Subgroup analyses of randomized clinical trials in heart failure: facts and numbers.

Subgroup analyses of major randomized clinical trials in heart failure are published frequently, but their impact on medical knowledge and practice guidelines has not been previously reported. In a novel analysis, we determined number of citations, impact factors, number of authors, and citations in guidelines of both parent trials and sub-studies; we also qualitatively assessed whether the analyses were described as post-hoc and non-pre-specified. A total of 229 sub-studies evaluating outcomes in patient subgroups were published (median 6, range 0-36 per trial). The number of subjects in the parent trials positively correlated with number of sub-studies (rho = 0.51,  = 0.009). The subgroups are frequently not pre-specified. The impact factors of sub-studies were lower in comparison to the parent trials as were the number of citations two years after the publication date; in addition, parent trials were cited more frequently in European and American professional guidelines compared with the sub-studies. We maintain that the sub-studies derived from major heart failure trials are frequently published, but their contribution to clinical guidelines and medical knowledge are highly debatable.