OBJECTIVES: The aim of this study was to investigate whether patients with 
systolic heart failure (HF) and abnormal thyroid function are at increased risk 
for death.
BACKGROUND: Thyroid hormone homeostasis is vital to the optimal functioning of 
the cardiovascular system, but an independent prognostic effect of thyroid 
abnormalities in patients with HF has not been established.
METHODS: In SCD-HeFT (Sudden Cardiac Death in Heart Failure Trial), which 
randomized patients with ischemic or nonischemic HF to placebo or amiodarone or 
implantable cardioverter-defibrillator therapy, thyroid-stimulating hormone 
(TSH) was measured at baseline and at 6-month intervals throughout the 5-year 
study.
RESULTS: Of 2,225 patients, the majority (87%) had normal TSH levels (0.3 to 5.0 
μU/ml) at baseline, 12% had values suggestive of hypothyroidism, and 1% had 
values consistent with hyperthyroidism. Compared with euthyroid patients, those 
hypothyroid at baseline were older and included more women and Caucasians (all p 
values <0.05). Over the median follow-up period of 45.5 months, among patients 
euthyroid at baseline, 89 developed abnormally low TSH levels, and 341 developed 
abnormally high values. Patients randomized to amiodarone (median dose 300 mg) 
had an elevated risk for developing abnormal TSH levels compared with 
implantable cardioverter-defibrillator therapy or placebo (p < 0.0001). Patients 
with baseline or new-onset abnormal thyroid function had a higher mortality than 
those with normal thyroid function, even after controlling for other known 
mortality predictors (hazard ratio: 1.58; 95% confidence interval: 1.29 to 1.94; 
p < 0.0001 for hypothyroid; hazard ratio: 1.85; 95% confidence interval: 1.21 to 
2.83; p = 0.0048 for hyperthyroid). Implantable cardioverter-defibrillator 
benefit did not vary with thyroid function.
CONCLUSIONS: Abnormal thyroid function in patients with symptomatic HF and 
ejection fractions ≤35% is associated with significantly increased risk for 
death, even after controlling for known mortality predictors.