Higher levels of thyroid-stimulating hormone (TSH) and free T4 concentrations are associated with more severe heart failure, according to research presented at ENDO 2017: the 99th Annual Meeting & Expo, April 1-4, 2017, in Orlando, Florida.
Researchers at the University of Pennsylvania in Philadelphia studied the prevalence of thyroid dysfunction and its association with cardiovascular outcomes in patients with preexisting heart failure. Although subclinical thyroid dysfunction has been found to increase heart failure incidence, its effects on patients with preexisting heart failure have not been evaluated. Therefore, the researchers examined 1382 patients (mean age, 57 years; 35% women) who were enrolled in the Penn Heart Failure Study to assess the relationship between thyroid dysfunction categories and New York Heart Association (NYHA) heart failure classes and atrial fibrillation.
The composite end point was designated as death, ventricular assist device placement, or heart transplantation using Cox proportional hazard models, adjusting for age, sex, race, body mass index, ischemic etiology, amiodarone use, and levothyroxine (LT4) use. Log-transformed levels of TSH, free T4, and total T3 were analyzed in additional models: without patients taking amiodarone or levothyroxine (n=1085) and only in patients with normal thyroid function (n=992).
Most of the patients were classified as either NYHA II (46%) or NYHA III (32%); 11% took amiodarone and 13% took levothyroxine. In terms of thyroid function, less than 1% were categorized as overtly hypothyroid and 6% as subclinically hypothyroid, 88% had normal thyroid function, and 5% were categorized as subclinically hyperthyroid and 1% as overtly hyperthyroid.
Higher TSH, higher free T4, and lower total T3 levels were associated with more severe heart failure (P <.05), with the exception of patients taking amiodarone and LT4 (P <.001) and restricted to individuals with normal thyroid function (P <.001). Higher levels of free T4 were associated with atrial fibrillation (P ≤.001), but TSH and total T3 were not. This positive association persisted even when restricted to the euthyroid range (P =.01).
During a median of 4.2 years of follow-up, there were a total of 450 composite end points. Subclinical hypothyroidism was associated with an increased risk for the composite end point (hazard ratio [HR], 1.81; 95% CI, 1.28-2.57; P =.001) compared with euthyroidism. Subclinical hypothyroidism with TSH ≥7.0 mlU/L was also associated with the composite end point compared with the euthyroid patients (HR, 2.99; 95% CI, 1.82-4.93; P <.001), but TSH levels between 4.5 and 6.9 mlU/L were not (HR, 1.38; 95% CI, 0.88-2.17; P =.16).
The researchers concluded that subclinical hypothyroidism with TSH ≥7.0 mlU/L is associated with worse survival in patients with preexisting heart failure.
Kannan L, Morley M, Brandimarto J, Cappola TP, Cappola AR. Thyroid dysfunction in heart failure is associated with cardiovascular outcomes: the Penn Heart Failure Study. Abstract OR37-1. Presented at: ENDO 2017; April 1-4, 2017; Orlando, FL.