Not only randomized controlled trials, but also case series should be considered in systematic reviews of rapidly developing technologies.

OBJECTIVE: Case series can influence clinical practice but are often omitted from systematic reviews. We evaluated the contribution of case series to a systematic review of radiofrequency catheter ablation (RFCA) for treatment of atrial fibrillation (AF). STUDY DESIGN AND
SETTING: Analysis of the results of a systematic review based on a search of 25 electronic databases and Internet sources.
RESULTS: We included eight controlled trials and 53 case series. Case series provided most patients longest follow-up and data on adverse events and complications. Rates of freedom from arrhythmia were comparable between case series, RFCA arms of controlled trials, and a survey of RFCA centers.
CONCLUSION: In the case of RFCA for AF, the case series make a useful contribution to the systematic review. Inclusion of case series can increase the evidence base and strengthen the credibility of a review of an emerging health technology. These advantages must be balanced against the risk of bias associated with the lack of a control group, potential publication bias, overrepresentation of results from specialist centers, and overlap of patients across series. Specification in the review protocol of inclusion criteria for outcomes and quality criteria is recommended to make optimum use of case series.