and its branches. Intraoperative TEE during repair of an aortic dissection is useful to evaluate which of the following? A. Malperfusion of the cerebral vessels during retrograde cardiopulmonary bypass by the femoral artery. B. Aortic valve competence after resuspension of the valve. C. Renal function. D. Neurologic function. E. Closure of the false lumen at the distal anastomotic site of the prosthetic graft. Long-term complications of aortic dissection that may contribute to late mortality and can be detected by TEE include which of the following? A. Persistent flow in the false lumen. B. Recurrent dissection. C. Aortic dilatation. D. Pseudoaneurysm formation due to prosthetic graft dehiscence. E. Aortic regurgitation. F. All of the above. CHEST / 116 / 6 / DECEMBER, 1999

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Answers 1. 2. 3. 4. 5.

A, C, D, E, F E A, B, D, E A, B, E F

Aortic Dissection Although not common, aortic dissection is a catastrophic illness with an extremely high mortality rate during the first 48 h of presentation. Survival, however, can be improved by early diagnosis and prompt initiation of aggressive medical and/or surgical therapy.6 In addition to the previous “gold standard” of aortography for the diagnosis of dissection, several new technologies including transthoracic echocardiography (TTE), TEE, CT, and MRI have roles in the diagnosis of dissection. Each of these diagnostic modalities has certain advantages and limitations, and no individual technique is superior in every clinical scenario. Nevertheless, accuracy, speed, relatively low cost, portability, and the capacity to comprehensively evaluate the heart, the aorta, and its branches for complications of dissection have made TEE an attractive first choice to diagnose dissection.7,8 Several criteria, some derived from the TTE literature, have been used for the diagnosis of aortic dissection by TEE.9 –11 The pathognomonic echocardiographic appearance of dissection is an undulating linear density (intimal flap) within the aortic lumen separating a true and false channel which have different Doppler color flow patterns. However, these criteria are restrictive, and experience has shown that broader criteria are needed. Thus, aortic dissection should be suspected whenever the normal appearance of the aortic wall consisting of a single dominant echo is replaced by two separate echoes, one presumably representing the intima plus the inner media, and the second representing the outer media and adventitia. Because of the acuity of the medical situation, diagnostic accuracy is of prime importance when selecting an initial diagnostic procedure to evaluate a patient with suspected aortic dissection. In addition to several small series, at least seven studies in the English literature involving $ 50 patients, including 2 with . 100 patients, have reported the sensitivity and specificity of monoplane and biplane TEE for the diagnosis of aortic dissection.11–17 In these studies, sensitivity has consistently been high, ranging from 97 to 100%, and specificity has ranged from 77 to 100%. In four of these studies, the diagnostic 1774

accuracy of TEE was compared to aortography, CT, and aortography plus CT.11,13,15,16 In all four studies, TEE was superior. In a large series of 110 patients with suspected aortic dissection, TEE, TTE, CT, and MRI were compared (see Table 1).14 While TEE performed well with a 98% sensitivity, the accuracy of MRI was outstanding. Based on these results, these investigators have suggested that MRI should be the initial diagnostic procedure for aortic dissection in stable patients, while reserving TEE for unstable patients. The surprisingly low range of specificities of TEE for the diagnosis of dissection can be attributed to reports from one group of investigators who found evaluation of the ascending aorta to be particularly problematic.14 If the results from this center are excluded, the range of specificities reported for TEE improves to 97 to 100%. Despite the impressive sensitivity and specificity of TEE, several other investigators have also expressed reservations about the accuracy of monoplane and biplane TEE for the diagnosis of localized DeBakey type II aortic dissection (dissections originating in and confined to the ascending aorta).11,16 Reverberation artifacts are not uncommon in dilated ascending aortas and can lead to false-positive diagnoses of type II aortic dissection.18 Conversely, false-negatives may occur when small dissections limited to the upper ascending aorta or proximal aortic arch are not visualized because of interference from the air-filled trachea (which creates a TEE blind spot), and when localized dissections of the ascending aorta with thrombosed false lumens and immobile intimal flaps are misdiagnosed as ectatic aortas containing intraluminal thrombus or atherosclerotic plaque.19,20 Recently, the diagnostic accuracy of multiplane TEE for the diagnosis of aortic dissection was assessed in two studies. In one study of 112 patients, the sensitivity of multiplane TEE was 98% and the specificity was 95%.21 In the second study involving 49 patients, sensitivity was 100% and specificity was 94%.22 Although it was hoped that the multiplane transducer would overcome the difficulties encountered with monoplane and biplane instruments in the evaluation of the ascending aorta, both investigators also encountered and commented on diagnostic problems in the ascending aorta. Other tacts have been investigated to improve the

Table 1—Sensitivities and Specificities of Four Imaging Modalities for Diagnosing Aortic Dissection Factor

TTE

TEE

CT

MRI

Sensitivity, % Specificity, %

59 83

98 77

94 87

98 98

Cardiology Practice Today

accuracy of TEE in the evaluation of the ascending aorta. Patients with suspected dissection of the ascending aorta (n 5 132) were assessed using TEEderived M-mode echocardiography to help identify reverberation artifacts originating from the posterior wall of the aorta or right pulmonary artery, and to differentiate these artifacts from dissection.17 The M-mode features of reverberation artifacts that facilitated their recognition were as follows: (1) location at a distance from their source that was predicted by ultrasound physical principles; and (2) motion that was parallel to the suspected source. The use of M-mode echocardiography significantly improved the sensitivity and specificity of TEE to 97% and 100% respectively, suggesting that M-mode echocardiography should be performed in ambiguous cases of DeBakey type II aortic dissection. Alternatively, other investigators have proposed a refinement in the diagnostic criteria of aortic dissection by TEE to improve accuracy. They found that in patients with thickening of the aortic walls, an inner echo that was smooth and highly echoreflective was characteristic of an intimal flap and helped distinguish dissection from aneurysms containing intraluminal thrombus or plaque.19 In addition to accuracy, other factors to consider when selecting an initial diagnostic modality to evaluate patients with suspected aortic dissection are speed, cost, portability, safety, and the ability to provide information that is comprehensive enough to guide therapy.8 TEE can be used to diagnose dissection faster than other techniques, often being completed in 15 to 20 min.23 The economic costs of TEE compare favorably with other modalities. Although semi-invasive, TEE is still one of the safest methods for evaluating dissection. While deaths have occurred in patients with dissection during TEE, it is not clear whether these deaths were due to the expected natural history of the dissection, or whether the adverse hemodynamic effects of TEE contributed to the aortic rupture.24 In comparison to TEE, both aortography and CT require the use of IV contrast with potential allergic, renal, and hemodynamic complications. Although MRI is noninvasive and does not require contrast, MRI (especially with the addition of cine MRI to evaluate aortic regurgitation) takes substantially longer to perform than TEE. Furthermore, while TEE can be carried out at the bedside with continuous monitoring, the performance of MRI requires the potentially unstable patient with dissection to be isolated with limited monitoring and access. In addition to confirming the diagnosis of dissection, other information that is useful for assessing prognosis and selecting the appropriate medical and/or surgical therapy include classification of the

dissection as proximal (DeBakey type I and II) vs distal (DeBakey type III) and communicating vs noncommunicating. The following are other relevant factors that influence the current therapeutic approach and modern surgical techniques in the treatment of acute aortic dissection: (1) the extent of the dissection; (2) the presence or absence of thrombosis in the false lumen; (3) the location of entry and reentry sites; (4) the patency and involvement of aortic branches including the coronary ostia in the dissection process; (5) the global and regional function of the left ventricle indicative of myocardial ischemia; (6) the etiology and severity of aortic regurgitation; and (7) the presence of extravasated blood in the mediastinal, pleural, or pericardial spaces due to penetration or rupture. These modern surgical techniques may include the following: (1) the closure of entry and exit sites; (2) the repair of branch vessels; (3) coronary artery bypass surgery; and (4) the replacement or resuspension of the aortic valve. Although TEE does not visualize the innominate artery or most of the abdominal aorta, TEE has the potential to provide accurate information about most of the other anatomic features of an aortic dissection that are important for surgical decision making. This suggests that select patients with dissections may undergo surgery after being evaluated only by TEE.8,25 Two studies with 45 and 48 patients, respectively, have demonstrated favorable outcomes in patients with dissection whose management was based solely on the results of TEE without the performance of other diagnostic tests.26 –27 Finally, TEE is the only diagnostic modality that can be used in the operating room during aortic dissection repair to do the following: (1) monitor retrograde flow in the thoracic aorta during cardiopulmonary bypass by the femoral artery, facilitating the detection and management of visceral and cerebral malperfusion; and (2) evaluate the results of attempted aortic valve repair by valve resuspension (and the need for further surgical interventions including aortic valve replacement) in patients with aortic dissection complicated by significant aortic regurgitation.28,29 A randomized, prospective trial comparing outcomes using the different modalities as the initial diagnostic procedure in aortic dissection has not been carried out. In the absence of such data, decision analysis is often used to compare management options in various disorders. Sarasin and coworkers30 performed a decision analysis comparing various diagnostic methods and strategies in acute aortic dissection. They concluded that the use of TEE as the initial diagnostic procedure yielded the best outcomes. However, they also caution that the threshold for performing a second diagnostic test should be low in patients with a relatively high CHEST / 116 / 6 / DECEMBER, 1999

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clinical probability of dissection if the results of TEE (or any other initially used diagnostic test) are negative or equivocal. In the years following their initial presentation, morbidity and mortality remain high for patients with surgically repaired (predominantly proximal) or medically managed (predominantly distal) aortic dissections. The late complications of dissection, some of which require reoperation, include aortic rupture, recurrent dissection, fluid extravasation into the mediastinum or pericardium, localized or diffuse aortic dilatation, aortic graft dehiscence with pseudoaneurysm formation, and aortic regurgitation. Well-tolerated and accurate methods of monitoring survivors of dissection are needed to detect these late complications and to identify patients requiring medical and/or surgical treatment. TEE has been reported to be well tolerated and to accurately detect such long term complications, including recurrent dissection, progressive aortic dilatation, pseudoaneurysm formation, mediastinal leaks (which appear as periaortic echo-free spaces), and aortic regurgitation.31–35 TEE has also demonstrated that flow persists in the false lumen in the majority of patients with repaired type I dissections and conservatively managed type III dissections.31 These patients with persistent flow in the false lumen have a worse prognosis than patients with complete thrombosis and spontaneous healing of the false lumen.31 Whether this difference in outcome will warrant more extensive surgery using intraoperative TEE guidance, with attempts to close all communications and obliterate the false lumen to promote thrombosis and healing of the false lumen, awaits confirmation by further studies. In our patient, TEE was the fastest and most accurate modality that was available. Not only was the dissection promptly detected, but its extent and the associated aortic regurgitation were defined, allowing a decision for surgery to be promptly made. Intraoperative TEE confirmed the adequacy of the aortic valve repair, helping to avoid an aortic valve replacement. Subsequently, TEE has confirmed stability in follow-up. 6. TEE can always differentiate AIH from noncommunicating dissection with complete thrombosis of the false lumen. A. True. B. False. 7. AIH may be complicated by which of the following? A. Progression to typical aortic dissection. B. Progressive aortic dilatation. C. Rupture of the aorta. D. Aortic regurgitation. E. Pericardial and pleural effusion. F. All of the above. 1776

Answers 6. B 7. F

AIH Since the introduction of modern diagnostic techniques that provide high-resolution images of the thoracic aorta, AIH and PAU have been increasingly recognized as causes of acute aortic pathology in addition to classic aortic dissection. Because of their common clinical manifestations, these three disorders have been collectively called “the acute aortic syndrome.”36 Although the pathogenesis and echocardiographic appearance of these three disorders differ, there is considerable overlap in their clinical presentation, natural history, and management. In particular, all three causes of the acute aortic syndrome can rapidly develop life-threatening complications. Therefore, the same urgent clinical approach that is used in patients with aortic dissection is warranted in patients with AIH and PAU, and the role of TEE in the diagnosis of these disorders is important to understand. Some uncertainty exists regarding the definition of AIH, particularly with respect to differentiating AIH from noncommunicating aortic dissection with a thrombosed false lumen. A pathologic definition of AIH is a localized separation of the layers of the aortic wall by partially or totally clotted blood in the absence of an intimal tear, presumably caused by rupture of the vasa vasorum in the media. Based on this definition, differentiation of a thrombosed noncommunicating dissection from AIH depends on the following: (1) the detection of an intimal tear or entry site (which may be difficult to identify at autopsy and difficult or impossible to identify antemortem with current imaging techniques); and (2) for some investigators, the longitudinal extension of the medial separation. Therefore, it is likely that some of the series of patients with AIH include patients with noncommunicating aortic dissection with a thrombosed false channel. In addition to difficulties with the definition of AIH, the studies that have attempted to define the role of TEE in the diagnosis of AIH have also been limited by small sample size. The four largest series have had between 19 and 27 patients.37– 40 These studies have proposed that the echocardiographic criteria for AIH are a $ 7-mm crescentic or circular thickening of the aortic wall extending 1 to 20 cm longitudinally along the thoracic aorta, with no evidence of Doppler flow in the thickened aortic wall, and the absence of an intimal laceration or flap. Cardiology Practice Today

Complementary but less-diagnostic echocardiographic features include a thrombus-like consistency and layered appearance with echolucent areas of the widened aortic wall and central displacement of intimal calcifications.37– 40 In the study of 27 patients with AIH, TEE had a 100% sensitivity for the diagnosis for AIH and a specificity of 91% using clinical course, CT, or MRI as the “gold-standard.”39 In a smaller series of 10 patients, the sensitivity of TEE was 90% and the specificity was 99%.21 In the two series that also evaluated angiography for the diagnosis of AIH, TEE outperformed angiography.37,38 These results were not unexpected because the angiographic diagnosis of aortic dissection depends on opacification of the false lumen through communications which by definition are absent in AIH. The observations made by TEE in these studies have contributed to our understanding of the natural history and pathogenesis of AIH and aortic dissection. In three of the four studies, the clinical course of AIH was remarkably similar to that of aortic dissection and was characterized by a high incidence of aortic dilatation due to expansion of the false lumen, pleural and pericardial effusions, aortic regurgitation, aortic rupture, and progression to classic aortic dissection.37–39 In one study, 5 of 15 patients (33%) progressed to typical dissection and 4 of 15 patients (27%) developed rupture.37 In another series, 4 of 11 patients (27%) with AIH of the descending aorta experienced aortic rupture.39 Another similarity between AIH and aortic dissection is the relationship of their prognosis to their anatomic location in the aorta. As in the case of aortic dissection, AIH involving the ascending aorta has a worse prognosis than AIH limited to the descending aorta. Surgical intervention appears to be indicated for AIH involving the ascending aorta, while AIH limited to the descending aorta can be managed with medical therapy and close surveillance.36 Another interesting observation in these TEE studies has been the discrepancy between the incidence of AIH detected by TEE among patients presenting with acute aortic syndrome and the incidence of “dissection” without intimal entry-site tear (presumably due to AIH) in autopsy series. In TEE studies, the incidence of AIH is between 17% and 27%, which is considerably higher than the 5 to 13% incidence of aortic “dissection” without entry-site tear reported in autopsy studies. A possible interpretation of this data is that some patients who present initially with AIH develop an intimal tear and progress to classic aortic dissection prior to death, accounting for the lower incidence of AIH in autopsy series. Recent documentation by TEE and other imaging modalities of some cases of AIH progressing

to classic aortic dissection antemortem, has lead to speculation that AIH is a common intermediate step in the development of aortic dissection. This has renewed interest in the controversy regarding the etiology of aortic dissection and has lent support to the theory that rupture of the vasa vasorum in the subadventitial media causing intramural hemorrhage is a more important cause of aortic dissection than currently suspected.

PAU of the Aorta PAU of the aorta occurs when an ulceration of an atherosclerotic plaque erodes through the internal elastic lamina into the media. This process may progress to life-threatening clinical sequelae such as saccular, fusiform, or false aneurysms of the thoracic aorta, AIH, typical dissection, or rupture. Because PAU of the aorta generally affects patients with advanced atherosclerosis of the thoracic aorta, patients with this disorder are typically older and have more cardiovascular risk factors and evidence of diffuse atherosclerosis than patients with aortic dissection or AIH.41 In contrast to aortic dissection and AIH, which tend to be widely distributed within all segments of the thoracic aorta, PAUs are predominantly located in the descending aorta where atherosclerosis tends to be more severe. The natural history and management of PAU of the aorta, which often effects patients with high surgical risk because of comorbidities, has not been defined.42 Although there are differences in the pathogenesis, location, clinical profile, and echocardiographic features of PAU of the aorta and the other two causes of the acute aortic syndrome, there are striking similarities in their initial clinical presentation and, in some cases, in the clinical course. Patients with all three disorders may present with acute excruciating back pain associated with pleural effusions and may rapidly deteriorate due to impending aortic rupture. Because of these similarities, many patients with PAU inevitably undergo TEE as an initial diagnostic procedure for suspected aortic dissection. TEE has been less well studied than CT and MRI for the diagnosis of PAU of the aorta, and the optimal diagnostic modality is currently unknown. Nevertheless, it is important to establish and become familiar with the diagnostic criteria of TEE for PAU of the aorta, so that those patients with PAUs who are initially screened for dissection by TEE will be recognized and receive the appropriate diagnosis. The TEE experience with PAU of the aorta consists of anectodal reports43 and a series of 12 patients.44 In this series, 12 of 194 patients with CHEST / 116 / 6 / DECEMBER, 1999

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suspected aortic dissection had a PAU, 18 had aortic aneurysms, and 93 had dissections. A PAU could be identified by TEE in 10 of 12 patients. However, at least four cases were diagnosed retrospectively, and it is unclear how many of the other cases were diagnosed prospectively. The echocardiographic features of a PAU were a crater-like out pouching of the aorta with jagged edges associated with complex atheromatous plaque. Associated intramural hemorrhage was characterized by aortic wall thickening and the inward displacement of intimal calcifications. Associated dissections were characterized by a location distant from the typical origin of type III dissection near the left subclavian artery and a thick calcified minimally mobile intimal flap. The observed association of PAU with aortic dissection and AIH supports PAU as a third precursor of aortic dissection, in addition to primary intimal tear and rupture of the subadventitial vasa vasorum. With greater clinical awareness of PAU as part of the differential diagnosis of aortic dissection, and increasing experience leading to refinement of the TEE diagnostic criteria for PAU of the aorta, TEE can be expected to have an increasingly important role in the management of PAU of the aorta, as it has with dissection and AIH. Part two of this review will discuss the evolving role of TEE in the diagnosis and management of atherosclerotic and traumatic diseases of the aorta. ACKNOWLEDGMENT: The authors gratefully acknowledge the assistance of Janet Fossum, William Kafitz, Billie Grover, Michael Rosenbloom, MD, and Michelle J. Enriquez in the preparation of this manuscript.

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