Published by Elsevier Inc. DownloaAbnormal Thyroid Function

We read with interest the excellent report byMitchell et al. (1) in this issue of JACC: Heart Failure. In brief, the investigators conducted a subset analysis of the SCD-HeFT (Sudden Cardiac Death in Heart Failure) trial that was originally published in 2005. They looked at the subset of patients with evidence of thyroid hormone dysfunction at the beginning of the trial and those who developed evidence of thyroid hormone dysfunction during the trial. The investigators found that evidence of abnormal thyroid function in patients with heart failure portends a poor prognosis and is associated with increased mortality. The study is based on clinical trial data, with a protocol for follow-up measures that should minimize bias. Various subgroup analyses were conducted that, if sufficiently powered, raise the question of whether the thyroid abnormalities have a causal relationship to mortality. See page 48 For instance, patients treated for hypothyroidism were found to have risk that was apparently not significantly different from those untreated. Furthermore, the increased mortality risk was reported to be similar for hyperthyroidism and hypothyroidism. Might the thyroid test abnormalities be only a marker for an underlying condition that is the actual causal factor for increased mortality? Unfortunately, the investigators present only p values, not confidence intervals, which would have assisted with interpretation as to whether there was a nonsignificant trend and its direction. An important aspect of this report is that treatment with an implantable cardioverter-defibrillator (ICD) was not *Editorials published in JACC: Heart Failure reflect the views of the authors and do no