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* From the Department of Medicine, Memorial Regional Hospital, Hollywood, FL, and the University of Miami School of Medicine, Miami, FL.
Correspondence to: Howard J. Willens, MD, 4925 Sheridan St, Suite 200, Hollywood, FL 33021
Abstract
Transesophageal echocardiography (TEE) has provided an accurate new window for the evaluation of diseases of the thoracic aorta. Experience with TEE has led to an increased recognition of atherosclerosis of the thoracic aorta as a source of cerebral and systemic embolism. Certain features of aortic plaque morphology detected by TEE may prove to have prognostic and therapeutic significance. The intraoperative assessment of thoracic aortic atherosclerosis by TEE may guide modifications in surgical techniques and aortic manipulations that reduce the incidence of perioperative neurologic complications. TEE has also become a valuable tool for the diagnostic evaluation of patients with blunt chest trauma. The precise role of TEE in the management of these disorders is currently under investigation.
Key Words: atherosclerosis of the thoracic aorta • blunt chest trauma • cerebrovascular accident • intra-aortic debris • systemic embolism • thoracic aorta • transesophageal echocardiography • traumatic aortic injury
In part one of this two-part series, the diagnostic value of the high-resolution images of the thoracic aorta now available using transesophageal echocardiography (TEE) was explored in patients presenting with acute aortic syndrome.1 In this second part of the series, a case-based discussion reviews the use of TEE in the diagnosis and management of traumatic and atherosclerotic diseases of the aorta.
Case History
A 69-year-old right-handed, hypertensive man with a history of hypercholesterolemia and a 35-pack-year history of smoking was admitted to the hospital with unstable angina. Seven years earlier, he had been hospitalized because of the sudden onset of right hemiplegia and aphasia. At that time, his symptoms improved in 4 days, but mild weakness of his right hand persisted. MRI of the brain demonstrated an ischemic left hemispheric infarction. The results of transthoracic echocardiography were normal. A carotid duplex study showed only 30% stenosis of the right carotid bulb. TEE demonstrated a large, irregular, protruding atheroma of the distal aortic arch containing mobile components and echolucent areas. A lipid profile revealed the following: total cholesterol, 218 mg/dL; low-density lipoprotein cholesterol, 149 mg/dL; high-density lipoprotein cholesterol, 32 mg/dL; and triglyceride concentration, 186 mg/dL. A regimen consisting of the daily administration of aspirin, a cholesterol-lowering diet, and a statin was begun. The patient did well until his current hospital admission for new-onset angina, which occurred with minimal exertion, was at times unprovoked, and was of 5 days duration. His pain was controlled with the administration of heparin and a nonselective ß-adrenergic antagonist. On the third hospital day, coronary angiography demonstrated severe proximal three-vessel coronary artery disease. Carotid duplex imaging demonstrated 40% stenosis in the right carotid bulb and nonocclusive intraluminal irregular plaque in the left internal carotid artery. During triple-vessel coronary artery bypass surgery, intraoperative TEE showed a large, sessile, irregular, hypoechoic plaque in the mid and distal aortic arch (Fig 1 ). To avoid this area of significant aortic atherosclerosis, the surgeon placed the arterial cannula distal to the left subclavian artery. The patient experienced an uncomplicated intraoperative and postoperative course.
|
1. Atherosclerosis of the thoracic aorta is associated with which of the following? A. Coronary artery disease B. Peripheral and cerebral emboli C. Blue toe syndrome D. Postoperative stroke after coronary artery bypass surgery E. Catheter-related embolism after cardiac catheterization and intra-aortic balloon pump (IABP) insertion F. Advanced age G. All of the above
2. The features of aortic plaque detected by TEE that predict
a high risk of embolization include which of the
following? A. Mobile components B. Protrusion into the aortic
lumen 
5 mm C. Calcifications D. Irregular surface
indicative of ulcerations E. Hypoechoic plaque
Answers
Atherosclerosis of the Thoracic Aorta
Evidence Linking Atherosclerosis of the Thoracic Aorta and Systemic
Embolism
The possibility that systemic emboli originate from
atherosclerotic plaques in the thoracic aorta has long been suspected
on the basis of postmortem studies and clinical
observations.2
3
During the past decade, this hypothesis
has been supported by TEE demonstration of severe atherosclerosis in
the thoracic aortas of patients with otherwise unexplained
cerebrovascular accidents and/or peripheral emboli. Karalis et
al4
introduced the term intra-aortic atherosclerotic
debris (IAD) to describe the complicated atherosclerotic plaques
detected by TEE, which protrude 5 mm into the lumen of the thoracic
aorta. In addition to several smaller studies, seven observational
studies involving 26 patients with significant atherosclerosis of
the thoracic aorta have reported a strong association between complex
atherosclerotic disease of the thoracic aorta detected by TEE and
systemic embolism.4
5
6
7
8
9
10
In four of these studies, the
incidence of IAD detected by TEE in patients undergoing the procedure
because of a history of systemic vascular events was compared with the
incidence in patients undergoing TEE for indications other than
suspected embolism. The incidence of IAD was consistently higher in
those patients with suspected peripheral and cerebral embolism compared
with that of the control group (Table 1
). Conversely, Karalis et al4
reported a 31% incidence of
systemic embolization in 36 patients with IAD compared with a 4%
incidence in patients without IAD.
|
4 mm thickness, compared with a 3% incidence in patients with
plaques 
1 mm in thickness. For other vascular events
(eg, retinal artery occlusion, myocardial infarction, and
peripheral emboli), the incidence was 26% in the group with 4 mm
plaques and 6% in the group with 1 mm
plaques.12 Although the strong association between IAD and systemic emboli in these studies suggests that atherosclerosis of the thoracic aorta is a source of systemic emboli, several authors caution against concluding that a causal relationship exists. The methodologic problems they point out include small sample size, referral bias in retrospective studies, inherent difficulty of accurately classifying ischemic vascular events as embolic or atherothrombotic, and the frequent coexistence of other sources of emboli and/or cardiovascular risk factors for ischemic vascular events in patients with IAD. For instance, several investigators have reported an association between IAD and the presence and severity of coexisting carotid artery disease, an established cause of arterio-arterial cerebral embolic disease.8 9 13 In addition, in the study presented by Di Tullio et al8 , although the incidence of IAD in stroke patients was significantly higher than that of control subjects, the incidence of IAD was unexpectedly similar in patients with cryptogenic stroke and stroke of known cause. Thus, an alternative explanation for the observed association between IAD and systemic embolization is that IAD is merely a marker for diffuse atherosclerosis that predisposes patients to systemic embolism by mechanisms other than IAD, such as carotid disease, coronary artery disease with intracardiac thrombus, and atrial fibrillation. Despite these reservations, the cumulative evidence supports the role of atherosclerosis of the thoracic aorta as an underrecognized source of systemic embolism and a possible cause of at least some of the approximately 40% of cerebrovascular accidents for which cause cannot be determined.
TEE studies have provided some insight into estimating the risk of systemic embolization in patients with thoracic aortic atherosclerosis based on plaque morphology. Increased plaque thickness, surface ulcerations, and mobility as assessed by TEE are associated with an increased risk of systemic embolization compared with less complex plaques.4 7 9 14 15 16 Karalis et al4 reported a history of systemic embolism in 8 of 11 patients (73%) who had plaque containing mobile components, compared with 3 of 25 patients (12%) who had nonmobile mural plaque. Stone et al15 detected plaque ulcerations by using TEE in 9 of 23 patients (39%) who had suffered cryptogenic strokes compared with 2 of 26 patients (7%) who had suffered strokes of known causes and 4 of 47 control subjects (8%). Cohen et al16 noted that increased plaque thickness, ulcerations, and the absence of calcium were associated with an increased risk of future vascular events in patients with previous ischemic stroke. The highest risk for recurrence was noted in patients with thick, hypoechoic, noncalcified plaques imaged by TEE in the aortic arch. Both Stone et al15 and Cohen et al16 discussed the similarities between the morphologic features of high-risk aortic plaque that they had observed and the vulnerable lipid-rich plaques in the coronary arteries thought to be the cause of the unstable coronary syndromes.
Role and Cost-effectiveness of TEE in the Management of Systemic
Embolism Caused by Thoracic Aortic Atherosclerosis
The recognition of IAD by TEE in patients with systemic embolism
(either with or without other potential sources of systemic embolism)
presents the clinician with a therapeutic dilemma.17
18
19
Current treatment options include surgery, thrombolysis,
anticoagulation, antiplatelet agents and lipid-lowering
agents.20
21
22
23
24
25
26
Selection of an optimal treatment strategy
in a given clinical scenario is challenging. Thrombectomy, aortic
endarterectomy with plaque debridement, and replacement of the diseased
section of the aorta have been performed in small numbers of patients
with favorable outcomes.20
21
22
However, because of the
inherent risks of surgical intervention and the advanced age and
multiple comorbidities of many patients with IAD who might be
considered for these procedures, surgery is currently reserved for
select patients with recurrent life-threatening or disabling embolic
episodes who are good surgical candidates.
The use of anticoagulants in patients with systemic emboli and IAD identified by TEE has not been extensively studied. Mixed outcomes have been reported for the small numbers of patients who have been studied. Several small nonrandomized trials have recently reported favorable results with the use of anticoagulation.24 25 26 In a nonrandomized study of 31 patients with mobile plaques detected by TEE and a history of systemic emboli, anticoagulation significantly reduced the incidence of recurrent vascular events.24 However, there were only five events in the group that did not receive anticoagulation and statistical significance was achieved only by including myocardial infarction as a vascular event. Because anticoagulation would be expected to decrease the incidence of recurrent myocardial infarction independent of its effects on aortic plaques, the results of this study are difficult to interpret. In a substudy of the Stroke Prevention in Atrial Fibrillation III trial, the relationship of several TEE parameters (including aortic plaque) to, and the effects of two different anticoagulation regimens on, the incidence of subsequent strokes in patients with nonvalvular atrial fibrillation were studied. A total of 136 patients with complex aortic plaque were identified. The stroke-rate per year was 15.8% for patients receiving a combination of low-intensity warfarin plus aspirin, compared with only 4% for patients receiving full anticoagulation.25 However, because of the design of this study, which focuses on atrial fibrillation, the reduction in stroke rate could not be definitively attributed to a beneficial effect of anticoagulation on aortic plaque. In another nonrandomized study, 14 patients with systemic emboli and mobile atheromatous plaques imaged by TEE were anticoagulated. No recurrent systemic embolic events were noted during a 6- to 30-month follow-up period.26 Laperche et al22 reported on 13 relatively young patients with a history of systemic embolism who had a variant of IAD consisting of mobile thrombi in the aortic arch in the absence of severe, diffuse aortic atherosclerotic disease. In the 12 patients receiving long-term anticoagulation therapy, no recurrent systemic emboli were observed during 18 months of follow-up.22
In contrast to the uniformly favorable results reported in these small nonrandomized series, other investigators have reported an inconsistent response to anticoagulation and even a possible exacerbation of embolization by anticoagulation in patients with IAD.4 11 27 28 29 30 Karalis et al4 observed systemic emboli in two patients with IAD who were well anticoagulated because of prosthetic valves. In the previously discussed prospective trial of Tunick et al,11 7 of 21 patients with protruding atheroma who were receiving anticoagulation experienced a subsequent vascular event. Hilton et al28 observed microembolization to the cerebral arteries, kidneys, and lower extremities (blue toe syndrome) in 4 of 38 patients with protruding plaques detected by TEE who had received anticoagulants. Therefore, although anticoagulation seems to be safe in the vast majority of patients with IAD and seems to prevent recurrent emboli in most, some patients do not respond to anticoagulation and, even more uncommonly, some experience a life-threatening exacerbation of symptoms because of cholesterol embolization.
The management of patients with IAD is further complicated by the potential for IAD to cause several different embolic syndromes that have different pathogenesis, clinical manifestations, and, conceivably, response to various therapies. These syndromes are microembolization of cholesterol crystals or atheromatous debris from disrupted plaques and micro- or macroembolization of platelet-fibrin thrombi that have formed on the denuded surfaces of plaques.17 An individual patient may experience more than one morphologic type of embolus. Although anticoagulation might be expected to benefit patients with thromboembolism, it may also conceivably promote cholesterol or atheromatous microembolization by removing or preventing the formation of the protective layer of thrombus coating eroded plaques. Recently, the characterization of plaque morphology by TEE has been validated in a study that correlated TEE findings with the histology of specimens removed at the time of aortic surgery.31 TEE accurately distinguished complicated plaques from less-advanced atherosclerosis by measuring the thickness of the intima-media complex and identifying ulcerations and calcifications. Intraluminal thrombi were identified as homogeneous masses with a smooth surface and low echodensity. Mobile lesions removed at the time of surgery were thrombi, but the numbers studied were too small to reach definite universal conclusions about all mobile components associated with plaques. IAD seem to represent a spectrum of plaque morphologies with varying amounts of thrombus, fibrous tissue, lipid, and calcium in an individual atherosclerotic lesion. Whether different morphologies are more prone to one of the previously described embolic syndromes compared with the others and whether characterization of these different plaque morphologies by TEE will allow tailoring of therapy and the prediction of patients who are predisposed to cholesterol or atheromatous microembolization after anticoagulation awaits further study.
To complicate issues further, Montgomery et al32 studied the natural history of thoracic aortic atherosclerosis by performing a follow-up TEE in patients with aortic plaque. They reported that individual lesion morphology is dynamic over time. Some plaques with mobile components at the time of initial study demonstrated resolution of the mobile components at the time of follow-up (presumably because of vascular healing). Conversely, some plaques had developed new mobile components at the time of the follow-up study (presumably because of intercurrent plaque rupture).32 The diagnostic and therapeutic implications of this new finding need further study.
The role of TEE in the evaluation of patients with cerebral and peripheral arterial emboli has not been defined. Although TEE is clearly superior to clinical evaluation and transthoracic echocardiography for the detection of potential cardiovascular sources of systemic emboli such as IAD, left atrial thrombus, left atrial spontaneous echo contrast, patent foramen ovale, and aneurysm of the interatrial septum, some investigators question the clinical relevance of these TEE-specific findings.33 In particular, left atrial thrombus and spontaneous echo contrast are found almost exclusively in patients with a history of atrial fibrillation in whom anticoagulation is recommended independent of the TEE findings. Also, the benefits of therapeutic interventions to prevent recurrent events have not been established for the other disorders. Warner and Momah34 have suggested the selective use of TEE in stroke patients who have clinical evidence of heart disease and are either in normal sinus rhythm at any age or have a history of atrial fibrillation but are < 60 years of age. They estimated that this strategy would have reduced the number of TEE examinations performed at their institution in patients with cerebral ischemia by 75% without resulting in the undertreatment of any patients who would have benefited from anticoagulation.34 McNamara et al35 used a Markov decision analysis model to evaluate the cost-effectiveness of nine different diagnostic strategies, consisting of various combinations and sequences of clinical history, transthoracic echocardiography, and TEE in the management of patients with first-time stroke. They found that both the selective use of TEE in patients with a cardiac history and the universal use of TEE in all patients were highly cost-effective ($9,000 per quality-adjusted year-life and $13,000 per quality-adjusted year-life, respectively) compared with nonintervention. They concluded that TEE should be considered in all new stroke patients.35 In these cost-effectiveness studies, no additional benefit was assumed for the detection or treatment of IAD with any therapy other than aspirin, which would be strongly considered by most clinicians in these scenarios empirically independent of the TEE findings. As the role of TEE in the diagnosis and management of IAD and systemic embolism evolves, more favorable cost/benefit ratios for TEE in these patients can be expected.
Intraoperative TEE to Prevent Perioperative Stroke
Postoperative stroke and cognitive dysfunction remain major causes
of poor outcomes after cardiac surgery, especially in the
elderly.36
The relative contributions of atherothrombotic
emboli, gaseous microemboli, and hypoperfusion to these neurologic
complications are currently unknown. Even before the introduction of
TEE, atherosclerosis of the thoracic aorta was recognized as an
important risk factor for perioperative stroke.36
37
Although the exact pathophysiology is unknown, a plausible mechanism by
which aortic atherosclerosis could cause stroke is the dislodgment and
embolization of thrombus or atherosclerotic debris during the
manipulation of the ascending aorta and aortic arch in surgery.
Territorial strokes due to major cerebral artery occlusion by large
emboli and smaller strokes or cognitive deficits without evidence of
infarction on neuroimaging studies due to occlusion of more distal
vessels by small emboli could conceivably be caused by this mechanism.
TEE has confirmed the association of aortic atherosclerosis and
perioperative stroke and has also provided an opportunity to reduce the
incidence of stroke by intraoperatively identifying patients who are at
high risk and who might benefit from modification of surgical
techniques.38
39
In a study of 130 patients undergoing
cardiac surgery and intraoperative TEE, Katz et al38
identified 23 patients with aortic arch atheromas protruding 5 mm,
including 12 with mobile components. Although the total number of
strokes in this study was small (n = 5), the incidence of
perioperative stroke was significantly higher in these patients than in
the patients with normal aortas or lesser degrees of aortic
atherosclerosis. There was also a trend toward fewer strokes occurring
in the 10 patients who had modifications of the operative technique,
including changing the site of arterial cannulation or debridement of
the aortic arch. However, small sample size contributed to a failure to
achieve statistical significance.38
In another study of 84
patients undergoing coronary artery bypass surgery and TEE, five
perioperative strokes occurred. Higher grades of aortic atherosclerosis
and plaque mobility in the aortic arch were significantly associated
with perioperative stroke.39
The role of epiaortic ultrasonography (imaging of the ascending aorta by direct application of a sterile sheathed transducer) in the intraoperative evaluation of aortic atherosclerosis and its value in guiding the modification of surgical techniques to reduce stroke has been studied.40 Wareing et al,40 using epiaortic ultrasonography, identified 68 patients in a group of 500 with significant atherosclerosis of the ascending aorta. Based on these observations, the surgical technique was modified by either changing the sites of aortic cross-clamping and cannulation or by replacing the ascending aorta. No strokes occurred in this cohort.40 Several investigators have reported that epiaortic ultrasonography is more accurate than TEE for detecting and characterizing the severity of plaque in the ascending aorta, where most surgical manipulation occurs.41 42 However, the disadvantages of epiaortic ultrasonography are the need to enter the surgical field, causing a delay in the operation and possible contamination, and suboptimal imaging of the aortic arch.43 The latter is important because, although the ascending aorta is the site of cross-clamping and arterial cannulation, flow from the arterial cannula may cause atheromatous debris in the aortic arch to loosen and embolize via a sandblast effect. In patients with significant atherosclerotic disease of the ascending aorta, TEE will usually detect atherosclerotic plaques in the aortic arch and descending aorta, reflecting the tendency for atherosclerosis to develop earlier in these segments of the aorta.24 39 43 44 Konstadt et al43 reported that the detection of atherosclerosis in any of the three segments of the thoracic aorta by TEE had a 100% sensitivity for the presence of significant atherosclerosis in the ascending aorta. The specificity of this finding was only 60%.43 Hartman et al45 reported a strong association between the grade of atherosclerotic plaque detected in the descending aorta (where TEE consistently provides high-resolution images) and the incidence of intraoperative stroke. The incidence of intraoperative stroke was 46% in those patients who had mobile plaques in the descending aorta detected by TEE.45 Hartman et al45 suggest that the optimal management of patients undergoing coronary artery bypass surgery is the initial screening of the entire thoracic aorta by TEE, especially in patients with multiple risk factors for aortic atherosclerosis. Those patients in whom atherosclerosis is detected by TEE in any segment of the aorta should have a thorough examination of the ascending aorta with epiaortic ultrasonography to help guide the surgeon.45
Other Uses of TEE in the Evaluation of Thoracic Aortic
Atherosclerosis
Several other clinical and research applications of TEE in the
assessment of thoracic aortic atherosclerosis have been studied.
Several groups have investigated whether aortic plaque detected by TEE
is a clinically useful marker for coronary artery disease, with the
specific goal of avoiding coronary angiography in patients whose
conditions are evaluated by TEE for noncoronary cardiovascular surgery.
A strong association between the presence and severity of aortic plaque
imaged by TEE and the presence and extent of coronary artery disease
has been identified.46
47
48
49
The sensitivity of aortic
plaque for predicting coexisting coronary artery disease ranges from 90
to 95%, and the specificity ranges from 47 to 90%.46
47
48
49
The negative predictive value of a normal aorta by TEE for excluding
coronary artery disease ranged from 82 to 99%. In these studies,
aortic plaque was a stronger predictor of coronary artery disease than
any of the standard cardiovascular risk factors. Although the
specificity of aortic plaque for coronary artery disease declines
dramatically for patients who are > 70 years of age, the sensitivity
and negative predictive value remain high, even in the
elderly.49
The few patients who had coronary artery
disease in the absence of aortic plaque tended to have less-extensive
coronary disease.46
47
49
Therefore, the absence of aortic
plaque revealed by TEE strongly suggests that the patient does not have
significant enough coronary artery disease to warrant coronary artery
bypass during other cardiac surgical procedures. Although TEE is not
advised as a screening procedure, the results of the TEE evaluation of
the aorta in patients undergoing the procedure as part of a diagnostic
workup for valve or other noncoronary cardiothoracic surgery can be
used in conjunction with other clinical criteria to decide about the
need for coronary angiography.
In patients requiring cardiac catheterization or an IABP, the grading of the severity of thoracic aortic atherosclerosis by TEE may predict patients at high risk for experiencing catheter-related embolism. Karalis et al50 reported a 17% incidence of systemic embolism in 59 patients with IAD undergoing femoral artery catheterization and a 50% incidence in 10 patients who had IABP. The incidence of embolization was particularly high in patients with mobile debris (37%). In 11 patients who had brachial artery catheterization rather than femoral catheterization because of IAD detected by TEE before the invasive study, no subsequent emboli occurred.50 Therefore, patients undergoing TEE before cardiac catheterization or IABP should be carefully evaluated for aortic atherosclerosis, and, if complicated plaques are discovered, consideration should be given to performing brachial artery catheterization and avoiding the use of IABP.
The TEE assessment of thoracic aortic atherosclerosis has also been used in several research applications. The relative contributions of the established cardiovascular risk factors to the development of atherosclerosis in the different arterial beds and to the various clinical manifestations of atherosclerotic vascular disease have not been precisely defined.51 TEE has been used to study the relationship between these cardiovascular risk factors and atherosclerosis of the thoracic aorta in Americans and Japanese. An association has been reported for age,44 47 49 52 hypercholesterolemia,44 47 52 diabetes mellitus,52 smoking,53 hypertension,44 46 47 and plasma homocysteine levels.54 Age consistently demonstrated the strongest correlation with thoracic aortic atherosclerosis. TEE has also been used to monitor the effects of lipid-lowering therapy on the plaque burden in the thoracic aorta.55
The structural and mechanical properties of the thoracic aorta have
been studied by measuring aortic wall thickness and stiffness with TEE.
Aortic wall thickness, which may be a marker for early atherosclerotic
changes, was associated with increasing age, hypertension,
hypercholesterolemia, and diabetes.52
56
Aortic wall
stiffness is strongly associated with age 50 years and
hypertension.52
56
57
Aortic wall thickness and stiffness
were only weakly related to each other. This suggests that increases in
aortic wall stiffness are more likely related to changes in vascular
smooth muscle tone or the structural elements of the aortic wall than
to geometric changes secondary to vascular remodeling.56
Nifedipine has been reported to decrease aortic stiffness measured by
TEE, probably because of smooth muscle relaxation.58
The patient described in the case history had high-risk plaque in his aortic arch detected by TEE, a clinical course consistent with a left middle cerebral artery embolus, and no other potential sources of cerebral embolism during his initial hospitalization. Although it is difficult to definitively prove cause and effect in any cerebrovascular accident, this patient most likely had cerebral embolization from plaque in his aortic arch. The use of aspirin and cholesterol-lowering agents to treat this patient was rational, although the benefits of these agents for the prevention of recurrent emboli caused by aortic atherosclerosis have not been established. At the time of his open-heart procedure, intraoperative TEE demonstrated the persistence of aortic arch plaque but with resolution of the mobile components. This is consistent with the lesion undergoing vascular healing, as proposed by Montgomery et al.32 Nevertheless, the placement of the arterial cannula distal to the plaque was judicious and may have reduced the patient’s risk of experiencing postoperative stroke.
Question
3. The TEE findings that are diagnostic or suggestive of traumatic aortic injury (TAI) include which of the following? A. Thick flaps B. Limited aortic dissection C. Complete obstruction of the thoracic aorta D. Pseudoaneurysm E. Intraluminal thrombus F. Mediastinal hematoma G. All of the above
Answer
3. G
Traumatic Diseases of the Aorta
Blunt chest trauma may cause damage to the thoracic aorta, with potentially catastrophic consequences. TAI is believed to account for between 15% and 20% of motor vehicle accident fatalities.59 Only 20% of patients with TAI will survive long enough to reach the hospital, and these survivors, many of whom have aortic rupture contained by the adventitia, will experience a high early mortality, particularly if diagnosis and surgical intervention are delayed.60 Current conventional management consisting of aortography in patients with clinical and chest radiographic signs consistent with TAI are unsatisfactory. Limitations of this approach include delays in the definitive treatment of potentially unstable patients with multiorgan trauma while being transported to the radiology department and undergoing aortography and the risks of contrast and further vascular trauma during the performance of the aortogram. In addition, the diagnostic yield of this strategy is extremely low. As in the case of aortic dissection, the speed and portability of TEE, combined with the ability to obtain high-resolution images of the aorta, make it an attractive diagnostic modality.61 In addition, TEE can be performed without interrupting ongoing measures to stabilize the trauma patient. Consequently, TEE has been widely used and studied for the evaluation of TAI.
Multiple echocardiographic signs of TAI have been described by various authors, reflecting both the variety of aortic lesions that may be caused by severe chest trauma and the current lack of a standardized nomenclature describing these echocardiographic signs. Recently, Goarin et al62 described the various TEE findings of TAI in 28 patients.62 The most common finding in their series was thick stripes, which contain the intima and much of the media reflecting deep damage to the aortic wall. These appear to be similar to lesions described by other investigators as thick protruding membranes and mural or medial flaps.63 64 Another important TEE finding of TAI reported by Goarin et al62 were intimal flaps, which appeared to be caused by less extensive damage to the aortic wall than thick stripes. They described two types of intimal flaps. Free-edge intimal flaps were characterized by a free flap protruding into the aortic lumen associated with a discontinuity in the inner wall of the aorta. The second type of intimal flap had an appearance that was similar to a nontraumatic aortic dissection.
Changes in the shape of the aorta were also commonly detected by TEE in
patients with TAI by Goarin et al62
The most typical
echocardiographic abnormality was a localized distortion in the
circular shape of the aorta due to a pseudoaneurysm. A less common but
highly suggestive finding revealed by TEE was fusiform dilation with
the diameter of the disrupted portion of the thoracic aorta measuring
1.5 times more than that of the uninvolved aorta. Lesser degrees of
dilation were also revealed by TEE but were less
specific.62
Uncommon echocardiographic findings of TAI
noted by Goarin et al62
were intraluminal thrombus, medial
hematoma, and complete obstruction of the thoracic aorta due to
compression by an expanding pseudoaneurysm. Abnormalities of Doppler
flow and increased aortic-probe distance due to mediastinal hematoma
were common but nonspecific signs of TAI.62
Vignon et al63 proposed a new classification of TAI into four types based on TEE features, which they think is potentially clinically useful. The first type of TAI in their schema is traumatic aortic intimal tears. These are superficial lacerations of the intima that do not involve the media or adventitia and are often detectable only by TEE. They are imaged by TEE as mobile, thin, linear echo densities that are attached to the inner surface of the aortic wall. They have a good prognosis and can be managed medically. The three other types of TAI in their classification are subclassified as subadventitial traumatic aortic disruptions, which are tears through the full thickness of the intima and media. Partial subadventitial aortic disruptions are deep tears into the media without extensive circumferential separation of the layers of the aortic wall. These appear as deep breaks in the continuity of the aortic wall as revealed by TEE, usually without associated flaps. Subtotal subadventitial aortic disruption is characterized by a tear that involves at least two thirds of the aortic circumference. The aortic wall is held together by a small section of intact media and adventitia. The pathognomic TEE feature is a thick linear flap that traverses the lumen of the aorta obliquely or vertically in the transverse plane and vertically in longitudinal images, while usually remaining nearly perpendicular to the wall of the descending aorta. In the last type, complete subadventitial aortic disruption, the media is completely separated from the adventitia along the entire circumference of the aorta. The TEE appearance is a thick circular flap lying within the aorta. All three types of subadventitial aortic disruption are at high risk for exsanguination and should be managed with emergent surgery.63
Although the studies of TAI by TEE have included large numbers of chest trauma patients who were screened for TAI, these investigations have been limited by the small numbers of patients with actual aortic injuries. Six series with five or more patients with TAI have evaluated the diagnostic accuracy of TEE for this disorder using surgery, autopsy, or angiography as a reference.63 64 65 66 67 68 In these studies, the sensitivity of TEE for diagnosing TAI has ranged from 57 to 100% and the specificity has ranged from 84 to 100%. Four of six studies, including the largest one involving 15 patients with TAI, reported that TEE was extremely accurate for diagnosing TAI with sensitivities ranging from 81 to 100% and specificities ranging from 88 to 100%.63 64 66 67 In one of the two series in which TEE performed less well, the TEE examinations were performed and interpreted by trauma surgeons rather than by cardiologists, possibly accounting for the difference in results.65
Thus far, there have been no studies that have investigated the clinical impact of using TEE in the diagnostic workup of patients with suspected TAI. However, the value of TEE in the evaluation of all cardiovascular abnormalities in chest trauma patients, including TAI, has been reported. The other cardiovascular abnormalities assessed by TEE in this study were myocardial contusion, pericardial effusion, valvular abnormalities, and hypovolemia. In this study, the TEE findings led to changes in management in 20% of the patients.69
There is no consensus regarding the role of TEE in the evaluation of chest trauma patients with suspected TAI.70 Two groups of investigators have suggested that TEE has the potential to replace aortography as the primary diagnostic modality in these patients because of its diagnostic accuracy and other advantages.63 64 However, one potential problem with relying exclusively on TEE in these patients is the inability to consistently image the distal ascending aorta and aortic arch branches, which can be injured by severe blunt chest trauma. This is supported by a recent retrospective review of 89 cases of TAI documented by angiography that demonstrated injuries in the distal ascending aorta and aortic branches that would not have been detected by TEE in 20% of the patients.71 Acknowledging this limitation, Vlahakes and Warren61 suggested that if TEE is used as the primary diagnostic modality in chest trauma patients, the threshold for proceeding to aortography in questionable cases should remain low. Patients with negative results of TEE in the presence of unexplained mediastinal widening or hematoma (who might have injury to the portion of the ascending aorta or aortic arch branches not imaged by TEE) and patients with equivocal results of TEE should undergo aortography.61
Other authors believe that the appropriate role of TEE is a supportive one, helping to select those trauma patients who need aortography.61 65 68 70 Currently, a widened mediastinum shown on chest radiographs is central to the selection of chest trauma patients for aortography, in part because of the close association between mediastinal hematoma and serious vascular injury. However, the low sensitivity and specificity of the chest radiograph for mediastinal hematoma contributes to the present practice of performing large numbers of negative angiograms in chest trauma patients. TEE has recently been shown to be more accurate than chest radiography for the diagnosis of mediastinal hematoma.72 This finding supports the use of TEE as an intermediate screening test before proceeding to aortography, particularly in chest trauma patients with equivocal chest radiographic and clinical findings.64 67 72 Thus, even if TEE does not become the primary diagnostic modality for the evaluation of TAI, it may still have an important adjunctive role as a minimally invasive screening modality to limit the number of unnecessary aortograms currently performed on chest trauma patients.
Conclusion
As demonstrated in this two-part case-based review, the high-resolution imaging offered by TEE has an important role in both defining the pathophysiology of aortic disease and in the management of patients with diseases of the thoracic aorta. The speed and portability of TEE are significant advantages for the evaluation of acute aortic pathologic abnormalities, such as aortic dissection, aortic intramural hematoma, penetrating atherosclerotic ulcer of the aorta, and TAI. TEE is particularly useful in the diagnosis of atherosclerotic diseases of the thoracic aorta because of its unique ability to obtain high-resolution images of the aortic intima-lumen interface. The exact position of TEE in the diagnostic armamentarium of aortic disease will continue to evolve as further studies define the role of TEE in these disorders.
Acknowledgements
The authors acknowledge the assistance of Janet Fossum, William Kafitz, Billie Grover, Michael Rosenbloom, MD, and Michelle J. Enriquez in the preparation of the manuscript.
Footnotes
Abbreviations: IABP = intra-aortic balloon pump; IAD = intra-aortic atherosclerotic debris; TAI = traumatic aortic injury; TEE = transesophageal echocardiography
Received for publication May 24, 1999. Accepted for publication May 25, 1999.
References
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