Systematic reviews and meta-analyses in cardiac surgery: rules of the road - 1

The number of cardiac surgical meta-analyses and systematic reviews published in the last decades has constantly increased, paralleling the exponential growth observed in virtually all other medical fields. However, meta-analyses are open to methodological flaws if best practices are not strictly followed. Assessment of the appropriateness of the research question is a crucial first step. Once a protocol has been developed, this should be registered before the work is initiated. The cornerstone of any systematic review or meta-analysis is a rigorous, comprehensive, and most of all reproducible search which follows a prespecified and clear strategy. Eligibility criteria must be discussed and agreed upon in advance to guide final study selection, which ultimately lays the foundation for subsequent data extraction. In case of missing or partially reported data, the authors of the original paper should be contacted. Adherence to rigorous methodological rules at each of these stages will warrant availability of good quality data for formal statistical analyses. The aim of the first part of this expert review is to discuss the limits and pitfalls of the meta-analytic approach and provide guidance on how to perform trial level meta-analyses, with particular reference to the identification of an appropriate research question, the definition and registration of the protocol, the search strategy, the study selection and the data abstraction.