Suspected Pulmonary Embolism
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《新英格兰医药杂志》
To the Editor: In their Clinical Practice article on suspected pulmonary embolism, Fedullo and Tapson (Sept. 25 issue)1 state that a positive computed tomographic (CT) angiogram in patients with a low clinical probability of pulmonary embolism confirms the diagnosis. Although probably consistent with current practice, this recommendation is not supported by Bayesian analysis.
The authors define a low clinical probability of pulmonary embolism as a prevalence of 5 to 10 percent. Even if CT angiography is assumed to have a sensitivity and a specificity of 95 percent (which is much higher than many published estimates2,3), with a positive CT angiogram, the post-test probability is only 50 to 68 percent. This is at least 20 percent lower than the recommended threshold for anticoagulation for venous thromboembolism.4 Since 25 to 65 percent of patients with suspected pulmonary embolism have a low clinical probability of embolism,1 relying solely on the CT angiogram, as the authors recommend, will result in many false positive diagnoses.
Sumant R. Ranji, M.D.
Kaveh G. Shojania, M.D.
University of California, San Francisco
San Francisco, CA 94143
sumantr@medicine.ucsf.edu
References
Fedullo PF, Tapson VF. The evaluation of suspected pulmonary embolism. N Engl J Med 2003;349:1247-1256.
Perrier A, Howarth N, Didier D, et al. Performance of helical computed tomography in unselected outpatients with suspected pulmonary embolism. Ann Intern Med 2001;135:88-97.
Rathbun SW, Raskob GE, Whitsett TL. Sensitivity and specificity of helical computed tomography in the diagnosis of pulmonary embolism: a systematic review. Ann Intern Med 2000;132:227-232.
Stein PD, Hull RD, Saltzman HA, Pineo G. Strategy for diagnosis of patients with suspected acute pulmonary embolism. Chest 1993;103:1553-1559.
To the Editor: In the article by Fedullo and Tapson, we were surprised by the lack of emphasis on the role of echocardiography. In contrast, a previous review in the Journal suggested that in critically ill patients with suspected pulmonary embolism, transthoracic echocardiography is particularly useful for identifying right ventricular pressure overload and myocardial infarction, aortic dissection, or pericardial tamponade, which may mimic pulmonary embolism.1 Furthermore, transthoracic echocardiography can be used to quantify pulmonary-artery pressures and assess right ventricular function, thereby allowing for rapid initiation of appropriate therapeutic interventions.2 Moreover, echocardiography may provide indirect evidence of pulmonary embolism by demonstrating a specific pattern of right ventricular dysfunction characterized by free-wall hypokinesis with apical sparing, a finding that is useful in differentiating pulmonary embolism from other causes of right ventricular dysfunction.3 Finally, echocardiography can be used to visualize massive pulmonary embolism directly in many patients.4 Therefore, we believe that echocardiography is a practical and readily available diagnostic tool that should be considered in the evaluation of patients with suspected pulmonary embolism.
Peter Rosenberger, M.D.
Stanton K. Shernan, M.D.
Harvard Medical School
Boston, MA 02115
Holger K. Eltzschig, M.D.
University Clinic for Anesthesiology and Intensive Care Medicine
D-72076 Tübingen, Germany
heltzschig@partners.org
References
Goldhaber SZ. Pulmonary embolism. N Engl J Med 1998;339:93-104.
Goldhaber SZ. Thrombolysis for pulmonary embolism. N Engl J Med 2002;347:1131-1132.
McConnell MV, Solomon SD, Rayan ME, Come PC, Goldhaber SZ, Lee RT. Regional right ventricular dysfunction detected by echocardiography in acute pulmonary embolism. Am J Cardiol 1996;78:469-473.
The diagnostic approach to acute venous thromboembolism: clinical practice guideline. Am J Respir Crit Care Med 1999;160:1043-1066.
To the Editor: In the article by Fedullo and Tapson, I was struck by the discrepancy between the proposed strategy and the final recommendation concerning the case vignette and the role of pulmonary angiography, which in my opinion seems to reflect a central problem in the evaluation of patients with suspected pulmonary embolism. In the diagnostic approach to a patient with an intermediate clinical probability of embolism, the authors recommend proceeding to pulmonary angiography if the results on CT scanning and duplex ultrasonography are negative, in order to reach a definite diagnosis (Figure 4 of the article). Adherence to this recommendation would lead to a high number of pulmonary angiograms, much higher than the number in daily clinical practice and also in our hospital. My impression of not always having implemented an adequate diagnostic approach myself was somewhat attenuated when I read the conclusion with respect to the case vignette, since Fedullo and Tapson seem to rule out pulmonary embolism on the basis of a negative CT scan combined with negative findings on duplex ultrasonography, without recommending pulmonary angiography.
Hannes Gaenzer
Bezirkskrankenhaus Hall
6060 Hall, Austria
hannes.gaenzer@uibk.ac.at
The authors reply: Although Ranji and Shojania are correct in their analysis, the published sensitivity and specificity of CT scanning involves an average of results derived from all vascular segments, as well as from a wide range of CT techniques. What remains inexactly defined in CT interpretive strategies is a precise definition of "positivity." It is our belief that CT positivity should be defined by compatible abnormalities involving only the main, lobar, and segmental pulmonary arteries. With the use of this criterion, the sensitivity approaches 98 percent, and the post-test probability falls within the range that warrants anticoagulation even in patients with a low clinical probability of embolism.1 Conventional pulmonary angiography should be reserved for patients in whom the estimated clinical probability diverges so substantially from the results of objective testing that the risk associated with that intervention is warranted.
We agree with Rosenberger and colleagues that echocardiography is capable of suggesting the diagnosis of embolism and of excluding certain competing diagnostic possibilities. Echocardiography may also have an important role in risk-stratification approaches. In terms of a diagnosis of embolism, however, the sensitivity of echocardiography has been reported to be approximately 50 percent.2,3 Furthermore, diagnostic criteria such as increased pulmonary-artery pressure, right ventricular dilatation, or both may be the consequence of a range of nonembolic clinical conditions (hypoxemia, sepsis, or acute lung injury) in critically ill patients. Given the availability of diagnostic techniques with a higher sensitivity and specificity, echocardiography should not be considered a primary diagnostic technique except when a patient with suspected massive embolism and an unstable condition cannot undergo another imaging study.
Gaenzer is correct in his perception of the discrepancy in our review, one that reflects residual uncertainties in the diagnostic approach to embolism. In a recent multicenter outcome study that used an empirical prediction rule, outpatients with a low or intermediate clinical probability of pulmonary embolism and with negative findings on spiral CT and compression ultrasonography had a rate of venous thromboembolic events of 0.8 percent at three months; however, the corresponding rate in inpatients was 4.8 percent.4 Exclusion of the possibility of embolism in the otherwise healthy outpatient discussed in our vignette was appropriate on the basis of the negative findings on spiral CT and compression ultrasonography, whereas conventional angiography might have been appropriate if the case had involved an inpatient with confounding medical problems. We again wish to emphasize that clinical prediction rules and diagnostic algorithms should be considered guidelines that complement rather than supplant informed clinical judgment, and that caution is needed when data derived from an outpatient population are applied to an inpatient setting.
Peter F. Fedullo, M.D.
University of California, San Diego
La Jolla, CA 92037
Victor F. Tapson, M.D.
Duke University Medical Center
Durham, NC 27710
References
Qanadli SD, Hajjam ME, Mesurolle B, et al. Pulmonary embolism detection: prospective evaluation of dual-section helical CT versus selective pulmonary arteriography in 157 patients. Radiology 2000;217:447-455.
Miniati M, Monti S, Pratali L, et al. Value of transthoracic echocardiography in the diagnosis of pulmonary embolism: results of a prospective study in unselected patients. Am J Med 2001;110:528-535.
Perrier A, Tamm C, Unger PF, Lerch R, Sztajzel J. Diagnostic accuracy of Doppler-echocardiography in unselected patients with suspected pulmonary embolism. Int J Cardiol 1998;65:101-109.
Musset D, Parent F, Meyer G, et al. Diagnostic strategy for patients with suspected pulmonary embolism: a prospective multicentre outcome study. Lancet 2002;360:1914-1920.
The authors define a low clinical probability of pulmonary embolism as a prevalence of 5 to 10 percent. Even if CT angiography is assumed to have a sensitivity and a specificity of 95 percent (which is much higher than many published estimates2,3), with a positive CT angiogram, the post-test probability is only 50 to 68 percent. This is at least 20 percent lower than the recommended threshold for anticoagulation for venous thromboembolism.4 Since 25 to 65 percent of patients with suspected pulmonary embolism have a low clinical probability of embolism,1 relying solely on the CT angiogram, as the authors recommend, will result in many false positive diagnoses.
Sumant R. Ranji, M.D.
Kaveh G. Shojania, M.D.
University of California, San Francisco
San Francisco, CA 94143
sumantr@medicine.ucsf.edu
References
Fedullo PF, Tapson VF. The evaluation of suspected pulmonary embolism. N Engl J Med 2003;349:1247-1256.
Perrier A, Howarth N, Didier D, et al. Performance of helical computed tomography in unselected outpatients with suspected pulmonary embolism. Ann Intern Med 2001;135:88-97.
Rathbun SW, Raskob GE, Whitsett TL. Sensitivity and specificity of helical computed tomography in the diagnosis of pulmonary embolism: a systematic review. Ann Intern Med 2000;132:227-232.
Stein PD, Hull RD, Saltzman HA, Pineo G. Strategy for diagnosis of patients with suspected acute pulmonary embolism. Chest 1993;103:1553-1559.
To the Editor: In the article by Fedullo and Tapson, we were surprised by the lack of emphasis on the role of echocardiography. In contrast, a previous review in the Journal suggested that in critically ill patients with suspected pulmonary embolism, transthoracic echocardiography is particularly useful for identifying right ventricular pressure overload and myocardial infarction, aortic dissection, or pericardial tamponade, which may mimic pulmonary embolism.1 Furthermore, transthoracic echocardiography can be used to quantify pulmonary-artery pressures and assess right ventricular function, thereby allowing for rapid initiation of appropriate therapeutic interventions.2 Moreover, echocardiography may provide indirect evidence of pulmonary embolism by demonstrating a specific pattern of right ventricular dysfunction characterized by free-wall hypokinesis with apical sparing, a finding that is useful in differentiating pulmonary embolism from other causes of right ventricular dysfunction.3 Finally, echocardiography can be used to visualize massive pulmonary embolism directly in many patients.4 Therefore, we believe that echocardiography is a practical and readily available diagnostic tool that should be considered in the evaluation of patients with suspected pulmonary embolism.
Peter Rosenberger, M.D.
Stanton K. Shernan, M.D.
Harvard Medical School
Boston, MA 02115
Holger K. Eltzschig, M.D.
University Clinic for Anesthesiology and Intensive Care Medicine
D-72076 Tübingen, Germany
heltzschig@partners.org
References
Goldhaber SZ. Pulmonary embolism. N Engl J Med 1998;339:93-104.
Goldhaber SZ. Thrombolysis for pulmonary embolism. N Engl J Med 2002;347:1131-1132.
McConnell MV, Solomon SD, Rayan ME, Come PC, Goldhaber SZ, Lee RT. Regional right ventricular dysfunction detected by echocardiography in acute pulmonary embolism. Am J Cardiol 1996;78:469-473.
The diagnostic approach to acute venous thromboembolism: clinical practice guideline. Am J Respir Crit Care Med 1999;160:1043-1066.
To the Editor: In the article by Fedullo and Tapson, I was struck by the discrepancy between the proposed strategy and the final recommendation concerning the case vignette and the role of pulmonary angiography, which in my opinion seems to reflect a central problem in the evaluation of patients with suspected pulmonary embolism. In the diagnostic approach to a patient with an intermediate clinical probability of embolism, the authors recommend proceeding to pulmonary angiography if the results on CT scanning and duplex ultrasonography are negative, in order to reach a definite diagnosis (Figure 4 of the article). Adherence to this recommendation would lead to a high number of pulmonary angiograms, much higher than the number in daily clinical practice and also in our hospital. My impression of not always having implemented an adequate diagnostic approach myself was somewhat attenuated when I read the conclusion with respect to the case vignette, since Fedullo and Tapson seem to rule out pulmonary embolism on the basis of a negative CT scan combined with negative findings on duplex ultrasonography, without recommending pulmonary angiography.
Hannes Gaenzer
Bezirkskrankenhaus Hall
6060 Hall, Austria
hannes.gaenzer@uibk.ac.at
The authors reply: Although Ranji and Shojania are correct in their analysis, the published sensitivity and specificity of CT scanning involves an average of results derived from all vascular segments, as well as from a wide range of CT techniques. What remains inexactly defined in CT interpretive strategies is a precise definition of "positivity." It is our belief that CT positivity should be defined by compatible abnormalities involving only the main, lobar, and segmental pulmonary arteries. With the use of this criterion, the sensitivity approaches 98 percent, and the post-test probability falls within the range that warrants anticoagulation even in patients with a low clinical probability of embolism.1 Conventional pulmonary angiography should be reserved for patients in whom the estimated clinical probability diverges so substantially from the results of objective testing that the risk associated with that intervention is warranted.
We agree with Rosenberger and colleagues that echocardiography is capable of suggesting the diagnosis of embolism and of excluding certain competing diagnostic possibilities. Echocardiography may also have an important role in risk-stratification approaches. In terms of a diagnosis of embolism, however, the sensitivity of echocardiography has been reported to be approximately 50 percent.2,3 Furthermore, diagnostic criteria such as increased pulmonary-artery pressure, right ventricular dilatation, or both may be the consequence of a range of nonembolic clinical conditions (hypoxemia, sepsis, or acute lung injury) in critically ill patients. Given the availability of diagnostic techniques with a higher sensitivity and specificity, echocardiography should not be considered a primary diagnostic technique except when a patient with suspected massive embolism and an unstable condition cannot undergo another imaging study.
Gaenzer is correct in his perception of the discrepancy in our review, one that reflects residual uncertainties in the diagnostic approach to embolism. In a recent multicenter outcome study that used an empirical prediction rule, outpatients with a low or intermediate clinical probability of pulmonary embolism and with negative findings on spiral CT and compression ultrasonography had a rate of venous thromboembolic events of 0.8 percent at three months; however, the corresponding rate in inpatients was 4.8 percent.4 Exclusion of the possibility of embolism in the otherwise healthy outpatient discussed in our vignette was appropriate on the basis of the negative findings on spiral CT and compression ultrasonography, whereas conventional angiography might have been appropriate if the case had involved an inpatient with confounding medical problems. We again wish to emphasize that clinical prediction rules and diagnostic algorithms should be considered guidelines that complement rather than supplant informed clinical judgment, and that caution is needed when data derived from an outpatient population are applied to an inpatient setting.
Peter F. Fedullo, M.D.
University of California, San Diego
La Jolla, CA 92037
Victor F. Tapson, M.D.
Duke University Medical Center
Durham, NC 27710
References
Qanadli SD, Hajjam ME, Mesurolle B, et al. Pulmonary embolism detection: prospective evaluation of dual-section helical CT versus selective pulmonary arteriography in 157 patients. Radiology 2000;217:447-455.
Miniati M, Monti S, Pratali L, et al. Value of transthoracic echocardiography in the diagnosis of pulmonary embolism: results of a prospective study in unselected patients. Am J Med 2001;110:528-535.
Perrier A, Tamm C, Unger PF, Lerch R, Sztajzel J. Diagnostic accuracy of Doppler-echocardiography in unselected patients with suspected pulmonary embolism. Int J Cardiol 1998;65:101-109.
Musset D, Parent F, Meyer G, et al. Diagnostic strategy for patients with suspected pulmonary embolism: a prospective multicentre outcome study. Lancet 2002;360:1914-1920.