Abstract 3768: Thyroid Function and Mortality in the Sudden Cardiac Death in Heart Failure Trial
Thyroid hormone homeostasis is vital to the optimal functioning of the cardiovascular system. However, conflicting data exist regarding the degree of increased risk associated with thyroid abnormality in heart failure patients. In The Sudden Cardiac Death in Heart Failure Trial (SCD-HeFT) that enrolled 2521 patients (pts) to evaluate the role of placebo vs. amiodarone vs. ICD therapy in pts with EF<35%, ischemic or non-ischemic HF and NYHA functional class II or III, thyroid stimulating hormone (TSH) was recorded at the start and at 6 month intervals throughout the study. Baseline TSH values were available for analysis in 93% of the cohort. At baseline, the majority of the pts (93%) had normal TSH values (0.3–5.0 μU/mL). Five percent had values suggestive of hypothyroidism and 2% had values consistent with hyperthyroidism. Abnormal TSH groups had more women than did the normal TSH group (38% vs. 22%, p=0.001). But there were no significant differences between TSH groups in age (≤/>60yo), race, NYHA class, etiology of heart failure, ejection fraction, or exercise tolerance as measured by the 6-minute walk test. Over the median follow-up of 45.5 months, pts randomized to the amiodarone group had a considerably elevated risk of developing an abnormal value (28% with TSH >5 μU/mL and 11% with a value <0.3 μU/mL) at any point, compared to ICD or placebo (p=0.001). ICD and placebo had similar rates of abnormal TSH values (12% and 10%, respectively; p=0.24). Throughout the course of the trial, the percent of pts on thyroid replacement therapy increased from 7% at baseline to 18% at the conclusion of the study. Mortality was associated with thyroid status. After controlling for known predictors of increased mortality (randomized treatment group, ejection fraction, time since heart failure diagnosis, medication use, 6-minute walk etc), there remained a greater than 50% relative risk of dying for those pts with an abnormal TSH at baseline (hazard ratio (95% CI) = 1.54 (1.17, 2.02); p=0.002). The major burden of this increased risk contributed by the low TSH group.
Conclusion: Pts in SCD-HeFT with an abnormal thyroid function at baseline had a significantly increased risk of dying over the course of the study irrespective of randomization to amiodarone, ICD or placebo treatment groups.