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Clinical Investigations: PULMONARY VASCULATURE |

Chest Radiographs in Acute Pulmonary Embolism*: Results From the International Cooperative Pulmonary Embolism Registry FREE TO VIEW

C. Gregory Elliott, MD, FCCP; Samuel Z. Goldhaber, MD, FCCP; Luigi Visani, MD; Marisa DeRosa, PhD
Author and Funding Information

*From the Department of Medicine (Dr. Elliott), the Pulmonary Divisions of the LDS Hospital and the University of Utah School of Medicine, Salt Lake City, UT; Cardiovascular Division (Dr. Goldhaber), Brigham and Women’s Hospital, Harvard Medical School, Boston, MA; HyperPhar Research (Dr. Visani), Milan, Italy; and CINECA (Dr. DeRosa), Bologna, Italy

Correspondence to: C. Gregory Elliott, MD, FCCP, Pulmonary Division, LDS Hospital, 8th Ave & C St, Salt Lake City, UT 84143; e-mail: ldgellio@ihc.com



Chest. 2000;118(1):33-38. doi:10.1378/chest.118.1.33
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Published online

Objectives: To characterize chest radiographic interpretations in a large population of patients who have received a diagnosis of acute pulmonary embolism and to estimate the sensitivity and specificity of chest radiographic abnormalities for right ventricular hypokinesis that has been diagnosed by echocardiography.

Design: A prospective observational study at 52 hospitals in seven countries.

Patients: A total of 2,454 consecutive patients who had received a diagnosis of acute pulmonary embolism between January 1995 and November 1996.

Results: Chest radiographs were available for 2,322 patients (95%). The most common chest radiographic interpretations were cardiac enlargement (27%), normal (24%), pleural effusion (23%), elevated hemidiaphragm (20%), pulmonary artery enlargement (19%), atelectasis (18%), and parenchymal pulmonary infiltrates (17%). The results of chest radiographs were abnormal for 509 of 655 patients (78%) who had undergone a major surgical procedure within 2 months of the diagnosis of pulmonary embolism: normal results for chest radiograph often accompanied pulmonary embolism after genitourinary procedures (37%), orthopedic surgery (29%), or gynecologic surgery (28%), whereas they rarely accompanied pulmonary emboli associated with thoracic procedures (4%). Chest radiographs were interpreted to show cardiac enlargement for 149 of 309 patients with right ventricular hypokinesis that was detected by echocardiography (sensitivity, 0.48) and for 178 of 485 patients without right ventricular hypokinesis (specificity, 0.63). Chest radiographs were interpreted to show pulmonary artery enlargement for 118 of 309 patients with right ventricular hypokinesis (sensitivity, 0.38) and for 117 of 483 patients without right ventricular hypokinesis (specificity, 0.76).

Conclusions: Cardiomegaly is the most common chest radiographic abnormality associated with acute pulmonary embolism. Neither pulmonary artery enlargement nor cardiomegaly appears sensitive or specific for the echocardiographic finding of right ventricular hypokinesis, an important predictor of mortality associated with acute pulmonary embolism.

The chest radiograph is a fundamental test for the evaluation of cardiopulmonary disease, and chest radiographic observations are integral to the clinician’s formulation of the probability that acute pulmonary embolism underlies cardiopulmonary symptoms.1 Chest radiographic interpretations influence both the decision to perform additional diagnostic tests for pulmonary embolism2and the likelihood that pulmonary embolism caused an abnormal lung scan pattern.3However, data that describe chest radiographic findings associated with the diagnosis of acute pulmonary embolism are limited because previous prospective studies involved relatively small numbers of patients45 or did not describe chest radiographic findings.6 Furthermore, no study has presented chest radiographic findings for important subgroups of patients with acute pulmonary embolism (eg, postoperative patients), and no study has described the relationship between echocardiographic evidence of right ventricular hypokinesis and chest radiographic abnormalities.

The International Cooperative Pulmonary Embolism Registry (ICOPER) prospectively enrolled 2,454 consecutive patients who had received a diagnosis of acute pulmonary embolism.7 The registry included patients with symptomatic and asymptomatic pulmonary embolism. It included patients who had received a diagnosis of pulmonary embolism based on current clinical practices using a variety of diagnostic tests (eg, pulmonary arteriography, ventilation and perfusion lung scans, compression ultrasonography of the lower extremities, and autopsy).

The purpose of the present study was to characterize chest radiographic interpretations in a large population of patients who have had acute pulmonary embolism. A secondary aim was to estimate the sensitivity and specificity of cardiomegaly or pulmonary artery enlargement that was detected by chest radiograph for the diagnosis of right ventricular hypokinesis and was confirmed by echocardiography.

The ICOPER investigators prospectively identified consecutive patients who had received a diagnosis of acute pulmonary embolism from January 1995 until November 1996 at 52 participating hospitals in seven countries. In order to be broadly representative, the registry did not restrict the criteria for the diagnosis of pulmonary embolism. Acute pulmonary embolism was defined as a diagnosis within 31 days of symptom onset. In order to characterize observations as they were made at the participating centers, the registry accepted the interpretations of imaging studies provided by physicians at the participating institutions.

The chest radiograph was first characterized as normal or abnormal. If it was characterized as abnormal, the investigators were asked to indicate the presence or absence of one or more of the following abnormalities: (1) pulmonary congestion; (2) pulmonary artery enlargement; (3) cardiac enlargement; (4) oligemia; (5) infiltrate; (6) elevated hemidiaphragm; (7) pulmonary infarction; (8) atelectasis; (9) pleural effusion; (10) overinflation; or (11) other abnormalities.

Patients

We registered 2,454 consecutive patients who had received a diagnosis of acute pulmonary embolism. Table 1 summarizes the methods by which the diagnosis of acute pulmonary embolism was confirmed.

Risk factors included the following: a body mass index of > 29 kg/m2 (29% of patients); major surgery within 2 months of diagnosis (29% of patients); bed rest for ≥ 5 days (28% of patients); prior venous thromboembolism (25% patients); cancer (23% of patients); current central venous catheter (8% of patients); and a known hypercoagulable state (5% of patients).

The majority of patients (89%) had symptoms of pulmonary embolism and were hemodynamically stable; 4% were hemodynamically unstable (systolic BP < 90 mm Hg), and 7% were asymptomatic. Principal symptoms included the following: dyspnea (82%); chest pain (49%); cough (20%); syncope (14%); and hemoptysis (7%). The mortality rate for all causes was 11.4% within 2 weeks after the pulmonary embolism was diagnosed, and 17.4% 3 months after the diagnosis.

Chest Radiographs

Chest radiographs were interpreted for 2,322 patients (95%). Five hundred sixty-three patients had normal results for chest radiographs (24%), and 1,759 patients (76%) had abnormal results. The most common abnormalities were cardiac enlargement, pleural effusion, elevated hemidiaphragm, pulmonary artery enlargement, atelectasis, and parenchymal pulmonary infiltrate (Table 2 ).

Chest radiographs were available for 39 of 61 patients for whom pulmonary embolism was not diagnosed until autopsy. Thirty-four of these 39 patients (87%) had abnormal results on chest radiographs. Pulmonary congestion, cardiac enlargement, and pleural effusions were the most common radiographic abnormalities in these patients (Table 3 ).

Chest radiographs were available for 659 of 700 patients (94%) who presented with isolated dyspnea, and the results of chest radiograph were normal for 156 patients (24%). Cardiomegaly (29%), elevated hemidiaphragm (19%), atelectasis (15%), and pulmonary artery enlargement (15%) were common abnormalities that were associated with isolated dyspnea. Chest radiographs were available for 364 of 401 patients (91%) who presented with syncope or hypotension. The chest radiograph result was normal for 93 of these patients (26%). Cardiomegaly (27% of patients), pulmonary artery enlargement (22% of patients), and elevated hemidiaphragm (19% of patients) were the most common abnormalities when patients with acute pulmonary embolism presented with syncope or hypotension.

Chest radiographs were available for 655 of 708 patients (92%) who had undergone major surgery within 2 months of the diagnosis of acute pulmonary embolism. The results of chest radiographs were normal for 146 of these patients (22%). The results of chest radiographs were normal for 16 of 43 patients (37%) who had undergone genitourinary procedures, for 67 of 232 patients (29%) who had undergone orthopedic procedures, and for 13 of 46 patients (28%) who had undergone gynecologic procedures; the results of chest radiographs were normal for only 21 of 133 patients (16%) who had undergone general abdominal surgical procedures and for 3 of 73 patients (4%) who had undergone thoracic surgical procedures.

The most common radiographic abnormality for patients who had received a diagnosis of acute pulmonary embolism after orthopedic surgery was an elevated hemidiaphragm (59 of 232 patients [25%]). Pleural effusions were identified less frequently in these patients (43 of 232 patients[ 19%]). In contrast, pleural effusion (44 of 133 patients [33%]), elevated hemidiaphragm (39 of 133 patients [29%]), and atelectasis (35 of 133 patients [26%]) were common chest radiographic abnormalities that were associated with acute pulmonary embolism after abdominal surgical procedures.

The results of chest radiographs were available for 171 of 183 patients (93%) who had a central venous catheter that was associated with acute pulmonary embolism. The results of chest radiographs were abnormal for 140 of these patients (82%). Common abnormalities included pleural effusion (57 of 171 patients [33%]), cardiac enlargement (49 of 171 patients [29%]), and pulmonary artery enlargement (46 of 171 patients [27%]).

Chest radiographs were available for 1,084 of 1,135 patients (96%) who underwent echocardiography. The finding of cardiomegaly on the chest radiograph appeared neither sensitive (estimated sensitivity, 0.48) nor specific (estimated specificity, 0.63) for the echocardiographic diagnosis of right ventricular hypokinesis that is associated with acute pulmonary embolism (Table 4 ). Similarly, the finding of pulmonary artery enlargement appeared neither sensitive (estimated sensitivity, 0.38) nor specific (estimated specificity, 0.76) for the echocardiographic diagnosis of right ventricular hypokinesis (Table 5 ).

Patients who were > 70 years of age were more likely to have an abnormal chest radiograph than those who were < 70 years of age (Table 6 ). Cardiomegaly and pulmonary congestion were more common in patients who were > 70 years of age with acute pulmonary embolism.

The ICOPER provides a unique perspective for reexamination of the chest radiographic findings in patients with acute pulmonary embolism, as well as an opportunity to evaluate chest radiographs from important subgroups of patients.

The ICOPER database confirms and extends previous observations of chest radiographic findings that are associated with acute pulmonary embolism. Patients with acute pulmonary embolism are likely to have an abnormal chest radiograph, as others have reported.45 The findings from the ICOPER database suggest that cardiomegaly is the most common chest radiographic abnormality that is associated with acute pulmonary embolism, whereas diaphragm elevation was the most common abnormality for 128 patients who were studied in the urokinase pulmonary embolism trial,5 and atelectasis was the most common abnormality described among 117 patients without prior cardiopulmonary disease who were enrolled in the prospective investigation of pulmonary embolism diagnosis.4

The differences between the present study and prior work likely represent differences in patient selection. The present study offers a broad view of the chest radiographic interpretations for patients diagnosed with acute pulmonary embolism. Unlike the study of Stein et al,4 the present study did not attempt to isolate chest radiographic abnormalities that may be unique to pulmonary embolism by eliminating patients with prior cardiopulmonary disease. The present study included all patients who were diagnosed with acute pulmonary embolism. Our observation that cardiomegaly was the most common chest radiographic abnormality associated with acute pulmonary embolism may reflect the propensity of acute pulmonary embolism to occur in the setting of underlying cardiac disease.

The ICOPER database provides the first description of chest radiographic abnormalities associated with acute pulmonary embolism after specific surgical procedures. Not surprisingly, the chest radiograph is usually abnormal when acute pulmonary embolism follows thoracic or general abdominal surgical procedures. In contrast, the ICOPER data suggest that the chest radiograph is normal in at least 25% of patients when acute pulmonary embolism follows orthopedic, gynecologic, or genitourinary surgical procedures. We observed certain chest radiographic abnormalities more often when acute pulmonary embolism followed certain surgical procedures (eg, pleural effusion and general abdominal surgery [33%]) than other procedures (eg, pleural effusion and orthopedic surgery [19%]). These differences may reflect the incidence of common radiographic abnormalities after specific surgical procedures, rather than different chest radiographic abnormalities caused by pulmonary embolism.

Previous investigators have drawn attention to the following three presenting syndromes of acute pulmonary embolism: (1) pulmonary infarction; (2) isolated dyspnea; and (3) circulatory collapse.9 The ICOPER registry also provided an opportunity to describe chest radiographic observations for a large number of patients who presented with pulmonary embolism and either isolated dyspnea or circulatory collapse. Cardiac enlargement was the most common abnormality associated with both of these clinical syndromes. Normal chest radiographs were found with equal frequency in patients with isolated dyspnea and in those with circulatory collapse. Only enlargement of the pulmonary artery was detected more often when circulatory collapse accompanied acute pulmonary embolism (22%) than when pulmonary embolism presented with the syndrome of isolated dyspnea (15%).

The results of a previous study found that chest radiographic abnormalities occurred with similar frequencies among all age groups with acute pulmonary embolism.10 However, the ICOPER data suggest that patients who are < 70 years of age are more likely to have a normal chest radiograph, and that cardiomegaly and pulmonary congestion are more likely to accompany acute pulmonary embolism in elderly patients. This observation may reflect an increased prevalence of chronic cardiac disease among patients aged > 70 years.

Unsuspected or undiagnosed pulmonary embolism, first recognized at autopsy, remains an important problem.1114 Two studies suggest that undiagnosed acute pulmonary embolism contributes to the death of approximately 5% of patients who undergo autopsies.1213 Morgenthaler and Ryu12 reported that typical symptoms and signs of acute pulmonary embolism do not identify such patients, in part because these patients are often unable to communicate. Chest radiographic abnormalities may provide a clue to diagnosis for such patients, but investigators have not described premortem chest radiographic findings when pulmonary emboli were first recognized postmortem. The ICOPER registry data suggest that patients in whom fatal pulmonary embolism is not diagnosed antemortem are more likely to have cardiomegaly, pulmonary congestion, and pleural effusions recognized on chest radiographs than other radiographic abnormalities.

Right ventricular hypokinesis, detected by echocardiography, is an important predictor of mortality that is associated with acute pulmonary embolism.7 An interpretation of enlarged central pulmonary artery or cardiomegaly on a chest radiograph is associated with increased mean pulmonary artery pressure.15However, the ICOPER data suggest that neither cardiomegaly nor pulmonary artery enlargement are sensitive or specific predictors of right ventricular hypokinesis. Our estimates of sensitivity and specificity are subject to bias because not all patients underwent echocardiography. However, the bias introduced by this methodology usually inflates estimates of sensitivity and specificity.16 Thus, our estimates are likely to overestimate the sensitivity and specificity of cardiomegaly and pulmonary artery enlargement for the detection of right ventricular hypokinesis, and our conclusions remain unaltered.

A major limitation of the present study is the absence of predefined criteria for the radiographic interpretations. The data represent unstandardized interpretations by numerous observers, and our results might have differed if specific criteria had been standardized for use by all investigators. Despite this limitation, our data provide a unique description of radiographic interpretations for a large population of patients diagnosed with acute pulmonary embolism. Intraobserver variability occurs with chest radiograph interpretations, and readers must recognize that our data may not apply to their clinical setting because of differences in chest radiographic interpretation.

In summary, the ICOPER database suggests that cardiomegaly is the most common chest radiographic abnormality associated with acute pulmonary embolism. Chest radiographic findings of cardiomegaly, pleural effusion, and pulmonary congestion may provide clues to unrecognized pulmonary emboli that contribute to death. Furthermore, neither chest radiographic findings of cardiomegaly nor pulmonary artery enlargement appear to be sensitive or specific clues to the presence of right ventricular hypokinesis in the setting of acute pulmonary embolism.

Abbreviation: ICOPER = International Cooperative Pulmonary Embolism Registry

Table Graphic Jump Location
Table 1. Methods Used to Diagnose Acute Pulmonary Embolism for 2,454 Patients*
* 

HPVQ = high-probability ventilation and perfusion lung scan; HPQ = high-probability perfusion lung scan (2); PA = pulmonary arteriogram; NVQ-DVT = nondiagnostic ventilation and perfusion lung scan and deep vein thrombosis confirmed by compression ultrasonography.

Table Graphic Jump Location
Table 2. Chest Radiographic Abnormalities Associated With Acute Pulmonary Embolism*
* 

See Table 1 for abbreviation.

Table Graphic Jump Location
Table 3. Chest Radiographic Interpretations for 39 Patients With Fatal Pulmonary Emboli Not Diagnosed Antemortem*
* 

CI = confidence interval. See Table 1 for other abbreviation.

Table Graphic Jump Location
Table 4. The Relationship Between Cardiac Enlargement Identified by Chest Radiograph and Right Ventricular Hypokinesis Identified by Echocardiography*
* 

Values given as No. of patients. RV = right ventricular hypokinesis. Method for determination of RV adapted from Goldhaber et al.8

 

Estimated sensitivity, 48% (95% CI, 42 to 54%); estimated specificity, 63% (95% CI, 59 to 67%); estimated positive predictive value, 46% (95% CI, 40 to 51%); estimated negative predictive value, 66% (95% CI, 61 to 70%).

Table Graphic Jump Location
Table 5. The Relationship Between Pulmonary Artery Enlargement Identified by Chest Radiograph and Right Ventricular Hypokinesis Identified by Echocardiography*
* 

Values given as No. of patients. See Tables 1 and 3 for abbreviations.

 

Estimated sensitivity, 38% (95% CI, 33 to 44%); estimated specificity, 76% (95% CI, 72 to 79%); estimated positive predictive value, 50% (95% CI, 43 to 56%); estimated negative predictive value, 66% (95% CI, 61 to 70%).

Table Graphic Jump Location
Table 6. Chest Radiograph Interpretations for Patients > 70 and ≤ 70 Years of Age*
* 

Values given as No. of patients (%), unless otherwise indicated.

Wells, PS, Ginsberg, JS, Anderson,, et al (1998) Use of a clinical model for safe management of patients with suspected pulmonary embolism.Ann Intern Med129,997-1005. [PubMed]
 
Miniati, M, Pistolesi, M, Marini, C, et al Value of perfusion lung scan in the diagnosis of pulmonary embolism: results of the prospective investigative study of pulmonary embolism diagnosis (PISA-PED).Am J Respir Crit Care Med1996;154,1387-1393. [PubMed]
 
Prospective Investigation of Pulmonary Embolism Diagnosis.. Value of the ventilation/perfusion scan in acute pulmonary embolism: results of the Prospective Investigation of Pulmonary Embolism Diagnosis (PIOPED).JAMA1990;263,2753-2759. [CrossRef] [PubMed]
 
Stein, PD, Terrin, ML, Hales, CA, et al Clinical, laboratory, roentgenographic and electrocardiographic findings in patients with acute pulmonary embolism and no pre-existing cardiac or pulmonary disease.Chest1991;100,598-601. [CrossRef] [PubMed]
 
Sasahara, AA, Hyers, TM, Cole, CM The urokinase pulmonary embolism trial: a national comparative study.Circulation1973;47(suppl),1-108
 
Hull, RD, Hirsh, J, Carter, CJ, et al Pulmonary angiography, ventilation lung scanning, and venography for clinically suspected pulmonary embolism with abnormal perfusion lung scan.Ann Intern Med1983;98,891-899. [PubMed]
 
Goldhaber, SZ, Visani, L, DeRosa, M Acute pulmonary embolism: clinical outcomes in the international cooperative pulmonary embolism registry (ICOPER).Lancet1999;353,386-389. [CrossRef] [PubMed]
 
Goldhaber, SZ, Haire, WD, Feldstein, ML, et al Alteplase versus heparin in acute pulmonary embolism: randomized trial assessing right-ventricular function and pulmonary perfusion.Lancet1993;341,507-511. [CrossRef] [PubMed]
 
Stein, PD, Henry, JW Clinical characteristics of patients with acute pulmonary embolism stratified according to their presenting syndromes.Chest1997;12,974-979
 
Stein, PD, Gottschalk, A, Saltzman, HA, et al Diagnosis of acute pulmonary embolism in the elderly.J Am Coll Cardiol1991;18,1452-1457. [CrossRef] [PubMed]
 
Patriquin, L, Khorasani, R, Polak, JF Correlation of diagnostic imaging and subsequent autopsy findings in patients with pulmonary embolism.AJR Am J Roentgenol1998;171,347-349. [PubMed]
 
Morgenthaler, TI, Ryu, JH Clinical characteristics of fatal pulmonary embolism in a referral hospital.Mayo Clin Proc1995;70,417-424. [CrossRef] [PubMed]
 
Stein, PD, Henry, JW Prevalence of acute pulmonary embolism among patients in a general hospital and at autopsy.Chest1995;108,978-981. [CrossRef] [PubMed]
 
Ryu, JH, Olson, EJ, Pellikka, PA Clinical recognition of pulmonary embolism: problem of unrecognized and asymptomatic cases.Mayo Clin Proc1998;73,873-879. [CrossRef] [PubMed]
 
Stein, PD, Athanasoulis, C, Greenspan, RH, et al Relation of plain chest radiographic findings to pulmonary arterial pressure and arterial blood oxygen levels in patients with acute pulmonary embolism.Am J Cardiol1992;69,394-396. [CrossRef] [PubMed]
 
Begg, CB Biases in the assessment of diagnostic tests.Stat Med1987;6,411-423. [CrossRef] [PubMed]
 

Figures

Tables

Table Graphic Jump Location
Table 1. Methods Used to Diagnose Acute Pulmonary Embolism for 2,454 Patients*
* 

HPVQ = high-probability ventilation and perfusion lung scan; HPQ = high-probability perfusion lung scan (2); PA = pulmonary arteriogram; NVQ-DVT = nondiagnostic ventilation and perfusion lung scan and deep vein thrombosis confirmed by compression ultrasonography.

Table Graphic Jump Location
Table 2. Chest Radiographic Abnormalities Associated With Acute Pulmonary Embolism*
* 

See Table 1 for abbreviation.

Table Graphic Jump Location
Table 3. Chest Radiographic Interpretations for 39 Patients With Fatal Pulmonary Emboli Not Diagnosed Antemortem*
* 

CI = confidence interval. See Table 1 for other abbreviation.

Table Graphic Jump Location
Table 4. The Relationship Between Cardiac Enlargement Identified by Chest Radiograph and Right Ventricular Hypokinesis Identified by Echocardiography*
* 

Values given as No. of patients. RV = right ventricular hypokinesis. Method for determination of RV adapted from Goldhaber et al.8

 

Estimated sensitivity, 48% (95% CI, 42 to 54%); estimated specificity, 63% (95% CI, 59 to 67%); estimated positive predictive value, 46% (95% CI, 40 to 51%); estimated negative predictive value, 66% (95% CI, 61 to 70%).

Table Graphic Jump Location
Table 5. The Relationship Between Pulmonary Artery Enlargement Identified by Chest Radiograph and Right Ventricular Hypokinesis Identified by Echocardiography*
* 

Values given as No. of patients. See Tables 1 and 3 for abbreviations.

 

Estimated sensitivity, 38% (95% CI, 33 to 44%); estimated specificity, 76% (95% CI, 72 to 79%); estimated positive predictive value, 50% (95% CI, 43 to 56%); estimated negative predictive value, 66% (95% CI, 61 to 70%).

Table Graphic Jump Location
Table 6. Chest Radiograph Interpretations for Patients > 70 and ≤ 70 Years of Age*
* 

Values given as No. of patients (%), unless otherwise indicated.

References

Wells, PS, Ginsberg, JS, Anderson,, et al (1998) Use of a clinical model for safe management of patients with suspected pulmonary embolism.Ann Intern Med129,997-1005. [PubMed]
 
Miniati, M, Pistolesi, M, Marini, C, et al Value of perfusion lung scan in the diagnosis of pulmonary embolism: results of the prospective investigative study of pulmonary embolism diagnosis (PISA-PED).Am J Respir Crit Care Med1996;154,1387-1393. [PubMed]
 
Prospective Investigation of Pulmonary Embolism Diagnosis.. Value of the ventilation/perfusion scan in acute pulmonary embolism: results of the Prospective Investigation of Pulmonary Embolism Diagnosis (PIOPED).JAMA1990;263,2753-2759. [CrossRef] [PubMed]
 
Stein, PD, Terrin, ML, Hales, CA, et al Clinical, laboratory, roentgenographic and electrocardiographic findings in patients with acute pulmonary embolism and no pre-existing cardiac or pulmonary disease.Chest1991;100,598-601. [CrossRef] [PubMed]
 
Sasahara, AA, Hyers, TM, Cole, CM The urokinase pulmonary embolism trial: a national comparative study.Circulation1973;47(suppl),1-108
 
Hull, RD, Hirsh, J, Carter, CJ, et al Pulmonary angiography, ventilation lung scanning, and venography for clinically suspected pulmonary embolism with abnormal perfusion lung scan.Ann Intern Med1983;98,891-899. [PubMed]
 
Goldhaber, SZ, Visani, L, DeRosa, M Acute pulmonary embolism: clinical outcomes in the international cooperative pulmonary embolism registry (ICOPER).Lancet1999;353,386-389. [CrossRef] [PubMed]
 
Goldhaber, SZ, Haire, WD, Feldstein, ML, et al Alteplase versus heparin in acute pulmonary embolism: randomized trial assessing right-ventricular function and pulmonary perfusion.Lancet1993;341,507-511. [CrossRef] [PubMed]
 
Stein, PD, Henry, JW Clinical characteristics of patients with acute pulmonary embolism stratified according to their presenting syndromes.Chest1997;12,974-979
 
Stein, PD, Gottschalk, A, Saltzman, HA, et al Diagnosis of acute pulmonary embolism in the elderly.J Am Coll Cardiol1991;18,1452-1457. [CrossRef] [PubMed]
 
Patriquin, L, Khorasani, R, Polak, JF Correlation of diagnostic imaging and subsequent autopsy findings in patients with pulmonary embolism.AJR Am J Roentgenol1998;171,347-349. [PubMed]
 
Morgenthaler, TI, Ryu, JH Clinical characteristics of fatal pulmonary embolism in a referral hospital.Mayo Clin Proc1995;70,417-424. [CrossRef] [PubMed]
 
Stein, PD, Henry, JW Prevalence of acute pulmonary embolism among patients in a general hospital and at autopsy.Chest1995;108,978-981. [CrossRef] [PubMed]
 
Ryu, JH, Olson, EJ, Pellikka, PA Clinical recognition of pulmonary embolism: problem of unrecognized and asymptomatic cases.Mayo Clin Proc1998;73,873-879. [CrossRef] [PubMed]
 
Stein, PD, Athanasoulis, C, Greenspan, RH, et al Relation of plain chest radiographic findings to pulmonary arterial pressure and arterial blood oxygen levels in patients with acute pulmonary embolism.Am J Cardiol1992;69,394-396. [CrossRef] [PubMed]
 
Begg, CB Biases in the assessment of diagnostic tests.Stat Med1987;6,411-423. [CrossRef] [PubMed]
 
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