Best Evidence Topics


Paul D. Stein, M.D., et al.
Multidetector Computed Tomography for Acute Pulmonary Embolism
The New England Journal of Medicine
June 2006; 354:2317-2327
  • Submitted by:James Mlejnek - Medical Student
  • Institution:American University of the Caribbean
  • Date submitted:21st September 2007
Before CA, i rated this paper: 7/10
1 Objectives and hypotheses
1.1 Are the objectives of the study clearly stated?
  Yes- the purposes of this study were two-fold: to determine whether multidetector CTA can reliably detect and rule out acute pulmonary embolism and whether the addition of CTV improves the ability to detect and rule out pulmonary embolism.
2 Design
2.1 Is the study design suitable for the objectives
  Yes- it is a prospective, multicenter study designed to determine wheter multidetector CTA can reliably detect and rule out acute pulmonary embolism and wheter the addition of CTV improves the ability to detect and rule out pulmonary embolism.
2.2 Who / what was studied?
  Eight-hundred twenty-four patients who had clinically suspected acute pulmonary embolism at eight participating clinical centers underwent clincal assessment (including Well's Scoring) and multidetector CTA and CTV to diagnose or rule out acute pulmonary embolis. After completing these studies, the authors compared the diagnosis of acute pulmonary embolis by CTA and CTA-CTV with those patients that had a reference diagnostic study that also indicated acute pulmonary embolism or deep venous thrombosis.
2.3 Was this the right sample to answer the objectives?
  Yes- patients over 18 with clinically suspected acute pulmonary embolism. Although most of the patients were deemed to have a low or moderate probability of pulmonary embolism on the basis of the Wells
2.4 Is the study large enough to achieve its objectives? Have sample size estimates been performed?
  Large sample size but size estimates were not described
2.5 Were all subjects accounted for?
  Of the 1090 patients enrolled, 28 did not undergo CT and 238 did not receive a reference test diagnosis (Figure 1).
2.6 Were all appropriate outcomes considered?
  Yes, a composite reference test was used to confirm or rule out the diagnosis of pulmonary embolism.
2.7 Has ethical approval been obtained if appropriate?
2.8 Was an independent blinded gold standard test applied to all subjects?
  Yes- patients underwent reference diagnostic testing including ventilation-perfusion scanning, venous compression ultrasonography of the lower extremities, and if necessary, pulmonary digital-subtraction angiography to obtain a diagnosis of acute pulmonary embolism or deep venous thrombosis.
3 Measurement and observation
3.1 Is it clear what was measured, how it was measured and what the outcomes were?
  Yes (Tables 2-4)
3.2 Are the measurements valid?
  Yes- but there is potential for bias based on interpretation of the radiographic studies by two certified readers.
3.3 Are the measurements reliable?
  Yes- the same confidence intervals are used for all groups
3.4 Are the measurements reproducible?
4 Presentation of results
4.1 Are the basic data adequately described?
  Yes (Table 4)
4.2 Are the results presented clearly, objectively and in sufficient detail to enable readers to make their own judgement?
4.3 Are the results internally consistent, i.e. do the numbers add up properly?
5 Analysis
5.1 Are the data suitable for analysis?
5.2 Are the methods appropriate to the data?
5.3 Are any statistics correctly performed and interpreted?
  Yes, standard methods were used to calculate the sensitivity, specificity, and positive and negative predictive values. Patients for whom results on CTA or CTA–CTV were unclassified were excluded from these calculations.
In a separate analysis, values for the sensitivity and specificity of CTA were adjusted for possible inaccuracy of the composite reference standard
with the use of the lowest reported false positive and false negative rates for the tests that make up that standard.
6 Discussion
6.1 Are the results discussed in relation to existing knowledge on the subject and study objectives?
6.2 Is the discussion biased?
7 Interpretation
7.1 Are the authors' conclusions justified by the data?
  Yes- the sensitivity of CTA-CTV for diagnosis of pulmonary embolism is higher than that of CTA alone. The false negative rate for CTA alone is quite high and therefore a CTA negative for pulmonary embolism does not completely rule out pulmonary embolism. Further diagnostic testing to rule out pulmonary embolism is therefore indicated in a patient with intermediate or high clinical probability and a negative CTA.
7.2 What level of evidence has this paper presented? (using CEBM levels )
7.3 Does this paper help me answer my problem?
  Yes- CTA used alone for the diagnosis of pulmonary embolism will miss a small number of patients positive for pulmonary embolism. Therefore, this should be kept in mind when using CTA to diagnose pulmonary embolism in a patient with intermediate or high clinical suspicion.
After CA, i rated this paper: 8/10
8 Implementation
8.1 Can the test be implemented in practice?
8.2 What aids to implementation exist?
  Screening of these patients using clinical assessment is already implemented in most institutions. Access to CT scanners is easier than ever because they are more readily available and the newer generation scanners are less time consuming than in the past. Many facilities already perform CTA for patients suspected of having pulmonary embolism.
8.3 What barriers to implementation exist?
  Patients with comorbid diseases, such as renal insufficiency, that are suspected of having a pulmonary embolism may develop contrast induced nephropathy if not screened for pre-exisiting renal disease before receiving the contrast media.
8.4 Are my patients the same as the patients tested?
  Yes- these patients were all over the age of 18 and selected based on clinical suspicion of having a pulmonary embolism. These patients were selected from both inpatient and outpatient facilities.
8.5 Will the test improve diagnosis in my patients?
  Yes- When compared to the gold standard, pulmonary angiography, which is both invasive and time consuming, CTA with CTV is approaching a similar sensitivity and specificity while offering a rapid, non-invasive diagnostic tool that can be used to diagnose pulmonary embolism. Along with clinical suspicion of pulmonary embolis, CTA with CTV will help improve the rapid diagnosis of this life threatening condition and therefore allow treatment to be initiated in a timely fashion.