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Database of Abstracts of Reviews of Effects (DARE): Quality-assessed Reviews [Internet].

Systematic review and meta-analysis of 12 years of endovascular abdominal aortic aneurysm repair

SC Franks, AJ Sutton, MJ Bown, and RD Sayers.

Review published: 2007.

CRD summary

This review estimated mortality and morbidity rates associated with endovascular repair of abdominal aortic aneurysms. From 1992 to 2002 the estimated mortality rates fell from 7.5% to 1.4%, ruptures from 5.0% to 0.4%, and total endoleaks from 43% to 13.5%. The estimated rates must be treated cautiously, but the overall finding that they were improving appears well supported by the evidence.

Authors' objectives

To estimate rates of mortality and vascular morbidity in patients undergoing endovascular repair (ER) of an abdominal aortic aneurysm (AAA), and to examine how these have changed over time.

Searching

MEDLINE and EMBASE were searched from inception to August 2003 for studies published in the English language; the search terms were reported.

Study selection

Study designs of evaluations included in the review

Case series with a minimum of five participants were eligible for inclusion.

Specific interventions included in the review

Studies of elective ER were eligible for inclusion. Studies were excluded if they reported emergency cases only, or if there was a duplication of data. Where studies reported data on both elective and emergency cases, emergency cases were removed from the analysis where this was feasible.

Participants included in the review

Studies of patients with degenerative infrarenal AAA were eligible for inclusion.

Outcomes assessed in the review

Studies that reported either mortality or endoleak rates as outcomes were eligible for inclusion. The outcomes reported in the review comprised operative mortality, all mortality, technical success (successful graft implant), post-operative aneurysm ruptures in survivors (and related mortality rates), endoleaks (total and subdivided by type), and rates of conversion to open repair (total rate, at time of initial operation (primary) or subsequently (secondary)). The outcomes were reported as overall incidence rates and also as annual incidence rates (to allow for different follow-up times in the studies).

How were decisions on the relevance of primary studies made?

The authors did not state how the studies were selected for the review, or how many reviewers performed the selection.

Assessment of study quality

The studies were assigned a level of evidence according to the criteria of Blankensteijn et al., which consider methods of participant selection and data collection, and also by whether the studies were single- or multi-centred.

The lead author performed the evaluation. Any questionable data were discussed between the co-authors for a consensus decision.

Data extraction

The lead author extracted the data and conferred with co-authors where the data were questionable.

Methods of synthesis

How were the studies combined?

Meta-analyses were stratified by outcome measure. Binary outcomes were combined on a log odds scale and then transformed into percentages. For incidence rate outcomes, a weighted Poisson regression was used. Funnel plots were used to check for publication bias.

Random-effects models and Stata software were used for all analyses.

How were differences between studies investigated?

Statistical heterogeneity was investigated using the chi-squared test. For the outcomes of operative mortality, post-operative rupture and total number of endoleaks, heterogeneity was also investigated with meta-regression analyses examining the effect of time (i.e. years in which the study was conducted), study size, length of follow-up, size of aneurysm, mean age, geographical location, and study inclusion criteria with regard to severity of medical condition.

Sensitivity analyses were conducted to investigate the effect of study quality on the results.

Results of the review

One hundred and sixty-one studies, with a total of 28,862 patients, were included in the review.

The overall pooled incidence rates were as follows: operative mortality 3.3% (95% confidence interval, CI: 2.9, 3.6), all endoleaks 22.8% (95% CI: 20.6, 25.2), all conversions to open repair 5.4% (95% CI: 3.1, 4.0; this value seems to be in error since it lies outside of the 95% confidence limits), post-operative rupture 1.3% (95% CI: 1.1, 1.7). The annual rates were as follows: type 1 endoleaks 8.4% (95% CI: 5.7, 12.2), type 2, 3 and 4 endoleaks 10.2% (95% CI: 7.4, 14.1), post-operative rupture 0.6% (95% CI: 0.5, 0.8).

The rates of operative mortality, post-operative rupture and total number of endoleaks all fell significantly over time (p<0.05). Estimates from the regression analysis indicated that from 1992 to 2002 approximate mortality rates fell from 7.5% to 1.4%, approximate rupture rates fell from 5.0% to 0.4%, and the approximate total endoleak rate fell from 43% to 13.5%. No other variables had a statistically significant effect over all three outcomes.

Further analyses were reported in the paper.

There was statistically significant heterogeneity between the studies for all outcomes (p<0.01), which the authors attributed to the large number of small studies, and the inclusion of results from the surgeons' 'learning curve' period. All the studies were hospital-based; 39 were prospective and hospital-based and 113 were retrospective. The authors noted that the effect of study quality on the results was hard to interpret but reported that there was little difference in all-mortality rates between the two different types of study. They also noted that many studies were poorly reported and that there could have been repetition of data between the studies, which could bias results as there is a greater risk that early results were counted twice.

Publication bias was also hard to evaluate on account of study heterogeneity in the funnel plots.

Authors' conclusions

Rates of mortality and morbidity associated with ER of AAA have improved rapidly over the years 1992 to 2002.

CRD commentary

The review question and inclusion criteria were clear. The search was adequate, though potentially limited by being restricted to published studies in the English language. The validity assessment was poorly reported and might have lacked rigour as it did not clearly address all the pertinent issues: in particular, rates of loss to follow-up. It was unclear how the authors classified studies that did not report whether the data were collected prospectively or retrospectively. The use of a single author to select studies and extract the data is a potential source of bias, though this was counteracted somewhat by the use of a co-author to comment where the primary author was in doubt.

There were few details of the characteristics of the individual studies, in particular no details on study setting or length of follow-up. The statistical methods of data synthesis appeared appropriate. As the authors noted, their findings were subject to the limitations of case-series evidence, compounded by poor reporting in the primary studies and the possibility of data duplication. Moreover, there was a high level of heterogeneity in the results for all outcomes. The authors' estimated mortality and morbidity rates must therefore be treated with caution, but their overall finding that rates are improving appears well supported by the evidence.

Implications of the review for practice and research

Practice: The authors stated that mortality and post-operative complication rates associated with ER for AAA are falling and are likely to improve further.

Research: The authors did not state any implications for further research.

Bibliographic details

Franks S C, Sutton A J, Bown M J, Sayers R D. Systematic review and meta-analysis of 12 years of endovascular abdominal aortic aneurysm repair. European Journal of Vascular and Endovascular Surgery 2007; 33(2): 154-171. [PubMed: 17166748]

Indexing Status

Subject indexing assigned by NLM

MeSH

Aortic Aneurysm, Abdominal /mortality /surgery; Follow-Up Studies; Humans; Retrospective Studies; Survival Rate /trends; Time Factors; Treatment Outcome; Vascular Surgical Procedures /methods /mortality

AccessionNumber

12007000852

Database entry date

31/10/2007

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.

CRD has determined that this article meets the DARE scientific quality criteria for a systematic review.

Copyright © 2014 University of York.

PMID: 17166748

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