CRD summary

This review concluded that multidetector computed tomography pulmonary angiography (CTPA) may increase the proportion of patients diagnosed with subsegmental pulmonary embolism without lowering the three-month risk of thromboembolism, which suggested that subsegmental pulmonary embolism may not be clinically relevant. These conclusions were appropriately cautious given substantial between-study heterogeneity and a lack of direct comparisons between single-detector and multidetector CTPA.

Authors' objectives

To assess the proportion of pulmonary embolisms diagnosed with single-detector and multidetector computed tomography pulmonary angiography (CTPA) and assess the safety of diagnostic strategies based on CPTA.

Searching

MEDLINE, EMBASE, Cochrane Central Register of Controlled Trials (CENTRAL) and HealthStar were searched to the second quarter of 2009. There were no language, publication type and date restrictions. The search strategy was reported in an online appendix. Bibliographies of included studies and review articles were screened for additional studies. A hand search was conducted of relevant journals and conference proceedings of the International Society of Thrombosis and Haemostasis (2003 to 2009).

Study selection

Prospective studies of diagnostic algorithms that included CTPA in consecutive patients with suspected pulmonary embolisms were eligible for inclusion. Included studies were required to report the primary outcome (diagnosis of subsegmental pulmonary embolism) or three-month thromboembolic risk of diagnostic strategies using a negative CTPA to rule out pulmonary embolism. Studies of asymptomatic pulmonary embolism were excluded. Included studies used single-detector or multidetector CTPA; no further patient or study characteristics were reported.

Two reviewers independently screened studies for inclusion using a structured form. Discrepancies were resolved by a third party.

Assessment of study quality

Two reviewers independently assessed the methodological quality of included studies using the Cochrane Risk of Bias Assessment Tool and Newcastle-Ottawa Quality Assessment scale for observational studies. Discrepancies were resolved by a third party.

Data extraction

Data were extracted on: numbers of pulmonary embolisms diagnosed on CTPA and numbers of subsegmental pulmonary embolisms (subsegmental pulmonary embolism was defined as the largest filling defect identified by CTPA with satisfactory visualization at the subsegmental pulmonary artery level); and number of symptomatic venous thromboembolism (VTE) in a three-month follow-up period in patients diagnosed negative for pulmonary embolism and untreated (based on CTPA). Reported rates were transformed into a quantity using the Freeman-Tukey variant of the arcsine square root transformed proportion. Corresponding authors were contacted where outcome measures were not reported.

Two reviewers independently extracted data using a standard form; discrepancies were resolved by a third party.

Methods of synthesis

Pooled event rates with 95% confidence intervals (CI) were calculated using a random-effects model weighted by sample size. Outcomes were stratified by single-detector and multidetector CTPA. Between-study heterogeneity was assessed with I².

Results of the review

Twenty-two studies (n=12,845 participants, range 20 to 3,306) were included in the review: 20 prospective cohorts and two randomised controlled trials (RCTs). The RCTs had adequate sequence generation, allocation concealment, blinding and outcome reporting. The cohort studies all had adequate representativeness and assessment of outcomes, 14 reported blinded assessment of CTPA and 10 had adequate follow-up.

The overall rate of subsegmental pulmonary embolism detection in patients with confirmed pulmonary embolism was 4.7% (95% CI 2.5 to 7.6%) for single-detector CTPA. For multidetector CTPA, the rate was 9.4% (95% CI 5.5 to 14.2%). There was substantial between-study heterogeneity for both estimates.

The risk of VTE after three months in untreated patients with suspected pulmonary embolism and negative CTPA was 0.9% (95% CI 0.4 to 1.4%) for single-detector and 1.0% (95% CI 0.7 to 1.4%) for multidetector CTPA. Between-study heterogeneity was low for both estimates.

Authors' conclusions

Multidetector CTPA appeared to increase the proportion of patients diagnosed with subsegmental pulmonary embolism without lowering the three-month risk of venous thromboembolism, which suggested that subsegmental pulmonary embolism may not be clinically relevant.

CRD commentary

The review reported clear inclusion criteria and searched a number of sources without restriction to identify relevant studies. The methodological quality of included studies was assessed and reported. Measures were taken throughout the review process to minimise error and/or bias. The meta-analytic methods used were broadly appropriate, but generation of a pooled estimate of pulmonary embolism rate from studies with substantial heterogeneity was of questionable value. The authors acknowledged that the analysis was limited by a lack of studies that directly compared single-detector and multidetector CTPA.

The authors conclusions were appropriately cautious, given the review limitations.

Implications of the review for practice and research

Practice: The authors stated that an increased incidence of subsegmental pulmonary embolism diagnosis meant there could be an increase in the need for anticoagulation treatment. Resource allocation and major bleeding complications needed to be considered.

Research: The authors stated that further prospective studies were needed to assess the risk benefit ratio of anticoagulation in patients with subsegmental pulmonary embolism.

Funding

Not stated.

Bibliographic details

Carrier M, Righini M, Wells PS, Perrier A, Anderson DR, Rodger MA, Pleasance S, Le Gal G. Subsegmental pulmonary embolism diagnosed by computed tomography: incidence and clinical implications; a systematic review and meta-analysis of the management outcome studies. Journal of Thrombosis and Haemostasis 2010; 8(8): 1716-1722. [PubMed: 20546118]

Original Paper URL

http://onlinelibrary.wiley.com/doi/10.1111/j.1538-7836.2010.03938.x/abstract

Indexing Status

Subject indexing assigned by NLM

MeSH

Algorithms; Cardiology /methods; Cohort Studies; Humans; Incidence; Outcome Assessment (Health Care); Pulmonary Embolism /diagnosis /epidemiology /radiography; Randomized Controlled Trials as Topic; Reproducibility of Results; Risk; Tomography, X-Ray Computed /methods; Treatment Outcome

AccessionNumber

12010007697

Database entry date

05/10/2011

Record Status

This is a critical abstract of a systematic review that meets the criteria for inclusion on DARE. Each critical abstract contains a brief summary of the review methods, results and conclusions followed by a detailed critical assessment on the reliability of the review and the conclusions drawn.