EVALUATION OF THE PATIENT WITH BLUNT CHEST TRAUMA: AN EVIDENCE BASED APPROACH

EVIDENCE BASED EMERGENCY MEDICINE: EVALUATION AND DIAGNOSTIC TESTING

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EVALUATION OF THE PATIENT WITH BLUNT CHEST TRAUMA: AN EVIDENCE BASED APPROACH Myles D. Greenberg, MD, and Carlo L. Rosen, MD

Chest trauma is the second commonest cause of traumatic death in the United States after head trauma, accounting for approximately 20% of deaths.49Many of these deaths are due to serious chest injuries that are reversible if discovered and treated in a timely fashion. Rapid detection and treatment of blunt chest injuries are essential to the resuscitation of the multiple trauma patient. For example, of those patients who sustain traumatic aortic disruption that is not immediately fatal, 71% to 84% will survive with prompt diagnosis and su~gery,7~, 82 whereas 90% will die without intervention.” Major injuries to the chest caused by blunt mechanism can be classified into chest wall injuries (e.g., rib fractures, flail chest, sternal fractures), pulmonary injuries (e.g., pulmonary contusion, hemothorax, pneumothorax, tracheobronchial disruption), cardiovascular injuries (e.g., myocardial contusion, aortic disruption, cardiac rupture/tamponade), and esophageal injuries. The diagnosis of these injuries depends on multiple modalities and has changed dramatically in recent years with the advent of newer imaging technology. We will examine the use of plain chest radiography and computed tomography (CT) to diagnose selected pulmonary and chest wall injuries. Because this has been an area of minimal controversy, however, there are few published data. Much of our current practice in diagnosing these injuries is not evidence based; presumably expert opinion or local

From the Department of Emergency Medicine, Beth Israel Deaconess Medical Center, Harvard Medical School (MDG); and the Harvard Affiliated Emergency Medicine Residency Program and Department of Emergency Medicine, Massachusetts General Hospital (CLR), Boston, Massachusetts

EMERGENCY MEDICINE CLINICS OF NORTH AMERICA

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practice drives these practices patterns. These injuries are very common, nevertheless. Pulmonary contusion is reported in 30% to 75% of patients with significant blunt chest trauma, and pneumothorax is present in 15% to 50% of these patients.18 Because most of the recent literature on blunt chest trauma focuses on the controversy regarding the diagnosis of blunt aortic and myocardial injuries, much of this article is devoted to the use of CT, transesophageal echocardiography (TEE), aortography, electrocardiography (ECG), transthoracic echocardiography (TTE), and biochemical markers to identify these injuries. The true incidence of these two entities is not entirely clear. The incidence of blunt myocardial injury is difficult to ascertain because of the lack of agreement on the criteria for diagnosis. Reported 46 incidences vary from 3% to 75% in series of chest trauma ~atients.3~. Thoracic great vessel injury accounts for approximately 8% to 9% of vascular injuries; however, most of these are caused by penetrating rne~hanisms.~~ Blunt disruption of the thoracic aorta usually is rapidly fatal prior to hospital arrival; it is estimated that only approximately 10% to 20% of patients with these injuries survive to reach the emergency department (ED).44, 86 METHODS MEDLINE was searched using the terms blunt chest trauma, aortic injury, and myocardial contusion for the years 1973 to 1998. All prospective and retrospective studies on the use of chest x-ray (CXR), chest computed tomography (chest CT), TEE, TTE, aortography, ECG, creatine kinase (CK) determination, and troponin determination were identified. In addition, reference lists in commonly available emergency medicine and trauma textbooks were examined for appropriate studies. All studies using CXR or chest CT for diagnosing chest wall and pulmonary injury, studies using CXR, TEE, or aortography for blunt aortic injury, and studies using ECG, TTE, TEE, CK, or troponin for blunt myocardial injury were included. Review articles, case reports, expert opinions, and letters to the editor (which were not actual studies) were excluded from consideration. One hundred twenty-seven articles were initially identified; of these, eighty met the criteria and were included in this analysis. CHEST WALL AND PULMONARY INJURY Chest Radiography

The primary use of CXR is in the initial resuscitation of blunt trauma patients for detection of rib fractures, flail chest, pneumothorax, hemothorax, tracheobronchial injuries, pneumomediastinum, mediastinal hematoma, and pulmonary contusion. The CXR is used both to

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diagnose these clinical entities and to direct the need for further diagnostic intervention. This latter use is more fully addressed in the discussion of aortic injury. The use of the CXR as the primary imaging modality for detection of these injuries is widespread; its use can be attributed to low cost and easy availability. There is little evidence on the sensitivity or specificity of plain CXR in the detection of pulmonary or thoracic injuries, however. Although the anteroposterior (AP) CXR has been used as the initial imaging modality of the blunt trauma patient, along with pelvis and cervical spine radiographs, there are several studies suggesting that there is a significant rate of missed serious chest injuries on the initial CXR. In one level I1 study, 11 of 37 patients (30%) had chest injuries missed on the initial trauma room CXR that were detected at autopsy. These included two diaphragmatic tears and an aortic injury.59In another level I1 study, 27 of 94 patients had serious injuries missed on the initial CXR. These included pneumothoraces, hemothoraces, injuries to the great vessels, and sternal or thoracic vertebral fractures. The erect AP CXR had a sensitivity of 79% for detecting serious injuries, whereas the supine CXR had a sensitivity of 58Y0.~~ CXR and Pneumothorax

Up to 57% of patients with blunt chest trauma will have ”occult” pneumothorax diagnosed by abdominal or chest CT, and not by the initial CXR.”,93 In one recent study, 43% of patients who had an occult pneumothorax detected by CT required changes in their initial therapeutic management.l’ CXR and Pulmonary Contusion

There are minimal human data on the use of CXR to detect pulmonary contusion; however, an animal study (using a canine model) found that immediately after experimentally induced pulmonary injury, CT detected the pulmonary contusion in 100% of patients, whereas CXR only detected 38% of these contusions. After 30 minutes, 75% were visible by plain radiograph. In 58% however, CXR underestimated the size of the contusion.” One human study showed a much lower rate of pulmonary contusion detection on CXR versus chest CT (23% vs. 40% incidence of contusion in study subjects, re~pectively).~~ Chest CT Scan

Chest CT is commonly considered to be the gold standard for the detection of other serious chest injuries, such as pulmonary contusion, pneumothorax, hemothorax, flail chest, and rib fractures. This belief has not been studied by a large randomized controlled trial, however. There are some data to suggest that the use of CT over CXR alone may result

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in changes in patient management. For example, 41% of patients in a recent prospective study (level 11) of 103 patients had findings on thoracic CT that resulted in a change in management when compared with plain radiograph findings. These injuries included diaphragmatic injury, aortic rupture, and hemopericardium. Thoracic CT was found to be more sensitive than CXR for the detection of pulmonary contusion, pneumothorax, and h e m o t h ~ r a x In . ~ ~another prospective study (level 11) of 73 patients with blunt torso trauma who underwent upright CXR and chest CT, CT was more sensitive for the detection of pleural effusion and pulmonary contusion than CXR. Of the 15 patients with pleural effusion by CT, only three had effusion detected by CXR. Of the 27 patients with pulmonary contusion by CT, 6 had contusion seen on upright CXR. Rib fractures, however, were detected more frequently by CXR than CT. Of six patients with rib fractures by CXR, only one had rib fractures detected by CT.80 Recommendations

Plain CXR should be used as the first imaging modality when one suspects chest wall or pulmonary injuries. This test is inexpensive, readily available, and has no morbidity associated with it. It appears that there is a significant missed injury rate to CXR, however. If suspicion is high for undetected injury, CXR should be followed by chest CT scanning. Because chest CT is more expensive and exposes the patient to the risk of IV contrast dye, however, it should be performed only if the results are expected to alter patient management.

BLUNT AORTIC INJURY CXR and Aortic Injury

Plain CXR is the least costly and invasive modality for imaging patients with suspected aortic injury; however, its utility as the sole diagnostic study for TAI is very limited. The recent literature has focused on the use of chest radiography as an indicator of traumatic aortic injury (TAI), and many standard textbooks of emergency medicine and trauma recommend further diagnostic testing on the basis of an abnormal chest 69,91 radi~graph.~ ~ ,The ~ ~ ,most sensitive sign of aortic injury and the focus of most of the literature is the finding of a widened mediastinurn, which has a sensitivity of 50% to 92%, specificity of 10%. Given the low prevalence of this injury and the large number of CXRs performed on trauma patients, however, the positive predictive value of widened mediastinum in most studies is only 10% to 20%. Moreover, the mediastinum will be normal in 5% to 7.3% of those patients with documented aortic injury.5,3", 31, 33, 45*63* 67* 76, 78, 85, 86 The CXR will be entirely normal in up to 15% to 28% of patients with aortic injury4,6o Mediastinal width

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depends on both patient position and on whether the film is taken during inspiration or e ~ p i r a t i o n . ~ ~ In the only large-scale, multicenter, prospective trial of CXR in blunt chest trauma, 93% of patients with TAI had abnormal initial films, with the commonest abnormalities being widened mediastinum (85%), indistinct aortic knob (24%),left pleural effusion (19”/.),apical cap (19”/.), first or second rib fracture (13%), tracheal deviation (12%), nasogastric tube deviation ( l l y ~ ) and , depressed left bronchus (59’0).~OA smaller prospective trial of 55 patients showed that 38% of patients with a widened mediastinum on supine CXR had a normal mediastinum on upright CXR; however, not all patients in this study underwent an aortogram. The authors of this study conclude that if the supine CXR is abnormal, an upright film should be performed if clinically feasible to avoid unnecessary further studies.76In the largest retrospective study prior to 1990, which included 173 patients, 43% of patients with a widened mediastinum had a traumatic aortic injury confirmed by aortography. Seventeen patients had an apical cap, and none had TAI. In this study, the sensitivity of widened mediastinum was 95% in patients under the age of 65 years; however, two thirds of patients over the age of 65 years with TAI did not have a widened mediastinum on CXR.30 In another retrospective study, 408 patients with widened mediastinum on CXR underwent aortography; 13% had injury to the aorta or one of its major branch vessels.67Other retrospective studies show that a widened mediastinum on CXR has a sensitivity of 82% to 100% and a specificity of 34% to 60% for predicting TAI. This includes studies that looked at either subjective impression of width or objective measurement of width > 8.0 cm. In this same group of studies, the test characteristics of other CXR findings for the presence of TAI were assessed. The included findings were abnormal aortic contour (sensitivity 53%-100%, specificity 21%-55%), tracheal deviation (sensitivity 12%-1007’0, specificity 80%%%), nasogastric tube deviation (sensitivity 23%-71%, specificity 90%%YO), left apical cap (sensitivity 20%-63%, specificity 75%-76%), and depressed left mainstem bronchus (sensitivity 7%-809’0, specificity 80%100~0).3, 6, 31, 44, 53, 54, 77,85, 95 Previous trauma care doctrine held that there was an association between high rib and sternal fractures and aortic injuryz4;however, more recent data suggest that thoracic rib fractures detected by CXR do not 48*94 Therehave a clinically relevant predictive value for aortic fore, the work-up should be based on other clinical or radiographic criteria. In addition, the presence of sternal fractures on CXR has been shown to have no predictive value for myocardial contusion.37 Recommendations

CXR is a useful initial screening tool for chest injury but cannot be used as the sole test for diagnosing or excluding aortic injury. High clinical suspicion in the setting of a normal CXR should prompt further testing. In addition, mediastinal abnormalities on the CXR should

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prompt further testing, although skeletal injuries on the CXR should not be used as a marker for aortic injury. Chest CT Scan

CT is a widely available and relatively rapid imaging modality. It is more expensive than CXR and requires IV contrast dye, yet is not an invasive procedure like aortography. Because of these beneficial qualities, chest CT has been extensively studied recently as a screening tool for the detection of traumatic aortic injury after blunt chest trauma. Table 1 summarizes the recent literature on the use of CT for detecting aortic injury. In a recent large multicenter trial (level 11) of TAI, CT was diagnostic of aortic injury in 74% of patients. An additional 23% had findings of mediastinal hematoma. Thus, only 3% of patients with a confirmed injury had a negative CT. The limitations of this study are that it was neither randomized nor controlled, and only 40% (88 of 220 patients) underwent both aortogram and CT.20Another recent prospective nonrandomized study reported that helical CT was actually more sensitive (100% vs. 94%), although less specific (82% vs. 96%), than aortography for the detection of aortic injury2*The limitations of these studies are that not all patients underwent aortography or surgery. In another smaller study of 28 patients, 12 of whom had aortic injury, there was only one false-negative CT, yielding a sensitivity of 92% and a specificity of 100%. This level I1 study documented a 67% decrease in the use of aortography when CT was used as the initial screening test. This study also demonstrated that chest CT may be limited in its ability to detect great vessel injury, which can occur in

Table 1. STUDIES ON THE USE OF CT FOR DETECTING AORTIC INJURY ~

Reference No.

~

Type of Study

20

Prospective level I1

10

Level I1

28

Prospective level 11 Prospective level I1 Retrospective level 111 Prospective level I1

23 58 68

~

No. of Patients

220 28

127 88 17 90

Accuracy

Sensitivity: 74% for actual injury, 97% for signs of * j y Sensitivity: 92% Specificity: 100% (1 false negative: left subclavian injury) Sensitivity: 100% Specificity: 82% No false negatives Sensitivity: 83% Specificity: 23% No false negatives

“Gold Standard”

Aortography, surgery Aortography, surgery

Surgery, clinical outcome, or aortography Aortography or clinical follow-up All had aortography Aortography or clinical follow-up

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association with TAI. Of the 28, 1 patient had a left subclavian injury that was missed.1° Other level I1 studies have confirmed that CT is helpful in determining the need for aortography but should not be used as the sole diagnostic modality in patients with high clinical suspicion for TAI.5s,68 Another use of helical CT in patients with suspected TAI is CT angiography. In this technique, multiple thin cuts are taken through the aorta during the injection of iodinated contrast. Three-dimensional reconstructions are used to demonstrate the injury. In a recent level I11 study of only five cases of surgically proven thoracic aortic ruptures, there was one case that was a false positive by both CT angiography and conventional angiography. The authors concluded that this technique had good correlation with conventional angi~graphy.~~ In another larger study, however, helical CT was found to be as accurate as CT angiography for the detection and definition of aortic Thus, CT angiography may be able to further define an aortic injury but does not appear to have a higher sensitivity than helical CT for the detection of TAI. Recommendations

The data presented support the use of CT as a screening test to diagnose TAI or to show mediastinal abnormalities, which should lead to further testing (i.e., angiography). The major advantages of CT are noninvasiveness and speed. In patients with a low clinical suspicion of aortic injury, a negative CT can be used to exclude the diagnosis and significantly decrease the number of aortograms necessary. It is not clear whether CT is adequate for detecting great vessel injuries or clearly defining the extent of an aortic injury. CT may demonstrate only the presence of a mediastinal hematoma or nonspecific aortic abnormality. Therefore, if the clinical suspicion is high or the CT demonstrates the nonspecific finding of mediastinal hematoma, aortography is required to confirm the presence of an aortic tear or to further define the injury prior to surgery. As the technology of CT and CT angiography improves, however, these modalities may eventually become the sole diagnostic procedures of choice for detecting TAI. Transesophageal Echocardiography For the detection of thoracic aortic injury, TEE has the advantage of being less invasive and more rapid than aortography. In addition, it can be performed at the bedside and does not require contrast administration; however, it is limited by the need for an experienced operator and is contraindicated in patients who have esophageal or cervical spine injuries. Table 2 shows a summary of the recent literature on the use of TEE for aortic injury. In an early prospective study (level 11) of 69 patients by Kearney, all

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Table 2. STUDIES ON THE USE OF TEE FOR DETECTING AORTIC INJURY Reference No.

Type of Study

No. of Patients

16

Prospective level I1 Prospective level I1 Prospective level I1 Retrospective level I11 Prospective level 11 Prospective level I1 Prospective level I1

89 88 71 81

13 42

Sensitivity Specificity “Gold Standard”

%

%

134

93

98

40

I00

88

32

91

100

114

63

84

93

100

98

126

100

100

Aortography in 25 patients Aortography, followUP Aortography, autopsy, surgery Aortography or surgery Aortography, surgery, autopsy Aortography, surgery

69

100

100

Aortography, surgery

of whom underwent both TEE and aortography, TEE had a diagnostic sensitivity and specificity of 100% when compared with thoracotomy or autopsy findings. In this study, aortography had a sensitivity of only 67% and specificity of 989’0.~~ In another prospective, nonrandomized study of 160 consecutive patients suspected of having traumatic aortic injury, 108 patients underwent TEE and aortography, 39 underwent aortography only, and 18 underwent TEE only. The sensitivity and specificity of TEE were 100%; however, 3 of the 121 studies (2.5%) were equivocal. Aortography had a sensitivity and specificity of 73% and 99%, re~pectively.’~ Using aortography, surgery, or autopsy results as the gold standard, Smith performed a prospective (level 11) study of 93 patients who underwent TEE followed by aortography. The mean study time to perform TEE was 29 k 12 minutes. The reported sensitivity and specificity were 100% and 98%, respectivelyFl In a prospective study (level 11) of 32 consecutive patients with suspected traumatic aortic injury based on mechanism plus widened mediastinum on CXR, overall sensitivity and specificity for detection of subadventitial tears were 91% and 100% respectively. One 2-mm medial tear was missed by TEE. The gold standards were aortography, surgery, or autopsy.88 Another prospective study (level 11) by the same author looked at patients with a normal mediastinum on CXR. In 40 consecutive patients with significant mechanism for TAI, all of whom underwent TEE, 6 patients (15%) had mediastinal hematoma and 2 patients (5%) had an aortic injury. Although both injuries were confirmed by aortography, only these six patients actually underwent a o r t ~ g r a p h y . ~ ~ Chirillo et a1 performed a prospective study (level 11) of 134 consecutive patients with clinical evidence of significant chest trauma or history of significant mechanism for aortic injury. Almost all patients (131 of 134) in this study underwent TEE. This study demonstrated a sensitivity

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of 93% and specificity of 98% for the detection of TAI. Furthermore, the time to surgery in those patients undergoing procedures solely on the basis of TEE was significantly shorter (30 min vs. 71 min). TEE also detected pleural effusion, pericardial effusion, valvular disruption, and blunt myocardial injury. Based on these findings, the authors conclude that TEE may complement but is not an alternative to aortography. The authors concluded that TEE can be used to select patients who can proceed directly to surgery (when the study demonstrates unequivocal evidence of aortic disruption). Furthermore, they concluded that patients with negative TEE and high clinical suspicion, evidence of periaortic hematoma, or indeterminate findings should undergo aortography.16 In a retrospective review (level 111), Saletta reported on 114 patients who underwent TEE as the initial diagnostic study for radiographic or clinical suspicion of traumatic aortic injury. In this study, 17 patients had indeterminant results. Definitive diagnosis of an aortic tear was made in only eight patients (7%),and only five patients were diagnosed correctly using surgery or aortography as the gold standard. The resulting test characteristics of TEE for detecting aortic injury were sensitivity 63%, specificity 84%, positive predictive value 23%, and negative predictive value 97%. This study tested TEE as the initial, sole diagnostic test for TAI.71 Recommendations

The data from the prospective studies suggest that TEE is a valuable tool for the diagnosis of TAI in experienced hands and may have a higher sensitivity than aortography for the diagnosis. Because operative repair can be performed without additional studies, TEE can significantly reduce the time to surgery. TEE also can detect other cardiac injuries such as pericardial effusions, valvular disruptions, and blunt myocardial injury. One retrospective study, however, suggests that TEE may not be appropriate as the initial screening study in blunt chest trauma, especially when chest CT is readily available.49Finally, the utility of this test is limited by the need to have an experienced operator immediately available to perform the study. Aortography

Aortography has long been considered the gold standard for traumatic aortic injury, although its invasiveness, risk, and expense have prompted many to search for an alternative screening tool. The advantage of aortography over TEE and chest CT is that it localizes the injury precisely, especially in the case of multiple aortic tears. It also is more accurate for the detection of great vessel injuries. The literature on the use of aortography for the detection of aortic injury is limited in that there is no true gold standard for the diagnosis aside from operative thoracotomy and autopsy. The more recent literature, therefore, focuses

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on comparing CT or TEE with aortography. In a level I1 study by Buckmaster et a1 and a level I11 study by Sturm et al, the sensitivity and specificity of aortography for traumatic aortic injury were 73% to loo%, and 99%, re~pectively.'~, In a recent level I1 study of 72 patients with aortic rupture, 1% had an injury to the distal ascending aorta, and 19% (17 patients) had aortic arch branch injuries. The authors of this study conclude that these types of injuries may be missed if TEE is used as the sole diagnostic test for aortic injury.4O Because aortography is more accurate than CT and TEE for detecting ascending aortic injuries, it is better able to determine the need for cardiopulmonary bypass for the operative management of these patients. In contrast to other studies, a recent prospective study (level 11) of TEE by Keamey for the detection of aortic injury found that aortography actually had a lower sensitivity than TEE (sensitivity of 67% and specificity of 98% versus an accuracy of 100%for TEE). Sixty-nine patients with suspected aortic injury underwent both TEE and aortography. There were two false-negative aortograms and one false-positive aortogram in this Recommendations Aortography is still considered the gold standard for diagnosing TAI; however, it appears that TEE and CT have greatly reduced the need for this invasive test. Aortography still should be used to diagnose nonaortic great vessel injury and also is frequently necessary to define the extent of an injury once it has been discovered by other modalities. Its invasiveness, cost, and iodinated-dye exposure risk probably will limit its future use to these indications. Patients with a suggestive mechanism and worrisome clinical or radiographic findings should undergo aortography because it provides anatomic detail that enables the cardiovascular surgeon to proceed to surgery. Additionally, in patients at very high risk for TAI by clinical suspicion, aortography should be ordered even if other studies are negative. This algorithm is summarized in Figure 1.

Low/Equivocal

1

Clinical Suspicion

7 ChestX-Ray I

+ Negative

1

Mediastinal Hematoma

I I

High I

.) Aortography

I

Figure 1. Diagnosis of thoracic aortic injuty.

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BLUNT MYOCARDIAL INJURY

There is no gold standard for the diagnosis of blunt myocardial injury, short of autopsy. Thus, it is difficult to interpret studies that report the test characteristics of any currently available diagnostic modality. Fortunately, the incidence of clinically significant complications that actually require treatment is negligible; therefore, even the necessity of making this diagnosis is in question. The goal is to differentiate low-risk patients who can be discharged safely from the ED from the small number of patients who may develop complications requiring treatment. Although there are several other tests that are currently used to diagnose and risk-stratify blunt myocardial injury, this article focuses on electrocardiography, biochemical marker determination, and echocardiography. Electrocardiography

ECG is a quick, inexpensive, and noninvasive test that is readily available in any ED. Although ECG is neither specific nor sensitive for blunt myocardial injury, it is the best screening test available in the ED. Table 3 summarizes the studies on the use of ECG to diagnose blunt myocardial injury. One recent study (prospective, level 11) demonstrated an incidence of 54% of abnormal ECG findings in patients with echocardiographic abnormalities after blunt myocardial injury. Forty-nine percent of the abnormalities were nonspecific ST-segment depression and T-wave changes and the rest constituted conduction abnormalities, axis deviation, and dy~rhythmias.~~ In a meta-analysis of 41 studies of blunt myocardial injury, an abnormal ED ECG correlated with complications requiring treatment (lethal dy~rhythmia).~~ Fildes et a1 prospectively reported on 74 hemodynamically stable patients less than 55 years of age with a normal initial ECG and no history of cardiac disease, who did not have associated injuries requiring surgery. None of these patients had a cardiac complication.22A level I1 retrospective study of 184 patients with blunt myocardial injury demonstrated that patients with a normal ED ECG did not develop complications requiring treatment.I7In contrast to this, in a prospective study (level 11) by Biffl and coworkers, 17 of 107 patients with contusion developed complications requiring treatment. Only 2 of 17 patients had an initial ECG that was abnormal; 3 had sinus tachycardiaP Another retrospective study looked at 133 patients admitted to two institutions with clinical suspicion for myocardial contusion. In this study, there were 13 patients (9.7%)who developed cardiac problems; no patient with a normal ED ECG developed a cardiac complication?* In a study by Miller et a1 only 4 of 172 patients had dysrhythmias requiring treatment. All four patients had abnormal initial ED ECGS.~~ Baxter et a1 also noted that nearly all cardiac complications in patients without preexisting cardiac disease sustaining blunt chest trauma were manifest on initial e~aluation.~ Wisner and coworkers stud-

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Table 3. STUDIES OF ECG USE FOR BLUNT MYOCARDIAL INJURY Reference No.

Type of Study

No. of Patients

17

Retrospective level I1

184

51

Meta-analysis level I

2,210 (prospective) 2,471 (retrospective)

22

Prospective level I1 Retrospective level 111

93

9

359

14

Prospective level I1

336

32

Prospective level I1

123

38

Retrospective level I1 Retrospective level I1 Prospective level 111

123

Retrospective level I1

104

92 35

83

95 68

Results

No complications for patients with normal ECG in ED; all with complications had arrhythmia or shock in ED Abnormal ECG correlated with complications: Odds ratios = 3.2 and 26.0 (prospective and retrospective data); normal ECG correlated with the lack of complications No complications 17 (5%) had complications; 2 of 17 had a normal ECG; 3 of 17 had sinus tachycardia (occurred at 6-22 hr) No cardiac complications in those admitted for abnormal initial ECG or mechanism; all 19 complications occurred in patients >60 yr old or with otherwise significant chest injury (i.e., 2 four rib fractures, pulmonary contusions, flail chest, major vascular injury, or severe associated injuries) ECG does not correlate well with cardiac complications or abnormal nuclear medicine study No complications in patients with normal ECGs Conduction abnormalities on initial ECG predicted serious arrhythmias 54% of patients had abnormal ECGs, no correlation with echo findings; authors did not report predictive factors for complications ECG did not predict complications that occurred in 23% of patients

ied 95 patients with suspected contusions and found that only four patients developed clinically significant dysrhythmias; only one of these patients had a normal initial ECG.92 In contrast, two other studies, one prospective and one retrospective, found no correlation between ECG findings and cardiac complicaCachecho and coworkers prospectively studied t i o n ~ .83~ Furthermore, ~, 336 patients with suspected myocardial contusion. In this study, none of the 198 patients admitted solely for mechanism of injury or abnormal initial ECG developed cardiac complications. The 19 patients who developed complications had four or more rib fractures, pulmonary contusion, flail chest, or extrathoracic injuries, or were over 60 years of age.I4 Nevertheless, most authors recommend that stable patients with normal

EVALUATION OF THE PATIENT WITH BLUNT CHEST TRAUMA

53

ECGs who are asymptomatic without other significant injuries can be safely discharged from the ED. Biochemical Markers Creatine Kinase (CK) Creatine kinase MB (CK-MB) is a relatively inexpensive, noninvasive test that is readily available and widely used for diagnosing nontraumatic cardiac injury. CK-MB fractions are frequently ordered as part of the work-up of patients to rule out blunt myocardial injury. The evidence in support of this practice is not substantial, however. All of the studies on the use of CK-MB for detecting myocardial injury suffer from the same major limitation: there is no clear definition of myocardial contusion, nor is there an established gold standard. Table 4 summarizes the studies on the use of CK-MB determination in blunt myocardial injury. In a retrospective study (level 11) of 182 patients with significant blunt chest trauma who underwent serial CK-MB fraction analysis, there Table 4. STUDIES OF CK-MB DETERMINATION IN BLUNT MYOCARDIAL INJURY Reference No.

Type of Study

No. of Patients

41

Meta-analysis level I1

4,681

9

Retrospective level I1

359

19

Prospective level I1

92

32

Prospective level I1 Prospective level I1 Prospective level I1

123

35 62 92 43 83 25

Retrospective level I1 Retrospective level I1 Retrospective level I1 Prospective level I1

68 172 95 182 104 58

Results

Abnormal CK-MB level correlated with increased complications (odds ratios 3.7 and 7.7 for prospective and retrospective data). 41% of patients with complications had elevated CK-MB level; 59% had normal CK-MB level. 52% patients with echo-demonstrated contusion had elevated CK-MB vs. 19% with elevations who had no echo findings Elevated CK-MB level not predictive of cardiac complications Elevated CK-MB level 17% sensitive for echo-demonstrated contusion No patients with elevated CK-MB level as sole diagnostic criterion for contusion developed complications. No correlation of elevated CK-MB level with complications No correlation of elevated CK-MB level with complications or echo/MUGA findings 23% developed complications but CKMB not predictive Elevated CK-MB did not correlate with TTE abnormalities.

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GREENBERG & ROSEN

was no correlation of CK-MB levels with ECG findings suggestive of myocardial injury. The major limitation of this study is that myocardial injury was confirmed in only ten patients who underwent 2-D echocardiography or multiple-gated acquisition (MUGA) ~cintigraphy.~~ Another investigator prospectively documented the lack of correlation of elevated CK-MB with abnormal nuclear medicine studies (MUGA) or cardiac morbidity.32A prospective study (level 11) of 68 patients demonstrated that 12 patients had elevated CK-MB levels; however, only 3 of these patients also had abnormal echocardiographic findings (present in 18 patients). These authors conclude that CK-MB may be used in conjunction with echocardiography and ECG to diagnose myocardial In a larger prospective study of 92 patients, all of whom underwent serial ECG, CK-MB analysis, continuous Holter monitoring, and noninvasive cardiac output measurement, 23 developed dysrhythmias. No patients required specific therapy, however. This highlights another area of confusion about the diagnosis of myocardial contusion; the incidence of clinically significant dysrhythmias that actually require treatment is negligible. Fifty-two percent of patients who developed dysrhythmias had an elevated CK-MB, whereas only nineteen percent of patients without dysrhythmia had CK-MB elevation. Although this difference was statistically significant in this study, the low sensitivity and specificity preclude its use clinically.” In another retrospective study of 359 patients, 217 of whom were admitted solely for the purpose of ruling out myocardial contusion, 107 (30%) were diagnosed with this injury based on either abnormal ECG findings or elevated CK-MB fractions. Sixteen percent of patients developed complications (dysrhythmias or cardiogenic shock) requiring treatment. Every patient with a complication had an abnormal ECG; however, only 41% had elevated CK-MB fractions. There were no complications among those patients with normal ECGs and elevated CK-MB fractions. Thus, in this study, an elevated CK-MB level was never the sole predictor of a complication after blunt myocardial i n j ~ r y . ~ An earlier study demonstrated that 58 of 291 patients (20%) who were assessed for possible cardiac injury had a CK-MB fraction elevation within 24 hours of the injury. Of these patients, five had dysrhythmias occurring within 72 hours of injury that were hemodynamically significant and required intervention. It is not clear from this study whether these patients had abnormalities on their initial ECGS.~~ Furthermore, in the study by Miller, none of the patients with isolated CK-MB elevations had complications.62Other retrospective studies have also documented the lack of utility of elevated CK-MB fractions in the prognosis of a patient with suspected blunt myocardial injurys3,92 Troponin

Troponin is a regulatory protein that is found only in cardiac tissue. Troponin I and T are sensitive and specific markers for myocardial infarction and are now being used for the detection of myocardial

EVALUATION OF THE PATIENT WITH BLUNT CHEST TRAUMA

55

injury.2,30 Troponin is more specific than CK-MB because it is not present in skeletal muscle. There are several recent studies that have investigated the use of troponin I for detecting blunt myocardial injury. Table 5 summarizes the studies on the use of troponin determination in the diagnosis of blunt myocardial injury. In a study of 44 patients, all 6 patients with cardiac injury diagnosed by echocardiogram had both elevated CK-MB levels and elevated troponin I. In the 37 patients without echo-detected cardiac injury, 26 had elevated CK-MB levels, yet none had elevated troponin I.' The major limitation of this study is that it used echocardiography as the sole test for diagnosis of cardiac injury. A more recent, very small (level 11) study of 28 patients, only 5 of whom had myocardial contusion diagnosed by TEE, reported 100% sensitivity and specificity of elevated serum troponin I for myocardial contusion for TEE-documented Other studies have looked at serum troponin T determination. A level I1 study of 29 patients with myocardial contusion found that troponin T was more sensitive (31%)than CK-MB (9%) for the detection of traumatic cardiac injury. The sensitivities were both far too low for clinical use of these tests, however. The gold standard in this study was the presence of rhythm or conduction abnormalities, abnormal echo, or hemopericardium.21Another study of troponin T in 71 patients found that the sensitivity and specificity of elevated troponin T for predicting clinically significant electrocardiographic abnormalities were 27% and 91%, respectively. Only 20 patients in this study had or developed a clinically significant ECG abnormality.26 Although these preliminary data suggest that troponin determination is a more specific indicator than CK-MB of myocardial injury after blunt trauma, troponin levels do not appear to have predictive value for the development of complications and need for hospital admission. Troponin I may be helpful in predicting echocardiographic abnormalities; however, troponin T determination appears to have little utility in the diagnosis of blunt myocardial injury. Table 5. STUDIES OF THE USE OF TROPONIN DETERMINATION IN BLUNT MYOCARDIAL INJURY Reference No. of No. Type of Study Marker Studied Patients

65

Level I1

Troponin I

28

21

Level I1

Troponin T

29

26

Level I1

Troponin T

71

1

Level I1

Troponin I

44

Results

100% sensitivity and specificity for echo-demonstrated contusion Sensitivity of troponin T better than CK-MB (31% vs 9%) Sensitivity = 27% and specificity = 91% for predicting significant ECG abnormalities 100% sensitivity and specificity for echo-demonstrated injury

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Transthoracic Echocardiography

TTE is another noninvasive bedside test that is frequently ordered from the ED for patients with suspected blunt myocardial injury, but its utility in patients who are hemodynamically stable is not well supported by the literature. Table 6 lists the studies on the use of TTE in the diagnosis of blunt myocardial injury. In a study by Frazee et al, of 58 patients with CK-MB elevations, 35 (60%) had normal 2-D echocardiography; 23 (40%) had abnormal 2-D echocardiography. The abnormalities were primarily right ventricular dyskinesias. Cardiac dysrhythmias occurred in only 1 of the 35 patients (3%) with a normal echocardiogram and 9 of 23 (39%) with an abnormal echocardiogram. The difference was statistically signifi~ant.~~ In a study by Beggs et al, TTE was performed on 40 patients with clinical suspicion of blunt chest trauma. One half of these patients manifested at least one abnormality on either ECG, cardiac enzyme analysis, or two-dimensional TTE. Twenty-three percent of these patients had echocardiographic abnormalities; however, there was no correlation between the echocardiographic abnormalities and ECG or enzyme abnormalities. Moreover, echocardiography did not predict complications. The one patient with pericardial tamponade had the diagnosis made on clinical grounds and then confirmed by echocardiography.* In a prospective study of 73 patients presenting with blunt chest trauma, all of whom underwent TTE, serial CK-MB measurements, and cardiac monitoring, 14 had echocardiographic abnormalities caused by chest injury. There was only one complication in the group with echocardiographic findings; this complication was a persistent ventricular dysrhythmia successfully treated with lidocaine. This patient also had an initially abnormal ECG, however. In the group without echocardiographic findings, there was one complication (frequent PVCs) also successfully treated with l i d ~ c a i n eIn .~~ another prospective study, 172 patients with myocardial injury suspected on clinical grounds underwent serial ECGs, serial CK-MB isoenzyme determinations, and 2-D echocar-

Table 6. STUDIES ON USE OF TTE IN BLUNT MYOCARDIAL INJURY Reference No.

TvDe

Of

Studv

No. of Patients

62

Prospective level I1

172

36

Prospective level I1

73

8

Prospective level I11

40

25

Prospective level I1

58

Results

No complications among those patients with isolated TTE abnormalities but normal ECGs Only 1 complication in each group; sensitivity = 50%, specificity = 82% Echocardiographic abnormalities did not predict complications 39% sensitive, 97% specific for complications

EVALUATION OF THE PATIENT WITH BLUNT CHEST TRAUMA

57

diography. The authors found that ECG abnormalities or shock were the only two predictors of the need for monitoring or further treatment. Furthermore, patients with abnormalities of CK-MB or on echocardiography without ECG abnormalities did not develop complications requiring treatment.62 Although there are several studies that investigate the use of TTE specifically for detecting pericardial effusion and tamponade after penetrating trauma, there are few data on its use for this purpose after blunt trauma.61,64, 66, 70 After blunt trauma, the incidence of cardiac rupture in patients presenting to the ED alive is low; probably the only survivable injury of this type is atrial rupture. Based on the existing literature on penetrating chest trauma, it appears that TTE is useful in the diagnosis of pericardial effusion and tamponade. One study by Plummer documented a sensitivity of 98% and specificity of 100% for this technique in the hands of emergency physicians.66 Transesophageal Echocardiography There are data that suggest TEE may be more accurate than TTE in the detection of blunt myocardial injury. Chirillo et a1 prospectively studied (level 11) 134 consecutive patients with severe blunt chest trauma. All patients underwent TTE and TEE within 8 hours of admission. TTE images were technically suboptimal in 62% of patients and demonstrated myocardial injury in only 15 patients, whereas TEE demonstrated myocardial injury in 45 of the 131 patients in whom the study was technically feasible. The study did not report the clinical significance of these findings. Based on these results, the authors conclude that TEE is more accurate than TTE for detecting myocardial injury and that TTE is not recommended as a routine study for patients with blunt chest trauma.16 In addition, TEE has the ability to demonstrate other cardiovascular abnormalities, such as valvular disruption, pericardial effusions, and TAI. The clinical significance of effusion detected by TEE remains to be determined, however.16,79 In a study comparing TEE to TTE for the detection of cardiac contusion and aortic injury, 50 patients with a suspected diagnosis of cardiac contusion or TAI underwent both studies. Cardiac contusion, as diagnosed by wall motion abnormalities, was detected in 26 patients (52%)by TEE, but TTE showed this abnormality in only 6 patients (12Y0).~~ Two other studies have documented the ability of TEE to detect segmental wall motion abnormalities in severely injured patients, some of whom could not undergo TTE because of severe external chest injuries.15,90 Another use for TEE may be in differentiating pericardial tamponade from right ventricular myocardial contusion. A recent article reported two such cases diagnosed by TEE.29 Recommendations

Based on the literature, the initial ED ECG is the best screening test for potential cardiac complications from blunt myocardial injury. Patients

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with a normal ECG, normal hemodynamics, and no other significant injuries can be safely discharged from the ED. Cardiac enzymes have no role in the prediction of complications in patients with blunt myocardial injury, although elevated serum troponin I levels may predict echocardiographic abnormalities. Echocardiography should not be used as a screening test to rule out myocardial contusion in the ED, however. Furthermore, echocardiographic abnormalities do not seem to predict clinical complications. The use of echocardiography should be reserved for unstable patients to detect pericardial tamponade and cardiac rupture. TTE should be the procedure of choice for this indication because there is no clear evidence that TEE is superior. There appear to be little data supporting the extra cost and invasiveness of TEE for the identification of blunt myocardial injury. RECOMMENDATIONS FOR FUTURE RESEARCH

The most pressing need for further research is in the search for a quick, noninvasive method for excluding the diagnosis of traumatic aortic injury. The current state of CT scan technology does not allow this modality to be used as the sole method of imaging the aorta in the patient with a high pretest suspicion for TAI. Early investigation into the use of CT angiography for this purpose seems promising, however. In addition, further research should be directed at the elucidation of blunt myocardial injury. There is no gold standard for the diagnosis; thus efforts to examine all current modalities are limited. In addition, there is much controversy about the need to make this diagnosis in the majority of patients with blunt chest trauma. References 1. Adams JE, Davila-Roman VG, Bessey PQ, et al: Improved detection of cardiac contusion with cardiac troponin I. Am Heart J 131:308, 1996 2. Adams JE, Davila-Roman VG, Delmez JA, et al: Cardiac troponin: I. A marker with high specificity for cardiac injury. Circulation 88:101, 1993 3. Akins CW, Buckley MJ, Daggett W, et al: Acute traumatic disruption of the thoracic aorta: A ten-year experience. Ann Thorac Surg 31:305, 1981 4. Applebaum A, Karp R, Kirklin J W Surgical treatment for closed thoracic aortic injuries. J Thorac Cardiovasc Surg 71:458, 1976 5. Ayella RJ, Hankins JR, Turney SZ, et al: Ruptured thoracic aorta due to blunt trauma. J Trauma 17199, 1977 6. Barcia TC, Levoni JI': Indications for angiography in blunt thoracic trauma. Radiology 147:15, 1983 7. Baxter BT, Moore EE, Moore FA, et al: A plea for sensible management of myocardial contusion. Am J Surg 158:557, 1989 8. Beggs CW, Helling TS, Evans LL, et al: Early evaluation of cardiac injury by twodimensional echocardiography in patients suffering blunt chest trauma. Ann Emerg Med 16:542, 1987 9. Biffl WL, Moore FA, Moore EE, et al: Cardiac enzymes are irrelevant in the patient with suspected myocardial contusion. Am J Surg 168:523, 1994

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10. Biquet JF, Dondelinger RF,Roland D Computed tomography of thoracic aortic trauma. Eur Radio1 625, 1996 11. Bridges KG, Welch G, Silver M, et al: CT detection of occult pneumothorax in multiple trauma patients. J Emerg Med 11:179, 1993 12. Brooks SW, Young JC, Cmolik B, et al: The use of transesophageal echocardiography in the evaluation of chest trauma. J Trauma 32:761, 1992 13. Buckmaster MJ, Kearney PA, Johnson SB, et al: Further experience with transesophageal echocardiography in the evaluation of thoracic aortic injury. J Trauma 37989,1994 14. Cachecho R, Grindlinger GA, Lee V W The clinical significance of myocardial contusion. J Trauma 33:68, 1992 15. Catoire P, Orliaguet G, Liu N, et al: Systematic transesophageal echocardiography for detection of mediastinal lesions in patients with multiple injuries. J Trauma 38:96, 1995 16. Chirillo F, Totis 0, Cavarzerani A, et al: Usefulness of transthoracic and transesophageal echocardiography in recognition and management of cardiovascular injuries after blunt chest trauma. Heart 75:301, 1996 17. Dowd MD, Krug S: Pediatric blunt cardiac injury: Epidemiology, clinical features, and diagnosis. Pediatric Emergency Medicine Collaborative Research Committee: Working Group on Blunt Cardiac Injury. J Trauma 40:61, 1996 18. Dougall AM, Paul ME, Finley RJ, et al: Chest trauma: Current morbidity and mortality. J Trauma 17547, 1977 19. Fabian TC, Cicala RS, Croce MA, et al: A prospective evaluation of myocardial contusion: Correlation of significant arrhythmias and cardiac output with CPK-MB measurements. J Trauma 31:653, 1991 20. Fabian TC, Richardson JD, Croie MA, et al: Prospective study of blunt aortic'injury: Multicenter trial of the American association for the surgery of trauma. J Trauma 42374, 1997 21. Ferjani M, Droc G, Dreux S, et al: Circulating cardiac troponin T in myocardial contusion. Chest 111:427, 1997 22. Fildes JF, Betlej TM, Mangliano R, et al: Limiting cardiac evaluations in patients with suspected myocardial contusion. Am Surg 612332, 1995 23. Fisher RG, Chasen MH, Lamki N: Diagnosis of injuries of the aorta and brachiocephalic arteries caused by blunt chest trauma: CT vs aortography. Am J Roentgenol 1621047, 1994 24. Fisher RG, Ward RE, Ben-Menachem Y, et al: Arteriography and the fractured first rib. Am J Roentgenol 138:1058, 1982 25. Frazee RC, Mucha P Jr, Farnell MB, et al: Objective evaluation of blunt cardiac trauma. J Trauma 26:510, 1986 26. Fulda GJ, Gilberson F, Hailstone D, et al: An evaluation of serum troponin T and signal-averaged electrocardiography in predicting electrocardiographic abnormalities after blunt chest trauma. J Trauma 43:304, 1997 27. Gavant ML, Flick P, Menke P, et al: CT aortography of thoracic aortic rupture: Am J Roentgenol 166:955, 1996 28. Gavant ML, Menke PG, Fabian T, et al: Blunt traumatic aortic rupture: Detection with helical CT of the chest. Radiology 197125, 1995 29. Goldberg SP, Karalis DG, Ross JJ Jr, et al: Severe right ventricular contusion mimicking cardiac tamponade: The value of transesophageal echocardiography in blunt chest trauma. Ann Emerg Med 22745, 1993 30. Gundry SR, Burney RE, McKenzie JR, et al: Indications for aortography in blunt thoracic trauma: A reassessment. J Trauma 22:664, 1982 31. Gundry SR, Burney RE, McKenzie JR, et al: Assessment of mediastinal widening associated with traumatic rupture of the aorta. J Trauma 23293, 1983 32. Gunnar WP, Martin M, Smith RF, et al: The utility of cardiac evaluation in the hemodynamically stable patient with suspected myocardial contusion. Am Surg 57373, 1991 33. Hanschen S, Snow NJ, Richardson JD: Thoracic aortic rupture in patients with multisystem injuries. South Med J 75:653, 1982 34. Hehir MD, Hollands MJ, Deane SA: The accuracy of the first chest x-ray in the trauma patient. Aust NZ J Surg 60:529, 1990

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35. Helling TS, Duke P, Beggs CW, et al: A prospective evaluation of 68 patients suffering blunt chest trauma for evidence of cardiac injury. J Trauma 29:961, 1989 36. Hiatt JR, Yeatman LA Jr, Child JS: The value of echocardiography in blunt chest trauma. J Trauma 28:914, 1988 37. Hills MW, Delprado AM, Deans SA, et a1 Sternal fractures: Associated injuries and management. J Trauma 35:55, 1993 38. Illig KA, Swierzewski MJ, Feliciano DV, et al: A rational screening and treatment strategy based on electrocardiogram alone for suspected cardiac con&sion. Am J Surg 162:537, 1991 39. Jones JW, Hewitt RL, Dropanns T Cardiac contusion: A capricious syndrome. Ann Surg 181:567, 1975 40. Kamran A, Smith D, Bansal RC, et a1 Angiography in blunt thoracic aortic injury. J Trauma 42665,1997 41. Karaaslan T, Meuli R, Androux R, et al: Traumatic chest lesions in patients with severe head trauma: A comparative study with computed tomography and conventional chest roentgenograms. J Trauma 39:1081, 1995 42. Kearney PA, Smith DW, Johnson SB, et a1 PM. Use of transesophageal echocardiography in the evaluation of traumatic aortic injury. J Trauma 34:696, 1993 43. Keller KD, Shatney C H Creatine phosphokinase-MB assays in patients with suspected myocardial contusion: Diagnostic test or test of diagnosis. J Trauma 28:58, 1988 44. Kirsch MM, Behrendt DM, Orringer MB, et al: The treatment of acute traumatic rupture of the aorta: A 10-year experience. Ann Surg 184:308, 1976 45. Kram HB, Appel PL, Wohlmath DA, et al: Diagnosis of traumatic thoracic aortic rupture: A ten-year retrospective analysis. Ann Thorac Surg 47282, 1989 46. Krefft S: Cardiac injuries in aircraft occupations resulting from aircraft accidents. Aviat Space Environ Med 46:1395, 1975 47. Lee FT Jr, Katzberg RW, Gutierrez OH, et al: Reevaluation of plain radiographic findings in the diagnosis of aortic rupture: The role of inspiration and positioning on mediastinal width. J Emerg Med 11:289, 1993 48. Lee J, Harris JH, Duke JH, et al: Noncorrelation between thoracic skeletal injuries and acute traumatic aortic tear. J Trauma 43:400, 1997 49. LoCicero J, Mattox KL Epidemiology of chest trauma. Surg Clin North Am 69:15,1989 50. Mach F, Lovis C, Chevrolet J-C et al: Rapid whole blood cardiospecific troponin T immunoassay for the diagnosis of acute myocardial infarction. Am J Cardiol 75:842, 1995 51. Maenza RL, Seaberg D, DiAmico F A meta-analysis of blunt cardiac trauma: Ending myocardial confusion. Am J Emerg Med 14:237, 1996 52. Markovchick V, Wolfe R Cardiovascular trauma. In Rosen P, Barkin R, Danzl D, et a1 (eds): Emergency Medicine: Concepts and Clinical Practice, ed 4. St. Louis, Mosby-Year Book, 1998, p 527 53. Marnocha KE, Maglinte DDT Plain film criteria for excluding aortic rupture in blunt chest trauma. Am J Radio1 144:19, 1985 54. Marsh DG, Sturm JT Traumatic aortic rupture: Roentgenographic indications for angiography. Ann Thorac Surg 21:337, 1976 55. Marts B, Rodney D, Shapiro M, et al: Computed tomography in the diagnosis of blunt thoracic injury. Am J Surg 168:688, 1994 56. Mattox KL, Feliciano DV, Beall AC, et al: Five thousand seven hundred sixty cardiovascular injuries in 4459 patients: Epidemiologic evolution 1958-1988. Ann Surg 209:698, 1989 57. Mattox KL, Wall MJ: Injury to the thoracic great vessels. In Feliciano DV, Moore EE, Mattox KL (eds): Trauma, ed 3. Stamford, CT, Appleton & Lange, 1996, p 423 58. McLean TR, Olinger GN, Thorsen MK: Computed tomography in the evaluation of the aorta in patients sustaining blunt chest trauma. J Trauma 31:254, 1991 59. McLellan BA, Ali J, Towers MJ, et a1 Role of the trauma-room chest x-ray film in assessing the patient with severe blunt traumatic injury. Can J Surg 39:36, 1996 60. Merrill WH, Lee RB, Hammon JW Jr, et a1 Surgical treatment of acute traumatic tear of the thoracic aorta. AM Surg 206:699, 1988

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Address reprint requests to Myles D. Greenberg, MD Department of Emergency Medicine Beth Israel Deaconess Medical Center 330 Brookline Avenue UL 202 Boston, MA 02215