Müller P, Dietrich JW, Lin T, et al. - By performing this open-label prospective cohort analysis with euthyroid heart failure patients with implantable cardioverter-defibrillators (ICD), researchers investigated if the incidence of ventricular arrhythmias in this patient population can be predicted by free thyroxine (FT4) and calculated thyroid parameters. The study sample included 115 consecutive euthyroid patients with a mean age of 62.9 ± 1.3 years, 87% were male, and 63% had ischemic cardiomyopathy. The participants were scheduled for primary prevention ICD implantation or exchange. One day prior to device operation, the measurement of serum levels of thyrotropin (TSH) and FT4 was obtained. Higher FT4 levels were detected in patients with appropriate ICD therapy (AIT) vs those without AIT. AIT incidences were shown to be predicted by Jostel's TSH index, indicating the central component of the hypothalamus-pituitary-thyroid loop, and SPINA-GT as surrogate markers for thyroid's secretory capacity, in Kaplan-Meier analysis. Overall, an increased incidence of ventricular arrhythmias in this patient population was predicted by FT4 concentration. Among these patients, an increased rate of AIT may be afforded by both impending primary hyperthyroidism and an elevated thyroid homeostasis set-point.